The URL can be used to link to this page

Home My WebLink AboutCT 15-01; Cascada Verde; Preliminary Storm Water Management Plant; 2015-08-04__ .s~:Q:____ __Jll::l~-- r£1 ~e PRELIMINARY STORM WATER MANAGEMENT PLAN FOR CASCADA VERDE (CT 15-01, PUD 15-03, SDP 15-02, HDP 15-02) August 4, 2015 Civil Engineering o Hydrology o Hydraulics o Sedimentation P.O. Box 9496 Rancho Santa Fe, CA 92067 (858) 692-0760 AUG 12 2015 j j j j j j j ~ j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j 'l -TABLE OF CONTENTS- 1.0 Introduction ....................................................................................................................... 1 1.1 Vicinity Map ..................................................................................................................... 1 1.2 Project Description ............................................................................................................ 2 1.3 Site Map ............................................................................................................................ 2 1.4 Constraints and Opportunities ........................................................................................... 2 2.0 Water Quality Environment .............................................................................................. 3 2.1 Beneficial Uses ................................................................................................................. 3 2.1.1 Inland Surface Waters ....................................................................................................... 4 2.1.2 Groundwater ..................................................................................................................... 4 3.0 Pollutants and Conditions of Concern .............................................................................. 4 3.1 Pollutants from Project Area ............................................................................................. 4 3.2 Pollutants of Concern in Receiving Waters ...................................................................... 5 4.0 Permanent Storm Water Best Management Practices ...................................................... 6 4.1 Standard Site Design BMPs .............................................................................................. 6 4.2 Source Control BMPs ....................................................................................................... 7 4.3 Low Impact Development Site Design BMPs .................................................................. 9 4.4 Treatment Control BMPs ................................................................................................ 10 4.5 Hydromodification .......................................................................................................... 1 0 5.0 Storm Water BMP Maintenance ..................................................................................... 12 6.0 Summary/Conclusions .................................................................................................... 13 7.0 Certification .................................................................................................................... 14 Storm Water Standards Questionnaire, E-34 .............................................................................. 15 2010 303(d) List .......................................................................................................................... 18 APPENDIX A. Low Impact Development and Hydromodification Analyses MAP POCKET Preliminary ttt Drainage Management Areas Exhibit 1.0 INTRODUCTION This preliminary Storm Water Management Plan (SWMP) addresses water quality requirements associated with Cascada Verde, which is a proposed townhome project in the city of Carlsbad. This SWMP accompanies the entitlement engineering plans (Site Development Plan) by the project's civil engineer, Hofman Planning and Engineering (Hofman), and follows the criteria outlined in the City of Carlsbad's January 14, 2011, Standard Urban Storm Water Management Plan (SUSMP). According to the City's Storm Water Standards Questionnaire E-34 (attached following this report text), the development is in the following five priority project categories: residential development; hillside development; street, road, and driveway; discharges to an Environmentally Sensitive Area; and more than 1-acre of disturbance. The SUSMP outlines the SWMP objectives, which are to identify site opportunities and constraints, identify pollutants and conditions of concern, follow low impact development design objectives, describe best management practices (BMPs ), and outline maintenance requirements. BMPs will be utilized to the maximum extent practicable to provide a long-term solution for addressing runoff water quality. BMPs were selected to meet the objectives. 1.1 Vicinity Map PROJECT LOCATION 1 1.2 Project Description The Cascada Verde project is a proposed residential development that will consist of 35 attached multi-family residences (townhomes) along with associated driveways, sidewalks, walkways, landscaping, and drainage facilities (see the Preliminary Site Plan following this report text). The development will be constructed within an undeveloped 3.68 acre parcel (Assessor's Parcel Number 215-240-36) along the north side of Alicante Road between Altisma Way and Altiva Place. Under pre-project conditions, the site is in a natural state and covered with vegetation ranging from grasses and weeds to brush and large trees. An unnamed natural drainage course flows in a southerly direction through the middle of the site. The drainage course contains dense, mature vegetation. The drainage course conveys storm runoff from the site and its upstream tributary area to a 72-inch culvert under Alicante Road. The culvert discharges into a concrete-lined trapezoidal channel that flows southerly through the La Costa Resort & Spa's South (golf) Course to a confluence with San Marcos Creek. San Marcos Creek continues westerly through the golf course where it discharges into Batiquitos Lagoon. Under post-project conditions, the multi-family buildings, driveways, parking, and recreation areas will be developed on both sides of the unnamed natural drainage course. A portion of the on-site drainage course will be channelized to allow development to occur immediately east and west of the channel. Retaining walls will be used along both channel banks and a vehicular crossing of the drainage course is proposed within the upstream portion of the site. Access entrances will be constructed along Altisma Way and Altiva Place. The 72-inch culvert under Alicante Road will be replaced with a larger culvert (up to 96-inch diameter) to lower the 1 00-year water surface elevations within the site. 1.3 Site Map The Preliminary Site Plan by Hofman is included following this report text. 1.4 Constraints and Opportunities The development will primarily occur within a moderately to steeply sloping undisturbed area. The pre-project drainage patterns are being maintained by the project in that the project runoff will continue to be conveyed to the drainage course that bisects the site. The development will consist of attached multi-family residences within hillside areas surrounding an unnamed natural watercourse. Retaining walls are needed to support the development. A drainage course must be maintained within the site that is capable of conveying the 1 00-year flow through the central portion. As a result, the central portion of the site will support natural vegetation. The central portion is constrained environmentally because it is within the waters of the US. Consequently, the development area is limited by the existing drainage course and processing is needed through the resource agencies (US Army Corps of Engineers, California Dept. of Fish and Wildlife, Regional Water Quality Control Board, etc.). Due to the relatively small development footprint, shared driveways with minimized widths are being utilized. 2 Bioretention basins are proposed on both sides of the drainage course. The project's storm runoff will be directed to a bioretention basin before discharging into the drainage course. The bioretention basins will be used to meet both treatment and hydromodification requirements. The bio-retention basins are being sized using the flow-through planter criteria to account for impervious liners (see Section 4.5), so flow-through planters are in effect being proposed. Additional BMPs that were considered are as follows. Dry wells and infiltration basins are not being proposed because the site contains hydrologic soil group D, which has a low infiltration rate. Cisterns are typically not preferred for multi-family homes for aesthetic reasons, space considerations, and low volume of flow capture. Pervious pavers will be used for the pedestrian walkways and sidewalks as well as portions of the driveways. 2.0 WATER QUALITY ENVIRONMENT 2.1 Beneficial Uses The beneficial uses for the hydrologic unit (see Section 3.1) are included in Tables 1 and 2. These tables were obtained from the Water Quality Control Plan for the San Diego Basin (9) compiled on August 28, 2012. The following contains definitions of the beneficial uses in the tables: MUN-Municipal and Domestic Supply: Includes uses of water for community, military, or individual water supply systems including, but not limited to, drinking water supply. AGR -Agricultural Supply (AGR): Includes uses of water for farming, horticulture, or ranching including, but not limited to, irrigation, stock watering, or support of vegetation for range grazing. RECl -Contact Recreation: Includes uses of water for recreational activities involving body contact with water, where ingestion of water is reasonably possible. These uses include, but are not limited to, swimming, wading, water-skiing, skin and SCUBA diving, surfing, white water activities, fishing, or use of natural hot springs. REC2 -Non-Contact Recreation: Includes the uses of water for recreational involving proximity to water, but not normally involving body contact with water, where ingestion of water is reasonably possible. These uses include, but are not limited to, picnicking, sunbathing, hiking, camping, boating, tide pool and marine life study, hunting, sightseeing, or aesthetic enjoyment in conjunction with the above activities. 3 WARM-Warm Freshwater Habitat: Includes uses of water that support warm water ecosystems including, but not limited to, preservation or enhancement of aquatic habitats, vegetation, fish or wildlife, including invertebrates. WILD -Wildlife Habitat: Includes uses of water that support terrestrial ecosystems including, but not limited to, preservation and enhancement of terrestrial habitats, vegetation, wildlife, (e.g., mammals, birds, reptiles, amphibians, invertebrates), or wildlife water and food sources. 2.1.1 Inland Surface Waters Inland surface waters for the Batiquitos Hydrologic Subarea (see Section 3.1) have the beneficial uses shown in Table 1: Table 1. Beneficial Uses for Inland Surface Waters Hydrologic Unit ::: -(':! s (.) .... ..::: ~ 0 Code ~ .... 0 6 (.) () "' OJ) '"0 Vl ::: .... .... 0 ~ ~ a:i ~ ~ ...... p., ~ p., 904.51 + • • • • + Exempted by the Regional Board from the municipal used designation. • Existing Beneficial Use 2.1.2 Groundwater '"0 ::9 Q) ::: ~ 0 a ~ 0. u ~ r./J • Groundwater beneficial uses for the Batiquitos Hydrologic Subarea are shown in Table 2 (no groundwater beneficial uses exist): Table 2. Beneficial Uses for Groundwater Hydrologic Unit Code ::: .... () ..::: .... ~ OJ) '"0 e Vl 6 ~ ::: ..... ...... p., ~ 904.51 3.0 POLLUTANTS AND CONDITIONS OF CONCERN 3.1 Pollutants from Project Area The project is located within the Batiquitos Hydrologic Subarea (904.51) ofthe San Marcos Hydrologic Area (904.50), which is within the Carlsbad Hydrologic Unit (904.00). The total drainage area of the hydrologic unit is approximately 210 square miles. Runoff from portions of the hydrologic subarea ultimately drains to Batiquitos Lagoon, which is west of the project 4 site. All of the project runoff will ultimately enter Batiquitos Lagoon. The project site represents less than one percent of the overall watershed. The following table lists pollutants of concern that are anticipated or can potentially exist at proposed priority development project sites. The pollutants are from the city of Carlsbad's SUSMP. The project falls within the attached residential development, hillside development, and streets, highways & freeways priority project categories (highlighted yellow in the table). All of the listed pollutants are either anticipated or can potentially exist at the developed site. Table 3. Priority Project Pollutants Priority Project Sediments Categories Detached Residential Development Attached Residential Development Commercial Development >one acre Heavy Industry Automotive Repair Shops Restaurants Hillside Development >5,000 ft2 Parking Lots Retail Gasoline Outlets Streets, Highways& Freeways 0 0 X = Anticipated P = Potential X X pOl X X p(l) X Heavy Organic Nutrients Metals Compounds X X pOl X p(2) X X X x<4J(s) X pOl X X X pOl X x<4J (I) A potential pollutant iflandscaping exists on-site Trash & Debris X X X X X X X X X X (2) A potential pollutant ifthe project includes uncovered parking areas (3) A potential pollutant if land use involves food or animal waste products (4) Including petroleum hydrocarbons (5) Including solvents 3.2 Pollutants of Concern in Receiving Waters Oxygen Oil Bacteria Demanding & & Pesticides Substances Grease Viruses X X X X pOl p(2) p X p(S) X p(3) p(S) X X X X X X pOl X X X pOl X p(l) X X p(S) X X pOl The primary receiving waters for the site are San Marcos Creek and Batiquitos Lagoon. According to the 2010 303(d) list (included following this report text) approved by the State Water Resources Control Board (and by the US EPA in October 2011), San Marcos Creek is 303(d) listed for DDE, phosphorus, sediment toxicity, and selenium. Batiquitos Lagoon, is not 303(d) listed. Neither of the two water bodies is subject to total maximum daily loads 5 (TMDLs). Based on this information, the project generates pollutants of concern in the receiving waters for sediment, nutrients (phosphorus), and pesticides (DDE). 4.0 PERMANENT STORM WATER BEST MANAGEMENT PRACTICES To address water quality for the project, best management practices (BMPs) will be implemented. The following discusses the Standard Site Design, Source Control, and Low Impact Development design BMPs for the project. 4.1 Standard Site Design BMPs The City of Carlsbad's standard objectives are required for all projects. The project will accomplish these goals through the following standard site design BMPs, which are from the Carlsbad SUSMP: Standard Stormwater Requirements Minimize Impervious Surfaces. The project will include pervious surfaces through landscaping and recreation areas within the development footprint. In addition, a portion of the hillside areas and the unnamed natural drainage course will be pervious areas. Finally, the walkways and sidewalks will be constructed with pervious materials as well as portions of the driveways. Disconnect Discharges. Roof drains will discharge to adjacent landscape areas, where feasible. The project discharges will be directed to a bioretention basin for treatment and hydromodification control. Conserve Natural Areas. The unnamed natural drainage course will remain although a portion will be realigned. The realigned reach will be planted with native, riparian vegetation. Stenciling Inlets and Signage. The curb cuts and inlets within the project will be stenciled with prohibitive language such as "No Dumping-I live downstream" or approved similar. Landscape Design. A landscape plan will be prepared that uses drought-tolerant species in accordance with the City's landscape manual. Native trees and shrubs will be preserved beyond the proposed grading footprint in order to maximize canopy interception and promote water conservation. The project will only use water as needed to support the landscaping. Water Efficient Irrigation. The irrigation systems will be designed to each landscaped areas water requirements to avoid over irrigation. Rain shutoff devices will be used to prevent irrigation after rain events. Protect Slopes And Channels. The design will prevent runoff from flowing uncontrolled over the tops of manufactured slopes. The proposed slopes will be landscaped. Riprap energy dissipaters will be used at storm drain outfalls. The realigned drainage channel will be designed to minimize erosive velocities. 6 Vegetate slopes with native or drought tolerant vegetation. Native and drought tolerant vegetation will be used to the extent feasible. Trash Receptacles. Each residence will have personal, covered trash receptacles. Material Storage Areas. The project does not propose outdoor material storage areas. Any required material storage shall be kept under cover. 4.2 Source Control BMPs Source control BMPs will consist of measures to prevent polluted runoff. The following addresses the source control BMPs from Appendix 1 of the Carlsbad SUSMP: Table 4. Pollutant Sources and Source Control Checklist Potential Source Permanent Source Operational Source of Runoff Pollutants Control BMPs Control BMPs On-site storm drain Mark all inlets with "No • Maintain and periodically inlets Dumping - I live downstream" repaint inlet markings • Provide stormwater pollution information to owners, lessees, and operators (Fact sheet SC- 44 from the CASQA Stormwater Quality Handbook at www.cabmphandbooks.com) • Owner/lessee agreements shall state "Tenant shall not allow anyone to discharge anything to storm drains or to store or deposit materials so as to create a potential discharge to storm drains. Need for future Buildings shall be designed to Integrated Pest Management (e.g., indoor & structural avoid openings that would the EPA's Citizen's Guide to Pest pest control encourage entry of pests. Control and Pesticide Safety) information shall be provided to owners, lessees, and operators. Landscape/Outdoor Final landscape plans will Maintain landscaping using Pesticide Use accomplish all of the minimum or no pesticides. following. See applicable operational BMPs • Preserve existing native trees, in Fact Sheet SC-41, "Building and Grounds Maintenance," and TC-shrubs, and ground cover to 30, "Vegetated Swale," in the the maximum extent possible. CASQA Stormwater Quality • Design landscaping to Handbooks at 7 minimize irrigation and www.cabmghandbooks.com runoff, to promote surface Integrated Pest Management (e.g., infiltration where the EPA's Citizen's Guide to Pest appropriate, and to minimize Control and Pesticide Safety) the use of fertilizers and information shall be provided to pesticides that can contribute owners, lessees, and operators. to stormwater pollution. • Where landscaped areas can retain or detain stormwater, specify plants that are tolerant of saturated soil conditions. • Consider using pest-resistant plants, especially adjacent to hardscape. • To ensure successful establishment, select plants appropriate to site soils, slopes, climate, sun, wind, rain, land use, air movement, ecological consistency, and plant interactions Pools, spas, ponds, If the local municipality See applicable operational decorative fountains, requires pools to be plumbed BMPs in Fact Sheet SC-72, and other water to the sanitary sewer, a "Fountain and Pool features connection will be made Maintenance," in the CASQA according to local Stormwater Quality Handbooks at www.cabmghandbooks.com requirements. Refuse areas Each residence shall have its Provide adequate number of own refuse and recycling receptacles. Inspect receptacles containers. Covered regularly; repair or replace containers shall be provided leaky receptacles. Keep receptacles covered. Prohibit/ in the common recreation prevent dumping of liquid or areas. Refuse and recycling hazardous wastes. Post "no pick up shall occur weekly. hazardous materials" signs. Inspect and pick up litter daily and clean up spills immediately. Keep spill control materials available on-site. See Fact Sheet SC-34, "Waste Handling and Disposal" in the CASQA Stormwater Quality Handbooks at www.cabmohandbooks.com Vehicle and The CC&Rs will define car 8 equipment cleaning washing requirements and restrictions at the site. The HOA will be responsible for enforcing the requirements and restrictions. Vehicle/Equipment The CC&Rs will prohibit Repair and repair and maintenance Maintenance activities in areas exposed to precipitation and storm flows. The HOA will be responsible for enforcing this requirement. Fire Sprinkler Test The architectural plans shall See the note in Fact Sheet SC-41, Water show fire sprinkler test water, "Building and Grounds if needed, draining to sanitary Maintenance," in the CASQA sewer. Stormwater Quality Handbooks at www .cabmphandbooks.com Condensate drain Condensate drain lines may lines discharge to landscaped areas ifthe flow is small enough that runoff will not occur. Condensate drain lines may not discharge to the storm drain system. Roofing, gutters, and The architectural design will trim avoid roofing, gutters, and trim made of copper or other unprotected metals that may leach into runoff. Plazas, sidewalks, Plazas, sidewalks, and parking lots and parking lots. shall be swept regularly to prevent the accumulation of litter and debris. Debris from pressure washing shall be collected to prevent entry into the storm drain system. Wash water containing any cleaning agent or degreaser shall be collected and discharged to the sanitary sewer and not discharged to a storm drain. 4.3 Low Impact Development Site Design BMPs Low Impact Development (LID) BMPs must be incorporated into the site design to meet the City of Carlsbad's January 14, 2011 SUSMP requirements. The integrated LID outlines five strategies: 9 1. Optimize the site layout by preserving natural drainage features and designing buildings and circulation to minimize the amount of roofs and paving. 2. Use pervious surfaces such as turf, gravel, or pervious pavement-or use surfaces that retain rainfall. All drainage from these surfaces is considered to be "self-retained". 3. Disperse runoff from impervious surfaces on to adjacent pervious surfaces (e.g., direct a roof downspout to disperse runoff onto a lawn). 4. Drain impervious surfaces to engineered Integrated Management Practices (IMPs), such as bioretention facilities. IMPs infiltrate runoff to groundwater and/or percolate runoff through engineered soil and allow it to drain away slowly. The project design is in compliance with these strategies. The site layout has been designed to preserve natural areas in the unnamed drainage course that flows through site as well as portions of the perimeter hillside. Shared drive aisles will provide access to the units and the on-site streets are being designed with minimal widths. Pervious surfaces are being proposed on the pedestrian walkways and sidewalks. Pervious pavement will also be incorporated within portions of the driveways and parking stalls, as needed, to help reduce the bioretention basin footprint to fit within the available space. Runoff from the roofs will flow towards pervious landscape areas, where possible, and ultimately enter a bioretention basin. Bioretention basins will be used to treat the on-site runoff and to meet hydromodification requirements (discussed in next section). Bioretention basins provide high to medium removal effectiveness for the pollutants generated by the project, which are listed in Table 3. Sizing is included in Appendix A of this report using City of Carlsbad's SUSMP sizing factors. 4.4 Treatment Control BMPs Treatment control BMPs were selected to treat the project pollutants of concern identified in Table 3. Bioretention basins will be used because they have a medium to high pollutant removal efficiency for the project's pollutants of concern. For treatment control only, a bioretention basin's surface area must be at least 4 percent of the total area determined from the drainage management areas. For the project, the bioretention basins will also provide hydromodification flow control. Since impervious liners are used, the bioretention basins are sized as flow-through planters. The sizing is discussed in the next section. 4.5 Hydromodification The January 14, 2011 SUSMP requires hydromodification (flow control) for priority development projects to ensure that post-development peak flows do not exceed pre- development peak flows. Cascada Verde is a priority development project and must meet the hydromodification requirement. This can be accomplished by sizing bioretention facilities using the criteria in the City of Carlsbad's SUSMP. 10 The proposed project will have at least two bioretention basins spread throughout the site (see the DMA Exhibit in the map pocket). The City's SUSMP sizing factors were used for the bioretention basin sizing. For current entitlement purposes, one bioretention will serve the area west of the unnamed drainage course and another will serve the area east of the unnamed drainage course. There is ample area for the east bioretention basin. The area at the west bioretention basin is more limited, but Hofman has verified that the conceptual grading shows that a single bioretention basin for the west development area is feasible. Data entry for hydromodification BMP sizing includes the lower flow threshold, soil group, slope, and rain gage. A lower flow threshold of 0.1 Q2 is used because a downstream channel screening assessment has not been performed. The site is within the Oceanside rainfall basin and contains soil group D. The majority of the development will occur within the steep hillsides (typically 2:1 so well over 15 percent slope) adjacent to the unnamed drainage course, so the slope category is "steep." The bioretention sizing analyses are included in Appendix A using the flow-through planter sizing factors because it is anticipated that the bioretention basins will be required to have impermeable liners. The DMA Exhibit in the map pocket delineates the drainage areas tributary to each of the two bioretention basins. Each drainage area is subdivided into its drainage management areas: roofs, asphalt (driveways), pervious pavement on driveways, pedestrian pavement (sidewalks, walkways), and landscaping. The results are included in Table 5. Table 5 contains the standard and minimum (see Section 4.4) treatment control surface area as well as hydromodification volumes for bioretention. Table 5. Summary of Bioretention Sizing BMP Sizing Calculator Results Area Drainage Bioretention Standard Req'd Req'd Reduced Provided Management Basin1 Surface Surface Subsurface Surface on Plans, Area Area (A), Volume Volume Area2, sf sf sf (VI), cf (V2), cf DMA1 East 2,330 1,942 1,398 888 900 DMA2 West 4,723 3,936 2,834 1,799 1,874 1BJOretentJOn basms were sized usmg flow-through planter factors to account for impervious !mer 2Reduced surface area reflects minimum surface area that still provides treatment control (based on 4% ofimpevious area) 3The volumes provided will match the required volumes from the table The County of San Diego's Final HMP states that the ponding layer and storage layer are converted to volumes "so that the project designer can flexibly configure the ponding layer and storage layer to meet site constraints" (see excerpt in Appendix A). For instance, the standard bioretention basin design contains a 10-inch surface ponding layer over a 4-foot subsurface layer (1.5 feet of growing medium on 2.5 feet of gravel). The surface ponding (V1) and gravel (V2) depths can be increased over these typical values to meet the volume requirements in instances where the available surface area is less than the area, A. The sum of the design surface and subsurface storage volumes must meet or exceed the volumes in Table 5. Furthermore, the surface area must be maintained greater than the values in the last 11 column of Table 5 to satisfy treatment control sizing. Since the project is a hillside development that is capable of supporting increased surface and subsurface depths, the intent is to minimize the bioretention basin surface areas. 5.0 STORM WATER BMP MAINTENANCE The developer will be responsible for funding and implementing the operations and maintenance of the project BMPs. Provisions will be made to transfer operations and maintenance to the new owner in the event of a change in ownership. The homeowner's association will ultimately be responsible for ongoing operations and maintenance. The following describes the specific BMP maintenance. Bioretention basins The drainage outlet from the basins shall be inspected monthly and after large storm events. Debris, sediment, and other obstructions shall be removed immediately from the outlet. The habitat shall also be inspected annually and replanted as needed to maintain an adequate cover. Pervious Pavement After installation, inspect pavement once a month for 4 to 6 months. After this period inspection can occur annually, particularly after there has been heavy rain or storms, for this is the time when the drainage voids can become clogged with organic debris. Sweep and/or vacuum the permeable surface every 3 months. Street and sidewalk sweepers that have a vacuum and brushes can be used. High pressure hosing shall be performed after sweeping/vacuuming. Voids should be kept filled with aggregate. Landscaping Maintenance will be performed by landscaping personnel. The vegetation will be maintained and inspected on a monthly basis by landscape maintenance staff and will be replaced or replanted, as necessary, to maintain a dense, healthy cover. The vegetation will also be inspected after major storm events. Maintenance shall include periodic mowing, weed control, irrigation, reseeding/replanting of bare areas, and clearing of debris. A design grass height of 6 inches is recommended for turf areas. Grass clippings shall not be left in grass swales. The private drainage system will shall be kept clear of debris and inspect prior to and during the rainy season to ensure it is free-flowing. Efficient Irrigation The landscaping personnel shall inspect and maintain the irrigation system on a regular basis. This will occur during the routine maintenance activities. All valves, heads, shutoff devices, lines, etc. shall be kept in a properly functioning condition. Any defective parts shall be replaced immediately. The irrigation system shall be adjusted to prevent excessive runoff from landscape areas. The irrigation schedule shall be adjusted based on seasonal needs. 12 Inlet Stenciling Any stenciling shall be inspected at the beginning and end of each rainy season and repaired or replaced, as needed. Hazardous Wastes Suspected hazardous wastes will be analyzed to determine disposal options. Hazardous materials are not expected to be generated on-site; however, if discovered, hazardous materials will be handled and disposed of according to local, state, and federal regulations. A solid or liquid waste is considered a hazardous waste if it exceeds the criteria listed in the California Code ofFederal Regulations, Title 22, Article 11 (State of California, 1985). 6.0 SUMMARY/CONCLUSIONS This preliminary SWMP has been prepared in accordance with the City of Carlsbad's January 14, 2011, Standard Urban Storm Water Management Plan, and has evaluated and addressed potential pollutants associated with the Cascada Verde project and its effects on water quality. This SWMP has been based on the preliminary entitlement plans by Hofman Planning and Engineering. The current water quality BMP sizing requirements are subject to change by December 2015. The project entitlement will include a Vesting Tentative Map so that the BMPs are grandfathered in accordance with the sizing criteria outlined in this SWMP. A summary of the facts and findings associated with the project and the measures addressed by this SWMP are as follows: • The beneficial uses for the receiving waters have been identified. BMPs wiH be used to protect the beneficial uses as outlined by the SUSMP. • The project will not significantly alter drainage patterns and will meet hydromodification requirements. • Permanent BMPs will be incorporated into the project design in the form of site design, source control, and LID treatment control. • Preliminary details for the treatment control bioretention BMPs are included after this text. • The proposed BMPs address mitigation measures to protect water quality and beneficial uses to the maximum extent practicable. 13 7.0 CERTIFICATION The selection, sizing, and preliminary design of stormwater treatment and other control measures in this plan meet the requirements of Regional Water Quality Control Board Order R9-2007-0001 and subsequent amendments. August4,2015 Wayne W. Chang, RCE 4 Date 14 STORM WATER STANDARDS QUESTIONNAIRE E-34 Development Services Land Development Engineering 1635 Faraday Avenue 760-602-2750 www.carlsbadca.gov To address post-development pollutants that may be generated from development projects, the City requires that new development and significant redevelopment priority projects incorporate Permanent Storm Water Best Management Practices (BMP's) into the project design per the City's Standard Urban Stormwater Management Plan (SUSMP). To view the SUSMP, refer to the Engineering Standards (Volume 4, Chapter 2). Initially this questionnaire must be completed by the applicant in advance of submitting for a development application (subdivision, discretionary permits and/or construction permits). The results of the questionnaire determine the level of storm water standards that must be applied to a proposed development or redevelopment project. Depending on the outcome, your project will either be subject to 'Standard Stormwater Requirements' or be subject to additional criteria called 'Priority Development Project Requirements'. Many aspects of project site design are dependent upon the storm water standards applied to a project. Your responses to the questionnaire represent an initial assessment of the proposed project conditions and impacts. City staff has responsibility for making the final assessment after submission of the development application. If staff determines that the questionnaire was incorrectly filled out and is subject to more stringent storm water standards than initially assessed by you, this will result in the return of the development application as incomplete. In this case, please make the changes to the questionnaire and resubmit to the City. If you are unsure about the meaning of a question or need help in determining how to respond to one or more of the questions, please seek assistance from Land Development Engineering staff. A separate completed and signee! questionnaire must be submitted for each new development application submission. Only one completed and signed questionnain:l is required when multiple development applications for the same project are submitted concurrently. In addition to this questionnaire, you must also complete, sign and submit a Project Threat Assessment Form with construction permits for the project. Please start by completing Step 1 and follow the instructions. When completed,. sign the form at the end and submit this with your application to the city. To determine if your project is a wiority development project, please answer the following questions: 1. Is your project LIMITED TO constructing new or retrofitting paved sidewalks, bicycle lanes or trails that meet the following criteria: (1) Designed and constructed to direct storm water runoff to adjacent vegetated areas, or other non-erodible permeable areas; OR (2) designed and constructed to be hydraulically disconnected from paved streets or roads; OR (3) designed and constructed with permeable pavements or surfaces in accordance with USEPA Green Streets guidance? 2. Is your project LIMITED TO retrofitting or redeveloping existing paved alleys, streets, or roads that are designed and constructed in accordance with the USEPA Green Streets guidance? YES NO X X If you answered "yes" to one or more of the above questions, then your project is NOT a priority development project and therefore is NOT subject to the storm water criteria required for priority development projects. Go to step 4, mark the last box stating "my project does not meet PDP requirements" and complete applicant information. If ou answered "no" to both questions, then go to Step 2. E-34 Page 1 of 3 Effective 6/27113 r STORM WATER STANDARDS QUESTIONNAIRE E-34 Development Services Land Development Engineering 1635 Faraday Avenue 760-602-2750 www.carlsbadca.gov o determine if your project is a priority development project, please answer the following questions: 1. Is your project a new development that creates 10,000 square feet or more of impervious surfaces over the entire project site? This includes commercial, industrial, residential, mixed-use, nrn>IA,T.<: On land. 2. Is your project creating or replacing 5,000 square feet or more of impervious surface collectively over project site on an existing site of 10,000 square feet or more of impervious surface? This includes ""',.,.,n'"'''~"''"' · and on land. 3. Is your project a new or redevelopment project that creates 5,000 square feet or more of im collectively over the entire project site and supports a restaurant? A restaurant is a facility that sells nro'n"''""'rt foods and drinks for consumption, including stationary lunch counters and refreshment stands selling '"~-'""'',_," foods drinks for immediate tion. 4. Is your project a new or redevelopment project that creates 5,000 square feet or more of im collectively over the entire project site and supports a hillside development project? A hillside rJe,vefiJnrmet1t project includes development on any natural slope that is twenty-five percent or greater. 5. Is your project a new or redevelopment project that creates 5,000 square feet or more of impe collectively over the entire project site and supports a parking lot. A parking lot is a land area or of motor vehicles used for business or for commerce. 6. Is your project a new or redeve,lopment project that creates 5,000 square feet or more of impe collectively over the entire project site and supports a street, road, highway freeway or driveway? road, highway, freeway or driveway is any paved impervious surface used for the "n,,rfi,,f;,,n mn,tn~r-lfr•to," and other vehicles. 7. Is your project a new or redevelopment project that creates or replaces 2,500 square feet or impervious surface collectively over the entire site, and discharges directly to an Environmentally "'"''n"'11r'""' Area (ESA)? "Discharging Dimctly to" includes flow that is conveyed overland a distance of 200 from the project to the ESA, or conveyed in a pipe or open channel any distance as an isolated flow to the ESA e. not with flows from an"'""''nt 8. Is your project a new development that supports an automotive repair shop? An automotive facility that is categorized in any one of the following Standard Industrial Classification (SIC) 501 5541 or 7539. 9. Is your project a new development that supports a retail gasoline outlet (RGO)? This category that meet the following criteria: (a) 5,000 square feet or more or (b) a project Average Daily Traffic 100 or more vehicles 1 O.ls your project a new or redevelopment project that results in the disturbance of one or more acres of are expected to generate pollutants post construction? X X X X X X X X X X the Pacific Ocean creates 2,500 square feet or I more of . X 1 s surface on the more than 10%? answered "yes" to one or more of the above questions, you ARE a priority development project therefore subject to plementing structural Best Mana~Jement Practices (BMP's) in addition to implementing Standard Storm Requirements such source control and low impact development BMP's. A Storm Water Management Plan (SWMP) be submitted with your for development. Go to step 3 for redevelopment projects. For new projects, go to 4 at the end of this uestionnaire, check the "my project meets PDP requirements" box and complete applicant i · you answered "no" to all of the above questions, you ARE NOT a priority development project and are therefore subject plementing only Standard Storm Water Requirements such as source control and low impact development BMP's required for ldeveiOPillent projects. A Storm Water Management Plan (SWMP) is not required with your application(s) for development. Go to at the end of this questionnaire, check the "my project does not meet PDP requirements" box and complete .... .-.... a, E-34 Page 2 of 3 Effective 6/27/13 ' .... r ·· Cityof crrrlsbad STORM WATER STANDARDS QUESTIONNAIRE E-34 Development Services Land Development Engineering 1635 Faraday Avenue 760-602-2750 www.carlsbadca.gov Does the redevelopment project result in the creation or replacement of imp!'rvious surface in an amount of less than tiO% of the surface area of the previously existing development? N/ A If you answered "yes," the structural BMP's required for Priority Development Projects apply only to the creation or replacement of impervious surface and not the entire development. Go to step 4, check the "my project meets PDP requirements" box and c:omplete applicant information. If you answered "no," the structural BMP's required for Priority Development Projects apply to the entire development. Go to step 4, c;heclk the "my project meets PDP requirements" box and complete applicant information. 1]1 My project meets PRIORITY DEVELOPMENT PROJECT (PDP) requirements and must comply with additional stormwater criteria per the SUSMP and I understand I must prepare a Storm Water Management Plan for submittal at time of application. I understand flow control (hydromodification) requirements may apply to my project. Refer to SUSMP for details. D My project does not meet PDP requirements and must only comply with STANDARD STORMWATER REQUIREMENTS per the SUSMP. As part of these requirements, I will incorporate low impact development strategies throughout my project. Applicant Information and Signature Box Address: Applicant Name: Applicant Signature: Accessor's Parcel Number(s): 215-240-26 Applicant Title: Date: This Box for City UsH Only City Concurrence: By: Date: Project ID: I YES I NO I I * Environmentally Sensitive Areas include but are not limited to all Clean Water Act Section 303(d) impaired water bodies; areas designated as Areas of Special Biological Significance by the State Water Resources Control Board (Water Quality Control Plan for the San Diego Basin (1994) and amendments); water bodies designated with the RARE beneficial use by the State Water Resources Control Board (Water Quality Control Plan for the San Diego Basin (1994) and amendments); areas designated as preserves or their quivalent under the Multi Species Conservation Program within the Cities and County of San Diego; and any other equivalent environmentally sensitive areas which have been identified by the Copermittees. E-34 Page 3 of 3 Effective 6/27113 317/2015 Statewide USEPA Final Approval: October 11, 2011 WNW.waterboards.ca.gov/waterjssuesiprogramsltmdii2010Statejr_reports/category5Jeport.shtml CATEGORY 5 Final 2010 Integrated Report (CWA Section 303(d) List I 305(b) Report) 2010 CALIFORNIA 303(d) LIST OF WATER QUALITY LIMITED SEGMENTS* Category 5 criteria: 1) A water segment where standards are not met and a TMDL is required, but not yet completed, for at least one of the pollutants being listed for this segment. * USGS HUC = US Geological Survey Hydrologic Unit Code. Calwater = State Water Resources Control Board hydrological subunit area or even smaller planning watershed. ** TMDL requirement status definitions for listed pollutants are: A= TMDL still required, B= being addressed by USEPA approved TMDL, C= being addressed by action other than a TMDL ***Dates relate to the TMDL requirement status, so a date for A= TMDL scheduled completion date, B= Date USEPA approved TMDL, and C= Completion date for action other than a TMDL 1 Bodega HU, Bay& 11522000 I • Invasive Species 810 Acres 2006 5A 2019 o Source Unknown Bodega Harbor HA Harbor 18010111 1 Bodega HU, Estero River & 11530000 I • Nutrients 38 Miles 1996 5A 2019 o Dairies Americano HA, Stream 18010111 Americano C_reek o Intensive Animal Feeding Operations o Manure Lagoons o Pasture Grazing-Riparian o Range Grazing-Riparian o Range Grazing-Upland The Bodega HU, Estero Americano HA, Americano Creek includes the following Calwater Super Planning Watersheds (SPWs): 115.30010 and 115.30011. A Water Quality Attainment Strategy is attempting to increase voluntary measures for attainment of standards & objectives, as was done in the Estero de San Antonia/Stemple Creek TMDL Water Quality Attainment Strategy, adopted by North Coast RWQCB in December 1997. 1 Bodega HU, Estero Estuary 11530012 I • Nutrients 199 Acres 1996 5A 2019 o Manure Lagoons Americano HA, 18010111 estuarv o Range Grazing-Riparian and/or Upland http://www.waterboards.ca.gov/water_issues/programs/tmdl/2010statejr_reports/category5_report.shtml 11430 317/2015 www.waterboards.ca.gov/water issueslprograms/tmdi/2010State. ir reports/category5 report.shtml 9 San Marcos Creek River & 90451000 I -1"\r"'\~ ·~ 19 Miles 2006 SA 2019 Stream 18070303 (DichlorQdiphen~ldichloroeth~lene) o Source Unknown • Phosphorus 19 Miles 2006 SA 2019 o Source Unknown o Unknown Nonpoint Source o Unknown Point Source o Urban Runoff/Storm Sewers • Sediment Toxicit~ 19 Miles 2006 SA 2019 o Unknown Nonpoint Source o Unknown Point Source o Urban Runoff/Storm Sewers • Selenium 19 Miles 2010 SA 2021 o Source Unknown 9 San Marcos Lake Lake & 904S2000 I • Ammonia as Nitrogen 17 Acres 2006 SA 2019 Reservoir 18070303 o Unknown Nonpoint Source o Unknown Point Source o Urban Runoff/Storm Sewers • Nutrients 17 Acres 2006 SA 2019 o Unknown Non point Source o Unknown Point Source o Urban Runoff/Storm Sewers 9 San Vicente Creek River & 90722000 I • Ammonia as NitrQgen (San Diego County) Stream 18070304 o Source Unknown 16 Miles 2010 SA 2021 • Benthic Communit~ Effects o Source Unknown 16 Miles 2010 SA 2021 • Total Nitrogen as N o Source Unknown 16 Miles 2010 SA 2021 http:/Jwww.waterboards.ca.gov/waterjssues/programsltmdl/2010state_ir_reports/category5_reJX)rt.shtml 418/430 APPENDIX A LOW IMPACT DEVELOPMENT AND HYDROMODIFICATION ANALYSES SUMMARY The SUSMP requires that drainage management areas (DMA) be delineated for various surface types. DMAs were determined for roofs, asphalt (driveways), pervious pavement on driveways, pedestrian pavement (sidewalks, walkways), stairs, and landscaping. These are shown on the DMA Exhibit in the map pocket. The attached spreadsheet summarizes the DMAs to each of the two bioretention basin areas and provides the standard and minimum bioretention surface area based on the flow-through planter sizing factors from the SUSMP. During final engineering, the County of San Diego's BMP Sizing Spreadsheet will be used for the final SWMP in order to also determine the required orifice sizing. For the current entitlement phase, only the surface area and volumes are determined in order to verify feasibility. The County of San Diego's Final HMP (see attached excerpt) states that the ponding layer and storage layer are converted to volumes "so that the project designer can flexibly configure the ponding layer and storage layer to meet site constraints." For instance, the standard bioretention basin design contains a 1 0-inch surface ponding layer over a 4-foot subsurface layer (1.5 feet of growing medium on 2.5 feet of gravel). The surface ponding (V1) and gravel (V2) depths can be increased over these typical values to meet the volume requirements in instances where the available surface area is less than the area, A. The sum of the design surface and subsurface storage volumes must meet or exceed the volumes on the attached spreadsheet. Furthermore, the surface area must be maintained greater than the minimum values in the spreadsheet to satisfy treatment control sizing. Since the project is a hillside development that is capable of supporting increased surface and subsurface depths, the intent is to minimize the bioretention basin surface areas. The attached results show that with the standard 10 inches of surface ponding, the surface area of the east and west bioretention basins should be 2,336 and 4,831 square feet respectively. This surface area can be reduced to as small as 4 percent of the total Area x Runoff Factor values and still meet treatment control requirements (see attached excerpts). The total Area x Runoff Factor values are 22,243 and 46,010 square feet, respectively, and 4 percent of these values are 890 and 1,840 square feet. For the east bioretention basin, Hofman is providing 900 square feet and for the west they are providing 1,874 square feet. In order to meet the VI requirement with the 900 and 1,874 square foot areas, the surface ponding depths must be increased from 10 inches to 2.16 feet and 2.15 feet, respectively, for the east and west basins. Similarly, in order to meet the V2 requirement, the gravel layer depths must be increased from the standard 2.5 feet to 4.89 and 4.87 feet, respectively. There is ample area for the east bioretention basin. However, the area at the west bioretention basin is limited. Increased pervious driveway pavement or a downstream channel assessment could be performed during final engineering to assist in reducing the bioretention basin size, if desired. CASCADA VERDE -BIORETENTION BASIN SIZING Parameters: 0.102, D Soil, Steep Slope, Oceanside Rain Gage, Flow-Through Planter Sizing Factors East Bioretention Basin (DMA 1) Runoff Area x Runoff Standard Required Required Min. Area Soil Type DMA Name Area, sf Factor Factor, sf A1, sf* V1, cf** V2, cf*** Needed, sf**** D Buildings 5,432 1.0 5,432 D Impervious Driveway I Parking 14,515 1.0 14,515 D Impervious Stairs 59 1.0 59 D Pervious Walkways 2,226 0.1 223 D Landscaping 20,143 0.1 2,014 Total 42,375 22,243 2,336 1,946 1,401 890 *Standard A 1 = 22,243 x 0.105 = 2,336 sf Area Provided 900 sf **Required V1 = 22,243 x 0.0875 = 1 ,946 cf V1 Provided 1,946 cf ***Required V2 = 22,243 x 0.0063 = 1 ,401 cf V2 Provided 1,401 cf ****Min. Area Needed= 22,243 x 0.040 = 890 sf West Bioretention Basin (DMA 2) Runoff Area x Runoff Required Required Required Min. Area Soil Type DMAName Area, sf Factor Factor, sf A1, sf* V1, cf** V2, cf*** Needed, sf**** D Buildings 21,200 1.0 21,200 D Impervious Driveway I Parking 19,475 1.0 19,475 D Impervious Sidewalk I Stairs 2,479 1.0 2,479 D Pervious Driveways/Walkways 10,313 0.1 1,031 D Landscaping 18,243 0.1 1,824 Total 71,710 46,010 4,831 4,026 2,899 1,840 Note: Minimum Area Needed represents minimum suface area for Treatment Control and is based on 4% of total Area x Runoff Factor *StandardA1 =46,010x0.105=4,831 sf Area Provided 1,874 sf **Required V1 = 46,010 x 0.0875 = 4.026 cf V1 Provided 3,967 cf ***Required V2 = 46,010 x 0.0063 = 2,899 cf V2 Provided 2,857 cf ****Min. Area Needed= 46,010 x 0.040 = 1,840 sf Section 7 Hydromodification Management Plan Table 7-4. Sizing Factors for Flow-Through Planters Lower Flow Soil Group Slope Rain Gauge A V1 v2 Threshold 0.302 0 Moderate Oceanside 0.090 0.0750 0.0540 0.302 0 Steep Oceanside 0.070 0.0583 0.0420 0.302 A Flat L Wohlford N/A N/A N/A 0.302 A Moderate L Wohlford N/A N/A N/A 0.302 A Steep L Wohlford N/A N/A N/A 0.302 B Flat L Wohlford N/A N/A N/A 0.302 B Moderate L Wohlford N/A N/A N/A 0.302 B Steep L Wohlford N/A N/A N/A 0.302 c Flat L Wohlford 0.085 0.0708 0.0510 0.302 c Moderate L Wohlford 0.085 0.0708 0.0510 0.302 c Steep L Wohlford 0.060 0.0500 0.0360 0.302 0 Flat L Wohlford 0.065 0.0542 0.0390 0.302 0 Moderate L Wohlford 0.065 0.0542 0.0390 0.302 0 Steep L Wohlford 0.050 0.0417 0.0300 0.102 A Flat Lindbergh N/A N/A N/A 0.102 A Moderate Lindbergh N/A N/A N/A 0.102 A Steep Lindbergh N/A N/A N/A 0.102 B Flat Lindbergh N/A N/A N/A 0.102 B Moderate Lindbergh N/A N/A N/A 0.102 B Steep Lindbergh N/A N/A N/A 0.102 c Flat Lindbergh 0.250 0.2083 0.1500 0.102 c Moderate Lindbergh 0.250 0.2083 0.1500 0.102 c Steep Lindbergh 0.185 0.1542 0.1110 0.102 0 Flat Lindbergh 0.200 0.1667 0.1200 0.102 0 Moderate Lindbergh 0.200 0.1667 0.1200 0.102 0 Steep Lindbergh 0.130 0.1083 0.0780 0.102 A Flat Oceanside N/A N/A N/A 0.102 A Moderate Oceanside N/A N/A N/A 0.102 A Steep Oceanside N/A N/A N/A 0.102 B Flat Oceanside N/A N/A N/A 0.102 B Moderate Oceanside N/A N/A N/A 0.102 B Steep Oceanside N/A N/A N/A 0.102 c Flat Oceanside 0.190 0.1583 0.1140 0.102 c Moderate Oceanside 0.190 0.1583 0.1140 0.102 c Steep Oceanside 0.140 0.1167 0.0840 0.102 0 Flat Oceanside 0.160 0.1333 0.0960 0.102 0 Moderate Oceanside 0.160 0.1333 0.0960 0.102 0 Steep Oceanside 0.105 0.0875 0.0630 0.102 A Flat L Wohlford N/A N/A N/A 7-13 Use of contents on this sheet is subject to the limitations specified at the end of this document. S:\Projects\San Diego County\ 133904-SDCo Hydromod Management Plan\WP\HMP\09Jinal HMP _Mar2011\104720_FINAL_San Diego HMP _Mar2011.docx J30 S'SO"N 33° 5'32"N Soil Map-San Diego County Area, California 476110 476170 476230 476290 476350 Map Scale: 1:2,670 if printed on A portrait (8.5'' X 11") sheet N o~----~3s~====~70-------------1~c===========~21~ A 0~----1~00====~200~----------400~===========~~ Map projection: Web Mercator Comerroordnates: WGS84 Edge lies: UTMZale 11NWGS84 USDA Natural Resources Web Soil Survey National Cooperative Soil Survey alii Conservation Service 476410 476470 12/5/2014 Page 1 of 3 i .~ ; ~ 5 u. :i ~ 1 1 . .8 ~ ! a. :i :1: i ~ .3 g. a e ~ .f t ~ ~ 0 5 10 Miles EXPLANATION --Precipitation Contours Lake \Nohlford Basin Lindbergh Basin Oceanside Basin Brown AND ~I E 7 ?? Rainfall Basin Map Page 60 of61 RAINFALL BASIN MAP SAN DIEGO HMP 1. Bioretention 2. Cistern with bioretention 3. Bioretention with flow control vault 4. flow-through planter 5. Dtywdl 6. Vegetated bioswale (for water quality treatment only) Non-structural strategies for stormwater management, such as pervious pavement, self-retaining areas, and self-treating areas will be described in separate memoranda. 4.1 Bioretention The bioretention facility consists of a surface ponding layer, a growing medium layer, and a bdow ground storage layer (Figure 6). The bioretention BMP captures water in the ponding layer, filters it through a growing medium that consists of soil and plant roots, percolates water from the growing medium into a storage layer, and then slowly discharges treated stormwater via exfilttation to surrounding native soils and regulated discharge through an underdrain pipe to the local stormwater drainage system. For applications with well-draining native soils (e.g., NRCS hydrologic group A orB soils), an underdrain pipe would not be included. For the HMP, we will simulate the bioretention BMP using separate a) ponding layer, b) growing medium, and c) storage layer components. We will assume the following depths for each layer: • • • Ponding layer: to-inches active storage, 2-inches of freeboard above overflow rdief Growing medium: 18-inches of soil at 40 percent porosity Storage layer: 30-inches of gravd at 40 percent porosity As described above in Section 3.1.2,the plan area of the BMP will be iterativdy sized until the BMP controls limit outflows to levels that are less than or equal to pre-project conditions across flow rates ranging from the lower flow control limit (O.lQ2, 0.3Q2 or O.SQ2) to the upper flow control limit (Q1o). The sizes of the ponding layer and storage layer will be converted into volumes, so that the project designer can flexibly configure the pending layer and storage layer to meet site constraints. For example, the design engineer could configure the pending layer with half the depth but twice the plan area called for by the sizing factor if this fits the project site. Additionally, the designer could use commercially-available storage vessds to meet the volume requirements instead of using gravel 12 S ECTION 4 : LID DESIGN GUIDE Bioretention Facilities Bioretencion facility configured for treatment-only requirements. Bioretencion facilities can rectangular, linear, or nearly any shape. Bioretention detains runoff in a surface reservoir, filters it through plant roots and a biologically active soil mix, and then infiltrates it into the ground. \.Vhere native soils are less permeable, an underdrain conveys treated runoff to storm drain or surface drainage. Bioretention facilities can be configured in nearly any shape. When configured as linear swales, they can convey high flows while percolating and treating lower flows. Bioretention facilities can be configured as in-ground or above- ground planter boxes, with the bottom open to allow infiltration to native soils underneath. If infiltration cannot be allowed, use the sizing factors and criteria for the Flow-Through Planter. ~ CRITERIA For development projects subject only to runoff treatment requirements, the following criteria apply: Parameter Soil mix depth Soil mix minimum percolation rate Soil mix surface area Criterion 18 inches minimum 5 inches per hour minimum sustained (1 0 inches per hour initial rate recommended) 0.04 times tributary im erv10us area or e uivalent) Best Uses • Commercial areas • Residential subdivisions • Industrial developments • Roadways • Parking lots • Fit in setbacks, medians, and other landscaped areas Advantages • Can be any shape • Low maintenance • Can be landscaped Limitations • Require 4% of tributary impervious square footage • Typically requires 3-4 feet of head • Irrigation typically required 85 City of Carlsbad SUSMP-January 14, 2011 I I I " \ \ .. .. 0 " ~ -_.:...-----" 0 ~ :.--=----_.J ______ '\ "''·~· \ ·, ' '•:, ~ ' \ ' \'' " ,. " '" ,, \ ,, ,, \ ,, \\ >£'9L ~LOl/ll/LO ··~.\ •<\ \ \\ \ '. •:\\~\ .... ,, 1\ ~ \ \ \ ' \ \~ \ \ ~ \\ \ ~ ,, '' ~ \ '\ \ ~ ~ e \ • ~ ,, 0 ~ ~ ~ II ' ~ '..:..-:_4 ..... .. 0 ..: ~~ ~a ~~ h · iS~~ ~§~ Iii~~ ~e~ ~~~ ~~ ~of~ ~i !i! ih "'o ~ ;t~;t 0 :z: '"'"'