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Home My WebLink AboutCUP 02-23; LARWIN PARK; STORM WATER MANAGEMENT PLAN; 2003-07-10CuP o2-2' STORM WATER MANAGEMENT PLAN FOR LARWIN PARK Carlsbad, California July 10, 2003 Prepared by: GVP Consultants 3764 Cavern Place Carlsbad, California 92008-6585 760.720.0500 jOF ESSI\ (4 Cm I P12 CC 1 - d' \41Z'i T2ff' < '9F Storm Water Management Plan LARWIN PARK CONTENTS Introduction Project Description Site Description General Soils Topography Drainage Patterns Water Quality Environment Beneficial Uses Pollutants of Concern Anticipated Pollutants Construction Post-construction Mitigation Measures Construction Post-construction Maintenance of BMPs Water Quality Calculations Summary Figures Figure 1 Vicinity Map Figure 2 Post-construction Pollutants Appendices Appendix A Water Quality Calculations Page I I 1 1 I 3 3 3 3 3 4 4 4 4 4 6 7 7 2 5 Storm Water Management Plan LARWIN PARK Introduction This Stormwater Management Plan (SWMP) is intended to analyze and mitigate potential post-construction impacts to water quality from the proposed Larwin Park improvements. Potential impacts to water quality during construction have been addressed in a Storm Water Pollution Prevention Plan (SWPPP) prepared by GVP Consultants dated July, 2003. This SWMP is intended to assist in compliance with San Diego Regional Water Quality Control Board (SDRWQCB) Order 2001-01, and is prepared pursuant to the City of Carlsbad Standard Urban Storm Water Mitigation Plan (SUSMP) Storm Water Standards. Project Description The proposed improvements include the development of a community park on the "northerly site" fronting Vancouver Street. Proposed improvements will involve minor grading and construction of a parking area, concrete walkways, tot lots, picnic areas and barbeques, a restroom, and landscaping with irrigation. Improvements at the "southerly site" consist of minor grading and construction of additional parking with a D.G. surfacing for the existing dog park. A volunteer-built trail is planned between the northerly and southerly sites. The trail will include a small 2:1 slope or gravity retaining wall, and will have a 6-foot wide trail bed of native soil. Total area to be disturbed is approximately 3.5 acres. To prevent further erosion to the existing natural canyon, most of the runoff from the northerly site will be directed to the existing storm drain in Vancouver Street. This storm drain outlets into an existing detention basin prior to release at the bottom of a northeasterly-facing canyon east of Vancouver Street. Site Description General The Larwin Park property is an irregularly-shaped collection of five parcels totaling 22.3 acres, bounded by Carlsbad Village Drive to the south, the Tanglewood attached single family home development to the west, Vancouver Street and single family homes to the east. A portion of the site adjacent to Carlsbad Village Drive has been developed as a dog park. Figure 1 is a vicinity map of the project. The total area of the parcel is approximately 22.3 acres. The location of the project site is shown in Figure 1. Soils Soils onsite are sands, clays, and sandy or silty clays typical of the Tertiary-aged Santiago Formation. The clay component gives the soil a high runoff coefficient, and makes it less prone to erosive I Storm Water Management Plan LARWIN PARK I %El Cam4no Country Club 31 El / / - ---- -, - - S - - / - - N - - LEGEND DRAINAGE BASIN (ONTO SITE) 0 APPROXIMATE AREA DRAINAGE BASIN N LOCATION OF DISCHARGE FROM SITE EXISTING STORM DRAIN PROPOSED STORM DRAIN q SPRING WETLANDS C WELL USGS Quad Map: San Luis Rey Scale 1'= 1000 SURFACE WATER BODY VICINITY MAP FIGURE 1 7 Storm Water Management Plan LARWIN PARK forces. The sand onsite would be prone to erosion, but would settle out relative quickly in a detention basin. Topography The site descends from Carlsbad Village Drive in several north- trending canyons separated by ridges. Adjacent to Vancouver Street a level plateau was created by grading done for the surrounding tract. Elevations range from 90 near the northernmost corner to 270 adjacent to Carlsbad Village Drive. Drainage Patterns The site currently drains to the north through natural canyons. An 18" storm drain drains a portion of the tract to the east into a canyon north of the plateau. The drainage from the site joins Buena Vista Creek approximately 1400 feet north of the northerly corner. No significant modification to existing drainage area boundaries is planned. A small diversion of drainage into the existing storm drain in Vancouver Street is proposed to reduce erosion due to drainage currently flowing westerly into the natural canyon. Water Quality Environment Beneficial Uses Larwin Park is located within the Buena Vista Creek Watershed, in Hydrologic Unit 4.21. The beneficial uses of Hydrologic Unit 4.21, consisting of Buena Vista Creek and Buena Vista Lagoon, include: Agricultural Supply (AGR) Industrial Service Supply (IND) Contact Water Recreation (REC-1) Non-contact Water Recreation (REC-2) Preservation of Biological Habitats of Special Significance (BIOL) Marine Habitat (MAR) Warm Freshwater Habitat (WARM) Wildlife Habitat (WILD) Rare, Threatened or Endangered Species (RARE) Potential Benefical Uses listed include: Estuarine Habitat (EST) Pollutants of Concern The El Salto HSA (904.21) is listed on the 1998 303(d) Waterbodies for the following pollutants/stressors: Bacterial indicators (coliform) Sedimentation/siltation Nutrients No modifications are currently proposed for the listing according to the latest staff report from the SDRWQCB. However a staff report did include as Constituents of Potential Concern for Buena Vista Creek: Benthic Community Degradation Eutrophication Storm Water Management Plan LARWIN PARK Benthic Community refers to clams, crustaceans and worms that live on or near the bottom sediments. Typically low levels of dissolved oxygen, ultimately caused by excessive nutrients in runoff, are the primary cause of benthic degradation. Toxic contaminants can also be involved. Eutrophication is a natural process of water bodies aging, but is drastically accelerated by excessive nutrients in a water body. Anticipated Pollutants Construction During construction, a variety of pollutants are onsite. Given the pollutants of concern for watershed, the anticipated pollutants requiring during construction include: anticipated to be the Buena Vista special concern Sediment BOD Nutrients Fertilizers Refer to the project SWPPP for more details on the anticipated pollutants during construction. Post-construction Common generalized pollutants found in post-construction runoff are shown in Figure 2. Based on the anticipated uses of the completed park facilities, post construction activities have the potential to generate oxygen demanding substances, nutrients and copper from landscape maintenance; bacteria and viruses from animal waste; floatable waste from trash; oil and grease and heavy metals from parked automobiles. Proposed Mitigation (Best Management Practices) To eliminate or reduce pollutants in stormwater runoff, Best Management Practices (BMPs) will be implemented during both construction and post-construction or operating phases. Construction As part of the construction drawings for the project, a detailed erosion control plan has been prepared in accordance with City of Carlsbad standards. In addition, a Storm Water Pollution Prevention Plan (SWPPP) has been prepared for the project in accordance with the State General Permit for Construction Activities. The BMPs specified on the erosion control plan and in the SWPPP include: Silt Fence Fiber Rolls Street Sweeping Stabilized Construction Entrance Storm Drain Inlet Protection Solid Waste Management 4 Storm Water Management Plan LARWIN PARK Major Source Pollutant SEDIMENTS Runoff from agriculture, construction, logging and mineral extraction NUTRIENTS Fertilizers, leachate from landfills and septic systems, atmospheric deposition, and erosion BACTERIA AND VIRUSES Sewage spills and overflows, illicit sanitary connections, septic systems, confined animal facilities, wild and domestic animal waste, and landfills OXYGEN DEMANDING Decaying vegetation (leaves and lawn clippings), animal SUBSTANCES excrement, street litter, and other organic matter OIL AND GREASE Vehicle operation and maintenance, industrial processes, Anti-freeze agriculture, home and garden care, landfills, hazardous waste Hydraulic Fluids sites, and leaking underground and above ground fuel storage Cleaners and Solvents tanks HEAVY METALS Vehicle operation and maintenance, industrial processes, paved surfaces (asphalt, deicing agents), structures (paint, wood preservatives, metal corrosion), and pesticides Chromium Vehicle operation and maintenance Copper Vehicle operation and maintenance, paint, and pesticides Lead Vehicle operation and maintenance, structures and roads, and paint Zinc Vehicle operation and maintenance, paved surfaces Iron Vehicular rust, structural rust Cadmium Vehicle tire wear (filler material), and pesticides Nickel Vehicular fuels, oil and parts wear, paved surfaces Manganese Vehicular parts wear TOXIC MATERIALS PCBs Vehicles: catalyst in synthetic tires, Other: electrical, insulation Pesticides and Herbicides General outdoor application, Structures: wood preservatives, paint FLOATABLES Litter: residential, commercial, industrial, recreation, waste disposal, vegetation POST-CONSTRUCTION POLLUTANTS FIGURE 2 Source: California Storm Water Best Management Practices Municipal Handbook Storm Water Management Plan LARWIN PARK Post Construction Construction BMPs will be installed and maintained to prevent or reduce the maximum extent practicable non-stormwater runoff from leaving the site. Refer to the SWPPP dated July 2003 for more detailed information. The preliminary design of the project includes integrated BMPs including: Use of permeable pavement (for the additional dog park parking) to minimize runoff. Design of the parking lot off Vancouver Street to drain through a vegetated swale. Use of vegetated swales on the northerly site to filter water before it enters a storm drain inlet. Grading the northerly site at gentle grades to avoid erosion. Posting signs prohibiting dogs in the northerly site to reduce pet waste that could potentially enter into storm water runoff. Providing pet litter bags and receptacles at the dog park. Re-configuring the drainage on the northerly site to reduce runoff into the westerly canyon and avoid the erosion of natural slopes. Placing trash containers in convenient locations to reduce trash blowing offsite or entering storm drains. In addition to the designed-in BMPs, the operation of the completed park is covered in the City of Carlsbad Jurisdictional Urban Runoff Management Plan (JURMP). Maintenance of BMPs The post-construction BMPs will be maintained by City staff, including: Maintaining vegetated swales in a healthy condition, adjusting irrigation and adding fertilizer as required. Emptying trash containers and picking up stray trash. Maintaining irrigation system to avoid erosion from broken pipes or sprinklers. Removing landscape maintenance clippings to avoid BOD impacts to storm water runoff. Street sweeping of parking area. Emptying pet waste containers at the dog park. The maintenance schedule varies based on the BMP and the season. Funding of BMP maintenance operations is included in the City budget. 6 Storm Water Management Plan LARWIN PARK Water Quality Calculations Water quality calculations have been performed for the grass swale treatment BMP for runoff from the paved parking lot off Vancouver Street. The calculations, included as Appendix A, use the flow-based standard of 0.2 inches per hour established by the Regional Water Quality Control Board Order 2001-01. The calculations indicate a water quality flow of 0.04 c.f.s. from the paved parking lot, resulting in a residence time in the grass swale of 2.4 minutes. Summary Through designed-in BMPs, the project will minimize impacts to storm water quality. Based on this preliminary SWMP, it appears that: The beneficial uses of the receiving waters will not be impaired or diminished. The drainage patterns will not be significantly altered by the project. The proposed construction and post-construction BMPs address mitigation measures to protect water quality and water quality objectives, and beneficial uses of the receiving waters to the maximum extent practicable (MEP). Storm Water Management Plan LARWIN PARK Appendix A Water Quality Calculations (Excerpts from Project Drainage Study) GVP CONSULTANTS 3764 Cavern Place CARLSBAD, CA 92008-6585 Ph (760) 720-0500 Fax (760) 720-2282 gvanpeski@horne.com JOB 144thL) ?/ (LIP oZ-Z, SHEET NO. -________________________ OF i CALCULATED BY___ DATE 8- 03 CHECKED BY DATE SCALE Undisturbed Natural Terrain Low Low Low Medium Density Residential Medium Density Residential Medium Density Residential Medium Density Residential High Density Residential High Density Residential Commercial/Industrial Commercial/Industrial Co-iimercial/Industrial Commercial/Industrial Commercial/Industrial Permanent Open Space Residential, 1.0 DU/A or less Residential, 2.0 DU/A or less Residential, 2.9 DU/A or less Residential, 4.3 DU/A or less Residential, 7.3 DU/A or less Residential. 10.9 DU/A or leSS Residential, 14.5 DU/A or less Residential, 24.0 DU/A or less Residential, 43.0 DU/A or less Neighborhood Commercial General Commercial Office Professional/Commercial Limited Industrial General Industrial Table 3-1 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use Runoff Coefficient "C" Soil Type NRCS Elements County Elements f % IMPER. A B C D 0* 0.20 0.25 0.30 10 0.27 0.32 0.36 0.41 20 0.34 0.38 0.42 0.46 25 0.38 0.41 0.45 0.49 30 0.41 0.45 0.48 40 0.48 0.51 0.54 0.57 45 0.52 0.54 0.57 0.60 50 0.55 0.58 0.60 0.63 65 0.66 0.67 0.69 0.71 80 0.76 0.77 0.78 0.79 80 0.76 0.77 0.78 0.79 85 0.80 0.80 0.81 0.82 90 0.83 0.84 0.84 0.85 90 0.83 0.84 0.84 0.85. 95 0.95-7 0.95-87 0.958' 0.958? Thie values associated with 0% impervious may be used for direct calculation of the runoff coefficient as described in Section 3.1.2 (representing the pervious runoff coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity. Justification must be given that the area will remain natural forever (e.g., the area is located in Cleveland National Forest). DU/'A = dwelling units per acre NRCS = National Resources Conservation Service -ri. IG9 Op t(a Laiwin Park Worksheet for Triangular Channel Project Description Project File c:\program fileshaestad\acadernic\fmw\larwin p.fm2 Worksheet Grass swale Flow Element Triangular Channel Method Mannings Formula Solve For Channel Depth - Input Data Mannings Coefficient 0.200 Channel Slope 0.010000 ft/ft Left Side Slope 10.000000 H V Right Side Slope 10.000000 H : V Discharge 0.04 cfs Results Depth 0.17 ft Flow Area 0.28 ft2 Wetted Perimeter 3.37 ft Top Width 3.36 ft Critical Depth 0.06 ft Critical Slope 1.858283 ft/ft Velocity 0.14 ft/s Velocity Head 0.31e-3 ft Specific Energy 0.17 ft Froude Number 0.09 Flow is subcritical. 05/08/03 Academic Edition FlowMaster v5.17 02:25:57 PM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1 iv• -. .. . . . -. .-- . .. 15 - -'----.'-, - ... //•f, / / 44 -' -. - .- -- ..c .. •4 ." 7y -- - /i/,/j2. 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