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HomeMy WebLinkAboutSDP 05-18A; ECR CORPORATE CENTER; STORM WATER MANAGEMENT PLAN; 2007-07-27r jc c1v6 Storm Water Management Plan ECR CORPORATE CENTER CITY OF CARLSBAD SAN DIEGO COUNTY, CALIFORNIA (MAP NO. 14543) SDP 05-18A April 16, 2007 Revised: July 27, 2007 Prepared for: ECR Corporate Center, L.P. 5600 Avenida Encinas, Suite 100 Carlsbad, CA 92008 CONTACT: John C. White, President Prepared by: 'S P RBF CONSULTING 5050 Avenida Encinas, Suite 260 Carlsbad, CA 92008 760.476.9193 CONSULTING Contact Person: ffj573 Tim Thiele, P.E. 1f_t C60283 9i17Z# RBF JN 55-100293 CNIL RIECEWED OCT 16 2001 ENGINEERING DEPARTMENT U STORM WATER MITIGATION PLAN TABLE OF CONTENTS TABLEOF CONTENTS..................................................................................................I IPURPOSE OF SCOPE...............................................................................2 2 PROJECT INFORMATION.........................................................................2 2.1 Project Description ...................................................................................... 2 2.2 Project Activities .........................................................................................2 3 WATER QUALITY CONDITIONS OF CONCERN......................................4 3.1.1' Potential Pollutants ..................................................................................... 4 3.1.2 Pollutants of Concern..................................................................................6 3.1.3 Conditions of Concern ................................................................................7 4 POST-CONSTRUCTION BEST MANAGEMENT PRACTICE PLAN..........8 4.1 Site Design BMPs.......................................................................................8 4.2 Source Control BMPs .................................................................................9 4.3 BMPs for Individual Project Categories.....................................................12 4.4 Treatment Control BMPs...........................................................................12 4.5 Construction-Phase BMPs........................................................................15 5 MAINTENANCE .......................................................................................16 POST-CONSTRUCTION BMP SITE MAP....................................................................17 TABLE OF FIGURES S Figure2-1 Vicinity Map ................................................................................................3 Figure 4-1 Kristar Floguard Plus® Inlet Insrt ............................................................ 15 LIST OF TABLES Table 3-1 Anticipated and potential pollutants by project type (San Diego County, 2002a) ........................................................................................................4 Table 3-2 Summary of 303(d) impairments of downsteam water bodies.....................7 Table 4-1 Site, design BMPs' alternatives.....................................................................8 Table 4-2 Source-control BMP alternatives.................................................................9 Table 4-3 Carlsbad SUSMP Individual Project Categories ......................................... 12 Table 4-4 Treatment Control BMP Selection Matrix (San Diego County, 2002a).......13 Table 4-5 Treatment-Control BMP alternatives.........................................................13 APPENDIX A STORM WATER REQUIREMENTS APPICABILITY CHECKLIST B BMP CALCULATIONS La Costa Greens - Lot I I Storm Water Mitigation Plan • • STORM WATER MITIGATION PLAN I PURPOSE AND SCOPE This report presents the water quality measures required for the development of Lot I of the La Costa Greens Development, in order to fulfill the requirements of the City of Carlsbad. This report also describes the implementation and maintenance of water quality Best-Management Practices that will be installed on the site. 2 PROJECT INFORMATION 2.1 Project Description The project is located within the City of Carlsbad in the La Costa Greens Development (CT-99-03). The project is adjacent to El Camino Real, just south of Town Garden Road (see Figure 2-1). The site will be rough graded per City Drawing No. 397-2Y and is currently vacant. Existing site conditions include one 7.7 acre graded pad with a vegetated parkway along El Camino Real. The project site contains side slopes of 2:1 or less. The project is not located within the Coastal Zone. Its land use designation is Medical. There are no water bodies, sanitary landfills, historical, archaeological or paleontological resources located within a half-mile of the project site. A conservation easement (within La Costa Greens Lot 20) borders the project area to the east. 2.2 Project Activities The project will consist of a medical office building (25,000 sq. ft.), a wellness facility (62,000 sq. ft.), and adjacent parking lots (160,000 sq. ft.). Landscaping will be incorporated into the planter medians and parkway strips surrounding each lot. There are two private driveways proposed as part of this project. The driveways will provide access to the site from El Camino Real and from Metropolitan Street. Drainage from the project will be directed into a proposed storm drain system and connected to an existing piping system that will outlet to open space located directly south of the project area on La Costa Greens Lot 2. Although the site is to be rough graded, approximately 90% of the site will be re-graded as partof this project. The project is considered a high priority project by the City of Carlsbad. (See Appendix A - "Storm Water Requirements Applicability Checklist") Therefore, the project will incorporate all applicable permanent storm water management requirements. These include the site design and source control BMPs, BMPs applicable to individual priority project categories, and treatment control BMP requirements. La Costa Greens - Lot 1 2 Storm Water Mitigation Plan PF STORM WATER MITIGATION PLAN Figure 2-1 Vicinity Map (Reference Thomas Bros. 1086) MOPNOMM 7 /EDE L S: VIDA A - i LL - r.) n1 IITE A') ,'A (fl() ©2005 Thomas Bros Maps La Costa Greens - Lot 1 Storm Water Mitigation Plan 3 WF STORM WATER MITIGATION PLAN :. Nutrients (since there will be landscaped areas on site); :. Organic compounds; :• Metals (associated with vehicle parking); :. Litter and trash collecting in the drainage systems; Oxygen-demanding substances including, biodegradable organic material and chemicals; + Oils, grease, and other hydrocarbons emanating from paved areas on the site; + Pesticides used to control nuisance growth; and 3.1.1 Sediment Sediments are soils or other surface materials eroded and then transported or deposited by the action of wind, water, ice, or gravity. Sediments can increase turbidity, clog fish gills, reduce spawning habitat, lower young aquatic organisms survival rates, smother bottom dwelling organisms, and suppress aquatic vegetation growth. 3.1.2 Nutrients Nutrients are inorganic substances, such as nitrogen and phosphorus. They commonly exist in the form of mineral salts that are either dissolved or suspended in water. Primary sources of nutrients in urban runoff are fertilizers and eroded soils. Excessive discharge of nutrients to water bodies and streams can cause excessive aquatic algae and plant growth. Such excessive production, referred to as cultural eutrophication, may lead to excessive decay of organic matter in the water body, loss of oxygen in the water, release of toxins in sediment, and the eventual death of aquatic organisms. 3.1.3 Metals Metals are raw material components in non-metal products such as fuels, adhesives, paints, and other coatings. The primary sources of metal pollution in storm water are typically commercially available metals and metal products. Metals of concern include cadmium, chromium, copper, lead, mercury, and zinc. Lead and chromium have been used as corrosion inhibitors in primer coatings and cooling tower systems. At low concentrations naturally occurring in soil metals are not toxic. However, at higher concentrations, certain metals can be toxic to aquatic life. Humans can be impacted from contaminated groundwater resources, and bioaccumulation of metals in fish and shellfish. Environmental concerns, regarding the potential for release of metals to the environment, have already led to restricted metal usage in certain applications. 3.1.4 Organic Compounds Organic compounds are carbon-based (commercially available or naturally occurring) substances found in pesticides, solvents, and hydrocarbons. Organic compounds can, at certain concentrations, indirectly or directly constitute a hazard to life or health. When rinsing off objects, toxic levels of solvents and cleaning compounds can be discharged to storm drains. Dirt, grease, and grime retained in the cleaning fluid or rinse water may also adsorb levels of organic compounds that are harmful or hazardous to aquatic life. La Costa Greens - Lot I . . 5 Storm Water Mitigation Plan . . WF STORM WATER MITIGATION PLAN 3.1.5 Trash and Debris Trash (such as paper, plastic, polystyrene packing foam, and aluminum materials) and biodegradable organic matter (such as leaves, grass cuttings, and food waste) are general waste products on the landscape. The presence 'of trash and debris may have a significant impact on the recreational value of a water body and aquatic habitat. Excess organic matter can create a high biochemical oxygen demand in a stream and thereby lower its water quality. Also, in areas where stagnant water exists, the presence of excess organic matter can promote septic conditions resulting in the growth of undesirable organisms and the release of odorous and hazardous compounds such as hydrogen sulfide. 3.1.6 Oxygen-Demanding Substances This category includes biodegradable organic material as well as chemicals that react with dissolved oxygen in water to form other compounds. Proteins, carbohydrates, and fats are examples of biodegradable organic compounds. Compounds such as ammonia and hydrogen sulfide are examples of oxygen-demanding compounds. The oxygen demand of a substance can lead to depletion of dissolved oxygen in a water body and possibly the development of septic conditions. 3.1.7 Oil and Grease Oil and grease are characterized as high-molecular weight organic compounds. The primary sources of oil and grease are petroleum hydrocarbon products, motor products from leaking vehicles, esters, oils, fats, waxes, and high molecular-weight fatty acids. Introduction of these pollutants to the water bodies are very possible due to the wide uses and applications of some of these products in municipal, residential, commercial, industrial, and construction areas; Elevated oil and grease content can decrease the aesthetic value of the water body, as well as the water quality. 3.1.8 Pesticides Pesticides (including herbicides) are chemical compounds commonly used to control nuisance growth of organisms. Excessive application of a pesticide may result in runoff containing toxic levels of its active component. 3.2 Pollutants of Concern The Environmental Protection Agency (EPA) is the primary federal agency responsible for management of water quality in the' United States. The Clean Water Act (CWA) is the federal law that governs water quality control activities initiated by the EPA and others. Section 303 of the CWA requires the adoption of water quality standards for all surface water in the United States. Under Section 303(d), individual states are required to develop lists of water bodies that do not meet water quality objectives after required levels of treatment by point source dischargers. Total maximum daily loads (TMDLs) for all pollutants for which these water bodies are listed must be developed in order to bring them into compliance with water quality'objectives. The project is located within the San Marcos hydrologic area of the Carlsbad hydrologic unit. Receiving waters for the project site include the Pacific Ocean. According to the La Costa Greens - Lot I 6. , WF Storm Water Mitigation Plan STORM WATER MITIGATION PLAN California 2002 303(d) list published by the San Diego Regional Water Quality Control Board (RWQCB Region 9), the project is not impaired by any of the potential sources. Table 3-2 summarizes the receiving waters and their classification by the RWQCB Region 9. Table 3-2 Summary of 303(d) impairments of downstream water bodies. Hydrologic Approximate 303(d) Receiving Water Unit Distance Code From Site impairment(s) Pacific Ocean Shoreline-, San Marcos HA 904.50 3.5 mi Bacteria indicators 3.3 Conditions of Coflcern According to the City of Carlsbad SUSMP, a change to a priority project site's hydrologic regime would be considered a condition of concern if the change would impact downstream channels and habitat integrity. However, the changes in hydrologic characteristics resulting from the development of this site have already been incorporated into the downstream storm drain system design. Runoff from this site will discharge into open space located south of the project area on La Costa Greens Lot 2. A separate drainage report (Master Drainage Report for La Costa Greens Project) has been prepared to support the design of the existing storm drain system. This study assumed future development within the watershed when determining pipe sizes and impacts to downstream facilities. Since runoff from the project discharges into new and existing drainage facilities that are verified to accommodate peak runoff flow rates from a 100-year storm event, there are no conditions of concern associated with the project. The Federal Insurance Rate Map (FIRM) for this area. shows that the project's location is out of the 100-year floodplain. La Costa Greens - Lot 1 7 PF Storm Water Mitigation Plan . STORM WATER MITIGATION PLAN 4 POST-CONSTRUCTION BEST MANAGEMENT PRACTICE PLAN The project site incorporates four major types of post-construction best management practices (BMPs). These types are (1) site design BMPs; (2) source control BMPs; (3) site design and source control BMPs for individual priority project categories; and (4) treatment control BMPs. In general, site design BMPs and source control BMPs reduce the amount of storm water and potential pollutants emanating from a site and focus on pollution prevention. Treatment-control BMPs target anticipated potential storm water pollutants. The project will apply these BMPs to the maximum extent practicable. 4.1 Site Design BMPs Site design BMPs aim to conserve natural areas and minimize impervious cover, especially impervious areas 'directly connected' to receiving waters, in order to maintain or reduce increases in peak flow velocities from the project site. The U.S. EPA (2002) has listed several site design BMPs that can be implemented in development projects. The project has incorporated site design BMPs to the maximum extent practicable. Table 4-1 lists site-design BMP alternatives and indicates the practices that have been applied to the project site. Table 4-1 Site design BMPs alternatives. Buffer Zones 0 Open Space Design Narrower Residential Streets . 0 "Green" Parking O Alternative Turnarounds o Alternative Payers O Urban Forestry •0 Conservation Easements Eliminating Curbs And Gutters 0 Landscape Design Other (Explained Below) 4.1.1 Minimize Impervious Footprint and Directly Connected Impervious Areas The project will minimize the-use of impervious surfaces in landscape design, such as decorative concrete, in order to minimize impervious footprint on the site and the amount of directly connected impervious surface. Building roof drains, parking lots, and sidewalks will discharge to vegetated swales and depressed areas, instead of directly to the storm drain collection system, to reduce the amount of directly connected impervious surface. Parking lots will be constructed to minimum widths and will drain to vegetated areas. Curbs have been elimihated in various areas to allow Sheet flow into Bio- Retention Areas. 4.1.2 Protect Slopes and Channels Site runoff will be directed away from the tops of slopes, and all slopes will be vegetated to provide permanent stabilization. S La Costa Greens - Lot 1 8 Storm Water Mitigation Plan WF STORM WATER MITIGATION PLAN 4.1.3 Bio-Retention. Areas The bio-retention areas function as a soil and plant-based filtration device that removes pollutants through a variety of physical, biological, and chemical treatment processes. These facilities normally consist of a grass buffer strip, sand bed, ponding area, organic layer or mulch layer, planting soil, and plants. Cost ranges between $10 and $40 per square foot depending on other drainage facilities associated with the bio-retention areas, such as drain piping. The, areas function to reduced the velocity of runoff by passing over or through buffer strip and subsequently distributed evenly along a ponding area. Exfiltration of the stored water in the bio-retention area planting soil into the underlying soils occurs over a period of days. (Refer to TC-32 in Appendix B). 4.2 Source Control BMPs Source-control BMPs are activities, practices, and procedures (primarily non-structural) that are designed to prevent urban runoff pollution. These measures either reduce the amount of runoff from the site or prevent contact between potential pollutants and storm water. In addition, source-control BMPs are often the best method to address non-storm (dry-weather) flows. Table 4-2 lists source-control BMP alternatives and indicates the practices that will be applied at the project site. Table 4-2 Source-control BMP alternatives. ID Storm Drain Stenciling and Signage 0 Homeowner Outreach. 0 Material and Trash Storage Area Design . 0 Lawn and Gardening Practices 0 Efficient Irrigation Systems 0 Water Conservation 0 Low-Irrigation Landscape Design 0 Hazardous Waste Management On-Lot Treatment Measures 0 Trash Management Riprap or Other Flow Energy Dissipation Outreach for Commercial Activities Other (Explained Below) 4.2.1 Efficient Landscape Design and Irrigation Practices Efficient landscape design and irrigation practices can be an effective source-control to prevent pollution in storm water and dry-weather flows. The completed project will implement principles of common-area efficient irrigation, runoff-minimizing landscape design, and an effective landscape maintenance plan to the maximum extent practicable. 4.2.1.1 Common-Area Efficient Irrigation Automatic irrigation systems should include water sensors, programmable irrigation timers, automatic valves to shut-off water in case of rapid pressure drop (indicating possible water leaks), or other measures to ensure the efficient application of water to the landscape and prevent unnecessary runoff from irrigation. Drip irrigation and other low-water irrigation methods should be considered where feasible. Common elements of efficient irrigation programs include: La Costa Greens — Lot I . 9 Storm Water Mitigation Plan PF STORM WATER MITIGATION PLAN :• Reset irrigation controllers according to seasonal needs. :. Do not over-water landscape plants or lawns. :. Keep irrigation equipment in good working condition. Promptly repair all water leaks. 4.2.1.2 Runoff-Minimizing Landscape Design Landscape designs that group plants with similar water requirements can reduce excess irrigation runoff and promote surface infiltration. Landscapö designs should utilize non- invasive native plant species and plants with low water requirements when possible. 4.2.1.3 Landscape Maintenance The landscape maintenance plan should include a regular sweeping program of impervious surfaces, litter pick-up, and proper equipment maintenance (preferably off- site), and proper use of chemicals to help eliminate sources of storm water pollutants. Common elements of an effective landscape maintenance plan include: Implementing a regular program of sweeping sidewalks, driveways, and gutters as part of the landscape maintenance plan. Pick-up litter frequently. Provide convenient trash receptacles for public use if necessary. Avoid using water to clean sidewalks, driveways, and other areas. :. Discourage washing of landscape maintenance equipment on-site. Minimize water use and do not use, soaps or chemicals. Use a commercial wash-rack facility whenever possible. :• Keep landscape maintenance equipment in good working order. Fix all leaks promptly, and use dnp pans/drip cloths when draining and replacing fluids. Collect all spent fluids and dispose, of them properly. Designate equipment maintenance areas that are away from storm water inlets. Perform major maintenance and repairs off-site if feasible. :• Materials with the potential to pollute runoff (soil, pesticides, herbicides, fertilizers, detergents, petroleum products, and other materials) should be handled, delivered, applied, and disposed of with care following manufacturer's labeled directions and in accordance with all applicable Federal, state; and local regulations. Materials will be stored under cover or otherwise protected when rain is forecast or during wet weather. :• Pesticides and. fertilizers, if used, will be applied according to manufacturer's directions and will not be applied prior to a forecast rain event. Any material broadcast onto paved surfaces (e.g. parking areas or sidewalks) will be promptly swept up and properly disposed. 4.2.2 Material and Trash Storage Area Design La Costa Greens - Lot 1 . . 10 Storm Water Mitigation Plan , STORM WATER MITIGATION PLAN There are no outdoor material storage areas associated with the proposed project. The trash storage area will be designed' to contain stored material to prevent debris from being distributed into storm water collection areas. For example, dumpsters with lids will be kept in a separate enclosed area to prevent debris from being scattered by wind or animals. The trash storage area will be paved with an impervious surface such as concrete or asphalt concrete. In addition, the trash storage area will be graded to prevent run-on from adjoining areas. 4.2.3 Pollution Prevention Outreach for Businesses One source-control best management practice for commercial sites is pollution prevention outreach. For instance, at the lease signing or as part of the lease, the tenant can be presented with a brochure to encourage them to develop and implement a pollution prevention program. The pollution prevention program would emphasize source reduction, reuse and recycling, and energy recovery. The following offer suggestions for measures to be included in these areas of pollution prevention. The pollution prevention outreach should choose the measures most applicable to the project site for the project site. 4.2.3.1 Source Reduction + Incorporating environmental considerations into the designing of products, buildings, and manufacturing systems enables them to be more resource efficient. Rethinking daily operations and maintenance activities can help industries eliminate wasteful management practices that increase costs and cause pollution. :. Controlling the amount of water used in cleaning or manufacturing can produce less wastewater. :• Re-engineering and redesigning a facility or certain operation can take advantage of newer, cleaner and more efficient process equipment. :. Buying the correct amount of raw material will decrease the amount of excess materials that are discarded (for example, paints that have a specified shelf life). 4.2.3.2 Reuse/Recycling :• Using alternative materials for cleaning, coating, lubrication, and other production processes can provide equivalent results while preventing costly hazardous waste generation, air emissions, and worker health risks. + Using "green" products decreases the use of harmful or toxic chemicals (and are more energy efficient than other products). + One company's waste may be another company's raw materials. Finding markets for waste can reduce solid waste, lessen consumption of virgin resources, increase income for sellers, and provide an economical resource supply for the buyers. La Costa Greens — Lot 1 11 MF Storm Water Mitigation Plan STORM WATER MITIGATION PLAN 4.2.3.3 Energy Recovery :• Using energy, water, and other production inputs more efficiently keeps air and water clean, reduces emissions of greenhouse gases, cuts operating costs, and improves productivity. 4.2.3 Storm Drain Stenciling and Signage All new storm drain grate inlets constructed as part of this project will be signed with the message "No Dumping - Drains, to Oceans" or equivalent message as directed by the City. 4.3 BMPs for Individual Project Categories The City of Carlsbad SUSMP lists ten individual project categories for which BMPs must be provided. Table 4-3 below lists these individual project categories and indicates that the individual category of parking areas is applicable to the proposed project. Inlets equipped with filter inserts treat any runoff generated and additional treatment is provided as discussed in Section 4.4. MOst parking areas will discharge to depressed vegetated areas, instead of directly to the storm drain collection system. Slopes will be vegetated to provide permanent stabilization and to prevent erosion. Table 4-3 Carlsbad SUSMP Individual Project Categories Private Roads Residential Driveways & Guest Parking O Dock Areas Maintenance Bays Vehicle Wash Areas O Outdoor Processing Areas Equipment Wash Areas Parking Areas Fueling Area Hillside Landscaping 4.4 Treatment Control BMPs Post-construction "treatment control" storm water management BMPs provide treatment for storm water emanating from the project site Structural BMPs are an integral element of post-construction storm water management and may include storage, filtration, and infiltration practices. BMPs have varying degrees of effectiveness versus different pollutants of concern. Table 4-4 below summarizes which treatment control BMPs and removal effectiveness for certain constituents. La Costa Greens - Lot I 12 Storm Water Mitigation Plan . , MF STORM WATER MITIGATION PLAN Table 4-5 Treatment-Control BMP alternatives. C1 Vegetated Swales and/or Strips 0 Wet Ponds/Wetlands o Dry Extended Detention Basins 0 Infiltration Basins o Bio-Retention Areas 0 Sand or Organic Filters o Hydrodynamic Separators 0 Infiltration Trenches Catch Basin/Inlet Inserts 0 Other (Explained Below) Of the treatment control options available for this project, infiltration practices are not feasible due to the preponderance of hydrologic soil type D throughout the site, which has poor infiltration properties. Wet ponds and constructed wetlands rely on a perennial water source, which is generally difficult to sustain in the project's and environment. While filtration devices, such as sand filters and media filters, typically have medium to high removal efficiencies for the project's pollutants of concern, they are aesthetically unsuitable for use in developments such as this project. An underground sand/media filter might improve aesthetics, but these are not recommended for drainage areas greater than 2 acres (2003 California New Development BMP Handbook, Fact Sheet TC-40), and the proposed project covers 7.7 acres. Since the proposed project site consists of a generally flat graded pad, implementing several filters for smaller drainage areas is not feasible due to the lack of required head needed to ensure that water passes through the filter. 4.4.1.1 Drainage Filter Inserts To provide additional treatment and removal of potential pollutants, drainage inlet inserts will be installed in all storm drain inlets capturing runoff from the parking lots. Kristar Floguard Plus® inserts or equivalent will be specified to treat runoff for hydrocarbons and trash/debris. The Kristar Floguard Plus® inlet insert is shown in Figure 4-1, and is similar in design and-function to other proprietary inlet inserts. Surface runoff .enters the inlet and passes over/through and adsorbent material to remove hydrocarbons, while sediments and trash/debris are collected in the hanging basket. Recommended maintenance consists of three inspections per year (once before the wet season and two during, or more as may be needed) plus replacement of the adsorbent when it is more than 50% coated with pollutants and removal of excessive sediment/debris. Each inlet insert costs about $570 and is available locally through Downstream Services (760-746- 2544 or 760-746-2667). The inserts can be installed by Downstream Services for additional cost or by the project construction contractor. Maintenance costs are estimated at about $400 per year. (Refer to Appendix B for design calculations). La Costa Greens — Lot 1 14 Storm Water Mitigation Plan MF STORM WATER MITIGATION PLAN 5 MAINTENANCE To ensure long-term maintenance of project BMPs, the project proponent will enter into a contract with the City of Carlsbad to obligate the project proponent to maintain, repair and replace the storm water BMP as necessary into perpetuity. Security will be required in the form of a Letter of Credit. The site shall be kept in a neat and orderly fashion with a regularly scheduled landscape maintenance crew in charge of keeping gutters and inlets free of litter and debris. The landscape crew will also maintain the landscaping to prevent soil erosion and minimize sediment transport. The groject consists of a series of Brooks boxes, which will include Kristar Floguard Plus inlet inserts. It is recommended that the hydrocarbon absorption booms be replaced four times per year. Currently the approximate cost to replace each boom is $100.00. This amounts to a maintenance cost of $400.00 per year, per inlet. The project also includes several bio-retention areas. These areas will require nothing more than the routine periodic maintenance that is required of any landscaped area. This includes regular pruning and weeding. Mulch should be replaced as erosion occurs or, at the very least, every 2-3 years prior to the wet season. Maintenance records shall be retained for at least 5-years. These records shall be made available to the City of Carlsbad for inspection upon request. La Costa Greens — Lot 1 16 Storm Water Mitigation Plan PF APPENDIX A - Storm Water Standards 4103/03 a. i APPENDIX A• STORM WATER REQUIREMENTS APPLICABILITY CHECKLIST Complete Sections 1 and 2 of the following checklist to determine your project's permanent and construction storm water best management practices requirements. This form must be completed and submitted with your permit application. Section 1. Permanent Storm Water BMP Requirements: If any answers to Part A are answered "Yes," your project is subject to the "Priority Project Permanent Storm Water BMP Requirements," and "Standard Permanent Storm Water BMP Requirements" in Section III, "Permanent Storm Water BMP Selection Procedure" in the Storm Water Standards manual. If all answers to Part A are "No," and any answers to Part B are "Yes," your project is only subject to the "Standard Permanent Storm Water BMP Requirements". If every question in Part A and B is answered "No," your project is exempt from permanent storm water requirements. Part A: Determine Priority Proiect Permanent Storm Water BMP Reauirements. Does the project meet the definition of one or more of the priority project N 0 categories?* categories?* Detached residential development of 10 or more units - X Attached residential development of 10 or more units - x Commercial development greater than 100,000 square feet x - Automotive repair shop - x Restaurant - X Steep hillside development greater than 5.000 square feet - x Project discharging to receiving waters within Environmentally Sensitive Areas - x Parking lots greater than or equal to 5,00 ft2 or with at least 15 parking spaces, and potentially exposed to urban runoff X - Streets, roads, highways, and freeways which would create a new paved surface that is 5,000 square feet or greater * Refer to the definitions section in the Storm Wafer Standards for expanded definitions of the priority project categories. Limited Exclusion: Trenching and resurfacing work associated with utility projects are not considered priority projects. Parking lots, buildings and other structures associated with utility projects are priority projects if one or more of the criteria in Part A is met. If all answers to Part A are "No, continue to Part B. 30 - L. Storm Water Standards 4103/03 Part B: Determine Standard Prmannt fnrm Wfr Rpniiirmnf Does the project propose: Yes No New impervious areas, such as rooftops, roads, parking lots, driveways, paths and sidewalks? - New pervious landscape areas and irrigation systems? x - Permanent structures within 100 feet of any natural water body? - x Trash storage areas? x - Liquid or solid material loading and unloading areas? - x Vehicle or equipment fueling, washing, or maintenance areas? - x Require a General NPDES Permit for Storm Water Discharges Associated with Industrial Activities (Except construction)?* - - Commercial or industrial waste handling or storage, excluding typical office or household waste? X Any grading or ground disturbance during construction? x - Any new storm drains, or alteration to existing storm drains? , x To find out if your project is required to obtain an individual General NPDES Permit for Storm Water Discharges Associated with Industrial Activities, visit the State Water Resources Control Board web site 1at, www.swrcb.ca.gov/stormwtr/industrial.html Section 2. Construction Storm Water BMP Requirements: If the answer to. question I of Part C is answered "Yes," your project is subject to Section IV, "Construction Storm Water BMP Performance Standards," and must prepare a Storm Water Pollution Prevention Plan (SWPPP). If the answer to question I is "No;" but the answer to any of the remaining questions is "Yes," your project is subject to Section IV, "Construction Storm Water BMP Performance Standards," and must prepare a Water Pollution Control Plan (WPCP). If every question in Part C is answered "No," your project is exempt from any construction storm water BMP requirements. If any of the answers to the questions in Part C are "Yes," complete the construction site prioritization in Part D, below. Part C: flfrmin Cnntnmtinn Phiqp tnrm W2fr Pi,rgminf Would the project meet any of these criteria during construction? Yes I No Is the project subject to California's statewide General NPDES Permit for Storm Water - Discharges Associated With Construction Activities? - Does the project propose grading or soil disturbance? x Would storm water or urban runoff have the potential to contact any portion of the x construction area, including washing and staging areas? - Would the project use any construction materials that could negatively affect water x quality if discharged from the site (such as, paints, solvents, concrete, and stucco)? - 31 Storm Water Standards 4/03/03 Part D: Determine Construction Site Priority In accordance with the Municipal Permit, each construction site with construction storm water BMP requirements must be designated with a priority: high, medium or low. This prioritization must be completed with this form, noted on the plans, and included in the SWPPP or WPCP. Indicate the project's priority in one of the check boxes using the criteria below, and existing and surrounding conditions of the project, the type of activities necessary to complete the construction and any other extenuating circumstances that may pose a threat to water quality. The City reserves the right to adjust the priority of the projects both before and during construction. [Note: The construction priority does NOT change construction BMP requirements that apply to projects; all construction BMP requirements must be identified on a case-by-case basis. The construction priority does affect the frequency of inspections that will be conducted by City staff. See Section IV.1 for more details on construction BMP requirements.] A) High Priority Projects where the site is 50 acres or more and grading will occur during the rainy season Projects 5 acres or more. 3) Projects 5 acres or more within or directly adjacent to or discharging directly to a coastal lagoon or other receiving water within an environmentally -sensitive area Projects, active or inactive, adjacent or tributary to sensitive water bodies Li B) Medium Priority 1) Capital Improvement Projects where grading occurs, however a Storm Water Pollution Prevention Plan (SWPPP) is not required under the State General Construction Permit (i.e., water and sewer replacement projects, intersection and street re-alignments, widening, comfort stations, etc.) - 2) Pémiit projects in the public right-of-way where grading occurs, such as installation of sidewalk, substantial retaining walls, curb and gutter for an entire street frontage, etc., however SWPPPs are not required. 3) Permit projects on private property where grading permits are required, however, Notice Of Intents (NOIs) and SWPPPs are not required. Li C) Low Priority Capital Projects where minimal to no grading occurs, such as signal light and loop installations, street light insiallations, etc. Permit projects in the public right-of-way where minimal to no grading occurs, such as pedestrian ramps, driveway additions, small retaining walls, etc. 3) Permit projects on private property where grading permits are not required, such as small retaining walls, single-family homes, small tenant improvements, etc. I- 32 APPENDIX B Bioretention TC-32 Design Considerations Soil for Infiltration Tributary Area a Slope Aesthetics Environmental Side-effects Description The bioretention best management practice (BMP) functions as a Targeted Constituents soil and plant-based filtration device that removes pollutants Sediment through a variety of physical, biological, and chemical treatment processes. These facilities normally consist of a grass buffer I Nutrients A strip, sand bed, ponding area, organic layer or mulch layer, E Trash planting soil, and plants. The runoffs velocity is reduced by IJ Metals U passing over or through buffer strip and subsequently distributed I1 Bacteria U evenly along a ponding area Exfihltration of the stored water in R1 Oil and Grease U the bioretention area planting soil into the underlying soils E?1 Organics occurs over a period of days. Legend (Removal Effeveness) California Experience Low U High None documented. Bioretention has been used as a stormwater A Medium BMP since 1992. In addition to Prince George's County, MD and Alexandria, VA, bioretention has been used successfully at urban and suburban areas in Montgomery County, MD; Baltimore County, MD; Chesterfield County, VA; Prince William County, VA, Smith Mountain Lake State Park VA; and Cary, NC. Advantages Bioretention provides stormwater treatment that enhances the quality of downstream water bodies by temporarily storing runoff in the BMP and releasing it over a period of four days to the receiving water (EPA, 1999). The vegetation provides shade and wind breaks, absorbs noise, and improves an area's landscape. a Limitations a The bioretention BMP is not recommended for areas with slopes greater than 20% or where mature tree removal would January 2003 California Stomiwater BMP Handbook 1 of 8 New Develo pthent and Redevelopment www.ca bmpha ndbooks.com TC-32 Bioretention be required since clogging may result, particularly if the BMP receives runoff with high sediment loads (EPA, 1999). Bioretention is not a suitable BMP at locations where the water table is within 6 feet of the ground surface and where the surrounding soil stratum is unstable. By design, bioretention BMPs have the potential to create very attractive habitats for mosquitoes and other vectors because of highly organic, often heavily vegetated areas mixed with shallow water. In cold climates the soil may freeze, preventing runoff from infiltrating into the planting soil Design and Sizing Guidelines The bioretention area should be sized to capture the design storm runoff. In areas where the native soil permeability is less than 0.5 in/hr an underdrain should be provided. Recommended minimum dimensions are 15 feet by 40 feet, although the preferred width is 25 feet. Excavated depth should be 4 feet Area should drain completely within 72 hours. Approximately 1 tree or shrub per 50 ft2 of bioretention area should be included. • Cover area with about 3 inches of mulch. Construction/Inspection Considerations Bioretention area should not be established until contributing watershed is stabilized. Performance Bioretention removes stormwater pollutants through physical and biological processes, including adsorption, filtration, plant uptake, microbial activity, decomposition, sedimentation and volatilization (EPA, 1999). Adsorption is the process whereby particulate pollutants attach to soil (e.g., clay) or vegetation surfaces. Adequate contact time between the surface and pollutant must be provided for in the design of the system for this removal process to occur. Thus, the infiltration rate of the soils must not exceed those specified in the design criteria or pollutant removal may decrease. Pollutants removed by adsorption include metals, phosphorus, and hydrocarbons. Filtration occurs as runoff passes through the bioretention area media, such as the sand bed, ground cove; and planting soil Common particulates removed from stormwater include particulate organic matter, phosphorus, and suspended solids. Biological processes that occur in wetlands result in pollutant uptake by plants and microorganisms in the soil. Plant growth is sustained by the uptake of nutrients from the soils, with woody plants locking up these nutrients though the seasons. Microbial activity within the soil also contributes to the removal of nitrogen and organic matter. Nitrogen is removed by nitrifying and denitriiring bacteria, while aerobic bacteria are responsible for the decomposition of the organic matter. Microbial processes require oxygen and can result in depleted oxygen levels if the bioretention area is not adequately 2 of 8 California Storrnwater BMP Handbook January 2003 New Development and Redevelopment www.cabmphandbooks.com Bioretention TC-32 aerated. Sedimentation occurs in the swale or ponding area as the velocity slows and solids fall out of suspension. The removal effectiveness of bioretention has been studied during field and laboratory studies conducted by the University of Maryland (Davis et a], 1998). During these experiments, synthetic stormwater runoff was pumped through several laboratory and field bioretention areas to simulate typical storm events in Prince Georges County, MD. Removal rates for heavy metals and nutrients are shown in Table 1. Table 1 Laboratory and Estimated Bioretention Davis et al. (1998); PGDER (1993) Pollutant Removal Rate Total Phosphorus 70-83% Metals (Cu, Zn, Pb) 93-98% TKN 68-80% Total Suspended Solids 90% Organics 90% Bacteria 90% Results for both the laboratory and field experiments were similar for each of the pollutants analyzed. Doubling or halving the influent pollutant levels had little effect on the effluent pollutants concentrations (Davis et a], 1998). The microbial activity and plant uptake occurring in the bioretention area will likely result in higher removal rates than those determined for infiltration BMPs. Siting Criteria Bio retention BMPs are generally used to treat stormwater from impervious surfaces at commercial, residential, and industrial areas (EPA, 1999). Implementation of bioretention for stormwater management is ideal for median strips, parking lot islands, and swales. Moreover, the runoff in these areas can be designed to either divert directly into the bioretention area or convey into the bioretention area by a curb and gutter collection system. The best location for bioretention areas is upland from inlets that receive sheet flow from graded areas and at areas that will be excavated (EPA, 1999). In order to maximize treatment effectiveness, the site must be graded in such a way that minimizes erosive conditions as sheet flow is conveyed to the treatment area Locations where a bioretention area can be readily incorporated into the site plan without further environmental damage are preferred. Furthermore, to ef1ctively minimize sediment loading in the treatment area, bioretention only should be used in stabilized drainage areas. January 2003 California Sthrrnwatnr BMP Handbook 3 of 8 New Development and Redevelopment www.cabmphandbooks.com TC-.32 Bioretention Additional Design Guidelines The layout of the bioretention area is determined after site constraints such as location of utilities, underlying soils, existing vegetation, and drainage are considered (EPA, 1999). Sites with loamy sand soils are especially appropriate for bioretention because the excavated soil can - be backfihled and used as the planting soil, thus eliminating the cost of importing planting soil. The use of bioretentionmaynotbe feasible given an unstable surrounding soil stratum, soils - _ with clay content greater than 25 percent; a site with slopes greater than 20 percent; and/or a site with mature trees that would be removed during construction of the BMP. Bioretention can be designed to be off-line or on-line of the existing drainage system (EPA, 1999). The drainage area for a bioretention area should be between 0.1 and 0.4 hectares (0.25 and 1.0 acres). Larger drainage areas may require multiple bioretention areas. Furthermore, the maximum drainage area for a bioretention area is determined by the expected rainfall intensity and runoff rate. Stabilized areas may erode when velocities are greater than 5 feet per second (1.5 meter per second). The designer should determine the potential for erosive conditions at the site. The size of the bioretention area, which is a function of the drainage area and the runoff generated from the area is sized to capture the water quality volume. The recommended minimum dimensions of the bioretention area are 15 feet (4.6 meters) wide by 40 feet (12.2 meters) long, where the minimum width allows enough space for a dense, randomly-distributed area of trees and shrubs to become established. Thus replicating a natural forest and creating a microclimate, thereby enabling the bioretention area to tolerate the effects of heat stress, acid rain, runoff pollutants, and insect and disease infestations which landscaped areas in urban settings typically are unable to tolerate. The preferred width is 25 feet (7.6 meters), with a length oftwice the width. Essentially, any facilities wider than 20 feet (6.1 meters) should be twice as long as they are wide, which promotes the distribution of flow and decreases the chances of concentrated flow. In order to provide adequate storage and prevent water from standing for excessive periods of time the ponding depth of the bioretention area should not exceed 6 inches (15 centimeters). Water should not be left to stand for more than hours. A restriction on the type of plants that can be used may be necessary due to some plaits' water intolerance. Furthermore, if water is left standing for longer than 72 hours mosquitoes and other insects may start to breed. The appropriate planting soil should be backfilled into the excavated bioretention area. Planting soils should be sandy loam, loamy sand, or loam texture with a clay content ranging from 10 to 25 percent. Generally the soil should have infiltration rates greater than 0.5 inches (1.25 centimeters) per hour, which is typical of sandy barns, loamy sands, or barns. The pH of the soil should range between 5.5 and 6.5, where pollutants such as organic nitrogen and phosphorus can be adsorbed by the soil and microbial activity can flourish. Additional requirements for the planting soil include a 1.5 to 3 percent organic content and a maximum 500 ppm concentration of soluble salts. 4 of 8 California StormwaIr BMP Handbook January 2003 New Development and Rieve!opment www.cabmphandbooks.com Bioretention TC-32 Soil tests should be performed for every 500 cubic yards (382 cubic meters) of planting soil, - with the exception of pH and organic content tests, which are required only once per bioretention area (EPA, 1999). Planting soil should be 4 inches (io.i centimeters) deeper than the bottom of the largest root ball and feet (1.2 meters) altogether. This depth will provide - adequate soil for the plants' root systems to become established, prevent plant damage due to severe wind, and provide adequate moisture capacity. Most sites will require excavation in order to obtain the recommended depth. Planting soil depths of greater than 4 feet (1.2 meters) may require additional construction practices such as shoring measures (EPA, 1999). Planting soil should be placed in 18 inches or greater lifts and lightly compacted until the desired depth is reached. Since high canopy trees may be destroyed during maintenance the bioretention area should be vegetated to resemble a terrestrial forest community ecosystem that is dominated by understory trees. Three species each of both trees and shrubs are recommended to be planted at a rate of 2500 trees and shrubs per hectare (i000 per acre). For instance, a 15 foot (4.6 meter) by 40 foot (12 meter) bioretention area (6o0 square feet or 55.75 square meters) would require 14 trees and shrubs. The shrub-to-tree ratio should be :i to :i. Trees and shrubs should be planted when conditions are favorable. Vegetation should be watered at the end of each day for fourteen days following its planting. Plant species tolerant of pollutant loads and varying wet and dry conditions should be used in the bioretention area. The designer should assess aesthetics, site layout, and maintenance requirements when selecting plant species. Adjacent non-native invasive species should be identified and the designer should take measures, such as providing a soil breach to eliminate the threat of these species invading the bioretention area Regional landscaping manuals should be consulted to ensure that the planting of the bioretention area meets the landscaping requirements established by the local authorities. The designers should evaluate the best placement of vegetation within the bioretention area. Plants should be placed at irregular intervals to replicate a natural forest Trees should be placed on the perimeter of the area to provide shade and shelter from the wind. Trees and shrubs can be sheltered from damaging flows if they are placed away from the path of the incoming runoff. In cold climates, species that are more tolerant to cold winds, such as evergreens, should be placed in windier areas of the site. Following placement of the trees and shrub; the ground cover and/or mulch should be established. Ground cover such as grasses or legumes can be planted at the beginning of the growing season. Mulch should be placed immediately after trees and shrubs are planted. Two to 3 inches (5 to 7.6 cm) of commercially-available fine shredded hardwood mulch or shredded hardwood chips should be applied to the bioretention area to protect from erosion. Maintenance The primary maintenance requirement for bioretention areas is that of inspection and repair or replacement of the treatment area's components. Generally, this involves nothing more than the routine periodic maintenance that is required of any landscaped area Plants that are appropriate for the site, climatic, and watering conditions should be selected for use in the bioretention cell. Appropriately selected plants will aide in reducing fertilizer, pesticide, water, and overall maintenance requirements. Bioretention system components should blend over time through plant and root growth, organic decomposition, and the development of a natural January 2003 California Stormwater BMP Handbook 5 of 8 New Development and Redevelopment www.cabrnphandbooks.com TC-32 Bioretention soil horizon. These biologic and physical processes over time will lengthen the facility's life span and reduce the need for extensive maintenance. Routine maintenance should include a biannual health evaluation of the trees and shrubs and subsequent removal of any dead or diseased vegetation (EPA, 1999). Diseased vegetation should be treated as needed using preventative and low-toxic measures to the etent possible. BMPs have the potential to create very attractive habitats for mosquitoes and other vectors because of highly organic, often heavily vegetated areas mixed with shallow water. Routine inspections for areas of standing water within the BMP and corrective measures to restore proper infiltration rates are necessary to prevent creating mosquito and other vector habitat. In addition, bioretention BMPs are susceptible to invasion by aggressive plant species such as cattails, which increase the chances of water standing and subsequent vector production if not routinely maintained. In order to maintain the treatment area's appearance it may be necessary to prune and weed. Furthermore, mulch replacement is suggested when erosion is evident or when the site begins to look unattractive. Specifically, the entire area may require mulch replacement every two to three years, although spot mulching maybe sufficient when there are random void areas. Mulch replacement should be done prior to the start of the wet season. New Jersey's Department of Environmental Protection states in their bioretention systems standards that accumulated sediment and debris removal (especially at the inflow point) will normally be the primary maintenance function. Other potential tasks include replacement of dead vegetation, soil pH regulation, erosion repair at inflow points, mulch replenishment; unclogging the underdrain, and repairing overflow structures. There is also the possibility that the cation exchange capacity of the soils in the cell will be significantly reduced over time. Depending on pollutant loads, soils may need to be replaced within 5-10 years of construction (LID) 2000). Cost Construction Cost Construction cost estimates for abioretention area are slightly greater than those for the required landscaping for a new development (EPA, 1999). A general rule of thumb (Coffman, 1999) is that residential bioretention areas average about $3 to $4 per square foot, depending on soil conditions and the density and types of plants used. Commercial, industrial and institutional site costs can range between $io to $40 per square foot, based on the need for control structures, curbing, storm drains and underdrains. Retrofitting a site typically costs more, averaging $6,00 per bioretention area. The higher costs are attributed to the demolition of existing concrete, asphalt; and existing structures and the replacement of fill material with planting soil The costs of retrofitting a commercial site in Maryland, Kettering Development, with 15 bioretention areas were estimated at $rn,600. In any bioretention area design, the cost of plants varies substantially and can account for a significant portion of the expenditures. While these cost estimates are slightly greater than those of typical landscaping treatment (due to the increased number of plantings, additional soil excavation, backfill material, use of underdrains etc.), those landscaping expenses that would be required regardless of the bioretention installation should be subtracted when determining the net cost. 6 of 8 California Stormwatr BMP Handbook January 2003 New Development and Redevelopment www.cabmphandbooks.com Bioretention TC-32 Perhaps of most importance, however, the cost savings compared to the use of traditional structural stormwater conveyance systems makes bioretention areas quite attractive financially. For example, the use of bioretention can decrease the cost required for constructing stormwater conveyance systems at a site. A medical office building in Maryland was able to reduce the amount of storm drain pipe that was needed from 800 to 230 feet - a cost savings of $24,000 (PGDER, 1993). And a new residential development spent a total of approximately $100,000 using bioretention cells on each lot instead of nearly $400,000 for the traditional stormwater ponds that were originally planned (Rapphrnock,). Also, in residential areas, stormwater management controls become a part of each property owner's landscape, reducing the public burden to maintain large centralized facilities. Maintenance Cost The operation and maintenance costs for a bioretention facility will be comparable to those of typical landscaping required for a site. Costs beyond the normal landscaping fees will include the cost for testing the soils and may include costs for a sand bed and planting soil. References and Sources of Additional Information Coffman, L.S., R. Goo and R. Frederick, 1999: Low impact development an innovative alternative approach to stormwater management. Proceedings of the 26th Annual Water Resources Planning and Management Conference ASCE, June 6-9, Tempe, Arizona. Davis, A-P., Shokouhian, M., Sharma, H. and Mimmi, C., "Laboratory Study of Biological Retention (Bioretention) for Urban Stormwater Management" Water Environ. Res., 73(115-:L4 (2001). Davis, AP., Shokouhian, M., Sharma, H., Minami C., and Winogrado D. "Water Quality Improvement through Bioretention Lead, Copper, and Zinc," Water Environ.. Res., accepted for publication, August 2002. Kim, H., Seagren, E.A., and Davis, A. P., "Engineered Bioretention for Removal of Nitrate from Stormwater Runofi" WPJTEC 2000 ConferenceProceedings on CDROMResearch Symposium, Nitrogen Removal, Session 19, Anaheim CA, October 2000. Hsieh, C.-h. and Davis, A.P. "Engineering Bioretention for Trealment of Urban Stormwater Ruriog" Watersheds 2oog, Proceedings on CDROM Research Symposium, Session 15, Ft Lauderdale, FL Feb. 2002. Prince George's County Department of Environmental Resources (PGDER), 1993. Design Manual for Use of Bioretention in Stormwater Management. Division of Environmental Management, Watershed Protection Branch. Landover, MD. U.S. EPA Office of Water, 1999. Stormwater Technology Fact Sheet: Bioretention. EPA 832-17- 99-012. Weinstein, N. Davis, A.P. and Veeramachaneni, R. "Low Impact Development (LID) Stormwater Management Approach for the Controlof Diffuse Pollution from Urban Roadways," 5th International ConferenceDiffuse/Nonp ointFollution and Watershed Management Proceedings, C.S. Meiching and Emre Alp, Eds. 2001 International Water Association January 2003 CalIfornia Stormwater BMP Handbook 7 of 8 New Development and Redevelopment www.cabmphandbooks.com TC-32 Bioretention CURB STONE DIAPHRAGM , 999ç' bV 4449 - GRASS FILTER STRIP OVERFLOW - - - P - nR'fttcu(rAIN CATCH BASI - - •••• DRAIN OVERFLOW BERM L UF1DERDRAIN COLLECTION SYSTEM PLAN VIEW TYPICAL SECTION PROFILE - Schematic of a Bio retention Facility (MDE, 2000) 8 of 8 California Stormwalr BMP Handbook January 2003 New Development and Redevelopment www.cabmphandbooks.com ii 11 (. CONSULTING I PLANNING N DESIGN U CONSTRUCTION 800.4793809 • WWW.RBF.COM - JOB. S3-/O0293 SHEET NO. OF CALCULATED BY l)L'() DATE ' CHECKED BY DATE SCALE .INLT A'EKr•TPE/tTME,VT....FI-Q.'Q LocfrrIoAJ i'tr ALL. 2.4't,AE' -R4TF JIV4E7-S 'oA OAJ. BAV .IrE.A14P YPE : 1LO- PL2S 1AR EN PR.sF , INC. C47c H. 6 A,5IA1 . I(..TE :I/t/ERT I 1LA-7. 6RATE.D LNtT. MODEL NO. 6-P-21F . . .••. (Rg TO A1t4ctiE0 MA(iwpAcT(,eEI iFK4Tto/J) C4PA.IV\' : so.LI1 .sRG-E__1:CS :) peg. -1EO fr L1ER4.PLQ ..( S. sPEc,Ps(Tlops TOTAL BASS. . TV,ETeP REA 57a .IA-,t/FML —t. r . ASSQME (D (OJ ft%'o,. 11 4 IV 1'44 ) I ..i 4 A (c.cre) T .=p A =. •q v,ce r"1e o-V 4-t.( e1r4'?..$. 40 ?k4 .. kqs f4-'ie ,$ cp,i.I3 IRBF (T CONSULTI NG PLANNING U DIGN U CONSTRUCTION 800.479.3808 • *WW.RBF.CDM JOB SS'-/po23 SHEET NO. OF CALCULATED BY 0 vi DATE CHECKED BY DATE SCALE - .......: S4.,ctks +0 k .Lbc.+fd .1.~cped f P°! rô4/pt Her ki re A*. drq,i s. Rerr 4o am1 iMcq -Lt c0k (oc44,on. 10 IIcAl S(e. . 4_c' Tc-3 lot, 1~ zj 17 . 3.I r'i't)(. skpes ..+•;iI Scipi: 41 .,q4er der+h . Z gii/Lr (i' bo er A 6c5j Rpor1 O.OLI tc4.4vt 4-ca Irr ,-1+I . "4 tj r-4t)*ptcS Rer± OD(L v,gc1+k - SoprS . 6 Dep . TDp Channel Report Hydraflow Express by Intelisolve <Name> Trapezoidal Botom Width (ft) = 0.50 Side Slopes (z:1) = 3.00, 3.00 Total Depth (ft) = 0.50 Invert Elev(ft) = 1.00 Slope (%) = 1.00 N-Value = 0.250 Calculations Compute by: Known Q Known Q(cfs) = 0.04 Depth (ft) = 0.23 Q(cfs) = 0.040 Area (sqft) = 0.27 Velocity (ftls) = 0.15 Wetted Perim (ft) = 1.95 Crit Depth, Yc (ft) = 0.06 Top Width (ft) = 1.88 EGL(ft) = 0.23 Highlighted Friday, May11 2007 Elev Section Depth (ft) 2.00 ------- 1.00 0.75 0.50 0.25 'XIII- - -------- -------- ---- ----- .5 1 1.5 2 2.5 3 Reach (ft) 3.5 4 4.5 Targeted Constituents Rl Sediment A 1 Nkitrients Trash E1 Metals A E1 Bacteria l and Grease A RI Organics A Legend (Removal Effectiveness) Low E High A Medium Vegetated Swale TC-30 Design Considerations Tributary Area Area Required Slope Description Vegetated swales are open, shallow channels with vegetation covering the side slopes and bottom that collect and slowly convey runoff flow to downstream discharge points. They are designed to treat runoff through filtering by the vegetation in the channel, ffltermg through a subsoil matrix, and/or infiltration into the underlying soils. Swales can be natural or manmade. They trap particulate pollutants (suspended solids and trace metals), promote infiltration, and reduce the flow velocity of stormwater runoff. Vegetated swales can serve as part of a stormwater drainage system and can replace curbs, gutters and storm sewer systems. California Experience Caltrans constructed and monitored six vegetated swales in southern California. These swales were generally effective in reducing the volume and mass of pollutants in runoff. Even in the areas where the annual rainfall was only about 10 inches/yr, the vegetation did not require additional irrigation. One factor that strongly affected performance was the presence of large numbers of gophers at most of the sites. The gophers created earthen mounds, destroyed vegetation, and generally reduced the effectiveness of the controls for ThS reduction. Advantages If properly designed, vegetated, and operated, swales can serve as an aesthetic) potentially inexpensive urban development or roadway drainage conveyance measure with significant collateral water quality benefits. January 2003 CaIforria Stormwater BMP Handbook 1 of 13 New Development and Redevelopment www.cabmphandbooks.com TC-30 Vegetated S.walé N Roadside ditches should be regarded as significant potential swale/buffer strip sites and should be utilized for this purpose whenever possible. Limitations Can be difficult to avoid thrnnelization. May not be appropriate for industrial sites or locations where spills may occur Grassed swales cannot treat a very large drainage area. Large areas maybe divided and - treated using multiple swales. Athick vegetative cover is needed for these practices to function properly. They are impractical in areas with steep topography. They are not effective and may even erode when flow velocities are high, if the grass cover is notproperly maintained.. In some place; their use is restricted bylaw: many local municipalities require curb and gutter systems in residential areas. Swales are mores susceptible to failure if not properly maintained than other treatment BMPs. Design and Sizing Guidelines How rate based design determined by local requirements or sized so that 8% of the annual runoff volume is discharged at less than the design rainfall intensity. Swale should be designed so that the water level does not exceed 2/3rd5 the height of the grass or 4 inches, which ever is less, at the design treatment rate. Longitudinal slopes should not exceed 2.5% Trapezoidal channels are normally recommended but other configurations, such as paraboli; can also provide substantial water quality improvement and maybe easier to mow than designs with sharp breaks in slope. Swales constricted in cut are preferred, or in fill areas that are far enough from an adjacent slope to minimize the potential for gopher damage. Do not use side slopes constructed of fill, which are prone to structural damage by gophers and other burrowing animals. A diverse selection of low growing, plants that thrive under the specific site, climatic, and watering conditions should be specified. Vegetation whose growing season corresponds to the wet season are preferred. Drought tolerant vegetation should be considered especially for swales that are not part of a regularly irrigated landscaped area The width of the swale should be determined using Mrnining's Equation using a value of 0.25 for Mrnning's n. 2 of 13 California Sthrmwater BMP Handbook January 2003 - New Development and Redevelopment www. cabmphancbooks. corn Vegetated Swale TC-30 Construction/Inspection Considerations Include directions in the specifications for use of appropriate fertilizer and soil amendments based on soil properties determined through testing and compared to the needs of the vegetation requirements. Install swales at the time of the year when there is a reasonable chance of successful establishment without irrigation; however, it is recognized that rainfall in a given year may not be sufficient and temporary irrigation may be used: If sod tiles must be used, they should be placed so that there are no gaps between the tiles; stagger the ends of the tiles to prevent the formation of channels along the swale or strip. Use a roller on the sod to ensure that no air pockets form between the sod and the soil. Where seeds are used, erosion controls will be necessary to protect seeds for at least 75 days after the first rainfall of the season. Performance J The literature suggests that vegetated swales represent a practical and potentially effective technique for controlling urban runoff quality. While limited quantitative performance data exists for vegetated swales, itis known that check dams, slight slopes permeable soils, dense grass cover, increased contact lime, and small storm events all contribute to successful pollutant removal by the swale system. Factors decreasing the effectiveness of swales include compacted soils short runoff contact tim; large storm events, frozen ground, short grass heights, steep slopes, and high runoff velocities and discharge rates. Conventional vegetated swale designs have achieved mixed results in removing-particulate pollutants. A study performed by the Nationwide Urban Runoff Program (NtJRP) monitored 4 three grass swales in the Washington, D.C., area and found no significant improvement in urban runoff quality for the pollutants analyzed. However, the weak performance of these swales was attributed to the high flow velocities in the swales, soil compaction, steep slopes, and short grass height Another project in Durham, NC, monitored the performance of a carefully designed artificial swale that received runoff from a commercial parking lot The project tracked ii storms and concluded that particulate concentrations of heavy metals (Cu, Pb, Zn, and Cd) were reduced by approximately 50 percent However, the swale proved largely ineffective for removing soluble nutrients. The effectiveness of vegetated swales can be enhanced by adding check dams at approximately 17 meter (50 foot) increments along their length (See Figure i). These dams maximize the retention time within the swale, decrease flow velocities, and promote particulate settling. Finally, the incorporation of vegetated filter strips parallel to the top of the chrn,T1d banks can help to treat sheet flows entering the swale. Only 9 studies have been conducted on all grassed channels designed for water quality (Table i). The data suggest relatively high removal rates for some pollutants, but negative removals for some bacteria, and fair performance for phosphorus. January 2003 California Stoanwater BMP Handbook 3 of 13 New Development and Redevelopment www.cabmphandbooks.com TC-30 Vegetated Swale Table 1 Grassed swale pollutant removal efficiency data Removal Efficiencies (% Removal) Study TSS TP TN NO3 Metals Bacteria Type altrans 2002 77 8 67 66 83-96 -33 dry swales Goldberg 1993 67.8 45 - 3L4 42-62 -100 grassed channel Seattle Metro and Washington 60 45 )epartment ofEcology 1992 - -25 2-16 -25 grassed channel Seattle Metro and Washington 83 29 - ej)artment of Ecology, 1992 -25 46-73 -25 grassed channel Wang et al, 1981 80 - - - 70-80 - thy swale Dorman et aL, 1989 98 18 - 45 37-81 - dry swale Harper, 1988 87 83 84 80 88-90 - dry swale Karcher at al., 1983 99 99 99 99 99 - thy swale Harper, 1988. 81 17 40 52 37-69 - et swale oon, 1995 67 39 - 9 -35 to 6 - vet swale While it is difficult to distinguish between different designs based on the small amount of available data, grassed diannels generally have poorer removal rates than wet and thy swales, although some swales appear to export soluble phosphorus (Harper, 1988; Koon, 1995). It is not dear why swales export bacteria. One explanation is that bacteria thrive in the warm swale soils. Siting Criteria The suitabilityofaswale at site will depend on laud use, size of the area serviced, soiltype, slop; imperviousness of the contributing watershed, and dimensions and slope of the swale system (Sthueler etaL, 1992). In general, swales can be used to serve areas of less than 10 acres, with slopes no greater than 5%. Use of natural topographic lows is encouraged and natural drainage courses should be regarded as significant local resources to be kept in use (Young et al., 1996). Selection Criteria (NCTCOG, 1993) Comparable performance to wet basins Limited to treating a few acres Availability of water during thy periods to maintain vegetation Sufficient available land area Research in the Austin area indicates that vegetated controls are effective at removing pollutants even when dormant Therefore, irrigation is not required to maintain growth during dry periods, but may be necessary only to prevent the vegetation from dying. 4 of 13 - - Cal lfbmla Stormwater BMP Handbook January 2003 New Development and Redevelopment www.cebmphandbocks.com Vegetated Swale TC-30 The topography of the site shouldpermit the design of a channel with appropriate slope and -. cross-sectional area. Site topography may also dictate a need for additional structural controls. Recommendations for longitudinal slopes range between 2 and 6 percent. Flatter slopes can be used, if sufficient to provide adequate conveyance. Steep slopes increase flow velocity, decrease detention time, and may require energy dissipating and grade check Steep slopes also can be managed using a series of check dams to ten-ace the swale and reduce the slope to within acceptable limits. The use of check dams with swales also promotes infiltration Additional Design Guidelines Most of the design guidelines adopted for swale design specify a minimum hydraulic residence time of 9 minutes. This criterion is based on the results of a single study conducted in Seattle, Washington (Seattle Metro and Washington Department of Ecology, 1992), and is not well supported. Analysis of the data collected in that study indicates that pollutant removal at a residence time of 5 minutes was not significantly different, although there is more variability in that data. Therefore, additional research in the design criteria for swales is needed. Substantial pollutant removal has also been observed for vegetated controls designed solely for conveyance (Barrett et a], 1998); consequently, some flexibility in the design is warranted. Many design guidelines recommend that grass be frequently mowed to imintain dense coverage near the ground surface. Recent research (Colwell et al., 2000) has shown mowing frequency or grass height has little or no effect on pollutant removal. Summary ofDesign Recommendations 1) The swale should have a length that provides a minimum hydraulic residence time of at least 10 minutes. The maximum bottom width should not exceed 10 feet unless a dividing berm is provided. The depth of flow should not exceed 2/3rdS the height of the grass at the peak of the water quality design storm intensity. The channel slope should not exceed 2.5%. A design grass height of6 inches isrecommended. Regardless of the recommended detention time, the swale should be not less than ioo feet in length. The width of the swale should be determined using Mrnining's Equation, at the peak of the design storm, using aMmmrngsnof0.25. The swale canbe sized as bath a treatment facility for the design storm and as a conveyance system to pass the peak hydraulic flows of the loo-year storm if it is located "on-line." The side slopes should be no steeper than :i (1±11). Roadside ditches should be regarded as significant potential swale/buffer strip sites and should be utilized for this purpose whenever possible. If flow is to be introduced through curb cuts, place pavement slightly above the elevation of the vegetated areas. Curb cuts should be at least 12 inches wide to prevent dogging. Swales must be vegetated in order to provide adequate treatment of runoff. It is important to maximize water contact with vegetation and the soil surface. For general purposes, select fine, dose-growing, water-resistant grasses. If possible, divert runoff (other than necessary irrigation) during the period of vegetation January 2003 California Stormwater BMP Handbock 5 of 13 New Development and Redevelopment www.cthmphaidbka corn TC-30 Vegetated Swale establishment Where runoff diversion is not possible, cover graded and seeded areas with suitable erosion control materials. Maintenance The useful life of a vegetated swale system is directly proportional to its maintenance frequency. If properly designed and regularly maintained, vegetated swales can last indefinitely. The maintenance objectives for vegetated swale systems include keeping up the hydraulic and removal efficiency of the channel and maintaining a dense, healthy grass cover. Maintenance activities should include periodic mowing (with grass never cut shorter than the design flow depth), weed control, watering dining drought conditions, reseeding of bare areas and clearing of debris and blockages. Cuttings should be removed from the channel and disposed in a local compostiñg facility. Accumulated sediment should also be removed manually to avoid concentrated flows in the swale. The application of fertilizers and pesticides should be minimal. Another aspect of a good maintenance plan is repairing damaged areas within a r}irnmeL For example, if the channel develops ruts or holes it should be repaired utilizing a suitable soil that is properly tamped and seeded. The grass cover should be thick, if itis not reseed as necessary. Any standing water removed during the maintenance operation must be disposed to a sanitary sewer at an approved discharge location. Residuals (e.g., sill; grass cuttings) must be disposed in accordance with local or State requirements. Maintenance of grassed swales mostly involves maintenance of the grass or wetland plant cover. Typical maintenance activities are summarized below: Inspect swales at least twice annually for erosion, damage in vegetation, and sediment and debris accumulation preferably at the end of the wet season to schedule summer maintenance and before major fall runoff to be sure the swale is ready for winter. However, additional inspection after periods of heavy runoff is desirable. The swale should be checked for debris and litter, and areas of sediment accumulation. Grass height and mowing frequency may not have a large impad on pollutant removal. Consequently, mowing may only be necessary once or twice a year for safety or aesthetics or to suppress weeds and woody vegetation. Trash tends to accumulate in swale areas, particularly along highways. The need for litter removal is determined through periodic inspection, but litter should always be removed prior to mowing. Sediment accumulating near culverts and in channels should be removed when it builds up to 75 mm (3 in-) at any spo1, or covers vegetation. Regularly inspect swales for pools of standing water. Swales can become a nuisance due to mosquito breeding in standing water if obstructions develop (e.g. debris accumulation, invasive vegetation) and/or if proper drainage slopes are not implemented and maintained. 6 of 13 California Stormwater BMP Handbook January 2003 New Development and Redevelopment www. cabmphan±ooks. corn IL- Vegetated Swale TC-30 Cost Construction Cost Little data is available to estimate the difference in costbetween various swale designs. One study (SWRPC, 1991) estimatedthe construction cost of grassed channels at approximately $0.25 per ft2. This price does not include design costs or contingencies. Brown and Schueler (1997) estimate these costs at approximately 32 percent of construction costs for most stormwater management practices. For swales, however, these costs would probably be• significantly higher since the construction costs are so low compared with other practices. A more realistic estimate would be a total cost of approximately $o.o per ft2, which compares favorably with other stormwater management practices. January 2003 California Stormwater BMP Handbook 7 of 13 New Development and Redevelopment www.cthmphendbooks.com c- TC-30 . Vegetated Swale. Table 2 Swale Cost Estimate (SEWRPC, 1991) Unit Cost Total Cost Low Moderate High Low Moderate High Component Unit Extent MobiiatjonI Swab 1 $107 $274 $441 $107 $274 $441 DemobIlIzation-light Site Prooaratia, Claaringb Aa-a 0.5 $2900 $3,800 $5,400 $1,100 $1,900 $2700 GrubbInd General Acre 0.25 $1,800 $5,200 $8.900 $950 $1,300 $1,650 Yd' 372 $2.10 $3.70 W30 $781 $1,376 $1,972 Lavabondlili' Yd' 1,210 1 $0.20 $0.36 $0.50 $242 $424 $905 Sites Dovalopmanl Salvaged Topsoil Seed, and MUIcW.. Yd2 1,210 $0Ao $1.00 $1.00 $484 $1,210 $1,930 Sodo ...................... 1,210 $1.20 32,40 $3.60 $1,452 $2004 . $4358 Subtotal . -- - - - -- $6,116 $9,388 $13,(180 Contlngânciee Swale 1 25% - 25% 25% $1,270 $2,347 $3415 Total -- - - - -- $0395 $11,Th5 $17,075 OQU191L vYF%r%.i, 1WWIJ Note MoblIltlon/dernobilatlon mtärato the organizatiri, and planning Involved in establishing a vegta3ve wiaIe. Swale has a bottom width of 1.0 foot, a top width of 10 feet with 1:3 side slopes, and a 1,000-foot length. b Area cleared = (top width + 10 fbat) x swals length. Area grubbed = (topwldth c wale length), 'Volume excavated =(0.67x top widthxswale depth) xswale length (parabolic cross-section). Area tilted= (top wldth s 8(swa1e depths) x swale length (parabolic cross-section), 20op width) 'Area seeded = area cleared x 0,5. Area sodded = area cleared x 0,5. 8 of 13 California Stormwater BMP Handbook January 2003 New Development and Redevelopment www.cabmphandbooks.com Vegetated Swale TC-30 Table 3 Estimated Maintenance Costs (SEWRPCV 1991) Swale Size (Depth and Top Width) 1.5 Foot Depth, One- 3-Foot Depth, 3-Foot Component Unit Cost Comment Foot Bottom Width, Bottom Width, 21-Foot 10.Foot Top Width Top Width Lawn Mowing 0.85(1,000fL1rnaving $0.141Iineerfcot $0.21 1 linear foot Lawn maintenance area -(lop widfti+ lo foot) x length. Maw eight timoB par year General Lawn Care $0.00 /1000 ft'lyear $0.18 llineerfaot $0.28 lllnear foot Lawn maIntenan area (tap width +lofeet)xlength Swale DeUda and Utter 60.101 moor foot I year $0.10 lilnearfoot $0.10 Iiinear foot - Rarnaval Grass Reseeding with $030/yd2 $0.01'/I1nearfoot $0.011 linear foot Area mvogototed equals 1% Mulch and Fertilizer a?iswn mairdenance area per year Program Administration and SOLI si linear Ibot /year, $0.15 I Iinearftmt $0.15 I linear foot Inspect four tinies per year Swale Inapecon plus $251 lnspecon Tothi -- O.S&/IInoarfao1 $O.7blllnaorfool - January 2003 California Stormwater BMP Handbook 9 of 13 New Development and Redevelopment www.cthmphandbooks.com - TC-30 . Vegetated Swàle Maintenance Cost Caltrans (2002) estimated the expected annual maintenance costfor a swale with atributaiy area of approximately 2 ha at approximately $2,700. Since almost all maintenance consists of mowing, the cost is fundamentally a function of the mowing frequency. Unit costa developed by SEWRPC are shown in Table 3. In many cases vegetated channels would be used to convey runoff and would require periodic mowing as well, so there may be little additional cost for the water quality component Since essentially all the activities are related to vegetation management, no special training is required for maintenance personnel. References and Sources of Additional Information Barrett; Michael E., Walsh, Patrick M., Mahna, Joseph F., Jr., Charbeneau, RandallJ, 1998, "Performance of vegetative controls for treating highway runoff," ASCE Journal of EnuironmentalEngineering, Vol. 124, No. Ii, pp.1121-1128. Brown, W., and T. Schueler. 1997. The Economics ofStormwater BMPs in the Mid-Atlantic Region. Prepared for the Chesapeake Research Consortium, Edgewater, MD, by the Center for Watershed Protection, Ellicott City, MD. Center for Watershed Protection (CWP). 1996. Design ofStormwater1iltering Systems. Prepared for the Chesapeake Research Consortium, Solomons, MD, and USEPA Region V, Chicago, IL, by the Center for Watershed Protection, Ellicott City, MD. Colwel], ShantiR., Homer, Richard R., and Booth, Derek B., 2000. Characterization of Performance Predictors andBvaluation ofMowing Practices in BiofiltraLion Swales. Report to King County Land And Water Resources Division and others by Center for Urban Water Resources Management, Department of Civil and Environmental Engineeiing, University of Washington, Seattle, WA Dorman, M.E., J. Hartigan, R.F. Steg, andT. Quasebarth. 1989. Retention, Detention and OverlandF! owforPoliutwitRemoual From Highway Stormwa ter Rtoioff Vol. 1. FHWA/RD 89/202. Federal Highway Administration, Washington, DC. Goldberg. 1993. Dayton Avenue Sthale Biofiltration Study. Seattle Engineering Department Seattle, WA. Harper, H. 1988. Effects ofStormwater Management Systems on Groundwater Quality. Prepared for Florida Department of Environmental Regulation, Tallahassee, FL, by Environmental Research and Design, Inc., Orlando, FL. Kereher, W.C., J.C. Landon, and R. Massarelli. 1983 Grassy swales prove cost-effective for water pollution control. Public Works, 16: 53-55. Kocm, J. 1995. Evaluatian of Water Quality Ponds and Swales in the Issaquah/EastLake Sammamish Basins. King County Surface Water Management, Seattle, WA, and Washington Department of Ecology, Olympia, WA. Metzger, M. E., D. F. Messer, C. L. Beitia, C. M. Myers, and V. L. Kramer. 2002. The Dark Side Of Storniwater Runoff Management Disease Vectors Associated With Structural BMPs. Stormwater 3(2): 24-39.0aldafld, P.H. 1983. An evaluation of stonnwater pollutant removal 10 of 13 Cal lfbrnla Stormwata- BMP Handbook January 2003 New Development and Redevelopment www. cabmphancbooks. corn Vegetated Swale TC-30 through grassed swale treatment In Proceedings of the International Symposium of Urban Hydrology, Hydraulics cmdSedimentContro4 Lexington, KY pp. 173-182. Occoquan Watershed Monitoring Laboratory. :L983. Final Report Metropolitan Washington Urban RwtoffProject. Prepared for the Metropolitan Washington Council of Governments, Washington, DC, by the Occoquan Watershed Monitoring Laboratory, Manassas, VA Pitt; R., andJ. McLean. 1986. Toronto Area WatershedManagement Strategy Study: Humber. River Pilot WatershedProject. Ontario Ministry of Environment, Toronto, ON. Schueler, T. 1997. Comparative Pollutant Removal Capability of Urban BMPs: Areanalysis. Watershed Protection Techniques 2(2):379-383. Seattle Metro and Washington Department of Ecology. 1992. Biofiltration Swale Performance: Recommendations cmdDesign Considerations. Publication No. 6. Water Pollution Control Department Seattle, WA. Soull eastern Wisconsin Rgional Pbrnrirng Commission (SWRPC). 1991. Costs of Urban Nonpoint Source Water Pollution Control Measures. Technical report no. 31. Southeastern Wisconsin Regional Planning Commission, Waukesha, WI. U.S. EPA, 1999, Starmwater Fact Sheet Vegetated Swales, Report # 832-F-99-006 http://www.epa.gov/owin/intb/vegswale.pdf, office of Water, Washington DC. Wang, T., D. Spyndakis, B. Mar, and R. Homer. 1981. Transport, Deposition and Control of Heavy Metals in I-llghway Runoff. FHWA-WA-RD-39-10. University of Washington, Department of Civil Engineering, Seattle, WA. Washington State Department of Transportation, 1995, Highway RunoffMarnial, Washington State Department of Transportation, Olympia, Washington. 0 Welborn, C., and J. Veenhuis. 1987. Effects ofRimoff Controls on the Quantity and Quality of Urban Runoffin Two Locations in Austin, 2X. USGS Water Resources Investigations Report' No. 87-4004.U.S. Geological Survey, Reston, VA. Yousef Y., M. Wanielista, H. Harper, D. Pearce, and R. Tolbert 1985 Best Management Practices: Removal of Highway Contaminants By Roadside Swales. University of Central Florida and Florida Department of IYansportation, Orlando, FL Yu, S., S. Barnes, and V. Gerde. 1993. Testing of Best Management Practicesfor Controlling Highway Runoff FHWA/VA-93-Ri.6. Virginia Transportation Research Council, Charlottesville, VA. Information Resources Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design Manual. www.mde.statemd.us/environment/wma/stormwatermanuaL Accessed May 22, 2001. Reeves, E. 1994. Performance and Condition of Bioffiters in the Pacific Northwest Watershed Protection Techniques 1(3):u7-119. January 2003 California Stormwater BMP Handbook 11 of 13 New Development and Redevelopment www.cabmphendbooks.com TC-30 Vegetated Swale Seattle Metro and Wahiiigton Department of Ecology. 1992. Biofiltration Swale Performance. Recommendations and Design Considerations. Publication No. 657. Seattle Metro and Washington Department of Ecology Olympia, WA USEPA 1993. Guidance Specifijing Management Measuresfor Sources ofNQnpoint Pollution in Coastal Waters. EPA-840-B-92-0o2. U.S. Environmental Protection Agency, Office of Water. Washington, DC. Watershed Management Institute (WMI). 1997. Operation, Maintenance, andManagement of Stormwater Management Systems. Prepared for U.S. Environmental Protection Agency, Office of Water. Washington, DC, by the Watershed Management Institute, Ingleside, MD. 12 of 13 California Stcrnwater BMP Handbook January 2003 New Development and Redevelopment www.cthmphand,00ks. corn