targeted drainage report horseman’s trail prd

Targeted Drainage Report Horseman’s Trail PRD

Technical Appendix A to the Horseman's Trail/ Frognal Estates PRD

Environmental Impact Statement Snohomish County, WA

Prepared for:

Snohomish County Planning and Development Services

Prepared by:

Anthony Burgess Consulting Inc., Redmond, WA

September 2013

Horseman’s Trail PRD September 2013 Targeted Drainage Report

TABLE OF CONTENTS

Form 3042

Executive Summary

1 Introduction ................................................................... 8

2 Drainage System .......................................................... 8

2.1 Picnic Point Creek Basin ........................................... 8

2.2 Site Existing Conditions ............................................ 8

2.3 Site Developed Conditions ...................................... 10

3 Analyses ...................................................................... 13

3.1 Flow Control ............................................................ 13

3.2 Water Quality .......................................................... 13

4 Erosion ......................................................................... 14

5 Upstream Analysis ..................................................... 14

6 Downstream Analysis ................................................ 16

7 Geotechnical Reports and Other Analyses ............. 16

8 References................................................................... 17


TABLES Table 2-1 Existing drainage basin characteristics Table 4-1 Estimated flows and frequency for off-site area discharging to west ravine

within Horseman’s Trail

FIGURES Figure 2-1 Picnic Point Creek Drainage Basin Figure 2-2 Existing Site Topography Figure 2-3 Site Geology Figure 2-4 Existing Site Drainage Basins Figure 2-5 Existing Conditions Drainage System Schematic Figure 2-6 Developed Site Topography Figure 2-7 Developed Site Drainage Basins Figure 2-8 Developed Conditions West TDA Drainage System Schematic Figure 2-9 Developed Conditions East TDA Drainage System Schematic Figure 3-1 Swale Cross Section Figure 4-1 Offsite Drainage Basins

ATTACHMENTS

Attachment A Stormwater Flow Control Calculations Attachment B Stormwater Quality Calculations Attachment C Construction Stormwater Pollution Prevention Plan


Form 3042 Project Total Area: 23 acres Project Development Area: Number of Lots: 112

Summary Table

Drainage Basin Information Individual Basin Information West East

On-Site Sub-Basin Area (acres) 15.988 6.349 Type of Storage Proposed Vault and rain

garden pond Vaults

Approx. Storage Volume (cu. ft.) 9,900 39,200 Soil Type(s) A/C and C A/B and C Pre-developed Runoff Rates Q (cfs) 2 yr. 0.109 0.082 10 yr. 0.216 0.160 100 yr. 0.353 0.259 Redevelopment Area Post-development Runoff Rates Q (cfs) 2 yr. 0.141 0.108 10 yr. 0.390 0.187 100 yr. 0.808 0.318 Offsite Upstream Area Number of acres 19.473 0 Offsite Downstream Flow Q (cfs) 100 yr. Estimated 287 cfs at mouth of Picnic

Point Creek


Executive Summary

This report has been prepared in support of a 112-lot subdivision on 23 acres near Mukilteo. The project includes a mix of public and private onsite roads as well as a series of pedestrian trails, some of which serve in lieu of on-street sidewalks and the others as a network of more primitive recreational trails. Mature second-growth forest covers the site, most of which will be removed. There is also significant elevation relief that will necessitate substantial regrading of the site to meet the maximum roadway grades. The soil profile on the site consists of forest duff /topsoil over dense glacial till overlying sandy gravel advance outwash. The degree of regrading on the site results in significant areas where removal of the overlying glacial till exposes the underlying, highly permeable sand layers. Conversely, filling existing low areas will result in covering some of the permeable outwash soils with less permeable till fill. Total flows from the site will continue to move as subsurface flows to their natural locations.

Drainage Plan Description

Drainage on the developed site will be managed primarily by "Low Impact Development" techniques supplemented by traditional storm sewer conveyance system. The principal devices used to treat and attenuate stormwater runoff are BRIAR swales (Bio-Retention, Infiltration and Recharge Swales). These facilities are located along the edge of the roadway and serve to collect, treat and convey runoff. During small rainfall events these swales will effectively retain the runoff, allowing it to infiltrate through the compost-amended soil and dissipate to groundwater and/or interflow. During larger or prolonged events, the BRIAR system is designed to convey runoff to the detention systems. . In addition to the BRIAR swales, a rain garden is proposed for the central area of the West Basin and a biofiltration swale is provided for treatment of runoff in the Northeast Basin.

Existing On-site Drainage Basins

There are two Threshold Discharge Areas on the site, West TDA and East TDA. The West TDA, which is the larger of the two, encompasses roughly 16 acres with the East TDA containing approximately 7 acres. The West TDA contains two ravines. Flows in the western ravine contribute to a wetland near the northwest corner of the property. Flow from this wetland discharges via a ditch to Picnic Point Creek. The eastern ravine's flow travels as groundwater and/or interflows to Picnic Point Creek. Runoff in the East TDA likewise does not appear as surface water. Runoff within this area is conveyed as subsurface flows to Picnic Point Creek valley and ultimately to Picnic Point Creek. Rainwater from the site infiltrates almost immediately, then travels as groundwater and/or interflow toward Picnic Point Creek.


Proposed On-site Drainage Basins

The proposed system will maintain the two Threshold Discharge Areas, with both TDA's being modeled using sub-basins. The largest of the West TDA sub-basins and three of the four East TDA sub basins will be routed through vaults. The remaining sub-basins will directly disperse runoff from the roof downspouts, footing drains and yards.

Proposed Drainage System

The goal of the drainage system is to allow as much runoff to return as subsurface flow as possible. The proposed drainage system will consist of low-impact development techniques supplemented by catchbasins and pipes. Alternative methods of managing storm water runoff from some individual homes such as flow attenuation swales and amended soil infiltration systems will be used. The proposal involves roadside BRIAR swales to collect street and yard runoff. The driveways will permit drainage through a prism of railroad ballast rather than traditional culverts. The driveways will also be constructed with a shallow "V" profile to intercept driveway runoff and direct it to the swales, as well as acting as an overflow channel for the swales.

Proposed Water Quality Measures Infiltration through compost-amended soils and biofiltration will provide water quality treatment. Water quality during construction will be ensured by application and maintenance of appropriate water quality BMPs.

Downstream analysis

The project is located in the Picnic Point Creek drainage basin. The easterly basin will discharge to an existing storm sewer system in Picnic Point Road. Flows from the westerly basin travel to a large wetland/stream system that begins near the northwest corner of the site. This stream continues down the west side of Picnic Point Road to discharge into Picnic Point Creek at the Picnic Point Road crossing. The stream is not listed as a fish-bearing. Snohomish County's Drainage Needs Report (DNR) analyzed this basin, and these data were supplemented as part of this study with a survey of the creek from the discharge of the Regatta Estates detention pond to the mouth of the creek. The DNR did not identify significant erosion or flooding problems, and this conclusion was corroborated by the recent survey. However, large woody debris was identified as restricting flow in culverts under the BNSF railroad and under the Picnic Point Road. This could lead to localized flooding, particularly at Picnic Point County Park. The flow from the site will be managed to maintain current flow conditions.

Upstream analysis

An area of 19.473 acres south of the site is developed as residential and discharges to the head of the west ravine, based on a review of drawings submitted to Snohomish County and site observations. However, discharge


to the site does not appear to result in any concentrated surface flow. There is no evidence of other surface flows entering the site from upstream areas. The upstream subsurface flow to the west ravine will be collected and conveyed by pipes and gravel drainage blankets constructed as part of this project.


1 Introduction

The Horseman’s Trail Planned Residential Development (PRD) is a 112-lot subdivision located near Mukilteo (Township 28N Range 4E Sections 32 and 33). The site occupies 23 acres south of Picnic Point Road and north of 136th Place SW. The site is forested with mature second growth and has considerable relief. Previous drainage studies for the site include a Targeted Drainage Report for a proposed development of 67 townhouses (Higa Engineering, Inc. 2000) and a Targeted Drainage Report for the currently proposed development (Lervik Engineering 2006). This Drainage Report has been prepared in accordance with the requirements of Snohomish County UDC Chapter 30 and POL-3042.

2 Drainage System

2.1 Picnic Point Creek Basin Picnic Point Creek basin has an area of about 1300 acres (approximately 2 square miles), of which about 1000 acres are upstream of the proposed development (Figure 2-1). The maximum elevation within the basin is 580 ft in the vicinity of Highway 99. Picnic Point Creek flows into Puget Sound at Picnic Point County Park, and the site is located about three-quarters of a mile from the mouth.

The geology and soils of the basin are dominated by Vashon till, a very dense, low permeability silty fine sand that underlies the low relief, higher elevation portions of the basin. Picnic Point Creek occupies a valley that is deeply incised into the till plain. Advance outwash deposits of sand and gravel that underlie the till form the valley sides in the middle and lower sections of the valley. Older deposits underlie the valley bottom from the mouth to about a mile upstream.

2.2 Site Existing Conditions The site is on the south side of the Picnic Point Creek valley with elevations ranging between 270 feet and 460 feet msl. The central and southern portions of the site are relatively flat-lying, with elevations above about 400 feet msl. The northern portion of the site occupies the valley side. The site is incised by two dry ravines running south to north. Areas south of the site and to the north of the eastern portion of the northern boundary have been developed with single-family residences. The remaining areas adjacent to the site are currently undeveloped. The existing topography is shown on Figure 2-2. The geology of the Horseman’s Trail site is shown in Figure 2-3. The upland central and southern portion of the site is underlain by Vashon till. Recessional outwash overlying the till was observed locally. The upper 3 to 5 feet of the till are frequently weathered and less dense than the underlying unweathered till. The thickness of the till varies from zero in the sides of the ravines and the slope above Picnic Point Road, to more than 50 feet where the ground elevation is highest in the southeast corner of the site. The base


of the till slopes to the northwest, from above 410 feet msl in the southeast to below 360 feet msl in the northwest. The till is dense to very dense grey silt and fine sand with occasional cobbles and boulders. The advance outwash forms the sides of the ravines and the north-facing slope above Picnic Point Road. This section of the advance outwash is a brown coarse sand and gravel. Near surface, it is frequently loosened by tree root growth and burrowing animals becoming dense to very dense with depth. The lower sections of the north slope are locally mantled by colluvium. This is soil that has been eroded, transported and deposited over geological time from higher up the slope. The colluvium is similar to the advance outwash in grain size, but is much less dense since it has not been subjected to consolidation by ice loading. Surficial soil conditions were evaluated by reviewing data available from the USDA Natural Resources Conservation Service (2008). Site soils are Alderwood gravelly sandy loam (2 to 8 percent slopes), and Alderwood-Everett gravelly sandy loams (25 to 70 percent slopes). The Alderwood gravelly sandy loam is formed where the underlying parent material is Vashon till. It forms the mineral soil in the higher southern and central areas of the site. The Alderwood-Everett gravelly sandy loams are a soil complex (mixture) of Alderwood and Everett soil types. As noted above, the Alderwood soils form on till, whereas the Everett soil type forms where the underlying material is outwash. The Alderwood-Everett soils are found on the slopes of the ravines and the sloping northern portion of the property. Based on topography, the site has been divided into two Threshold Discharge Areas (TDAs). A TDA is defined by Ecology as an “… onsite area draining to a single natural discharge or multiple… locations that combine within one-quarter mile downstream.” The West TDA is formed by the west basin, and extends from the western property line to the topographic spine east of the east ravine. The East TDA, formed by the northeast and southeast basins, occupies the remainder of the site (Figure 2-4). All basins are forested with till (soil type C) underlying the upland portions, and advance outwash (soil type A/B) forming the ravine and valley slopes. Basin characteristics are summarized in Table 2-1.

Table 2-1. Existing drainage basin characteristics.

Drainage Basin Characteristics

West Basin

(acres)

Northeast Basin (acres)

Southeast Basin (acres)

A/B forest flat 0 0.002 0 A/B forest moderate 0.910 0.028 0.065 A/B Forest steep 6.936 0.202 0.229 C Forest flat 1.213 0.370 C Forest moderate 2.573 1.413 0.423 C Forest steep 4.357 1.929 1.690 Total areas 15.988 3.943 2.406


A schematic of the drainage system is shown on Figure 2-5. Surface water from the residential areas south of the site discharge to the west ravine (see Section 4). The west TDA discharges by interflow to the wetland immediately north of the property. This discharges via a roadside ditch to Picnic Point Creek immediately downstream of the Picnic Point road crossing. Stormwater from 133rd Avenue SW also discharges to this wetland based on a Regatta Estates drawing (Trepanier Engineering 1993)). The east TDA includes the northeast and southeast basins. The northeast basin discharges by interflow to the The only evidence of surface water flow on the Horseman’s Trail site occurs where the west ravine crosses the southern property line. The area was visited shortly after a heavy rain on snow event in December 2007. For a short distance north from the property line, the forest duff had been eroded and washed sand and gravel was observed around vegetation clumps. The course of the water was indistinct and disappeared about 100 feet north of the property line. The source of the run-on to the property is believed to be stormwater discharge form the developed area south of the site (see Section 4).

Over the remainder of the Horseman’s Trail site, there is no evidence of surface water. All precipitation infiltrates into the forest duff and underlying mineral soil.

2.3 Site Developed Conditions Grading the site to meet development requirements will result in changes to existing drainage systems, and an increase in runoff since the interception and evapotranspiration provided by the forest cover will be lost by clearing of approximately 17.2 acres. Additionally, fill will be placed over some areas of permeable soils, and in other areas, lower permeability till soils will be removed exposing underlying more-permeable outwash soils. Site contours and soil types following grading are shown on Figure 2-6. The principal change from the existing conditions is the filling of the two ravines using soil excavated from the central area of the site. It is anticipated that the excavated soil will be primarily till, and therefore the resulting fill will be low permeability. The hydraulic conductivity of compacted fill was determined in laboratory to be of 0.011 ft/day (Anthony Burgess Consulting Inc. 2013b) The stormwater management proposed for the development is a combination of conventional and Low Impact Drainage (LID) technologies, including:

• Detention in ponds and vaults, with controlled discharge, • Reduction of impervious area to minimize runoff generation, • Use of compost-amended soil to promote storage and infiltration, and

reduce runoff, • Dispersion of runoff from non-pollution generating surfaces, • Swales to convey stormwater and allow infiltration, • Rain gardens for storage and infiltration of runoff.


The drainage basins for the developed site are shown in Figure 2-7. The West and East TDAs are described below. Details of calculations for stormwater quantity and water quality treatment are provided in Attachment A. The West TDA consists of the basins identified as West 1 through 6, Northwest and North. The West TDA will discharge via interflow and surface flow to the west ravine and wetland and is shown schematically in Figure 2-8. The north basin includes the roofs and backyards of lots 9 through 28. The stormwater will infiltrate into compost-amended and native soil. Lots 9 through 15 will be located on the fill for the east ravine. As noted above, this material will be predominately till and will have a low permeability. In order to avoid introducing runoff into the fill retaining structure, drainage will be provided to an infiltration trench to the west for runoff that exceeds the local infiltration capacity. The northwest basin is a small area on the west side of the west ravine. This area will not be changed from the existing conditions and will remain forest. Basins west 6 and west 1 cover lots 7 and 8, lots 29 through 47, the open space east of lots 47 and 48, the front yards of lots 9 through 28, and 58th Place W between lots 7 and 30. Basin west 6 represents the area underlain by fill, whereas basin west 1 is underlain by advance outwash. Drainage is to a BRIAR swale (Bio-retention, Infiltration and recharge Swale) along the south side of 58th Place SW. The swale will discharge to a vault located on the east side of the west ravine and behind lots 29 and 30. From the vault, stormwater will discharged to the west ravine. The channel in the ravine will include rock weirs and armoring to prevent erosion. Because of the potential for erosion, alternatively, discharge could be reduced or eliminated by additional infiltration or conveyed around the valley to Picnic Point Road drainage along existing easements. The ravine channel discharges to the wetland immediately north of the site property boundary, and ultimately to Picnic Point Creek immediately downstream of the Picnic Point Road crossing. Analyses of the BRIAR swale include infiltration and storage for the section in basin west 1 located on the advance outwash, but only storage for the section in basin west 6 located on fill. The swale will also provide water quality treatment. Basins west 3 and west 2 cover the roofs and backyards of lots 48 to 60 and the open space to the north of these lots. Basin west 3 represents the area underlain by fill, and till whereas basin west 2 is underlain by advance outwash. Drainage is to a BRIAR swale along the northern side of the open space. The swale will discharge to a rain garden at the western end of the open space. This will provide storage and infiltration of runoff, with overflow directed to the vault behind lots 29 and 30. Basins west 5 and west 4 cover lots 61 through 85, the front yards of lots 48 through 60, and 60th Avenue W. Basin west 5 represents the area underlain by till or fill. Basin 4 is predominately underlain by advance outwash, except for the western portion where there is fill for the west ravine. Drainage is to a BRIAR swale along the southern side 60th Avenue W. The swale will discharge to a vault located on the east side of the west ravine and behind


lots 29 and 30. Analyses of the BRIAR swale include infiltration and storage for the section in basin west 4 located on the advance outwash, but only storage for the sections in basins west 4 and 5 located on fill. The swale will also provide water quality treatment. The East TDA consists of basins northeast 1 and 2, east and southeast, and is shown schematically in Figure 2-9. Basin northeast 2 covers lots 86 through 94, the section of 60th Avenue W adjacent to lots 92 through 94, the front yards of lots 98 through 106 and the adjacent section of the private road. The entire basin is underlain by till. Drainage from lots 86 through 94 will be to the east. A BRIAR swale along the east side of the private road will convey runoff to basin northeast 1. Since the swale is located on till, it will provide water quality treatment and storage, but not infiltration. Basin northeast 1 covers lots 1 through 6, lots 95 through 97, the roofs and backyards of lots 98 through 100, the eastern portion of the open area north of lot 98, and adjacent sections of 60th Avenue W and 58th Place SW. Drainage from 60th Avenue W and the BRIAR swale from the northeast 2 basin will be conveyed in a pipe to the head of a sinuous rock lined open channel with weirs leading down the slope from 60th Avenue W to 58th Place SW. The BRIAR swale along the southwest side of 58th Place SW will convey this runoff together with runoff from lots 1 through 6 and the adjacent section of 58th Place SW to a vault southeast of lot 1, and will provide water quality treatment, storage and infiltration. The vault is located on advance outwash and will be constructed to allow infiltration. From the vault, stormwater will discharge to the roadside ditch on the south side of Picnic Point Road that ultimately discharges to Picnic Point Creek immediately downstream of the Picnic Point Road crossing. The east basin covers the roofs and backyards of lots 101 through 110. The stormwater will be dispersed and infiltrate into compost-amended and native soil. Ground surface will be sloped to the northeast to direct any interflow to the undisturbed forest area. From the forest area at the foot of the slope, any remaining interflow will be intercepted by the drainage system for the retaining structure on the west side of 58th Place W in Regatta Estates. Drainage for this section of Regatta Estates is conveyed to the retention pond on the north side of Picnic Point Road at 133rd Place SW. The southeast basin covers the front yards of lots 107 through 110, lots 111 and 112, and the eastern end of the private road. Drainage will be provided by a BRIAR swale along the northeastern side of the private road. Since the basin is underlain by till, the swale will provide only water quality treatment and stormwater storage. The swale will discharge to a vault between lots 111 and 112. The vault will discharge by a pipe to the drainage system for Regatta Estates. Addition of this stormwater flow was included in the design of the Regatta Estates drainage system.


3 Analyses

3.1 Flow Control The stormwater management system is designed to meet Minimum Requirement #7 for flow control in the Stormwater Manual for Western Washington (SMWW, 2005). Minimum Requirement #7 specifies that stormwater discharges to streams shall match developed discharge durations to predeveloped durations for the range of predeveloped discharge rates from 50% of the 2-year peak flow up to the full 50-year peak flow. In general, matching discharge durations between 50% of the 2-year and 50-year will result in matching the peak discharge rates in this range. Analyses were performed using the Western Washington Hydrologic Model WWHM3 (Washington Department of Ecology 2007). Details of the analyses and results are presented in Attachment A. The principal flow control features are:

• Infiltration of roof downspout flows for lots that are located on outwash soils,

• BRIAR swales to convey stormwater and allow infiltration where the swales are located on outwash soils,

• A rain garden in the western part of the site (east of lots 31 and 32) with dimensions 50 feet by 42 feet and a depth of 2.1 feet to the top of the riser,

• An infiltration vault (West Vault) west of lots 29 and 30, with dimensions 20 feet by 20 feet and depth of 5 feet to the top of the riser,

• An infiltration vault (Northeast Vault) southeast of lot 1, with dimensions 80 feet by 40 feet and depth of 10 feet to the top of the riser,

• A vault (Southeast Vault) in the cul-de-sac adjacent to lots 110, 111, and 112, with dimensions 40 feet by 20 feet and depth of 9 feet to the top of the riser.

3.2 Water Quality Water quality treatment will be provided by the BRIAR swales. Where swales are located over till or fill soils, infiltration will be negligible and the swales will provide biofiltration treatment. Swales located on outwash soils will provide infiltration as well as biofiltration. Design of the swales follows the approach in the Surface Water Manual for Western Washington (Department of Ecology 2005). Detailed calculations are presented in Attachment B. A typical swale cross-section is shown in Figure 3-1. The base width of all swales will be 2 feet, except for the swale for the southeast basin which will have a base width of 2.5 feet. This additional width is required to provide adequate treatment and compensate for the short available length of the swale. The swales are designed for continuous inflow along the length of the swale, with an average residence time of 18 minutes.


4 Erosion

The erosion hazard for the site is evaluated based upon the criteria identified in Snohomish County Rule 3044 (2006). The site soils are Alderwood and Everett, with erosion hazard values of Medium and Low respectively. The parent materials are Vashon till and advance outwash, with the steepest slopes in the range of 15 to 25 percent, for an erosion hazard value of Medium. Overall, the site therefore has an erosion hazard value of Medium. The area of the site that will be disturbed for construction is 17.2 acres (Snohomish County 2008 Table 2.6-1). For the disturbed area, the maximum average slope is less than 15 percent and the steepest slope is less than 33 percent. A critical area (wetland) is located with in one-quarter mile downstream of the stormwater discharge from the West TDA. The site is upstream of a stormwater path that does not flow directly into an ESA stream, and additional BMPs can be implemented as corrective measures. The site is therefore assessed as in the High Risk category for erosion. Winter grading of the site may be considered and therefore a Level 2-3 Stormwater Pollution Prevention Plan (SWPPP) is required. The SWPPP for the site is presented in Attachment C.

5 Upstream Analysis

Stormwater runoff from about 10.5 acres of the residential area south of the site discharges to the head of the west ravine (Figure 4-1). Review of drawings submitted to Snohomish County identified four drainage basins:

• Offsite basin 1. This basin covers 61st Place W and 139th Place SW (Forest Landing Divisions 1 and 2) and is based on Kegel & Associates (1981). The basin has an area of 5.996 acres and contains 18 single family residences. The drawing shows drainage to a pond and depression in the northwest corner of the plat, and then north to a drainage easement on Windsound Division 5 (offsite basin 2).

• Offsite basin 2. This basin covers the western portion of 137th Place SW and is based on Lovell-Sauerland & Associates, Inc. (1983). The basin has an area of 7.769 acres and contains 25.5 single family residences. The drawing shows drainage from offsite basin 1 entering the plat with an intake and trash screen to a 12-inch CMP located between lots 25 and 26. Discharge from offsite basin 2 is a manifold outfall near the northern plat boundary between lots 11 and 12.

• Offsite basin 3. This basin covers 136th Place SW and is based on Columbia Land Surveying and Engineering (1987). The basin has an area of 4.190 acres and contains 10 single family residences. The drawing shows drainage collection by a 12-inch CMP with discharge to the west ravine between lots 7 and 8. Drainage from offsite basin 2 enters this basin at the head of the west ravine on lot 8 as surface flow.

• Offsite basin 4. This basin covers the east end of 136th Place SW and is based on Lovell-Sauerland & Associates, Inc. (1983). The basin has an area of 1.518 acres and contains 5 single family residences. The drawings indicate that the basin discharges from a pipe to the


head of the west ravine on lot 7, where surface flow from offsite basin 3 enters.

Estimates of runoff from the offsite basins has been estimated using WWHM3 (Washington Department of Ecology 2007). Details are provided in Attachment A and summarized in Table 4-1.


Table 4-1. Estimated flows and frequency for off-site area discharging to west ravine within Horseman’s Trail.

Flow Frequency

(years) Flow (cfs)

2 1.5459 5 2.2471

10 2.7663 25 3.4859 50 4.0691 100 4.6933

6 Downstream Analysis

The downstream analysis for the proposed site development is contained in a separate report (Anthony Burgess Consulting 2013c)

7 Geotechnical Reports and Other Analyses

A number of geotechnical studies have been undertaken for the site by Associated Earth Sciences, Inc. (1998, 2005, 2006a and 2006b). Based on these studies it was concluded that the site could be developed for single family residential development. The geology and geotechnical properties of the subsurface was investigated and documented in these reports. In late 2007, Snohomish County retained Anthony Burgess Consulting Inc. to provide a peer review of geological, groundwater and surface water related to the proposed development. The results of the reviews are presented in reports to Snohomish County (Anthony Burgess Consulting Inc. 2013a, 2013b and 2013c)


8 References

Anthony Burgess Consulting Inc. 2013a. Geotechnical Conditions Report Horseman’s Trail PRD. Technical Appendix B to the Horseman's Trail/Frognal Estates PRD Environmental Impact Statement, Snohomish County, WA.

Anthony Burgess Consulting Inc. 2013b. Groundwater Conditions Report Horseman’s Trail PRD. Technical Appendix D to the Horseman's Trail/Frognal Estates PRD Environmental Impact Statement, Snohomish County, WA.

Anthony Burgess Consulting Inc. 2013c. Off Site Analysis Report Horseman’s Trail PRD. Technical Appendix C to the Horseman's Trail/Frognal Estates PRD Environmental Impact Statement, Snohomish County, WA.

Associated Earth Sciences, Inc. November 1998. Subsurface Exploration, Geologic Hazards, and Preliminary Geotechnical Engineering Report, Horseman’s Trail Development.

Associated Earth Sciences, Inc. 2005. Revised Subsurface Exploration, Geologic Hazards, and Preliminary Geotechnical Engineering Report, Horseman’s Trail Development.

Associated Earth Sciences, Inc. 2006a. Supplementary Subsurface Exploration, Geologic Hazards, and Preliminary Geotechnical Engineering Study, Horseman’s Trail Development.

Associated Earth Sciences, Inc. 2006b. Revised Supplementary Subsurface Exploration, Geologic Hazards, and Preliminary Geotechnical Engineering Study, Horseman’s Trail Development.

Columbia Land Surveying and Engineering. August 7. 1987. Stormwater Detention System Design & Site Development Plan for Plat of Picnic Point Place No. 2.

Higa Engineering, Inc. 2000. Revised Targeted Drainage Report and Erosion Risk Assessment for Horseman’s Trail Manor PFN 99 104777.

Kegel & Associates. February 27, 1981. Road and Drainage Plan and Profile for Forest Landing Divisions 1 and 2, Sheet 2 of 3.

Lervik Engineering. December 2006,.Horseman’s Trail Revised Targeted Drainage Report.

Lovell-Sauerland & Associates, Inc. April 1983. Road and Storm Drainage Plan for Windsound Division No. 5, Sheet 1 of 3.

Lovell-Sauerland & Associates, Inc. April 1983. Road and Storm Drainage Plan for Windsound Division No. 7, Sheet 1 of 2.

Snohomish County Surface Water Online Data 2008. Water Quality Data for Picnic Point Creek http://web5.co.snohomish.wa.us/spw_swhydro/wq-search.asp?siteid=583&isSelect=true&siteCnt=1.

Snohomish County Planning and Development Services 2008. Horseman’s Trail. A Planned Residential Development (PRD). Draft Environmental Impact Statement.

http://web5.co.snohomish.wa.us/spw_swhydro/wq-search.asp?siteid=583&isSelect=true&siteCnt=1



Trepanier Engineering. October 25, 1993. Road and Drainage Plan Regatta Estates, Sheet 3 of 15.

Western Region Climate Center 2008. Precipitation data for Everett Junior College http://www.wrcc.dri.edu/summary/Climsmwa.html

Washington Department of Ecology 2005. Stormwater Management Manual for Western Washington.

Washington Department of Ecology. 2007. Western Washington Hydrologic Model WWHM 3 Version 1.0.

http://www.wrcc.dri.edu/summary/Climsmwa.html

Figures

West TDA

East TDA

West

Northeast

Wetland

Picnic Point Creek

Regatta

Estates 133rd

Ave SW

Regatta

Estates

58th Pl W

Pond

Pond

East end

136th Pl SW

139th Pl SW &

61st P

l W

137th Pl SW

Surface water

Groundwater

Southeast

Ditch

Figure 2-5

Existing Conditions Drainage

System Schematic

Horseman’s Trail PRD

Targeted Drainage Report

Wetland

Drainage basin

Roadside ditch

Storm

water pond

On site

Off site

Note

Surface water includes interflow.

Vault

Storm

water

vault

Figure 2-8

Developed Conditions West TDA

Drainage System Schematic



Wetland

Picnic Point Creek

Regatta

Estates 133rd

Ave SW

Pond

East end

136th Pl SW

139th Pl SW

& 61st Pl W

137th Pl SW

West 3

North-

west

Rain

garden

Vault

Swale

Swale

West 5

Swale

Surface water

Groundwater

West 2

Swale

West 6

West 1

Swale

West 4

Swale

Drainage basin

Drainage swale

Stormwater pond

Wetland

Stormwater

vault

On site

Off site

Notes

Groundwater flow from basins omitted for clarity.

Surface water includes interflow.

North

Figure 2-9

Developed Conditions East TDA

Drainage System Schematic



Picnic Point Creek

Regatta

Estates

58th Pl W

Pond

Northeast

2

East

Southeast

Vault

Swale

Swale

Northeast

1

Swale

Vault

Ditch

Surface water

Groundwater

Drainage basin

Drainage swale

Stormwater pond

Wetland

Stormwater

vault

On site

Off site

Roadside ditch

Notes

Groundwater flow from basins

omitted for clarity.

Surface water includes

interflow.

Figure 3-1

Swale Cross Section

12"

2'

See Note

11

21

Top of

checkdam

Compost

amended soil

Natural soil

18"

18"



Note: Swale bottom width 2' except for Southeast swale,

which has a bottom width of 2.5 ‘

21

Attachment A

Stormwater Flow Control Calculations

Horseman’s Trail September 2013 Stormwater Flow Control

Page A-2

TABLE OF CONTENTS

A1 WWHM3 Analyses Input Data ................................................. 4

A1.1 Existing Conditions ..............................................................4

A1.2 Developed Conditions ..........................................................5

A2 West TDA WWHM Analyses .................................................... 8

A3 East TDA WWHM Analyses ................................................... 32

A4 References ............................................................................... 51


Page A-3

TABLES

Table A1-1 Existing Conditions Input for WWHM Table A1-2 Developed Land Use West TDA Table A1-3 Developed Land Use East TDA Table A1-4 Hydraulic Conductivity Data


Page A-4

A1 WWHM3 Analyses Input Data

A1.1 Existing Conditions The contact between the till and advance outwash was identified based on boring and test pit data. The contact elevation was used for input to surface contouring software (Surfer 8.05 by Golden Software, Inc. 2005) and geographical information system software (Manifold 8.0 by CDA International Ltd. and Manifold Net Ltd.2008). Threshold discharge areas (TDAs) and drainage basins were delineated based on contour data for the existing ground surface. Neither TDA shows evidence of surface water flow. A schematic of the drainage system is shown in Figure A1-1. The West TDA contains both the east and west ravines and the northern slope of the site. Flows from the West TDA contribute to a wetland adjacent to the northwest corner of the site. Discharge from the residential area south of the site enters at the head of the west ravine. The East TDA contains two basins (northeast and southeast) and drains by interflow to Regatta Estates and Picnic Point Creek. A nominal section of Picnic Point Creek has been included in the WWHM analyses to define the point of compliance for comparison of the existing and developed conditions fro both the West TDA and East TDA. A schematic of the drainage for the existing conditions is shown in the Targeted Drainage Report Figure 2-5. The existing land use is forest. Using Manifold, areas of slopes in three groups: less than 5 percent, 5 to 15 percent, and greater than 15 percent, were identified. These correspond to the flat, moderate and steep categories in WWHM3. The slope areas were intersected with the drainage basins to calculate the areas of the slope categories for input to WWHM. The results are presented in Table A1-1.


Page A-5

Table A1-1 Existing Conditions Input for WWHM.

TDA Basin Soil type Slope

(percent) Area

(acres)

West

West outwash < 5.00 0.000 West outwash 5.00 - 15.00 0.910 West outwash > 15.00 6.936 West till < 5.00 1.213 West till 5.00 - 15.00 2.573 West till > 15.00 4.357

East

Northeast outwash < 5.00 0.002 Northeast outwash 5.00 - 15.00 0.028 Northeast outwash > 15.00 0.202 Northeast till < 5.00 0.370 Northeast till 5.00 - 15.00 1.413 Northeast till > 15.00 1.929 Southeast outwash 5.00 - 15.00 0.065 Southeast outwash > 15.00 0.229 Southeast till < 5.00 0.000 Southeast till 5.00 - 15.00 0.423 Southeast till > 15.00 1.690

A1.2 Developed Conditions Schematics for the developed West TDA and East TDA are shown in the Targeted Drainage Report Figures 2-2 and 2-3, respectively. Areas of cut and fill were developed in Manifold by cutting the existing surface with the surface following construction grading. Negative values represented the depth of cut and positive values the depth of fill. The surface geology following grading for construction was developed in Manifold by cutting the till – outwash surface with the graded surface. The result was a drawing of the soil types (till, outwash, fill) following grading. TDAs were defined consistent with the existing conditions. The TDAs were divided into sub-basins representing similar soil types. Using Manifold, the land-use for the site was divided into forest, landscape, road and single family residences (SFRs). Areas of lots, roof, and driveway were calculated using drawings by Land Technologies (2005). The divide between some sub-basins is located within SFRs, with the roof and backyard in one basin and the driveway and front yard in an adjoining sub-basin. For groups of SFRs, the area was therefore broken down further into front (29 percent) and back (71 percent). Land use data are presented in Table A1-2 and A1-3 for the west and east TDAs respectively.


Page A-6

Table A1-2 Developed Land Use West TDA.

Pervious Land Areas (acres)

West1 West2 West3 West4 West5 West6 North North-

west A B Forest Flat 0.003 A B Forest Steep 0.022 0.004 3.427 0.318 A B Lawn Flat 1.153 0.713 0.022 0.304 0.019 0.724 0.007 C Forest Steep 0.306 0.195 C Lawn Flat 0.072 0.33 1.013 0.804 0.381 0.39 C Lawn Steep 0.275 Impervious Land Areas (acres) West1 West2 West3 West4 West5 West6 North Roads Flat 0.301 0.237 0.1 0.1 Roads Mod 0.184 0.202 0.113 0.113 Roof Tops Flat 0.557 0.289 0.178 0.565 0.225 0.225 0.719 Driveways Flat 0.26 0.217 0.108 0.108

Table A1-3 Developed Land Use East TDA.

Pervious Land Areas (acres) Northeast2 Northeast1 East Southeast A B Forest Steep 0.582 A B Lawn Flat 0.319 C Forest Mod 0.127 C Forest Steep 0.012 0.145 C Lawn Flat 1.019 1.143 0.489 0.325 Impervious Land Areas (acres) Northeast2 Northeast1 East Southeast Roads Flat 0.204 0.342 0.246 Roads Mod 0.239 Roof Tops Flat 0.341 0.424 0.362 0.083 Driveways Flat 0.192 0.104 0.049

Low impact development is proposed for the development, including infiltration of discharge from roof downspouts, compost amended soil, BRIAR swales (Bio-retention, Infiltration and Recharge Swale), infiltration vaults, and rain gardens. Infiltration will be limited to areas where the surface soils are advance outwash. In these areas, the Stormwater Manual for Western Washington (SMWW) allows infiltration of roof downspout discharge to be excluded in calculations for sizing flow control structures (Washington Department of Ecology 2005). LID credits for infiltration from downspouts have been included for the following:

• Lots 16 through 43,


Page A-7

• Lots 54 through 63, and • Lots 70 through 74

The infiltration rate for the rain garden, infiltration vaults and BRIAR swales has been determined based on field measurements of hydraulic properties of the advance outwash and from estimates based on textural classification and grain size analyses (Anthony Burgess Consulting 2013, Washington Department of Ecology 2005). These data are summarized in Table A1-4.

Table A1-4 Hydraulic Conductivity Data. Hydraulic Conductivity (in/hr)

Method Measured Estimated Reduction

Factor Design Value

Slug tests 0.2 - 1.7 0.2 - 1.7 Preliminary infiltration test ~20 .2 4

Textural description 2 - 8 .25 0.5 - 2 Grain size analyses 17 - 44 .2 3.3 - 8.8 D10 grain size 0.4 - 2.3

The reduction factors are based on recommendations in the SMWW. Based on these data the average design hydraulic conductivity or infiltration rate value is 2.6 in/hr. In order to allow for lower permeability lenses within the advance outwash, a conservative design value of 1.5 in/hr (measured value 6 in/hr and reduction factor 4) is used in the WWHM calculations. The BRIAR swale will have a bottom width of 2 feet and a depth of 18 inches with side slopes of 2H:1V (Figure A1-4). The base and sides will be over-excavated to accommodate 18 inches of compost-amended soil. Check dams will have a height of 12 inches above the swale bottom. Where driveways cross the swale, it will be backfilled with ½ inch to 1½ inch ballast with 10 percent compost. The driveway grade will be lowered 4 inches over the swale to provide overflow. The porosity of the compost-amended soil is assumed to be 40 percent as recommended in SMWW Volume III Appendix C Section 7.7.3. The storage provided by the compost-amended soil is modeled by increasing the swale depth by 40 percent of the thickness of the compost–amended soil, i.e. 7 inches. The rain garden will have a similar design to the BRIAR swale, with a maximum depth of 18 inches and 18 inches of compost-amended soil in the base and sides. Higa Engineering, Inc. (2000) noted that the design of the Regatta Estates drainage/detention system included runoff from the 12-acre eastern portion of the Horseman’s Trail site. As currently defined, the East TDA has an area of 6.75 acres. Design of the stormwater management system for the East TDA is in accordance with the SMWW which requires that developed runoff be no greater than runoff for predeveloped conditions. The developed runoff from the East TDA will therefore not exceed the allowance built into the design for the Regatta Estates stormwater detention pond.


Page A-8

A2 West TDA WWHM Analyses Western Washington Hydrology Model PROJECT REPORT ___________________________________________________________________ Project Name: westtdalid Site Address: City : Report Date : 7/10/2008 Gage : Everett Data Start : 1948/10/01 Data End : 1997/09/30 Precip Scale: 0.80 ___________________________________________________________________ ___________________________________________________________________ PREDEVELOPED LAND USE Name : West Bypass: No GroundWater: No Pervious Land Use Acres A B, Forest, Mod .91 A B, Forest, Steep 6.936 C, Forest, Flat 1.213 C, Forest, Mod 2.573 C, Forest, Steep 4.357 Impervious Land Use Acres ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater PPC, PPC, ___________________________________________________________________ Name : PPC Bottom Length: 5ft. Bottom Width : 5ft. Manning's n : 0.03 Channel bottom slope 1: 0.01 To 1 Channel Left side slope 0: 2 To 1


Page A-9

Channel right side slope 2: 2 To 1 Discharge Structure Riser Height: 0 ft. Riser Diameter: 0 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Channel Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 0.000 0.001 0.000 0.000 0.000 0.111 0.001 0.000 0.644 0.000 0.222 0.001 0.000 2.068 0.000 0.333 0.001 0.000 4.120 0.000 0.444 0.001 0.000 6.755 0.000 0.556 0.001 0.000 9.955 0.000 0.667 0.001 0.000 13.72 0.000 0.778 0.001 0.001 18.04 0.000 0.889 0.001 0.001 22.94 0.000 1.000 0.001 0.001 28.42 0.000 1.111 0.001 0.001 34.49 0.000 1.222 0.001 0.001 41.16 0.000 1.333 0.001 0.001 48.46 0.000 1.444 0.001 0.001 56.38 0.000 1.556 0.001 0.001 64.95 0.000 1.667 0.001 0.002 74.18 0.000 1.778 0.001 0.002 84.09 0.000 1.889 0.001 0.002 94.69 0.000 2.000 0.002 0.002 106.0 0.000 2.111 0.002 0.002 118.0 0.000 2.222 0.002 0.002 130.8 0.000 2.333 0.002 0.003 144.3 0.000 2.444 0.002 0.003 158.5 0.000 2.556 0.002 0.003 173.6 0.000 2.667 0.002 0.003 189.4 0.000 2.778 0.002 0.003 206.0 0.000 2.889 0.002 0.004 223.5 0.000 3.000 0.002 0.004 241.8 0.000 3.111 0.002 0.004 260.9 0.000 3.222 0.002 0.004 280.9 0.000 3.333 0.002 0.004 301.8 0.000 3.444 0.002 0.005 323.6 0.000 3.556 0.002 0.005 346.3 0.000 3.667 0.002 0.005 369.9 0.000 3.778 0.002 0.005 394.4 0.000 3.889 0.002 0.006 419.9 0.000 4.000 0.002 0.006 446.3 0.000 4.111 0.003 0.006 473.7 0.000 4.222 0.003 0.007 502.1 0.000 4.333 0.003 0.007 531.5 0.000 4.444 0.003 0.007 561.9 0.000 4.556 0.003 0.007 593.4 0.000 4.667 0.003 0.008 625.8 0.000


Page A-10

4.778 0.003 0.008 659.4 0.000 4.889 0.003 0.008 693.9 0.000 5.000 0.003 0.009 729.6 0.000 5.111 0.003 0.009 766.3 0.000 5.222 0.003 0.009 804.2 0.000 5.333 0.003 0.010 843.2 0.000 5.444 0.003 0.010 883.3 0.000 5.556 0.003 0.010 924.5 0.000 5.667 0.003 0.011 966.9 0.000 5.778 0.003 0.011 1010. 0.000 5.889 0.003 0.012 1055. 0.000 6.000 0.003 0.012 1101. 0.000 6.111 0.003 0.012 1148. 0.000 6.222 0.004 0.013 1196. 0.000 6.333 0.004 0.013 1246. 0.000 6.444 0.004 0.013 1296. 0.000 6.556 0.004 0.014 1348. 0.000 6.667 0.004 0.014 1402. 0.000 6.778 0.004 0.015 1456. 0.000 6.889 0.004 0.015 1512. 0.000 7.000 0.004 0.016 1569. 0.000 7.111 0.004 0.016 1628. 0.000 7.222 0.004 0.016 1688. 0.000 7.333 0.004 0.017 1749. 0.000 7.444 0.004 0.017 1811. 0.000 7.556 0.004 0.018 1875. 0.000 7.667 0.004 0.018 1940. 0.000 7.778 0.004 0.019 2007. 0.000 7.889 0.004 0.019 2075. 0.000 8.000 0.004 0.020 2144. 0.000 8.111 0.004 0.020 2215. 0.000 8.222 0.004 0.021 2287. 0.000 8.333 0.005 0.021 2360. 0.000 8.444 0.005 0.022 2435. 0.000 8.556 0.005 0.022 2512. 0.000 8.667 0.005 0.023 2590. 0.000 8.778 0.005 0.023 2669. 0.000 8.889 0.005 0.024 2750. 0.000 9.000 0.005 0.024 2833. 0.000 9.111 0.005 0.025 2917. 0.000 9.222 0.005 0.025 3002. 0.000 9.333 0.005 0.026 3089. 0.000 9.444 0.005 0.027 3178. 0.000 9.556 0.005 0.027 3268. 0.000 9.667 0.005 0.028 3359. 0.000 9.778 0.005 0.028 3453. 0.000 9.889 0.005 0.029 3547. 0.000 10.00 0.005 0.029 3644. 0.000 10.11 0.005 0.030 3742. 0.000 ___________________________________________________________________ Name : West3 Bypass: No GroundWater: No


Page A-11

Pervious Land Use Acres A B, Lawn, Flat .022 C, Lawn, Flat .33 Impervious Land Use Acres ROOF TOPS FLAT 0.178 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater West2 swale, West2 swale, ___________________________________________________________________ Name : West2 Bypass: No GroundWater: No Pervious Land Use Acres A B, Lawn, Flat .713 C, Lawn, Flat .072 Impervious Land Use Acres ROOF TOPS FLAT 0.031 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater West2 swale, West2 swale, ___________________________________________________________________ Name : West6 Bypass: No GroundWater: No Pervious Land Use Acres A B, Forest, Flat .004 A B, Lawn, Flat .019 C, Lawn, Flat .567 C, Lawn, Steep .275 Impervious Land Use Acres ROADS FLAT 0.1 ROADS MOD 0.113 ROOF TOPS FLAT 0.373 DRIVEWAYS FLAT 0.108


Page A-12

___________________________________________________________________ Element Flows To: Surface Interflow Groundwater West1 swale, West1 swale, ___________________________________________________________________ Name : West1 Bypass: No GroundWater: No Pervious Land Use Acres A B, Forest, Steep .022 A B, Lawn, Flat 1.233 Impervious Land Use Acres ROADS FLAT 0.301 ROADS MOD 0.184 ROOF TOPS FLAT 0.102 DRIVEWAYS FLAT 0.26 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater West1 swale, West1 swale, ___________________________________________________________________ Name : West5 Bypass: No GroundWater: No Pervious Land Use Acres C, Forest, Steep .195 C, Lawn, Flat .805 Impervious Land Use Acres ROADS FLAT 0.187 ROADS MOD 0.187 ROOF TOPS FLAT 0.239 DRIVEWAYS FLAT 0.156 ___________________________________________________________________


Page A-13

Element Flows To: Surface Interflow Groundwater West4 swale, West4 swale, ___________________________________________________________________ Name : West4 Bypass: No GroundWater: No Pervious Land Use Acres A B, Forest, Steep .004 A B, Lawn, Flat .304 C, Forest, Steep .306 C, Lawn, Flat 1.013 Impervious Land Use Acres ROADS FLAT 0.237 ROADS MOD 0.202 ROOF TOPS FLAT 0.358 DRIVEWAYS FLAT 0.217 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater West4 swale, West4 swale, ___________________________________________________________________ Name : North Bypass: No GroundWater: No Pervious Land Use Acres A B, Forest, Steep 3.428 A B, Lawn, Flat .55 C, Lawn, Flat .296 Impervious Land Use Acres ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater PPC, PPC, ___________________________________________________________________


Page A-14

Name : Northwest Bypass: No GroundWater: No Pervious Land Use Acres A B, Forest, Steep .318 A B, Lawn, Flat .007 Impervious Land Use Acres ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater PPC, PPC, ___________________________________________________________________ Name : West2 swale Bottom Length: 280ft. Bottom Width: 2ft. Depth : 2.1ft. Volume at riser head : 0.0540ft. Infiltration On Infiltration rate : 6 Infiltration saftey factor : 0.25 Wetted surface area On Side slope 1: 2 To 1 Side slope 2: 0 To 1 Side slope 3: 2 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 1.6 ft. Riser Diameter: 48 in. Element Flows To: Outlet 1 Outlet 2 Rain garden, ___________________________________________________________________ Pond Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 0.000 0.013 0.000 0.000 0.000 0.023 0.013 0.000 0.000 0.020 0.047 0.014 0.001 0.000 0.020 0.070 0.015 0.001 0.000 0.021 0.093 0.015 0.001 0.000 0.021 0.117 0.016 0.002 0.000 0.022 0.140 0.016 0.002 0.000 0.022


Page A-15

0.163 0.017 0.002 0.000 0.023 0.187 0.018 0.003 0.000 0.023 0.210 0.018 0.003 0.000 0.024 0.233 0.019 0.004 0.000 0.024 0.257 0.019 0.004 0.000 0.025 0.280 0.020 0.005 0.000 0.025 0.303 0.021 0.005 0.000 0.025 0.327 0.021 0.006 0.000 0.026 0.350 0.022 0.006 0.000 0.026 0.373 0.022 0.007 0.000 0.027 0.397 0.023 0.007 0.000 0.027 0.420 0.024 0.008 0.000 0.028 0.443 0.024 0.008 0.000 0.028 0.467 0.025 0.009 0.000 0.029 0.490 0.025 0.009 0.000 0.029 0.513 0.026 0.010 0.000 0.030 0.537 0.027 0.011 0.000 0.030 0.560 0.027 0.011 0.000 0.031 0.583 0.028 0.012 0.000 0.031 0.607 0.028 0.013 0.000 0.031 0.630 0.029 0.013 0.000 0.032 0.653 0.030 0.014 0.000 0.032 0.677 0.030 0.015 0.000 0.033 0.700 0.031 0.015 0.000 0.033 0.723 0.031 0.016 0.000 0.034 0.747 0.032 0.017 0.000 0.034 0.770 0.033 0.018 0.000 0.035 0.793 0.033 0.018 0.000 0.035 0.817 0.034 0.019 0.000 0.036 0.840 0.034 0.020 0.000 0.036 0.863 0.035 0.021 0.000 0.037 0.887 0.036 0.022 0.000 0.037 0.910 0.036 0.022 0.000 0.038 0.933 0.037 0.023 0.000 0.038 0.957 0.037 0.024 0.000 0.038 0.980 0.038 0.025 0.000 0.039 1.003 0.039 0.026 0.000 0.039 1.027 0.039 0.027 0.000 0.040 1.050 0.040 0.028 0.000 0.040 1.073 0.040 0.029 0.000 0.041 1.097 0.041 0.030 0.000 0.041 1.120 0.042 0.031 0.000 0.042 1.143 0.042 0.032 0.000 0.042 1.167 0.043 0.032 0.000 0.043 1.190 0.043 0.034 0.000 0.043 1.213 0.044 0.035 0.000 0.044 1.237 0.045 0.036 0.000 0.044 1.260 0.045 0.037 0.000 0.045 1.283 0.046 0.038 0.000 0.045 1.307 0.046 0.039 0.000 0.045 1.330 0.047 0.040 0.000 0.046 1.353 0.048 0.041 0.000 0.046 1.377 0.048 0.042 0.000 0.047 1.400 0.049 0.043 0.000 0.047 1.423 0.049 0.044 0.000 0.048 1.447 0.050 0.046 0.000 0.048 1.470 0.051 0.047 0.000 0.049


Page A-16

1.493 0.051 0.048 0.000 0.049 1.517 0.052 0.049 0.000 0.050 1.540 0.052 0.050 0.000 0.050 1.563 0.053 0.052 0.000 0.051 1.587 0.054 0.053 0.000 0.051 1.610 0.054 0.054 0.039 0.052 1.633 0.055 0.055 0.237 0.052 1.657 0.055 0.057 0.525 0.053 1.680 0.056 0.058 0.881 0.053 1.703 0.057 0.059 1.294 0.053 1.727 0.057 0.061 1.756 0.054 1.750 0.058 0.062 2.263 0.054 1.773 0.058 0.063 2.811 0.055 1.797 0.059 0.065 3.398 0.055 1.820 0.060 0.066 4.020 0.056 1.843 0.060 0.067 4.676 0.056 1.867 0.061 0.069 5.364 0.057 1.890 0.061 0.070 6.084 0.057 1.913 0.062 0.072 6.833 0.058 1.937 0.063 0.073 7.610 0.058 1.960 0.063 0.075 8.414 0.059 1.983 0.064 0.076 9.246 0.059 2.007 0.064 0.078 10.10 0.060 2.030 0.065 0.079 10.98 0.060 2.053 0.066 0.081 11.89 0.061 2.077 0.066 0.082 12.82 0.061 2.100 0.067 0.084 13.77 0.062 ___________________________________________________________________ Name : West1 swale Bottom Length: 660ft. Bottom Width: 2ft. Depth : 2.1ft. Volume at riser head : 0.1273ft. Infiltration On Infiltration rate : 6 Infiltration saftey factor : 0.25 Wetted surface area On Side slope 1: 2 To 1 Side slope 2: 0 To 1 Side slope 3: 2 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 1.6 ft. Riser Diameter: 48 in. Element Flows To: Outlet 1 Outlet 2 West vault, ___________________________________________________________________ Pond Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs)


Page A-17

0.000 0.030 0.000 0.000 0.000 0.023 0.032 0.001 0.000 0.047 0.047 0.033 0.001 0.000 0.048 0.070 0.035 0.002 0.000 0.049 0.093 0.036 0.003 0.000 0.050 0.117 0.037 0.004 0.000 0.051 0.140 0.039 0.005 0.000 0.052 0.163 0.040 0.006 0.000 0.053 0.187 0.042 0.007 0.000 0.054 0.210 0.043 0.008 0.000 0.056 0.233 0.044 0.009 0.000 0.057 0.257 0.046 0.010 0.000 0.058 0.280 0.047 0.011 0.000 0.059 0.303 0.049 0.012 0.000 0.060 0.327 0.050 0.013 0.000 0.061 0.350 0.052 0.014 0.000 0.062 0.373 0.053 0.016 0.000 0.063 0.397 0.054 0.017 0.000 0.064 0.420 0.056 0.018 0.000 0.065 0.443 0.057 0.019 0.000 0.066 0.467 0.059 0.021 0.000 0.067 0.490 0.060 0.022 0.000 0.068 0.513 0.061 0.024 0.000 0.070 0.537 0.063 0.025 0.000 0.071 0.560 0.064 0.026 0.000 0.072 0.583 0.066 0.028 0.000 0.073 0.607 0.067 0.030 0.000 0.074 0.630 0.068 0.031 0.000 0.075 0.653 0.070 0.033 0.000 0.076 0.677 0.071 0.034 0.000 0.077 0.700 0.073 0.036 0.000 0.078 0.723 0.074 0.038 0.000 0.079 0.747 0.076 0.040 0.000 0.080 0.770 0.077 0.041 0.000 0.081 0.793 0.078 0.043 0.000 0.083 0.817 0.080 0.045 0.000 0.084 0.840 0.081 0.047 0.000 0.085 0.863 0.083 0.049 0.000 0.086 0.887 0.084 0.051 0.000 0.087 0.910 0.085 0.053 0.000 0.088 0.933 0.087 0.055 0.000 0.089 0.957 0.088 0.057 0.000 0.090 0.980 0.090 0.059 0.000 0.091 1.003 0.091 0.061 0.000 0.092 1.027 0.093 0.063 0.000 0.093 1.050 0.094 0.065 0.000 0.094 1.073 0.095 0.067 0.000 0.096 1.097 0.097 0.070 0.000 0.097 1.120 0.098 0.072 0.000 0.098 1.143 0.100 0.074 0.000 0.099 1.167 0.101 0.077 0.000 0.100 1.190 0.102 0.079 0.000 0.101 1.213 0.104 0.081 0.000 0.102 1.237 0.105 0.084 0.000 0.103 1.260 0.107 0.086 0.000 0.104 1.283 0.108 0.089 0.000 0.105 1.307 0.109 0.091 0.000 0.106


Page A-18

1.330 0.111 0.094 0.000 0.107 1.353 0.112 0.097 0.000 0.109 1.377 0.114 0.099 0.000 0.110 1.400 0.115 0.102 0.000 0.111 1.423 0.117 0.105 0.000 0.112 1.447 0.118 0.107 0.000 0.113 1.470 0.119 0.110 0.000 0.114 1.493 0.121 0.113 0.000 0.115 1.517 0.122 0.116 0.000 0.116 1.540 0.124 0.119 0.000 0.117 1.563 0.125 0.121 0.000 0.118 1.587 0.126 0.124 0.000 0.119 1.610 0.128 0.127 0.039 0.120 1.633 0.129 0.130 0.237 0.122 1.657 0.131 0.133 0.525 0.123 1.680 0.132 0.136 0.881 0.124 1.703 0.134 0.140 1.294 0.125 1.727 0.135 0.143 1.756 0.126 1.750 0.136 0.146 2.263 0.127 1.773 0.138 0.149 2.811 0.128 1.797 0.139 0.152 3.398 0.129 1.820 0.141 0.156 4.020 0.130 1.843 0.142 0.159 4.676 0.131 1.867 0.143 0.162 5.364 0.132 1.890 0.145 0.166 6.084 0.134 1.913 0.146 0.169 6.833 0.135 1.937 0.148 0.172 7.610 0.136 1.960 0.149 0.176 8.414 0.137 1.983 0.151 0.179 9.246 0.138 2.007 0.152 0.183 10.10 0.139 2.030 0.153 0.186 10.98 0.140 2.053 0.155 0.190 11.89 0.141 2.077 0.156 0.194 12.82 0.142 2.100 0.158 0.197 13.77 0.143 ___________________________________________________________________ Name : West4 swale Bottom Length: 375ft. Bottom Width: 2ft. Depth : 2.1ft. Volume at riser head : 0.0724ft. Infiltration On Infiltration rate : 6 Infiltration saftey factor : 0.25 Wetted surface area On Side slope 1: 2 To 1 Side slope 2: 0 To 1 Side slope 3: 2 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 1.6 ft. Riser Diameter: 48 in. Element Flows To: Outlet 1 Outlet 2 West vault,


Page A-19

___________________________________________________________________ Pond Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 0.000 0.017 0.000 0.000 0.000 0.023 0.018 0.000 0.000 0.027 0.047 0.019 0.001 0.000 0.027 0.070 0.020 0.001 0.000 0.028 0.093 0.020 0.002 0.000 0.029 0.117 0.021 0.002 0.000 0.029 0.140 0.022 0.003 0.000 0.030 0.163 0.023 0.003 0.000 0.030 0.187 0.024 0.004 0.000 0.031 0.210 0.024 0.004 0.000 0.032 0.233 0.025 0.005 0.000 0.032 0.257 0.026 0.006 0.000 0.033 0.280 0.027 0.006 0.000 0.033 0.303 0.028 0.007 0.000 0.034 0.327 0.028 0.007 0.000 0.035 0.350 0.029 0.008 0.000 0.035 0.373 0.030 0.009 0.000 0.036 0.397 0.031 0.010 0.000 0.037 0.420 0.032 0.010 0.000 0.037 0.443 0.032 0.011 0.000 0.038 0.467 0.033 0.012 0.000 0.038 0.490 0.034 0.013 0.000 0.039 0.513 0.035 0.013 0.000 0.040 0.537 0.036 0.014 0.000 0.040 0.560 0.037 0.015 0.000 0.041 0.583 0.037 0.016 0.000 0.041 0.607 0.038 0.017 0.000 0.042 0.630 0.039 0.018 0.000 0.043 0.653 0.040 0.019 0.000 0.043 0.677 0.041 0.020 0.000 0.044 0.700 0.041 0.020 0.000 0.045 0.723 0.042 0.021 0.000 0.045 0.747 0.043 0.022 0.000 0.046 0.770 0.044 0.023 0.000 0.046 0.793 0.045 0.024 0.000 0.047 0.817 0.045 0.026 0.000 0.048 0.840 0.046 0.027 0.000 0.048 0.863 0.047 0.028 0.000 0.049 0.887 0.048 0.029 0.000 0.050 0.910 0.049 0.030 0.000 0.050 0.933 0.049 0.031 0.000 0.051 0.957 0.050 0.032 0.000 0.051 0.980 0.051 0.033 0.000 0.052 1.003 0.052 0.035 0.000 0.053 1.027 0.053 0.036 0.000 0.053 1.050 0.053 0.037 0.000 0.054 1.073 0.054 0.038 0.000 0.054 1.097 0.055 0.040 0.000 0.055 1.120 0.056 0.041 0.000 0.056 1.143 0.057 0.042 0.000 0.056


Page A-20

1.167 0.057 0.044 0.000 0.057 1.190 0.058 0.045 0.000 0.058 1.213 0.059 0.046 0.000 0.058 1.237 0.060 0.048 0.000 0.059 1.260 0.061 0.049 0.000 0.059 1.283 0.061 0.050 0.000 0.060 1.307 0.062 0.052 0.000 0.061 1.330 0.063 0.053 0.000 0.061 1.353 0.064 0.055 0.000 0.062 1.377 0.065 0.056 0.000 0.063 1.400 0.065 0.058 0.000 0.063 1.423 0.066 0.059 0.000 0.064 1.447 0.067 0.061 0.000 0.064 1.470 0.068 0.063 0.000 0.065 1.493 0.069 0.064 0.000 0.066 1.517 0.069 0.066 0.000 0.066 1.540 0.070 0.067 0.000 0.067 1.563 0.071 0.069 0.000 0.068 1.587 0.072 0.071 0.000 0.068 1.610 0.073 0.072 0.039 0.069 1.633 0.073 0.074 0.237 0.069 1.657 0.074 0.076 0.525 0.070 1.680 0.075 0.078 0.881 0.071 1.703 0.076 0.079 1.294 0.071 1.727 0.077 0.081 1.756 0.072 1.750 0.077 0.083 2.263 0.073 1.773 0.078 0.085 2.811 0.073 1.797 0.079 0.087 3.398 0.074 1.820 0.080 0.088 4.020 0.074 1.843 0.081 0.090 4.676 0.075 1.867 0.081 0.092 5.364 0.076 1.890 0.082 0.094 6.084 0.076 1.913 0.083 0.096 6.833 0.077 1.937 0.084 0.098 7.610 0.078 1.960 0.085 0.100 8.414 0.078 1.983 0.086 0.102 9.246 0.079 2.007 0.086 0.104 10.10 0.079 2.030 0.087 0.106 10.98 0.080 2.053 0.088 0.108 11.89 0.081 2.077 0.089 0.110 12.82 0.081 2.100 0.090 0.112 13.77 0.082 ___________________________________________________________________ Name : Rain garden Bottom Length: 50ft. Bottom Width: 42ft. Depth : 2.6ft. Volume at riser head : 0.1324ft. Infiltration On Infiltration rate : 6 Infiltration saftey factor : 0.25 Wetted surface area On Side slope 1: 3 To 1 Side slope 2: 3 To 1 Side slope 3: 3 To 1 Side slope 4: 3 To 1


Page A-21

Discharge Structure Riser Height: 2.1 ft. Riser Diameter: 24 in. Element Flows To: Outlet 1 Outlet 2 West vault, ___________________________________________________________________ Pond Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 333.5 0.048 0.000 0.000 0.000 333.5 0.049 0.001 0.000 0.074 333.6 0.049 0.003 0.000 0.074 333.6 0.049 0.004 0.000 0.075 333.6 0.050 0.006 0.000 0.075 333.6 0.050 0.007 0.000 0.076 333.7 0.050 0.009 0.000 0.076 333.7 0.051 0.010 0.000 0.077 333.7 0.051 0.011 0.000 0.078 333.8 0.052 0.013 0.000 0.078 333.8 0.052 0.014 0.000 0.079 333.8 0.052 0.016 0.000 0.079 333.8 0.053 0.017 0.000 0.080 333.9 0.053 0.019 0.000 0.081 333.9 0.053 0.021 0.000 0.081 333.9 0.054 0.022 0.000 0.082 334.0 0.054 0.024 0.000 0.083 334.0 0.055 0.025 0.000 0.083 334.0 0.055 0.027 0.000 0.084 334.0 0.055 0.028 0.000 0.084 334.1 0.056 0.030 0.000 0.085 334.1 0.056 0.032 0.000 0.086 334.1 0.057 0.033 0.000 0.086 334.2 0.057 0.035 0.000 0.087 334.2 0.057 0.037 0.000 0.088 334.2 0.058 0.038 0.000 0.088 334.3 0.058 0.040 0.000 0.089 334.3 0.059 0.042 0.000 0.089 334.3 0.059 0.043 0.000 0.090 334.3 0.059 0.045 0.000 0.091 334.4 0.060 0.047 0.000 0.091 334.4 0.060 0.048 0.000 0.092 334.4 0.061 0.050 0.000 0.093 334.5 0.061 0.052 0.000 0.093 334.5 0.061 0.054 0.000 0.094 334.5 0.062 0.056 0.000 0.095 334.5 0.062 0.057 0.000 0.095 334.6 0.063 0.059 0.000 0.096 334.6 0.063 0.061 0.000 0.097 334.6 0.064 0.063 0.000 0.097 334.7 0.064 0.065 0.000 0.098 334.7 0.064 0.066 0.000 0.099 334.7 0.065 0.068 0.000 0.099


Page A-22

334.7 0.065 0.070 0.000 0.100 334.8 0.066 0.072 0.000 0.101 334.8 0.066 0.074 0.000 0.101 334.8 0.067 0.076 0.000 0.102 334.9 0.067 0.078 0.000 0.103 334.9 0.067 0.080 0.000 0.103 334.9 0.068 0.082 0.000 0.104 334.9 0.068 0.084 0.000 0.105 335.0 0.069 0.086 0.000 0.106 335.0 0.069 0.088 0.000 0.106 335.0 0.070 0.090 0.000 0.107 335.1 0.070 0.092 0.000 0.108 335.1 0.070 0.094 0.000 0.108 335.1 0.071 0.096 0.000 0.109 335.1 0.071 0.098 0.000 0.110 335.2 0.072 0.100 0.000 0.110 335.2 0.072 0.102 0.000 0.111 335.2 0.073 0.104 0.000 0.112 335.3 0.073 0.106 0.000 0.113 335.3 0.074 0.108 0.000 0.113 335.3 0.074 0.110 0.000 0.114 335.3 0.074 0.113 0.000 0.115 335.4 0.075 0.115 0.000 0.116 335.4 0.075 0.117 0.000 0.116 335.4 0.076 0.119 0.000 0.117 335.5 0.076 0.121 0.000 0.118 335.5 0.077 0.123 0.000 0.118 335.5 0.077 0.126 0.000 0.119 335.6 0.078 0.128 0.000 0.120 335.6 0.078 0.130 0.000 0.121 335.6 0.079 0.132 0.016 0.121 335.6 0.079 0.135 0.143 0.122 335.7 0.080 0.137 0.335 0.123 335.7 0.080 0.139 0.575 0.124 335.7 0.080 0.142 0.855 0.124 335.8 0.081 0.144 1.169 0.125 335.8 0.081 0.146 1.515 0.126 335.8 0.082 0.149 1.889 0.127 335.8 0.082 0.151 2.290 0.127 335.9 0.083 0.153 2.716 0.128 335.9 0.083 0.156 3.165 0.129 335.9 0.084 0.158 3.637 0.130 336.0 0.084 0.161 4.130 0.130 336.0 0.085 0.163 4.643 0.131 336.0 0.085 0.166 5.176 0.132 336.0 0.086 0.168 5.728 0.133 336.1 0.086 0.171 6.298 0.134 336.1 0.087 0.173 6.887 0.134 ___________________________________________________________________ Name : West vault Bottom Length: 20ft. Bottom Width: 20ft. Depth : 6ft. Volume at riser head : 0.0459ft. Infiltration On


Page A-23

Infiltration rate : 6 Infiltration saftey factor : 0.25 Side slope 1: 0 To 1 Side slope 2: 0 To 1 Side slope 3: 0 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 5 ft. Riser Diameter: 18 in. Orifice 1 Diameter: 2 in. Elevation: 0 ft. Orifice 1 Diameter: 4 in. Elevation: 3 ft. Element Flows To: Outlet 1 Outlet 2 PPC, ___________________________________________________________________ Pond Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 305.0 0.009 0.000 0.000 0.000 305.1 0.009 0.001 0.027 0.014 305.1 0.009 0.001 0.038 0.014 305.2 0.009 0.002 0.047 0.014 305.3 0.009 0.002 0.054 0.014 305.3 0.009 0.003 0.061 0.014 305.4 0.009 0.004 0.066 0.014 305.5 0.009 0.004 0.072 0.014 305.5 0.009 0.005 0.077 0.014 305.6 0.009 0.006 0.081 0.014 305.7 0.009 0.006 0.086 0.014 305.7 0.009 0.007 0.090 0.014 305.8 0.009 0.007 0.094 0.014 305.9 0.009 0.008 0.098 0.014 305.9 0.009 0.009 0.101 0.014 306.0 0.009 0.009 0.105 0.014 306.1 0.009 0.010 0.109 0.014 306.1 0.009 0.010 0.112 0.014 306.2 0.009 0.011 0.115 0.014 306.3 0.009 0.012 0.118 0.014 306.3 0.009 0.012 0.121 0.014 306.4 0.009 0.013 0.124 0.014 306.5 0.009 0.013 0.127 0.014 306.5 0.009 0.014 0.130 0.014 306.6 0.009 0.015 0.133 0.014 306.7 0.009 0.015 0.136 0.014 306.7 0.009 0.016 0.138 0.014 306.8 0.009 0.017 0.141 0.014 306.9 0.009 0.017 0.144 0.014 306.9 0.009 0.018 0.146 0.014 307.0 0.009 0.018 0.149 0.014 307.1 0.009 0.019 0.151 0.014 307.1 0.009 0.020 0.153 0.014 307.2 0.009 0.020 0.156 0.014 307.3 0.009 0.021 0.158 0.014


Page A-24

307.3 0.009 0.021 0.160 0.014 307.4 0.009 0.022 0.163 0.014 307.5 0.009 0.023 0.165 0.014 307.5 0.009 0.023 0.167 0.014 307.6 0.009 0.024 0.169 0.014 307.7 0.009 0.024 0.172 0.014 307.7 0.009 0.025 0.174 0.014 307.8 0.009 0.026 0.176 0.014 307.9 0.009 0.026 0.178 0.014 307.9 0.009 0.027 0.180 0.014 308.0 0.009 0.028 0.182 0.014 308.1 0.009 0.028 0.292 0.014 308.1 0.009 0.029 0.339 0.014 308.2 0.009 0.029 0.376 0.014 308.3 0.009 0.030 0.407 0.014 308.3 0.009 0.031 0.434 0.014 308.4 0.009 0.031 0.459 0.014 308.5 0.009 0.032 0.483 0.014 308.5 0.009 0.032 0.504 0.014 308.6 0.009 0.033 0.525 0.014 308.7 0.009 0.034 0.544 0.014 308.7 0.009 0.034 0.563 0.014 308.8 0.009 0.035 0.581 0.014 308.9 0.009 0.036 0.598 0.014 308.9 0.009 0.036 0.614 0.014 309.0 0.009 0.037 0.630 0.014 309.1 0.009 0.037 0.646 0.014 309.1 0.009 0.038 0.661 0.014 309.2 0.009 0.039 0.676 0.014 309.3 0.009 0.039 0.690 0.014 309.3 0.009 0.040 0.704 0.014 309.4 0.009 0.040 0.718 0.014 309.5 0.009 0.041 0.731 0.014 309.5 0.009 0.042 0.744 0.014 309.6 0.009 0.042 0.757 0.014 309.7 0.009 0.043 0.769 0.014 309.7 0.009 0.043 0.782 0.014 309.8 0.009 0.044 0.794 0.014 309.9 0.009 0.045 0.806 0.014 309.9 0.009 0.045 0.818 0.014 310.0 0.009 0.046 0.829 0.014 310.1 0.009 0.047 1.092 0.014 310.1 0.009 0.047 1.563 0.014 310.2 0.009 0.048 2.169 0.014 310.3 0.009 0.048 2.885 0.014 310.3 0.009 0.049 3.696 0.014 310.4 0.009 0.050 4.591 0.014 310.5 0.009 0.050 5.563 0.014 310.5 0.009 0.051 6.606 0.014 310.6 0.009 0.051 7.716 0.014 310.7 0.009 0.052 8.888 0.014 310.7 0.009 0.053 10.12 0.014 310.8 0.009 0.053 11.41 0.014 310.9 0.009 0.054 12.75 0.014 310.9 0.009 0.054 14.15 0.014 311.0 0.009 0.055 15.59 0.014 311.1 0.009 0.056 17.09 0.014


Page A-25

___________________________________________________________________ Name : PPC Bottom Length: 5ft. Bottom Width : 5ft. Manning's n : 0.03 Channel bottom slope 1: 0.01 To 1 Channel Left side slope 0: 2 To 1 Channel right side slope 2: 2 To 1 Discharge Structure Riser Height: 0 ft. Riser Diameter: 0 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Channel Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 0.000 0.001 0.000 0.000 0.000 0.111 0.001 0.000 0.644 0.000 0.222 0.001 0.000 2.068 0.000 0.333 0.001 0.000 4.120 0.000 0.444 0.001 0.000 6.755 0.000 0.556 0.001 0.000 9.955 0.000 0.667 0.001 0.000 13.72 0.000 0.778 0.001 0.001 18.04 0.000 0.889 0.001 0.001 22.94 0.000 1.000 0.001 0.001 28.42 0.000 1.111 0.001 0.001 34.49 0.000 1.222 0.001 0.001 41.16 0.000 1.333 0.001 0.001 48.46 0.000 1.444 0.001 0.001 56.38 0.000 1.556 0.001 0.001 64.95 0.000 1.667 0.001 0.002 74.18 0.000 1.778 0.001 0.002 84.09 0.000 1.889 0.001 0.002 94.69 0.000 2.000 0.002 0.002 106.0 0.000 2.111 0.002 0.002 118.0 0.000 2.222 0.002 0.002 130.8 0.000 2.333 0.002 0.003 144.3 0.000 2.444 0.002 0.003 158.5 0.000 2.556 0.002 0.003 173.6 0.000 2.667 0.002 0.003 189.4 0.000 2.778 0.002 0.003 206.0 0.000 2.889 0.002 0.004 223.5 0.000 3.000 0.002 0.004 241.8 0.000 3.111 0.002 0.004 260.9 0.000 3.222 0.002 0.004 280.9 0.000 3.333 0.002 0.004 301.8 0.000 3.444 0.002 0.005 323.6 0.000 3.556 0.002 0.005 346.3 0.000 3.667 0.002 0.005 369.9 0.000


Page A-26

3.778 0.002 0.005 394.4 0.000 3.889 0.002 0.006 419.9 0.000 4.000 0.002 0.006 446.3 0.000 4.111 0.003 0.006 473.7 0.000 4.222 0.003 0.007 502.1 0.000 4.333 0.003 0.007 531.5 0.000 4.444 0.003 0.007 561.9 0.000 4.556 0.003 0.007 593.4 0.000 4.667 0.003 0.008 625.8 0.000 4.778 0.003 0.008 659.4 0.000 4.889 0.003 0.008 693.9 0.000 5.000 0.003 0.009 729.6 0.000 5.111 0.003 0.009 766.3 0.000 5.222 0.003 0.009 804.2 0.000 5.333 0.003 0.010 843.2 0.000 5.444 0.003 0.010 883.3 0.000 5.556 0.003 0.010 924.5 0.000 5.667 0.003 0.011 966.9 0.000 5.778 0.003 0.011 1010. 0.000 5.889 0.003 0.012 1055. 0.000 6.000 0.003 0.012 1101. 0.000 6.111 0.003 0.012 1148. 0.000 6.222 0.004 0.013 1196. 0.000 6.333 0.004 0.013 1246. 0.000 6.444 0.004 0.013 1296. 0.000 6.556 0.004 0.014 1348. 0.000 6.667 0.004 0.014 1402. 0.000 6.778 0.004 0.015 1456. 0.000 6.889 0.004 0.015 1512. 0.000 7.000 0.004 0.016 1569. 0.000 7.111 0.004 0.016 1628. 0.000 7.222 0.004 0.016 1688. 0.000 7.333 0.004 0.017 1749. 0.000 7.444 0.004 0.017 1811. 0.000 7.556 0.004 0.018 1875. 0.000 7.667 0.004 0.018 1940. 0.000 7.778 0.004 0.019 2007. 0.000 7.889 0.004 0.019 2075. 0.000 8.000 0.004 0.020 2144. 0.000 8.111 0.004 0.020 2215. 0.000 8.222 0.004 0.021 2287. 0.000 8.333 0.005 0.021 2360. 0.000 8.444 0.005 0.022 2435. 0.000 8.556 0.005 0.022 2512. 0.000 8.667 0.005 0.023 2590. 0.000 8.778 0.005 0.023 2669. 0.000 8.889 0.005 0.024 2750. 0.000 9.000 0.005 0.024 2833. 0.000 9.111 0.005 0.025 2917. 0.000 9.222 0.005 0.025 3002. 0.000 9.333 0.005 0.026 3089. 0.000 9.444 0.005 0.027 3178. 0.000 9.556 0.005 0.027 3268. 0.000 9.667 0.005 0.028 3359. 0.000 9.778 0.005 0.028 3453. 0.000 9.889 0.005 0.029 3547. 0.000 10.00 0.005 0.029 3644. 0.000


Page A-27

10.11 0.005 0.030 3742. 0.000 ___________________________________________________________________ MITIGATED LAND USE ___________________________________________________________________ ANALYSIS RESULTS Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.109354 5 year 0.172867 10 year 0.216214 25 year 0.271331 50 year 0.312252 100 year 0.352857 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.141221 5 year 0.279309 10 year 0.389766 25 year 0.546599 50 year 0.673793 100 year 0.808346 ___________________________________________________________________ Yearly Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1950 0.014 0.118 1951 0.147 0.133 1952 0.095 0.128 1953 0.076 0.075 1954 0.077 0.050 1955 0.125 0.102 1956 0.213 0.298 1957 0.135 0.139 1958 0.178 0.310 1959 0.147 0.549 1960 0.122 0.166 1961 0.117 0.175 1962 0.119 0.473 1963 0.073 0.226 1964 0.123 0.158 1965 0.121 0.159 1966 0.094 0.076 1967 0.055 0.015 1968 0.170 0.159 1969 0.162 0.271 1970 0.076 0.137 1971 0.079 0.065 1972 0.139 0.114 1973 0.133 0.413


Page A-28

1974 0.061 0.079 1975 0.102 0.120 1976 0.085 0.072 1977 0.091 0.172 1978 0.034 0.116 1979 0.082 0.020 1980 0.212 0.473 1981 0.089 0.114 1982 0.095 0.044 1983 0.129 0.196 1984 0.091 0.152 1985 0.105 0.143 1986 0.166 0.174 1987 0.427 0.597 1988 0.142 0.214 1989 0.093 0.112 1990 0.087 0.013 1991 0.095 0.114 1992 0.112 0.119 1993 0.081 0.093 1994 0.057 0.086 1995 0.047 0.089 1996 0.093 0.128 1997 0.255 0.277 1998 0.479 1.009 ___________________________________________________________________ Ranked Yearly Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.4787 1.0089 2 0.4271 0.5972 3 0.2552 0.5490 4 0.2130 0.4734 5 0.2123 0.4731 6 0.1779 0.4130 7 0.1700 0.3103 8 0.1657 0.2979 9 0.1621 0.2770 10 0.1471 0.2714 11 0.1469 0.2265 12 0.1424 0.2138 13 0.1386 0.1957 14 0.1349 0.1746 15 0.1327 0.1743 16 0.1286 0.1722 17 0.1252 0.1661 18 0.1230 0.1594 19 0.1217 0.1587 20 0.1205 0.1576 21 0.1191 0.1522 22 0.1173 0.1431 23 0.1121 0.1385 24 0.1052 0.1370 25 0.1022 0.1326 26 0.0953 0.1283 27 0.0951 0.1280


Page A-29

28 0.0947 0.1202 29 0.0941 0.1193 30 0.0932 0.1176 31 0.0925 0.1162 32 0.0914 0.1144 33 0.0909 0.1142 34 0.0890 0.1142 35 0.0869 0.1115 36 0.0852 0.1022 37 0.0816 0.0933 38 0.0809 0.0887 39 0.0793 0.0856 40 0.0766 0.0786 41 0.0764 0.0761 42 0.0762 0.0745 43 0.0733 0.0724 44 0.0613 0.0650 45 0.0568 0.0501 46 0.0551 0.0440 47 0.0474 0.0202 48 0.0337 0.0155 49 0.0138 0.0129 ___________________________________________________________________ POC #1 The Facility PASSED The Facility PASSED. Flow(CFS) Predev Dev Percentage Pass/Fail 0.0547 3340 745 22 Pass 0.0573 2972 708 23 Pass 0.0599 2757 685 24 Pass 0.0625 2511 652 25 Pass 0.0651 2268 621 27 Pass 0.0677 2125 603 28 Pass 0.0703 1892 579 30 Pass 0.0729 1741 552 31 Pass 0.0755 1570 520 33 Pass 0.0781 1405 493 35 Pass 0.0807 1313 469 35 Pass 0.0833 1200 439 36 Pass 0.0859 1121 421 37 Pass 0.0885 1009 388 38 Pass 0.0911 910 364 40 Pass 0.0937 848 348 41 Pass 0.0963 773 324 41 Pass 0.0989 724 308 42 Pass 0.1015 656 295 44 Pass 0.1041 606 273 45 Pass 0.1067 573 269 46 Pass 0.1093 536 252 47 Pass 0.1119 512 244 47 Pass 0.1145 481 233 48 Pass 0.1171 444 219 49 Pass 0.1197 417 210 50 Pass


Page A-30

0.1223 377 200 53 Pass 0.1249 354 194 54 Pass 0.1275 322 182 56 Pass 0.1301 295 169 57 Pass 0.1327 279 163 58 Pass 0.1353 256 151 58 Pass 0.1379 246 147 59 Pass 0.1405 237 137 57 Pass 0.1431 221 131 59 Pass 0.1457 216 127 58 Pass 0.1483 201 116 57 Pass 0.1509 195 110 56 Pass 0.1535 183 103 56 Pass 0.1561 170 96 56 Pass 0.1587 166 92 55 Pass 0.1613 154 87 56 Pass 0.1640 146 84 57 Pass 0.1666 135 83 61 Pass 0.1692 129 77 59 Pass 0.1718 124 74 59 Pass 0.1744 118 72 61 Pass 0.1770 115 69 60 Pass 0.1796 110 67 60 Pass 0.1822 107 66 61 Pass 0.1848 106 65 61 Pass 0.1874 106 63 59 Pass 0.1900 103 63 61 Pass 0.1926 102 62 60 Pass 0.1952 101 60 59 Pass 0.1978 98 59 60 Pass 0.2004 97 58 59 Pass 0.2030 97 58 59 Pass 0.2056 91 57 62 Pass 0.2082 91 57 62 Pass 0.2108 91 56 61 Pass 0.2134 86 56 65 Pass 0.2160 83 55 66 Pass 0.2186 81 55 67 Pass 0.2212 77 55 71 Pass 0.2238 77 55 71 Pass 0.2264 76 54 71 Pass 0.2290 73 53 72 Pass 0.2316 69 52 75 Pass 0.2342 69 51 73 Pass 0.2368 68 50 73 Pass 0.2394 67 49 73 Pass 0.2420 64 49 76 Pass 0.2446 63 48 76 Pass 0.2472 60 46 76 Pass 0.2498 59 45 76 Pass 0.2524 58 45 77 Pass 0.2550 57 45 78 Pass 0.2576 55 45 81 Pass 0.2602 54 44 81 Pass 0.2628 54 43 79 Pass 0.2654 54 41 75 Pass 0.2680 53 40 75 Pass


Page A-31

0.2706 52 40 76 Pass 0.2732 51 37 72 Pass 0.2758 51 37 72 Pass 0.2784 50 36 72 Pass 0.2810 49 35 71 Pass 0.2836 48 34 70 Pass 0.2862 48 33 68 Pass 0.2888 48 33 68 Pass 0.2914 47 33 70 Pass 0.2940 46 33 71 Pass 0.2966 45 33 73 Pass 0.2992 44 32 72 Pass 0.3018 43 30 69 Pass 0.3044 43 29 67 Pass 0.3070 42 28 66 Pass 0.3097 42 28 66 Pass 0.3123 42 27 64 Pass _____________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC 1. On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. ___________________________________________________________________ This program and accompanying documentation is provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by the user. Clear Creek Solutions and the Washington State Department of Ecology disclaims all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions and/or the Washington State Department of Ecology be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions or the Washington State Department of Ecology has been advised of the possibility of such damages.

Figure A2-1 West TDA Flow Durations


Page A-32

A3 East TDA WWHM Analyses Western Washington Hydrology Model PROJECT REPORT ___________________________________________________________________ Project Name: easttdalid Site Address: City : Report Date : 8/7/2008 Gage : Everett Data Start : 1948/10/01 Data End : 1997/09/30 Precip Scale: 0.80 ___________________________________________________________________ ___________________________________________________________________ PREDEVELOPED LAND USE Name : Northeast Bypass: No GroundWater: No Pervious Land Use Acres A B, Forest, Flat .002 A B, Forest, Mod .028 A B, Forest, Steep .202 C, Forest, Flat .37 C, Forest, Mod 1.413 C, Forest, Steep 1.929


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Impervious Land Use Acres ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater PPC, PPC, ___________________________________________________________________ Name : Southeast Bypass: No GroundWater: No Pervious Land Use Acres A B, Forest, Mod .065 A B, Forest, Steep .229 C, Forest, Mod .423 C, Forest, Steep 1.69 Impervious Land Use Acres ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater PPC, PPC, ___________________________________________________________________ Name : PPC Bottom Length: 5ft. Bottom Width : 5ft. Manning's n : 0.03 Channel bottom slope 1: 0.01 To 1 Channel Left side slope 0: 2 To 1 Channel right side slope 2: 2 To 1 Discharge Structure Riser Height: 0 ft. Riser Diameter: 0 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Channel Hydraulic Table


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Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 0.000 0.001 0.000 0.000 0.000 0.111 0.001 0.000 0.644 0.000 0.222 0.001 0.000 2.068 0.000 0.333 0.001 0.000 4.120 0.000 0.444 0.001 0.000 6.755 0.000 0.556 0.001 0.000 9.955 0.000 0.667 0.001 0.000 13.72 0.000 0.778 0.001 0.001 18.04 0.000 0.889 0.001 0.001 22.94 0.000 1.000 0.001 0.001 28.42 0.000 1.111 0.001 0.001 34.49 0.000 1.222 0.001 0.001 41.16 0.000 1.333 0.001 0.001 48.46 0.000 1.444 0.001 0.001 56.38 0.000 1.556 0.001 0.001 64.95 0.000 1.667 0.001 0.002 74.18 0.000 1.778 0.001 0.002 84.09 0.000 1.889 0.001 0.002 94.69 0.000 2.000 0.002 0.002 106.0 0.000 2.111 0.002 0.002 118.0 0.000 2.222 0.002 0.002 130.8 0.000 2.333 0.002 0.003 144.3 0.000 2.444 0.002 0.003 158.5 0.000 2.556 0.002 0.003 173.6 0.000 2.667 0.002 0.003 189.4 0.000 2.778 0.002 0.003 206.0 0.000 2.889 0.002 0.004 223.5 0.000 3.000 0.002 0.004 241.8 0.000 3.111 0.002 0.004 260.9 0.000 3.222 0.002 0.004 280.9 0.000 3.333 0.002 0.004 301.8 0.000 3.444 0.002 0.005 323.6 0.000 3.556 0.002 0.005 346.3 0.000 3.667 0.002 0.005 369.9 0.000 3.778 0.002 0.005 394.4 0.000 3.889 0.002 0.006 419.9 0.000 4.000 0.002 0.006 446.3 0.000 4.111 0.003 0.006 473.7 0.000 4.222 0.003 0.007 502.1 0.000 4.333 0.003 0.007 531.5 0.000 4.444 0.003 0.007 561.9 0.000 4.556 0.003 0.007 593.4 0.000 4.667 0.003 0.008 625.8 0.000 4.778 0.003 0.008 659.4 0.000 4.889 0.003 0.008 693.9 0.000 5.000 0.003 0.009 729.6 0.000 5.111 0.003 0.009 766.3 0.000 5.222 0.003 0.009 804.2 0.000 5.333 0.003 0.010 843.2 0.000 5.444 0.003 0.010 883.3 0.000 5.556 0.003 0.010 924.5 0.000 5.667 0.003 0.011 966.9 0.000 5.778 0.003 0.011 1010. 0.000 5.889 0.003 0.012 1055. 0.000 6.000 0.003 0.012 1101. 0.000 6.111 0.003 0.012 1148. 0.000


Page A-35

6.222 0.004 0.013 1196. 0.000 6.333 0.004 0.013 1246. 0.000 6.444 0.004 0.013 1296. 0.000 6.556 0.004 0.014 1348. 0.000 6.667 0.004 0.014 1402. 0.000 6.778 0.004 0.015 1456. 0.000 6.889 0.004 0.015 1512. 0.000 7.000 0.004 0.016 1569. 0.000 7.111 0.004 0.016 1628. 0.000 7.222 0.004 0.016 1688. 0.000 7.333 0.004 0.017 1749. 0.000 7.444 0.004 0.017 1811. 0.000 7.556 0.004 0.018 1875. 0.000 7.667 0.004 0.018 1940. 0.000 7.778 0.004 0.019 2007. 0.000 7.889 0.004 0.019 2075. 0.000 8.000 0.004 0.020 2144. 0.000 8.111 0.004 0.020 2215. 0.000 8.222 0.004 0.021 2287. 0.000 8.333 0.005 0.021 2360. 0.000 8.444 0.005 0.022 2435. 0.000 8.556 0.005 0.022 2512. 0.000 8.667 0.005 0.023 2590. 0.000 8.778 0.005 0.023 2669. 0.000 8.889 0.005 0.024 2750. 0.000 9.000 0.005 0.024 2833. 0.000 9.111 0.005 0.025 2917. 0.000 9.222 0.005 0.025 3002. 0.000 9.333 0.005 0.026 3089. 0.000 9.444 0.005 0.027 3178. 0.000 9.556 0.005 0.027 3268. 0.000 9.667 0.005 0.028 3359. 0.000 9.778 0.005 0.028 3453. 0.000 9.889 0.005 0.029 3547. 0.000 10.00 0.005 0.029 3644. 0.000 10.11 0.005 0.030 3742. 0.000 ___________________________________________________________________ Name : Northeast2 Bypass: No GroundWater: No Pervious Land Use Acres C, Forest, Steep .012 C, Lawn, Flat .76 Impervious Land Use Acres ROADS FLAT 0.204 ROADS MOD 0.239 ROOF TOPS FLAT 0.341 DRIVEWAYS FLAT 0.192 ___________________________________________________________________


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Element Flows To: Surface Interflow Groundwater Northeast1 swale, Northeast1 swale, ___________________________________________________________________ Name : Northeast1 Bypass: No GroundWater: No Pervious Land Use Acres A B, Lawn, Flat .319 C, Forest, Steep .145 C, Lawn, Flat 1.401 Impervious Land Use Acres ROADS FLAT 0.342 ROOF TOPS FLAT 0.424 DRIVEWAYS FLAT 0.104 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Northeast1 swale, Northeast1 swale, ___________________________________________________________________ Name : Southeast Bypass: No GroundWater: No Pervious Land Use Acres C, Forest, Mod .127 C, Lawn, Flat .325 Impervious Land Use Acres ROADS FLAT 0.246 ROOF TOPS FLAT 0.083 DRIVEWAYS FLAT 0.049 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Southeast vault, Southeast vault, ___________________________________________________________________


Page A-37

Name : East Bypass: No GroundWater: No Pervious Land Use Acres A B, Forest, Steep .582 C, Lawn, Flat .489 Impervious Land Use Acres ROOF TOPS FLAT 0.362 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater PPC, PPC, ___________________________________________________________________ Name : Northeast1 swale Bottom Length: 330ft. Bottom Width: 2ft. Depth : 2ft. Volume at riser head : 0.0379ft. Infiltration On Infiltration rate : 6 Infiltration saftey factor : 0.25 Side slope 1: 3 To 1 Side slope 2: 0 To 1 Side slope 3: 3 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 1 ft. Riser Diameter: 48 in. Element Flows To: Outlet 1 Outlet 2 Northeast vault, ___________________________________________________________________ Pond Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 0.000 0.015 0.000 0.000 0.000 0.022 0.016 0.000 0.000 0.023 0.044 0.017 0.001 0.000 0.023 0.067 0.018 0.001 0.000 0.023 0.089 0.019 0.002 0.000 0.023 0.111 0.020 0.002 0.000 0.023


Page A-38

0.133 0.021 0.002 0.000 0.023 0.156 0.022 0.003 0.000 0.023 0.178 0.023 0.003 0.000 0.023 0.200 0.024 0.004 0.000 0.023 0.222 0.025 0.004 0.000 0.023 0.244 0.026 0.005 0.000 0.023 0.267 0.027 0.006 0.000 0.023 0.289 0.028 0.006 0.000 0.023 0.311 0.029 0.007 0.000 0.023 0.333 0.030 0.008 0.000 0.023 0.356 0.031 0.008 0.000 0.023 0.378 0.032 0.009 0.000 0.023 0.400 0.033 0.010 0.000 0.023 0.422 0.034 0.010 0.000 0.023 0.444 0.035 0.011 0.000 0.023 0.467 0.036 0.012 0.000 0.023 0.489 0.037 0.013 0.000 0.023 0.511 0.038 0.014 0.000 0.023 0.533 0.039 0.015 0.000 0.023 0.556 0.040 0.015 0.000 0.023 0.578 0.041 0.016 0.000 0.023 0.600 0.042 0.017 0.000 0.023 0.622 0.043 0.018 0.000 0.023 0.644 0.044 0.019 0.000 0.023 0.667 0.045 0.020 0.000 0.023 0.689 0.046 0.021 0.000 0.023 0.711 0.047 0.022 0.000 0.023 0.733 0.048 0.023 0.000 0.023 0.756 0.049 0.024 0.000 0.023 0.778 0.051 0.026 0.000 0.023 0.800 0.052 0.027 0.000 0.023 0.822 0.053 0.028 0.000 0.023 0.844 0.054 0.029 0.000 0.023 0.867 0.055 0.030 0.000 0.023 0.889 0.056 0.031 0.000 0.023 0.911 0.057 0.033 0.000 0.023 0.933 0.058 0.034 0.000 0.023 0.956 0.059 0.035 0.000 0.023 0.978 0.060 0.037 0.000 0.023 1.000 0.061 0.038 0.000 0.023 1.022 0.062 0.039 0.129 0.023 1.044 0.063 0.041 0.365 0.023 1.067 0.064 0.042 0.671 0.023 1.089 0.065 0.043 1.032 0.023 1.111 0.066 0.045 1.443 0.023 1.133 0.067 0.046 1.897 0.023 1.156 0.068 0.048 2.390 0.023 1.178 0.069 0.049 2.920 0.023 1.200 0.070 0.051 3.484 0.023 1.222 0.071 0.052 4.081 0.023 1.244 0.072 0.054 4.708 0.023 1.267 0.073 0.056 5.364 0.023 1.289 0.074 0.057 6.049 0.023 1.311 0.075 0.059 6.760 0.023 1.333 0.076 0.061 7.497 0.023 1.356 0.077 0.062 8.259 0.023 1.378 0.078 0.064 9.045 0.023


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1.400 0.079 0.066 9.855 0.023 1.422 0.080 0.068 10.69 0.023 1.444 0.081 0.069 11.54 0.023 1.467 0.082 0.071 12.42 0.023 1.489 0.083 0.073 13.32 0.023 1.511 0.084 0.075 14.23 0.023 1.533 0.085 0.077 15.17 0.023 1.556 0.086 0.079 16.13 0.023 1.578 0.087 0.080 17.11 0.023 1.600 0.088 0.082 18.11 0.023 1.622 0.089 0.084 19.12 0.023 1.644 0.090 0.086 20.15 0.023 1.667 0.091 0.088 21.20 0.023 1.689 0.092 0.090 22.27 0.023 1.711 0.093 0.092 23.36 0.023 1.733 0.094 0.095 24.46 0.023 1.756 0.095 0.097 25.58 0.023 1.778 0.096 0.099 26.72 0.023 1.800 0.097 0.101 27.87 0.023 1.822 0.098 0.103 29.04 0.023 1.844 0.099 0.105 30.23 0.023 1.867 0.100 0.107 31.43 0.023 1.889 0.101 0.110 32.65 0.023 1.911 0.102 0.112 33.88 0.023 1.933 0.103 0.114 35.13 0.023 1.956 0.104 0.117 36.39 0.023 1.978 0.105 0.119 37.66 0.023 2.000 0.106 0.121 38.96 0.023 2.022 0.107 0.124 40.26 0.023 ___________________________________________________________________ Name : Southeast vault Bottom Length: 40ft. Bottom Width: 20ft. Depth : 9ft. Volume at riser head : 0.0000ft. Side slope 1: 0 To 1 Side slope 2: 0 To 1 Side slope 3: 0 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 8 ft. Riser Diameter: 18 in. Orifice 1 Diameter: 0.25 in. Elevation: 0 ft. Orifice 1 Diameter: 1 in. Elevation: 6 ft. Element Flows To: Outlet 1 Outlet 2 PPC, ___________________________________________________________________ Pond Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs)


Page A-40

0.000 0.018 0.000 0.000 0.000 0.100 0.018 0.002 0.001 0.000 0.200 0.018 0.004 0.001 0.000 0.300 0.018 0.006 0.001 0.000 0.400 0.018 0.007 0.001 0.000 0.500 0.018 0.009 0.001 0.000 0.600 0.018 0.011 0.001 0.000 0.700 0.018 0.013 0.001 0.000 0.800 0.018 0.015 0.001 0.000 0.900 0.018 0.017 0.002 0.000 1.000 0.018 0.018 0.002 0.000 1.100 0.018 0.020 0.002 0.000 1.200 0.018 0.022 0.002 0.000 1.300 0.018 0.024 0.002 0.000 1.400 0.018 0.026 0.002 0.000 1.500 0.018 0.028 0.002 0.000 1.600 0.018 0.029 0.002 0.000 1.700 0.018 0.031 0.002 0.000 1.800 0.018 0.033 0.002 0.000 1.900 0.018 0.035 0.002 0.000 2.000 0.018 0.037 0.002 0.000 2.100 0.018 0.039 0.002 0.000 2.200 0.018 0.040 0.002 0.000 2.300 0.018 0.042 0.002 0.000 2.400 0.018 0.044 0.003 0.000 2.500 0.018 0.046 0.003 0.000 2.600 0.018 0.048 0.003 0.000 2.700 0.018 0.050 0.003 0.000 2.800 0.018 0.051 0.003 0.000 2.900 0.018 0.053 0.003 0.000 3.000 0.018 0.055 0.003 0.000 3.100 0.018 0.057 0.003 0.000 3.200 0.018 0.059 0.003 0.000 3.300 0.018 0.061 0.003 0.000 3.400 0.018 0.062 0.003 0.000 3.500 0.018 0.064 0.003 0.000 3.600 0.018 0.066 0.003 0.000 3.700 0.018 0.068 0.003 0.000 3.800 0.018 0.070 0.003 0.000 3.900 0.018 0.072 0.003 0.000 4.000 0.018 0.073 0.003 0.000 4.100 0.018 0.075 0.003 0.000 4.200 0.018 0.077 0.003 0.000 4.300 0.018 0.079 0.003 0.000 4.400 0.018 0.081 0.003 0.000 4.500 0.018 0.083 0.003 0.000 4.600 0.018 0.084 0.004 0.000 4.700 0.018 0.086 0.004 0.000 4.800 0.018 0.088 0.004 0.000 4.900 0.018 0.090 0.004 0.000 5.000 0.018 0.092 0.004 0.000 5.100 0.018 0.094 0.004 0.000 5.200 0.018 0.096 0.004 0.000 5.300 0.018 0.097 0.004 0.000 5.400 0.018 0.099 0.004 0.000 5.500 0.018 0.101 0.004 0.000 5.600 0.018 0.103 0.004 0.000


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5.700 0.018 0.105 0.004 0.000 5.800 0.018 0.107 0.004 0.000 5.900 0.018 0.108 0.004 0.000 6.000 0.018 0.110 0.004 0.000 6.100 0.018 0.112 0.012 0.000 6.200 0.018 0.114 0.016 0.000 6.300 0.018 0.116 0.019 0.000 6.400 0.018 0.118 0.021 0.000 6.500 0.018 0.119 0.023 0.000 6.600 0.018 0.121 0.025 0.000 6.700 0.018 0.123 0.026 0.000 6.800 0.018 0.125 0.028 0.000 6.900 0.018 0.127 0.029 0.000 7.000 0.018 0.129 0.031 0.000 7.100 0.018 0.130 0.032 0.000 7.200 0.018 0.132 0.033 0.000 7.300 0.018 0.134 0.034 0.000 7.400 0.018 0.136 0.036 0.000 7.500 0.018 0.138 0.037 0.000 7.600 0.018 0.140 0.038 0.000 7.700 0.018 0.141 0.039 0.000 7.800 0.018 0.143 0.040 0.000 7.900 0.018 0.145 0.041 0.000 8.000 0.018 0.147 0.042 0.000 8.100 0.018 0.149 0.505 0.000 8.200 0.018 0.151 1.350 0.000 8.300 0.018 0.152 2.445 0.000 8.400 0.018 0.154 3.741 0.000 8.500 0.018 0.156 5.211 0.000 8.600 0.018 0.158 6.837 0.000 8.700 0.018 0.160 8.604 0.000 8.800 0.018 0.162 10.50 0.000 8.900 0.018 0.163 12.52 0.000 9.000 0.018 0.165 14.66 0.000 9.100 0.018 0.167 16.90 0.000 ___________________________________________________________________ Name : Northeast vault Bottom Length: 80ft. Bottom Width: 40ft. Depth : 10ft. Volume at riser head : 0.6693ft. Infiltration On Infiltration rate : 6 Infiltration saftey factor : 0.25 Side slope 1: 0 To 1 Side slope 2: 0 To 1 Side slope 3: 0 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 9 ft. Riser Diameter: 18 in. Orifice 1 Diameter: 1 in. Elevation: 0 ft. Orifice 1 Diameter: 2 in. Elevation: 6 ft. Element Flows To:


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Outlet 1 Outlet 2 PPC, ___________________________________________________________________ Pond Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 0.000 0.073 0.000 0.000 0.000 0.111 0.073 0.008 0.009 0.111 0.222 0.073 0.016 0.012 0.111 0.333 0.073 0.024 0.015 0.111 0.444 0.073 0.033 0.018 0.111 0.556 0.073 0.041 0.020 0.111 0.667 0.073 0.049 0.021 0.111 0.778 0.073 0.057 0.023 0.111 0.889 0.073 0.065 0.025 0.111 1.000 0.073 0.073 0.026 0.111 1.111 0.073 0.082 0.028 0.111 1.222 0.073 0.090 0.029 0.111 1.333 0.073 0.098 0.030 0.111 1.444 0.073 0.106 0.032 0.111 1.556 0.073 0.114 0.033 0.111 1.667 0.073 0.122 0.034 0.111 1.778 0.073 0.131 0.035 0.111 1.889 0.073 0.139 0.036 0.111 2.000 0.073 0.147 0.037 0.111 2.111 0.073 0.155 0.038 0.111 2.222 0.073 0.163 0.039 0.111 2.333 0.073 0.171 0.040 0.111 2.444 0.073 0.180 0.041 0.111 2.556 0.073 0.188 0.042 0.111 2.667 0.073 0.196 0.043 0.111 2.778 0.073 0.204 0.044 0.111 2.889 0.073 0.212 0.045 0.111 3.000 0.073 0.220 0.045 0.111 3.111 0.073 0.229 0.046 0.111 3.222 0.073 0.237 0.047 0.111 3.333 0.073 0.245 0.048 0.111 3.444 0.073 0.253 0.049 0.111 3.556 0.073 0.261 0.050 0.111 3.667 0.073 0.269 0.050 0.111 3.778 0.073 0.278 0.051 0.111 3.889 0.073 0.286 0.052 0.111 4.000 0.073 0.294 0.053 0.111 4.111 0.073 0.302 0.053 0.111 4.222 0.073 0.310 0.054 0.111 4.333 0.073 0.318 0.055 0.111 4.444 0.073 0.326 0.055 0.111 4.556 0.073 0.335 0.056 0.111 4.667 0.073 0.343 0.057 0.111 4.778 0.073 0.351 0.057 0.111 4.889 0.073 0.359 0.058 0.111 5.000 0.073 0.367 0.059 0.111 5.111 0.073 0.375 0.059 0.111 5.222 0.073 0.384 0.060 0.111


Page A-43

5.333 0.073 0.392 0.061 0.111 5.444 0.073 0.400 0.061 0.111 5.556 0.073 0.408 0.062 0.111 5.667 0.073 0.416 0.063 0.111 5.778 0.073 0.424 0.063 0.111 5.889 0.073 0.433 0.064 0.111 6.000 0.073 0.441 0.064 0.111 6.111 0.073 0.449 0.100 0.111 6.222 0.073 0.457 0.115 0.111 6.333 0.073 0.465 0.127 0.111 6.444 0.073 0.473 0.137 0.111 6.556 0.073 0.482 0.146 0.111 6.667 0.073 0.490 0.154 0.111 6.778 0.073 0.498 0.161 0.111 6.889 0.073 0.506 0.168 0.111 7.000 0.073 0.514 0.175 0.111 7.111 0.073 0.522 0.181 0.111 7.222 0.073 0.531 0.187 0.111 7.333 0.073 0.539 0.192 0.111 7.444 0.073 0.547 0.198 0.111 7.556 0.073 0.555 0.203 0.111 7.667 0.073 0.563 0.208 0.111 7.778 0.073 0.571 0.213 0.111 7.889 0.073 0.580 0.218 0.111 8.000 0.073 0.588 0.223 0.111 8.111 0.073 0.596 0.227 0.111 8.222 0.073 0.604 0.232 0.111 8.333 0.073 0.612 0.236 0.111 8.444 0.073 0.620 0.241 0.111 8.556 0.073 0.629 0.245 0.111 8.667 0.073 0.637 0.249 0.111 8.778 0.073 0.645 0.253 0.111 8.889 0.073 0.653 0.257 0.111 9.000 0.073 0.661 0.261 0.111 9.111 0.073 0.669 0.806 0.111 9.222 0.073 0.677 1.799 0.111 9.333 0.073 0.686 3.083 0.111 9.444 0.073 0.694 4.604 0.111 9.556 0.073 0.702 6.328 0.111 9.667 0.073 0.710 8.235 0.111 9.778 0.073 0.718 10.31 0.111 9.889 0.073 0.726 12.53 0.111 10.00 0.073 0.735 14.90 0.111 10.11 0.073 0.743 17.41 0.111 ___________________________________________________________________ Name : PPC Bottom Length: 5ft. Bottom Width : 5ft. Manning's n : 0.03 Channel bottom slope 1: 0.01 To 1 Channel Left side slope 0: 2 To 1 Channel right side slope 2: 2 To 1 Discharge Structure Riser Height: 0 ft. Riser Diameter: 0 in.


Page A-44

Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Channel Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 0.000 0.001 0.000 0.000 0.000 0.111 0.001 0.000 0.644 0.000 0.222 0.001 0.000 2.068 0.000 0.333 0.001 0.000 4.120 0.000 0.444 0.001 0.000 6.755 0.000 0.556 0.001 0.000 9.955 0.000 0.667 0.001 0.000 13.72 0.000 0.778 0.001 0.001 18.04 0.000 0.889 0.001 0.001 22.94 0.000 1.000 0.001 0.001 28.42 0.000 1.111 0.001 0.001 34.49 0.000 1.222 0.001 0.001 41.16 0.000 1.333 0.001 0.001 48.46 0.000 1.444 0.001 0.001 56.38 0.000 1.556 0.001 0.001 64.95 0.000 1.667 0.001 0.002 74.18 0.000 1.778 0.001 0.002 84.09 0.000 1.889 0.001 0.002 94.69 0.000 2.000 0.002 0.002 106.0 0.000 2.111 0.002 0.002 118.0 0.000 2.222 0.002 0.002 130.8 0.000 2.333 0.002 0.003 144.3 0.000 2.444 0.002 0.003 158.5 0.000 2.556 0.002 0.003 173.6 0.000 2.667 0.002 0.003 189.4 0.000 2.778 0.002 0.003 206.0 0.000 2.889 0.002 0.004 223.5 0.000 3.000 0.002 0.004 241.8 0.000 3.111 0.002 0.004 260.9 0.000 3.222 0.002 0.004 280.9 0.000 3.333 0.002 0.004 301.8 0.000 3.444 0.002 0.005 323.6 0.000 3.556 0.002 0.005 346.3 0.000 3.667 0.002 0.005 369.9 0.000 3.778 0.002 0.005 394.4 0.000 3.889 0.002 0.006 419.9 0.000 4.000 0.002 0.006 446.3 0.000 4.111 0.003 0.006 473.7 0.000 4.222 0.003 0.007 502.1 0.000 4.333 0.003 0.007 531.5 0.000 4.444 0.003 0.007 561.9 0.000 4.556 0.003 0.007 593.4 0.000 4.667 0.003 0.008 625.8 0.000 4.778 0.003 0.008 659.4 0.000 4.889 0.003 0.008 693.9 0.000 5.000 0.003 0.009 729.6 0.000 5.111 0.003 0.009 766.3 0.000


Page A-45

5.222 0.003 0.009 804.2 0.000 5.333 0.003 0.010 843.2 0.000 5.444 0.003 0.010 883.3 0.000 5.556 0.003 0.010 924.5 0.000 5.667 0.003 0.011 966.9 0.000 5.778 0.003 0.011 1010. 0.000 5.889 0.003 0.012 1055. 0.000 6.000 0.003 0.012 1101. 0.000 6.111 0.003 0.012 1148. 0.000 6.222 0.004 0.013 1196. 0.000 6.333 0.004 0.013 1246. 0.000 6.444 0.004 0.013 1296. 0.000 6.556 0.004 0.014 1348. 0.000 6.667 0.004 0.014 1402. 0.000 6.778 0.004 0.015 1456. 0.000 6.889 0.004 0.015 1512. 0.000 7.000 0.004 0.016 1569. 0.000 7.111 0.004 0.016 1628. 0.000 7.222 0.004 0.016 1688. 0.000 7.333 0.004 0.017 1749. 0.000 7.444 0.004 0.017 1811. 0.000 7.556 0.004 0.018 1875. 0.000 7.667 0.004 0.018 1940. 0.000 7.778 0.004 0.019 2007. 0.000 7.889 0.004 0.019 2075. 0.000 8.000 0.004 0.020 2144. 0.000 8.111 0.004 0.020 2215. 0.000 8.222 0.004 0.021 2287. 0.000 8.333 0.005 0.021 2360. 0.000 8.444 0.005 0.022 2435. 0.000 8.556 0.005 0.022 2512. 0.000 8.667 0.005 0.023 2590. 0.000 8.778 0.005 0.023 2669. 0.000 8.889 0.005 0.024 2750. 0.000 9.000 0.005 0.024 2833. 0.000 9.111 0.005 0.025 2917. 0.000 9.222 0.005 0.025 3002. 0.000 9.333 0.005 0.026 3089. 0.000 9.444 0.005 0.027 3178. 0.000 9.556 0.005 0.027 3268. 0.000 9.667 0.005 0.028 3359. 0.000 9.778 0.005 0.028 3453. 0.000 9.889 0.005 0.029 3547. 0.000 10.00 0.005 0.029 3644. 0.000 10.11 0.005 0.030 3742. 0.000 ___________________________________________________________________ MITIGATED LAND USE ___________________________________________________________________ ANALYSIS RESULTS Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs)


Page A-46

2 year 0.081828 5 year 0.128413 10 year 0.160042 25 year 0.200114 50 year 0.229781 100 year 0.259156 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.107591 5 year 0.152511 10 year 0.18656 25 year 0.234764 50 year 0.274624 100 year 0.318031 ___________________________________________________________________ Yearly Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1950 0.011 0.075 1951 0.110 0.162 1952 0.072 0.089 1953 0.058 0.088 1954 0.058 0.104 1955 0.094 0.144 1956 0.158 0.163 1957 0.101 0.089 1958 0.133 0.122 1959 0.110 0.211 1960 0.091 0.091 1961 0.088 0.086 1962 0.089 0.232 1963 0.056 0.117 1964 0.094 0.179 1965 0.090 0.091 1966 0.069 0.062 1967 0.041 0.064 1968 0.126 0.210 1969 0.122 0.133 1970 0.057 0.189 1971 0.059 0.076 1972 0.103 0.121 1973 0.099 0.202 1974 0.047 0.107 1975 0.076 0.118 1976 0.063 0.110 1977 0.068 0.103 1978 0.026 0.077 1979 0.061 0.081 1980 0.158 0.176 1981 0.067 0.077 1982 0.071 0.087 1983 0.095 0.097 1984 0.067 0.097 1985 0.078 0.102 1986 0.123 0.140


Page A-47

1987 0.315 0.211 1988 0.105 0.129 1989 0.069 0.081 1990 0.066 0.109 1991 0.070 0.069 1992 0.083 0.093 1993 0.061 0.086 1994 0.043 0.071 1995 0.036 0.065 1996 0.069 0.076 1997 0.189 0.116 1998 0.354 0.338 ___________________________________________________________________ Ranked Yearly Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.3540 0.3379 2 0.3152 0.2321 3 0.1889 0.2114 4 0.1583 0.2108 5 0.1579 0.2097 6 0.1326 0.2022 7 0.1260 0.1887 8 0.1228 0.1787 9 0.1221 0.1758 10 0.1101 0.1631 11 0.1098 0.1617 12 0.1055 0.1436 13 0.1028 0.1402 14 0.1012 0.1328 15 0.0993 0.1288 16 0.0952 0.1217 17 0.0944 0.1208 18 0.0942 0.1178 19 0.0913 0.1169 20 0.0904 0.1156 21 0.0888 0.1097 22 0.0878 0.1089 23 0.0828 0.1066 24 0.0777 0.1044 25 0.0761 0.1026 26 0.0716 0.1017 27 0.0713 0.0969 28 0.0703 0.0968 29 0.0693 0.0927 30 0.0691 0.0914 31 0.0688 0.0906 32 0.0680 0.0887 33 0.0674 0.0886 34 0.0669 0.0883 35 0.0655 0.0867 36 0.0632 0.0864 37 0.0613 0.0862 38 0.0611 0.0807 39 0.0585 0.0807 40 0.0582 0.0772


Page A-48

41 0.0578 0.0765 42 0.0568 0.0762 43 0.0559 0.0755 44 0.0467 0.0753 45 0.0426 0.0713 46 0.0412 0.0686 47 0.0358 0.0653 48 0.0260 0.0643 49 0.0110 0.0617 ___________________________________________________________________ POC #1 The Facility PASSED The Facility PASSED. Flow(CFS) Predev Dev Percentage Pass/Fail 0.0409 3112 2442 78 Pass 0.0428 2822 2205 78 Pass 0.0447 2593 1984 76 Pass 0.0466 2384 1805 75 Pass 0.0485 2191 1614 73 Pass 0.0505 2003 1445 72 Pass 0.0524 1805 1284 71 Pass 0.0543 1631 1141 69 Pass 0.0562 1493 1018 68 Pass 0.0581 1356 935 68 Pass 0.0600 1247 844 67 Pass 0.0619 1152 769 66 Pass 0.0638 1056 706 66 Pass 0.0657 973 626 64 Pass 0.0676 891 572 64 Pass 0.0695 808 532 65 Pass 0.0714 748 492 65 Pass 0.0733 694 446 64 Pass 0.0753 634 410 64 Pass 0.0772 595 375 63 Pass 0.0791 554 347 62 Pass 0.0810 528 316 59 Pass 0.0829 496 293 59 Pass 0.0848 468 267 57 Pass 0.0867 439 245 55 Pass 0.0886 392 222 56 Pass 0.0905 365 208 56 Pass 0.0924 330 194 58 Pass 0.0943 313 185 59 Pass 0.0962 286 168 58 Pass 0.0981 272 156 57 Pass 0.1001 252 147 58 Pass 0.1020 240 140 58 Pass 0.1039 229 133 58 Pass 0.1058 217 125 57 Pass 0.1077 211 120 56 Pass 0.1096 195 110 56 Pass 0.1115 185 104 56 Pass 0.1134 173 99 57 Pass


Page A-49

0.1153 167 94 56 Pass 0.1172 160 86 53 Pass 0.1191 151 81 53 Pass 0.1210 142 78 54 Pass 0.1229 132 75 56 Pass 0.1249 125 69 55 Pass 0.1268 121 68 56 Pass 0.1287 116 63 54 Pass 0.1306 111 57 51 Pass 0.1325 109 56 51 Pass 0.1344 104 54 51 Pass 0.1363 104 51 49 Pass 0.1382 104 49 47 Pass 0.1401 100 45 45 Pass 0.1420 100 40 40 Pass 0.1439 99 37 37 Pass 0.1458 94 34 36 Pass 0.1477 94 33 35 Pass 0.1497 92 32 34 Pass 0.1516 88 30 34 Pass 0.1535 87 29 33 Pass 0.1554 85 28 32 Pass 0.1573 83 28 33 Pass 0.1592 80 27 33 Pass 0.1611 79 27 34 Pass 0.1630 76 23 30 Pass 0.1649 76 22 28 Pass 0.1668 72 21 29 Pass 0.1687 71 20 28 Pass 0.1706 68 19 27 Pass 0.1725 66 18 27 Pass 0.1745 66 18 27 Pass 0.1764 65 17 26 Pass 0.1783 63 17 26 Pass 0.1802 61 14 22 Pass 0.1821 60 14 23 Pass 0.1840 57 14 24 Pass 0.1859 57 14 24 Pass 0.1878 56 14 25 Pass 0.1897 54 12 22 Pass 0.1916 54 12 22 Pass 0.1935 53 12 22 Pass 0.1954 53 12 22 Pass 0.1973 52 12 23 Pass 0.1993 50 12 24 Pass 0.2012 50 12 24 Pass 0.2031 50 11 22 Pass 0.2050 49 10 20 Pass 0.2069 48 10 20 Pass 0.2088 47 10 21 Pass 0.2107 47 9 19 Pass 0.2126 47 6 12 Pass 0.2145 46 6 13 Pass 0.2164 45 6 13 Pass 0.2183 44 6 13 Pass 0.2202 43 6 13 Pass 0.2222 43 6 13 Pass


Page A-50

0.2241 42 6 14 Pass 0.2260 41 6 14 Pass 0.2279 41 6 14 Pass 0.2298 41 6 14 Pass _____________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC 1. On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. ___________________________________________________________________ This program and accompanying documentation is provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by the user. Clear Creek Solutions and the Washington State Department of Ecology disclaims all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions and/or the Washington State Department of Ecology be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions or the Washington State Department of Ecology has been advised of the possibility of such damages.


Page A-51

Figure A2-2 East TDA Flow Durations

A4 References

Anthony Burgess Consulting Inc. 2013. Geotechnical Conditions Report Horseman’s Trail PRD. Technical Appendix B to the Horseman's Trail/Frognal Estates PRD Environmental Impact Statement, Snohomish County, WA. Higa Engineering, Inc. 2000. Revised Targeted Drainage Report and Erosion Risk Assessment for Horseman’s Trail Manor PFN 99 104777, prepared for Horseman’s Trail, LLC Snohomish County Surface Water Online Data 2008. Water Quality Data for Picnic Point Creek http://web5.co.snohomish.wa.us/spw_swhydro/wq-search.asp?siteid=583&isSelect=true&siteCnt=1 Washington Department of Ecology 2005. Stormwater Management Manual for Western Washington Western Region Climate Center 2008. Precipitation data for Everett Junior College http://www.wrcc.dri.edu/summary/Climsmwa.html



Attachment B

Stormwater Quality Calculations

Horseman’s Trail August 2008 Water Quality Calculations

Page B2

TABLE OF CONTENTS

B1 Biofiltration Swales ................................................................... 3

B1.1 Analysis Approach and Results ...........................................3

B1.2 WWHM3 Calculations ..........................................................3

B1.3 Swale Design Calculations ..................................................3

B2 Bio-infiltration Swales .............................................................. 4

B2.1 Analysis Approach ...............................................................4

B3 References ................................................................................. 4

TABLES

Table B1-1 Biofiltration swale design parameters

ATTACHMENTS

Attachment B1 Biofiltration Swale Calculations

Attachment B2 Stormwater Quality Calculations WWHM Output


Page B3

B1 Biofiltration Swales

B1.1 Analysis Approach and Results The sections of swales located on native till or on fill are designed as biofiltration swales without infiltration. The design method is presented in the Stormwater Management Manual for Western Washington Volume V Chapter 9 (Department of Ecology 2005). For the Horseman’s Trail site, the approach used is as follows:

• Land use data for the drainage areas to each of the biofiltration swales was determined using data generated for the flow control calculations,

• Using the Western Washington Hydrologic Model WWHM3 (Department of Ecology 2007), the 15 min water quality flow, and the 25 year and 100 year flows were determined,

• The calculation procedure was implemented in Mathcad 13 (Mathsoft Engineering & Education, Inc 2005) and the minimum swale lengths determined.

The analyses assumed that the swale slope would be 1.5 percent, controlled where necessary by check dams. The default swale base width of 2 feet was satisfactory for all swales except for the southeast, where it was necessary to increase the base width to 2.5 feet. All swales were analyzed for continuous inflow. The results of the analyses are summarized in Table B1-1. Table B1-1 Biofiltration swale design parameters

Flow

Swale Length Qwq Q25 Q100 Base width

Calculated minimum

length ft cfs cfs cfs ft ft West3 240 0.0042 0.0175 0.0233 2.0 100 West5 420 0.1248 0.5165 0.6770 2.0 259

West6 315 0.2136 0.3674 0.4394 2.0 295 Northeast2 500 0.1100 0.4456 0.5756 2.0 251 Southeast 180 0.0455 0.1800 0.2344 2.5 163

B1.2 WWHM3 Calculations Output files from WWHM3 are presented in Attachment B1.

B1.3 Swale Design Calculations Mathcad files for the swale designs are presented in Attachment B2.


Page B4

B2 Bio-infiltration Swales

B2.1 Analysis Approach Sections of swales located on outwash are designed to provide infiltration. Details are provided in Attachment A Flow Control Calculations. The design method is presented in the Stormwater Management Manual for Western Washington Volume V Chapter 9 (Department of Ecology 2005). The following design features are included to address the water quality aspects of the swales:

• Check dams will have a height of 12 inches, producing an average maximum ponding level for each section between check dams of 6 inches,

• The base of the swale will be underlain by 18 inches of compost amended soil with a CEC of at least 5 meq/100 gm dry soil, and organic content of at least 1 percent,

• The design infiltration rate is 1.25 inches/hour, based on a estimated infiltration rate of 6 inches per hour and a reduction factor of 4.

B3 References

Mathsoft Engineering & Education, Inc 2005. Mathcad 13. Washington Department of Ecology 2005. Stormwater Management Manual

for Western Washington. Washington Department of Ecology. 2007. Western Washington Hydrologic

Model WWHM 3 Version 1.0.

Attachment B1

Biofiltration Swale Calculations

Horseman's TrailAttachment B1

Biofiltration SwalesCalculations

August 2008

BIOFILTRATION SWALE DESIGN

Refs King County Surface Water Design Manual, 1998

Section 6.3.1 page 6-37

Stormwater Manual for Western Washington, Department of Ecology 2005

Volume V Chapter 9 BMP T9.10

PROJECT Horseman's Trail West3 swale

Note: units are cfs, ft

Step 1 Design flows

Qwq 0.0042:= water quality design flow from WWHM

Q25 0.0175:= 25 yr peak flow

100 yr peak flowQ100 0.0233:=

Step 2 Calculate swale bottom width

nwq .2:= Manning's roughness coeff for Qwq flow

y4

12:= flow depth, default 2 ins for urban area but can go to 4

ins

y 0.333=

ss 0.015:= swale slope ss, 1% minimum for dry bioswale,

underdrains required for < 1.5%

bQwq nwq⋅

1.49 y1.67⋅ ss

.5⋅:=

b 0.029= swale bottom width ft: must be >2ft and <10ft

b if b 2< 2, b,( ):=

check if b 10> "increase ss (max 6%), increase depth (max 4 ins)", "base width OK",( ):=

check "base width OK"=

b 2=

Page B1-2



August 2008

yQwq nwq⋅

1.49 ss0.5⋅ b⋅

3

5

:=

y 0.026=

Step 3 Determine design flow velocity

Z 3:= side slope horizontal:vertical

Awq b y⋅ Z y⋅ y⋅+:=

VwqQwq

Awq:=

Vwq 0.077= design flow fps, must be less than 1 fps

Step 4 Calculate swale length

Fconst 1080:= 540 for through flow, 1080 for continuous inflow

Lswale Fconst Vwq⋅:= length ft, must be > 100 ft

Lswale 83.509=

Step 5 Adjust length

bss 2 y⋅ Z⋅:=

Atop b bss+( ) Lswale⋅:= treatment top area, sf/ft

Atop 180.113=

bf 2:= trial adjusted final bottom width, must be equal to or

greater than calculated width, b

LfAtop

bf bss+:= adjusted length

Lf 83.509=

Page B1-3



August 2008

Q Qwq:=

n nwq:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.026= depth of flow for water quality design flow (ft)

P bf Z y⋅+( ) y⋅:= Area bf Z y⋅+( ) y⋅:= RhydArea

P:=

VwqQwq

Area:=

Vwq 0.077= confirm less than 1 fps

Step 6 Provide conveyance capacity for flows > Qwq

Q Q100:=

nhf .03:= high flow Manning's coef 0.03

n nhf:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.023=

yins100 y 12⋅:=

yins100 0.281= depth of flow for 100y 24hr peak flow inches

Page B1-4



August 2008

Area bf Z y⋅+( ) y⋅:=

V100Q100

Area:=

V100 0.48= flow velocity must be less than 3 fps

nhf .2:= check with WQ flow Manning's coef 0.2

n nhf:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.072=

yins100 y 12⋅:=



V100Q100

Area:=


Page B1-5



August 2008



Step 1 Design flows


Q25 0.5165:= 25 yr peak flow

100 yr peak flowQ100 0.677:=



y4


ins

y 0.333=

ss .015:= swale slope ss, 1% minimum for dry bioswale,


bQwq nwq⋅

1.49 y1.67⋅ ss

.5⋅:=


b if b 2< 2, b,( ):=



b 2=

yQwq nwq⋅

1.49 ss0.5⋅ b⋅

3

5

:=

Page B1-6



August 2008

y 0.2=




VwqQwq

Awq:=





Lswale 259.23=


bss 2 y⋅ Z⋅:=


Atop 829.506=



LfAtop


Lf 259.23=

Q Qwq:=

n nwq:=

Page B1-7



August 2008

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=



P:=

VwqQwq

Area:=



Q Q100:=


n nhf:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.168=

yins100 y 12⋅:=



Page B1-8



August 2008

V100Q100

Area:=



n nhf:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.467=

yins100 y 12⋅:=



V100Q100

Area:=


Page B1-9



August 2008



Step 1 Design flows


Q25 0.3674:= 25 yr peak flow

100 yr peak flowQ100 0.4394:=



y4


ins

y 0.333=



bQwq nwq⋅

1.49 y1.67⋅ ss

.5⋅:=


b if b 2< 2, b,( ):=



b 2=

yQwq nwq⋅

1.49 ss0.5⋅ b⋅

3

5

:=

y 0.276=

Page B1-10



August 2008




VwqQwq

Awq:=





Lswale 295.455=


bss 2 y⋅ Z⋅:=


Atop 1.08 103×=



LfAtop


Lf 295.455=

Q Qwq:=

n nwq:=

Page B1-11



August 2008

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=



P:=

VwqQwq

Area:=



Q Q100:=


n nhf:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.131=

yins100 y 12⋅:=



Page B1-12



August 2008

V100Q100

Area:=



n nhf:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.374=

yins100 y 12⋅:=



V100Q100

Area:=


Page B1-13



August 2008

PROJECT Horseman's Trail Northeast2 swale


Step 1 Design flows


Q25 0.4456:= 25 yr peak flow

100 yr peak flowQ100 0.5756:=



y4


ins

y 0.333=



bQwq nwq⋅

1.49 y1.67⋅ ss

.5⋅:=


b if b 2< 2, b,( ):=



b 2=

yQwq nwq⋅

1.49 ss0.5⋅ b⋅

3

5

:=

Page B1-14



August 2008

y 0.185=




VwqQwq

Awq:=





Lswale 250.685=


bss 2 y⋅ Z⋅:=


Atop 780.223=



LfAtop


Lf 250.685=

Q Qwq:=

n nwq:=

Page B1-15



August 2008

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=



P:=

VwqQwq

Area:=



Q Q100:=


n nhf:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.153=

yins100 y 12⋅:=



Page B1-16



August 2008

V100Q100

Area:=



n nhf:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.43=

yins100 y 12⋅:=



V100Q100

Area:=


Page B1-17



August 2008

PROJECT Horseman's Trail Southeast swale


Step 1 Design flows


Q25 0.1800:= 25 yr peak flow

100 yr peak flowQ100 0.2344:=



y4


ins

y 0.333=



bQwq nwq⋅

1.49 y1.67⋅ ss

.5⋅:=


b if b 2< 2, b,( ):=



b 2=

yQwq nwq⋅

1.49 ss0.5⋅ b⋅

3

5

:=

Page B1-18



August 2008

y 0.109=




VwqQwq

Awq:=





Lswale 193.411=


bss 2 y⋅ Z⋅:=


Atop 513.499=

bf 2.5:= trial adjusted final bottom width, must be equal to or


LfAtop


Lf 162.759=

Q Qwq:=

n nwq:=

Page B1-19



August 2008

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=



P:=

VwqQwq

Area:=



Q Q100:=


n nhf:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.081=

yins100 y 12⋅:=



Page B1-20



August 2008

V100Q100

Area:=



n nhf:=

f y( )1.49

nbf Z y⋅+( ) y⋅

bf y⋅ Z y2⋅+

bf 2 y⋅ 1 Z2+( ).5+

.67

⋅ ss.5⋅

⋅ Q−:=

y root f y( ) y,( ):=

y 0.24=

yins100 y 12⋅:=



V100Q100

Area:=


Page B1-21

Attachment B2

Stormwater Quality Calculations

WWHM Output

Horseman’s Trail PRD August 2008 Stormwater Quality Calculations WWHM Output

Page B2-2

West TDA

The following file has been edited to delete extraneous data. Point of compliance (POC) locations are as follows:

• POC 4 Outflow from West3 swale



Western Washington Hydrology Model PROJECT REPORT ___________________________________________________________________ Project Name: westwq Site Address: City : Report Date : 7/16/2008 Gage : Everett Data Start : 1948/10/01 Data End : 1997/09/30 Precip Scale: 0.80 ___________________________________________________________________ MITIGATED LAND USE Name : West3 basin Bypass: No GroundWater: No Pervious Land Use Acres A B, Lawn, Flat .713 C, Lawn, Flat .072 Impervious Land Use Acres ROOF TOPS FLAT 0.031 Element Flows To: Surface Interflow Groundwater West3 swale, West3 swale, Name : West3 swale Bottom Length: 240ft. Bottom Width: 2ft. Depth : 2ft. Volume at riser head : 0.0016ft. Side slope 1: 2 To 1 Side slope 2: 0 To 1 Side slope 3: 2 To 1 Side slope 4: 0 To 1 Discharge Structure


Page B2-3

Riser Height: 0.1 ft. Riser Diameter: 48 in. Element Flows To: Outlet 1 Outlet 2 West2 swale, ___________________________________________________________________ Name : West5 basin Bypass: No GroundWater: No Pervious Land Use Acres A B, Forest, Steep .004 A B, Lawn, Flat .304 C, Forest, Steep .306 C, Lawn, Flat 1.013 Impervious Land Use Acres ROADS FLAT 0.237 ROADS MOD 0.202 ROOF TOPS FLAT 0.358 DRIVEWAYS FLAT 0.217 Element Flows To: Surface Interflow Groundwater West5 swale, West5 swale, Name : West5 swale Bottom Length: 420ft. Bottom Width: 2ft. Depth : 2ft. Volume at riser head : 0.0021ft. Side slope 1: 2 To 1 Side slope 2: 0 To 1 Side slope 3: 2 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 0.1 ft. Riser Diameter: 48 in. Element Flows To: Outlet 1 Outlet 2 West4 swale, ___________________________________________________________________ Name : West6 basin Bypass: No GroundWater: No


Page B2-4

Pervious Land Use Acres A B, Forest, Steep .022 A B, Lawn, Flat 1.233 Impervious Land Use Acres ROADS FLAT 0.301 ROADS MOD 0.184 ROOF TOPS FLAT 0.102 DRIVEWAYS FLAT 0.26 Element Flows To: Surface Interflow Groundwater West6 swale, West6 swale, Name : West6 swale Bottom Length: 315ft. Bottom Width: 2ft. Depth : 2ft. Volume at riser head : 0.0037ft. Side slope 1: 2 To 1 Side slope 2: 0 To 1 Side slope 3: 2 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 0.1 ft. Riser Diameter: 48 in. Element Flows To: Outlet 1 Outlet 2 West1 swale, ___________________________________________________________________ ANALYSIS RESULTS ___________________________________________________________________ Flow Frequency Return Periods for Mitigated. POC #4 Return Period Flow(cfs) 2 year 0.008007 5 year 0.011469 10 year 0.014004 25 year 0.017487 50 year 0.020288 100 year 0.023269 Water Quality BMP Flow and Volume for POC 4. On-line facility volume: 0.0041 acre-feet On-line facility target flow: 0.01 cfs. Adjusted for 15 min: 0.0042 cfs. Off-line facility target flow: 0.0021 cfs. Adjusted for 15 min: 0.0023 cfs. ___________________________________________________________________ Flow Frequency Return Periods for Mitigated. POC #5 Return Period Flow(cfs) 2 year 0.187897 5 year 0.255771


Page B2-5

10 year 0.303591 25 year 0.367356 50 year 0.417326 100 year 0.469443 Water Quality BMP Flow and Volume for POC 5. On-line facility volume: 0.0683 acre-feet On-line facility target flow: 0.01 cfs. Adjusted for 15 min: 0.2136 cfs. Off-line facility target flow: 0.0562 cfs. Adjusted for 15 min: 0.1228 cfs. ___________________________________________________________________ Flow Frequency Return Periods for Mitigated. POC #6 Return Period Flow(cfs) 2 year 0.246497 5 year 0.346402 10 year 0.418512 25 year 0.516488 50 year 0.594525 100 year 0.676952 Water Quality BMP Flow and Volume for POC 6. On-line facility volume: 0.1042 acre-feet On-line facility target flow: 0.01 cfs. Adjusted for 15 min: 0.1248 cfs. Off-line facility target flow: 0.066 cfs. Adjusted for 15 min: 0.0703 cfs. ___________________________________________________________________ This program and accompanying documentation is provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by the user. Clear Creek Solutions and the Washington State Department of Ecology disclaims all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions and/or the Washington State Department of Ecology be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions or the Washington State Department of Ecology has been advised of the possibility of such damages.


Page B2-6

East TDA

The following file has been edited to delete extraneous data. Point of compliance (POC) locations are as follows:

• POC 1 Outflow from Northeast2 swale

• POC 3 Outflow from Southeast swale

Western Washington Hydrology Model PROJECT REPORT ___________________________________________________________________ Project Name: eastwq Site Address: City : Report Date : 7/16/2008 Gage : Everett Data Start : 1948/10/01 Data End : 1997/09/30 Precip Scale: 0.80 ___________________________________________________________________ ___________________________________________________________________ MITIGATED LAND USE Name : Northeast2 Bypass: No GroundWater: No Pervious Land Use Acres C, Forest, Steep .012 C, Lawn, Flat .76 Impervious Land Use Acres ROADS FLAT 0.204 ROADS MOD 0.239 ROOF TOPS FLAT 0.341 DRIVEWAYS FLAT 0.192 Element Flows To: Surface Interflow Groundwater Northeast2 swale, Northeast2 swale, Name : Northeast2 swale Bottom Length: 500ft. Bottom Width: 2ft. Depth : 2ft. Volume at riser head : 0.0379ft. Side slope 1: 3 To 1 Side slope 2: 0 To 1


Page B2-7

Side slope 3: 3 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 1 ft. Riser Diameter: 48 in. Element Flows To: Outlet 1 Outlet 2 Northeast1 swale, ___________________________________________________________________ Name : Southeast Bypass: No GroundWater: No Pervious Land Use Acres C, Forest, Mod .127 C, Lawn, Flat .325 Impervious Land Use Acres ROADS FLAT 0.246 ROOF TOPS FLAT 0.083 DRIVEWAYS FLAT 0.049 Element Flows To: Surface Interflow Groundwater Southeast swale, Southeast swale, Name : Southeast swale Bottom Length: 180ft. Bottom Width: 2ft. Depth : 2ft. Volume at riser head : 0.0379ft. Side slope 1: 3 To 1 Side slope 2: 0 To 1 Side slope 3: 3 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 1 ft. Riser Diameter: 48 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ ANALYSIS RESULTS Flow Frequency Return Periods for Mitigated. POC #1


Page B2-8

Return Period Flow(cfs) 2 year 0.221288 5 year 0.305335 10 year 0.365163 25 year 0.445579 50 year 0.509035 100 year 0.575575 Water Quality BMP Flow and Volume for POC 1. On-line facility volume: 0.0923 acre-feet On-line facility target flow: 0.01 cfs. Adjusted for 15 min: 0.118 cfs. Off-line facility target flow: 0.0613 cfs. Adjusted for 15 min: 0.0658 cfs. ___________________________________________________________________ Flow Frequency Return Periods for Mitigated. POC #3 Return Period Flow(cfs) 2 year 0.087474 5 year 0.121911 10 year 0.14661 25 year 0.180006 50 year 0.206493 100 year 0.234377 Water Quality BMP Flow and Volume for POC 3. On-line facility volume: 0.0372 acre-feet On-line facility target flow: 0.01 cfs. Adjusted for 15 min: 0.0455 cfs. Off-line facility target flow: 0.024 cfs. Adjusted for 15 min: 0.0254 cfs. ___________________________________________________________________ This program and accompanying documentation is provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by the user. Clear Creek Solutions and the Washington State Department of Ecology disclaims all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions and/or the Washington State Department of Ecology be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions or the Washington State Department of Ecology has been advised of the possibility of such damages.

Attachment C

Construction Stormwater Pollution Prevention Plan

Horseman’s Trail September 2013 SWPPP

Page C2

TABLE OF CONTENTS

C1 Site Setting .................................................................... 4

C1.1 Location .................................................................... 4

C1.2 Slopes ....................................................................... 4

C1.3 Critical Areas ............................................................ 4

C1.4 Adjacent Areas ......................................................... 4

C1.5 Construction Phasing ................................................ 4

C2 Erosion Risk Analysis .................................................. 6

C3 Plan Elements ............................................................... 6

C3.1 Mark Clearing Limits ................................................. 6

C3.2 Establish Construction Access .................................. 7

C3.3 Detain Flows ............................................................. 7

C3.4 Install Sediment Controls .......................................... 7

C3.5 Stabilize Soils ........................................................... 8

C3.6 Protect Slopes........................................................... 8

C3.7 Protect Drain Inlets ................................................... 8

C3.8 Stabilize Channels and Outlets ................................. 8

C3.9 Control Pollutants ...................................................... 9

C3.10 Control De-Watering ............................................... 10

C3.11 Maintain BMPs ........................................................ 10

C3.12 Manage the Project ................................................. 10

C4 References................................................................... 11


Page C3

FIGURES

Figure C1-1 Existing Site Topography Figure C1-2 Developed Site Topography Figure C1-3 Site Segments for Soil Management During Grading


Page C4

C1 Site Setting

C1.1 Location The Horseman’s Trail Planned Residential Development (PRD) is a 112-lot subdivision located near Mukilteo (Township 28N Range 4E Sections 32 and 33). The site occupies 23 acres south of Picnic Point Road and north of 136th Place SW.

C1.2 Slopes The site is forested with mature second growth with elevations ranging between 270 feet and 460 feet msl. The central and southern portions of the site are relatively flat-lying, with elevations above about 400 feet msl. The steepest slopes (up to 60 percent) are located along the northern portion of the site that occupies the valley side and the sides of two incised dry ravines running south to north. Existing site topography is shown on Figure C1-1 Grading of the site for construction will involve balanced cut and fill, removing soil form the higher central and southern portions of the site and using the material to fill the east and west ravines. Engineered retaining structures will used at select locations along the northern boundary of the site for fills, and along the southern boundary for cuts. Elsewhere, within the developed area maximum slopes will be 25 percent. The topography for the developed site is shown on Figure C1-2.

C1.3 Critical Areas A Category 3 wetland is located northwest of the site (Wetland Resources, Inc. 2005). The minimum distance from the property boundary to the wetland is about 80 feet. However, with the exception of a recreation path and erosion control measures for the discharge from the west vault to the west ravine, site construction activities will be more than 180 feet from the wetland and separated by natural vegetation on the north slope.

C1.4 Adjacent Areas Areas south of the site and to the north of the eastern portion of the northern boundary have been developed with single-family residences. The remaining areas adjacent to the site are currently undeveloped.

C1.5 Construction Phasing Engineering grading plans estimate that approximately 275,000 cubic yards of cut and a nearly equal amount of fill will be required to produce design grades on the site. This overall volume of material to be moved is comprised of organic surface soils, a weathered subsurface layer, lodgement till, and outwash sands. The site will be segregated into three areas for soil management during grading (see Figure C1-3). Segment 1 will be the along 58th Place W, and will include Lots 6 to 47; Segment 2 will be the area south of Segment 1 along 60th Avenue W (the east-west leg), including Lots 48 to 85. Segment 3 will consist of the remainder of the site – primarily the area to the east that is referred to as Lot 1 of Regatta Estates, including Lots 1 through 5, and Lots 86 through 112. These segments will be generally defined and will not necessarily be absolute as earthwork management areas. The segregations


Page C5

described here are unrelated to site development criteria; materials may be moved into and out of each segment as needed to facilitate overall project implementation. Organic Surface Soils. The organic layer will produce about 15,000 to 20,000 cubic yards of organic surface soils. This surface layer will be saved for reuse in the Low Impact Stormwater Management facilities for treatment and attenuation of runoff. These organic soils will be mixed with selected and imported compost to create an “engineered” soil with appropriate characteristics for stormwater management. Surface soils will require management and will have to be moved at least twice before final placement. Initially, surface soils will be stockpiled in a temporary location on the bench/plateau of the western portion of the property; referred to above as Segment 2. The valley and the north half of the plateau (Segment 1) will be stripped and the strippings will be stockpiled on the south half of the plateau. Fill areas in the valleys will be “keyed” into undisturbed material and structural materials from Segment 1 will be placed in the valley. Once the subgrade as been established on the north half the plateau, organic soils will be moved to excavated surfaces for later processing into engineered soils. Hauling the strippings from Segment 1 to Segment 2 in preparation for structural grading will take about one week. These soils will be stockpiled for approximately three weeks before they are moved back to the subgrade of the graded half of the site. All surface soils and wood chips/sawdust will be moved to the graded area for temporary stockpiling and processing. Moving the rest of the organic soils to the stockpile will take approximately 2 weeks. The surface soils and chips will be left in roughly mixed stockpiles and seeded with Dutch white clover while the rest of the site grading is being completed. These surface soils will be stockpiled for about 12 weeks. Structural Grading. To manage soil movements described above, grading will start in segments of the site and those segments will be finished to subgrade as other areas are started. The first area to be graded (Segment 1) will be the north half of the site or one lot deep along both sides of the alignment of 58th Place W. Each of the three segments will have adequate “cut” (excavation) to supply fill requirements. There may be some sharing (i.e., redistribution) of material between segments to balance the total earthwork onsite. When a site segment is ready for grading, fill areas will be prepared. The major fill area for Segment 1 will be the east ravine that crosses the site along the 60th Avenue W alignment (see Figure C1-3, above). After stripping, the toe of the fill area will be surveyed and located. A keyway will be dug out of the toe area of the beginning of the fill, and benches will be excavated in accordance with directions from project geotechnical engineers, including guidance based on specific on site observations. The spall drainage blanket will be placed at the direction of the geotechnical engineer as the fill progresses.


Page C6

It will take about 4 weeks to excavate the north segment of the site to subgrade. Once the subgrade or near sub-grade is established, the organic soils will be moved to process areas north of the 58th Place W alignment. Organic soils from the entire site will be stockpiled again in this area, and re-seeded with Dutch white clover for stabilization while in storage. It will take approximately 2 weeks to move organic soils to the stockpile/process area. The earthwork production may be controlled by retaining structure construction, and it will take approximately 5 weeks to grade Segment 3 (the eastern portion of the site above Regatta Estates) to subgrade. The construction schedule has not been determined, but it is tentatively anticipated that site clearing will start in spring 2015.

C2 Erosion Risk Analysis

The erosion hazard for the site is evaluated based upon the criteria identified in Snohomish County Rule 3044 (2006). The site soils are Alderwood and Everett, with erosion hazard values of Medium and Low respectively. The parent materials are Vashon till and advance outwash, with the steepest slopes in the range of 15 to 25 percent, for an erosion hazard value of Medium. Overall, the site therefore has an erosion hazard value of Medium. The area of the site that will be disturbed for construction is 17.2 acres (Snohomish County 2008 Table 2.6-1). For the disturbed area, the maximum average slope is less than 15 percent and the steepest slope is less than 33 percent. A critical area (wetland) is located with in one-quarter mile downstream of the stormwater discharge from the West TDA. The site is upstream of a stormwater path that does not flow directly into an ESA stream, and additional BMPs can be implemented as corrective measures. The site is therefore assessed as in the High Risk category for erosion.

C3 Plan Elements

The twelve plan elements required by Rule 3044 (Snohomish County 2006) and the Stormwater Management Manual for Western Washington (SMMWW) published by the Department of Ecology (2005) are presented below. Best Management Practices (BMPs) are identified by the reference number and description in Volume II of the SMMWW.

C3.1 Mark Clearing Limits Prior to beginning earth-disturbing activities, including clearing, grubbing and grading, all clearing limits will be clearly identified on appropriate site plans and marked in the field. Recommended BMPs are:

• BMP C101 Preserving Natural Vegetation. • BMP C103 High Visibility Plastic or Metal Fence


Page C7

C3.2 Establish Construction Access Construction vehicle access will be to one location at the northern end of 60th Avenue West. This access location will be stabilized with quarry spalls or crushed rock to minimize tracking of soils onto public roads. Recommended BMPs are:

• BMP C105 Stabilized Construction Entrance • BMP C107 Construction Road/Parking Area Stabilization • BMP C106 Wheel Wash (required for winter grading operations)

Contingency BMPs. In the event that the recommended BMPs are insufficient to prevent tracking of soils onto public roads, the following BMP may be required:

• BMP C106 Wheel Wash

C3.3 Detain Flows Construction stormwater will be detained on site by temporary sediment ponds and early construction and operation of the detention vaults. Sediment control structures (traps, ponds) will be located upstream of any permanent infiltration facility used during construction, to minimize infiltration degradation by settling of suspended solids. Recommended BMPs are:

• BMP C240 Sediment Trap • BMP C241 Sediment Pond

C3.4 Install Sediment Controls All stormwater that leaves the site or is infiltrated on site will pass through an appropriate sediment removal BMP. Runoff from fully stabilized areas may be discharged without a sediment removal BMP, but must meet flow control standards. Snohomish County will inspect and approve areas stabilized by means other than pavement or quarry spalls. BMPs intended to trap sediments on site will be constructed as one of the first steps in grading. These BMPs will be functional before other land disturbing activities take place. Recommended BMPs are:

• BMP C230 Straw Bale Barrier • BMP C231 Brush Barrier • BMP C232 Gravel Filter Berm • BMP C233 Silt Fence • BMP C235 Straw Wattles • BMP C240 Sediment Trap • BMP C241 Temporary Sediment Pond

Contingency BMPs. In the event that the recommended BMPs are insufficient to prevent discharge of sediments, the deployment of the recommended BMPs may be increased, and/or the following BMPs may be required:

• BMP C250 Construction Stormwater Chemical Treatment • BMP C251 Construction Stormwater Filtration


Page C8

C3.5 Stabilize Soils All exposed and unworked soils will be stabilized by application of effective BMPs, which will protect the soil from the erosive forces of raindrop impact, flowing water and wind erosion. From October 1 to March 31, no soils will remain exposed and unworked for more than 2 days. This condition applies to all soils on site, whether at final grade or not. Applicable practices include temporary and permanent seeding, sodding, mulching, plastic covering, the early application of gravel base on areas to be paved or graveled, and dust control. Soil stabilization measures selected should be appropriate for the time of year, site conditions, estimated duration of use, and potential water quality impacts that stabilization agents may have on downstream waters or ground water. Soil stockpiles must be stabilized and protected with sediment trapping measures. Recommended BMPs are:

• BMP C120 Temporary and Permanent Seeding • BMP C121 Mulching • BMP C123 Plastic Covering

C3.6 Protect Slopes Cut and fill slopes will be protected from erosive flows and concentrated flows until permanent cover and drainage conveyance systems are in place. Recommended BMPs are:

• BMP C101 Preserving Natural Vegetation • BMP C201 Grass-Lined Channels • BMP C121 Mulching • BMP C123 Plastic Covering • BMP C130 Surface Roughening • BMP C200 Interceptor Dikes & Swales

Contingency BMPs. In the event that the recommended BMPs are insufficient to protect slopes, the area contributing to drainage will be reviewed to determine if runoff can be diverted away from the slope. If gravity drainage is not possible, the use of sumps, pumps and tight lines will be necessary

C3.7 Protect Drain Inlets Drain inlets installed by this project will be protected from sediment-Iaden flows, and directed to sediment trapping facilities. Recommended BMPs are:

• BMP C220 Storm Drain Inlet Protection • BMP C240 Sediment Trap • BMP C241 Temporary Sediment Pond

C3.8 Stabilize Channels and Outlets Temporary and permanent conveyance systems shall be stabilized to prevent erosion during and after construction. Wherever possible, permanent erosion


Page C9

control features such as check dams in the drainage swales, will be installed at the time of construction. Recommended BMPs are:

• BMP C120 Temporary and Permanent Seeding (PS) • BMP C121 Mulching • BMP C202 Channel Lining • BMP C209 Outlet Protection

C3.9 Control Pollutants All pollutants, including waste materials and demolition debris, that occur on-site during construction will be handled and disposed of in a manner that does not cause contamination of storm water. Cover, containment, and protection from vandalism will be provided for all chemicals, liquid products, petroleum products, and non-inert wastes present on the site (see Chapter 173-304 WAC for the definition of inert waste). Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and other activities which may result in discharge or spillage of pollutants to the ground or into storm water runoff must be conducted using spill prevention measures, such as drip pans. The Contractor shall maintain appropriate spill control kits in active work areas, and train staff in the correct use of the kits. Contaminated surfaces will be cleaned immediately following any discharge or spill incident. For emergency repairs temporary plastic sheeting shall be placed beneath and, if raining, over the vehicle. Application of agricultural chemicals, including fertilizers and pesticides, will be conducted in a manner and at application rates that will not result in the conveyance of chemical into storm water runoff. Manufacturers' recommendations will be followed for application rates and procedures. Management of ph-modifying sources will prevent contamination of runoff and storm water collected on the site. These sources include, but are not limited to, bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, and concrete pumping and mixer washout waters. Recommended BMPs are:

• The Contractor for the project shall obtain a copy of DOE Storm water Management Manual for Western Washington Volume IV Source Control BMPs.

• BMP C160 Certified Erosion & Spill Control Lead Contingency BMP. In the event of a spill of a potential contaminant or hazardous material, the Contractor will follow procedures in their spill control plan, including health and safety measures and requirements for reporting the spill the appropriate agencies.


Page C10

C3.10 Control De-Watering Construction activities below the site groundwater level are not anticipated. However, there may be occasional collection of water in excavations (for example utility trenches) that requires pumping and disposal. All turbid de-watering water, which has similar characteristics to storm water runoff at the site, will be discharged into a controlled environment such as a vegetated strip, or drainage ditch and sediment pond. Clean non-turbid water may be directly discharged to receiving waters. Recommended BMPs are:

• BMP C234 Vegetated Strip • BMP C240 Sediment Trap • BMP C241 Sediment Pond

Highly turbid or otherwise contaminated dewatering water, such as from washing of construction equipment will be handled separately from storm water at the site. Disposal options will depend upon the water quality. Recommended BMPs are:

• Infiltration by pumping to vegetated areas for dissipation • Transport off-site in vehicle, such as a vacuum flush truck, for legal

disposal in a manner that does not pollute state waters • On-site treatment using chemical treatment or other suitable treatment

technologies.

C3.11 Maintain BMPs All temporary and permanent erosion and sediment control BMPS will be maintained and repaired as needed to assure continued performance of their intended function. All maintenance and repair will be conducted in accordance with BMPs. Sediment control BMPs will be inspected after a runoff-producing storm event during the dry season and daily during the wet season. All temporary erosion and sediment control BMPs will be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment will be removed or stabilized on site. Disturbed soil areas resulting from removal of BMPs or vegetation will be permanently stabilized.

C3.12 Manage the Project The project will be conducted in such a manner so as to prevent, to the maximum extent practicable, the transport of sediment from the development site during construction. Revegetation of exposed areas and maintenance of that vegetation will be an integral part of the clearing activities. Based on the information provided, and/or local weather conditions, the local permitting authority may expand or restrict the seasonal limitation on site disturbance. If, during the course of any construction activity or soil disturbance during the seasonal limitation period, silt-laden runoff leaving the construction site causes a violation of the surface water quality standard or if clearing and grading limits or erosion and sediment control measures shown in the approved plan are not maintained, the local permitting authority may take


Page C11

enforcement action, including, but not limited to a notice of violation, administrative order, penalty, or stop-work order . The routine maintenance and necessary repair of erosion and sediment control BMPs are exempt from the seasonal clearing and grading limitations: All BMPs will be inspected, maintained, and repaired as needed to assure continued performance of their intended function. Whenever inspection and/or monitoring reveals that the BMPs identified in the Construction SWPPP are inadequate, due to the actual discharge of or potential to discharge a significant amount of any pollutant, the SWPPP will be modified, as appropriate, in a timely manner. This Construction SWPPP will be retained on-site or within reasonable access to the site. The Construction SWPPP will be modified whenever there is a significant change in the design, construction, operation, or maintenance of any BMP. Recommended BMP is:

• BMP C160 Contractor Erosion & Spill Control Lead

C3.13 Contingency Planning In the event that construction extends into the period from October 1st to March 31st or if unseasonably rainy periods occur during construction, additional temporary erosion and sediment control (TESC) measures may need to be implemented to prevent erosion or sediment-Iaden runoff from leaving the site and/or entering critical areas. Currently, construction is scheduled to begin in the spring. The majority of the utility and roadway construction operations on the site will likely be complete and stabilized within eight (8) weeks of commencement. Site grading and stabilization of slopes will continue for another four (4) weeks. Final hard surface installation (pavement, concrete, etc.) within the rights-of-way will be completed at about the same time. Risk of construction interruption during the proposed schedule due to adverse weather is low. The Contractor will be prepared to implement contingency BMPs identified in Sections C3.1 thorough C3.12 above.

C4 References

Snohomish County Department of Planning and Development Services 2006. Rule 3044 Standards for Construction Stormwater Pollution Prevention Plans.

Snohomish County Planning and Development Services 2008. Horseman’s Trail. A Planned Residential Development (PRD). Draft Environmental Impact Statement.

Washington Department of Ecology 2005. Stormwater Management Manual for Western Washington.

Wetland Resources, Inc. 2005. Critical Area Reconnaissance Report - 21.38 acre site located SW of Picnic Point Road in Urban Snohomish County, WA. Tax Parcel Numbers 00473300002800 and 00853500000100. Prepared for Horseman’s Trail LLC, Everett, WA.

Figure C1-3

Site Segments for Soil

Management During Grading


targeted drainage report horseman’s trail prd

Documents