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HomeMy WebLinkAboutCT 04-21; CARLSBAD VILLAGE TOWNHOMES; PRELIMINARY STORM WATER MANAGEMENT PLAN; 2005-05-02S . Preliminary Storm Water Management Plan.MCD.1 PRELIMINARY STORM WATER MANAGMENT PLAN for Carlsbad Village Town homes 2683 & 2687 Roosevelt St Carlsbad, CA prepared by: Tim Graves, P.E. 27003 (exp 3/1/0) 9373 Hazard Way, #101 San Diego, CA 92123 858.5659512 5/2/05 4ofESSio4, IMOTHY' ( GRAVES No. 27003 II EM-31 -0 1j*1 OF j1 METHOD Preliminary Storm Water Management Plan.MCD.2 This preliminary study was prepared pursuant to the County of San Diego - SUSMP Manual. Hydrology is based upon by the San Diego County department of Pubic Works, Flood Control Division, Hydrology Manual, 2003. TIME PERIOD The time periods for calculation of design flows is: EXISTING CON DlTlONS(PRE-DEVELOPMEND AND PROPOSED CONDITIONS (POST DEVELOPMENT) RATIONAL METHOD TheRational Method Formula is 0 = C X I X A 0 is the peak design discharge In cubic feet per second C Is the coefficient of runoff I is the rainfall intensity in inches per hour A is the tributary drainage area in acres Run-off Coefficients - Soil Group 0 Run-off Coefficients - Soil Group D Native 0.45 Landscaped Areas 0.45 Pavement 0.90 Roof Surfaces 0.90 Summary of Results Area Existino ProDosed "Pre-Development" "Post-Development" CHANGE Sub-Basin "A: Drainage Area 0.46 Ac 0.46 Ac Run-Off Coef. 0.88 0.86 Design Runoff 0.0161 ac-ft 0.0199 ac-ft +23.6% Conclusion: The proposed project will result is an increase in total volume, of run-off from thre project site (23.6%) due to the increase in the amount of impervious surfaces. Most of the runoff is conveyed to the stormdrain system via surface flow over paved areas. The recommended mitigation of the increased run-off volume is to route the run-off from the paved areas into shallow depressions in the Landscaped areas to increase the amount of percolation thereby decreasing the amount of run-off. All runoff, therefore, is filitered prior to discharge across the property line. Attachments: 85th Percentile Precipitation lsopluvial Map S S Sub-Basin A (Existing) Preliminary Storm Water Management Plan.MCD.3 4.3 Site Hydrology Run-off Coefficient - Soil Type D Runoff Coefficient Al := 6721 + 4163 Area of Impervious Surfaces (Roof, Patio, Pave, etc) C1 := 0.9 Ap := 800 + 8537 Area of Pervious Surfaces (Landscaping, natural, etc) Cp 0.45 A:= (Al + Ap).Ac Totalarea - Ac A=0.46 % Impervious Percentl := AI-Ac Percenti = 0.54 % Pervious Percentp P Percent p = 0.46 C:= Ci.Percent,+ CpPercentp c= 0.69 Intensity based upon 85th Pecentile 24Hr Storm 0.6 Design Stomiwater Runoff for Sub-Basin - Total 12 = 0.0161 ac-ft Sub-Basin A (Proposed) 4.3 Site Hydrology Run-off Coefficient- Soil Type D A1 := 13895 + 4486 Area of Impervious Surfaces (Roof, Patio, Pave, etc) Ap := 1840 Area of Pervious Surfaces (Landscaping, natural, etc) A:= (Al + Ap).Ac Total area - Ac % Impervious Percenti := Al Ac A % Pervious Percentp ApAc A C:= C Percenti + Cp.Percentp Intensity based upon 85th Pecentile 24HrStorm 0.6 Design Stormwater Runoff for Sub-Basin - Total Runoff Coefficient C:= 0.9 Cp:= 0.45 A=0.46 Percentl = 0.91 Percentp = 0.09 c=0.86 ac-ft 12 Preliminary Storm Water Management Plan.MCD.4 4.4 Water Quality Treatment Volume Based Upon Water Quality Design Storm runoff from tributary to BMP Flow Based BMP - per SUSMP Section 4.3.2 Intensity based 0.2 in/Hr I 0.2 Water Quality Design Stormwater Runoff Rate Q_Treatment := C.A.l.(7.48).60 Q_Treatment = 35.79 gpm - Required Treatment Capacity at BMP Use (2) 20 gpm Filter Catch Basins List Of Pollutants: This Report is prepared pursuant to the standards contained in the Manual for Permanent Storm Water Best Management Requirements. The following pollutants have been identified as project specific areas of concern: 01 Organic Compounds, including cleansing agents 02 Trash & Debris, including recyclable plastics, paper, etc 03 Oil & Grease including paint and solvents 04 Pesticides and Fertilizers The receiving waters for the discharge from the site is the Buena Vista Lagoon and ultimately into the Pacific Ocean. The stormwater will be transmitted via the existing concrete swale on the adjacent property to the west, then into the City Street drainage system that flows on the pavement of State Street to the north, then down storm water drains continuing to the north to the discharge entry into the Buena Vista Lagoon near the intersection of Highway 101 at State Street in the northwest area of Carlsbad. Site Design BMPs: The project site design has incorporated the following BMPs into the plan: 01 The post development water runoff discharge rates have been reduced, by directing all surface and roof drainage to the rear. All roof drains exit into landscape plantings areas to reduce flows, then all excess runoff is collected in area drains and piped through on-site subsurface pipes into a discharge manifold on the property. The low level light wells and the minor surface flows that collect at the rear of the parking garage are pumped to the discharge manifold via a small sump pump; This system reduces and mitigates the post development discharge to below the existing 1.7 cfs site discharge rate; 02 New sidewalk drains to landscaping and plantings areas for sediment control and deposit prior to entering any underground landscape drain. Each landscape NDS area drain has a built in sediment trap bottom; 03 The minimal slope of the underground drainage system around the perimeter of the site will minimize the flow velocities, and the drainage flows will exit the property through a filtered discharge manifold system with retention capacity to reduce the post development discharge to below the existing condition; 04 The new impervious drives and walkways have been kept to a minimum solely to accommodate the functional use; 05 The new planting areas around the perimeter of the structure have been incorporated into the final plan to increase on-site absorption in the post development condition; 06 There are no new slopes to stabilize; and 07 Existing vegetation & trees have been replaced to the extent possible. Source Control BMPs: The following source control BMPs are included in the final plan and are to be used the the owner of the property: 01 All hazardous materials, such as fertilizers and paints shall be kept in storage cabinets in the garage as shown on the first floor plan; 02 No outdoor storage areas are permitted; 03 Trash storage shall also be in City containers and dumpsters in the covered garage and therefore not exposed to stormwater; 04 To the extent possible, pest-resistant plants will be specified in the landscape plan, and the use of pesticides by the gardener or homeowner shall be applied according to the manufacturer's instructions as written on the packaging; 05 The Irrigation system shall have a rain sensor and auto shut-off, with drip emitters for shrubs and pop-up misters for ground cover and planting areas to minimize over spray; 06 Parking areas are covered, preventing stormwater from coming into contact with possible pollutants on the pavement. 07 All catch basins shall be filtered, and routinely cleaned by the gardener; 08 A warning "stencil" shall be imprinted on the concrete adjacent to the catch basin retention sump at the rear of the parking garage drive, and shall state "Dumping of oil, paint, etc. or other hazardous pollutants is strictly prohibited"; Responsible Party for Maintenance: Since this is a multi-family development, the Homeowners Association shall retain the long-term responsibility for adherence to and compliance with these BMPs. Any gardeners or "handymen" who are hired to perform tasks at the property shall be informed of their responsibility to additionally comply with the written and implied intent of these guidelines. Applicability Review of BMPs: Section 3 - Erosion & Sediment Control From Table 3 - I of the BMP Handbook, the following BMPs have been determined to apply to the Project Site: EC -I Scheduling yes most of work during dry season EC -2 Preservation of no no steep slopes Existing Vegetation EC -3 Hydraulic Mulch no no steep slopes to protect EC-4 Hydroseeding no no steep slopes EC - 5 Soil Binders yes reliable stabilant EC -6 Straw Mulch yes good temp. cover until final planting EC -7 Geotextiles & Mats no for more severe conditions EC -8 Wood Mulching no straw OK EC -9 Earth Dikes & Swales no no place to divert to, full site impact EC - 10 Velocity Dissipation no no erosive velocities EC - 11 Slope Drains no no slopes to protect EC - 12 Streambank Stabilization no no applicability EC * 13 Polyacrylamide no no applicability From Table 3 - 2, Temporary Sediment Control BMPs, the following BMPs have been determined to apply to the Project Site: SE - 1 Silt Fence SE -2 Sediment Basin SE-3 Sediment trap SE -4 Check Dam SE - 5 Fiber Rolls SE-6 Gravel Bag Berm SE-7 Street Sweeping SE-8 Gravel Bag Barrier SE-9 Straw Bale Barrier SE - 10 Storm Drain Inlet Protection yes at perimeter no for larger sites yes perfect for project size no no fast moving runoff yes good perimeter measure no for larger projects yes if required yes as alternate to fiber / straw rolls no for larger slopes yes inlet to west in State Street From Table 3 - 3, Wind Erosion Control, since the site is in a wind sheltered area this BMP does not apply, but is included for reference if it may be required. From Table 3 - 4, Tracking Control BMPs, since vehicle deliveries will be dropping materials to the existing concrete driveway, and the majority of the work will take place during the "dry" season, no Tracking BMPs will be applicable. There will be no continuous heavy equipment entering nor leaving the site on a daily basis. The bobcat work, restricted to the site shall be carefully monitored for mud-free wheels when the equipment is reloaded onto the truck. Section 4 - Non-Stormwater Management and Material Management BMPs From Table 4 - 1, Non-Stormwater Management BMPs, the following BMPs have been determined to be applicable to the Project Site: NS - I Water Conservation Practice yes NS -2 Dewatering Operations no none to be used NS-3 Paving & Grinding Operations yes concrete drives & patios NS -4 Temporary Stream Crossing no no applicability NS -5 Clear Water Diversion no no applicability NS -6 Illicit Connection I Discharge yes NS-7 Potable Water I Irrigation yes NS -8 Vehicle & Equipment Cleaning no none on site NS -9 Vehicle & Equipment Fueling no none on site NS - 10 Vehicle & Equipment Maintenance no none on site NS - 11 Pile Driving Operations no none on site NS - 12 Concrete Curing no none to be used NS - 13 Concrete Finishing yes NS - 14 Material & Equip Use Over Water no no applicability NS - 15 Demolition Adjacent to Water no no applicability NS - 16 Temporary Batch Plants no no applicability From Table 4 - 2, Waste Management & Materials Pollution Control BMPs, the following BMPs have been determined to be applicable to the Project Site: WM - I Material Delivery & Storage yes WM-2 Material Use yes WM -3 Stockpile Management no no applicability WM-4 Spill Prevention & Control yes WM-5 Solid Waste Management yes WM-6 Hazardous Waste Management yes WM-7 COntaminated Soil Management no no applicability WM -8 Concrete Waste Management yes WM -9 Sanitary I Septic Waste Management yes WM - 10 Liquid Waste Management no no applicability Implementation: All of the applicable Best Management Practices are included herein the appendix of this report and become an integral part of the Stormwater Pollution Control Plan. Compliance with these regulations shall be sole responsibility of the Contractor. Any violations cited by the Architect of Record or by the City Building Inspector shall be immediately addressed and corrected so that the work may progress in an orderly manner, and contribute to preserving the general water quality in the village area of the City of Carlsbad, California. Post Construction Report, & Owner Responsibility: The site design has captured the potential rainfall and use of construction water and will direct it to the northesst corner of the property for disposition following the natural contours and topograhpy of the existing street. No offsite stormwater or rainfall runoff is anticipated to migrate onto the construction site due to the natural direction of existing offsite drainage away from the site and the existing drainage of the street at the front of the property toward the north. The Owner of the property shall retain the long-term post construction responsibility to assure that the implied or required maintenance of each Best Management Practice is adhered to. This will include weekly trash removal in City approved containers, weeding of planting beds and proper mowing of lawns with proper disposal of cuttings, routine checks of hose bibbs & irrigation components for leaks, proper leaf removal from street trees, and proper disposal of used containers from general household cleaning products. The landscape drains shall be kept free from debris, and the sump shall be routinely maintained by the Homeowner's Association to be certain that the disconnect alarm sensor is fully functional. A final report shall be prepared by the contractor, and shall be provided to the Building Inspector at final inspection, identifying the procedures that were used to control the following sources of potential pollution that the construction materials & methods of installation would have caused had they been improperly handled: 01 vehicle, equipment and/ or tool fluids; 02 concrete and concrete rubble; 03 paints and solvents; 04 mortar mix and slurry residues; 05 masonry rubble and chipped pieces; 06 wood framing fragments, waste and remnants; 07 clay tile roofing and waste; 08 plumbing solder and flux; 09 sandbags and/or straw mulch; 10 packaging and wrapping, including styrofoam, plastic and cardboard; 11 raw landscaping materials, topsoil, plants, fertilizers, pesticides; 12 used form boards; 13 removal of contaminated soil at sediment trap; 14 disposal of excess straw mulch after use complete; 15 removal of temporary sanitary unit; 16 general trash removal; 17 itemization of any unanticipated spills and remedy methods; and 18 other potential items as may be identified by Architect during construction. I -]( R I E R SIDE COUNTY c h1t H?(T S5th Percentile Precipitation isopluvial Map Rainfall in Inches Ott DRAFT 6127101 C) / C.