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City of Los Angeles USC Development Plan SCH. No. 2009011101 May 2010

Page IV.F-1 WORKING DRAFT - Not for Public Review

IV. Environmental Impact Analysis F.1 Surface Water Hydrology

1. Introduction

This section provides an analysis of potential surface water hydrology impacts associated with the proposed Project. Information for this analysis was provided by the Hydrology Study for the USC Development Project prepared by KPFF Consulting Engineers. This study is provided in Appendix G of this Draft EIR.

2. Environmental Setting

a. Existing Conditions

(1) Hydrological Conditions

As shown in Figure IV.F-1 on page IV.F-2, the Project site is located within the Santa Monica Bay Watershed Management Area (WMA). The WMA includes several watersheds, with Malibu Creek and Ballona Creek being the two largest watersheds. Specifically, the Project site is located at the downstream end of the highly urbanized watershed of approximately 2,191 acres, which is part of the larger Ballona Creek watershed, as shown in Figure IV.F-2 on page IV.F-3. This watershed drains stormwater runoff in a southwesterly direction to its outlet at Ballona Creek.

The Project site is generally flat and existing vegetation (i.e., pervious surfaces) consists of mature trees and grass. According to the Los Angeles County Department of Public Works Hydrology Manual, the 50-year 24-hour isohyet is approximately 5.45 inches.1 Drainage across the Project site is generally by sheet flow to the southwest of the Project site. Existing peak runoff flows and volumes during a 50-year storm event for Subareas 1, 2, and 3 of the Project site are provided in Table IV.F-1 on page IV.F-4.

1 Isohyet is a line drawn on a map connecting points that receive equal amounts of rainfall. The 50-year

24-hour isohyet represents the rainfall isohyets received per 24-hour during a 50-year storm event.

Figure IV.F-1

Santa Monica Bay Watershed Management Area

Source: Los Angeles Regional Water Quality Control Board, December 5, 2002

Project Site

Page IV

.F-2

Page IV.F-3Source: KPFF, 2010.

LOS ANGELES

Figure IV.F-2

Ballona Creek Watershed

N

Project Site

Not to Scale

IV.F.1 Surface Water – Hydrology



(2) Existing Storm Drain Infrastructure

As indicated above, the Project watershed area drains runoff in a southwesterly direction to its outlet at Ballona Creek. Rainfall is conveyed by a non-erosive storm drain system consisting of catch basins and storm drain piping. There are five major storm drain infrastructure systems located north and east of the Project area that route stormwater from the USC watershed to two large westerly flowing storm drains located west of the Project area. The entire network of storm drains that exit the Project site eventually convey flows into the Santa Monica Bay via Ballona Creek. The large diameter pipelines and box culverts are either managed by the Los Angeles County Department of Public Works or the Los Angeles County Flood Control District. Below is a description of the existing storm drain system in the Project area:

(a) Existing Off-Site Storm Drain Systems

The off-site tributary areas are the areas located directly upstream of the Project area. There are five main tributary areas that contribute stormwater runoff to the Project area via five storm drain systems. As further described below, these storm drain infrastructure systems include the Orchard Avenue Storm Drain System, the University Avenue Storm Drain System, the Figueroa Street Storm Drain System, the Exposition Boulevard Storm Drain System, and the Jefferson Boulevard Storm Drain System. Please refer to the exhibits in Appendix G for these off-site storm drain systems.

(i) Orchard Avenue Storm Drain System

The Orchard Avenue Storm Drain System collects stormwater from a 70-acre tributary area. Approximately three percent of the runoff that enters the Project area is

Table IV.F-1 Existing 50-Year Storm Event Flow Rates and Volumes

Impervious Ratio a

Existing Flow Rate (cfs)

Existing Volume (AF)

Subarea 1 0.83 214.14 57.94

Subarea 2 0.95 21.05 4.29

Subarea 3 0.70 55.83 9.51

Note: cfs = cubic feet per second; AF = acre feet

a Impervious ratio was approximated based on aerial photographs of the Subarea. Source: KPFF Consulting Engineers, Hydrology Study for the USC Development Project, 2009. (see

Appendix G of this Draft EIR)




conveyed via this system. The pipe size for this system is 33 inches in diameter. The primary pipes for this system enter the Project area at two locations: 30th Street and Orchard Avenue, 30th Street and Hoover Street.

(ii) University Avenue Storm Drain System

The University Avenue Storm Drain System collects stormwater from a 502-acre tributary area. Approximately 23 percent of the runoff that enters the Project area is conveyed via this system. Pipe sizes for this system range from 24 to 72 inches in diameter except for a box culvert that is located adjacent to the Los Angeles Convention Center in Downtown. Stormwater from this system enters the Project area at University Avenue and Jefferson Boulevard.

(iii) Figueroa Street Storm Drain System

The Figueroa Street Storm Drain System collects stormwater from a 548-acre tributary area. Approximately 25 percent of the runoff that enters the Project area is conveyed via this system. The pipes for this system range from 24 to 72 inches in diameter and enter the Project area at Figueroa Street and Jefferson Boulevard.

(iv) Exposition Boulevard Storm Drain System

The Exposition Boulevard Storm Drain System collects stormwater from a 30-acre tributary area. Approximately one percent of the runoff that enters the Project area is conveyed via this system. The pipes for this system vary from a 24-inch diameter pipe to a 100-inch by 96-inch high rectangular concrete box (RCB). This system enters the Project area at two locations: Figueroa Street and Jefferson Boulevard, and Figueroa Street and Exposition Boulevard.

(v) Jefferson Boulevard Storm Drain System

The Jefferson Boulevard Storm Drain System conveys stormwater runoff from a tributary area that comprises approximately 1,041 acres, the largest of the off-Campus tributary areas. Approximately 48 percent of the stormwater runoff that enters the Project area is conveyed via this storm drain system. The pipes for this storm drain system range from 21 to 57 inches in diameter from the upstream end and empty into a box culvert as it enters the core Campus at Jefferson Boulevard and Figueroa Street. The box culvert is 100 inches wide by 96 inches high.

(b) Existing On-Site Storm Drain Systems

The on-site drainage system consists of a number of pipes and rectangular culverts that intercept stormwater runoff from on-site catch basins and collect the runoff from the




five off-site tributary areas. There are five on-site storm drain systems as summarized in Table IV.F-2 on page IV.F-7. Figures IV.F-3 through IV.F-7 on pages IV.F-8 through IV.F-12 show the existing on-site storm drain systems.

There are four discharge points for the Project site:

93-inch wide by 89-inch high rectangular culvert pipe that discharges to the west on 35th Street crossing Vermont Avenue;

90-inch diameter reinforced concrete pipe that discharges to the west on Jefferson Boulevard crossing Vermont Avenue;

39-inch diameter reinforced concrete pipe that discharges to the southwest at the intersection of McClintock Avenue and Exposition Boulevard; and

27-inch diameter reinforced concrete pipe that discharges at 35th Street and Vermont Avenue.

(c) Analysis of Existing Storm Drain Systems

A previous hydrology study2 prepared for the University indicates that the existing public storm drain system serving the Project site and its upstream tributary areas is presently under-designed for the majority of the site to accommodate the stormwater runoff in the drainage basin. Specifically, with the exception of the McClintock storm drain system, the existing public storm drains are under designed to accommodate the runoff during 10-year and 25-year storm events. Additionally, based on field observations, buildings situate on the east side of Campus presently show signs of flooding during rain events. The hydraulic grade line3 for the existing storm drain primary collectors is close to or above the finished grade.4

2 University of Southern California, Hydrology Study, AC Martin Partners Inc May 4, 1999. This report

examined the core Campus (Subarea 1) and the existing flooding problems in this area. The study was done for the 10-year and 25-year design storm.

3 In fluid mechanics, the hydraulic grade line represents the elevations that stormwater would reach under atmospheric pressure during a design storm event.

4 In a closed channel (e.g., storm drain pipes), the hydraulic grade line represents the elevations that water would reach under atmospheric pressure during a design storm event. It’s ideal for the hydraulic grade line to be below the flow line elevations of storm drain collectors like catch basins to prevent the water from “bubbling” up and causing flooding. Ideally, storm drain systems should be designed to keep the water contained below the finished surface for the design storm event.




Table IV.F-2 On-Site Storm Drain System

Location Size

Orchard Avenue On-Site Storm Drain System Hoover Boulevard between 30th Street & Jefferson Boulevard 33” RCP Jefferson Boulevard between University Avenue & Vermont Avenue 90” RCP Orchard Avenue between 29th Street & 30th Street 30” RCP Orchard Avenue between 29th Street & 30th Street 33” RCP McClintock Avenue between Jefferson & 34th Street 36” RCP McClintock Avenue between 34th Street & 35th Street 42” RCP 35th Place between McClintock Avenue & Vermont Avenue 89” x 93”

University Avenue On-Site Storm Drain System University Avenue between 30th Street & Jefferson Boulevard 63” RCP Jefferson Boulevard between University Avenue & Vermont Avenue 90” RCP

Figueroa Street On-Site Storm Drain System Figueroa Street between 30th Street & Jefferson Boulevard 72” RCP Jefferson Boulevard between Figueroa Street & University Avenue 54” x 93” Jefferson Boulevard between Hoover Street & Vermont Avenue 90” RCP Watt Way between Jefferson Boulevard & W. 34th Street 76” x 79” Watt Way between W. 34th Street & 35th Place 89” x 93” 35th Place between Watt Way & Vermont Avenue 89” x 93”

Exposition Boulevard On-Site Storm Drain System Jefferson Boulevard between Grand Avenue & Figueroa Street 96” x 100” Jefferson Boulevard between Figueroa Street & University Avenue 54” x 93” Jefferson Boulevard between Hoover Street & Vermont Street 90” RCP 34th Street between Figueroa Street & University Avenue 96” x 100” 34th Street between University Avenue & Watt Way 96” x 100” Exposition Boulevard between Hope Street & Figueroa Street 24” RCP 37th Street between Flower Street & Figueroa Street 27” RCP 36th Street between Figueroa Street & University Avenue 27” RCP 35th Place between University Avenue & Watt Way 30” RCP Watt Way between Jefferson Boulevard & W. 34th Street 76” x 79” 35th Place between Watt Way & Vermont Avenue 89” x 93”

Jefferson Boulevard On-Site Storm Drain System Jefferson Boulevard between Hill Street & Figueroa Street 96” x 100” Jefferson Boulevard between Figueroa Boulevard & University Avenue 93” x 54” Jefferson Boulevard between Hoover Street & Vermont Avenue 90” RCP 34th Street between Figueroa Street & University Avenue 135” x 74” 34th Street between University Avenue & Watt Way 72” x 74” Watt Way between Jefferson Boulevard & W. 34th Street 69” RCP Watt Way between W. 34th Street & 35th Place 89” x 93” 35th Place between Watt Way & Vermont Avenue 89” x 93”

Source: KPFF Consulting Engineers, Hydrology Study for the USC Development Project, 2009. (see

Appendix G)

Figure IV.F-3Orchard Avenue

On-Site Storm Drain System

Source: KPFF Consulting Engineers, 2009.

Page IV

.F-8

Figure IV.F-4University Avenue



Page IV

.F-9

Figure IV.F-5Figueroa Street


Page IV.F-10


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Figure IV.F-6Exposition Boulevard



Page IV

.F-11

Figure IV.F-7Jefferson Boulevard



Page IV

.F-12




(3) USC Best Management Practices

Stormwater Best Management Practices (BMPs) are control measures that are implemented to minimize the effects of stormwater pollution due to changes in the quantity and quality of urban runoff. BMPs are designed to reduce stormwater volume, peak flows, and/or pollutants in stormwater runoff through evapotranspiration, infiltration, detention, and filtration or biological and chemical actions. Stormwater BMPs can be structural or non-structural.

The University has installed stormwater BMPs to detain and/or infiltrate stormwater as appropriate on each of their recently constructed projects. Along Downey Way between Watt Way & McClintock Avenue a stormwater detention pipe and drywells were installed. For the Parkside Apartments located at the intersection of McClintock & 37th Place a stormwater detention pipe was implemented. For the USC School of Cinematic Arts, an infiltration trench was installed which resulted in reducing the 50-year peak runoff from the existing peak runoff of 8.52 cubic feet per second (cfs) to 7.84 cfs.

(4) Flood Zones

Subarea 3 and a portion of Subarea 1 are designated as Zone X. Zone X is classified by Federal Emergency Management Agency (FEMA) as areas with a 0.2 percent chance of flooding (i.e., 500-year return period/frequency) or a 1 percent chance of flooding (i.e., 100-year return period/frequency) with average depths less than one foot or where the contributing drainage area is less than one square mile. Subarea 2 is not located within any flood zone.

The Project site is not located within a 100-year flood zone as indicated in a FEMA Flood Insurance Rate Map (FIRM).5 Therefore, the project will not impede or re-direct flows within a 100-year flood hazard area and no further analysis of this issue is required.

(5) Soil Type and Characteristics

The soil classification of the Project area is mapped as soil type number 6 (Hanford Fine Sandy Loam). Based on the Geotechnical Report prepared for the Project site, underlying soils generally consist of silty sands and sands.6 Artificial fill varies from 0 to 17.5 feet. Groundwater levels below the Project site are deeper than 70 feet.

5 City of Los Angeles Planning Department, Safety Element of the General Plan, Exhibit F, 100-Year and

500-Year Flood Plains, March 1994. 6 Geotechnologies, Inc., “Geotechnical Engineering Evaluation for the Proposed University of Southern

California Specific Plan Area,” May 14, 2009.




The percolation rate, which is the rate that represents how fast water will travel through the soil in a specific length of time, was tested for the Project area. Percolation rates are important considerations for the design of BMPs since the City generally requires infiltration if possible. Based on the supplement to the Geotechnical Report addressing stormwater infiltration, percolation testing for previous development within the Project area resulted in rates between 2 and 23 minutes per inch.7 It should be noted that the percolation rates are based on testing at discrete locations and percolation rates could vary. The percolation rates of the Project area indicate that infiltration could be possible, contingent on site-specific geotechnical investigations that confirm that infiltration is acceptable.

b. Regulatory Framework

(1) County of Los Angeles Hydrology Manual

Drainage and flood control in the area of the Project site is regulated by the Los Angeles County Department of Public Works and the City of Los Angeles Department of Public Works. The County has jurisdiction over regional drainage facilities and drainage facilities.

The Los Angeles County Department of Public Works’ Hydrology Manual requires that a storm drain conveyance system be designed for a 25-year storm event and that the combined capacity of a storm drain and street flow system accommodate flow from a 50-year storm event. Areas with sump conditions are required to have a storm drain conveyance system capable of conveying flow from a 50-year storm event.8 The County also limits the allowable discharge into existing stormdrain facilities based on the MS4 Permit and is enforced on all new developments that discharge directly into the County’s stormdrain system. Any proposed drainage improvements of County owned stormdrain facilities such as catch basins and stormdrain lines requires the approval/review from the County Flood Control District department.

(2) Los Angeles Municipal Code

Any proposed drainage improvements within the street right of way or any other property owned by, to be owned by, or under the control of the City requires the approval of a B-permit (Section 62.105, LAMC). Under the B-permit process, storm drain installation plans are subject to review and approval by the City of Los Angeles Department of Public

7 Geotechnologies, Inc., “Supplement to the Geotechnical Engineering Evaluation for the Proposed

University of Southern California Specific Plan Area,” June 3, 2009. 8. Los Angeles County Department of Public Works Hydrology Manual, January 2006,

http://ladpw.org/wrd/Publication/engineering/2006_Hydrology_Manual/2006%20Hydrology%20Manual-Divided.pdf, accessed March 19, 2009.




Works Bureau of Engineering.9 Additionally, any connections to the City’s storm drain system from a property line to a catch basin or a storm drain pipe requires a storm drain permit from the City of Los Angeles Department of Public Works, Bureau of Engineering.

(3) City of Los Angeles Stormwater Program

As discussed further in Section IV.F.2, Surface Water Quality, within the City, the National Pollutant Discharge Elimination System (NPDES) requirements mandate that stormwater Best Management Practices (BMPs) be implemented during Project construction into Storm Water Pollution Prevention Plans (SWPPPs) and during Project operation into Standard Urban Stormwater Management Plans (SUSMPs). The requirements are enforced through the City’s plan review and approval process. During the review process, projects plans are reviewed for compliance with the City’s General Plans, zoning ordinances, and other applicable local ordinances and codes, including stormwater requirements. Plans and specifications are reviewed to ensure that the appropriate BMPs are incorporated to address stormwater pollution prevention goals.

The purposes of the SWPPP are to identify potential pollutant sources that may affect the quality of discharge associated with construction activity, identify non-stormwater discharges, and design the use and placement of BMPs to effectively prohibit the entry of pollutants from the project site into the public storm drain system during construction.

The purpose of SUSMP is to reduce the discharge of pollutants in stormwater by outlining BMPs which must be incorporated into the design plans of new development and redevelopment. The SUSMP provisions that are applicable to new residential and commercial developments include, but are not limited to, the following:10

Peak Stormwater Runoff Discharge Rate: Post-development peak stormwater runoff discharge rates shall not exceed the estimated pre-development rate for developments where the increased peak stormwater discharge rate will result in increased potential for downstream erosion.

9 Los Angeles County Department of Public Works, Bureau of Engineering, http://eng.lacity.org/index.cfm;

accessed March 19, 2009. 10 City of Los Angeles Stormwater Program website, http://www.lastormwater.org/siteorg/businesses/susmp/

industrial.htm; http://www.lastormwater.org/siteorg/businesses/susmp/housing.htm; accessed August 2, 2009.




3. Environmental Impacts

a. Methodology

The analysis of surface water hydrology impacts is based in part on the Hydrology Study prepared by KPFF Consulting Engineers. This study is provided in Appendix G of this Draft EIR. The surface water hydrology analysis in the Hydrology Study includes a calculation of pre-Project and post-Project runoff flow rates and volumes during a 50-year storm event. The analysis assesses whether the existing stormdrain infrastructure would be adequate to accommodate post-Project stormwater runoff.

b. Significance Thresholds

Appendix G of the State CEQA Guidelines provides a set of sample questions that address impacts with regard to hydrology. These questions are as follows:

Would the project:

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 (e.g., the production rate of pre-existing nearby wells would drop to a level which would not support existing land uses or planned uses for which permits have been granted)?

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?

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 that would result in flooding on- or off-site?

Create or contribute runoff water which would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional sources of polluted runoff?

Place housing within a 100-year flood plain as mapped on federal Flood Hazard Boundary or Flood Insurance Rate Maps or other flood hazard delineation maps?

Place within a 100-year flood plain structures which would impede or redirect flood flows?

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?




In the context of these questions from Appendix G of the CEQA Guidelines, the City of Los Angeles CEQA Thresholds Guide states that a project would normally have a significant impact on surface water hydrology if it would:

Cause flooding during the projected 50-year developed storm event which would have the potential to harm people or damage property or sensitive biological resources;

Substantially reduce or increase the amount of surface water in a water body; or

Result in a permanent, adverse change to the movement of surface water sufficient to produce a substantial change in the current or direction of water flow.

c. Project Design Features

As further described in Section IV.F.2, Surface Water Quality, to address stormwater runoff during construction activities for the proposed Project, the Project Applicant would prepare and implement site-specific SWPPPs. The SWPPPs would specify BMPs to be used during construction. BMPs would include temporary stormwater controls to be implemented and would but not be limited to: erosion control, sediment control, and non-stormwater management and material management.

With regard to operation, the Project Applicant would prepare and implement SUSMP requirements throughout the operational life of the proposed Project. The SUSMP would specify site-specific operational BMPs to be implemented for each new development project within the Project area. (Please refer to Section IV.F.2, Surface Water Quality, for further discussion of the SUSMP). Operational BMPs would reduce the peak discharge rate (detention) and/or reduce the amount of stormwater that enters the existing storm drain systems by implementing infiltration systems that recharges the groundwater. Detention BMPs would not result in a net increase in the rate of stormwater runoff entering the storm drainage system as compared to existing flow rates and thus would not increase the likelihood for flooding during a 50-year storm event. Infiltration BMPs would also decrease the amount of stormwater runoff that enters the storm drain system and Ballona Creek.

As an example of the type of BMPs that would be installed for the proposed Project, the USC School of Cinematic Arts Project included installation of an infiltration trench. This infiltration trench resulted in reducing the 50-year peak runoff from the existing peak runoff of 8.52 cfs to 7.84 cfs. The BMPs to be implemented with the proposed Project would ensure that at a minimum no change in flows would result with the proposed Project.




Specifically, volume-based treatment control BMPs will be designed to treat:

1. The 85th percentile 24-hour runoff event determined as the maximized captured stormwater volume for the area, from the formula recommended in Urban Runoff Quality Management, WEF Manual of Practice No. 23 / ASCE Manual of Practice No. 87, (1998), or

2. The volume of annual runoff based on unit basin storage water quality volume, to achieve 80 percent or more volume treatment by the method recommended in California Stormwater Best Management Practices Handbook – Industrial / Commercial, (1993), or

3. The volume of runoff produced from a 0.75 inch storm event, prior to its discharge to a stormwater conveyance system, or

4. The volume of runoff produced from a historical-record based reference 24-hour rainfall criterion for “treatment” (0.75 inch average for the Los Angeles County area) that achieves approximately the same reduction in pollutant loads achieved by the 85th percentile 24-hour runoff event.

Infiltration/Retention: The infiltration type of BMPs utilizes the natural filtering ability of the soil to remove pollutants in stormwater runoff. Infiltration facilities store runoff until it gradually exfiltrates through the soil and eventually into the water table. This practice has high pollutant removal efficiency and can also help recharge groundwater, thus helping to maintain low flows in stream systems. Infiltration basins can be challenging to apply on many sites because of soils requirements. Pretreatment using buffer strips, swales, or detention basins is important for limiting amounts of coarse sediment entering the trench which can clog and render the trench ineffective. Examples of infiltration and retention BMPs include infiltration basins, cisterns, drywells, and extended detention ponds.

Pervious Pavement: Pervious paving may be considered for light vehicle loading in parking areas and pedestrian areas. The term describes a system comprising a load-bearing, durable surface together with an underlying layered structure that temporarily stores water prior to infiltration or drainage to a controlled outlet. The surface can itself be porous such that water infiltrates across the entire surface of the material (e.g., turf and gravel surfaces, porous concrete, and porous asphalt), or can be built up of impermeable blocks separated by spaces and joints, through which the water can drain. This latter system is termed ‘permeable’ paving. Advantages of pervious pavements are that they reduce runoff volume while providing treatment, and are unobtrusive resulting in a high level of acceptability. Asphalt porous pavements, concrete block porous pavements, and structural soil are part of pavement BMPs.




Media Filtration: Stormwater media filters are usually two-chambered including a pretreatment settling basin and a filter bed filled with sand or other absorptive filtering media. As stormwater flows into the first chamber, large particles settle out, and then finer particles and other pollutants are removed as stormwater flows through the filtering media in the second chamber. There are a number of design variations including the Austin sand filter, Delaware sand filter, and multi-chambered treatment train.

d. Analysis of Proposed Project Impacts

(1) Construction

Construction activities for the proposed Project would involve the removal of existing structures as well as the clearing and grading of development areas. In addition, new roadways, buildings, open spaces, and drainage improvements would be developed. Such activities would temporarily alter existing drainage patterns and flows. However, construction of new drainage facilities would be required in a manner and sequence that would preclude flooding during Project construction. As discussed in Section IV.F.2, Surface Water Quality, during construction, a SWPPP and Erosion Control Plan would be implemented to provide for temporary stormwater management. These plans would minimize and/or control construction stormwater flows.

In addition, new storm drains would be constructed to support development and would be in place and functioning as development progresses to serve their respective catchments. Construction under the proposed Project would not subject adjacent properties to proposed Project-related floodwaters because any alteration of flows on-site during construction would be controlled and then conveyed to existing off-site regional storm drain facilities by temporary flood control improvements established in compliance with applicable agency standards. As a result, street surface flow would also remain the same. Therefore, construction-related impacts on hydrology would be less than significant.

(2) Operation

Operation of the proposed Project would develop new buildings and paved areas, thus resulting in an increase in impervious surfaces within the Project site. It is estimated that impervious surfaces would increase from 83 percent to 95 percent in Subarea 1 and from 70 percent to 90 percent in Subarea 3. Impervious surfaces would continue to comprise 95 percent in Subarea 2. Consequently, the proposed Project would result in a change in stormwater runoff flows. Post-project peak runoff flow rates and volumes during a 50-year storm event were calculated for each of the Subareas of the Project site as shown in Table IV.F-3 on page IV.F-20.




Within Subarea 1, new buildings would generally be developed on existing vacant and/or underutilized sites. The post-Project peak runoff flow rate and volume in Subarea 1 would be approximately 220.96 cubic feet per second (cfs) and 59.26 acre feet (AF). This represents a flow rate increase of 6.82 cfs and an increase in volume of approximately 1.32 AF (or an approximate 3.2 percent increase) as compared to the existing conditions shown in Table IV.F-1 on page IV.F-4.

Within Subarea 2, Project development would consist of urban infill type projects that would replace impervious surface areas and/or buildings with new impervious surface areas and/or buildings. As such, impervious surfaces are expected to be similar to existing conditions (i.e., 95 percent of the area) and post-Project peak runoff flow rates and volumes would remain the same as existing conditions at 21.05 cfs and 4.29 AF, respectively.

Within Subarea 3, Project development would replace the majority of existing buildings with new development that would be organized along various landscaped pedestrian pathways and open space areas, including a central plaza approximately midblock on McClintock Avenue. Impervious surfaces are expected to increase from existing conditions (from 70 to 90 percent of the area). Therefore, post-Project peak runoff flow rates and volumes would be increased to approximately 60.64 cfs and 11.44 AF, respectively. This represents a flow rate increase of 4.81 cfs and an increase in volume of 1.93 AF (or an approximate 8.6 percent increase) as compared to existing conditions.

As previously stated, as part of the SUSMP requirements, site-specific operational detention or infiltration BMPs would be implemented for each new development within the Project site. Detention BMP systems would reduce the peak discharge rate to existing or below existing rates per City or County guidelines. Infiltration BMP systems would recharge groundwater by means of infiltration while reducing stormwater discharge to existing drainage facilities. The infiltration and detention BMPs will result in no net increase to the rate and volume of runoff to existing stormdrain systems and ultimately the Ballona

Table IV.F-3 Post-Project 50-Year Storm Event Flows and Volumes

Impervious Ratio

Proposed Flow Rate (cfs)

Proposed Volume (AF)

Subarea 1 0.85 220.96 59.26

Subarea 2 0.95 21.05 4.29

Subarea 3 0.90 60.64 11.44

Source: KPFF Engineers, 2009.




Creek. Therefore, stormwater discharge for the design storm up to and including the 50-year storm would be maintained or reduced. Thus, the proposed Project would not exacerbate the existing conditions on-site during the projected 50-year developed storm event, which would have the potential to harm people or damage property or sensitive biological resources. Additionally, the proposed Project would not substantially reduce or increase the amount of surface water in a water body.

Additionally, the proposed Project would not create adverse changes to the movement of surface water or change the direction of flow. Most of the drainage patterns have already been established with the constructed stormwater system that conveys all the stormwater to the south. Each new development would direct flows similar to existing conditions and would drain to the pipes that currently serve the Project area. Therefore, impacts on surface water hydrology would be less than significant.

(3) Transfers of Floor Area

The proposed Project would include flexibility to allow for transfers of floor area for academic/University uses and student housing between Subarea 1 and Subarea 3A on a per square foot basis. While transfers of floor area across Subareas would be permitted, the maximum amount of floor area would not exceed 30 percent of the Subarea total for Subarea 1 and 15 percent of the Subarea total for Subarea 3A. In addition, the maximum Project total of 5,230,000 square feet may not be exceeded. Floor area transfers would not result in new impacts with regard to surface water hydrology. Any new Project development (regardless of where land uses would specifically occur within the Project site) would incorporate the Project Design Features previously described (e.g. SWPPP, SUSMP, etc). As such, floor area transfers would not alter the conclusions with regard to surface water hydrology impacts. Should academic/University or student residential floor area be transferred across the Subareas, the resulting impacts would be similar to those evaluated herein.

4. Cumulative Impacts

The geographic context for the cumulative impact analysis on surface water hydrology is the Ballona Creek watershed. The proposed Project in conjunction with forecasted 2030 growth in the Ballona Creek watershed (inclusive of the 30 related projects identified in Section III, Environmental Setting, of this Draft EIR) would cumulatively increase stormwater runoff flows potentially resulting in cumulative impacts to surface water hydrology. However, in accordance with City requirements, related projects and other future development projects would be required to implement BMPs such that post-development peak stormwater runoff discharge rates would not exceed the estimated pre-development rates. Implementation of these mandatory BMPs would help alleviate the pre-




existing flooding problem experienced by the local storm drain system. Furthermore, the City of Los Angeles Department of Public Works would review each future development project on a case-by-case basis to ensure sufficient local and regional drainage capacity is available to accommodate stormwater runoff. Therefore, cumulative impacts on surface water hydrology would be less than significant.

5. Mitigation Measures

Project-level and cumulative impacts on surface water hydrology would be less than significant. Therefore, no mitigation measures would be required.

6. Level of Significance After Mitigation

As indicated above, Project-level and cumulative impacts on surface water hydrology would be less than significant and thus, no mitigation measures would be required.

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