4.0 environmental impact assessment - smcgov.org

Environmental Impact Assessment Page 4-1

Edgewood Canyon Estates Supplemental Draft EIR March 2011

4.0 ENVIRONMENTAL IMPACT ASSESSMENT As stated in Chapter 1, Introduction of this document, the San Mateo County Planning and Building Department has determined that a Supplemental EIR is the best documentation pursuant to CEQA Guidelines to evaluate the proposed changes to the 1992 Edgewood Canyon EIR. Section 15163 (2) of the CEQA Guidelines state that a Supplemental EIR need contain only the information necessary to make the previous EIR adequate for the project as revised. Therefore, the following information is presented in exactly the same format as was contained in the 1992 EIR. 4.1 GEOLOGY This section updates the 1992 EIR’s geology analysis. As was done for the 1992 EIR, the Applicant has obtained the services of a professional engineering firm to update, assess, and as necessary, mitigate any geological and geotechnical hazards of the site as a result of the proposed project. The County’s Planning and Building Department, Geotechnical Section, has reviewed the project’s geotechnical reports, grading plans, and drainage plans and an independent engineering firm has also provided peer review of the proponent’s geotechnical site assessment. These updated reports are contained in Appendix B-1 of this Supplemental EIR, and include: Updated 2010 Project Geotechnical Reports

“Report on a Geotechnical Investigation for the Planned Two-Lot, Palomar Canyon Subdivision, San Mateo County, California,” prepared by Jo Crosby & Associates (JCA), February 14, 2002.

“Requested Supplemental Information Regarding the Proposed Two-Lot, Palomar Canyon Subdivision, San Mateo County, California,” prepared by JCA, September 5, 2002.

“New Engineer-of-Record & Supplemental Recommendations, Two Single-Family Residences, Palomar Canyon Subdivision, Edgewood Road, San Mateo County, California,” prepared by Murray Engineers, Inc., November 14, 2008.

“Supplemental Slope Stability Study, Palomar Canyon Subdivision, Edgewood Road, San Mateo County, California,” prepared by Murray Engineers, January 14, 2009.

“Grading and Drainage Plan, Edgewood Road,” prepared by MacLeod and Associates, August 30, 2010.

“Peer Review – Edgewood Canyon Subdivision,” prepared by Bay Area Geotechnical Group (BAGG) Engineers, June 14, 2010.

“Response to Peer Review Comments, Palomar Canyon Subdivision, Edgewood Road, San Mateo County, California,” prepared by Murray Engineers, June 30, 2010.

“Geotechnical Plan Review and Response to County Review Comments, Edgewood Canyon Subdivision, 2050 Edgewood Road, San Mateo County, California,” prepared by Murray Engineers, September 1, 2010.

“Response to Peer Review Comments, Edgewood Canyon Subdivision, 2050 Edgewood Road, San Mateo County, California,” prepared by Murray Engineers, October 28, 2010.

“Supplemental Information, Edgewood Canyon Subdivision, 2050 Edgewood Road, San Mateo County, California,” prepared by Murray Engineers, February 23, 2011.

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A series of reports were prepared for the originally proposed six-lot development by JCA, at the time the geotechnical consultant to the Applicant, dating between January 1990 and May 1992 (January 16, 1990, January 7, 1991, July 18, 1991, October 19, 1991, May 14, 1992, and July 9, 1992). These reports are contained in Appendix B-2 to this EIR, and are bound separately. Appendix B-2 is available for review at the San Mateo County Planning and Building Department’s Office. 4.1.1 1992 EIR Analysis The 1992 EIR described that the project site lay between the San Andreas Fault Zone to the west and the San Francisco Peninsula foothills to the east, within the California Coast Range geomorphic region. The 1992 EIR also described that the project site was underlain by a hardened and fractured Jurassic to Cretaceous-aged Franciscan sandstone and that soils at the site consisted of sandy silts, silty sands, and artificial fill of varying depth and composition. The 1992 EIR determined the primary geologic concerns at the site were seismic hazards, the presence of non-engineered, artificial fill on the site and access roads, and slope stability, including soil creep. The 1992 EIR described that overall, the Applicant’s geotechnical consultant found the proposed six-lot subdivision project feasible and that all potential impacts would be less than significant with implementation of mitigation measures. 1992 Site Grading The 1992 EIR described that site preparation and grading activities would require an estimated 7,200 cu yds of cut and 10,000 cu yds of fill, forty-eight percent of which would be for the construction of the access road to Lot 5. This roadway would be cut into the side of a steep slope, which had been artificially steepened by past grading activities to a 1:1 slope. The 1992 EIR described that County grading standards generally require a minimum of 2:1 ratio for all graded areas and that the Applicant requested an exception to this standard for the Lot 5 road. The Applicant’s geotechnical consultant at the time reviewed the possibility of “stair-stepping” this slope, but found this action would only give shallow stability and therefore recommended that rock bolting be used in areas where additional slope support was needed (JCA 1992). The 1992 EIR determined the project’s potential grading impacts would have locally important effects. Mitigation required in the 1992 EIR to reduce these effects to less than significant levels, required the following:

1) The Applicant to submit a final grading plan for review by the County Department of Public Works.

2) Regular inspection and maintenance of retaining walls, graded slopes, slope planting, rockbolting and steel mesh on rock faces.

3) Slopes with a ratio of 1:1 to be rockbolted, or in areas were stability can be obtained, benched or “stair-stepped” instead of or in combination with rockbolting.

4) Site preparation, fill construction, location of keys, benches, and foundation exaction to be approved in the field by a qualified geotechnical engineer.

5) Non-engineered fill must be over excavated and replaced with engineered fill. The 1992 EIR described that the project could impact the San Francisco Water Department’s (SFWD) water supply pipes located beneath the access road from Edgewood Road into the



project and considered this a potentially significant impact. To mitigate this potentially significant impact to less than significant, the EIR required the Applicant to meet SFWD and County grading requirements and provide documentation to the County that they have a right to grade on SFWD lands 1992 Seismic Hazards The 1992 EIR described that major seismic events occurring on any of the active faults in the San Francisco Bay area will affect the site, with the most potentially significant risks associated with the San Andreas Fault Zone (1.7 miles to the southeast of the project site), and, to a lesser extent, the Hayward and Calaveras faults. The 1992 EIR described that U.S. Geological Survey (USGS) earthquake intensity maps indicated the project site was susceptible to “Grade D” or “Strong” intensity earthquakes that could fall chimneys, crack masonry, brickwork, foundations, etc., and potentially lurch a building. The 1992 EIR also identified that the project site was mapped as a Category II landslide area according to the USGS maps, indicating the area had a “low susceptibility to landsliding”. 1992 EIR identified that the likelihood for ground rupture or landslides resulting from a seismic event was low and that due to the clay composition of the site soils identified in the Applicant’s geotechnical report there was no potential for liquefaction (JCA 1990). The 1992 EIR determined the presence of non-engineered fill, steep slopes, potentially unstable soils, and the overall potential seismic activity of the region would have a potential locally important effect on structures built at the site and, as mitigation to reduce this effect to a less than significant level, required a range of house construction measures be incorporated into the design of each house. The geotechnical consultant recommended that all houses be constructed on a pier and grade beam foundation to reduce movement caused by soil creep, shrink/swell soils, and unconsolidated or poorly compacted fill. 1992 Non-engineered Fill The 1992 EIR described that the project site had been widened and leveled between 1961 and 1974 and contained non-engineered artificial fill of varying composition and depth. On-site geotechnical exploration to determine the extent and nature of the non-engineered artificial fill hazard revealed that fill soils extend to the slope on the east wall of the valley, potentially affecting the roads, structures, and septic fields for Lots 2, 3, and 4. In 1992, the Applicant’s geotechnical reports identified that the access road from Edgewood Road into the site was underlain by up to 30 feet of artificial fill and recommended this fill be excavated and engineered to support road activities (JCA 1990). The geotechnical consultant also identified that the driveway to Lot 4, which included a three-point turn area for emergency vehicle access, was partially underlain by artificial fill and recommended the fill be excavated to a depth of 3 to 4 feet and re-compacted. The geotechnical consultant also recommended the driveway be constructed with minimum three percent slope crown grade (JCA 1990). The 1992 EIR identified that homes built on Lots 2 and 3 could be damaged from irregular or differential settling of underlying artificial fill with high clay contents, which could also exhibit

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shrink-swell behavior. In 1992, the Applicant’s geotechnical consultant recommended that houses and garages on these lots be built on pier and grade beam and slab foundations, respectively (JCA 1990). The 1992 EIR described that the San Mateo County Department of Environmental Health does not allow septic drainfields on fill soil and that the project’s geotechnical investigation had identified a suitable site for drain fields. 1992 Slope Stability The 1992 EIR described that the site-specific geotechnical investigation commissioned by the Applicant found several small areas and one large area of instability on the canyon slopes, above areas of road construction. The slope movement in these areas was restricted to the soil layer and the weathered rock beneath the soil layer. The largest slide was located on the west wall above Lot 3 and was roughly 35 feet wide by 60 feet long, the result of a failure plane parallel to the slope. In 1992, the Applicant’s geotechnical consultant also modeled two cross sections of the site to analyze the potential for deep-seated rotational failure and determine the minimum safety factor associated with site slopes. The modeling indicated the site slopes had a low probability of failure (JCA 1990). The 1992 EIR described that the portions of the access road from Edgewood Road and secondary access road beyond the site boundary on Hermosa Road would need to be widened and were of undetermined stability. The 1992 EIR also identified that the main access road and Edgewood road slope cutback should generally result in stable slopes. For Hermosa Road, the Applicant’s geotechnical consultant recommended that the roadbed be relocated off the existing fill and into the upper slope. For the Lot 5 Roadway to Hermosa Road, which would traverse steep slopes, the EIR described that the slopes above and below the roadway would be engineered to a 1:1: slope and rockbolted or benched (i.e., “stair-stepped”) to increase slope stability. The area above the roadbed to be stabilized was approximately 340 feet long and 16 to 28 feet above the roadbed, while the area below the roadbed to be stabilized was approximately 175 feet long and from eight to 44 feet below the roadway. The EIR also described that retaining walls would be used at the base of the slope below the roadbed. The 1992 EIR also described that the soil failure at the site could result from soil creep, which would impose lateral loading on retaining walls and building foundations or possible rock or debris falls on the cut slopes of Lots 2 and 3. The 1992 EIR determined the impacts from soil stability and soil creep at the site would have locally important effects and, as mitigation to reduce these effects to less than significant, required:

1) Regular inspection and maintenance of proposed grading and slope stability features. 2) Slopes with a 1:1 ratio be rockbolted to strengthen joint systems in the bedrock or, where

equivalent stability can be obtained, benched or “stair-stepped. 3) Fill slopes below existing road alignments be analyzed for stability and concurrence with

grading standards.



The 1992 EIR also identified 16 grading and construction techniques considered good practices that the Applicant should implement to assure slope stability. 4.1.2 2010 Environmental Setting This section updates the 1992 EIR setting where necessary. The geologic setting of the site has not changed since the certification of the 1992 EIR. The site remains at an elevation of about 200 feet above mean sea level (ft amsl) at the southern boundary to 400 ft amsl at the northern boundary. Site topography remains characterized by slopes that range from 3% on the valley floor to 125% in the northern and western portions of the site that have been artificially steepened by historical site activities. The site is underlain by Jurassic to Cretaceous-aged Franciscan sandstone that is hardened and fractured into a series of interconnecting joint patterns. Soils on the site slopes consist of silt and silty sands ranging from one to four feet deep that are highly erodible, permeable, and have very low cohesion. Soils on the valley floor vary from gravelly clays and silts to soft organic clays and silts as a result of past dumping activities. Valley floor soils range from five to 30 feet thick and have low permeability. The presence of clays in the valley floor soils indicates the soils may be subject to shrinking and swelling. The Applicant’s updated site geotechnical investigation did not identify any significant new geotechnical constraints or hazards at the site (JCA 2002). Research identified a potentially active fault approximately 0.5 miles southwest of the project site and forecast a maximum capable earthquake event magnitude of 8.3 for the site. Potential slope movement remains confined to the surface soils and shallow rock layers and updated slope stability modeling indicated the existing and planned bedrock cut and fill slopes have a low potential for movement or failure. Test borings taken in 2002 encountered groundwater at varying levels throughout the site, ranging from two feet at the southern end of Lot 1 to 28 feet at the eastern side of Lot 2. 4.1.3 2010 Regulatory Setting This section identifies the regulatory requirements designed to prevent the effects of geologic and soils hazards present in the project area. All infrastructure associated with the project would be subject to these regulations. Federal There are no federal regulatory requirements that apply to this project. State Alquist-Priolo Earthquake Fault Zoning Act The California Alquist-Priolo Earthquake Fault Zoning Act requires the delineation of zones along active faults in California with the purpose of regulating development on or near an active fault trace, and includes certain requirements for sites within those zones. The project area is not



located in, and does not cross, an Alquist-Priolo Earthquake Fault Zone. In the instance of seismic activity, however, it is important to note that a surface fault rupture may not be restricted to areas within the Alquist-Priolo Fault Zones, and that in many cases surface rupture is likely to occur outside of these fault zones as well as inside them. The project site is located within 1.7 miles of the San Andreas Fault zone and the possible seismic hazards associated with the rupture of this fault are discussed in the impact analysis below. Seismic Hazards Mapping Act The California Seismic Hazards Mapping Act became effective January 1, 1992, and was developed to protect the public from the effects of ground shaking, liquefaction, landslides, and other hazards caused by seismic activities. The act requires the delineation of various seismic hazard zones and the regulation of development within these hazardous zones. The Act permits lead agencies to withhold development permits until site-specific geologic and soil investigations are performed and measures developed and incorporated into project plans that will reduce seismic-related hazards. California Uniform Building Code Title 24, Part 2 of the California Code of Regulations (CCR), also known as the California Building Code (CBC), contains regulations governing building standards for the State of California. The 2010 CBC became effective on January 1, 2011. The 2010 CBC assigns a seismic design category to each structure based on the existing acceleration and site classification, as well as the intended used of the structure, which affects the seismic design requirements for that structure. Local and Regional Association of Bay Area Governments (ABAG) Hazard Mitigation Plan ABAG is a regional planning agency for the nine‐county San Francisco bay area, including San Mateo County. ABAG has developed a Hazard Mitigation Plan with appendices for local governments that identity five hazards related to earthquakes (faulting, shaking seismically induced landslides, liquefaction, and tsunamis), and four related to weather (flooding, landslides, fire, and drought), as well as policies and actions that local agencies may implement to reduce the potential for loss of life and property damage in areas affected by these hazards. San Mateo County General Plan The following General Plan policies pertain to geological impacts of the proposed project: The County of San Mateo General Plan includes a natural hazards element that identifies policies and actions that may be implemented by the County to reduce the potential for loss of life and property damage based on an analysis of earthquakes, floods, wildland fires, and landslides in terms of frequency, intensity, location, history, and damage effects. The following policies would apply to the proposed 2010 project: General Plan Policy 15.20‐b, Review Criteria for Locating Development in Geotechnical Hazard Areas: Whenever possible, avoid construction in steeply (>30 percent) sloping areas.



General Plan Policy 15.20‐d, Review Criteria for Locating Development in Geotechnical Hazard Areas: In extraordinary circumstances when there are no alternative building sites available, allow development in geotechnically hazardous and/or steeply sloping areas when appropriate structural design measures to ensure safety and reduce hazardous conditions to an acceptable level are incorporated into the project. General Plan Policy 15.21‐a, Requirement for Detailed Geotechnical Investigations. In order to more precisely define the scope of the geotechnical hazards, the appropriate locations for structures on a specific site and suitable mitigation measures, require an adequate geotechnical investigation for public or private development proposals located: (1) in an Alquist‐Priolo Special Studies Zone, or (2) in any other area of the County where an investigation is deemed necessary by the County Department of Public Works. San Mateo County Grading Regulations The San Mateo County grading regulations (Division VII, Chapter 8, Sections 8600 – 8609 of the San Mateo County Ordinance Code) are designed to promote the conservation of natural resources and protect health and safety. The regulations establish grading permit application requirements and minimum performance to be met during the project. 4.1.4 Thresholds of Significance This updated SEIR analysis considers whether the proposed project would result in new or substantially more severe impacts than indentified in the 1992 EIR and also whether the project would result in a potential geology or soils impact as identified in Appendix G of the CEQA Guidelines. According to Appendix G of the CEQA Guidelines, the proposed project would have a significant environmental impact on geologic resources if it would:

a) Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving:

i. Rupture of a known earthquake fault, as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault (Refer to Division of Mines and Geology Special Publication 42);

ii. Strong seismic ground shaking; iii. Seismic related ground failure, including liquefaction; and iv. Landslides;

b) Result in substantial erosion or the loss of topsoil; c) Be located on a geologic unit or soil that is unstable, or that would become unstable as a

result of the project and potentially result in on- or off-site landslide, lateral spreading, subsidence or collapse;

d) Be located on expansive soil, as defined in the latest edition of the California Building Code, creating substantial risks to life or property; or

e) Have soils incapable of adequately supporting the use of septic tanks or alternative waste water disposal systems where sewers are not available for the disposal of waste water.



4.1.5 2010 Project Impacts Since the geologic and geotechnical constraints of the site have not substantially changed since certification of the 1992 EIR, the 2010 project remains subject to the same hazards and impacts as identified in the 1992 EIR. Although the proposed 2010 project involves substantially more grading than the 1992 project (see Table 2-1 of the Project Description), this activity does not change the fundamental geotechnical constraints of the project site (e.g., slope stability), nor does it affect the potential for people and structures to be exposed to hazards associated with regional seismic activity since this hazard exists regardless of the grading activities undertaken. According to the geotechnical reports prepared for the 2010 project, the increase in grading would not result in new or substantially more severe hazards associated with soil erosion, proposed cut/fill slopes, and site drainage beyond that identified in the 1992 EIR, as long as the recommended design measures are implemented as proposed. The 2010 project would, however, reduce the number of future homes on the site from six to two and therefore reduce the potential exposure of people and structures to the adverse effects associated with regional, local, and site geologic, soils, and geotechnical hazards. The 2010 project would not require the construction of retaining walls, cutting back the existing slope on Edgewood Road east of the project access road, spanning or improving access through the San Francisco Water Department right-of-way, nor widening and upgrading of Hermosa Road. The potentially significant geotechnical impacts associated with these activities would no longer occur. The 2010 project, therefore, would not result in any new or more severe geologic impacts than considered in the 1992 EIR and thus this analysis focuses on the potential for the 2010 project to be exposed to or result in a significant geologic, soils, or geotechnical impacts based on the information contained in the Applicant’s geotechnical reports provided as Appendix B-1 to this EIR and the criteria listed in Appendix G of the CEQA Guidelines. Overall, the Applicant’s geotechnical consultants found the proposed project feasible, provided that recommended measures are incorporated into the project’s plans. An independent review of the adequacy of the conclusions and recommendations of the Applicant’s geotechnical reports was conducted for this EIR process by BAGG Engineers and submitted to the County for review, as was also the Applicant’s response to the BAGG peer review (see Appendix B-1). Seismic Hazards – Fault rupture, ground shaking, liquefaction, landslides, differential settlement, and lateral spreading As in 1992, the most significant geologic risk to the site is associated with its proximity to the San Andreas Fault Zone, which lies approximately 1.7 miles southwest of the site. Dislocation of a potentially active fault located approximately 0.5 miles southwest of the site could occur in conjunction with a major seismic event along the San Andreas Fault Zone. Based on procedures described in Chapter 16, section 1613 of the 2010 California Building Code, the Applicant’s geotechnical consultant has determined that the project site classification is “C”, consisting of very dense soil and soft rock, with potential short (0.2 second) and long (one second) spectral accelerations of 1.997 and 1.064g, respectively (MEI 2008).



The Applicant’s geotechnical consultant has recommended that all houses be constructed on a pier and grade beam foundation. This foundation type reduces the potential for long term settlement of fill materials by transferring building loads to solid ground. The geotechnical consultant recommends piers have a minimum diameter of 16-inches and be embedded a minimum of 8 feet into firm weathered bedrock. Figure 4-1 shows the “possible house footprint” locations for Lots 1 and 2. Based on the amount of fill proposed for these locations , the piers for Lot 1would range in depth from approximately 8 feet for the western (uphill) half of Lot 1 and up to 48 ft for the eastern (downhill) half of Lot 1; the piers for Lot 2 would be approximately 28 feet in depth (MEI 2010a). The project building sites are not subject to significant potential hazards from seismic-related liquefaction, differential settlement, and lateral spreading hazards since these sites will be underlain by engineered fill and very dense to hard weathered Franciscan bedrock (JCA 2002). During site investigations, the Applicant’s geotechnical consultant identified three minor landslide features at the site (See Figure 4-1). All three features were located immediately above a man-made road cut or excavation, and slope movement was restricted to the soil mantle and/or shallow zone of weathered rock beneath the soil. Only one of these features has the potential to interfere with the proposed cut and fill slopes of the project and is located along the southwestern edge of the Lot 1 building pad (MEI 2010a). The Applicant’s geotechnical consultant has recommended that keyways and benchways be extended to remove undocumented fill and anticipates this landslide would be removed or repaired as part of fill slope construction (MEI 2010a). Site Grading The 2010 project’s grading estimates are presented in Table 2-1 of the Project Description. The 2010 project site preparation and grading activities include: cut and fill to create level lots, construction of drainage features, construction of the main access road, construction of building pads and driveways, and construction of slope stability features such as rockbolting or tiebacks, geogrids, and engineered slopes. The 1992 analysis did not consider grading of building pads or driveways. 2010 project grading involves substantially more cut and fill activities than in 1992. The Applicant is proposing to place approximately 60 feet of engineered fill along the southeast facing slope of the Lot 1 parcel and to also cut into this side slope up to roughly 28 feet in height, resulting in cut and fill slope gradients that are approximately 1:1. Grading for the Lot 2 parcel is more moderate, involving the placement of up 20 feet of artificial fill to level the building pad area. Lot 2 fill slopes, however, would also be an approximate 1:1 gradient (MEI 2009). The access road would require the placement of up to 30 feet of artificial fill to meet the proposed finished grades for Lots 1 and 2 (JCA 2002). County grading standards generally require a minimum 2:1 gradient for all graded slopes, but the Applicant is requesting an exception to this since the County standards would result in more cut and fill activities than the proposed grading plan. The Applicant’s geotechnical consultant recommended the use of rock bolting and geotextile reinforcements on existing and planned cut and fill slopes greater than 2:1 to provide adequate slope stability (JCA 2002 and MEI 2008). The exception to the 2:1 gradient requirement and stability reinforcements is generally required for Lot 1 development given the existing topography, the need to level the site to enable home



construction, and the existing road location, which cannot be moved further east without cutting into the eastern wall of the valley. Erosion, Subsurface Drainage, Topsoil Loss, and Soil Creep The 2010 project would cut and fill approximately 88,485 cubic yards of earth material during construction. The Applicant would implement standard measures to control wind and water erosion and potential sediment runoff during construction. Following construction, erosion and sediment runoff would be controlled by the project’s landscaping and drainage plans. The Applicant’s drainage plan shows that surface drainage from both Lot 1 and Lot 2 would be routed via buried storm drain pipes to a main storm drain pipe along the east side of the private road and discharged at a headwall at the southwestern end of Lot 1. No drainage would be discharged on or into proposed fill. Inadequate site drainage could reduce the stability of the existing and planned cut and fill slopes. The Applicant’s geotechnical consultant has recommended that the project’s civil engineer and general contractor install sub-drains in areas having potential water sources, such as at the toe of the fill slope, in the existing swale area near the access road, and the where the planned fill makes contact with the existing fill in order to provide adequate subsurface drainage on site (JCA 2002). The precise locations and exact number of sub-drains will not be known until grading is underway. Subdrains may be required on or adjacent to the building envelope as a result of field conditions, and the Applicant’s geotechnical consultant has recommended that the location of subdrains on or adjacent to the building envelope be surveyed during installation to prevent pier drilling from potentially damaging the subdrains (MEI 2010b). The Applicant’s geotechnical consultant has also recommended that subdrains include cleanout risers at their up-gradient ends and at most sharp directional changes to facilitate maintenance of the subdrains (MEI 2010b). The cut and fill activities would remove surface vegetation and organic topsoil. The Applicant’s geotechnical consultant has recommended that this organic topsoil should not be used as fill material and should instead be stockpiled on site for future landscaping purposes. During site investigation, the Applicant’s geotechnical consultant observed evidence of soil creep on site at various locations. Soil creep is a phenomenon whereby soils on slopes move downhill slowly under the forces of gravity during prolonged periods of elevated moisture content (JCA 2002). Soil creep would impose lateral loading on building foundations or result in rock or debris fall as topsoil is pushed over a steep slope such as would exist at the planned Lot 1 cut slope. The Applicant’s geotechnical consultant has recommended foundation design measures to reduce the potential impact of soil creep at the site. Non-Engineered Fill, Expansive Soils, Long-term Fill Settlement, and Septic Drainfields Building Pad Construction: The Applicant’s geotechnical consultant encountered approximately 10 feet of artificial fill in the existing valley on Lot 1 and 30 feet of artificial fill within the flat basin of Lot 2. The fill material is associated with past quarry operations and is slightly less dense at depth (JCA 2002). Variable in nature, the fill has a high degree of soft-to-firm, organic silts and clays mixed with gravels, which could exhibit expansive, or shrink-swell, behavior.



In order to provide a stable base for the proposed Lot 1 house pad, the geotechnical consultant has recommended removing the entire thickness of the existing non-engineered fill beneath Lot 1 so that a new engineered fill slope may be constructed. The Lot 1 fill removal would occur to at least the southwestern edge of Lot 2, where the approximately 10-foot tall 1:1 geogrid reinforced fill slope would be constructed separating the two lots. The non-engineered would be removed, and if it meets the soil requirements of the required fill, could be put back in place following the recommended measures for engineered fill placement. The majority of the fill underlying the Lot 2 building pad area, however, is proposed to remain in place (expect for fill in the area of the drainfields) since the grading of Lot 2 is expected to be benched. The existing fill to remain in place is confined on three sides by native soil and/or bedrock, will be buttressed on the southwest by the new engineered fill slope, and will not form an unstable slope face (JCA 2002 and MEI 2010). The potential for long term differential settlement of consolidated fill materials would be on the order of 2 to 6 inches for Lot 1 building pad and 5.2 inches for the Lot 2 building pad (JCA 2002 and MEI 2009). The Applicant’s geotechnical consultant has recommended measures related to fill selection, compaction, and foundation design that reduce the potential impacts associated with long term fill settlement. Septic Drainfield Construction: San Mateo County regulations prohibit septic drain fields from being located in areas with more than 12 inches of fill and from being closer than 50 feet to any filled place on slopes greater than 35 percent. The Lot 1 primary and expansion septic drainfields (See Figures 2-12 and 2-13) are located in native soil on a knoll and would not be covered by fill. The drainfields are approximately 260 feet from the possible house footprint for Lot 1. The Lot 2 primary septic drainfield is located in an area of existing non-engineered fill, approximately 52 feet from the possible house footprint for Lot 2. The construction of the Lot 2 drainfield would require the removal and stockpiling of approximately 20 feet of existing fill, installation of the Lot 2 drainfield into competent native soil and/or bedrock, and backfilling of the drainfield area (MEI 2010b). The Lot 2 expansion septic drainfield is also located in an area of existing non-engineered fill, approximately 190 feet from the possible house footprint for Lot 2. The construction of the Lot 2 expansion drainfield would therefore also require the removal and stockpiling of approximately 20 feet of existing fill prior to installation of the drainfield. The sequence of construction for the Lot 2 septic drainfield would consist of removal existing non-engineered fill, construction of the primary, expansion and emergency overflow drainfields in native soil, and then the placement of the engineered fill needed to construct the house pad for Lot 2. The Applicant would be required to install both the Lot 1 and Lot2 primary and expansion drainfield areas, as well as the Emergency Overflow trench at the time of initial site construction per conditions imposed on the project in 1992 (see Section 4.6.1 in Public Health). The proposed Lot 2 house footprint is located over 100 feet from the proposed primary drainfield and therefore pier drilling for the house foundation would not impact the proposed Lot 2 drainfield (MEI 2010b). Additionally, the location of the recommended subdrains would have to take into consideration the drainfields and be routed around them. The subdrains would be sited



during construction based on field conditions and could be designed to avoid the septic drainfields. Please refer to Section 4.6, Public Health and Safety for further discussion and analysis of the proposed septic drainfields. Slope Instability The Applicant’s geotechnical consultants have performed slope stability modeling on the existing and planned bedrock cut slopes and on the planned fill slopes. At the time of the initial stability modeling in 2002, the Applicant was proposing fill slope gradients of approximately 2:1 along the edge of the proposed building pads and cut slopes of 1:1. Although the Applicant’s 2002 stability modeling indicated the existing and planned bedrock cut and planned fill slopes had a low probability of failure and were therefore stable, the potential for slope instability remained in the event substantial zones of more weathered or fractured bedrock were encountered during grading activities (JCA 2002). To mitigate this potential impact, the Applicant’s geotechnical consultant at the time recommended cutting bedrock slopes to a maximum gradient of 2:1 and/or incorporating rock bolts and wire fabric in conjunction with the rock bolting. The Applicant has revised the site plans since 2002 to include planned fill slopes of 1:1 in the southern portion of the Lot 1 building pad and between Lots 1 and 2 along the southwestern edge of the Lot 2 building pad. Supplemental slope stability modeling performed on two cross sections in accordance with California Division of Mines and Geology guidelines for evaluating and mitigating seismic hazards indicates the proposed 1:1 bedrock cut and proposed 1:1 fill slopes at Lot 1 would have a low probability of failure. The Applicant’s geotechnical consultant has recommended the use of geotextile reinforcements on proposed 1:1 fill slopes and the use of tieback anchors, rock bolts, or soil nails on proposed bedrock cut slopes in the eastern portion of Lot 1 (see Figures 2 and 3 in MEI, 2010a). The Applicant’s geotechnical consultant has also performed supplemental slope stability modeling to demonstrate the global stability of the interface between the proposed fill material and the underlying native material in response to the County’s geotechnical review and concern over the capability of the underlying natural materials to support the weight of the proposed fill materials. This supplemental modeling indicates that the underling native soil and bedrock materials can support the proposed fill so long as the planned engineered fill is keyed and benched into competent native soil and bedrock in accordance with all geotechnical engineering and field recommendations. 4.1.6 2010 Mitigation Measures The Applicant is seeking an amendment to the recorded Final Subdivision Map and Grading Permit. The Applicant’s geotechnical analyses indicate that the foundations must be capable of resisting movement of the support soil imposed by the sloping terrain, potential fill settlement, and future earthquakes and that some remedial work on existing landslides is necessary to develop the project. As in 1992, the Applicant’s current geotechnical consultant has found the proposed 2010 project is feasible based on their observations, subsurface investigations, lab testing, and engineering analysis, provided the geotechnical recommendations made in the



reports identified at the beginning of this section are carefully followed and implemented by the Applicant. The project’s 2010 geotechnical recommendations are based on the proposed 2010 grading plan and update the 1992 EIR’s mitigation measures. As in 1992, mitigation measures which are conditions on the Grading permit would be detailed in a letter from the County to the Applicant and must be fulfilled before that permit is issued. Many of the updated 2010 geotechnical mitigation measures would be listed as conditions on both the 2010 Grading Permit and Subdivision Map. Mitigation Measures to Reduce Potential Grading Impacts Impact GEO-1: Project grading and slope stability features throughout the site should be constructed in accordance with the County Grading Ordinance. After construction these features may need monitoring to assure safety on the privately maintained project roads and engineered slopes. Mitigation Measure GEO-1: As a condition of tentative map approval, regular inspection and maintenance of graded slopes, slope planting, rockbolting, and steel mesh on rock faces will be provided by a management entity meeting the requirements of San Mateo County or a geologic hazard abatement district as specified in Section 5105 of the Streets and Highway Code.

Effectiveness: Would ensure geotechnical engineering features installed to protect slope stability operate as planned and would reduce potentially significant impacts to less than significant.

Implementation: Provided for by the Covenants, Conditions, and Restrictions filed with the Final Subdivision Map.

Timing: On-going regular inspection required during life of the project. Monitoring: San Mateo County Planning and Building Department shall ensure

measure is incorporated into the subdivision’s Covenants, Conditions, and Restrictions. The property owners shall request a written report from the management entity inspecting the project features and shall retain the reports as proof of regular inspection and maintenance of project features. The property owners shall provide the inspection reports to the County upon request.

Impact GEO-2: Project development could be compromised if it is not designed and constructed according the recommendations of the geotechnical reports. Mitigation Measure GEO-2: The project shall be designed and constructed according to the following recommendations (Measure 1 from JCA, 2002; Measures 2 - 4 from MEI, 2010; Measure 5 required by San Mateo County):

1) All unretained temporary cuts into weathered bedrock shall be a maximum of 1:1. All temporary cuts into soil should be a maximum of 1.5:1. Excavations less than 5 feet high may be cut vertical. In the event ground water is encountered, slopes may require flattening.



2) Existing undocumented fill underlying areas to receive new engineered fill should be removed and replaced or reworked as engineered fill by the project’s geotechnical engineer-of-record.

3) The construction contractor shall be responsible for all shoring and bracing of temporary slopes and trenches excavated at the site in accordance with all applicable local, state, and federal safety regulations, including the current OSHA excavation and trench safety standards.

4) Due to the potential for variable soil conditions, field modifications of temporary cut slopes may be required, particularly below the groundwater level. Unstable materials encountered on the slopes during the excavation should be trimmed off, even if this requires cutting the slope back at a flatter inclination.

5) The Applicant must provide a final grading plan for review by the Department of Public Works and Building Inspection’s Geotechnical Section. Effectiveness: Would reduce potentially significant impact to less than significant Implementation: Required as a condition of the new Grading Permit/Final Grading Plan Timing: Measures would implemented during project construction Monitoring: San Mateo County Department of Public Works and Building

Inspection’s Geotechnical Section Mitigation Measures to Reduce Potential Erosion, Topsoil Loss, and Soil Creep Impacts Impact GEO-3: Improper drainage at the site could cause erosion or other soil slope instability. Mitigation Measure GEO-3: The control of surface run-off and subsurface drainage at the site is essential for continued slope stability and for minimizing erosion. Surface run-off and subsurface drainage shall be controlled by: Surface Run-off

1) Run-off along the slopes above the residential developments should be intercepted in lined ditches and carried to a natural drainage course.

2) Run-off should not be allowed to pond adjacent to building foundations. 3) Ground adjacent to building foundations should slope at no less than 2 percent from the

structure for a minimum of 10 feet 4) All roof downspouts and concentrated drainage shall be placed in a closed pipe collector

and directed away from the planned building to a suitable point of discharge. 5) Water collected in surface and subsurface drainage systems shall not be allowed to

discharge freely onto the ground surface adjacent to fill slope foundation soils and shall be conveyed away from fill slopes via buried closed conduits.

6) Surface runoff shall not be allowed to flow over the top of any artificial slope. 7) The ground surface at the top of the slope shall be graded away from the slope or a berm

or lined drainage ditch shall be provided at the top of the slope. 8) Lined swales shall be provided at the bases of descending slopes. 9) Annual maintenance of the surface drainage systems shall be performed. This

maintenance shall include inspection of surface drainage outfall locations to verify that introduced water flows freely through the discharge pipes and that no excessive erosion has occurred. If erosion is detected, the project’s engineer-of-record shall be contacted to evaluate its extent and to provide mitigation recommendations, if needed.



Subsurface Drainage Surface runoff measures 1 – 4 and subsurface drainage measures 1 – 3d from JCA, 2002; Surface runoff measures 5 – 10 and subsurface drainage measures 3e from MEI, 2009; Subsurface drainage measure 3f from MEI, 2009 as amended in MEI, 2010b; Subsurface drainage measure 3g from MEI, 2010b.

1) Subsurface drainage shall be incorporated into the design of the fill slope. 2) Subdrains shall be placed in areas identified as having potential water sources such as the

toe of the fill slope within the confines of the existing swale area near the existing site access road, where the planned fill makes contact with the existing fill or in areas of observed bedrock seeps.

3) For placement of subsurface drainage within the planned fill slope: a. A keyway shall be placed at the base of the fill slope. The keyway shall be a

minimum of 10-feet wide and extend a minimum of 1-foot into competent material. The excavation shall be cleaned of all loose material. The base of the key shall be graded to create a two percent (2%) minimum tilt toward the rear.

b. A toe drain is recommended for the planned fill slope. This drain shall consist of a minimum 4-inch diameter, perforated, Schedule 40 or equivalent, PVC pipe placed near the back edge of the key. The pipe shall be wrapped with filter fabric to prevent piping of soil materials into the drain. The pipe must have positive flow to a point of discharge outside the planned fill boundary. Solid pipe shall be used after the drain leaves the keyway area. A minimum 12-inch layer of approved drain rock shall be placed over the base of the key. The rock shall envelop the drain pipe in such a fashion that a minimum 2-inch clearance is kept between the pipe and native ground.

c. Additional subsurface drains shall be incorporated along the base of the fill slope at select intervals determined in the field by the project’s civil engineer and general contractor. Such a drain system shall consist of a minimum 4-inch diameter, perforated, Schedule 40 or equivalent PVC pipe placed near the back edge of the benched surface. The pipe shall be wrapped with filter fabric to prevent piping of soil materials into the drain. The pipe must have positive flow to a point of discharge outside the planned fill boundary. Solid pipe shall be used after the drain leaves the keyway area. A minimum 12-inch layer of approved drain rock shall be placed along the back edge of the bench and extend a minimum of 3-feet in vertical elevation from the back base of the bench. The dimensions of the drain rock will be contingent on actual field conditions encountered. The rock shall envelop the drain in such a fashion that a minimum 2-inch clearance is kept between the pipe and the native ground.

d. Subsurface drainage shall not be placed beneath the planned building envelope (“possible house footprint”). This is to reduce the potential for damage of the subdrain system that could result during drilling for the foundation piers.

e. Schedule 80 PVC shall be used in areas where bench and keyway subdrain pipes will be buried beneath more than 20-feet of fill.

f. To avoid damaging pipes during pier drilling for the proposed residences, subdrain pipes on or adjacent to building envelopes shall be surveyed at the time of installation.

g. Subdrains shall be provided with cleanout risers at their up-gradient ends and at sharp directional changes to facilitate maintenance.



Effectiveness: Would reduce potentially significant impact to less than significant Implementation: Measures to be incorporated into the Grading Permit/Final Grading

Plan Timing: The measures shall be implemented during project construction Monitoring: San Mateo County Department of Public Works and Building

Inspection’s Geotechnical Section Impact GEO-4: Project grading would remove site topsoil. Mitigation Measure GEO-4: On-site soils having an organic content greater than 3 percent by volume should not be used as fill material under structures and pavements and shall be stockpiled for use in site landscaping (Recommended by JCA 2002, as modified by MEI 2010).

Effectiveness: Would ensure soil meeting the requirements for engineered fill would be used on site. Would reduce a potentially significant impact to less than significant.

Implementation: Measure to be incorporated into the Grading Permit/Final Grading Plan

Timing: Measure to be implemented during project construction Monitoring: San Mateo County Department of Public Works and Building

Inspection’s Geotechnical Section Impact GEO-5: Soil creep could present a hazard to permanent structures built at the site. Mitigation Measure GEO-5: The potential hazards of soil creep would be mitigated through the pier and gradebeam foundation design measures discussed under Mitigation Measure GEO-6 below (Recommended by JCA 2002).

Effectiveness: Would reduce potentially significant impact to less than significant. Implementation: Mitigation Measure GEO-6 to be incorporated into the Grading

Permit/Final Grading Plan Timing: Pier and gradebeam foundation design measures to be implemented

during home design and construction Monitoring: San Mateo County Department of Public Works and Building

Inspection’s Geotechnical Section Mitigation Measures to Reduce Seismic Hazards Impact GEO-6: The presence of deep non-engineered fill, steep slopes, soil creep and the project’s location in a region of seismic activity could present hazards to the permanence of structures built at the site. Mitigation Measure GEO-6: Potential hazards associated with regional seismicity shall be mitigated by: Design standards from MEI, 2008 and MEI, 2011; Fill material measures 1 – 4 and 7 from JCA, 2002; Fill material measures 5, 6, 8, and 9 from MEI, 2009; Pier and gradebeam foundation measures 1 – 9 from JCA, 2002 as revised by MEI, 2008;



Design Standards All improvements shall be designed according to the 2010 California Building Code (CBC) Earthquake Design Parameters. The following seismic design parameters apply to the project:

Site Class C Soil profile: very dense soils and soft rock (Table 1613.5.2) Mapped Spectral Accelerations for 0.2 section Period: Ss=1.997 (Site Class B) Mapped Spectral Accelerations for a 1-second Period: S1=1.064 (Site Class B) Design Spectral Accelerations for 0.2 second Period SDS=1.331 (Site Class C) Design Spectral Accelerations for a 1-second Period SD1=0.922 (Site Class C)

Fill Material

1) Fill material shall be compacted with reference to the most recent edition of the American Society of Testing and Materials’ (ASTM) test Designation D1557.

2) All fill material shall be placed in uniform lifts that do not exceed 8-inches in uncompacted thickness, moisture conditioned to achieve a moisture content of optimum moisture or slightly above, and compacted to 90 percent relative compaction. Any surface to receive fill should be scarified for the upper 6-inches and recompacted to 90 percent relative compaction.

3) Placement of fill against slopes shall be performed by excavating a key at the base of the fill slope and then benching compacted soil into the hillside as grades are raised. The depth of the keys shall be established in the field by an engineering geologist or geotechnical engineer.

4) Uncontaminated, on-site soil and/or weathered bedrock, may be suitable for fill provided it is free of rocks or lumps greater than 6-inches in longest dimension, non-expansive, and with limited deleterious material.

5) The use of on-site soils with greater than 3 percent organics by volume as fill material is not permitted. Any required import fill should have a plasticity index of less than 15 percent and should be predominately granular material with less than 5 percent fines (material passing a No. 200 sieve) and 100 percent of particle sizes smaller than 1-inch. Pea gravel will generally not be allowed. The project’s geotechnical engineer-of-record will review the fines content of the proposed fill materials prior to importing to the site and may allow a fines content of up to 60% in the fill material to be used on site.

6) The project’s geotechnical engineer-of-record shall be notified to observe and, if necessary, test selected fill soil at least three days prior to it being brought to the site. The imported fill shall require approval from the project geotechnical engineer-of-record prior to being imported to the site.

7) The project’s geotechnical engineer-of-record shall be notified at least 48 hours prior to the start of the site preparation, fill placement, and foundation installation phases of construction in order to coordinate work with the grading contractor.

8) The project’s geotechnical engineer of record shall observe and test all site preparation, fill placement, and foundation installation activities at the site in order to confirm conformance with the recommendations contained in the project’s geotechnical reports and allow for design changes in the event that subsurface conditions differ from those anticipated and analyzed.



9) Existing undocumented fill underlying areas to receive new engineered fill shall be removed and replaced or reworked as engineered fill, as deemed necessary in the field by a geotechnical engineer or engineering geologist. Excavations that extend below existing or finished grade resulting from removal of undocumented fill material shall be backfilled with engineered fill, placed and compacted as discussed in the JCA report.

Foundations The two proposed single family wood-framed structures shall be placed on pier and grade foundations. All piers shall be extended through any existing and planned fill and derive their end bearing capacity from the underlying weathered bedrock. The following criteria shall apply to the pier and gradebeam foundation design:

Pier and Gradebeam Foundations

1) All piers shall have a minimum diameter of 16-inches, and be cage reinforced. Loose

material existing at the base of any pier shall be adequately tamped or removed. 2) All piers for the planned building foundations shall be embedded a minimum depth of 8-

feet into firm weathered bedrock. The actual depth, however, will be contingent on design loads and may change based on field conditions encountered.

3) All grade beams shall be embedded a minimum of 12-inches below subgrade surface and contain a minimum of two No. 5 steel reinforcing bars placed near the top and bottom of the beam. However, actual type and location of such reinforcement shall be established by the Project Structural Engineer.

4) All foundation piers shall be designed for an allowable end bearing bedrock value of 8,300 psf. The allowable end bearing capacity of the piers shall be increased by one-third for temporary loads such as wind or seismic.

5) Piers extended through the planned and existing fill shall be designed to resist potential down drag forces imposed on the pier perimeter from anticipated fill settlement. A down drag pressure equivalent to 500 psf acting along the outer pier surface shall be incorporated into the design of the pier.

6) Due to the noted sandy soil characteristics and high ground water levels observed, particularly in the area of the Lot 2 building pad, there is a strong probability that portions of the pier excavations may require casing until the steel reinforcing and concrete has been placed. This will be determined by the on-site geologist.

7) Some of the Franciscan bedrock material may offer substantial resistance to light drilling equipment. A geotechnical engineer or engineering geologist shall be on-site to observe all pier drilling for the planned pier foundations in order to note conformance with recommendations and, if necessary, to make additional recommendations concerning pier depths in the field as warranted by changing field conditions.

8) Exterior concrete flatwork, walkways, or steps should be independent of the pier and grade beam foundations in order to reduce the potential for differential movement if the supporting soils change in volume.

Effectiveness: Would reduce potentially significant impact to less than significant

levels Implementation: Measure to be incorporated into Grading Permit/Final Grading Plan Timing: Measures to be implemented during final project design and

construction



Monitoring: San Mateo County Department of Public Works and Building Inspection’s Geotechnical Section

Impact GEO-7: Existing shallow landslides on-site could affect the stability of the proposed grading and future shallow landslides could occur where there is top soil above more stable rock below or on the face of a planned fill slope. Mitigation Measure GEO-7: The existing and potential shallow landslides and the impact on slope stability shall be controlled by (JCA 2002): Existing Shallow Landslides

1) The shallow slide mapped on the southwest portion of Lot 1 shall be removed during grading for the planned fill slope.

Future Landslide Potential The site’s future landslide potential shall be mitigated through the use of slope stability enhancement measures discussed under Mitigation Measure GEO-10 below.

Effectiveness: Would reduce potentially significant impact to less than significant Implementation: Measure to be incorporated into Final Grading Plan/Grading Permit Timing: Measure to be implemented during project construction Monitoring: San Mateo County Department of Public Works and Building

Inspection’s Geotechnical Section Mitigation Measures to Reduce Non-Engineered Fill, Expansive Soils, Long-term Fill Settlement, and Septic Drainfield Impacts Impact GEO-8: There exists a potential for long term settlement of the existing and proposed fill in the area planned for development. Mitigation Measure GEO-8: The potential impacts associated with long-term settlement shall be mitigated by (Concrete slab-on-grade measures from Crosby, 2002; appurtenant structure measures 1 - 3 from JCA, 2002 as modified by MEI, 2009; appurtenant structure measure 4 from MEI, 2009): Concrete Slab-On-Grade

1) Slab-on-grade flooring is not permitted. 2) For garage slabs, no reinforcing steel shall pass from the slab to the building foundation. 3) The subgrade surface shall be adequately compacted prior to the placement of base rock.

The slab shall rest on a minimum bed of 8-inches of Class 2 aggregate base rock, covered by polyethylene sheeting and 2 inches of sand. Closely spaced construction joints within the floor slabs are recommended to control cracking. Exterior concrete slabs, and steps shall not be structurally tied to the foundation of the planned residences.



Appurtenant Structures

1) Appurtenant structures such as pavements, pools, tennis courts and other improvements, including utilities could be designed as rigid elements capable of sustaining differential settlement.

2) Hardscapes and other site structures such as utility lines not supported on piers shall be designed to tolerate the potential long term settlement of the underlying fill.

3) An effort shall be made to align utility lines in such a manner as to minimize abrupt changes in differential settlement that could occur where existing fill thicknesses vary over short distances.

4) Improvements for which the anticipated differential fill settlement is not acceptable shall be supported on piers gaining supporting the underlying bedrock.

Effectiveness: Would reduce potentially significant impact to less than significant Implementation: Measure to be incorporated into Final Grading Plan/Grading Permit Timing: Measures to be incorporated into final project design and implemented

during construction Monitoring: San Mateo County Department of Public Works and Building

Inspection’s Geotechnical Section Impact GEO-9: The proposed Lot 2 drainfield would require the removal and stockpiling of non-engineered fill, resulting in potentially unstable temporary slopes from stockpiled material. Mitigation Measure GEO-9: The impacts associated with potentially unstable slopes created during installation of the Lot 2 drainfield shall be mitigated by (MEI 2010b):

1) All fill shall be removed in accordance with applicable local, state, and federal safety regulations, including the current OSHA excavation and trench safety standards.

2) The project contractor shall take measures to protect stockpiled soil from saturating during rainstorm events and spread this material relatively uniformly across the stockpiling area to minimize surcharge loading.

3) The placement of significant amounts of stockpiled soils adjacent to the planned Lot 2 drainfield should be avoided to reduce the potential for high surcharge loads and subsequent failure of temporary cut slopes.

4) The suitability of the planned stockpile location shall be reviewed in the field by the project’s geotechnical engineer.

5) Replaced fill should be keyed and benched into competent native soil and bedrock in accordance with Mitigation Measures GEO-6 and field recommendations made by the project’s geotechnical engineer at the time of grading.

Effectiveness: Would reduce potentially significant impact to less than significant Implementation: Measure to be incorporated into Final Grading Plan/Grading Permit Timing: Measures to be implemented during construction Monitoring: San Mateo County Department of Public Works and Building

Inspection’s Geotechnical Section



Mitigation Measures to Reduce Slope Instability Impacts Impact GEO-10: There is the potential for slope instability on existing and planned cut slopes and planned fill slopes with gradients steeper than 2:1 (horizontal to vertical). Mitigation Measure GEO-10: The potential impacts associated with slope instability shall be mitigated by (Stability measure from JCA, 2002 and MEI, 2009; Existing and planned cut slope measure from JCA, 2002 and MEI, 2009; Planned fill slope measure from MEI, 2009):

1) Existing and planned 1:1: cut slopes and planned 1:1 fill slopes shall be graded to a 2:1 (horizontal to vertical) gradient to provide adequate slope stability or be reinforced in accordance with measure 3 below.

2) Existing and planned cut slopes steeper than 2:1 shall be rockbolted to provide adequate slope stability. If implemented, the following design considerations shall apply to rock bolting:

The rock bolting should concentrate on increasing the stability of the intersecting joint patterns that fall outside of stable zones implied in geotechnical analysis.

Rock bolts shall consist of 1-inch minimum diameter bolts placed on ten foot centers in each direction and the bolts shall be placed a minimum of 10-feet deep. The bolts shall be grouted or epoxied for the final three feet of depth.

The attitude of the bolts, their depth, and their frequency will be laid out in the field during placement. It is anticipated that a portion of the slope will require the use of a wire fabric in conjunction with the bolting.

In the more weathered areas of slope, wire fabric in conjunction with bolting shall be used as determined in the field by a geotechnical engineer or engineering geologist.

Tensioning of the bolts will be moderate and large deflections of the surface material are considered undesirable.

The landscape contractor shall select a native erosion control grass seed mix per the Preliminary Landscaping Plan that will become established on the bolted slope.

Alternatively, the material encountered at the proposed 1:1 cut slope surface shall be assessed by the project’s geotechnical engineer. If soft bedrock or bedrock with fracturing or bedding orientation substantially different from that anticipated in the project’s geotechnical analyses are encountered, the use of grouted tiebacks or soil nailing may be used to stabilize portions of the cut slopes. If implemented, the following design considerations shall apply to tiebacks and soil nails:

The tieback anchors or soil nails should be designed to resist dead plus live loads using an allowable skin fraction value of 750 pounds per square foot (psf) for the length of the anchor embedded into competent sandstone or shale with a one-third increase allowed for transient loads, including wind and seismic forces.

The length of the tiebacks or soil nails in non-competent material (i.e., soil or rock) shall be neglected for support of vertical loads.

The tiebacks and soil nails shall be constructed at an angle of no more than 20 degrees from the horizontal to limit the influence of vertical forces on the system and to facilitate the placement of grout.



A minimum of approximately 10 percent of the total number of tiebacks or soil nails should be pull tested to a minimum of 1.5 times the design pullout resistance.

3) Planned fill slopes steeper than 2:1 and greater than 2 feet in height shall be reinforced with geotextiles to achieve long term slope stability as follows:

1:1 fill slopes between approximately 2 feet and 15 feet in height should be provided with minimum geogrids lengths of 80% of the total slope height with a maximum vertical spacing of 2 feet.

1:1 fill slopes greater than 15 feet in height should be provided with geogrids lengths up to approximately 150% of the total height located in approximately the lower 35% of the slope, gradually reducing to approximately 100% of the slope height in the upper 25 percent of the slope.

The project civil engineer shall work with the earthwork contractor to develop the final fill slope geogrids reinforcement design and configuration.

Effectiveness: Would reduce potentially significant impact to less than significant Implementation: Measure to be incorporated into Final Grading Plan/Grading Permit/ Timing: Measures to be implemented during construction Monitoring: San Mateo County Department of Public Works and Building

Inspection’s Geotechnical Section



4.2 HYDROLOGY 4.2.1 1992 EIR Analysis The hydrological impacts described in the 1992 EIR were associated with storm water runoff, changes to drainages, and the effects of erosion on San Francisco Water Department lands and the Hetch Hetchy water pipeline. The 1992 EIR identified the permits required for relocation of the drainage, and recommended consultation with the Regional Water Quality Control Board (RWQCB), U.S. Army Corps of Engineers (USACE), the California Department of Fish and Game (CDFG), and the San Francisco Water Department as mitigation. The 1992 EIR noted that the lower portions of Cordilleras Creek have long created drainage problems to the cities of San Carlos and Redwood City because of flooding caused by insufficient culvert capacity, adjustments in the creek bed alignment, and blockage of culverts by debris and sedimentation upstream. The project site was described as being located in a north-to-south canyon basin, surrounded by steep slopes. There are no year-round water flows on the site. The north and west slopes are dissected by six deeply cut ravines that carry storm water into the project site during rainfall events. Four of the ravines flow west-to-east and two flow north-to-south. The two north-to-south ravines and one of the west-to-east ravines carry storm water into the northern end of the canyon floor. Most of the canyon floor was widened and leveled between 1961 and 1974. The 1992 EIR stated that the maximum storm water runoff from the entire drainage basin surrounding and including the site is estimated to be approximately 20 cubic feet per second for a 25-year storm of one hour duration, based on the San Mateo County design criteria for residential areas. Mitigation Measures identified in the 1992 EIR were for potentially significant impacts associated with increased storm water runoff, improperly or inadequately sized drainage facilities constructed for the project, and potential loss of soil (erosion) as a result of the project’s grading activities. It also recommended that the Applicant consult with the CDFG and the USACE to determine whether permits were required under California Fish and Game Code section 1600 or the federal Clean Water Act for relocation of the ephemeral drainage channel. For more detailed information about the agency consultation as a result of the 1992 EIR process, please see Section 4.3, Biology, in this Chapter. Additionally, the 1992 EIR considered the visual impact of altered drainages to be a locally important effect. For a detailed analysis of the visual effects of this project, please see Section 4.4, Aesthetics, of this Chapter. 4.2.2 2010 Environmental Setting This section updates the 1992 EIR setting where necessary. According to the most recent FEMA Flood Insurance Rate Map (FIRM), the project site is not within a 100-year flood zone. The nearest 100-year flood zone is located where Edgewood Road crosses Cordilleras Creek about 0.66 mile south of the project site and is designated a “Special Flood Hazard Area” (FEMA 2010).



TRA analysts conducted two site visits during wet weather (Feb 2 and Feb 10, 2010) to determine if the hydrologic setting changed since the 1992 EIR was prepared. Both site visits occurred within a couple of days of storm events. No substantive changes to the hydraulic setting have occurred in the intervening 20 years. As stated in Chapter 2, Project Description, the project site is a relatively flat-bottomed canyon, open to the south and surrounded by steep-sided slopes on the west, north, and east, as shown in Figure 2-4, Existing Topography. The elevation ranges from 200 feet above mean sea level to just over 400 feet. Slopes are generally 20 percent to 50 percent but some portions of the site have slopes greater than 50 percent. The steeper portions of the site are not developed and are mostly covered with native oak woodland and non-native plants. Chapter 2 also notes that the past quarry activities created a steep, bare rock face on the western side of the canyon and removed much of the native vegetation in places around the canyon walls and bottom. The quarrying activities also removed natural drainage features and altered the drainage patterns on the canyon floor. The flat canyon bottom contains soil imported to the site for fill. Additional fill has been imported since 1992 under the approvals granted for that project. As the canyon opens out into its widest part, where the two lots are proposed to be located, the canyon floor is mostly covered with imported fill. Storm water flows across the site and collects in a drainage at the base of the eastern slope, where it is eventually conveyed to Cordilleras Creek. The drainage is ephemeral; it only flows after storms. Aerial photographs taken on May 23, 2004, four days after a storm event, show that storm water collects at the base of the two north-to-south ravines. One area of flooding covers less than 1,600 square feet (0.04 acre) and extends less than ten feet from the base of the western north-to-south ravine, while another area of flooding covers less than 150 square feet (0.003 acre) and extends less than eight feet from the base of the eastern north-to-south ravine. These areas of flooding were also observed during the two wet weather site visits conducted in February 2010. 4.2.3 2010 Regulatory Setting This section identifies the regulatory requirements designed to prevent the effects of hydrologic hazards present in the project area. All infrastructure associated with the project would be subject to these regulations. Federal The federal nexus of regulations is focused on jurisdictional wetlands, and is discussed in Section 4.3, Biology of this Chapter. State California National Pollution Discharge Elimination System (NPDES) Program and Storm Water Pollution Prevention Plans (SWPPPs) Clean Water Act Section 402 provides for U.S. Environmental Protection Agency (EPA) regulation of non-point source pollution within the National Pollutant Discharge Elimination System (NPDES) program, but the EPA has delegated administration of California’s NPDES program to the California State Water Resources Control Board (SWRCB). Under the California



program, if a project involves construction activities on an area one acre or greater (including clearing, grading, stockpiling or excavation), the project must submit a Notice of Intent (NOI) to the SWRCB, apply to SWRCB for coverage under the NPDES General Permit for Discharges of Storm Water Associated with Construction Activity (General Permit), and prepare a Storm Water Pollution Prevention Plan (SWPPP). Although an inquiry regarding coverage of the 1992 Project under NPDES was submitted to the SWRCB in 1996 when the subdivision map was originally filed, the project applicant must submit an NOI and officially apply for coverage under the General Permit only when there are plans to initiate construction. The SWPPP must identify potential sources of sediment and other pollutants that affect the quality of storm water discharges and must describe Best Management Practices (BMPs) that will be implemented in order to reduce or eliminate sediment and other pollutants in storm water and non-storm water discharges. Additionally, the SWPPP must describe a monitoring program, which is to be implemented if any of the BMPs fail. A SWPPP will be prepared for the project according to NPDES requirements. Local San Mateo County General Plan The following General Plan policies pertain to hydrological impacts of the proposed project: General Policy 1.22, Regulation of Development: Regulate development to protect vegetative, water, fish and wildlife resources. Regulate land uses and development activities to prevent, and if infeasible mitigate to the extent possible, significant adverse impacts on vegetative, water, fish and wildlife resources. Place a priority on the managed use and protection of vegetative, water, fish and wildlife resources in rural areas of the County. General Policy 1.25, Protect Water Resources: Ensure that development will: (1) minimize the alteration of natural water bodies, (2) maintain adequate stream flows and water quality for vegetative, fish and wildlife habitats; (3) maintain and improve, if possible, the quality of groundwater basins and recharge areas; and (4) prevent to the greatest extent possible the depletion of groundwater resources. Consistency: Impacts to vegetation and wildlife are discussed in section 4.3 Biology. Both the approved 1992 project and the currently proposed two-lot subdivision would alter existing on-site drainage patterns in several ways; including relocation of the ephemeral drainage channel (see section 4.3 Biology for a description of the channel). The current project proposes to construct a vegetated swale along the canyon’s eastern side to collect and carry surface water runoff and a bio swale along the proposed access road to catch and hold runoff from the road surface. Both the approved 1992 project and the proposed 2010 project would manage storm water runoff so that runoff volumes do not exceed pre-development volumes. Neither project would affect groundwater resources. Both the 1992 and the proposed 2010 project would be consistent with these General Plan policies regarding the protection of water resources.



Provision C3 of the San Mateo County NPDES Permit Because San Mateo County discharges storm water to San Francisco Bay via county-managed storm drains, the County is required by the federal Clean Water Act and the California Porter-Cologne Water Quality Control Act to have its own NPDES permit. Provision C.3.f of the County’s permit states that Hydro-Modification Management Plans (HMPs) must be implemented for government and private development and re-development projects that occur within the county so that post-project runoff rates and durations do not exceed pre-project runoff rates and durations. Consistency: Both the approved 1992 project and the proposed 2010 project would be consistent with the San Mateo County C3 regulations. Storm water runoff would be managed so that runoff rates and durations do not exceed pre-development amounts. 4.2.4 Thresholds of Significance This SEIR analysis considers whether the proposed 2010 project would result in new or substantially more severe impacts than identified in the 1992 EIR and also examines whether the project would result in a potential hydrology impact as identified in Appendix G to the CEQA Guidelines. In accordance with Appendix G of the CEQA Guidelines, the proposed project could have a significant environmental impact on hydrology if it would:

a) Violate any water quality standards or waste discharge requirements; b) Substantially deplete groundwater supplies or interfere substantially with groundwater

recharge such that there would be a net deficit in aquifer volume or a lowering of the local groundwater table level;

c) Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river, in a manner which would result in substantial erosion or siltation on- or off-site;

d) Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river, or substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off-site;

e) Create or contribute runoff water which would exceed the capacity of existing or planned storm water drainage systems or provide substantial additional sources of polluted runoff;

f) Otherwise substantially degrade water quality; g) Place housing within a 100-year flood hazard area as mapped on a federal Flood Hazard

Boundary or Flood Insurance Rate Map or other flood hazard delineation map; h) Place within a 100-year flood hazard area structures which would impede or redirect

flood flows; i) Expose people or structures to a significant risk of loss, injury or death involving

flooding, including flooding as a result of the failure of a levee or dam; and j) Inundation by seiche, tsunami, or mudflow

4.2.5 2010 Project Impacts The proposed project is consists of fewer lots than the currently approved 1992 project but the types of potential hydrologic impacts remain the same. The proposed project could create



potentially significant impacts, especially since the amount of grading is greater than the original 1992 project. Impacts to waters of the State are discussed in Section 4.3, Biology of this Chapter. The project would not use groundwater and therefore would not deplete groundwater supplies or interfere substantially with groundwater recharge. The project site is not located in a FEMA 100-year flood zone and therefore would not place housing within a 100-year flood hazard area or impede or redirect flood flows. The project would not have discharges of water that would violate any water quality standards or waste discharge requirements. The project is not subject to inundation by seiche, tsunami, or mudflow. Changes to Drainage Patterns The 2010 drainage plan prepared by MacLeod and Associates (Figures 2-10 and 2-11) is similar to the 1992 drainage plan. Runoff would be collected from up slope areas, directed through a series of lined ditches, headwalls, culverts, energy dissipaters, catch basins, and subdrains and ultimately discharged to the ephemeral drainage channel south of the access road to the Curia parcel. The proposed drainage system would also include vegetated swales, a bioswale, drain boxes and pipes, headwalls, culverts, energy dissipaters, catch basins, and underground collection systems (subdrains) for drainage in fill areas (Figures 2-10 and 2-11). As stated in Chapter 2, Project Description, multiple drainage lines are proposed for the two parcels. All lines would eventually discharge into a main drain pipe along the eastern edge of the proposed private road and ultimately be released into the ephemeral drainage channel on the west side of the entrance road (just south of the access road to the Curia parcel). High points on both lots generally bisect the lots on a north to south axis. This means that the majority of drainage on both parcels is directed toward the eastern and western edges of the parcels. Runoff from the eastern canyon wall (area of Scenic Easement) would be collected in the vegetated swale constructed at the toe of the eastern slope. A 240-foot long bio-swale would be installed on the west side of the roadway north of the driveway to the Curia property. This bio-swale would collect and filter runoff from the new paved roadway surface. Typical sections located in the upper left corner of Figure 2-10 indicate the bio-swale on the west side of the roadway and also a vegetated swale along the east side of the roadway. The bio-swale would be approximately six feet wide and one foot deep. The bottom of the swale would have 1 ½ inches of drain rock wrapped with filter fabric, then covered with one foot of top soil and which would extend up the sides of the swale. The bio-swale would be planted with suitable plants to aid in the filtration process. Increased Storm Water Runoff Based on the 1992 Grading Plan, the infrastructure improvements for that project would result in 61,550 sq. ft. of paving (excluding any impervious surfaces associated with the individual houses/driveways). The increase in storm water runoff was not calculated. Under the currently proposed project, the area of impervious surface due to infrastructure improvements (access road and turnaround) is estimated by MacLeod and Associates to be 15,662 sq. ft. or 0.36 acres. This estimate for increased impervious surfaces does not consider any impervious surfaces associated with the two future houses/driveways. Based on the infrastructure impervious surfaces, the increase in storm water runoff is estimated to be 0.35 cfs



at peak flow rate, based upon 10-year storm event and San Mateo County Rainfall Data. Furthermore, it is estimated that under existing conditions the onsite drainage basin (12.9 ac+/-) will discharge 12.64 cfs and the offsite drainage basin (21.86 ac.) will discharge 21.41 cfs. Both the 1992 approved project and 2010 proposed project must comply with San Mateo County C3 regulations regarding storm water runoff. Both projects would provide features that would detain runoff from all development within the site (impervious surfaces associated with the infrastructure and construction within the individual lots) as well as surface water runoff that enters the site from the surrounding canyon slopes. Preliminary plans for the 2010 project show 24-inch diameter detention pipes in the vicinity of the Curia property which would be designed to detain any increase in runoff. The runoff would be discharged through a smaller diameter pipe attached to the drain box structure at this location. In this way, runoff is controlled as the flow is restricted through the smaller diameter pipe. Final drainage plans must be prepared and reviewed by San Mateo County before the proposed 2010 Final Map Amendment is allowed to be recorded. Detention of additional runoff from the future homes and associated pavement will be designed as part of the building permit process. Final drainage plans will be prepared and reviewed by the Department of Public Works before the current Final Map Amendment is allowed to be recorded. The drainage plan must account for an increase in storm water runoff from all new impervious surfaces (including roads, building, patios, decks, etc) as well as the addition of storm water runoff from portions of the northern end of the site where storm water is currently retained. Alteration of Drainage Patterns Resulting in Erosion or Siltation The proposed drainage system is similar to the system proposed and approved in the 1992 EIR and would alter existing on-site drainage patterns in several ways. Under the proposed grading plan, storm water runoff from the upper slopes of the canyon must be diverted away from cut and fill faces within the project site. Therefore the proposed drainage system would collect runoff from up slope areas, direct it around the cut/fill areas in storm drain lines, direct the runoff through the detention pipes, and then discharge it to the existing drainage on the west side of the entrance road (just south of the driveway to the Curia parcel) (see Figure 2-10). North of the driveway to the Curia property, a 240-foot long bio-swale would collect and treat runoff from the new paved roadway surface. The proposed storm drain system would consist of County-approved underground pipes, inlets, drainage structures and retention systems. As such, runoff would be redirected into the proposed drainage system, thereby reducing the potential for erosion over the existing condition. The drainage system would prevent run off from up-slope areas from contacting fill areas, thereby reducing the likelihood of erosion or siltation. The geotechnical report (Murray 2002) prepared for the project calls for the installation of subdrains to be placed under the soil in cut and fill slopes. The subdrains are necessary for the stabilization of the fill and to protect it from eroding. These subdrains are not shown in the project plans, but will be incorporated into final improvement plans for review by the County Public Works Department and the County geologist prior to issuance of the final grading permit. The subdrains would discharge the collected water into the proposed drainage infrastructure.



Currently, the main drainage channel on the site is eroding. This drainage channel formed along the eastern foot of the canyon wall after previous alterations of the site’s drainage patterns. The project proposes to move this drainage channel east to accommodate the construction of the access road. The relocated drainage would be constructed as a swale as described in the Project Description. The redesign of the existing drainage will eliminate the erosion in the water channel that is currently occurring. 4.2.6 2010 Mitigation Measures The following mitigation measures are recommended to reduce potentially significant water quality impacts to less than significant levels. Impact HYDRO-1: Grading activities may cause erosion and/or siltation and other water quality impacts in the channel down-stream of the project site. Mitigation Measure HYDRO-1: To avoid erosion and siltation impacts the following measures shall be implemented:

1) The project shall control surface runoff in accordance with Mitigation Measure GEO-3. 2) If construction activities are not completed by the start of the wet season, winterization

controls will be installed on exposed slopes and drainage swales to control and dissipate runoff and prevent surface soil erosion.

3) A watering truck shall be used to reduce dust during the grading and soil hauling activities.

4) As part of the erosion control plan, the Applicant will revegetate all disturbed areas (cut and fill slopes and areas disturbed by utility installation) with native species proposed by a landscape architect and approved by the Community Development Director.

5) As required by the Statewide NPDES General Permit for Discharges of Storm Water Associated with Construction Activity (General Permit) the Applicant shall file a Notice of Intent with the SWRCB and prepare a project-specific SWPPP that incorporates BMPs to control erosion and to protect the quality of surface water runoff during the construction period

6) Where the vegetation surrounding natural drainages channels has been disturbed or destroyed by project grading activities, native replacement plants shall be planted and maintained for three (3) years in order to restore the vegetation around the channel to its pre-existing state.

Effectiveness: Implementation of these measures will reduce impacts to less than

significant levels Implementation: San Mateo County shall incorporate the measures into the Final

Grading and Drainage Plan. The Applicant shall implement the measures during project construction.

Timing: At the commencement of any grading and construction of the project. Monitoring: San Mateo County Public Works Department and San Mateo County

Planning and Building Department Impact HYDRO-2: The project will lead to a permanent increase in impervious surfaces resulting in an increase in rate and peak flows of storm water runoff leaving the site and entering Cordilleras Creek.



Mitigation Measure HYDRO-2: The following measures shall be implemented

1) The Applicant shall prepare a final drainage analysis of the subdivision and submit it to the San Mateo County Planning & Building Department for review and approval. The analysis shall consider storm water received from off-site as well as the accommodation of on-site storm water and the discharge of storm water from the subdivision.

2) As part of the analysis, the Applicant will demonstrate that peak runoff (both in terms of peak flows and velocities) is not increased by grading and construction of the property.

3) The property owners of the two subdivision lots shall be responsible for maintaining all components of the drainage system in full functioning order such that it functions as designed during and after all storm events. Routine maintenance will be required at the property owner’s expense, including inspection of the system after storm events and regular cleaning of the check dam, trash rack, and retention basin. Inspections and maintenance should be carried out by a qualified management entity meeting the requirements for San Mateo County.

Effectiveness: Implementation of these measures will reduce impacts to less than

significant levels Implementation: San Mateo County shall incorporate the measures into the Final

Grading and Drainage Plan and Grading Permit. The Applicant shall implement the measures during project construction.

Timing: At the commencement of any grading and construction of the project. Monitoring: San Mateo County Public Works Department and San Mateo County

Planning and Building Department



4.3 BIOLOGY 4.3.1 1992 EIR Analysis The information presented in the 1992 EIR was based on four site visits by TRA biologists, an interview of San Mateo County planner and botanist, Roman Gankin, review of a “Preliminary Sensitive Biological Resources Assessment” by Redwood Consulting Group (April 1991), and a tree survey conducted by S.P. McClenahan. The setting reported in 1992 described a site surrounded on all sides by low-density suburban development, with vegetation that was dominated by native oak woodland with an understory of introduced annual grasses. Site surveys determined that serpentine grassland and riparian habitats do not occur at the site. Surveys did not identify any habitat for species listed as special-status species in 1992, however it noted that two species of deciduous oak that are in decline in California were present: the blue oak and the valley oak. The potentially significant biological impacts identified in the 1992 EIR were for a six-lot subdivision impacting 12.9 acres. The potentially significant impacts were loss of native vegetation, especially blue and valley oaks, and alterations to the on-site drainage that could result in impacts downstream. Only the loss of vegetation required a mitigation measure; the drainage issues were anticipated to be addressed by the County in the process of obtaining grading permits. With regard to vegetation impacts, the arborist’s survey identified trees on site with a diameter at breast height (dbh) of at least 6 inches located within 25 feet of building envelopes and leachfields and within 12 feet of public improvements and access roads. In the mitigation measures the EIR defines a “significant” tree as greater than 6 inches dbh. Of the 89 trees greater than 6 inches dbh to be removed, the 1992 EIR estimated that 76 were healthy native trees and 13 were unhealthy trees. No heritage trees on the San Mateo County list of heritage trees occurred at the site. Mitigation required in the 1992 EIR to reduce significant biological impacts included minimizing and avoiding removal of oak trees, particularly blue and valley oak, and especially any trees larger than 12 inches dbh. Blue or valley oaks removed for construction were to be replaced in a three-to-one ratio using the same species and in an appropriate location as close as possible to the site of the removed tree. All other trees removed for construction were also to be replaced at a three-to-one ratio, and the new plantings were to be designed to blend with the existing vegetation in appearance and species composition. The recommendations of a qualified tree specialist were to be followed in order to enhance the survival of existing trees near construction, and trees greater than 6 inches dbh were to be protected with barriers installed at the dripline. Additional recommended mitigation included using native species in landscaping, restricting the use of invasive exotic species, and removing existing invasive exotic species (such as broom and pampas grass). The 1992 EIR described six ravines on the site. Two ravines fed the ephemeral drainage channel located along the eastern side of the canyon, and four of the ravines contribute water to a relatively flat area of artificial fill on the bottom of the canyon which was reported to become saturated and/or flood in years of normal rainfall. There were no perennial stream flows on the site; the ephemeral drainage flowed to Cordilleras Creek. Because of downstream flooding issues



on Cordilleras Creek, mitigation in the 1992 EIR required no net increase in peak storm flows caused by the project. The 1992 EIR Hydrology and Biology sections recommended that the applicant consult with CDFG and the USACE to determine whether permits were required under California Fish and Game Code section 1600 or the federal Clean Water Act. After the 1992 project was approved, the applicant pursued permits with the USACE, CDFG and the RWQCB. With regard to the RWQCB, NPDES coverage was not required for the subdivision map, but would be required prior to construction (RWQCB, March 14, 1996 memo). The governmental affairs consultant for the 1992 project consulted the USACE in May and June 1996, and requested confirmation that the drainage on the property was not jurisdictional. The USACE recommended that he work with the County to determine whether the site contained waters of the U.S. and required a permit from the USACE. Subsequent memos from San Mateo County to the USACE indicate that the County did not find jurisdictional waters on the property, but that it would defer to the USACE if alternate guidance was provided. The USACE never responded, and the final conclusion was that the site did not contain waters of the U.S. under the jurisdiction of the USACE. After a site visit and researching applicable data in 1995, the CDFG stated that the “proposed work site” did not require a Streambed Alteration Agreement or any further notification to CDFG (State of California, 3/28/95). 4.3.2 2010 Environmental Setting This section updates the 1992 EIR setting where necessary. To determine whether the environmental setting of the project site has changed since 1992, TRA biologists conducted three site visits, two in February and one in September 2010. The February site visits occurred within a day of storm events, and the September visit was to observe dry season conditions. TRA also conducted an updated nine-quad (U. S. Geological Survey quadrangle topographic map) search of the California Natural Diversity Database (CNDDB) to determine current information about the presence of sensitive plant communities and special status species in the area (see Appendix C for results of the CNDDB search). The environmental setting reported in 1992 has not substantially changed. The site is still dominated by oak woodland with a grassland understory. The differences are:

A more detailed description of the ephemeral channel is provided; An updated arborist’s report was completed, including tree preservation guidelines; the San Mateo County tree ordinances are described and the mitigation is revised

(discussed under Regulatory Setting); CEQA was amended to require mitigation for conversion of oak woodland (discussed

under Regulatory Setting); bat species are afforded protection under CDFG code; in particular, the pallid bat, which

potentially occurs on the site, is now listed as a special status species; the impacts of tree removal on nesting birds are required to be mitigated because of

CDFG code and the federal Migratory Bird Treaty Act;



the San Francisco dusky-footed woodrat is a California species of special concern and is found at the site;

wildlife corridors are in the CEQA Guidelines’ thresholds of significance and were not discussed in 1992;

more fill was placed in the bottom of the canyon after the 1992 project was approved; As a result of a court case known as SWANCC (531 U.S. 159, 2001), the RWQCB issued

guidance indicating it maintains its jurisdiction over waters protected by the Clean Water Act regardless of USACE jurisdiction, thus a Clean Water Act Section 401 Certification may be required (discussed in Regulatory Setting).

Ephemeral Channel: TRA reviewed historic aerial photography and the U.S. Geological Survey Woodside quadrangle topographic map (U.S. Geological Survey, 1961) and determined that the canyon never contained a blueline stream. Historically, storm water from the canyon walls sheet flowed across the site toward Cordilleras Creek, but likely did not reach a high enough volume (cubic feet per second) to create a bed, bank and channel until near the canyon opening. There is a creek channel downstream of the existing driveway (off-property) that has existed long enough to support riparian vegetation dominated by willows (Salix sp.). Fill placed on the property altered the drainage by causing ponding at the upper end of the canyon and on the fill, and by concentrating flows from the eastern slopes into the area where the base of the natural slope and the base of the fill slope meet. Today there is still seasonal ponding at the upper end of the canyon; these areas were wet in February and dry in September. A small amount of wetland vegetation occurs in one of the ponded areas, covering an area of less than 150 square feet. These areas may provide a seasonal water source for wildlife, but otherwise provide few ecological functions. There is also an ephemeral channel at the base of the eastern slope, caused by erosion that occurred after fill was placed on the site. This feature has a defined bed, bank and channel and is State jurisdictional water. However, because it is an erosion gully the County’s assessment in 1996 that it is not under USACE jurisdiction remains accurate, and after a site visit in 1995 it was determined by CDFG to not require a Streambed Alteration Agreement. Bats: Several bat species are declining in number in California, and since 1992 concerns about their population status have increased. Bats and other mammals are protected under Fish and Game Code section 4150 (see the discussion under Regulatory Setting, below). Pallid bat is now a California species of special concern that was identified in the 1992 EIR as potentially occurring on site. A discussion of Fish and Game Code section 4150 is presented in the Regulatory Setting section. Nesting Birds: The project site provides nesting habitat for birds. Nesting birds are protected under California Fish and Game code (Sections 3503 and 3513) and the federal Migratory Bird Treaty Act. Birds may nest in trees, shrubs or grassy areas of the site. Nesting season is generally mid-February to the end of August. The Migratory Bird Treaty Act and California Fish and Game codes are discussed in the Regulatory Setting section. San Francisco Dusky-footed Woodrat: A San Francisco dusky-footed woodrat (Neotoma fuscipes annectens, SFDW) house was found on the site during site visits in 2010. The SFDW is a California species of special concern. Woodrats build molded stick houses that range in size from 3 to 8 feet across at the base, and contain several chambers, including a nest, a latrine and a



larder. They appear to be tolerant of human uses nearby. Woodrats use the houses year-round, and pass ownership along family lines from mother to daughter. A house may be occupied by the same familial line for decades. The structure also provides cover for a variety of other small rodent, reptile, amphibian and insect species. Construction disturbance may impact woodrat house(s), and thus mitigation for SFDW is needed. Wildlife Corridors: The CEQA Guidelines include a threshold of significance that addresses wildlife movement and whether the project will interfere substantially with native species movement or impede the use of a wildlife nursery. This threshold was not discussed in the 1992 EIR. Wildlife movement includes migration (i.e., usually one way per season), inter-population movement (i.e., long-term genetic flow) and small travel pathways (i.e., daily movement corridors within an animal’s territory). While small travel pathways usually facilitate movement for daily home range activities, such as foraging or escape from predators, they also provide connection between outlying populations and the main corridor, permitting an increase in gene flow among populations. These linkages among habitats can extend for miles and occur on a large scale throughout California. Habitat linkages facilitate movement between populations located in discrete areas and populations located within larger habitat areas. Additional Fill: Soil imported to the site after the project was approved in 1992 was stockpiled on the canyon bottom, and is believed to have been placed in areas of existing fill so that the elevation is higher but the footprint is not substantially larger. Tree Survey: An updated tree survey was completed for the site. To date, 14 of the trees planned to be removed by the previously approved project have been removed. These have not been replaced yet. These trees will be included in the total number of trees removed at the site to properly account for the number of trees that require mitigation. A discussion of the San Mateo County Significant Tree Ordinance is provided in the following section. Tree Preservation and Protection Plan: The Tree Preservation and Protection Plan prepared by the arborist (McClenahan Consulting), includes the following recommendations:

To minimize injury to trees as a result of construction (including mechanical injuries to trunks, roots and branches, and injury as a result of changes that occur in the growing environment), grading operations should encroach no closer than five times the trunk diameter, (e.g., 30" diameter tree x 5=150" distance). At this distance, buttress/anchoring roots would be preserved and minimal injury to the functional root area would be anticipated. Should encroachment within the area become necessary, hand digging is mandatory.

Tree protection fencing will be installed to separate trees to remain from construction areas. Fencing should be installed in a semicircular fashion from the north to east to south sides of tree groupings. The landscape plan should specify the tree protection fencing, and that the fencing should be installed prior to the start of construction.

Fencing should be installed around: Southwest group on Lot 1: Fence the dripline area of tree 308, 309, 30, 31, 33 to 36, 300, 310. West group Lot 1: Fence on east side of driplines of trees 311 to 316. Two small groups of trees on Lot 2: Fence at the dripline of trees 45, 251 to 253, 1 to 4, and 248 to 250. The 32 trees on the west bluff of Lot 2 only need to be fenced if grading will occur within 10-feet of dripline.



Place tree protection fencing around individual trees and/or groups of trees as the existing environment dictates. Due to the steep grades, orange plastic fencing may be used. This will be in the best interest of worker safety, especially for trees well outside the grading areas. The tree protection fencing will protect trunks, roots and branches from mechanical injury, will inhibit stockpiling of construction materials or debris within the sensitive dripline areas and will prevent soil compaction from increased vehicular/pedestrian traffic.

No storage of material, topsoil, vehicles or equipment shall be permitted within the tree enclosure area. The ground around the tree canopy shall not be altered.

The tree protection fencing will remain in place until final inspection for the grading permit, except for work specifically required in the approved plans to be done under the trees to be protected. Designated areas beyond the driplines of any trees should be provided for construction materials and onsite parking.

Should any roots within a tree’s dripline that is greater than one inch (1") in diameter be damaged,· broken or severed during or upon completion of any trenching/grading , the damaged root should be pruned to include flush cutting and sealing of exposed roots. This pruning should occur, within 24 hours of the damage to the root and be accomplished under the supervision of a qualified arborist.

Under the supervision of a certified arborist, trees within the immediate construction area should undergo pruning of the foliar canopies to include removal of deadwood prior to construction operations. Such pruning will provide any necessary construction clearance, will lessen the likelihood or potential for limb breakage, reduce 'windsail' effect and provide an environment suitable for healthy and vigorous growth.

For those trees with the potential to be impacted by construction, a program of fertilization by means of deep root soil injection will be implemented including applications in spring and summer. This treatment will start prior to construction.

All coast live oaks to remain will be treated with Agri-Fos to aid in prevention of Sudden Oak Death. These treatments should occur once in spring and once in fall and then annually in fall. This treatment will start prior to construction and be finished upon the completion of construction.

For trees within the construction zone. mulching with wood chips (maximum depth 3") within tree environments (outer foliar perimeter) will lessen moisture evaporation from soil, protect and encourage adventitious roots and minimize possible soil compaction.

Periodic inspections (once per month) by the Site Arborist should be conducted during construction activities, particularly as trees are impacted by trenching/grading operations. The arborist shall prepare a site inspection report listing the findings of the inspection and submit the report to the Planning and Building Department.

4.3.3 2010 Regulatory Setting Federal Endangered Species Act The federal Endangered Species Act (ESA) of 1973 (16 USC §§ 1531 et seq.) protects fish and wildlife species that are listed as threatened or endangered, and their habitats. “Endangered” refers to species, subspecies, or distinct population segments that are in danger of extinction in all or a significant portion of their range. “Threatened” refers to species, subspecies, or distinct



population segments that are considered likely to become endangered in the future. The USFWS oversees implementation of the ESA. Migratory Bird Treaty Act The Federal Migratory Bird Treaty Act (MBTA) (16 U.S.C. 703 et seq.), Title 50 Code of Federal Regulations (CFR) Part 10, prohibits taking, killing, possessing, transporting, and importing of migratory birds, parts of migratory birds, and their eggs and nests, except when specifically authorized by the Department of the Interior. As used in the act, the term “take” is defined as meaning, “to pursue, hunt, capture, collect, kill or attempt to pursue, hunt, shoot, capture, collect or kill, unless the context otherwise requires.” With a few exceptions, most birds are considered migratory under the MBTA. Disturbance that causes nest abandonment and/or loss of reproductive effort would be in violation of the MBTA. The vegetation removal planned as part of project construction could adversely impact nesting birds and result in the significant impact of violating the MBTA if the vegetation removal occurs during the nesting season and birds are nesting in the vegetation. Mitigation measure BIO-2 is recommended to avoid significant impact. Clean Water Act, Sections 404 & 401 The implementation of the Clean Water Act is the responsibility of the U.S. Environmental Protection Agency. That agency depends on other agencies, such as the individual states and the U.S. Army Corps of Engineers (USACE), to assist in implementing the Act. The objective of the Clean Water Act is to “restore and maintain the chemical, physical, and biological integrity of the Nation’s waters”. Sections 401 and 404 apply to project activities that would impact wetlands. The California State Water Resources Control Board enforces section 401 of the Clean Water Act and the USACE enforces Section 404. A discussion of section 401 is provided under State, below. The EPA regulates the discharge of dredged or fill material into “Waters of the US” under Section 404 of the Act, and the discharge of dredged or fill material into waters of the U.S. is prohibited under the Clean Water Act except when it is in compliance with Section 404 of the Act. Enforcement authority for Section 404 was given to the USACE, which it accomplishes under its regulatory branch through either an Individual Permit or through the Nationwide Permit Program. The County previously determined that the site does not contain features under the jurisdiction of the USACE. The project site contains erosional gullies that do not contain perennial water flow. Under the Rapanos decision, described below, the USACE would not take jurisdiction over these features. The areas of seasonal ponding described earlier are isolated and would not fall under USACE jurisdiction under the SWANCC decision. These two court decisions are briefly summarized below. SWANCC In response to a court case known as SWANCC (531 U.S. 159, 2001), the USACE and EPA determined that field staff should not assert Clean Water Act jurisdiction over isolated waters or wetlands. Isolated waters are those which have no connection to navigable waters, and are not immediately adjacent to waters of the U.S. This guidance is reflected in Regulatory Guidance Letter (RGL) 07-01.



Rapanos On December 2, 2008, the USACE issued a memorandum titled, “Clean Water Act Jurisdiction Following the U.S. Supreme Court’s Decision in Rapanos v. United States & Carabell v. United States” (US Army Corps of Engineers, 2008). The key points are summarized in the guidance as follows: “The agencies will assert jurisdiction over the following waters:

Traditional navigable waters Wetlands adjacent to traditional navigable waters Non-navigable tributaries of traditional navigable waters that are relatively permanent

where the tributaries typically flow year-round or have continuous flow at least seasonally (e.g ., typically three months)

Wetlands that directly abut such tributaries The agencies will decide jurisdiction over the following waters based on a fact-specific analysis to determine whether they have a significant nexus with a traditional navigable water:

Non-navigable tributaries that are not relatively permanent (where the tributaries typically flow year-round or have continuous flow at least seasonally (e.g ., typically three months))

Wetlands adjacent to non-navigable tributaries that are not relatively permanent Wetlands adjacent to but that do not directly abut a relatively permanent nonnavigable

tributary The agencies generally will not assert jurisdiction over the following features:

Swales or erosional features (e .g., gullies, small washes characterized by low volume, infrequent, or short duration flow)

Ditches (including roadside ditches) excavated wholly in and draining only uplands and that do not carry a relatively permanent flow of water

In 1996, communication with USACE staff led the County to conclude that the USACE did not consider the drainage channel or the areas that flooded during storm events to be jurisdictional (See discussion in the 1992 EIR section above). This remains true for existing conditions because the water features on the site are either isolated (per SWANCC) or consist of an erosional gully caused by the placement of fill (Rapanos). State Section 401 and the State/Regional Water Quality Control Boards The State Water Resources Control Board (SWRCB) sets statewide policy related to water quality, coordinates and supports regional water quality control boards, and reviews petitions that contest regional board actions. The RWQCB sets water quality standards, waste discharge requirements for its region, determines compliance with those standards, and takes enforcement action. The RWQCB issues and enforces permits for discharge of treated water, landfills, storm



water runoff, filling of any surface waters or wetlands, dredging, agricultural activities and wastewater recycling. The SWRCB defines its jurisdiction more broadly than the USACE does; under the Porter-Cologne Water Quality Control Act, all waters in the state are within jurisdiction of the SWRCB and impacts to those waters requires a Clean Water Act Section 401 Certification. The 401 Certification is provided by the State Water Resources Control Board, but is initiated through the local Regional Water Quality Control Board (RWQCB). The RWQCB recommends the application be made at the same time that any applications are provided to other agencies, such as the USACE, USFWS, or NOAA Fisheries. Application is not final until completion of environmental review under the California Environmental Quality Act (i.e., CEQA certification). The application to the RWQCB is similar to the pre-construction notification that is required by the USACE in the Nationwide Permit Program under the federal Clean Water Act. It must include a description of the habitat that is being impacted, a description of how the impact is proposed to be minimized and proposed mitigation measures with goals, schedules, and performance standards. Mitigation must include a replacement of functions and values, and replacement of wetland at a minimum ratio of 2:1, or twice as many acres of wetlands provided as are removed. The RWQCB looks for mitigation that is on site and in-kind, with functions and values as good as or better than the water-based habitat that is being removed. If there is not any other state or federal agency involvement, as is the case with this project, the SWRCB still requires a 401 certification for impacts to waters of the state. The water features at the site are waters of the state. Mitigation measure BIO-8 recommends consultation with the RWQCB and to obtain 401 certification, if required by the RWQCB. California Endangered Species Act and Native Plant Protection Act California enacted similar laws to the federal ESA, including the California Native Plant Protection Act (NPPA) in 1977 and the California Endangered Species Act (CESA) in 1984. The CESA expanded upon the original NPPA and enhanced legal protection for plants, but the NPPA remains part of the California Fish and Game Code. To align with the federal ESA, CESA created the categories of “threatened” and “endangered” species. It converted all “rare” animals into the CESA as threatened species, but did not do so for rare plants. Thus, these laws provide the legal framework for protection of California-listed rare, threatened, and endangered plant and animal species. The CDFG implements the NPPA and CESA, and the CDFG Wildlife and Habitat Data Analysis Branch maintains the California Native Diversity Database (CNDDB), a computerized inventory of information on the general location and status of California’s rarest plants, animals, and natural communities. Fully Protected Species & Species of Concern The classification of “fully protected” was the CDFG’s initial effort to identify and provide additional protection to those animals that were rare or faced possible extinction. Lists were created for fish, amphibian and reptiles, birds, and mammals. Most of the species on these lists have subsequently been listed under the CESA and/or the ESA. The California Fish and Game Code sections (fish at §5515, amphibian and reptiles at §5050, birds at §3511, and mammals at §4700) dealing with “fully protected” species states that these species “…may not be taken or possessed at any time and no provision of this code or any other law shall be construed to



authorize the issuance of permits or licenses to take any fully protected species,” although take may be authorized for necessary scientific research. This language makes the “fully protected” designation the strongest and most restrictive regarding the “take” of these species. In 2003, the code sections dealing with fully protected species were amended to allow the CDFG to authorize take resulting from recovery activities for state-listed species. There are no fully protected species at the site. Species of special concern are broadly defined as animals not listed under the ESA or CESA, but which are nonetheless of concern to the CDFG because they are declining at a rate that could result in listing, or historically occurred in low numbers and known threats to their persistence currently exist. This designation is intended to result in special consideration for these animals by the CDFG, land managers, consulting biologist, and others, and is intended to focus attention on the species to help avert the need for costly listing under the ESA and CESA and cumbersome recovery efforts that might ultimately be required. This designation also is intended to stimulate collection of additional information on the biology, distribution, and status of poorly known at-risk species, and focus research and management attention on them. Although these species generally have no special legal status, they are given special consideration under CEQA during project review. Species of special concern that could occur on the site include the pallid bat, which may roost in the oak woodland that is proposed to be removed, and San Francisco dusky-footed woodrat, which may build homes and nest in stick piles in oak woodland habitat on site. The pallid bat has not been surveyed for; the SFDW has been confirmed present at the site. California Fish and Game Code, Sections 3503 & 3513 (Nesting Birds) Nesting birds, including raptors, are protected by the California Fish and Game Code section 3503, which reads, “It is unlawful to take, possess, or needlessly destroy the nest or eggs of any bird, except as otherwise provided by this code or any regulation made pursuant thereto.” As such, the CDFG typically recommends surveys for nesting birds that could potentially be directly (actual removal of trees/vegetation) or indirectly (noise disturbance) impacted by project-related activities. Disturbance during the breeding season could result in the incidental loss of fertile eggs or nestlings, or otherwise lead to nest abandonment. Disturbance that causes nest abandonment and/or loss of reproductive effort is considered “taking” by the CDFG. The proposed project requires the removal of mature trees and vegetation that provide nesting habitat. Loss of eggs or chicks due to tree removal or ground disturbance would result in a violation of Fish and Game Code 3503. Mitigation measure BIO-2 is included to prevent impacts to nesting birds and insure that the project does not violate Fish and Game Code 3503. California Native Plant Society The California Native Plant Society (CNPS) publishes and maintains an Inventory of Rare and Endangered Vascular Plants of California. The inventory lists the plants according to their endangerment. Per CEQA Guidelines, the plants on any of the CNPS lists are considered in the impact analysis. No CNPS listed plants occur at the site. A list of the plants considered is included in Appendix A.



California Fish and Game Code, Section 4150 (Bat Roosts and Colonies) Considered nongame mammals, bats are protected by CDFG code section 4150, which reads “all mammals occurring naturally in California which are not game mammals, fully protected mammals, or fur-bearing mammals, are nongame mammals. Nongame mammals or parts thereof may not be taken or possessed except as provided in this code or in accordance with regulations adopted by the commission.” Bat roosts are essential to survival, and a bat disturbed during roosting or excluded from a roost may not survive. Bats can roost in trees, particularly trees with cavities, fissures, or exfoliating bark. Bats may use separate roosts for day and night, and female bats form roosting colonies during the breeding season. Day roosts are selected that provide a consistent temperature, protect the bat from predation, and that allow ease of entrance and exit. Disturbance of day roosting bats may cause the bat to flee its roost. Bats are disoriented in daylight and are prone to predation and may not find another suitable roost. Maternity roost size and configuration varies by species, with some maternity roosts supporting hundreds of females. Disturbance of maternity roosts may result in the loss of juveniles that cannot yet fly or forage. Disturbance of maternity roosts may be considered a significant effect under CEQA. The CEQA planning process provides the main protection for bat roosts and maternity colonies. Although loss of an individual roosting bat, for example, in the bark of a tree, would not be considered a significant impact under CEQA unless the bat was listed as threatened or endangered, loss of a roost site where multiple individuals are present would be considered significant, particularly for the special-status species. If a project were to destroy or disturb a bat maternity colony site it would significantly impact the local and/or regional population of the species. The roost sites with multiple individuals and the maternity colonies usually occur in a cavity, such as a hole in a tree, a cave, or a structure. The impact is significant because roost sites are usually limited in availability and often have very specific habitat and/or microclimate conditions. When a roost site is lost, individuals may not be able to find an alternate roost in sufficient time to survive the elements or predators. The vegetation removal planned as part of project construction could adversely impact bat roost and colonies and could violate CDFG Code if the vegetation removal occurs during the bat nesting season. California Fish and Game Code, Section 1602 (Streambed Alteration Agreement) Any activity that will do one or more of the following generally requires a 1602 Lake and Streambed Alteration Agreement: (1) substantially obstruct or divert the natural flow of a river, stream, or lake; (2) substantially change or use any material from the bed, channel, or bank of a river, stream, or lake; or (3) deposit or dispose of debris, waste, or other material containing crumbled, flaked, or ground pavement where it can pass into a river, stream, or lake. The term “stream”, which includes creeks and rivers, is defined in the California Code of Regulations (CCR) as follows: “a body of water that flows at least periodically or intermittently through a bed or channel having banks and supports fish or other aquatic life”. CDFG determined that a Streambed Alteration Agreement was not required for the previous project; the site conditions and impact area of this project are the same, and a Streambed Alteration Agreement is not expected to be required.



CDFG conducted a site visit in 1996 and determined that the project site did not warrant a streambed alteration agreement (See discussion in the 1992 EIR section above). CDFG will review the currently proposed project as a trustee agency under CEQA. Sensitive Vegetation Communities The CDFG ranks sensitive communities as “threatened” or “very threatened” and keeps records of their occurrences in the CNDDB. Sensitive vegetation communities are also identified by CDFG on its List of California Natural Communities recognized by the CNDDB. Impacts to sensitive natural communities and habitats identified in local or regional plans, policies, regulations or by federal or state agencies must be considered and evaluated under the CEQA (CCR: Title 14, Div. 6, Chap. 3, Appendix G). Where determined to be a significant impact under CEQA, the potential impact would require mitigation through avoidance, minimization of disturbance or loss, or some type of compensatory mitigation when unavoidable. Site surveys determined that no listed sensitive communities occur at the site or would be affected by the project. No sensitive vegetation communities occur on site. CEQA Requirements Regarding Conversion of Oak Woodland (California Public Resources Code 21083.4) Under State Public Resources Code Section §21083.4, a county shall determine whether a project within its jurisdiction may result in conversion of oak woodland habitat that will have a significant effect on the environment. If a significant effect is determined, the following mitigation alternatives are given:

1. Conserving oak woodlands through the use of conservation easements. 2. Planting an appropriate number of trees, including maintaining the plantings and

replacing dead or diseased trees. Required maintenance of trees terminates seven years after the trees are planted. This type of mitigation should not fulfill more than half of the mitigation requirement for the project.

3. Contribute funds to the Oak Woodlands Conservation Fund. 4. Other mitigation measures developed by the county.

The project includes a proposed conservation easement on the densely forested eastern portion of the site and a Landscape and Restoration Plan (Figure 2-16 and 2-17) to meet alternatives 1 and 2. Local County of San Mateo General Plan The following General Plan policies pertain to biological impacts of the proposed project: General Policy 1.20, Importance of Sensitive Habitats: Consider areas designated as sensitive habitats as a priority resource requiring protection. Sensitive habitats are defined as any area where the vegetative, water, fish and wildlife resources provide especially valuable and rare plant and animal habitats that can be easily disturbed or degraded. These areas include but are



not limited to: (1) habitats containing or supporting rare or unique species; (2) riparian corridors; (3) marine and estuarine habitats; (4) wetlands; (5) sand dunes; (6) wildlife refuges, reserves, and scientific study areas; and (7) important nesting, feeding, breeding or spawning areas. General Policy 1.22, Regulation of Development: Regulate development to protect vegetative, water, fish and wildlife resources. Regulate land uses and development activities to prevent, and if infeasible mitigate to the extent possible, significant adverse impacts on vegetative, water, fish and wildlife resources. Place a priority on the managed use and protection of vegetative, water, fish and wildlife resources in rural areas of the County. General Policy 1.23, Regulate Location, Density and Design of Development to Protect Vegetative, Water, Fish and Wildlife Resources: Regulate the location, density and design of development to minimize significant adverse impacts and encourage enhancement of vegetative, water, fish and wildlife resources. General Policy 1.24, Protect Vegetative Resources: Ensure that development will: (1) minimize the removal of vegetative resources and/or; (2) protect vegetation which enhances microclimate, stabilizes slopes or reduces surface water runoff, erosion or sedimentation; and/or (3) protect historic and scenic trees. General Policy 1.25, Protect Water Resources: Ensure that development will: (1) minimize the alteration of natural water bodies, (2) maintain adequate stream flows and water quality for vegetative, fish and wildlife habitats; (3) maintain and improve, if possible, the quality of groundwater basins and recharge areas; and (4) prevent to the greatest extent possible the depletion of groundwater resources. General Policy 1.26, Protect Fish and Wildlife Resources: Ensure that development will minimize the disruption of fish and wildlife and their habitats. The Sensitive Habitats Map in the General Plan does not show sensitive habitats at the project site. However, the oak woodland at the project site could meet the above definition of a sensitive habitat because it supports San Francisco dusky-footed woodrat, a species of special concern. Measures to protect San Francisco dusky-footed woodrat and to preserve woodland habitat values at the site are included in the mitigation measures described below, and in the Tree Preservation Plan proposed for the project. The project also includes a preliminary landscape plan that replaces habitat lost during construction with native trees and grasses. The project also proposes a bioswale and detention pipes to protect Cordilleras Creek downstream of the project site. Additional mitigation measures to protect biological resources are proposed under Mitigation, below. San Mateo County Significant Tree Ordinance (Section 12000) San Mateo County regulates the removal of trees through the Significant Tree Ordinance. The ordinance requires a permit for the removal of any tree species in the Design Review (DR) district greater than 6 inches in diameter at breast height (dbh; measured 4.5 feet above grade), and/or the removal of a community of trees, unless the tree cutting has been authorized by the Planning Commission, Design Review Committee, or Community Development Director as part of a permit approval process in which the provisions of the Significant Tree Ordinance have been considered and applied (Section 12,020.1(e)). A community of trees is defined as “a group of



trees of any size which are ecologically or aesthetically related to each other such that loss of several of them would cause a significant ecological, aesthetic, or environmental impact in the immediate area.” The project site is in the Palomar Park Design Review district and is subject to the provisions of the Significant Tree Ordinance. A permit is normally required for the cutting down, removing, poisoning or otherwise killing or destroying or causing to be removed any significant tree or community of trees, whether indigenous or exotic, on any private property. However, Section 12,020.1(e) lists certain exemptions from the permit requirement including, “tree cutting which has been authorized by the Planning Commission, Design Review Committee, or Community Development Director as part of a permit approval process in which the provisions of this Part have been considered and applied.” Therefore, a separate significant tree removal permit is not required for the tree removal proposed under the 2010 project, but the provisions contained in the Ordinance still apply to the project and would be enforced through the grading permit. In granting a permit which includes tree removal, the Community Development Director, Planning Commission, or Board of Supervisors may attach reasonable conditions to insure compliance with the intent and purpose of this ordinance including, but not limited to the following:

Replacement plantings of trees at a rate that is acceptable to the Community Development Director.

Use of measures to effect erosion control, soil and water retention and diversion or control of increased flow of surface waters.

Use of measures to insure that the contemplated action will not have adverse environmental effects relating to shade, noise buffers, protection from wind, air pollution and historic features.

The project would result in the removal of trees protected by this ordinance, and includes a landscape plan to replace trees lost at a 3:1 ratio. A Storm Water Pollution Prevention Plan would be prepared to address erosion and storm water runoff during construction. Existing trees would be protected during construction through implementation of the arborist’s recommendations described above in the Environmental Setting. Additional mitigation is proposed under Mitigation, below. San Mateo County Heritage Tree Ordinance Any person desiring to cut down, destroy, move or trim one or more heritage trees (as listed by the San Mateo County Planning and Building Department) on public or private property must apply to the San Mateo County Planning and Building Department for a Heritage Tree Removal/Trimming Permit. No trees listed by San Mateo County as heritage trees occur on the site as none meet the size and species requirements of the Heritage Tree Ordinance as specified in Section 11.050.(g).



4.3.4 Thresholds of Significance This updated SEIR analysis considers whether the proposed 2010 project would result in new or substantially more severe impacts than identified in the 1992 EIR and also examines whether the project would result in a potential biological impact as identified in Appendix G to the CEQA Guidelines. In accordance with Appendix G of the CEQA Guidelines, the proposed project could have a significant environmental impact on biological resources if it would:

a) Have a substantial adverse effect, either directly or through habitat modifications, on any species identified as a candidate, sensitive, or special-status species in local or regional plans, policies, or regulations or by the California Department of Fish and Game or United States Fish and Wildlife Service;

b) Have a substantial adverse effect on any riparian habitat or other sensitive natural community identified in local or regional plans, policies, or regulations or by the California Department of Fish and Game or United States Fish and Wildlife Service;

c) Have a substantial adverse effect on federally protected wetlands as defined by Section 404 of the Clean Water Act (including, but not limited to, marsh, vernal pool, coastal, etc.) through direct removal, filling, hydrological interruption, or other means;

d) Interfere substantially with the movement of any native resident or migratory fish and wildlife species or with established native resident or migratory wildlife corridors, or impede the use of a native wildlife nursery site;

e) Conflict with any local polices or ordinances protecting biological resources, such as a tree preservation policy or ordinance; or

f) Conflict with the provisions of an adopted Habitat Conservation Plan, Natural Community Conservation Plan, or other approved local, regional, or state habitat conservation plan.

4.3.5 2010 Project Impacts Similar to the 1992 project, the potentially significant impacts of the 2010 proposed project are associated with vegetation removal, including loss of habitat protected by the tree ordinance, impacts to nesting birds, impacts to roosting bats, and impacts to special status species identified by the State of California. Both projects also include impacts to waters of the State from relocation of the existing drainage channel. This Supplemental EIR identifies more impacts associated with the 2010 proposed project than the 1992 EIR identified for the six-lot subdivision because of changes in species status and in governing regulations. The 1992 EIR did not address impacts to bats, nesting birds, or loss of oak woodland under CEQA regulations. If constructed now, both projects would have similar impacts and would require similar mitigation measures to reduce impacts to less than significant levels. This Supplemental EIR recommends eight biological mitigation measures. Implementation of these measures would reduce the project’s potentially significant biological impacts to less than significant levels.



The project will not conflict with the provisions of an adopted Habitat Conservation Plan, Natural Community Conservation Plan, or other approved local, regional, or state habitat conservation plan, as none of these plans exist or are proposed in the area. Vegetation The project site is 13.2 acres; project grading will impact 4.78 acres, and will affect both ruderal habitat and oak woodland, but will predominantly affect ruderal habitat because that is what is present in the canyon bottom development area (see Figure 2-3 in Project Description). Impacts to oak woodland and the trees protected by ordinance are discussed further below. The project will protect 1.56 acres of native oak woodland in a scenic easement, and includes a preliminary landscape plan to replace the approximately 62 trees to be removed by the project with 186 native trees (3:1 replacement ratio). The project will not affect riparian habitat or any other sensitive natural community identified in local or regional plans, policies, or regulations or by the CDFG or USFWS. The project, as approved in 1992, includes measures to protect water quality, protect oak woodland in a scenic easement, and replace trees removed during grading. A minimal amount of wetland vegetation (150 sf) may be impacted by the project, but the loss of this vegetation is not a significant impact because the area is very small and provides limited functions and values. The project proposes a bioswale that should be enhanced to replace the wetland vegetation removed by the project (see recommended mitigation measure BIO-7). Ordinance Trees: The 1992 EIR estimated that a total of 89 trees greater than 6 inches in diameter at breast height would be removed by the project. This estimated tree total was included to provide a general indication of the extent of tree loss expected. The 1992 document noted that actual trees to be cut “cannot be known precisely at this time, because the exact locations of the house sites, driveways, and leachfields would be determined by the individual home owners and may vary from those shown on the site plan.” This estimated total of 89 trees includes those that were identified as dead, dying or hazardous. Of these 89 trees, 14 trees have already been removed (11 trees on Lot 1 and three trees on Lot 2) and have not been replaced yet. These trees, because they have already been removed will factor into the total number of trees that are to be removed by the proposed 2010 project, and therefore will be mitigated for. Project plans show that a total of 62 trees (including dead and dying trees) have been or will be removed by the proposed project (14 which were already removed, plus an additional 48 trees). Lot 1 requires an additional 45 trees to be removed. Eight (8) trees occur in the area of the septic leach field and the remaining 37 trees would be removed due to grading of Lot 1. Lot 2 requires the removal of a total of three (3) trees to accommodate grading across the site (no trees are required to be removed in the area of the septic leach field on Lot 2). The tree species are predominantly coast live oaks, but also include a few blue oak, buckeye, and California bay laurel. The 14 trees already removed were not identified as to size or species or condition. For purposes of this analysis, it is assumed that these were ordinance trees which were all healthy native trees in order to provide for a worst-case-scenario. It is possible that they were non-native invasive trees, such as acacia, and their removal would have provided a biological benefit.



Figures 2-14 and 2-15 in Project Description show the location of trees to be removed. The arborist report recommends several measures for protecting trees that will remain on the two lots (presented in the Environmental Setting section). The two lots contain approximately 122 trees of at least 6-inches diameter at breast height, excluding the woodland in the scenic easement. Approximately 68 trees of at least 6-inches dbh will be retained in the area of the two lots (24 on Lot 1 and 44 on Lot 2), not including the trees in the scenic easement which will permanently protect 1.56 acres of oak woodland on the project site. The applicant has prepared a preliminary landscape plan (see Project Description) that includes replacement of the trees to be removed at a ratio of 3:1. The preliminary plan must provide for the planting of approximately 186 new trees. However, a finalized plan based on the actual number of healthy trees removed will be prepared prior to the issuance of a grading permit. Lot 1 contains about 1.5 acres of oak woodland that could also be protected by an easement, although mitigation requiring this has not been recommended in this Supplemental EIR. None of the trees on the site are designated as heritage trees by the San Mateo County Heritage Tree Ordinance as none are designated as Heritage Trees by the Board of Supervisors and none meet the size and species requirements as listed in the ordinance. Removal of the trees that are protected by San Mateo County’s Significant Tree Ordinance is a potentially significant impact under the CEQA Guidelines thresholds of significance because it would not comply with the local tree ordinance. To reduce the impacts to a less-than-significant level, the project must comply with the ordinance. This requires replacing the trees to be removed at a 3:1 ratio with native tree species. As noted above, the 1992 project, as approved, includes mitigation that complies with the ordinance by replacing specific native tree species lost. Because it includes a mix of tree species it will also replace the tree community, as required under the ordinance. Mitigation Measure BIO-3 requires the implementation of a landscape plan designed to meet the Significant Tree Ordinance requirements. The landscape plan must take into consideration the County’s requirements for a 100 ft fuel break around residential properties located in high fire hazards areas, such as the project site (see discussion in section 4.5 Public Services). Modifications to the specifications in the preliminary landscape plan are proposed in mitigation measure BIO-5. One modification is to either replace California bay laurel with another native species (e.g., toyon) or monitor the bay laurel for sudden oak death disease, and remove any trees that are carrying the sudden oak death (SOD) fungus. This is because California bay laurel can survive even if infected with SOD, and end up transmitting it to other trees that do not usually survive SOD (for example, oaks and tanoaks). This is recommended even though the preliminary landscape plan includes treatment of coast live oaks with Agri-Fos to aid in prevention of SOD. Another modification is to include performance standards and monitoring in the landscape specifications, since the purpose of the landscape plan is to mitigate project impacts. A third modification is to remove invasive exotic species from the site in a way that does not disperse their seed in order to reduce development activity impacts and the need to do extensive weed management in the future. Considering the effort to protect and replace oak woodland, the house site development should be restricted from using invasive exotic plant species in future (as yet to be proposed) landscaping, and should be encouraged to use native species that typically occur in oak woodland.



Wildlife Special-Status Species: Per CEQA Guidelines Thresholds of Significance, the project may have a substantial adverse effect, either directly or through habitat modifications, on the San Francisco dusky-footed woodrat and the pallid bat, both California species of special concern. Although the 1992 EIR identified the possible presence of pallid bat on the project site, the bat was not identified as a species of special concern then. The pallid bat was designated a species of special concern by the CDFG in 1993. No bat surveys have been conducted on the site, but bats potentially roost in the stands of mature trees (greater than 25-inch dbh) and in dead snags or felled trees that occur on the site. Removal or disturbance of roost habitat during the bat hibernation or maternity season can cause harm, death, displacement and/or disruption of pallid bats and/or nursery colony roosts; this impact would be significant because it would impact a species of special concern. Impacts to other, more common, bat species would also be a significant impact because it would not comply with Fish and Game code section 4150. The woodrat was not discussed in the 1992 EIR. This species could be directly impacted when vegetation is removed from the site, and indirectly impacted by a loss of oak woodland habitat. The loss of habitat could affect long-term population levels of these species. Mitigation is recommended to avoid direct impacts to both bats and the San Francisco dusky-footed woodrat (see measures BIO-1 and BIO-4 below). The project includes a preliminary landscape plan that replaces the oak woodland habitat that will be removed by the project, in compliance with measure BIO-3, below. Measure BIO-3 was included in the conditions of approval of the 1992 project, measures BIO-1 and BIO-4 were not. TRA conducted site visits to identify the habitats present, and searched the California Natural Diversity Database for sensitive species with the likelihood to occur in or near the site. The project site does not contain suitable habitat for federally listed species. Most of the species found in the CNDDB search are species found in areas of serpentine soil and the project site does not contain serpentine soils or serpentine grassland habitat. The site is not hydrologically connected to known occupied habitat of the California red-legged frog (CRF). There are no CNDDB records of CRF in Cordilleras Creek. The closest, known occurrences of CRF are at Filoli Estate Gardens, 1.3 miles to the west, and at upper Crystal Springs Reservoir, approximately 2.5 miles to the northwest. Ponds form on site during rainfall, but are too small and isolated to support CRF. Nesting Birds: Birds may nest in trees or shrubs on site, and trimming or removal of woody vegetation during the nesting season may impact nests containing eggs or chicks. Further, construction noise in proximity to active nests may result in nest abandonment. The impact of woody vegetation removal on nesting birds is a potentially significant impact because it would violate California Fish and Game code and the federal Migratory Bird Treaty Act. While it was not common in 1992, it is now recognized that either construction needs to occur outside of the nesting season, or surveys for nesting birds need to be conducted prior to grading and vegetation removal to prevent violation of California Fish and Game code and the Migratory Bird Treaty Act. The 1992 EIR provided a list of birds that were identified during site visits (Biology section), but did not discuss the potential for bird nesting. No bird nesting surveys have been conducted on the site, but nesting habitat is present and will be removed. Measure BIO-2 is recommended to reduce impacts to nesting birds to less than significant.



Wildlife Corridors: The project site is located in an area of low-density residential development. While there is no obvious direct corridor connecting the site with open space to the south and west, wildlife is currently able to move unimpeded through the site and into adjoining areas, including open space lands. The 2010 project includes enough undeveloped space to prevent substantial interference with wildlife movement; however, fences could present a barrier to wildlife. Mitigation measure BIO-6 is recommended to reduce impacts to wildlife corridors and minimize the cumulative biological impacts of development in the area. Restricting wildlife movement is a potentially significant impact under the CEQA thresholds. Aquatic Resources: The project will grade two areas where water collects at the head of the canyon and direct that water to the project’s surface water drainage system. The RWQCB must be consulted during the design of the bioswale, particularly if Clean Water Act 401 Certification is required for the project. The bioswale should be designed to both protect water quality and to replace the small amount of wetland habitat (150 sf) that will be removed by the project. 4.3.6 2010 Mitigation Measures The following mitigation measures are recommended to reduce potentially significant impacts to biological resources to less than significant levels. Impact BIO-1: Removal or disturbance of roost habitat during the bat hibernation or breeding season has potential to result in harm, death, displacement and/or disruption of pallid bats and/or nursery colony roosts. This impact was not discussed in the 1992 EIR. Mitigation Measure BIO-1: To avoid impacts to roosting bats (including the special-status species, the pallid bat), removal of mature trees, large snags, and felled trees shall take place outside of the bat breeding season and before bat hibernation season which is a short window of time between September 1 when the breeding season ends and October 31 when hibernation begins. However, if tree removal is to occur during the bat breeding season or during the bat hibernation season, a qualified biologist shall conduct a survey for bats no more than 30 days prior to removal. If bats are detected, CDFG shall be contacted on how to proceed. Typically, a 50-foot buffer exclusion zone would have to be established around each occupied snag or tree until the roosting/breeding/hibernation activities have ceased. If a bat survey is conducted, the results of the survey shall be submitted to the Planning and Building Department prior to the removal of any root trees. All construction employees shall receive training (handout, tailgate training) from a biologist regarding special status species at the project, including the pallid bat.

Effectiveness: Will reduce a potentially significant impact to less than significant levels

Implementation: Measure shall be a condition of project approval and shall be implemented by the applicant.

Timing: Tree removal should occur after September 1 or before October 31. If a bat survey is required because tree removal will occur before September 1 or after October 31, the survey shall be conducted within 30 days of construction.



Monitoring: If a bat survey is conducted, the results of the survey shall be submitted to the San Mateo County Planning and Building Department prior to the removal of any roost trees.

Impact BIO-2: Construction activities including vegetation removal, noise and vibration have a potential to result in direct (i.e., death or physical harm) and indirect (i.e., nest abandonment) impacts to nesting birds, in violation of state and federal codes. This impact was not discussed in the 1992 EIR. Mitigation Measure BIO-2: To avoid impacts to nesting birds, tree removal and ground disturbance should take place outside of the bird breeding season (the breeding season is from February 15 to August 31). However, if tree removal or ground disturbance is to occur within any area during the breeding season, a qualified biologist shall conduct a survey for nesting birds within that area no more than three days prior to the commencement of ground disturbance or vegetation removal within that area. If active nests are not present, tree removal can take place as scheduled. However, if active nests are detected, CDFG should be contacted on how to proceed. Typically, tree removal would have to be delayed until chicks have fledged, and a no-work buffer would be established around the nest. CDFG usually accepts a 50-foot radius buffer around passerine and non-passerine nests, but can require up to a 250-foot radius for raptors.

Effectiveness: Will prevent significant impacts to bird populations, and will assure compliance with state and federal code.

Implementation: Measure shall be a condition of project approval and shall be implemented by the applicant.

Timing: Measure to be implemented by Applicant prior to the start of construction

Monitoring: San Mateo County Planning and Building Department; if a nesting survey is conducted, the results of the survey shall be submitted to the Planning and Building Department prior to the start of disturbance.

Impact BIO-3: Grading associated with the 2010 project will result in the removal of trees that are protected by the San Mateo County Significant Tree Ordinance. This impact was discussed in the 1992 EIR, and the preliminary landscaping plan provides replacement trees of the same species in compliance with the ordinance. Mitigation Measure BIO-3:

Trees removed for construction shall be replaced in a three-to-one ratio for the project site as a whole. New plantings shall be designed to blend with the existing vegetation in appearance and composition.

The grading plan currently shows a loss of 62 trees due to the proposed 2010 project; therefore approximately 186 trees will need to be planted to mitigate the loss. Actual tree removal counts and replacement trees will be determined prior to issuing the grading permit

Replacement trees require a surety deposit for both performance (installation of tree, staking, irrigation system) and maintenance. Maintenance shall be required for no less than two years, but no more than five years.



The Tree Preservation and Protection Plan recommended by McClenahan Consulting (described above under 4.3.2) shall be followed, and the specifications shall be added to the landscape plan.

Effectiveness: Would reduce a potentially significant impact to less than significant Implementation: Measure shall be a condition of project approval and shall be

implemented by the applicant. Timing: Trees shall be replaced within one year of being removed, or when

construction is completed, as required by the tree ordinance, whichever is less.

Monitoring: Applicant shall prepare a Final Landscape Plan for review and approval by the San Mateo County Planning and Building Department. An annual monitoring report shall be submitted to the San Mateo County Planning and Building Department for five years or as specified by the Community Development Director (see BIO-5).

Impact BIO-4: Removal of vegetation on the site could cause direct and indirect impacts to San Francisco dusky-footed woodrat by destroying existing woodrat houses and/or by removing suitable habitat. This impact was not discussed in the 1992 EIR. Mitigation Measure BIO-4: Indirect impacts to SFDW will be addressed under Mitigation Measure BIO-3 which requires protection and replacement of the oak woodland community. Direct impacts shall be minimized by conducting a survey for SFDW houses within 30 days prior to construction and establishing a 10 foot buffer around the houses or moving them in consultation with the California Department of Fish and Game. All construction employees shall receive training (handout, tailgate training) from a biologist regarding special status species at the project, including bats and SFDW.

Effectiveness: Will reduce a potentially significant impact to less than significant Implementation: Measure shall be a condition of approval and shall be implemented by

the applicant. Timing: Measure shall be implemented prior to start of construction Monitoring: Results of the woodrat survey, construction crew training materials,

and a record of the training event shall be submitted to the San Mateo County Planning and Building Department.

Impact BIO-5: The project could result in significant adverse impacts on biological resources by removing oak woodland and introducing invasive plant species to the site. The project includes a preliminary landscape plan that specifies all native species, but does not specify monitoring requirements, and does not include landscaping proposed in the future around the houses. Inclusion of California bay laurel trees may make it difficult to control Sudden Oak Death in the future. This impact was partially addressed in the 1992 EIR with the requirement to replace tree species removed by the project. Mitigation Measure BIO-5: The preliminary landscape plan replaces oak woodland as previously required, but needs additional specificity to insure that the mitigation is achieved. The specifications in the landscape plan should include the recommendations made in the arborist report for the project (see BIO-3), a 5-year monitoring period and require replacement of dead



trees so that a minimum of 62 trees, including a mix of species, survive to maturity and provide habitat over the long term. This is to insure that the habitat removed for the project is replaced. Landscape plans prepared for the houses should be restricted from including invasive plant species as defined/listed by the California Invasive Plan Council (Cal-IPC). Existing pockets of invasive plants should be mapped by a biologist and removed from the site. The landscape plan and Tree Preservation and Protection Plan include measures to spray oaks with Agri-Fos in order to combat Sudden Oak Death, however, it is recommended that the California bay laurel in the landscape plan either be replaced with another native (e.g., toyon), or be monitored for sudden oak death disease and any California bay laurel (or other plants that carry the fungus) found to be infested with Sudden Oak Death be removed or treated using recommended arborist protocols for safe removal of diseased trees to prevent further contamination of surrounding areas.

Effectiveness: Improves effectiveness of landscaping plan in providing/protecting natural habitat and further reduces an already less than significant impact

Implementation: Measure shall be a condition of approval and incorporated into final landscape plan specifications. Project Applicant shall carry out measures. Restriction on planting invasive plant species shall be made a part of the subdivision’s CC&Rs.

Timing: Site shall be surveyed for invasive plants at the time trees are planted. Annual inspections of tree installation for five years in addition to any inspections required of the landscape installer.

Monitoring: The Applicant shall submit annual monitoring reports for five years after installation of mitigation trees to the Planning and Building Department.

Impact BIO-6: If the new home owners erect perimeter fencing it could adversely affect wildlife movement in the local area, triggering the CEQA threshold of significance related to wildlife corridors. This impact was not addressed in the 1992 EIR. Mitigation Measure BIO-6: If fencing is installed along the property boundaries (this does not apply to fencing adjacent to the houses used, for example, to confine pets or protect gardens), it shall be designed to allow wildlife passage by being short enough for deer to jump over, and having space at the bottom for mammals to move under, and/or should include gaps.

Effectiveness: Would reduce a potentially significant impact to less than significant. Implementation: Measure shall be implemented by property owner. Timing: Per property owners Monitoring: Condition of subdivision; condition should be placed in any CC&Rs

enacted for the subdivision Impact BIO-7: The bioswale could be used to replace the small amount of wetland vegetation (150 sf) that will be removed by the project, in addition to complying with the Clean Water Act Section 401 certification if required by the RWQCB (see BIO-8). This impact was not addressed in the 1992 EIR. It has not been identified as a significant impact, and this is an additional recommended mitigation measure. Mitigation Measure BIO-7: Design the bioswale to provide wetland habitat and replace the values of existing wetland habitat on the site (wetland vegetation, seasonal water source for



wildlife). The current species list for the bioswale includes grasses and one species of sedge. It is recommended that the species list be revised to also include rushes and, if possible, cattails. If the bioswale also provided a seasonal water source for wildlife it would replace the wetland habitat that may be removed by the project.

Effectiveness: Would further reduce an already less than significant impact Implementation: Applicant shall incorporate measure into final grading plans, and final

landscape plan. Timing: Bio swale shall be constructed in accordance with this measure upon

completion site grading Monitoring: San Mateo County Planning and Building Department

Impact BIO-8: The project will impact waters of the state and may require Clean Water Act 401 Water Quality Certification from the Regional Water Quality Control Board. Mitigation Measure BIO-8: After the CEQA process is complete, the applicant shall consult with the Regional Water Quality Control Board and obtain 401 Water Quality Certification as necessary. Certification may require changes to the project to further protect water quality or additional mitigation to replace waters of the state removed during project grading. The bioswale proposed for the project may be modified to provide mitigation (see BIO-7), or off-site mitigation may be required by the RWQCB.

Effectiveness: Will assure compliance of the project with the Clean Water Act. Implementation: By the applicant; may be reflected in the conditions of project

approval Timing: After CEQA, but prior to final approvals of grading and landscape

plans Monitoring: Applicant to submit documentation of consultation to the San Mateo

County Planning and Building Department



4.4 AESTHETICS 4.4.1 1992 EIR Analysis The 1992 EIR described the visual character of the project site as a wooded canyon and the visual character of the Palomar Park area as containing older, single-family homes on large lots in hilly terrain. Site topography ranges from 200 feet above mean sea level (amsl) on the canyon floor to roughly 425 feet amsl at the canyon rim. Site vegetation consisted of disturbed oak/bay woodland, non-native grass and native and non-native shrubs. The 1992 EIR identified that, in general, the project site had been vacant for some time and did not contain any structures or other improvements; however, there were a number of other disturbances that detracted from the site’s visual character, including an area of cut slopes and fill at the back of the canyon, several roads and tracks that criss-crossed the canyon slopes and floor, including the unpaved Hermosa Road extension, debris from illegal dumping activities, and the adjacent remnants of a demolished house on the Morgan Capital property (now Lands of the Donald J. Curia Trust). The 1992 EIR determined that the project would be visible from residences on Montalvo Road, South Palomar Drive, Cervantes Road, portions of Emerald Lake Hills across Edgewood Road, and portions of Edgewood County Park, but not from Interstate 280 (I-280), a State-designated Scenic Highway. The 1992 EIR analyzed the potential aesthetic impacts from changes in existing visual character of the site and vicinity, as well as from the proposed project’s infrastructure and site improvements and concluded that the project would introduce urban land uses into an open space site, and noted that a small portion of the project would be visible from Edgewood Road, a County-designated scenic road, and Edgewood County Park. The 1992 EIR also noted that the project would have a different character than existing development due to updated County standards for roads, driveways, emergency access, etc. as well as home-building trends. A scenic easement would be established along the east side of the main access road and cul-de-sac to provide a permanent wooded area which would act as a visual refuge and buffer to residences on the canyon rim and the Emerald Hills neighborhood of Redwood City. The 1992 EIR acknowledged that the six-lot project would result in a locally important change in visual character from open space with some previous disturbance to a residential subdivision, but concluded the incremental aesthetic impact of the project would not result in a significant impact. The 1992 EIR considered the various infrastructure components of the site plan that contributed to the project’s change in aesthetic character, including access roads and driveways, retaining walls, drainage features, the Hermosa Road upgrade, and the loss of trees associated with these structures. The EIR described that the access road serving Lots 1, 5, and 6 and connecting to Hermosa Road would wrap around the face of a knoll and have 1:1 slopes above and below the road that would require rockbolting (tiebacks) or benching to increase slope stability. The 1992 EIR described that this portion of road would not promote visually attractive development as addressed in the Visual Quality Policy of the County’s General Plan. The visual impact of the rockbolting and benching was considered to be a potentially significant impact and, as mitigation, required benching to be used in place of rockbolting wherever possible and landscaping to be installed above and below the road where rockbolting or benching occurred.



The 1992 EIR concluded that with mitigation the potentially significant visual impact from rockbolting and benching would be reduced to less than significance. The 1992 project required retaining walls that would vary between 3 to 10 feet in height. The visual impact of the retaining walls was considered to be a potentially significant impact and, as mitigation, required retaining walls over four feet in height to be a crib wall design planted with drought tolerant plants. The 1992 EIR concluded that with mitigation the potentially significant visual impact from retaining walls would be reduced to less than significant. The 1992 project would use engineered “natural” drainages that would not have an aesthetic impact, and that a storm water retention facility near the project entrance was not expected to be large or have adverse aesthetic impacts since the project was not expected to substantially increase storm water runoff. The EIR considered the visual impacts of these features to be a locally important effect. To reduce these local effects, the EIR required a civil engineer to prepare and a landscape architect to review a plan for designing project drainage facilities. The project would result in the loss of 13 dead, dying, or hazardous trees and 76 healthy, non –hazardous trees, including one large oak tree on Hermosa Road. The 1992 EIR considered the visual impact of this tree removal to be a potentially significant impact and, as mitigation, required 1) all possible efforts be made to avoid removal of the large oak tree on Hermosa Road and 2) a licensed landscape architect submit a tree planting plan providing for the planting of three trees for each tree removed. The 1992 EIR concluded that with mitigation the potentially significant tree removal impact would be reduced to less than significance. The 1992 EIR also required the applicant to implement Good Practice Measures to prevent loss or damage to trees during construction. The 1992 EIR considered the aesthetic impacts of the six individual lots and concluded that the aesthetic impacts of the individual homes would depend on the home design, construction materials, and topographic or vegetative screening, but did note that Lots 1 – 3, 5 and 6 would have homes and features that would be highly visible to surrounding neighbors because of their prominent location on the west-facing canyon wall. The 1992 EIR also considered the project’s conceptual landscaping plan. As good practice, the 1992 EIR incorporated mitigation that required the applicant to incorporate final site design changes into the conceptual landscaping plan. Finally, the 1992 EIR noted that the Palomar Park area is subject to the requirements of the San Mateo County Design Review District Regulation that required the project grading plan to be reviewed in light of Palomar Park design review standards. The grading plan was found to be in conformance with design standards and it was noted that future homes would be subject to the Palomar Park Design Review process as well. 4.4.2 2010 Environmental Setting This section updates the 1992 EIR setting where necessary, as well as summarizes the main changes to the visual character of the project itself. The project site has not substantially changed since 1992. The general visual character of the project site remains an undeveloped, wooded canyon. Changes to the visual setting include the



addition of one home on what was formerly the Morgan Capital property, which also includes a paved driveway from the edge of the project site’s southern boundary; an increase in the amount of fill stockpiled on the canyon floor, the removal of debris that was illegally dumped on site, and the installation of a gate at the entrance to the site at Edgewood Road. The project applicant has stockpiled additional fill material approved under the 1992 project which has changed the topography and elevation of the canyon floor. However, there have been no substantial changes to site vegetation although 14 trees have been removed under the permits obtained for the 1992 project and in general, tree and shrub vegetation has matured since 1992. The project site remains visible from existing residences on or near Montalvo Road, South Palomar Drive, Cervantes Road, portions of Emerald Lake Hills across Edgewood Road and portions of Edgewood County Park. The site is not visible from I-280, and the entrance road is only visible from a short stretch of Edgewood Road. Figure 2-3 in Project Description presents an aerial photograph of the project site and vicinity and Figure 2-6 provides photographs of the project site taken in February 2010. 4.4.3 2010 Regulatory Setting This section identifies the regulatory requirements designed to prevent aesthetic impacts within San Mateo County. There are no applicable Federal or State regulations pertaining to visual resources. San Mateo County Zoning Regulations As described in Chapter 3 of this document, the San Mateo County Zoning Regulations S-101 Combining District governs development of the project site and establishes requirements for features affecting aesthetic impact like lot coverage, building setback, and building height. Other zoning ordinances designed to regulate the appearance of development include the Significant Tree Ordinance, Heritage Tree Ordinance, Grading and Excavation Ordinance, and the Subdivision Ordinance. These ordinances are discussed in Chapter 3. Specifically relevant to aesthetic impact are allowable building heights. Section 6300.10.90 of the County zoning regulations restricts building heights on these lands to a maximum of 28 ft, measured as the vertical distance from: 1) any point on the natural grade to the topmost point of the building immediately above, or 2) any point on the lowest floor, if the lowest floor is below the natural grade, to the topmost point of the building immediately above. Future homes proposed for the site would have to be consistent with this height restriction. Palomar Park Design Review District Standards The Palomar Park area is a design review (DR) district subject to the design review standards contained in Section 6565.16 of the San Mateo County Zoning Regulations. The Bayside Design Review Committee will have the opportunity to review the proposed 2010 grading plan and this Supplemental EIR and provide an advisory recommendation to the Planning Commission at the time the Supplemental EIR is certified. The houses proposed for the site would also be required to go through the design review process. See additional discussion of the design review district requirements in Chapter 3.



Section 6565.20 of the Design Review District standards address the protection of trees and vegetation in areas designated as a design review district. In the Palomar Park area, these standards apply to trees 6 inches or more in diameter or 19 inches or more in circumference. The standards prohibit tree removal unless there is no alternative building site for the house and require each tree that is lost be replaced with three or more trees of the same species using at least five gallon size stock. The standards also protect all significant and heritage trees from damage during construction activities. The Preliminary Landscape and Revegetation Plan is shown in Figures 2-16 and 2-17 and described in Project Description. The plan recommends that removed trees be replaced in a 3:1 ratio and would be consistent with the Design Review District tree removal standards. As described in Chapter 3 of this document, the proposed project would conflict with Design Review District standards related to minimizing tree removal and minimizing alterations to topography. The tree removal would be mitigated by the implementation of the landscape and revegetation plan as described in Mitigation Measure BIO-3. The 2010 project proposes up to 40 feet of fill and cuts to the western canyon walls that would extend for 100 feet and be a maximum of 35 feet high and would not be consistent with Design Review District standard of minimizing alterations to topography. San Mateo County General Plan The 1986 San Mateo County General Plan contains two goals applicable to the visual quality of San Mateo County and this project: Goal 4.3 Protection of Vegetation Minimize the removal of visually significant trees and vegetation to accommodate structural development.

Goal 4.4 Appearance of Rural and Urban Development Promote aesthetically pleasing development in rural and urban areas. The General Plan contains 56 policies designed to achieve the County’s goals and objectives for visual quality, a subset of which applies to urban development, including: The 1986 San Mateo County General Plan also contains the following pertinent General Policies: Policy 4.14 Appearance of New Development Regulate development to promote and enhance good design, site relationships and other aesthetic considerations.

a. Regulate land divisions to promote visually attractive development. Policy 4.35 Urban Area Design Concept

a. Maintain and, where possible, improve upon the appearance of visual character of development in urban areas.



b. Ensure that new development in urban areas is designed and constructed to contribute to the orderly and harmonious development of the locality.

The 2010 project would be consistent with San Mateo County General Plan goals and policies listed above that are related to visual quality. Chapter 3 describes that the 2010 project would eliminate certain features of the 1992 project that were visually unattractive such as the driveways to Lots 1, 5, and 6 and the Hermosa Road connection located on the western canyon wall, as well as the retaining walls located throughout the site. However, the changes in topography associated with the 2010 proposed project could also be considered visually unattractive. 4.4.4 Thresholds of Significance This updated SEIR analysis considers whether the proposed project would result in a new significant aesthetic effect or a substantially more severe aesthetic impact than indentified in the 1992 EIR and also considers whether the project would result in significant aesthetic impacts as identified in Appendix G of the CEQA Guidelines. According to Appendix G of the CEQA Guidelines, the proposed project would have a significant aesthetic impact if it would:

a) Have a substantial adverse effect on a scenic vista; b) Substantially damage scenic resources, including, but not limited to, trees, rock

outcroppings, and historic buildings within a state scenic highway; c) Substantially degrade the existing visual character or quality of the site and its

surroundings; d) Create a new source of substantial light or glare which would adversely affect day or

nighttime views in the area. In addition, this analysis also considers whether the project would result in a potentially significant aesthetic impact if it is not consistent with an applicable San Mateo County General plan or policy governing aesthetics and visual resources. 4.4.5 2010 Project Impacts The proposed 2010 project site plan is different than the original site plan due primarily to the reduction in the number of proposed lots from six to two and the increase in fill that would be imported to the site to create the two level lots. Table 2-1 in Project Description summarizes and compares the major components of the 1992 and 2010 site plans, including number of lots, amount of cut and fill, reduction in scenic easement, prominent features of the plan, tree removal, and drainage features. Under the 2010 site plan, the proposed scenic easement would be reduced by 33% to accommodate realignment of the main access road and a proposed 15 ft public utility easement. The 2010 site plan also requires substantially more cut and fill than the 1992 site plan to create level lots. The 2010 project proposes roughly 11,600 cubic yard more cut and 59,685 cubic yards more fill over the 1992 project (see Table 2-1). The existing elevations for the Lot 1 pad range from approximately 240 to 320 ft. above mean sea level (amsl); under the 2010 site plan the Lot 1 pad area would be leveled to a finished grade of 280 ft amsl. The existing elevations at the Lot 2 pad range from approximately 270 to 300 ft



amsl; under the 2010 site plan the Lot 2 pad area would be leveled to a finished grade of 290 ft amsl. The leveled grades would accommodate drainage features and be suitable for home construction, thus, no additional grading would be required to install drainage features or construct the homes. A comparison with the 1992 project house pad grades cannot be made because the six houses would be constructed individually and the house pad elevations are not available for analysis. The 1992 project only contemplated grading necessary for infrastructure improvement. Grading for each of the six house pads was not analyzed. Under the current proposal however, all grading is now being analyzed. Once grading for the proposed 2010 project is completed, no additional grading would be necessary for house construction except for minor grading required for driveways and house foundations. Thus, the analysis of grading impacts associated with the two different projects is not exactly comparable. As with the 1992 project, the 2010 site plan may require installation of rockbolting (also referred to as tiebacks) or soil nails on the cut rock face in Lot 1 for slope stability. The area requiring rockbolting is much smaller than what was proposed under the 1992 project since the access road to Lots 1, 5, and 6 is not part of the 2010 proposal. The 2010 site plan also does not require cutting back the embankment on Edgewood Road or upgrading Hermosa Road to provide secondary emergency access to the project site. In addition, the 2010 site plan results in the loss of 27 fewer trees than the 1992 site plan (62 trees in 2010 site plan vs. 89 trees in 1992 site plan; 14 of which have already been removed under permits obtained for the 1992 project). This Supplemental EIR analyzes the aesthetic impact of the change in topography associated with this activity. The proposed project would result in one new aesthetic impact associated with grading and leveling the proposed two-lot subdivision. All other project aesthetic impacts would not be substantially more severe than identified in the 1992 EIR, and in some cases would even reduce the magnitude of the 1992 impacts. Degrade the Visual Character or Quality of the Site Similar to the 1992 project, the proposed 2010 project would produce a locally important change in visual character by introducing an urban land use into an existing undeveloped wooded canyon. As in 1992, the 2010 project would be visible to residences surrounding the canyon rim and a small portion of the project could be briefly glimpsed from Edgewood Road, a county-designated scenic road. The 2010 project, however, contains two lots as opposed to the original six lots analyzed in the 1992 EIR. The 2010 project would result the construction of fewer houses and would be less dense than the 1992 project. The 2010 project includes grading and filling the proposed subdivision lots, a site improvement not proposed and analyzed in the 1992 EIR. Thus, the grading and filling of the two lots is considered a new site improvement impact that cannot be compared to the 1992 EIR. The 2010 project would require 18,800 cubic yards of cut, 69,685 cubic yards of fill and the import of 50,885 cubic yards of fill material to carry out the grading. The applicant proposes to raise the Lot 1 and 2 pads to level grades of 280 ft. and 290 ft., respectively. Table 4-1 Proposed 2010 Elevation Changes summarizes the proposed grading and leveling activities required to achieve the desired leveled grade.



Table 4-1. Proposed 2010 Elevation Changes

Lot

Lot Area

Existing Grade

Leveled Grade

Max Elevation Change

1 312,600 sq. ft. (7.2 acres)

240 – 320 ft. 280 ft. ~ 40 ft.

2 262,250 sq. f.t (6.02)

270 – 300 ft. 290 ft. ~ 20 ft.

Total 574,850 sq. ft. (13.22)

-- -- --

The largest area of proposed cut in Lot 1 would occur in the western portion of the lot, where a side ridge would be cut back a distance of approximately 100 ft. The maximum height of the cut in this location would be approximately 35 ft. The largest elevation increase for Lot 1 would occur in the eastern portion of the lot, where approximately 40 ft. of engineered fill would be placed. The largest elevation decrease for Lot 2 would occur on the eastern portion of the lot, where a small side ridge would be cutback a distance of approximately 20 ft. The maximum height of the cut in this location would be approximately 10 ft. The largest elevation increase for Lot 2 would occur on the southern portion of the lot, where approximately 20 ft. of engineered fill would be compacted. In order to illustrate the proposed changes in topography, existing and proposed topography have been modeled in the following figures. Figure 4-2 View Point Locations depicts the project boundary, existing topography of the project site and immediate vicinity in 10-foot contour intervals, and the three viewpoints for which the terrain modeling is presented. The viewpoint locations were selected based on the location of representative sensitive receptors. The elevation of each viewpoint is indicated on the graphic and range from 305 to 445 feet amsl. The “possible house footprints” are shown on the canyon floor. The graphic illustrates the extent of the proposed cut of the western canyon slopes in order to create a level pad for Lot 1. Lot 2 does not require as much grading to create a level pad. Figure 4-3 Terrain Modeling Existing and Proposed Topography is a terrain model showing the entire site with existing and proposed topography with 2-foot contour intervals. This figure shows how the 2010 proposed grading plan would cut back the western canyon slopes in Lot 1, widen the narrow canyon entrance by cutting back a portion of the toe of the eastern slope to allow for the access road, level out the canyon floor through cut and fill, and create a 10-foot grade difference between Lot 1 and Lot 2. Figures 4-4 to 4-6, Views 1-3 illustrate the changes in topography resulting from the 2010 proposed grading plan as seen from the selected view points. In each view the dark green area represents the project boundary (grey areas are outside the project boundary). The light green area on the canyon floor represents the “possible house footprint” shown on the project plans. The “possible house footprint” represents an area where a house could be placed, not the actual size of the house. In each viewpoint a 6-foot tall person has been placed somewhere in the “possible house footprint” to illustrate scale. The person appears as a small black “dot” in the simulations In the Proposed viewpoints, the person is sometimes covered by fill and therefore not visible. Lot 1 is a slightly lighter shade of green than Lot 2.



In each of the views, the existing and proposed topography is shown in 10-foot contour intervals. View 1: This viewpoint is modeled from the back of the canyon looking towards the mouth of the canyon and illustrates how moderate grading would level Lot 2 in the foreground, while the cut of the western slope in Lot 1 would be clearly visible. The Existing and Proposed views demonstrate how the side ridge in Lot 1 would be cut back approximately 100 feet and fill would level out the lower portions of the lot. The resulting level lots would be apparent in the otherwise hilly area. View2: This simulation was prepared at 445 amsl and looks down into the middle of the canyon. Because of property boundaries, this view is set back somewhat from the eastern project boundary and there is mature vegetation between the nearby house and the project site. View 2 clearly shows the extent of the cut and fill of Lot 1. In the Existing view the slopes of the western canyon wall extend into the middle of the project site. In the Proposed view, the lower portion of Lot 1 is entirely flat. View 3: Illustrates the changes in topography as viewed from the middle of the site at elevation 305 amsl. The terrain modeling from this viewpoint depicts the changes in topography, especially in Lot 1. In the Existing view, the possible house footprint is shown stretching up the sides of the western canyon wall. In the Proposed view, the possible house footprint is shown in the newly created flat pad, demonstrating that much of the lower slope of the western canyon wall is removed and fill is placed to create the level pad. The terrain modeling indicates that the proposed grading and leveling activities would substantially modify the existing topography, which would conflict with Palomar Park Design Review standards and San Mateo County Subdivision Regulations that require that the natural topographic features of the site be preserved as much as possible. Not conforming to these standards does not infer that the project would result in a significant aesthetic impact since the standards apply to only one specific feature (topography) out of many that must be considered when analyzing the visual attributes of the project. Other features considered include vegetation, the extent to which the grading conflicts with the natural site topography, the type and nature of the surrounding land uses, and the general public visibility of the project itself. Although the project would substantially modify the existing topography of the lots, it would not substantially degrade the overall visual character and quality of the project site. The topography of the site has already been significantly altered by past quarrying activities and there are existing unsightly rock faces. The proposed project would remove approximately 62 trees (14 have already been removed), but would plant roughly 183 trees of the exact species removed in locations that would soften the changes to topography once the vegetation became established. The slopes of the lot pads would be constructed at 1:1 slopes and vegetated with indigenous species of plants which would blend in with the existing site vegetation. Landscaping of the level lot pads would be proposed and undergo design review at the time of house construction. Finally, although the project would be visible from residences along the canyon rim and may be visible from Emerald Lake Hills, the proposed residential development would be consistent with the type and nature of the surrounding residential land uses and would therefore blend in with the overall visual quality of the Palomar Park area once landscaping vegetation became established. Since the proposed grading activities would not be impacting a pristine area, and would not be



highly visible from any public viewpoint, the project’s lot improvements would result in less than significant aesthetic impacts. The 2010 project would not result in any new significant or substantially more severe changes in visual character than analyzed in the 1992 EIR. The proposed 2010 project reduces the number of proposed lots from six to two, and therefore reduces the magnitude of many of the infrastructure and lot impacts associated with the 1992 project. Road System As in 1992, the project’s road system must conform to San Mateo County Subdivision Ordinance and County Fire Warden requirements. Thus, as in 1992, conformance to these requirements means that the proposed 2010 main access road would be 20-feet in width and subsequent driveways would be 16 feet wide. The 2010 project, however, would end in a hammerhead “T” that is 70 ft. in diameter, five feet less than the 75-ft diameter cul-de-sac bulb proposed in 1992. The County standard for cul-de-sac bulbs is 600 ft. The 2010 project main access road would be approximately 1,060 feet in length, 550 feet less than the 1,200-ft. main access road proposed in 1992. The 2010 project would not require construction of the Lot 1, 5, and 6 access road as proposed in 1992. The 1992 EIR considered the visual impact of rockbolting and benching associated with the Lot 1, 5, and 6 access roads to be a potentially significant impact. Since the 2010 project does not require construction of this access road it would avoid this potentially significant impact entirely. The 2010 project does not require cutting back the embankment on Edgewood Road to meet traffic safety standards, nor does it require upgrading Hermosa Road to provide emergency access to the site. The 1992 EIR identified that the Hermosa Road upgrade could remove a large oak tree, which would be a locally important significant impact. Since the 2010 project does not require upgrading Hermosa Road it would avoid this locally important impact. Retaining Walls The 1992 project required retaining walls from 3 to 10 ft in height throughout the site in order to provide slope stability. The 1992 EIR considered the visual impact of retaining walls to be a potentially significant impact and recommended mitigation that required any retaining wall over four feet in height to be a crib wall designed and planted with native vegetation. The 2010 project would not require any retaining walls. Drainage Features The 2010 drainage plan is similar to the 1992 drainage plan. Runoff would be collected from up slope areas, directed through a series of lined ditches, headwalls, culverts, energy dissipaters, catch basins, and subdrains and ultimately discharged to a swale on the east side of the access road. The 1992 EIR considered the visual impact of altered drainages to be a locally important effect. The 2010 project would result in a similar impact that would not be substantially more severe than the 1992 impact. The 2010 project does incorporate a drainage and a bio swale which would be considered semi-natural, visually attractive features (see Figure 2-16 and 2-17 Preliminary Landscape/Revegetation Plan).



Tree Removal The 2010 project would remove approximately 62 trees, 27 less than the 89 total trees (77 of which were determined healthy) proposed for removal in 1992 (including the oak tree associated with the Hermosa Road upgrade). The applicant has already removed 14 trees under the approved and recorded Tentative Map for the 1992 project. As in 1992, trees removed during construction would be replaced in a three-to-one ratio, with plantings designed to blend with the existing vegetation in appearance and species composition. The 1992 EIR considered the loss of 76 healthy trees to be a potentially significant impact but found this impact could be mitigated to less than significant through replacement of the removed trees at a three-to-one ratio. Although the 2010 project would remove 27 less trees than the 1992 project, the loss of 62 trees is still considered a potentially significant impact. The project therefore, would result in tree removal impacts that are less severe than the 1992 EIR but still potentially significant. With implementation of the1992 EIR mitigation, the 2010 project impacts from tree removal would be less than significant (see mitigation section below). Lot Impacts The 1992 project consisted of a six-lot subdivision with proposed site improvements related to access and site roads, driveways, erosion control features, emergency access, and utilities. The Hermosa Road connection and the driveways for Lots 5 and 6 would have required substantial grading and rockbolting or benching of the canyon wall. These features in particular would have been highly visible from surrounding areas and unsightly because of the exposed bedrock and rockbolted areas. These features have been dropped from the 2010 project; however, the overall grading proposed under the 2010 project would result in significant changes to site topography, which over time, would be mitigated by the establishment of vegetation planted under the Landscape and Revegetation Plan. While the grading would be significant, the reduced number of lots associated with the 2010 project reduces the total visual change to the project site, as well as reduces the number of ancillary structures associated with home construction such as driveways, drainage features, etc. In this regard the proposed 2010 project does not result in lot impacts that are new or substantially more severe than considered in the 1992 EIR. Scenic Easement The 1992 project established a 2.31 acre scenic easement along the sides of the eastern canyon wall in order to provide a permanent visual buffer for residents surrounding the site. The current 2010 project proposal reduces the scenic easement by 33% to 67,782 square feet. The reduction in size of the scenic easement results from moving the location of the site access road to the east and having to cut back the lower portion of the eastern slope (see Figures 2-10 and 2-11). All the scenic easement in Lot 2 would be eliminated and only the portion in Lot 1 would remain. The scenic easement remaining protects the mid to upper slopes of the eastern wall and will continue to provide a permanent visual buffer. Have a substantial adverse effect on a scenic vista; Substantially damage scenic resources, including, but not limited to, trees, rock outcroppings, and historic buildings within a state



scenic highway; or substantially degrade the existing visual character or quality of the site and its surroundings? Entrance road improvements would begin at the southern project boundary which is set back from Edgewood Road and not clearly visible. Since the 2010 project reduces the amount of development that is introduced in the canyon and is not part of a scenic vista except for residents around the rim of the canyon, the proposed project would not have a significant impact on scenic vistas and resources. The proposed site is not located in a state- or county-designated scenic corridor. The project site is not visible from I-280, a state-designated scenic highway. Edgewood Road is a county-designated scenic road. The 2010 project proposal would be less visible from Edgewood Road than the 1992 project because the 2010 proposal does not propose site entrance road improvements as were proposed in the 1992 project. Create a new source of substantial light or glare which would adversely affect day or nighttime views in the area. The 2010 project would introduce similar sources of light and glare as the 1992 project, primarily consisting of exterior night lights of the homes and driveways. Instead of six homes and the associated lighting, the 2010 project would only have two homes, thus reducing night lighting within the project site. The homes would be subject to design review which would ensure that any exterior lighting would not result in any direct glare impacts and thus represent a less than significant impact. 4.4.6 2010 Mitigation Measures The 1992 EIR identified several mitigation measures to reduce potential aesthetic impacts of the 1992 project. The 2010 project does not involve, retaining walls, or upgrading Hermosa Road and therefore the 1992 mitigation pertaining to these impacts are no longer necessary. Additionally, a preliminary drainage plan and preliminary landscape and revegetation plan have been prepared for the 2010 project and the need for the mitigation measure addressing altered drainages has been eliminated. The following mitigation measures would apply to the proposed 2010 project: Impact AES-1: Geology mitigation for slope stability including rockbolting, benching, or use of soil nails could be visually unattractive. Mitigation Measure AES-1: Benching is aesthetically preferable over rockbolting and benching should be used wherever possible. The rockbolted area must be landscaped with screening shrubs and/or groundcover that should be planted immediately after construction of the area and maintained until it becomes established.

Effectiveness: Would help to reduce an already less than significant visual impact of geotechnical design measures.

Implementation: Required as a condition of the new Grading Permit Timing: Measure to be implemented during construction Monitoring: Applicants Engineer of Record shall communicate to the County the

ability of the project to implement this measure based on field conditions.



Impact AES-2: Removal of approximately 62 trees would result in a significant impact to the visual character of the project site. Mitigation Measure AES-2: See Mitigation Measure BIO-3. Prior to issuance of a grading permit, a landscaping/tree planting plan prepared by a licensed landscape architect must be submitted, showing the exact location, size, and type of each of the trees to be planted on site. Trees removed shall be replaced at a 3:1 ratio using a mix of native species similar to the ones removed.

Effectiveness: Would reduce potentially significant impact to less than significant Implementation: Required as a conditions of the new Grading Permit Timing: Final landscape/tree planting plan shall be submitted prior to issuance

of new Grading Permit and revised, if necessary, based on actual field conditions. Trees shall be planted upon completion of all grading

Monitoring: San Mateo County Planning and Building Department



4.5 PUBLIC SERVICES 4.5.1 1992 EIR Analysis The proposed project for the 1992 EIR was a revision of an earlier proposal that was the subject of an Initial Study and two Negative Declarations. The 1992 EIR focused on issues identified as potentially significant in the Negative Declarations and in the public’s response to them. Public services of fire protection, water service and police protection were the only areas that were identified to have potentially significant impacts. Fire Protection The 1992 EIR described three fire protection service providers and their estimated response times to the project site: the Palomar Park Volunteer Fire Company located at 178 S. Palomar Drive (response time 5 to 6 minutes), the San Mateo County Emerald Lake Hills fire station at the junction of Jefferson and California (response time under 10 minutes), and the City of San Carlos Fire Station 16, located on Alameda de las Pulgas near Howard Avenue (response time within 5 minutes). The 1992 EIR noted that San Mateo County, in conjunction with the California Department of Forestry and Fire Protection (now CalFire), was assessing the need to construct a new fire station on Edgewood Road east of Interstate-280 (I-280). The 1992 EIR also noted, however, that San Mateo County Fire Department consistently meets the County’s General Plan rural fire protection service goal of 10 minutes or less 90 percent of the time for the rural areas east of I-280. The 1992 EIR identified that the project site was located within the California Department of Forestry and Fire Protection’s (now CalFire) Fire Hazard Severity Zone #3305 and was designated as having a “Moderate” fire danger. The EIR noted the project would be subject to San Mateo County Fire Ordinance requirements, including requirements for potable water (Section 3435.1), traffic access and circulation patterns (Section 3435.8), fire hydrants (Article 8), and fuel breaks (Section 3434.5). The EIR described that the project would have to design and construct a road connecting the proposed cul-de-sac with Hermosa Road and upgrade more than 800 feet of Hermosa Road in order to provide unobstructed, emergency access as required by the County Fire Ordinance. The 1992 EIR analyzed the project’s potential effects on fire protection service capabilities and concluded the project would not adversely impact fire protection services nor require additional fire protection staff or equipment. The EIR noted that the surrounding residential development is subject to existing fire hazard risks due to its location along ridgelines that are covered with flammable vegetation and subject to prevailing westerly winds. The project would improve fire suppression capabilities at the project site and the surrounding areas since the proposed Tentative Map substantially conformed to County Fire Ordinance and County Fire Warden requirements which included the installation of fire hydrants and on-site turnarounds. The EIR noted that although the proposed main access road length exceeded the County Fire Ordinance’s proscribed maximum cul-de-sac length of 1,000 feet (600 feet for a hazardous fire area), the project Applicant had agreed to a new road connection to, and upgrade of, Hermosa Road to reduce potential risks associated with the cul-de-sac design. The applicant also instituted a number of good practices into the project’s design designed to reduce potential risks of fire



hazards, including construction of a secondary ingress-egress path from the Lot 4 turnaround to the house pad. The 1992 EIR documented a minimum fire flow requirement for the project of 500 gallons per minute at 20 pounds per square inch (psi) residual pressure, in addition to domestic consumption, for a two-hour duration and concluded that San Mateo County Water District #3’s existing water storage capacity of 108,000 gallons and pumping ability would be able to provide the required minimum fire flow. The EIR concluded, however, that inadequate fire flows could cause a potentially significant public safety hazard and, therefore, required the applicant to mitigate this impact by conducting field tests to determine that actual water conveyance conditions would meet engineering assumptions used to design and construct the project’s fire suppression system. Water Service The 1992 EIR identified San Mateo County Waterworks District No. 3 as the water service provider for the Palomar Park area. In 1992, District No.3 operated under a water rationing regime and the EIR assumed an average household water consumption rate for the project of 330 – 370 gallons per day (gpd). In 1992 District No. 3 had 108,000 gallons of potable water storage capacity for domestic and fire protection services. The applicant did not propose to interconnect, loop, or grid the project’s water system and was required to construct eight-inch water mains in order to meet County Fire Warden requirements. The EIR documented that the project would connect to an existing six-inch water main located at the junction of Hermosa Road and Palomar Drive. The proposed eight-inch water main would run under Hermosa Road and down the access road to Lots 1 and 5 to the main cul-de-sac, with water main extensions to serve Lots 4 and 6. The domestic water lines would extended into each lot by the new parcel owners at the time of home construction. The 1992 EIR analyzed the project’s water consumption impact and concluded that the existing water allotments and storage capacity for District No. 3 was adequate to the serve the domestic and fire flow requirements for the proposed six-lot subdivision. The EIR acknowledged that replacement of the existing water main on Hermosa Road would cause temporary impacts but result in long term benefits in terms of increased flow capacities and fire hydrants. The EIR did not require implementation of any management practices or mitigation for water service. Police Protection The 1992 EIR identified the San Mateo County Sheriff’s Department as the police protection provider for the project. The Sheriff’s office was located at the Hall of Justice in Redwood City and the Department had an emergency response time of 5 to 6 minutes. The EIR described that the Sheriff’s Department does not receive many calls from the Palomar Park area and concluded that the project would not adversely impact the County Sheriff’s Department. The EIR did not require implementation of any mitigation or management practices for police protection. 4.5.2 2010 Environmental Setting This section updates the 1992 EIR setting where necessary.



Fire Protection Fire risks and fire protection services in the Palomar Park area have not substantially changed since 1992. The CalFire designated fire danger for the site increased from “Moderate” to “Very High” (CDFP, 2008; Dave Sapsis, Assistant Fire Chief, pers. comm.). The primary fire protection provider is no longer the Palomar Park volunteer fire company but is San Mateo County Fire Station 18, located at 300 Edmonds Road approximately 0.8 mile west of the site. Fire Station 18 has a response time to the site of less than three minutes, an improvement over 1992 response times (Dave Sapsis, Assistant Fire Chief, pers. comm.). The Natural Hazard Component of the San Mateo County General Plan, Background and Issues volume, contains County-stated service goal of having a response time of three minutes or less in rural areas 90 percent of the time (Paul Clowdes, County Fire Engineer, pers. comm.). This response time is less than the stated service-goal of 10 minutes or less identified in the 1992 EIR. Water Service Water service to the project site has changed since 1992. The water service provider at the site is no longer San Mateo County Waterworks District No. 3 but is now California Water Service Company (Cal Water). Cal Water purchases water from the San Francisco Water Department (Leighton Low, Superintendent of Construction, per. comm.). Cal Water has upgraded parts of the system so that it meets current water delivery and fire protection standards. At the time of the 1992 project there was a drought and the water service provider had imposed water rationing. Currently, Cal Water does not impose water rationing restrictions. Police Protection Police protection services have not changed since 1992. The site is still serviced by the County Sheriff’s Department, now located at 300 Bradford Road in Redwood City, California. As in 1992, the Sheriff’s Department does not receive many calls for the Palomar Park area because of the homogeneous nature of the single-family residential development (Larry Shumaker, Patrol Officer, pers. comm.). The procedure for emergency calls is the same as in 1992. Patrol units leave the office and are out in the field. When an emergency call comes in the closest unit(s) are dispatched. Response time to an emergency depends on many factors including location of the units, weather and traffic conditions but should be within three minutes (Larry Shumaker, Patrol Officer, pers. comm.). 4.5.3 2010 Regulatory Setting This section identifies the regulatory requirements designed to ensure that public services can be provided to the proposed project. All infrastructure associated with the project would be subject to these regulations. Federal There are no federal regulatory requirements that apply to this project.



State There are no state regulatory requirements that apply to this project. Local Fire Protection The regulations that govern fire protection services have not changed substantially since 1992. As in 1992, the project would be subject to the fire protection design and improvement regulations contained in the San Mateo County Subdivision Regulations (Chapter 3, Article 5, §7025): Subdivisions within a Fire District. For a subdivision of a property located in a fire district, the subdivider must install water mains, fire hydrants, gated connections and other facilities needed to provide water supply of sufficient volume and pressure for fire protection in conformance with standards established in the fire district. Prior to the recordation of any final map or parcel map, the subdivider must furnish a letter from the fire district certifying that such improvements have been installed and are operative; or that a bond or cash deposit in an amount set by the Director of Public Works has been filed with the County Clerk guaranteeing installation of said facilities within 12 months of the date of recording of the map. When a bond or cash deposit has been made, construction beyond the foundation shall not be permitted, and placement or storage of combustible construction materials on site is prohibited, unless approved mitigation to the satisfaction of the fire authority and water purveyor has been installed. The proposed project is also subject to the requirements of the San Mateo County Fire Code and the California Fire Code (Marc Colbert, Deputy Fire Warden, pers. comm.). The following fire protection standards must be incorporated into the project’s design in response to County Fire Warden requirements: Potable water: The project’s potable water distribution system must meet the County Fire Warden’s minimum fire flow standard of 1,000 to 2,000 gallons per minute (gpm) at 20 psi residual operating pressure for two hours, as well as meet domestic demand (Marc Colbert, Deputy Fire Warden, pers. comm.). Fire flow is determined by the largest proposed building (using square footage of all floors) in a subdivision. Specifically, homes that are:

3,600 sq ft. or less must provide 1,000 gpm for two hours, plus domestic demand; 3,600 to 4,800 sq ft. must provide 1,300 gpm for two hours, plus domestic demand; 4,800 to 6,000 sq. ft. must provide 1,500 gpm for two hours, plus domestic demand.

The proposed project’s fire flows will be available from County Standard 6-inch Wet Barrel Fire Hydrant, with a configuration of one 4.5 inch outlet and one 2.5 inch outlet located no more than 200 feet from the building. Each hydrant must be at least 400 feet apart (Marc Colbert, Deputy Fire Warden, pers. comm.). Land division: No minor or major land division shall be approved or filed until the County Fire Warden certifies that it complies with the following traffic access and circulation patterns, unless



otherwise approved by the Planning Commission or the Board of Supervisors (Marc Colbert, Deputy Fire Warden, pers. comm.):

All dead end roadways shall be terminated by a turnaround bulb of not less than 96 feet in diameter. Alternatives such as a hammerhead turnaround shall be 70 feet in diameter and may be approved by the County Fire Warden.

No dead-end or cul-de-sac roadway shall exceed 1,000 feet in length. All dead-end roadways shall be appropriately marked. Metal signs of a size approved by the County Fire Warden with the designation Fire

Escape Route shall be placed in all locations specified by the County Fire Warden. When only one means of access exists to the land to be divided and the County Fire

Warden has requested an alternative means of access, an alternate means of access or other fire safety measures approved by the County Fire Warden shall be provided by the land divider.

In any hazardous fire area of San Mateo County no dead-end or cul-de-sac roadway shall exceed 600 feet in length.

The proposed project cul-de-sac is approximately 1,060-feet in length and exceeds the maximum cul-de-sac length of 600 feet for hazardous fire areas; the applicant would request an exception to this requirement and comply with all conditions required by the County Fire Warden necessary to grant this request. Fuel breaks: The project must conform to the requirements of Article 5, Section 3434.5 which requires property owners in forest, brush or grass-covered lands to maintain fuel breaks around each structure within their property. In 2006, a change in Public Resources Code (PRC) (14 CCR 1299 (d) 4291) extended fuel breaks for residential properties from 30 feet (as identified in the 1992 EIR) to 100 feet. A homeowner’s clearing responsibility is limited to 100 feet away from their building or to the property line, whichever is less. Water Service The regulations governing water service in the project area have not changed since 1992. The project’s potable water distribution system would meet County Fire Warden standards for fire flow (see discussion above under 1. a., Fire Protection). In addition, the new water main must be a minimum of 6 inches in diameter. If the mains are not interconnected, looped or gridded, and if they exceed 600 feet in length, the new water main(s) must be at least 8 inches in diameter. Police Protection There are no regulatory requirements for police protection. 4.5.4 Thresholds of Significance This updated Supplemental EIR analysis considers whether the proposed project would result in new or substantially more severe impacts than indentified in the 1992 EIR and also whether the project would result in a potential public service impact as identified in Appendix G to the CEQA Guidelines.



Fire Protection Based on Appendix G to the CEQA Guidelines, the proposed project would have a significant environmental impact associated with fire protection if it would:

a) Result in substantial adverse physical impacts associated with the provision of new or physically altered governmental facilities, need for new or physically altered governmental facilities, the construction of which could cause significant environmental impacts, in order to maintain acceptable fire service ratios, response times or other performance objectives for fire services; or

b) Expose people or structures to a significant risk of loss, injury or death involving wildland fires, including where wildlands are adjacent to urbanized areas or where residences are intermixed with wildlands.

Water Service Based on Appendix G to the CEQA Guidelines, the proposed project would have a significant environmental impact in regards to water supply if it would:

a) Require or result in the construction of new water facilities or expansion of existing facilities, the construction of which could cause significant environmental effects; or

b) Not have sufficient water supplies available to serve the project from existing entitlements and resources, or if new or expanded entitlements are needed.

Police Protection Based on Appendix G of the CEQA Guidelines, the proposed project would have a significant environmental impact related to police services if it would:

a) Result in substantial adverse physical impacts associated with the provision of new or physically altered governmental facilities, need for new or physically altered governmental facilities, the construction of which could cause significant environmental impacts, in order to maintain acceptable police service ratios, response times or other performance objectives for police services.

4.5.5 2010 Project Impacts Fire Protection The proposed project would not result in any new or substantially more severe impacts than considered in the 1992 EIR, would not result in adverse physical impacts associated with new or altered facilities necessary to maintain fire protections services, and would not expose people or structures to new significant risks from wildland fires. Since 1992, the CalFire designated fire danger for the site has gone from “Moderate” to “Very High”, however, the primary fire protection provider for the project is now San Mateo County Fire Station 18, located at 300 Edmonds Road approximately 0.8 mile west of the site, which has a response time to the site of less than three minutes, an improvement over 1992 response times (Dave Sapsis, Assistant Fire Chief, pers. comm.).



The project would not adversely impact the Fire Department’s service capability or require additional facilities, staff, or equipment. The development of a two unit subdivision would have no more impact on the various responding Fire Departments than two units developed elsewhere in the County, as long as conditions for fire safety are met (Marc Colbert, Deputy Fire Warden, pers. comm.). The surrounding residential development is mostly along ridgelines covered in flammable vegetation. With the prevailing westerly winds, the threat of encroaching wildfire already exists for these homes. Recommended conditions of approval for the subdivision would improve the fire suppression capability within the project site and in the area immediately surrounding the site because a new source of water to fight fires would be provided at the bottom of the canyon. The proposed tentative map substantially conforms to the requirements of the County Fire Warden. However, the main access route does exceed the 600-foot fire hazard length by approximately 250 feet. As a result, the Applicant is required to construct the hammerhead turnaround 70 feet in diameter to provide adequate turning radius for emergency equipment, and the fire hydrants would be spaced 400 feet apart. To ensure that the fire hydrants are installed according to specifications of the County Fire Warden, the Applicant would post a bond of the amount approved by the County covering the cost of installation. The hydrant must be installed prior to placement of combustible materials. According to Cal Water, the water system will meet the minimum fire flow requirements of 1,000 to 2,000 gpm at 20 psi residual operating pressure for two hours as well as meet domestic demand (Leighton Low, Superintendent of Construction, pers. comm.). However, field testing of the existing water system must be done to determine if field conditions match the assumptions of Cal Water. Field testing will be conducted by the County Fire Warden. If field testing determines that the existing water system cannot deliver the required fire flows without off-site improvements to the system, the project Applicant must design and fund the construction of all necessary improvements, and dedicate the completed work to San Mateo County. San Mateo County would review all engineering plans, conduct inspections of construction work, and inspect the completed work prior to accepting the dedication of improvements. Engineering plans of all required improvements shall be submitted for review and be approved by San Mateo County prior to approval of the Final Map. The building permit and/or plan approval issued for construction shall meet the intent of California Building Code (CBC) Chapter 7A (Material and Construction Methods for Exterior Wildfire Exposure). CBC §701A.3.2.2 requires the building official, prior to construction, provide the owner or applicant a “certification” that the building as proposed to be built complies with all applicable state and local building standards, including those for materials and construction methods for wildfire exposure as described in Chapter 7A. Additional on-site infrastructure and facilities would incorporate a full sprinkler fire protection system as required by the California Uniform Fire Code. Based on the analysis above, the proposed project would have a less than significant impact on fire protection services.



Water Service The proposed project would reduce the number of lots from six to two, and thereby reduce potential water demand associated with the project. Cal Water’s existing water allotment of water is adequate to service the project (Leighton Low, Superintendant of Construction, pers. comm.). The proposed water supply system must be designed and constructed to the standards and requirements of Cal Water and the County Fire Warden. The water system must be installed and functional prior to the issuance of building permits for new structures, unless otherwise approved by the Fire Warden. All work would be at the expense of the project Applicant. The Applicant would also be required to pay Cal Water for fire service to the new subdivision. The construction of necessary water facilities will take place within existing roadways and easement, and would result in less than significant physical impacts. Water service to the proposed project will be supplied by connecting to an existing six-inch water main located in at 120 Cervantes Road at the intersection of Cervantes Road and South Palomar Drive. The water and utility lines will run from the point of connection on Cervantes Road to the project site via a 15-foot wide Public Utility Easement at the north easterly property line of 120 Cervantes Road. The proposed system would be interconnected and no leg of the main would exceed 450 feet in length. The water main must be installed and functional, prior to the issuance of building permits for new structures, unless otherwise approved by the Fire Warden. The proposed project would not result in any new or substantially more severe impacts than considered in the 1992 EIR, would not result in the construction of new or expanded water facilities which would cause significant environmental effects, and would not result in any water supply impacts. The impacts to water services created by the proposed project would be less than significant. Police Protection As in 1992, the proposed project would not adversely impact the County Sheriff’s Department. The project does not require the construction or modification of any facilities related to police protections services. Access to the site currently occurs through a gate and this would not change; homeowners would provide access to police and emergency service personnel during an emergency. The proposed road improvements would provide adequate internal access to the site. Thus, the impacts to police protection services as a result of the proposed project would not be new or substantially more severe than identified in 1992 and would be less than significant according to the CEQA Guidelines. 4.5.6 2010 Mitigation Measures Fire Protection The analysis above shows that there will be no issues related to the provision of fire protection services that exceed significance criteria. However, as stated above, the CalFire designated fire danger for the site has increased from “Moderate” in 1992 to the current designation of “Very High.” CalFire’s recommendations of “good practice” should be implemented: Impact SERV-1: The project is being constructed in an area rated as “Very High” for fire danger.



Mitigation Measure SERV-1: The project must conform to the following fire protection requirements: San Mateo County Fire Ordinance Section 3435.4. No building permit shall be issued by the Building Official for a proposed structure within the boundaries of an area served by a public water system unless the requirements of Section 3435.1 are already present or are required as part of the building permit. No certificates of Occupancy shall be issued by the Building Official until the County Fire Warden certifies the fire protection requirements of Section 3435.1 or 3435.5 are complete and functional. Additional requirements include:

The water system shall be installed, and functional, prior to the issuance of building permits for new structures, unless otherwise approved by the Fire Warden.

The subdivider shall record deed restrictions, to the satisfaction of County Counsel, requiring that all future structures be equipped with automatic fire sprinkler systems.

The main road shall be constructed prior to the issuance of building permits for homes on the new parcels, unless otherwise approved by the Fire Warden.

The Applicant shall submit revised grading plans reflecting the approved conditions to the County Fire Warden.

All internal combustion engine powered equipment utilized in the grading operations shall be provided with approved spark arrester or exhaust systems, in accordance with the Vehicle Code.

Effectiveness: Would further reduce an already less than significant impact Implementation: Measure shall be made a condition of approval. Required by the San

Mateo County Fire Protection Regulations, the County Fire Warden, and the San Mateo County Grading Ordinance and Subdivision regulations.

Timing: Measures incorporated into final project design Monitoring: San Mateo County Planning and Building Department

Water Service The project would not have significant impacts on the ability of Cal Water to provide service or create the need for construction of new facilities. No mitigation measures are necessary. Police Protection The project would not have significant impacts on the County Sheriff’s Department and no mitigation measures are necessary.



4.6 PUBLIC HEALTH AND SAFETY 4.6.1 1992 EIR Analysis The 1992 EIR analyzed two health and safety issues: the disposal of wastewater by septic systems and the presence of hazardous wastes on the site. Septic Systems In 1992, the Palomar Park area was outside the jurisdiction of both the San Carlos and Redwood City wastewater treatment districts, thus all residences in the Palomar Park area were on individual septic systems. The 1992 EIR identified that each of the proposed six-lots would also rely on septic tanks and drainfields for wastewater disposal. The EIR described the septic system that would be installed, the San Mateo County regulations and ordinances that would apply to the system, the potential site constraints (e.g., areas where slopes exceed 50 percent, areas of impermeable clay-bearing soils, etc.) and summarized the percolation tests that were conducted to identify and design the drainfields for the project. The 1992 EIR documented that slope and soil conditions at Edgewood Canyon constrained the siting of individual septic systems. After several alterations, the Applicant identified drainfield locations for the six proposed lots. Although all the drainfields technically met the County’s 1992 design and siting requirements, several drainfields were very near the County limits of these requirements. The 1992 EIR also identified that, because of the soil and slope conditions at the Edgewood Canyon subdivision site, each lot would be required to construct both the primary and expansion drainfield as a condition of individual septic permit approval. The County Environmental Health Specialist reviewed and approved the septic system and drainfields for each of the six lots proposed under the 1992 project. The 1992 EIR concluded that the project could result in a potential significant impact from septic systems located on steep slopes and above road cuts that could result in the day lighting of effluent or cause the instability of steep slopes. In order to mitigate these potential impacts, the applicant was also required to submit a final septic system plan to the County Department of Environmental Health showing drainfield layout and percolation test results. For Lots 1, 5, and 6 with slopes greater than 20 percent, the final plan was required to include data showing that there will be no daylighting of effluent or slope instability. Finally, the 1992 EIR documented that individual septic systems in San Mateo County are expected to have an average life span of 75 years, and that the County does not normally monitor drainfield operation. In the event of drainline failure the homeowner would activate another drainline. Hazardous Wastes The 1992 EIR identified that illegal dumping of rubbish containing paint cans and car batteries lead to a concern that there could be household hazardous waste at the site and that the non-engineered fill at the back of the canyon could contain contaminated soils or buried materials. The EIR documented that test pits excavated for the geotechnical investigation and percolation tests found the fill material to be clean. To mitigate this potential impact, the EIR required that



potentially hazardous chemicals and toxic materials found on site be removed and properly disposed of prior to any construction. 4.6.2 2010 Environmental Setting This section updates the 1992 EIR setting where necessary. Wastewater Disposal The environmental setting described in the 1992 EIR remains unchanged. The Palomar Park District is not within the jurisdiction of either the San Carlos or Redwood City wastewater treatment districts. Consequently, all residences in the area are on individual septic systems. Thus the current two-lot proposal would rely on septic tanks and leachfields for sewage disposal, as did the 1992 project. Hazardous Waste Since 1992, the project site has been gated and all illegal dumping activities have been halted. In addition, all previously identified hazardous chemicals and toxic materials have since been removed from the site. Hazardous wastes from illegal dumping at the site are no longer a concern and, therefore, are not discussed further in this document. 4.6.3 2010 Regulatory Setting This section identifies the regulatory requirements designed to prevent the effects of public health hazards present in the project area. All infrastructure associated with the project would be subject to these regulations. Federal As hazardous waste concerns are no longer present at the site, there are no federal regulatory requirements that apply to this project. State There are no federal regulatory requirements that apply to this project. Local San Mateo County As in 1992, the siting, design, and construction of septic systems are governed by San Mateo County ordinance No. 0370. Siting, Design, and Construction In October 1996, the County adopted Ordinance No. 03740 which amended, renumbered, and redesignated the former “Ordinance Governing Individual Septic Systems” (Chapter 6, Division VII, Sections 8500 through 8509.10) to the “Regulation of Individual Onsite Wastewater



Treatment and Disposal Systems” (Chapter 4, Division VII, Sections 9300 through 9340). The Ordinance lists the standards that must be met in order to obtain a permit from the County Department of Environmental Health allowing construction of or improvements to an individual sewage disposal system. The Ordinance has been approved by the State RWQCB. The Ordinance covers the type of equipment required, the siting of the septic tank and drainfield, the construction of the drainfield, methods of testing percolation rates for drainfield sites, and the permit application process. The following are the standards for siting leachfields relevant to the situation at Edgewood Canyon. Section 9321. Location: No drainfield or other leaching system shall be located closer than:

10 feet of any building. 10 feet of any property line. 100 feet of the top of bank of a stream. 50 feet from a ditch, cut bank or slope over 50 percent.

Performance standards for the approval of individual sewage onsite wastewater treatment and disposal systems:

B. The Drainfield System (4) Each half of the drainfield shall, whenever possible, be located on one contour (one elevation) (13) No portion of any drainfield shall be located in fill over 12 inches deep. No portion of any drainfield shall be located within 50 lateral feet of any fill placed on slopes of 35 percent or greater. F. Slope of Terrain (a) When slopes in excess of 20 percent are proposed for use substantiating detailed geotechnical data shall be provided to demonstrate that sewage surfacing will not occur throughout the drainfield and expansion areas. (c) Drainfields located in slopes of 35 percent or greater shall utilize a pressure dosing design to distribute the wastewater uniformly throughout the drain line.

San Mateo County Department of Environmental Health Percolation Tests As in 1992, the County Department of Environmental Health requires percolation tests to determine the length of drainline needed to efficiently handle wastes generated by homes of various sizes. Each drainfield must show three percolation rates within standards accepted by the Department of Environmental Health. Slower percolation rates require longer drainlines, or if



percolation is too slow, a failed percolation rate results. Percolation rates that are too fast for County standards do not allow adequate filtering of effluent and also results in a failed test. The following are the percolation rates taken from the County Ordinance that are used to assess percolation tests for failure or adequacy. The three passing rates are assigned a grade. Each grade results in a different requirement for drainfield lines.

Table 4-2. San Mateo County Required Leachfield Percolation Rates

Percolation Rate* Pass/Fail Grade

Length of Drainfield Line (3 bedroom house)

Length of Line Required per Additional Bedroom

Above 12.0 Fail …. ….. ….

2.0 – 12.0 Pass A 2 lines @70 feet 20 feet per line

1.0 – 1.99 Pass B 2 lines @ 125 feet 40 feet per line

0.75 – 0.99 Pass C 2 lines @180 feet 60 feet per line

Less than 0.75 Fail … ….. …. * Inches percolating per hour 4.6.4 Thresholds of Significance This updated Supplemental EIR analysis considers whether the proposed project would result in new or substantially more severe impacts than indentified in the 1992 EIR and also examines whether the project would result in a potential public health and safety impact as identified in Appendix G to the CEQA Guidelines. Wastewater Disposal Based on Appendix G to the CEQA Guidelines, the proposed project would have a significant environmental impact associated with wastewater disposal if it would:

a) Have soils incapable of adequately supporting the use of septic tanks or alternative waste water disposal systems where sewers are not available for the disposal of waste water?

4.6.5 2010 Project Impacts Wastewater Disposal The proposed project would not result in any new or substantially more severe impacts from wastewater disposal than identified in the 1992 EIR. The septic systems would be designed and installed per County standards and regulations as specified in San Mateo County Ordinance Code Chapter 4 Sections 9300 et seq. The County has reviewed and conditionally approved the two proposed septic systems and drainfield locations, and the project would not result in impacts from soils incapable of supporting the septic system. As described in the Project Description, the primary and expansion drainfield area for Lot 1 is the County-approved drainfield area proposed for Lot 4 in the 1992 plan. Figure 2-12 depicts the location of this drainfield, which is located approximately 325 feet from the possible house footprint for Lot 1. This location is in native soil, roughly 60 feet upslope from slopes greater



than 50 percent and above a road cut. The percolation test results for this drainfield indicate the Lot 1 drainfield site resulted in a Grade B percolation rate (1.0 to 1.99 inches percolating per hour). The Applicant’s 2010 Septic Plan identifies two 125-foot primary drain lines, two 80-foot primary drain lines, two 125-foot expansion lines, two 45-foot expansion lines, and one 40-foot expansion line, as well as inspection risers. These plans are based on a five bedroom home. As required by County Ordinance, the home builder would be required to extend the lines by 20-feet for each additional bedroom constructed. The Lot 2 primary and expansion drainfield area is the County-approved drainfield area proposed for Lot 6 in 1992. For Lot 2, the center of the primary and expansion leach fields are located 125 feet and 225 feet, respectively, north of the possible building envelope as shown on Figure 2-13. The percolation test results for this drainfield indicate the Lot 2 drainfield site resulted in a Grade A percolation rate (2.0 to 12.0 inches percolating per hour). The Applicant’s 2010 Septic Plan identifies four 55-foot primary drain lines and four 55-foot expansion drain lines, as well as inspection risers. These plans are based on a five bedroom home. As required by County Ordinance, the homebuilder would be required to extend the leach lines an additional 20 feet for each additional bedroom constructed. The Lot 2 drainfields would be located in areas that currently contain undocumented, stockpiled fill material up to 30 feet in depth. County ordinance restricts drainfields from being located on more than 12 inches of fill. Thus, the entire undocumented fill material located on top of the Lot 2 drainfield would have to be removed in accordance with all applicable local, state and federal safety regulations, including the current OSHA excavation and trench safety standards. The stockpiled soils would first be placed on the gently sloped proposed house footprint area of Lot 2. The Lot 2 drainfield would then be constructed and engineered fill material placed back on top of it. Because of this construction scenario, the Lot 2 drainfield will likely be installed prior to other site improvements at an elevation such that the proposed drainfield trenches discharge effluent into the competent native soil and/or bedrock. The Applicant’s 2010 Septic Plan details that the proposed septic tanks and pump chamber would contain risers to enable tank cleaning and maintenance activities. In the event of a prolonged pump outage, effluent would be discharged to a 40 foot gravity fed leachfield trench adjacent to the pump chamber. The septic plans depict the control and alarm panels for the systems to be located at the proposed house locations, and the drainlines would have inspection risers to facilitate maintenance. The Lot 2 drain lines would be located under approximately 20 feet of fill but are anticipated to last for the life of the residences. If drain line maintenance is required, the drain lines would be snaked from the septic tank and pump chamber. As required in the 1992 EIR, both the primary, expansion, and emergency drainfields for both Lots 1 and 2 would be constructed during initial site construction activities given the soil and fill conditions at the site. 4.6.6 2010 Mitigation Measures Wastewater Disposal The 1992 mitigation measure for the drainfields (page III-72 of 1992 EIR) stated that the "applicant must submit a final septic system plan to the Department of Environmental Health Services (EHS) which will show drainfield layout and percolation test results. For Lots 1, 5, and



6 [now Lot 1 drainfield] with slopes greater than 20 percent, the final plan must also include hard data showing that there will be no effluent surfacing downslope from drainfields and that drainfields will not occasion downslope instability". All data was provided to the EHS and approved by Mr. Stan Low prior to final 1992 approvals. Therefore, this mitigation measures has been satisfied. The analysis above shows that there will be no impacts from soils incapable of supporting a septic system. However, as stated above, the slope and soil conditions at the site constrain drainfield locations and the following measures shall be implemented: Impact SAFE-1: The soil and fill conditions at the site constrain drainfield locations. Mitigation Measure SAFE-1: Potential drainfield constraints shall be mitigated by (Final septic system plan required by Ordinance; irrigation and installation measures from 2010 Septic System Plan (Hartsell 2010); drainfield construction measure recommended in 1992 EIR):

1) The Applicant shall submit a final septic system plan to the San Mateo County Environmental Health Division which will show drainfield layout and percolation test results. The final plan shall be based on the final number of bedrooms identified for construction.

2) Irrigation in leach field areas should be avoided to the maximum extent possible and limited to the minimum amount necessary to preserve plantings.

3) The septic system installation contractor shall have at least ten years experience installing at least five septic systems a year in San Mateo County. When the system is installed, the system designer shall meet with the selected contractor to approve work details before work commences and after it is done.

4) The Lot 1 and Lot 2 primary and expansion drainfields shall be installed at the same time.

Effectiveness: Further reduces an already less than significant impact Implementation: Measure shall be made condition of approval and reflected in the Final

Grading Plan/ Grading Permit. Timing: Final septic system plan shall be submitted prior to issuance of grading

permit. Monitoring: San Mateo County Planning and Building Department and San Mateo

County Environmental Health Division



4.7 TRAFFIC Updated traffic analyses has been prepared for this project in order to document any changes in traffic conditions since 1992 and to analyze the traffic and traffic safety impacts associated with the current 2010 project proposal. These updated reports are contained in Appendix E of this Supplemental EIR, and include: Updated 2010 Project Traffic Reports

“Edgewood Canyon Estates Construction Traffic” Memorandum prepared by Hexagon Transportation Consultants, Inc. (Hexagon), April 13, 2010. Contains a discussion of traffic safety and line-of-sight issues and addressed the traffic impacts associated with project construction and occupancy.

“Edgewood Canyon Estates, unincorporated San Mateo County” Letter prepared by RKH Civil and Transportation Engineering (RKH), November 5, 2008. Contains a discussion of the traffic safety issues associated with the new project driveway connection at Edgewood Road.

4.7.1 1992 EIR Analysis The 1992 EIR relied upon an evaluation of traffic volumes and safety conducted by RKH, data from the San Mateo County Department of Public Works, and a line of sight diagram from Hawk Engineers to prepare the traffic analysis. The 1992 EIR described that primary access to the project would be from Edgewood Road, which connects with Interstate 280 to west and Alameda de Las Pulgas to the east. Emergency access to the project would be provided via Hermosa Road, which connects with Palomar Drive. The EIR documented that nearby Cervantes road is a private road, does not conform to County standards, and is blocked above Edgewood Road. The EIR also documented that although the project site did not contain any formal connection with a trail network, the site was used by non-vehicular traffic such as pedestrians and equestrians. The San Mateo County General Plan Road System Map classifies Edgewood Road as an arterial highway. The EIR described that the posted speed limit for Edgewood Road was 45 mph and documented an average daily traffic (ADT) volume of 11,700 vehicles per day, with peak traffic periods occurring between 7:30 to 9:30 am and 5:30 to 6:30 pm. The EIR documented that peak period traffic was about 12% of the ADT, or about 1,400 cars per hour, and that California Highway Patrol accident statistics reported a total of 19 accidents for Edgewood Road in 1990. The 1992 EIR analyzed short-term construction and long-term occupancy traffic volume (trip generation) impacts and concluded the project would results in less than significant trip generation impacts. For construction, the EIR considered the project would result in up to 500 total truck trips for importing fill, or 5.0 trips per day, and documented that the County would require all hauling traffic to be restricted to off-peak hours and that ingress and egress of haul trucks would be conducted by a flag person posted a the project entrance. For residential occupancy, the 1992 EIR assumed that 10 trips per day per lot would add up to 60 trips per day to Edgewood Road, a 0.5% increase above 1992 ADT. The EIR also assumed that



10% of the project trip generation, or 6 trips, would occur during the peak time periods, a 0.4% increase above 1992 peak traffic volumes. The EIR considered these trip generation rates to be an insignificant increase in traffic volumes. The 1992 EIR also analyzed potential traffic safety impacts associated with ingress and egress directly onto Edgewood Road. The EIR documented that immediately east of the project’s primary access road, Edgewood Road is bordered by a steep embankment 10 to 30 feet high, which blocks the view of oncoming, westbound-travelling traffic and makes a left turn (i.e., eastbound) onto Edgewood Road difficult and risky. RKH Civil and Transportation Engineering (RKH) determined that this existing condition permitted a sight distance on the order of 160 feet, or 2.5 seconds of travel time at 45 mph. RKH analyzed this condition according to two standard measures established by Caltrans for State highways, Stopping Sight Distance, or SSD (the distance required, at a given speed, to perceive an object, react, and stop) and Corner Sight Distance (CSD) using a 7.5 second criterion (the distance required to allow a driver at least 7.5 seconds to see oncoming traffic and make a left turn, without requiring oncoming traffic to slow down). RKH determined the existing condition did not provide the minimum 360-foot SSD nor the minimum 495-foot CSD necessary to provide adequate sight, time, and safety for vehicles to turn left onto Edgewood Road. The EIR considered this to be a potentially significant impact and evaluated several mitigation options, including requiring exiting vehicles to make a right turn only, reducing speeds on Edgewood Road, relocating the project entrance, and cutting back the embankment that causes the reduced visibility. The EIR concluded, and the County Department of Public Works concurred, that cutting back the embankment was the environmentally preferable solution and required the applicant to prepare a plan for cutting back the embankment to meet the minimum SSD criterion of 360 feet as mitigation. 4.7.2 2010 Environmental Setting This section updates the 1992 EIR setting where necessary. The only change to the traffic setting since 1992 has been the installation of a traffic light at the intersection of Edgewood Road and Cordilleras Road, approximately 350 feet west of the new proposed entrance to the project site. According to the memo prepared for the project by Hexagon (Appendix E), ADT on Edgewood Road is now 13,150 vehicles per day, with 10%, or 1,300 vehicles, occurring during the peak hour periods (7:00 to 9:00 am and 4:00 to 6:00 pm). 4.7.3 2010 Regulatory Setting This section identifies the regulatory requirements designed to prevent the effects of traffic impacts as a result of implementing the proposed project. All infrastructure associated with the project would be subject to these regulations. Federal There are no federal regulatory requirements that apply to this project.



State There are no state regulatory requirements that apply to this project. Local Since 1992, San Mateo County has adopted a number of plans designed to manage traffic congestion. The following policies would apply to the proposed 2010 project: San Mateo County Countywide Transportation Plan 2010 The goal of the Countywide Transportation Plan is to reduce traffic congestion by increasing capacity and performance of all transportation systems, increasing demand for transit travel, and decreasing demand for automobile travel, especially single occupant travel. San Mateo County Congestion Management Program (CMP) (2009) The purpose of the CMP is to identify strategies to respond to future transportation needs, develop procedures to alleviate and control congestion, and promote countywide solutions. The CMP is required to be consistent with the Metropolitan Transportation Commission (MTC) planning process that includes regional goals, policies, and projects for the Regional Transportation Improvement Program (RTIP). The 2009 CMP, which is developed to be consistent with MTC’s Transportation 2035 Plan, provides updated program information and performance monitoring results for the CMP roadway system. The CMP roadway system comprises of 53 roadway segments and 16 intersections. The roadway network includes all of the State highways within the County in addition to Mission Street, Geneva Avenue, and Bayshore Boulevard. Because the project does not add more than 100 peak hour trips to the regional roadway network, no analysis under the CMP is required. San Mateo County General Plan The San Mateo County General Plan contains traffic circulation policies that encourage the County to address traffic, transit, and circulation issues. None of the policies directly relate to this project, thus are not presented here. 4.7.4 Thresholds of Significance This updated SEIR analysis considers whether the proposed project would result in new or substantially more severe impacts than indentified in the 1992 EIR and also examines whether the project would result in a potential traffic impact as identified in Appendix G to the CEQA Guidelines. According to Appendix G of the CEQA Guidelines, a project will normally have a significant traffic effect if it would:

a) Conflict with an applicable plan, ordinance, or policy establishing measures of effectiveness for the performance of the circulation system, taking into account all modes of transportation including mass transit, and non-motorized travel and relevant



components of the circulation system, including but not limited to intersections, streets, highways and freeways, pedestrian and bicycle paths, and mass transit;

b) Conflict with an applicable congestion management program, including, but not limited to level of service standards and travel demand measures, or other standards established by the county congestion management agency for designated roads and highways;

c) Substantially increase hazards due to a design feature (e.g., sharp curves or dangerous intersections) or incompatible uses (e.g., farm equipment);

d) Result in inadequate emergency access; 4.7.5 2010 Project Impacts The proposed project would result in more construction traffic trips but less daily occupancy traffic than identified in the 1992 EIR. Construction Trip Generation Soil Import: The 1992 EIR stated that: “The project engineer has estimated that 500 truck trips importing fill and base rock for road construction into the site would be required over the 100- to 150-day construction period. This is an average of 3.3 to 5.0 trips per day, if truck traffic is assumed to be spread evenly over the construction period”. The 2010 project would require the import of roughly 50,900 cu yds of fill, which would increase the number of haul truck trips required by the project from an estimated 10 total trips per day (five in, five out) in 1992 to an estimated 84 total trips per day (42 in, 42 out), or an average of 12 total trips per hour (one trip every five minutes) for the approximately four months of site grading (88 working days). This would result in an estimated 7,392 soil haul truck trips during the four month construction period (84 total daily trips x 88 working days) (see Hexagon report in Appendix E for calculation of haul trips). For the purposes of determining operational characteristics, large trucks typically are assumed to have a passenger car equivalent (PCE) of 2.0 (source: 2000 Highway Capacity Manual). This means that, when determining the operating characteristics of an intersection or freeway segment, each large truck has the same impact as approximately two passenger vehicles. This methodology accounts for the different operational characteristics of large trucks vs. passenger vehicles and takes into account the type of vehicle generating the trip when determining intersection or freeway level of service. When converted to PCEs, the project’s grading phase would generate 168 daily trips (84 inbound/84 outbound), including 24 hourly trips (12 inbound/12 outbound) for the four months of site grading. Hexagon concluded that the project’s construction impact would be less than significant based on the information discussed below.

The amount of project traffic would be very small relative to the existing traffic load and carrying capacity on Edgewood Road. When converted to passenger car equivalents, the project’s percentage of existing traffic would be approximately 1.3%. This is well within daily count error and would be imperceptible to traffic on Edgewood Road.

The project would restrict truck traffic to largely off-peak time periods of the day. The highest concentration of ambient traffic typically occurs during the 7 AM - 9 AM and 4 PM - 6 PM periods. Traffic impact analyses typically focus on these periods because they



represent the periods when impacts are most likely. During non-commute hours, traffic volumes are considerably lower and there is much more available capacity.

The project would control access on Edgewood Road with a temporary traffic control plan and a flagger. The flagger would minimize the disruption of turning truck traffic to and from Edgewood Road and also ensure that access is safe and orderly.

All truck traffic would occur on major streets (I-280 and Edgewood Road). Major streets have structural sections and design characteristics (such as turn radii, lane markings, etc…) to accommodate heavy vehicles.”

The project applicant has taken a number of steps to ensure the increase in haul truck trips would not result in a new or substantially more severe impact than previously addressed. The applicant has identified a construction haul route entering and exiting the site via Edgewood Road and Interstate 280. The applicant has committed to restricting truck traffic to between the hours of 8:30 am to 4:30 pm, avoiding much of the peak hour time periods. The applicant has also identified that flaggers and advanced signage would be placed at the site entrance to direct traffic as necessary during construction. The Hexagon evaluation determined the frequency of two trucks on the narrow driveway traveling in opposite directions (one inbound and one outbound) would be a low-frequency event with a 1 in 10 chance of occurring. In the event this did occur, Hexagon concluded the flagger could clear the driveway in order to enable the inbound truck (i.e., the truck turning left off of Edgewood Road) to get onsite quickly. Hexagon determined that the project’s haul truck traffic could produce vehicle queues on Edgewood Road on the order of 5 to 10 vehicles, an amount typical for a low volume signalized intersection, and concluded that the proposed haul truck trip generation would not result in a significant impact. Home Construction: Once site preparation is completed, additional construction traffic would be generated by the building phase of project construction. The proposed two-lot subdivision would require less building construction activity than the six-lot subdivision considered in the 1992 EIR and is therefore likely to result in less truck trips associated with delivering construction materials and construction worker vehicles. Construction traffic would not conflict with an applicable plan, ordinance, or policy establishing measures of performance of the circulation system. Occupancy Trip Generation Assuming an average of 10 trips per day per lot, the same assumption as made in the 1992 EIR, the proposed two-lot subdivision would produce 20 trips per day and 2 trip per peak hour time period, less than the 60 trips per day and the 6 trips per peak hour time period considered in the 1992 EIR. The project, therefore, would not result in a new or more severe impact from occupant trip generation. Furthermore, the addition of 20 trips per day and two trips per peak hour results in a 0.15% increase in trip generation above existing ADT (13,150) and peak hourly (1,300) conditions on Edgewood Road, an insignificant increase in traffic volume. Occupancy trip generation would not conflict with an applicable plan, ordinance, or policy establishing measures of performance of the circulation system.



Substantially Increase Hazards due to a Design Feature RKH determined that for a road with a 45mph speed limit, the minimum corner sight distance is 360 feet. RKH reviewed the proposed driveway intersection with Edgewood Road and found that the driveway intersection meets the minimum stopping sight distance criteria with the driver (of a vehicle on the driveway) situated 10 feet back of the white, edge of the pavement line. Additionally, it was found that the traffic signal on Edgewood Road at Cordilleras Road, located 350 feet west of the driveway together with an advance warning flashing beacon and sign located 70 feet east of the driveway combine to slow traffic through the area. The report found the driveway as proposed would not pose a traffic safety problem and that the minimum stopping distance can be met as described above. Please refer to Appendix E for RKH’s complete letter report regarding Edgewood Canyon Estates traffic safety. 4.7.6 2010 Mitigation Measures Since the completion of the original EIR in 1992, a stoplight has been installed at the intersection of Edgewood Road and Cordilleras Road, approximately 350 feet west of the entrance to the Edgewood Canyon Subdivision site. A review by RKH found that the driveway as proposed would not pose a traffic safety problem and that the minimum stopping distance can be met as described above. Therefore, the previous mitigation measure proposed in the 1992 EIR requiring the applicant to cut back the slope at the entrance to the site is no longer applicable. The following mitigation measure is recommended to further reduce an already less than significant impact. This mitigation measure will ensure that soil haul traffic does not create significant traffic impacts. Impact TRAF-1: Truck traffic generated by the import of fill could cause traffic delays along Edgewood Road near the site entrance. Mitigation Measure TRAF-1: The following measures shall be implemented during the soil haul phase of project construction to ensure soil haul trucks do not create delays along Edgewood Road:

1) Soil haul truck traffic shall be restricted to between the hours of 8:30 am to 4:30 pm to avoid as much of the peak hour commute periods as possible.

2) The project would control access on Edgewood Road with a temporary traffic control plan and a flagger. The flagger would minimize the disruption of turning truck traffic to and from Edgewood Road and also ensure that access is safe and orderly.

3) A construction haul route shall be identified so that soil haul truck access the site via Interstate 280 and Edgewood Road and avoid traveling through Redwood City.

Effectiveness: Would further reduce an already less than significant impact Implementation: Measure to be incorporated into conditions of project approval and

Grading Permit Timing: Measure to be implemented during project construction Monitoring: San Mateo County Planning and Building Department



4.8 NOISE 4.8.1 1992 EIR Analysis The 1992 EIR characterized the noise setting of the proposed project area as quiet, marked by brief episodes of noise from distinct sources such as automobiles and trucks travelling on Edgewood Road, airplanes passing overhead, and residential activities. In 1992, the average daily traffic volume on Edgewood Road, the largest consistent noise source in the project vicinity, was 11,700 daily vehicle trips. The EIR identified day-night average (Ldn) background noise levels at the site to be 48 decibels (dB) up the canyon, away from Edgewood Road, and 51 dB near the former Morgan Capital property (now Lands of the Donald J. Curia Trust). The 1992 EIR did not find any evidence that the Canyon basin and exposed rock walls act as an amphitheater to magnify sound, in fact, the EIR did note that sound source level measurements conducted for the project identified slightly greater noise attenuation with distance than theoretical values. The 1992 EIR considered two project impacts: the project’s compatibility with the existing on-site noise environment and the project’s potential to generate construction and operational noise impacts at the twenty residences adjacent to the project site. The 1992 EIR compared measured Ldn background sound levels of 48 and 51 dB to the County’s 55 dBA noise level standard for single family residences as receiving land use and concluded the project was compatible with the existing outdoor environment (i.e., less than significant). The 1992 EIR concluded in the future, after project completion, residents would experience the same noise sources as the existing surrounding residences at the time. The 1992 EIR analyzed potential construction noise generation activities including site clearing, site grading, road paving, and home construction. The analysis assumed the applicant would complete road and utility work in one construction season (April through October), but that home construction would be spread out over a number of years. The 1992 EIR found that road construction equipment such as jack hammers, rock drills, earth moving, and paving equipment would generate noise levels of 80 to 90 dBA at a distance of 50 feet and could result in noise levels of 70 to 80 dBA at properties close to Edgewood Road. The 1992 EIR also found that construction of Lot 5 and the secondary access road would produce sound levels of 70 to 80 dBA further up the canyon. The EIR found annoyance and short term impacts would occur within 1,000 feet of the project for outdoor sensitive receptors and within 250 feet for an indoor receptor. The EIR concluded construction noise would be less than significant since the San Mateo County noise standard exempts construction noise during the 7:00 am to 6:00 pm daylight period and the proposed subdivision and construction noise levels would not exceed generally accepted noise exposure standards. The EIR did, however, recommend, that good neighbor practices be implemented to maintain County construction time-of-day restrictions and to follow required use of noise abatement equipment (e.g. low noise air compressors and mufflers on diesel engines). The 1992 EIR analyzed potential long-term noise impacts associated with the occupancy of six new homes in the canyon and concluded that an increase in new neighbors adds to the potential for increased neighbor disturbance. The EIR noted that homes closer to Edgewood Road would experience minimal impact from the new homes since existing noise levels are dominated by traffic on Edgewood Road. The EIR analyzed the potential increase in sound and concluded that



the addition of six new homes to the canyon would not significantly increase the ambient noise environment at any existing home. The EIR also concluded that the noise generated from the addition of up to 60 vehicle trips per day would not result in a significant impact, and that the project would not significantly change noise propagation in the canyon nor produce a general amphitheater effect. 4.8.2 2010 Environmental Setting This section updates the 1992 EIR setting where necessary. The noise environment of the site has not changed substantially since the 1992 analysis. The former Morgan Capital property (now Lands of the Donald J. Curia Trust), used to contain a vacant residence, now contains a new single-family residence. Thus, there are now twenty-two rather than twenty-one single family residences on the canyon rim. Regional population growth has increased the amount of vehicle traffic on Edgewood Road and aircraft flyovers, the two main noise sources for the canyon, occur. In 2005, average daily traffic on Edgewood Road measured 13,150 vehicles, an increase of 1,800 vehicles above 1992 traffic volumes (Hexagon Transportation Consultants Inc. 2010 (see Appendix E)). On February 18, 2010, TRA Environmental Sciences, Inc. (TRA) staff took 15 minute spot noise measurements at three locations on the project site in order to determine whether there had been any substantial changes in the noise environment of the project site since it was characterized in 1992. The measurements were taken near the southern project boundary, near the middle of the canyon and at the north end of the canyon. During the noise measurements, aircraft flyovers occurred an average of once every eight minutes, more than the “occasional” flyover mentioned in the 1992 EIR. The background noise measurements conducted by TRA, however, indicate that although the frequency of noise sources has changed the background noise levels at the project site remains between the 48 dBA to 51 dBA average observed in 1992. 4.8.3 2010 Regulatory Setting This section identifies the regulatory requirements designed to prevent the effects of excessive noise present in the project area. All infrastructure associated with the project would be subject to these regulations. Federal There are no federal regulatory requirements that apply to this project. State There are no state regulatory requirements that apply to this project. Local San Mateo County Noise Ordinance



San Mateo County noise control standards applied to the 1992 project and would apply to the 2010 project as well. Although the specific code citations have changed since 1992, the noise control standards that apply to the project have not substantially changed.

Noise Ordinance 4.88.330 for exterior noises states that daytime noise levels are to be lower than 55 dBA in single-family residential areas (See Table 4.3 below);

Noise Ordinance 4.88.360 exempts noise sources associated with demolition, construction, repair, remodeling or grading of any real property that occurs between 7:00 A.M. and 6:00 P.M. weekdays and 9:00 A.M. and 5:00 P.M. weekends.

4.8.4 Thresholds of Significance This updated Supplemental EIR analysis considers whether the proposed project would result in new or substantially more severe noise impacts than indentified in the 1992 EIR. According to Appendix G of the CEQA Guidelines, the proposed project would have a significant environmental noise impact if it would:

a) Expose persons to or generate noise levels in excess of standards established in the local general plan or noise ordinance, or applicable standards of other agencies.

b) Expose persons to or generate excessive groundborne vibration or groundborne noise levels.

c) Cause a substantial permanent increase in ambient noise levels in the project vicinity above levels existing without the project.

d) Cause a temporary or periodic increase in ambient noise levels in the project vicinity above levels existing without the project.

Consistent with the 1992 EIR, the proposed project would result in a significant impact if it:

1) Results in construction activities outside of the 7:00 AM to 6:00 PM time period on weekdays or the 9:00 AM to 5:00 PM time period on weekends; or

2) Exceeds San Mateo Noise Ordinance single family exterior noise level standards, as outlined in Table 4-3 below

Table 4-3. San Mateo County Noise Level Standards For a Single-Family Residence as a Receiving

Land Use

Cumulative Number of Minutes in any one-hour

period

Daytime 7 am to 10 pm

Not to exceed (dBA)

Nighttime 10 pm to 7 am

Not-to-exceed (dBA) 30 55 50 15 60 55 5 65 60 1 70 65

0 (Not-to-exceed) 75 70 Source: San Mateo County Code: Div IV, Part Two; Chapter 4.88, Noise Control; Article 4.88.330, Table I. 4.8.5 2010 Project Impacts The 2010 project consists of a two-lot subdivision, which is four less homes than the six-lot subdivision analyzed in the 1992 EIR. The two-lot subdivision would produce similar short-term



construction activities and less long-term occupancy noise. Project construction is expected to occur over an approximately one year period. For this and the other reasons discussed below, the 2010 project would not result in any new or substantially more severe noise impacts than considered in the 1992 EIR. Expose persons to or generate noise levels in excess of standards established in the local general plan or noise ordinance, generate excessive groundborne vibration, or cause a permanent or temporary increase in ambient noise levels above levels existing without the project. TRA identified background noise levels at the site on February 18, 2010 to be between 48 to 51 dBA, the same range identified in the 1992 EIR. Thus, the project site is compatible with the proposed residential uses. Short-Term Construction Noise Impacts The proposed 2010 construction duration and activities are substantially similar to those analyzed in the 1992 EIR. Site preparation for the 1992 project was expected to take three and a half to four and a half months; the project applicant estimates that the 2010 project’s site preparation will take roughly four months. Home construction activities for the 2010 project may take less time since only two homes would be constructed instead of six. The 2010 project contains more soil hauling and cut and fill activities than the 1992 project but eliminates construction on the upper canyon slopes such as the driveways to Lots 5 and 6 and the Hermosa Road connection. The additional soil haul and cut and fill activities would not extend the daily or seasonal construction schedule analyzed in the 1992 EIR. Construction of the 2010 project would require the use of earthmoving and building construction equipment that is substantially the same as the 1992 project, including compactors, excavators, graders, drill rigs, pile drivers, and rock hammers. As described in the 1992 EIR and Section 4.8.3 above, construction noise is exempt from the County’s noise ordinance if it occurs between 7:00 AM and 6:00 PM on weekdays and 9:00 AM and 5:00 PM on weekends. The 1992 EIR concluded that short-term construction noise would result in annoying sound levels for outdoor sensitive receptors within 1,000 feet of the construction activities and indoor sensitive receptors within 250 feet of construction activities. This conclusion remains valid for the 2010 project and, consistent with the 1992 EIR, the project would implement the following good management practices:

Limit construction activities to 7:00 AM to 6:00 PM on weekdays and 9:00 AM to 5:00 PM on weekends ; and

Abate construction noise through the use of low-noise air compressors and the use of mufflers on all gas and diesel engines.

Long-Term Occupancy Noise Impacts The 1992 EIR found that occupancy of up six new homes and their resulting 60 vehicle trips per day would result in a less than significant impact. The proposed 2010 project would construct four less homes and result in approximately 40 less vehicle trips per day than considered in the



1992 EIR and, therefore, would also result in a less than significant impact from occupancy noise. 4.8.6 2010 Mitigation Measures The proposed 2010 project would not have any potentially significant noise impacts and mitigation is not required.



4.9 AIR QUALITY AND GREENHOUSE GAS EMISSIONS 4.9.1 1992 EIR Analysis The proposed project for the 1992 EIR was a revision of an earlier proposal that was the subject of an Initial Study and two Negative Declarations. In these earlier documents, air quality was not identified as having a potentially significant impact and therefore was not addressed in the 1992 EIR. In January 2010, the CEQA Guidelines were amended to include analysis of greenhouse gas emissions. This Supplemental EIR contains an air quality section in order to analyze the air quality and greenhouse gas emissions associated with the currently proposed project. 4.9.2 2010 Environmental Setting Air quality is a function of pollutant emissions and topographic and meteorological influences. The physical features and atmospheric conditions of a landscape interact to affect the movement and dispersion of pollutants and determine its air quality. Greenhouse gases (GHG) are chemical compounds that trap heat in the Earth’s atmosphere and contribute to the regulation of the Earth’s climate. Unlike air quality, which is influenced by local and regional factors and is therefore considered on the local or regional scale, GHGs influence global climate patterns and are best considered on a broader state, national, or global scale. The proposed project lies within the San Francisco Bay Area Air Basin (SFBAAB). The SFBAAB is a management area designated by the California Air Resource Board (ARB) over all or portions of the nine counties surrounding the San Francisco Bay. The Bay Area Air Quality Management District (BAAQMD) is the primary agency responsible for monitoring and maintaining air quality in the SFBAAB. The environmental and regulatory settings related to air quality and GHG emissions in the SFBAAB are described below. SFBAAB Topography and Meteorology The topography and meteorology of the SFBAAB are characterized by the coast mountain ranges and the seasonal migration of the Pacific high-pressure cell. Airflow in the SFBAAB is affected by the coast mountain ranges, which create complex terrains consisting of mountains, valleys, and bays. The Coast Range splits into eastern and western ranges in the SFBAAB; the Golden Gate to the west and the Carquinez Strait to the east are gaps in the mountain ranges that allow air to flow into and out of the SFBAAB. In the summer, winds from the northwest are drawn and channeled through the Golden Gate and other narrow openings, resulting in localized areas of high wind speeds. Air flowing from the coast inland is called the sea breeze and begins developing in the late morning or early afternoon; air flowing from the inland regions back to the coast, or drainage, occurs at night. The SFBAAB is most susceptible to air pollution during the summer when cool marine air flowing through the Golden



Gate can become trapped under a layer of warmer air (known as an inversion) and prevented from escaping the valleys and bays created by the Coast Ranges. The SFBAAB’s climate is influenced by the Pacific high-pressure cell, a semi-permanent area of high pressure. In the summer, the cell is centered over the northeastern Pacific Ocean, pushing storms to the north and resulting in generally stable conditions within the Bay Area. In the winter the cell weakens and migrates south, bringing cooler temperatures and stormy conditions. Wintertime inversions are weaker and more localized and are the result of rapid heat radiation from the earth’s surface. Bay area summers are generally hot and dry. Daytime summer temperatures can vary by as much as 35 degrees Fahrenheit between the coast and inland regions as a result of daytime temperature differences between land and water surfaces. Winters are cooler and wetter, with winter rains accounting for 75 percent of average annual rainfall. In the winter, temperature differences between the coast and inland regions are more pronounced at night. SFBAAB Air Quality The federal and state governments have established ambient air quality standards for “criteria” pollutants considered harmful to the environment and public health. National Ambient Air Quality Standards (NAAQS) have been established for carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), “fine” particulate matter (particles 2.5 microns in diameter and smaller, or PM2.5), “inhalable coarse” particulate matter (particles between 2.5 and 10 microns in diameter, or PM10), and sulfur dioxide (SO2). California Ambient Air Quality Standards (CAAQS) are more stringent than the national standards and include the following additional pollutants: hydrogen sulfide (H2S), sulfates (SOX), and vinyl chloride. In addition to these criteria pollutants, the federal and state governments have classified certain pollutants as hazardous air pollutants (HAPs) or toxic air contaminants (TACs). The following is a discussion of criteria pollutants and HAPs based on information published by the U.S. EPA and ARB: Carbon Monoxide (CO) CO is an odorless, colorless gas that is formed by the incomplete combustion of fuels. Motor vehicles are by far the single largest source of CO in the Bay Area. At high concentrations, CO reduces the oxygen-carrying capacity of the blood and can aggravate cardiovascular disease and cause headaches, dizziness, unconsciousness, and even death. Lead Lead is a heavy-metal that occurs naturally in the environment as well as in man-made products. Historically, the combustion of leaded gasoline in motor vehicles was the major contributor to lead emissions in the air. The U.S. EPA began to phase out the use of lead in the 1970’s and banned its use in highway vehicles in December 1995. As a result of this phase-out and ban of lead in gasoline ambient concentrations of lead have decreased significantly. Industrial sources such as incinerators, utilities, and lead-acid battery manufacturers, however, continue to emit lead. Lead exposure can impair the nervous and immune systems and cause neurological effects in children.



Nitrogen Dioxide (NO2) NO2 is a by-product of combustion. NO2 is not directly emitted, but is formed through a reaction between nitric oxide (NO) and atmospheric oxygen. NO and NO2 are collectively referred to as NOx and are major contributors to ozone formation. NO2 also contributes to the formation of particulate matter. NO2 can cause breathing difficulties at high concentrations. Ozone Ground level ozone, often referred to as smog, is not emitted directly, but is formed in the atmosphere through complex chemical reactions between nitrogen oxides (NOx) and reactive organic gases (ROG) in the presence of sunlight. The principal sources of NOx and ROG, often termed ozone precursors, are combustion processes (motor vehicle engines) and evaporation of solvents, paints, and fuels. Motor vehicles are the single largest source of ozone precursor emissions in the Bay Area. Exposure to ozone can cause eye irritation, aggravate respiratory diseases and damage lung tissue, as well as damage vegetation and reduce visibility. Particulate Matter (PM10 and PM2.5) Particulate matter includes a wide range of solid or liquid particles, including smoke, dust, aerosols and metallic oxides. The U.S. EPA groups particulate pollution into two categories: 1) PM10, or inhalable coarse particles larger than 2.5 micrometers and smaller than 10 micrometers in diameter; and 2) PM2.5, or fine particles 2.5 micrometers in diameter and smaller. In the SFBAAB, motor vehicles account for nearly 50 percent of particulate emissions. Other sources of particulates include combustion, factories, construction activities, agricultural activities, and wood-burning fireplaces and stoves. PM10 and PM2.5 are of concern because they can bypass the body’s natural filtration system more easily than larger particles, and can lodge deep in the lungs. Health effects of PM10 vary depending on a variety of factors but elevated PM10 concentrations can aggravate chronic respiratory illness such as bronchitis and asthma. PM2.5 poses an increased health risk because these fine particles can contain substances such as diesel particulates that are harmful to human health. Hydrogen Sulfide (H2S) H2S is a colorless gas with a strong “rotten egg” odor that can be smelled at very low concentrations. H2S is also an irritant that can affect the eyes and lungs. H2S is formed under anaerobic conditions and is a by-product of refining crude oil. Sulfur Dioxide (SO2) SO2 is a colorless gas with a pungent odor. It is formed from the combustion of fuel containing sulfur compounds, as well as from industrial sources such as petroleum refining. SO2 is an irritant that can affect the lungs and increase risks of respiratory disease. Sulfates (SO4

2-) SO4

2- are the fully oxidized ionic form of sulfur. SO42- are primarily produced from fuel

combustion. Suflur compounds in the fuel are oxidized to SO2 during the combustion process



and subsequently converted to sulfate compounds in the atmosphere. SO42- exposure can increase

risks of respiratory disease. Vinyl Chloride Vinyl chloride, or chloroethene, is a colorless gas with a mild, sweet odor that is used to make polyvinyl chloride products. Exposure to high levels of vinyl chloride may result in neurological effects and liver damage. The ARB identified vinyl chloride as a TAC in 1990. Visibility Reducing Particles (VRP) VRP consist of suspended particles that vary greatly in shape, size, and chemical composition, contribute to regional haze, and impair and reduce visibility. HAPs and TACs Hazardous air pollutants (HAPs) or toxic air contaminants (TACs) are a group of pollutants than cause severe health effects. Many of these pollutants are harmful at very low concentrations and are confirmed or suspected carcinogens. The U.S. EPA has identified 187 HAPs, including such substances as benzene and formaldehyde. The ARB list of TACs also includes particulate emissions from diesel-fueled engines (diesel PM) and environmental tobacco. The exhaust from diesel engines includes hundreds of different gaseous and particulate components, many of which are toxic. Many of the toxic compounds adhere to the particles, and because diesel particles are very small (less than 2.5 microns in diameter), they penetrate deeply into the lungs. The ARB has identified diesel PM as a human carcinogen. Mobile sources, including trucks, buses, automobiles, trains, ships and farm equipment, are by far the largest source of diesel emissions. Diesel emissions account for roughly one‐sixth of total emissions of carbonaceous PM2.5 in the Bay Area. Studies show that diesel PM concentrations are much higher near heavily traveled highways and intersections. SFBAAB Emissions Summary and Attainment Status Table 4-4 below presents the ARB’s estimated emissions summary for the SFBAAB.

Table 4-4. SFBAAB 2008 Estimated Criteria Pollutant Emissions

Source Pollutant Emissions (tons per day)

CO NOx ROG SOx1 PM10 PM2.5

Stationary 44.3 50.6 107 46.0 16.3 12.1

Areawide2 162 16.9 87.9 0.62 176 52.9

Mobile 1,542 381 183 14.9 20.3 16.3

Total 1,748 448 378 61.5 212 81.3 Source: ARB, 2010. Notes: Totals may not equal due to rounding. 1. Includes SO2. 2. Area wide sources include solvent evaporation, residential fuel combustion, farming operations, construction operations, fugitive windblown dust, road dust, fires, and cooking sources.



Areas where pollutant concentrations exceed established air quality standards are referred to as non-attainment areas. Federal and state laws require non-attainment areas to develop strategies, plans, and control measures to reduce pollutant concentrations to levels that meet, or attain, standards. As summarized in Table 4-5, the SFBAAB currently meets all ambient air quality standards except for national and state ozone and particulate matter standards.

Table 4-5. Ambient Air Quality Standards and SFBAAB Attainment Status

Pollutant Averaging

Time

California AAQS1 National AAQS2

Standard3 Attainment

Status4 Standard3

Attainment Status

Ozone 1 Hour 180 µg/m3 N --5

8 Hour 137 µg/m3 N 147 µg/m3 N6

Carbon Monoxide

1 Hour 23,000 µg/m3 A 40,000 µg/m3 A

8 Hour 10,000 µg/m3 A 10,000 µg/m3 A

Nitrogen Dioxide

1 Hour 339 µg/m3 A 188 µg/m3 U7

Annual Arithmetic

Mean

57 µg/m3

100 µg/m3

A

Sulfur Dioxide

1 Hour 655 µg/m3 A 196 µg/m3 U8

24 Hour 105 µg/m3 A 365 µg/m3 A8

Annual Arithmetic

Mean 80 µg/m3 A8

Particulate Matter

PM10

24 Hour

50 µg/m3 N 150 µg/m3 U

Annual Arithmetic

Mean 20 µg/m3 N

Particulate Matter

PM2.5

24 Hour 35 µg/m3 N9

Annual Arithmetic

Mean 12 µg/m3 N 15 µg/m3 A

Sulfates 24 Hour 25 µg/m3 A

Lead

30 Day Average

1.5 µg/m3) A

Calendar Quarter

1.5 µg/m3 A



Pollutant Averaging

Time

California AAQS1 National AAQS2

Standard3 Attainment

Status4 Standard3

Attainment Status

Hydrogen Sulfide

1 Hour 42 µg/m3 U

Vinyl Chloride 24 Hour 26 µg/m3 No

information available

Visibility Reducing Particles

8 Hour

(10:00 to 18:00 PST)

See Note 10 U

Source: Modified from ARB 2010a, BAAQMD 2010, and U.S. EPA 2010. Notes: All standards shown in terms of micrograms per cubic meter (µg/m3) for comparison purposes. 1. California standards for ozone, carbon monoxide (except Lake Tahoe), sulfur dioxide (1 and 24-hour), nitrogen

dioxide, suspended PM10 and PM2.5, and visibility reducing particles are values that are not to be exceeded. The standards for sulfates, Lake Tahoe carbon monoxide, lead, hydrogen sulfide, and vinyl chloride are not to be equaled or exceeded. The Lake Tahoe CO standard is 7,000µg/m3, a level one-half the national standard and two-thirds the state standard.

2. National standards shown are the "primary standards" designed to protect public health. National standards (other than ozone, particulate matter, 1 hour sulfur dioxide, and those based on annual averages or annual arithmetic mean) are not to be exceeded more than once a year. The ozone standard is attained when the 4th highest eight hour concentration in a year, averaged over three years, is equal to or less than the standard. The 1 hour sulfur dioxide standard is met when 99 percent of the daily maximum 1-hour average concentrations at each monitoring site, averaged over three years, do not exceed 196 µg/m3 (75 ppb). Except for particulate matter standards, annual standards are met if the annual average falls below the standard at every site. The national annual particulate standard for PM10 is met if the 3-year average falls below the standard at every site. The annual PM2.5 standard is met if the 3-year average of annual averages spatially-averaged across officially designed clusters of sites falls below the standard. The 24-hour PM10 standard is attained when the expected number of days per calendar year with a 24-hour average concentration above 150 µg/m3 is equal to or less than one. The 24-hour PM2.5 standard is attained when 98 percent of the daily concentrations, averaged over three years, are equal to or less than the standard. The U.S. EPA maintains certain “secondary” air quality standards designed to protect public welfare. The secondary standard for sulfur dioxide (24-hour and annual arithmetic mean) is 1,300 µg/m3, based on a three-hour averaging time, not to be exceeded more than once per year. The secondary standards for lead, nitrogen dioxide (annual) particulate matter (PM10 and PM2.5), and ozone are equal to the primary standards. The U.S. EPA has not established secondary standards for carbon monoxide, nitrogen dioxide (1 hour), and sulfur dioxide (1 hour).

3. Concentrations based on reference temperature of 25 degrees Celsius and reference pressure of 760 torr. The U.S. EPA’s national primary AAQS are the levels of air quality necessary, with an adequate margin of safety, to protect public health.

4. A= Attainment, N= Nonattainment, U=Unclassifiable. 5. The U.S. EPA revoked the 1 hour ozone standard on Jun 15, 2005. The BAAQMD does not have a continuing

obligation to meet this standard under the Clean Air Act’s anti-backsliding provisions. 6. In June 2004, the U.S. EPA designated the Bay Area as an area of marginal nonattainment for the national 8-

hour ozone standard. The U.S. EPA lowered the national 8-hour ozone standard from 157 to 147 µg/m3, effective May 27, 2008. The U.S. EPA is in the process of issuing final designations for the 2008 ozone standard.

7. Standard effective January 22, 2010. To attain this standard the three-year average of the 98th percentile of the daily maximum 1-hour average at each monitor within an area must not exceed the standard.

8. On June 2, 2010, the U.S. EPA strengthened the primary NAAQS for sulfur dioxide by establishing a new 1-hour standard at a level of 75 ppb (196 µg/m3) and revoking the 24 hour and annual arithmetic mean because the existing standards will not add additional public health protection in light of the new 1 hour standard. The U.S. EPA plans to complete designations under the new standard by June 2012. To attain this standard the three-year average of the 99th percentile of the daily maximum 1 hour average at each monitor within an area must not exceed the standard.



9. Nonattainment designation effective December 14, 2009. The BAAQMD has until December 14, 2012 to submit a State Implementation Plan to the U.S. EPA that demonstrates how the Bay Area will achieve the standard.

10. VRP Standard is an extinction coefficient of 0.23 per kilometer – visibility of ten miles or more (0.07 – 30 miles or more for Lake Tahoe) due to particles when the relative humidity is less than 70 percent.

Local Monitoring Station Data The BAAQMD operates a network of monitoring sites in the area and maintains a database of air quality data collected from these monitoring locations. The monitoring network provides the data required to determine attainment status of both National and State ambient air quality standards. The closest monitoring site to the proposed project site is in Redwood City at 897 Barron Avenue, about 3.8 miles away from the project boundary. According to the ARB, during the most recent three years of monitoring (2006 to 2009) this site recorded no exceedances of any ozone standards. For 24 hour PM2.5, the site recorded two days above the national standard in 2007. For annual average PM2.5, the site recorded annual average concentrations of PM2.5 that were below state and national standards. For 24 hour PM10, the site recorded six days above the state standard in 2007. For annual average PM10, the site recorded annual average concentrations that were below the state standard; however, data was insufficient to determine annual values in 2008 and 2009. Sensitive Receptors A sensitive receptor is generically defined as a location where human populations, especially children, seniors, and sick persons, are located where there is reasonable expectation of continuous human exposure to air pollutants according to the averaging period for the AAQS (e.g., 24-hour, 8-hour, 1-hour). These typically include residences, hospitals, and schools. The closest sensitive receptors to the proposed project are the residences adjacent to the project and surrounding the site. The nearest hospital is Sequoia Hospital at 170 Alameda De Las Pulgas, Redwood City, CA, located about one mile east of the project site. The nearest public Elementary school is Clifford Elementary School, at 750 Bradford Street, Redwood City, 0.5 miles east of the project site. SFBAAB Greenhouse Gas Emissions Greenhouse gases that contribute to climate regulation are a different type of pollutant than criteria or hazardous air pollutants because climate regulation is global in scale, both in terms of causes and effects. Climate change poses a direct threat to air quality and public health in the Bay Area, however, there are no state or national standards that directly govern concentrations of greenhouse gases in the atmosphere. There are dozens of greenhouse gases (GHGs), but four gases and two groups of gases in particular are the primary contributors to climate change. These six gases were originally identified in the United Nation’s 1997 Kyoto Protocol and are: Carbon Dioxide (CO2) CO2 is released to the atmosphere when fossil fuels (oil, gasoline, diesel, natural gas, and coal), solid waste, and wood or wood products are burned.



Methane (CH4) CH4 is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from the decomposition of organic waste in municipal solid waste landfills and the raising of livestock. Nitrous oxide (N2O) N2O is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels. Sulfur hexafluoride (SF6) SF6 is commonly used as an electrical insulator in high voltage electrical transmission and distribution equipment such as circuit breakers, substations, and transmission switchgear. Releases of SF6 occur during maintenance and servicing as well as from leaks of electrical equipment. Hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) HFCs and PFCs are generated in a variety of industrial processes. Although these gases are small in terms of their absolute mass, they are potent agents of climate change due to their high global warming potential. GHGs can remain in the atmosphere long after they are emitted. The potential for a GHG to absorb and trap heat in the atmosphere is considered its global warming potential (GWP). The reference gas for measuring GWP is CO2, which has a GWP of one. By comparison, CH4 has a GWP of 21, which means that one molecule of CH4 has 21 times the effect on global warming as one molecule of CO2. Multiplying the estimated emissions for non-CO2 GHGs by their GWP determines their carbon dioxide equivalent (CO2e), which enables a project’s combined global warming potential to be expressed in terms of mass CO2 emissions. Table 4-6 below presents the GWPs and estimated atmospheric lifetimes of the common GHGs.

Table 4-6. GHG Global Warming Potentials (100-Year Time Horizon)

GHG GWP GHG GWP

Carbon Dioxide (CO2) 1 Perfluorocarbons (PFCs)

Methane (CH4) 21 CF4 6,500

Nitrous Oxide (N2O) 310 C2F6 9,200

Hydrofluorocarbons (HFCs) C4F10 7,000

HFC-23 11,700 C6F14 7,400

HFC-134a 1,300 Sulfur Hexafluoride (SF6) 23,900

HFC-152a 140

HCFC-22 1,700 Source: ARB 2009.



California produced 474 million metric tons of carbon dioxide equivalents (MMCO2e) annually averaged over the 2002 - 2004 period (ARB 2008). Table 4-7 below presents the GHG emission emitted by San Mateo County and the Bay Area. Transportation accounts for the most GHG emissions in both San Mateo County (approximately 61 percent) and the Bay area (approximately 39 percent).

Table 4-7. 2007 San Mateo County and Bay Area GHG Emissions

Area CO2 CH4 N20 Total MMTCO2e

San Mateo County 7.7 0.01 0.00 8.5

Bay Area 87.7 .12 0.005 95.8 Source: BAAQMD 2010a. MMCO2e = Million Metric Tons of Carbon Dioxide Equivalents.

GHG emissions from human activities contribute to GHG concentrations in the atmosphere, and governments have become increasingly concerned about the effects of these emissions on global climate change. Human (anthropogenic) production of GHGs has increased steadily since pre-industrial times and atmospheric CO2 concentrations have increased from a pre-industrial value of 280 ppm to 387 ppm in 2010 (NOAA 2010). The United Nations’ International Panel on Climate Change (IPCC) fourth assessment report (AR4) concluded that recent regional climate changes, particularly temperature increases, are affecting many natural systems including water, ecosystems, food, coasts, and health (IPCC 2007). The AR4 concluded that most of the observed increase in global average temperature since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations (IPCC 2007a). The anticipated impacts of GHG emissions include indirect effects associated with climate change, such as sea level rise (threatening coastal areas, the bay and the delta, as well as key infrastructure), reduced Sierra snowpack (vital to the water supply), increased wildfires, and higher levels of air pollution due rising temperatures. 4.9.3 2010 Regulatory Setting Federal, state, and local governments control emissions of criteria air pollutants, hazardous air pollutants, and GHGs through the implementation of laws, ordinances, regulations, and standards. This section summarizes the major regulations that apply to the proposed project. Federal and State Federal and State Clean Air Acts The Federal Clean Air Act governs air quality in the United States. In addition to being subject to federal requirements, air quality in California is also governed by more stringent regulations under the California Clean Air Act. In California, both the federal and state Clean Air Acts are administered by the ARB. It sets all air quality standards including emission standards for vehicles, fuels, and consumer goods as well as monitors air quality and sets control measures for toxic air contaminants. The ARB oversees the functions of local air pollution control districts and Air Quality Management Districts, which in turn administer air quality activities at the regional level.



U.S. EPA Endangerment Finding On December 7, 2009, the USEPA issued an endangerment finding that current and projected concentrations of six GHGs, CO2, CH4, N2O, HFCs, PFCs, and SF6, in the atmosphere threaten the public health and welfare of current and future generations. This finding came in response to the Supreme Court ruling in Massachusetts v. EPA, which found that GHGs are pollutants under the Clean Air Act (CAA). The finding does not impose any requirements on industry, but is a prerequisite to finalizing the proposed GHG standards for light-duty vehicles. California Global Warming Solutions Act In 2006, the California State Legislature adopted the California Global Warming Solutions Act of 2006, Assembly Bill (AB) 32, which required the ARB to: 1) determine 1990 statewide GHG emissions, 2) approve a 2020 statewide GHG limit that is equal to the 1990 emissions level, 3) adopt a mandatory GHG reporting rule for significant GHG emission sources, 4) adopt a Scoping Plan to achieve the 2020 statewide GHG emissions limit, and 5) adopt regulations to achieve the maximum technologically feasible and cost-effective reductions. In 2007, the ARB approved a statewide 1990 emissions level and corresponding 2020 GHG emissions limit of 427 million metric tons of carbon dioxide equivalents (MTCO2e) (ARB 2007). Almost 90 percent of the total GHG identified in the inventory is CO2. The majority of 1990 emissions are tied to fuel use activities such as electrical generation, transportation, and industrial operations (ARB 2007). In 2008, the ARB approved the AB 32 Climate Change Scoping Plan, which projects, absent regulation or under a “business as usual” (BAU) scenario, 2020 statewide GHG emissions levels of 596 million MTCO2e and identifies the measures (i.e., mandatory rules and regulations and voluntary measures) that will achieve at least 169 million MTCO2e of reductions and reduce statewide GHG emissions to 1990 levels by 2020 (ARB 2008). The key elements of the Scoping Plan include:

Expanding and strengthening existing energy efficiency programs as well as building and appliance standards;

Achieving a statewide renewables energy mix of 33 percent; Developing a California cap-and-trade program that links with other Western Climate

Initiative partner programs to create a regional market system; Establishing targets for transportation-related greenhouse gas emissions for regions

throughout California, and pursuing policies and incentives to achieve those targets; Adopting and implementing measures pursuant to existing State laws and policies,

including California’s clean car standards, goods movement measures, and the Low Carbon Fuel Standard; and

Creating targeted fees, including a public goods charge on water use, fees on high global warming potential gases, and a fee to fund the administrative costs of the State’s long term commitment to AB 32 implementation.



California Sustainable Communities and Climate Protection Act of 2008 (SB 375) SB 375 requires the ARB to develop 2020 and 2035 regional greenhouse gas emission reduction targets for passenger vehicles for each of the State’s 18 metropolitan planning organizations (MPOs). Each MPO must then prepare a sustainable communities strategy (SCS) that demonstrates how the region will meet its reduction target. The ARB has not established reduction targets for the Bay Area. California 2010 Green Building Standards Code (CALGreen) The CALGreen code is the 11th of 12 parts to Title 24 of the California Code of Regulations, also known as the California Building Standards Code. The purpose of the CALGreen code is to improve public health, safety and general welfare by enhancing the design and construction of buildings through the use of building concepts having a reduced negative impact, or positive environmental impact and encouraging sustainable construction practices relates to planning and design, energy efficiency, water efficiency and conservation, material conservation and resource efficiency, and environmental quality. The code becomes effective January 1, 2011. Local and Regional Bay Area Air Quality Management District California is divided into air basins governed by air districts. The Bay Area Air Quality Management District (BAAQMD) is the local agency responsible for monitoring and enforcing Ambient Air Quality Standards (AAQS), implementing control measures, and developing attainment plans designed to attain national and state AAQS. Below is a discussion of the air quality plans the BAAQMD has prepared to attain AAQS. Bay Area 2010 Clean Air Plan On September 15, 2010 the BAAQMD adopted the Bay Area 2010 Clean Air Plan. The 2010 Clean Air Plan is focused on a specific, manageable subset of pollutants, namely:

Ground level ozone and ozone precursors: ROG and NOx Particulate matter (PM): both directly emitted PM and secondary PM Key air toxics, such as diesel PM and benzene, and The “Kyoto 6” greenhouse gases (GHGs) (carbon dioxide, methane, nitrous oxide,

hydroflourocarbons, perflourocarbons sulfur hexafluoride). The 2010 Clean Air Plan contains 55 control strategies that describe specific measures and actions that the Air District and its partners will implement to improve air quality, protect public health, and protect our climate. These measures focus on stationary and area sources, mobile sources, transportation control measures, land use, and energy and climate measures. The 2010 Clean Air Plan updates the 2005 Ozone Strategy, address ozone, PM, toxic air contaminant, and greenhouse gas emissions in a single, integrated document, and establish emission control measures to be adopted or implemented in the 2010 to 2012 timeframe.



BAAQMD GHG Regulation Regionally, the BAAQMD has adopted regulations and guidelines to track and reduce GHG emissions from industrial, stationary GHG emission sources. In 2005, the BAAQMD established is Climate Protection Program to reduce pollutants that contribute to the global climate change. In 2008, the BAAQMD adopted a GHG fee of 4.4 cents per metric ton of GHG emissions that applies to permitted industrial facilities and businesses. In 2010, the BAAQMD adopted updated CEQA Air Quality Guidelines that establish significance thresholds for GHG emissions from land use and stationary source projects. San Mateo County General Plan The San Mateo County Planning and Building Department is in process of updating the conservation element of the San Mateo County General Plan to include a new element on conservation and energy efficiency which will investigate the feasibility of developing a Climate Action Plan for the County. 4.9.4 Thresholds of Significance Based on Appendix G of the CEQA Guidelines, the proposed project would have a significant air quality impact if it would:

Conflict with or obstruct implementation of the applicable air quality plan Violate any air quality standard or contribute substantially to an existing or projected air

quality violation Result in a cumulatively considerable net increase of any criteria pollutant for which the

region is non-attainment under an applicable federal or state standard (including releasing emissions which exceed quantitative thresholds of ozone precursors)

Expose sensitive receptors to substantial pollutant concentrations Create objectionable odors affecting a substantial number of people.

To help lead agencies apply the above criteria, the BAAQMD has prepared its CEQA Air Quality Guidelines to assist lead agencies in assessing and mitigating potential air quality impacts. The District’s guidelines contain screening criteria to provide lead agencies with a conservative indication of whether a proposed project could result in potentially significant air quality impacts. Consistent with the District’s guidance, if a project meets all of the screening criteria then the project would result in a less than significant air quality impact and a detailed air quality assessment is not required for the project. The District’s guidelines also contain emissions quantification guidance and thresholds of significance to assist lead agencies in determining the significance of potential air quality impacts. Table 4-8 below presents the BAAQMD’s construction- and operational-related thresholds of significance for criteria pollutants and toxic air contaminants.



Table 4-8. BAAQMD Thresholds of Significance Criteria Pollutants and Toxic Air Contaminants

Pollutant BAAQMD Project-Level Threshold of Significance

Construction Emissions Operational Emissions

Daily Emissions (lb/day)

Daily Emissions (lb/day)

Annual Emissions (tons per year)

ROG 54 54 10

NOX 54 54 10

Exhaust PM10 82 82 15

Exhaust PM2.5 54 54 10

Fugitive Dust PM10/PM2.5 Best Management Practices

None

Local CO None 9.0 ppm (8-hr. avg.),

20.0 ppm (1-hr. avg.)

Risks and Hazards – New Source/Receptor (Individual)

1) Compliance with Qualified Community Risk Reduction Plan; or

2) Increased cancer risk of >10.0 in a million; and

Increased non-cancer risk of >1.0 Hazard Index (chronic or acute); and

Ambient PM2.5 increase: >0.3μg/m3 annual average

Risks and Hazards – New Source/Receptor (Cumulative)

1) Compliance with Qualified Community Risk Reduction Plan; or

2) Increased cancer risk of >100 in a million (from all local sources); and

Increased non-cancer risk of >10.0 Hazard Index (from all local sources) (chronic); and

Ambient PM2.5 increase: >0.8μg/m3 annual average (from all local sources)

Accidental Release of Acutely Hazardous Pollutants

None Storage or use of acutely hazardous materials locating near receptors or receptors locating near stored or used acutely hazardous materials considered significant

Odors None Complaint History – 5 confirmed complaints per year averaged over three years

Source: BAAQMD 2010b. Note: The zone of influence for new source/receptor risks and hazards is 1,000-foot radius from fence line of source/receptor. Consistent with the BAAQMD’s CEQA Air Quality Guidelines, project’s that do not exceed the applicable screening criteria or significance threshold are considered to have a less than significant air quality impact. Projects that exceed the thresholds, however, are considered potentially significant impacts that would result in an individual and cumulatively significant and unavoidable air quality impact unless mitigated to below significance thresholds.



Based on Appendix G to the CEQA Guidelines, the proposed project would have a significant GHG emissions impact if it would:

Generate greenhouse gas emissions, either directly or indirectly, that may have a significant effect on the environment

Conflict with an applicable plan, policy, or regulation adopted for the purpose of reducing greenhouse gases.

The BAAQMD’s CEQA Air Quality Guidelines also contain guidance for lead agencies to asses and mitigate GHG emissions impacts. The BAAQMD has not adopted a threshold of significance for construction-related GHG emissions, but Section 8.2 of the District’s CEQA Air Quality Guidelines encourages lead agencies to quantify and disclose construction-related GHG emissions, determine the significance of these emissions, and incorporate best management practices to reduce construction-related GHG emissions. The BAAQMD has adopted the following thresholds of significance for operational-related GHG emissions generated by land use projects:

Table 4-9. BAAQMD Thresholds of Significance Construction and Operational GHG Emissions

Pollutant BAAQMD Project-Level Threshold of Significance

Construction Emissions Operational Emissions

GHG – Non Stationary Source None 1) Compliance with Qualified Greenhouse Gas Reduction Strategy; or

2) 1,100 MTCO2e/yr; or

3) 4.6 MTCO2e/SP/yr (residents and employees)

GHG – Stationary source None 10,000 MTCO2e/yr Source: BAAQMD 2010b. Consistent with the BAAQMD’s CEQA Air Quality Guidelines, project’s that do not exceed the BAAQMD’s operational-related GHG emissions significance threshold are considered to have a less than significant air quality impact. Projects that exceed the thresholds, however, are considered to have potentially significant impacts that would result in an individual and cumulatively significant and unavoidable air quality impact unless mitigated to below significance thresholds. 4.9.5 2010 Project Impacts The 2010 project consists of a two-lot subdivision, which is four homes less than the six-lot subdivision analyzed in the 1992 EIR. Project construction would generate fugitive dust, criteria air pollutants, and GHG emissions during site preparation and home construction activities. Once construction is complete and the homes occupied ( i.e., “operational”), the project would also generate a minimal amount of emissions from area sources (e.g., space heating, landscaping equipment and vehicle trips.



Although the 1992 EIR did not analyze air quality, overall construction emissions between the 1992 project proposed and the current project proposal are expected to be similar. The 1992 proposal would result in less fill hauling and associated haul truck and site preparation (e.g., fill compaction) emissions than the 2010 proposal, but more grading emissions due to the need to grade and prepare six lots (instead of two), more access roads, and the Hermosa Road connection. Operational emissions would be less under the current proposal (20 vehicle trips per day instead of 60 as noted in the 1992 EIR). Construction Emissions The project would generate fugitive dust and combustion-related emissions from site preparation and home construction activities. TRA estimated the proposed project’s criteria pollutant and GHG construction emissions using URBEMIS2007 Version 9.2.4. The pollutant model uses a construction scenario to represent the type and duration of various activities. The scenario is used for estimating emissions and is not a proposed permit condition. The complete URBEMIS construction phase assumptions and project output files are contained in Appendix D. Project Comparison to BAAQMD Screening Criteria The proposed project is below the BAAQMD’s single-family land use criteria air pollutant construction screening level size (114 dwelling units), however, an air quality assessment has been prepared consistent with the BAAQMD’s CEQA Air Quality Guidelines, which states that project’s having more than 10,000 cubic yards (cu yds) of soil hauling activities require a more detailed air quality assessment. Construction Criteria Pollutant Emissions Table 4-10 below presents the project’s estimated equipment type, amount, and duration of use during site preparation and home construction activities. Equipment would be staged on-site, and daily equipment operations would range between four to eight hours per day.

Table 4-10. Project Construction

Equipment Type No. On-Site1 No. of Days on Site

Site Preparation

Compactor* 1 88

Water Truck 1 88

Backhoe 1 50

Excavator* 1 30

Dozer* 1 30

Scraper* 2 15

Grader* 1 5

Home Construction

Crane 1 122

Forklift 2 122



Equipment Type No. On-Site1 No. of Days on Site

Generator Set 1 122

Tractor 2 122

Welders 3 122

Cement and Mortar Mixer 2 15

Drill Rig 1 10

Paver 1 5

Roller 1 5 Source: Site preparation equipment provided by applicant; home construction equipment is based on URBEMIS default equipment assumptions * Indicates equipment meets U.S. EPA TIER 3 emission requirements 1. Reflects the maximum number of each piece of equipment that would be on-site at any given time.

Site preparation would involve grading of the canyon slopes, excavating and replacing non-engineered fill, importation and placement of 50,900 cu yds of new fill, installation of utility lines and subdrains, construction of retaining walls, and paving the access road. Site preparation would take approximately four months (88 construction days) to complete. The majority of the construction equipment used during site preparation would meet U.S. EPA Tier 3 emissions standards for non-road diesel equipment and the remainder of the equipment would consist of lower-tiered equipment (i.e, uncontrolled or Tier 1 and Tier 2 equipment). The applicant has not identified the source of the fill, but presumes that a source of fill that meets the geotechnical requirements of the project would be obtained from a source within 15 miles of the project site. The applicant would transport fill in semi end-dump and semi-bottom dump trucks that have 12 to 14 and 14 to 18 cu yds of haul capacity; the applicant estimates approximately 80 percent of soil hauling activities would occur in the larger capacity haul trucks. This construction analysis assumes that fill hauling would occur five days a week, eight hours per day for the four month site preparation period in haul trucks that would average 17 cu yds of capacity, resulting in approximately 68 total truck trips per day, for a total of approximately 5,990 total trips during site preparation. Home construction would include drilling or driving piers to support home foundations, paving up to 0.5 acres of the access road, coating (e.g., painting) operations, and framing, concrete pouring, and other building construction activities. For this air quality analysis, home construction was assumed to last approximately nine months. This construction analysis assumes that the last three months of home construction would consist of finishing activities that would not require the use of diesel construction equipment (e.g., electrical and plumbing, hanging drywall, etc.) Table 4.11 below summarizes the proposed project’s total unmitigated and mitigated construction emissions, in tons per year, from fugitive dust, equipment exhaust, and off-gassing (e.g., evaporative emissions from asphalt and solvents contained in paints, primers, and other surface coatings). Mitigated construction emissions reflect implementation of BAAQMD fugitive dust control measures and low VOC coatings.



Table 4-11. Total Project Construction Emissions, Tons1

Emissions Source ROG NOX PM10 PM2.5

Fugitive Dust - - 2.21 0.46

Mobile Sources (exhaust) 0.37 3.29 0.16 0.15

Off-Gassing 0.05 - - -

Total Unmitigated Emissions 0.42 3.29 2.37 0.61

Total Basic Mitigated Emissions2 0.40 3.29 1.21 0.37

BAAQMD Threshold,

tons per year.3 10 10 15 10

Exceed BAAQMD Threshold? No No No No 1 Emissions estimated using URBEMUS2007 V 9.2.4. Estimate is based on 88 active construction days for site preparation and 199 active construction days for home construction (287 days total). Please refer to Appendix D for URBEMIS output files. 2 Mitigated emissions include use of non-flat high gloss architectural coating with 150 g/l VOC limit per BAAQMD Regulation 8, Rule 3 and the implementation of BAAQMD Basic Construction Mitigation Measures. 3 BAAQMD, 2010b. The significance thresholds for PM10 and PM2.5 apply to exhaust emissions only. The proposed project would not exceed the BAAQMD’s average daily significance thresholds for ROG, NOX, and PM2.5 (54 lbs/day) nor PM10 (82 lbs/day).

As shown in Table 4-11, project construction emissions would not exceed BAAQMD criteria pollutant significance thresholds and would therefore be less than significant. As recommended by the BAAQMD, the project would incorporate basic dust control mitigation measures (see mitigation discussion below). Construction Greenhouse Gas Emissions Project construction would generate combustion-related GHG emissions. As calculated using URBEMIS, the proposed project would emit a total of 454 metric tons of carbon dioxide; other GHG emissions from construction-related fuel combustion would be negligible. Although the BAAQMD does not set a GHG significance threshold for construction, this level of GHG emissions is well below the BAAQMD’s operational land-use threshold of 1,100 MTCO2e and is therefore less than significant. Construction Toxic Air Contaminants As shown in Table 4-11 above, project construction would emit 0.15 tons of PM2.5 from equipment exhaust. Nearly all of the project’s PM2.5 emissions from equipment exhaust would be diesel particulate matter (diesel PM), a TAC. Approximately 25 percent of the estimated PM2.5 exhaust emissions, or 0.04 tons, would be generated from on-road hauling activities that would primarily occur off-site. The majority of equipment used during site preparation activities, which is when the most diesel-powered equipment would operate, would meet U.S. EPA Tier 3 emissions standards, which reduce emissions of particulate matter by as much as 63 percent when compared to older, uncontrolled (Tier 0) and Tier 1 and 2 equipment that would comprise the remainder of the construction equipment fleet.



All but one of the existing homes on the rim of the canyon are located at least 280 feet (ft) (85 meters (m)) from the daylight cut/fill line for the project. A single home at the northern end of the canyon is located approximately 230 ft (70 m) from the cut/fill line. Site preparation and home construction would occur over a period of 287 days. Although the project would emit criteria and hazardous air pollutants, these emissions would be well below the BAAQMD’s construction Thresholds of Significance. In addition, the short construction period for the project and the distance between the construction sites and existing homes would reduce pollutant concentrations, including concentrations of TACs, at sensitive receptor locations, to less than significant levels. Operational Emissions The project would generate operational emissions from area sources such as natural gas heating and landscaping equipment (e.g., mowers, blowers, etc.) as well as emissions from vehicle trips. The proposed project would not result in any long term odor impacts Project Comparison to BAAQMD Screening Criteria The proposed project consists of two single-family housing units, which is below the BAAQMD screening level sizes for operational criteria pollutants (325 dwelling units) and operational GHG emissions (56 dwelling units). The BAAQMD maintains no other screening criteria for operational criteria pollutants and GHG emissions. The proposed housing units would result in 20 vehicle trips per day once built and would not increase traffic volumes above BAAQMD CO screening levels of 44,000 vehicles per hour or 24,000 vehicles per hour where horizontal or vertical mixing is limited due to features such as tunnels, garages, underpasses, canyons, or below grade roadways. The proposed project is located near an odor-generating land use type identified in the BAAQMD CEQA Air Quality Guidelines and would not expose a substantial number of people to long-term odors. Consistent with the BAAQMD’s CEQA Air Quality Guidelines, projects that meet all applicable screening criteria would not result in emissions that exceed BAAQMD significance thresholds and would therefore result in a less than significant individual and cumulative impact to air quality. Community Risk and Hazard Impacts The proposed project would site two new receptors (homes) in San Mateo County. The proposed project is not located in an impacted community, as identified under the BAAQMD’s Community Air Risk Evaluation (CARE) program, which the BAAQMD initiated in 2004 to identify locations with high levels of risk from TACs. The closest stationary source of emissions to the project is an emergency generator (Facility ID 6308) located south of Edgewood Road, more than 1,150 ft. away from the edge of the closest home pad. The closest surface street to the project is Edgewood Road, with an average daily traffic volume of 13,150 trips per day; Edgewood Road is located more than 1,050 feet from the daylight cut/fill line for Lot 1. The closest highway to the project is Interstate 280, located more



than one mile from the project site. Consistent with the BAAQMD’s Recommended Methods for Screening and Modeling Local Risks and Hazards phased approach for estimating the risks and hazards to new receptors, since there are no stationary and roadway sources within 1,000 feet of the project the risk and hazards from PM2.5 and carcinogenic and non-carcinogenic toxic air contaminants are considered less than significant (BAAQMD 2010c). Cumulative Impacts The proposed project is a two-lot subdivision that is consistent with the BAAQMD’s draft 2010 Clean Air Plan. The project would not result in construction or operational emissions that exceed BAAQMD thresholds of significance. In developing its CEQA significance thresholds, the BAAQMD considered the emission levels at which a project’s individual emissions would be cumulatively considerable. The BAAQMD considers project’s that result in emissions that exceed its CEQA significance thresholds to result in individual impacts that are cumulatively considerable and significant. Since the proposed project would not individually exceed any BAAQMD CEQA significance thresholds the proposed project would result in less than significant cumulative air quality impacts. 4.9.6 2010 Mitigation Measures Construction Emissions The proposed project would result in less than significant construction emission impacts. The BAAQMD, however, recommends the implementation of all BAAQMD Basic Construction Mitigation Measures regardless of whether or not construction related emissions exceed applicable thresholds of significance. Consistent with this recommendation, the applicant shall implement all BAAQMD Basic Construction Mitigation Measures during project construction. Impact AIR-1: Project construction would generate fugitive dust (PM10 and PM2.5). Mitigation Measure AIR-1: The applicant shall implement all BAAQMD Basic Construction Mitigation Measures during project construction:

1) All exposed surfaces (e.g. parking areas, staging areas, soil piles, graded areas and unpaved access roads) shall be watered two times daily.

2) All haul trucks transporting soil, sand, or other loose material off-site shall be covered. 3) All visible mud or dirt track-out onto adjacent public roads shall be removed using wet

power vacuum street sweepers at least once per day. The use of dry power sweeping is prohibited.

4) All vehicle speeds on unpaved roads shall be limited to 15mph. 5) All roadways, driveway, and sidewalks to be paved shall be completed as soon as

possible. Building pads shall be laid as soon as possible after grading unless seeding or soil binders are used.

6) Idling times shall be minimized either by shutting equipment off when not in use or reducing the maximum idling time to 5 minutes (as required by the California airborne toxics control measure Title 13, Section 2485 of California Code of Regulations [CCR]). Clear signage shall be provided for construction workers at all access points.



7) All construction equipment shall be maintained and properly tuned in accordance with manufacturer’s specifications. All equipment shall be checked by a certified mechanic and determined to be running in proper condition prior to operation

8) Post a publicly visible sign with the telephone number and person to contact at the Lead Agency regarding dust complaints. This person shall respond and take corrective action within 48 hours. The Air District’s phone number shall also be visible to ensure compliance with applicable regulations.

Effectiveness: This measure will reduce fugitive dust emissions of PM10 and PM2.5

by approximately 52 percent. Implementation: San Mateo County shall incorporate these measures into all building

/grading permit and site plans and the applicant shall incorporate all these measures into construction contracts and implement these measures during construction.

Timing: The applicant shall incorporate the measures in Mitigation Air-1 into all plans and documents prior to commencing any construction-related activities at the site.

Monitoring: Project construction plans and construction contracts. Implementation of mitigation measure AIR-1 would further reduce the project’s less than significant construction emissions. The analysis of construction related greenhouse gas emissions indicates that the project would not have significant greenhouse gas emissions and no mitigation is required. Operational Emissions The project size (two units) is below the screening criteria for both criteria pollutants and greenhouse gas. The operation of the project would not have a significant air quality impact and no mitigation is required.

BH-2BH-1

BH-3

BH-4

BH-5

BH-6

BH-7

BH-8

BH-9

BH-10BH-11

SITE PLAN

SEPTEMBER 2010 FIGURE 1PROJECT NO.880-1L3

EDGEWOOD CANYON SUBDIVISIONEDGEWOOD ROAD

SAN MATEO COUNTY, CALIFORNIA

LEGEND

BH-1

For Site Geology, Please Refer to Site Plan/Geology Figure Contained in Jo Crosby & Associates Report, February 14, 2002

Approximate Location of Bore Hole by Jo Crosby & Associates, February 14, 2002

Approximate Location of Cross-Section (see Figures 3 & 4)

Approximate Locaton of Landslide Boundary mapped by Jo Crosby & Associates (February 2002)- Arrow indicates direction of movement

Approximate Location of Fill mapped by Jo Crosby & Associates

Base: Grading and Drainage Plan (C-1 & C-2) by MacLeod & Associates, dated August 30, 2010

Approximate Scale: 1 inch = 100 feet

E'

F'

EF

LOT 2

LOT 1

LEGEND

B-1 Approximate Location of Boring by Murray Engineers, Inc. October 25, 2007

Approximate Limits of Fill and Fill Slope

Approximate Limits of Cut Slope

Base: Site Survey by NNR Engineering, dated June 12, 2007

Approximate Scale: 1 inch = 30 feet

Proposed HouseFootprint (Shaded)

Proposed HouseFootprint (Shaded)

Area of Existing Residenceto Remain (Hatched)

Area of Existing Residence to beRemoved (Shaded)

EDISON WAYArea of Proposed 2-Story

Addition (Cross-Hatched)

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TmKJfm

E E'

B-1

Monterey Formation

Franciscan Complex Mélange

Approximate Location of Soil Boring by Murray Engineers, Inc., November 24, 2008

Trench by Murray Engineers, Inc., November 12 & 13, 2008

Approximate Location of Trench by Cleary Consultants, Inc.,February 2004

Approximate Location of Cross-Section (see Figure A-5)

Fault Trace, barbs on upthrown side of fault

Dls

Als

Als

Als

Als

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Figure 4-1. 2010 Geologic Survey Site Plan

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130.00'

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87.32'

VIEW 1 EYELEVEL: 409'

VIEW 2 EYELEVEL: 445.0'

VIEW 3 EYELEVEL: 305.0'

SITE PLAN

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CONTOURS AT 10'INTERVALS

PROPERTY LINE

AREA OF 3D MODEL

JOHNMATTHEWSARCHITECTS

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Figure 4-2. View Point Locations

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Figure 4-3. Terrain Modeling Existing and Proposed Topography



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Figure 4-4. View 1 – Existing and Proposed



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4.0 environmental impact assessment - smcgov.org

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