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HomeMy WebLinkAboutCT 09-01; ROBERTSON RANCH PA 22; STORM WATER MANAGEMENT PLAN; 2010-01-21STORM WATER MANAGEMENT PLAN For ROBERTSON RANCH PA22 SWMP09-28 -ZC.T.09~~ b.p.x. U9= M.P. 02-03(B) P.U.D. 09-01 S.D.P. 09-01 z.c. 09-01 January 21,2010 IN: 081245-5 Prepared by: O'DA Y CONSULTANTS, iNc. 2710 Loker Avenue West, Suite 100 Carlsbad, California 92010-6609 Tel: (760) 931-7700 Fax: (760) 931-8680 RCE 32014 Exp. 12/31/10 ( • • • STORM WATER MANAGEMENT PLAN For ROBERTSON RANCH PA22 SWMP09-28 C.T.09-01 G.P.A. 09-01 M.P. 02-03 (B) P.U.D. 09-01 S.D.P. 09-01 Z.C.09-01 January 21,2010 IN: 081245-5 Prepared by: O'DA Y CONSULTANTS, INC. 2710 Loker Avenue West, Suite 100 Carlsbad, California 92010-6609 Tel: (760) 931-7700 Fax: (760) 931-8680 •• • • STORM WATER MANAGEMENT PLAN ROBERTSON RANCH PA 22 TABLE OF CONTENTS Section 1.0 Vicinity Map Section 2.0 Project Description • NalTative of Project Activities • Introduction of Storm Water Pollution Prevention· Section 3.0 Site MaplBMP Exhibit Section 4.0 Pollutants and Conditions of Concern Pollutants of Concern • Name and Number of Carlsbad Watershed Hydrological Unit Impaired Water Bodies Downstream of the Project and Impairm~nt • San Diego Region Hydrological Units, Areas, and Subareas (Fig. 1-2) • 2006 CW A Section 303 (d) List of Water Quality Limited Segments • Storm Water Requirements Applicability Checklist (Appendix A) • Construction Site Priority (Part D) • Standard Development Project & Priority Project Storm Water BMP Requirements Matrix (Table 1) Conditions of Concern Section 5.0 Site Design BMPs Section 6.0 Source Control BMPs Fact & Maintenance Requirement Sheets for: • City of Carlsbad OS-16: Refuse Bin Enclosures • CASQA SD-lO: Site Design and Landscape Planning • CASQA SD-11: Roof Runoff Controls • • • STORM WATER MANAGEMENT PLAN ROBERTSON RANCH PA 22 TABLE OF CONTENTS (CONTINUED) • CASQA SD-12: Efficient Irrigation • CASQA SD-13: Storm Drain Stenciling • CASQA SD-32: Trash Enclosures Section 7.0 Structural Treatment BMPs • Anticipated and Potential Pollutants Generated by Land Use Type (Table 2) • Numeric Sizing Treatment Standards (Table 3) • Structural Treatment Control BMP Selection Matrix (Table 4) • Fact Sheets for BMPs including Inspection, Maintenance, Costs and Training for: • CASQA TC-30: Vegetated Swale • CASQA MP-52: Drain Inserts • CASQA TC-60: Multiple System Fact Sheet • CASQA SD-20: Pervious Pavements • CASQA TC-32: Bioretention • Section 6: Long-term Maintenance of BMPs Section 8.0 Post Construction BMPs Maintenance Co~t Responsibilities Section 9.0 Drainage Study for Robertson Ranch PA 22 STORM WATER MANAGEMENT PLAN ROBERTSON RANCH PA 22 Ie SECTION 1.0: VICINITY MAP • CITY OF OCEANSIDE NOT TO SCALE PACIFIC 78 CITY VICINITY MAP NO SCALE STORM WATER MANAGEMENT PLAN ROBERTSON RANCH P.A. 22 • Section 2.0 • • Project Description Federal, state and local agencies have established goals and objectives for storm water quality in the region. The proposed project is a priority project as defined in Order No. 2007-01 by the San Diego Region of the California Water Quality Control Board. As a result, the project is subject to SUSMP requirements. In addition, prior to the start of construction activities, the project will comply with all federal, state and local permits including the Stormwater Management Plan (SWMP) required under the County of San Diego Watershed Protection, Stormwater Management, and Discharge Control Ordinance (WPO) (section 67.871), the City of Carlsbad's Standard Urban Storm Water Mitigation Plan, and the National Pollution Discharge Elimination System (NPDES) from the Regional Water Quality Control Board (RWQCB). The purpose of this SWMP is to address the water quality impacts from the proposed improvements as shown on the Grading Plan. This report will provide guidelines in developing and implementing post construction Best Management Practices (BMPs) for storm water qUality. Planning Area 22 (P A 22), located south of Cannon Road, will contain approximately 0.5 acres of RV storage. The SWMP for the entire Robertson Ranch East Village project includes the PA 22 site for the temporary RV parking. This SWMP details the BMP's specific for this Grading Plan. See Section 9.0 for the Hydrology Study and Section 10.0 , for Storm Water Management Plan Exhibit. In the 2006 CW A Section 303( d) List of Water Quality Limited Segments, Agu~ Hendionda Creek as an impaired water body. Portions of Carlsbad where construction sites have the potential to discharge into a tributary of a 303(d) or directly into a 303(d) water body or sites located within 200 feet of an ESA require additional BMP implementation . -1 - STORM WATER MANAGEMENT PLAN ROBERTSON RANCH P.A. 22 Section 4.0 Pollutants of Concern The project is located in the Los Monos Hydrologic Subarea (904.31) of the Agua Hedionda Watershed in the Carlsbad Hydrologic Unit in the San Diego Region. The stormwater runoff from the site enters the public storm drain, discharges into Agua Hedioda Creek and ultimately drains into Agua Hedionda Lagoon. In the 2006 CW A Section 303( d) List of Water Quality Limited Segments, Agua Hendionda Creek as an impaired water body. This watershed is tagged by the San Diego Regional Water Quality Control Board as receiving storm water runoff with high levels of manganese, selenium, sulfates, total dissolved solids, indicator bacteria and sediment/siltation. See the attached Hydrologic Unit Map and List. Portions of Carlsbad where construction sites have the potential to discharge into a tributary of a 303(d) or directly into a 303(d) water body or sites located within 200 feet • of an ESA require additional BMP implementation. " Storm Water Requirements Applicability Checklist As part of the submittal for an application for a grading and improvement permit, the Stormwater Standards Questionnaire in Appendix A of the City of Carlsbad Standard " Urban Storm Water Mitigation Plan (SUSMP), revised June 4, 2008, must be completed. The purpose of this checklist is to confirm/determine the priority of the proposed development based on several factors, including the type of on-site development proposed and the total area and location of such development. Once the priority of the project is determined, Table Nos. 1 and 2 of the City SUSMP" must be completed in order to select which BMP's are to be considered and which pollutants are anticipated and which have the potential to be generated on site due to the future and continued use of the developed project. -1 - STORM WATER MANAGEMENT PLAN ROBERTSON RANCH P.A. 22 !e Conditions of Concern • In order to determine if the project proposed drainage patterns will affect the downstream conditions, a copy of the project's Drainage Study is included in Section 9.0. This report is titled "Drainage Study for Robertson Ranch P A 22" by O'Day Consultants, Inc~ dated November 5,2009. Based on the findings in this drainage study, the onsite water will be treated per this report . -2- ", . ',,' :: .. :!',:.:': . c. ,'16 . _-=:;=I_ .... _MI~~s o 4 8 ..... 1:760,000. .. . Derived fram en edledvetsion af Calwater2.2f to camplywithth& 1994 BasIn Plan Map crealed Oelaber2004 SlataWaferResautcesControlBaaid . :.'" '.:" .--,.-ot"'--""" : - . i.SED 2006 CWA SECTION 303(d) LIST \,.... ~.~ QUALITY LIMITED SEGl\'IENTS SAN DIEGO REGIONAL BOARD • SWRCB APPROVAL DATE: OCTOBER 25, 1006 (iKON TVPE NAME !)l R Agu HecIioIIda Creek §) iE /\gUll Hcdivuu La&ooa ;;, ~ Aliso Creek CALWATU WATERSHED 9143UMII !HI43UMMI !I01131M1O POU.VTANT/STBESSOR M-IIPRC'C SeleaiIUD Sulfate5 Toal DiIIoIved Solids lJulieator baderia Sedimep'atioalSiUatiH POT&NTIAL SOIlRCES SoIIn:c lJlIkIloWII Source lJDkaoWll Source lJlIkaowa lJrbu RIuIoffJStel'lll Sewen lJDIIatnq NCNIpOiDt Source lJDIIatnq peiIIt 10_ NoapeiatIPajat Source NupoiII&IPtWd Souce ESTIMATED SIZE AFFECTED ·7 Miles 7 Miles 7 Miles 7 Miles ,oS Ael"a 6.8 AereJ PROPOSED TMDL COMPLETION 2019 2019 2019 2019 201Ki 2019 Iadicator IIactcria 19 Miles 200S TlU6lJ#mcfor indit:tuw ~ IIpplies 10 the JUUg Cnld;mmiJStem and all the lIIIIjor rriblltilries of Aliso Creek which lITe Sv{pIucr ~ Wood Ca)'DII. &Yo KIllI ~ DIIi1y Forlr. Il1III English Omyon. U ..... lluMIIISc8naSewen U ...... ,.mt .. _ NOIIpOiatIPoiat~ PIIoipiIenI5 19 Miles 2019 TIds lUIbtgfor plw6phonu IIpplitts 10 theAliso Owk IfIIliMIem IUIIIIlU the _lor rriblllt.lries of Aliso Creek which Ilre SvJp/uIr end; Wood CaIt)'lNl, AliIIo Hilb ~ DIlUy Fork. IUIII English Omyoll. PageltJ/27 U .... JIiuIeIfIStong $ewers Uakaowa NIIIIPOiat8Hn:e U __ wa~ .. urce . ~ • APPENDIX :& STORM WATER STANDARDS QUESTIONNAIRE; I INSTRUCTIONS: This questionnaire must be completed by the applicant in advance of submitting for a development application (subdivision and land use planning approvals and construction permits). The results of the questionnaire determihe the level of storm water pollution prevention standards applied to a proposed development or redevelopment project. Many aspects of project site design are dependent upon the storm water pollution protection standards applied to a project. Applicant responses to the questionnaire represent an initial assessment of the proposed projeet conditions and impacts. City staff has responsibility for making the final assessment after submission of the development application. A staff determination that the development application is subject to more stringent storm water standards, than initially assessed by the applicant, will result in the return of the development application as incomplete. If applicants are unsure about the meaning of a question or need help in determining how to respond to one or more of the questions, they are advised to seek assistance from Engineering Department Development Services staff. -'-,- A separate completed and signed questionnaire must be submitted for each new development application submission. Only one completed and signed questionnaire is required when multiple development applications for the same project are submitted concurrently. In addition to this questionnaire, applicants for construction permits must also complete, sign and submit a Construction Activity Storm Water Standards Questionnaire . To address pollutants that may be generated from new development, the City requires that new development and significant redevelopment priority projects incorporate Permanent Storm Water Best Management Practices (BMPs) into the project design, which are described in Chapter 2 of the City's Storm Water Standards Manual This questionnaire should be used to categorize new development and significant redevelopment projects as priority or non-priority, to determine what level of storm water standards are required or if the project is exempt. I 1. Is your project a significant redevelopment? Definition: I Significant redevelopment is defined as the creation, addition or replacement of at least 5,000 square feet of impervious surface on an a/ready existing developed site. Significant redevelopment includes, but is not limited to: the expansion of a building footprint; addition to or replacement of a structure; structural development including an increase in gross floor area and/or exterior construction remodeling; replacement of an impervious surface that is not part of a routine maintenance activity; - and land disturbing activities related with structural or impervious surfaces. Replacement of impervious surfaces includes any activity that is not part of a routine maintenance activity where impervioUs material(s) are removed, exposing underlying soil during construction. Note: If the Significant Redevelopment results in an increase of less than fifty percent of the impervious surfaces of a previously existing development, and the existing development was not subject to SUSMP requirements, the numeric sizing criteria discussed in Table 3 of 2.3.3.4 applies only to the addition, and not to the entire development. 2. If your project IS considered significant redevelopment, then please skip Section 1 and proceed with Section 2. (. 3. If your project IS NOT considered significant redevelopment, then please proceed to Section 1. --. .. 21 SWMP Rev 6/4/08 ~. • I SECTION 1 NEW DEVELOPMENT PRIORITY PROJECT TYPE YES NO Does you project meet one or more of the following criteria: ·1. Home subdivision of 100 units or more. V Includes SFD, MFD, Condominium and Apartments 2. Residential develo12ment of 10 units or more. I/" Includes SFD, MFD, Condominium and Apartments 3. Commercial and industrial devel012.ment greater than 100,000 square feet including 12arking areas; Any development on private land that is not for heavy industrial or residential uses. Example: Hospitals, v' Hotels, Recreational Facilities, Shopping Malls, etc. 4. Heavv Industrial/Industry greater than 1 acre (NEED SIC CODES FOR PERMIT BUSINESS TYPES) V SIC codes 5013,5014,5541,7532-7534, and 7536-7539 5. Automotive re12.air sh012.. V SIC codes 5013,5014,5541, 7532-7534, and 7536-7539 6. A New Restaurant where the land area of devel012.ment is 5,000 square feet or more including l2arking V ~ SIC code 5812 ' .... - 7. Hillside devel012.ment V (1) greater than 5,000 square feet of impervious surface area and (2) development will grade on any natural slope that is 25% or greater 8. Environmentallv Sensitive Area (ESA). V' Impervious surface of 2,500 square feet or more located within, "directly adjacent,,2 to (within 200 feet), or "discharging directly to,,3 receiving water within the ESA 1 9. Parking lot. .,/ Area of 5,000 square feet or more, or with 15 or more parking spaces, and potentially exposed to urban runoff 10. Retail Gasoline Outlets -serving more than 100 vehicles 12.er da'i / Serving more than 100 vehicles per day and greater than 5,000 square feet 11. Streets, roads, drivewa't.s, high wa 't.s, and freewa't.s. ,. V Project would create a new paved surface that is 5,000 square feet or greater. 12. Coastal Development Zone. V Within 200 feet of the Pacific Ocean and (1) creates more than 2500 square feet of impermeable surface or (2) increases impermeable surface on property by more than 10%. . 1 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 Efiological Significance by the State Water Resources Control Board (Water Quality Control Plan for the San Diego Basin (1994) and C'lmendments); 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) ;;Ind amendments); - areas designated as preserves or their equivalent under the Multi Species Conservation Program within the Cities and count of San Diego; and any other equivalent environmentally sensitive areas which have been identified 'by the Copermittees. 2 "Directly adjacent" means situated within 200 feet of the environmentally sensitive area. 3 "Discharging directly to" means outflow from a drainage conveyance system that is composed entirely of flows from the subject development or redevelopment site, and not commingled with flow from adjacent lands. Section 1 Results: If you answered YES to ANY of the questions above you have a PRIORITY project and PRIORITY project requirements DO apply. A Storm Water Management Plan, prepared in accordance with City Storm Water Standards, must be submitted at time of application. Please check the "MEETS PRIORITY REQUIREMENTS" box in Section 3. If you answered NO to ALL of the questions above, then you are a NON·PRIORITY project and STANDARD requirements apply. Please check the "DOES NOT MEET PRIORITY Requirements" box in Section 3. SWMP Rev (i/4/08 I SECTION 2 SIGNIFICANT REDEVELOPMENT: YES NO 1. Is the project redeveloping an existing priority project type? (Priority projects are defined in Section 1) If you answered YES, please proceed to question 2. If you answered NO, then you ARE NOT a significant redevelopment _ and you ARE NOT subject to PRIORITY project requirements, only STANDARD requirements. Please check the "DOES NOT MEET PRIORITY Requirements" box in Section 3 below. 2. Is the project solely limited to one of the following: a. Trenching and resurfacing associated with utility work? b. Resurfacing and reconfiguring existing surface parking lots? c. New sidewalk construction, pedestrian ramps, or bike lane on public and/or private existing roads? d. Replacement of existinj:J damaged pavement? If you answered NO to ALL of the questions, then proceed to Question 3. If you answered YES to ONE OR MORE of the questions then you ARE NOT ~ significant redevelopment and you ARE NOT subject to PRIORITY project requirements, only STANDARD requirements. Please check the "DOES NOT MEET PRIORITY Requirements" box in Section 3 below. 3. Will the development create, replace, or add at least 5,000 square feet of impervious surfaces on an existing development or, be located within 200 feet of the Pacific Ocean and (1 )create more than 2500 square feet of impermeable surface or (2) increases impermeable surface on property by more than 10%? If you answered YES, you ARE a significant redevelopment, and you ARE subject to PRIORITY project requirements. Please check the "MEETS PRIORITY REQUIREMENTS" box in Section 3 below. If you answered NO, you ARE NOT a significant redevelopment, and you ARE-NOT subject to PRIORITY project requirements, only STANDARD requirements. Please check the "DOES NOT MEET PRIORITY Requirements" box in Section 3 below. I SECTION 3 Questionnaire Results: o Address: MY PROJECT MEETS PRIORITY REQUIREMENTS, MUST COMPLY WITH PRIORITY PROJECT STANDARDS AND MUST PREPARE A STORM WATER MANAGEMENT PLAN FOR SUBMITTAL AT TIME OF APPLICATION. MY PROJECT DOES NOT MEET PRIORITY REQUIREMENTS AND MUST ONLY COMPLY WITH STANDARD STORM WATER REQUIREMENTS. Applicant InfOImation and Signature Box This 80x for CitY' Use Dilly Assessors Parcel Numbcr(s): City Concurrence: I YES INO 68-050-5$ I I Applicant Title: By: Dale: Applicant Signature: Date: ProjocllD: SWMP Rev 6/4/08 • . STORM WATER MANAGEMENT PLAN ROBERTSON RANCH, PA 22 APPENDIX C: CITY OF CARLSBAD STANDARDS EXCERPTS Table 1: Standard Development Project & Priority Project Storm Water BMP Requirements Matrix BMPs A .,~, ,LI., to T • ..1: .. :..1 •• 1 -cr •• _. ---- ~ • W, <OJ Proiect n (3) ...... '" <!) c3 ] o'/l '" '" '" '" ~ '" ~ '" bO E: '" '" gp ~ .S .~ ~ ~ -5i 'fJl g. '" bO /XI ~ <!) I': u '" 0 .<:: u ;J;! ] '" ~ 8 '" J: "0 '" ~ ~ j ~ «l '" j i './:I ~ ~ !! I': <!) <!) <!) <!) 0 j 'tl g ~ Site Source '" :;abO 11 .~ .S< "E Treatment ;> :a a ~~ $ := <!) ~ 0 Design Control ;E .1a 0 ::?J ~ 0 tI.l ~ Cqntrol BMPs(l) BMPs(2) .; ..oP-. <> --d cU .... bh ..c:l .~ :...; BM]>s(4) ~ ... ..I. L'd Pi.ujt:\:uo R R 0 0 0 0 0 0 0 0 0 0 0 -n.' ,', -n -" LAVAUY .L Detached Residential -R R R R R S Dl-v. .1, Attached Residential R R R S n",,,·1 Commercial Development R R R R R R S > I.QQ,OOO ft2 A. .<, ,ve Repair R R R R R R R S R R R R S Hillside Development R R R R S <5, 000 ft2 Pru-king LQts -~ _R 1~J5L S Streets, Highways, & R R S ~ .• "'''' ,0.:1" R = Required; select one or more applicable and appropriate BMPs from the applicable steps in Section III.2.a-d, or equivalent as identified in Appendix C. o = Optional or may be required by City Staff. As appropriate, applicants are encouraged to incorporate treatment control BMPs and BMPs applicable to individual priority project categories into the project design. City staff may require one or more of these BMPs, where applicable. S = Select one or more applicable and appropriate treatment control BMPs from Appendix C. (1) Refer to Section III.2.A. (2) (3) (4) (5) Refer to Section III.2.B. Priority Project categories must apply specific storm water BMP requirements, where applicable. Priority projects are subject to the requirements 0f all priority project categories that apply. Refer to Section III.2.D. Applies if the paved area totals >5,000 square feet or with >15 parkign spaces and is.potentially exposed to urban run-off. Source: City of Carlsbad Public Works Department Standard Urban Storm Water Mitigation Plan Storm Water Standards (2008, page 6) Ie STORM WATER MANAGEMENT PLAN ROBERTSON RANCH, P.A. 22 Section 5.0 SITE DESIGN BMPS (LOW IMPACT DEVELOPMENT) Site Design BMPs are comprised of the following BMPS: • Maintain Pre-Development Rainfall Runoff Characteristics o Minimize Impervious Footprint o Conserve Natural Areas (Open Space, Lot 4) o Minimize Directly Connected Impervious Areas o Maximize Canopy Interception and Water Conservation Consistent with the Carlsbad Landscape Manual • Protect Slopes and Channels o Convey Runoff Safely From Tops of Slopes o Vegetate Slopes with Natural or Drought Tolerant Vegetation o Stabilize Permanent Channel Crossings o Install Energy Dissipaters 1. MAINTAIN PRE-DEVELOPMENT RAINFALL RUNOFF CHARACTERISTICS This Site Design BMP entails controlling post construction peak storm water discharge at the rate and velocities of the pre-developed condition. 2. MINIMIZE IMPERVIOUS FOOTPRINT This Site Design BMP and L.l.D. requirement entails minimizing the proposed site impervious footprint through increasing ~uilding densities, utilizing pervious construction materials on walkways, driveways, trails, patios, overflow parking areas, alleys ,and low traffic areas. Examples of materials that can be used are pervious concrete, porous asphalt, unit pavers, and granular materials. In addition, streets, sidewalks, and parking lot aisles can be designed to minimum widths, provided pedestrian safety is not compromised. And lastly, this can be accomplished through the minimization of use of impervious surfaces, such as decorative concrete in landscape design. The proposed design of the project will attempt to utilize this Site Design BMP by minimizing the impervious footprint to the maximum extent practicable. 3. CONSERVE NATURAL AREAS (OPEN SPACE, LOT 4) This Site Design BMP entails concentrating or clustering development on the least environmentally sensitive portions of a site while leaving the remaining land in a natural, undisturbed condition and incorporates the use of natural drainage systems to the maximum extent practicable 4. MINIMIZE DIRECTLY CONNECTED IMPERVIOUS AREAS This Site Design BMP entails minimizing directly connect impervious areas where landscaping is proposed and attempt to direct runoff from -1 - STORM WATER MANAGEMENT PLAN ROBERTSON RANCH, P.A. 22 impervious surfaces such as sidewalks, parking lots, walkways, and patios to landscaping areas. 5. MAXIMIZE CANOPY INTERCEPTION AND WATER CONSERVATION CONSISTENT WITH THE CARLSBAD LANDSCAPE MANUAL This Site Design BMP entails maximizing canopy interception and water conservation consistent with the Carlsbad Landscape Manual to preserve existing native trees and shrubs, to plant additional native or drought tolerant trees, and to plant large shrubs in place of non-drought tolerant exotic species. The project will utilize this Site Design BMP by haying the landscaping designer utilize the applicable City of Carlsbad Landscape Manual and any other applicable City of Carlsbad Standards. . 6. CONVEY RUNOFF SAFELY FROM TOPS OF SLOPES This Site Design BMP entails conveying runoff safely from the tops of slopes and in channels. The project will utilize this Site Design BMP as much as possible. There are tops and bottoms of slopes on the project. site. Each top and bottom of slope will be designed so that runoff will safely be conveyed away from them. . 7. VEGETATE SLOPES WITH NATURAL OR DROUGHT TOLERANT VEGETATION This Site Design BMP entails the vegetation of slopes with native or drought tolerant vegetation where practically consistent with the Carlsbad Landscape Manual. The project will utilize this Site Design BMP by having the landscaping designer utilize the applicable City of Carlsbad Landscape Manual and any other applicable City of Carlsbad Standards. 8. STABILIZE PERMANENT CHANNEL CROSSINGS This site Design BMP entails the stabilization of permanent channel crossings. This Site Design BMP will not be applicable to the project due to no permanent channel crossing being present on the existing or proposed site designs. 9. INSTALL ENERGY DISSIPATERS This Site Design BMP entails installing energy dissipaters at the outlets of new storm drains, culverts, conduits, or channels that enter unlined channels. This is to be done in accordance with the applicable standards and specifications to minimize erosion. Energy dissipaters shall be installed in such a fashion as to minimize impacts to the receiving waters. The project will utilize this Site Design BMP as needed to protect the proposed and existing storm drain inlets, culverts, conduits, and channels. -2- STORM WATER MANAGEMENT PLAN ROBERTSON RANCH P.A. 22 • Section 6.0 SOURCECONTROLBMWS .- Source Control BMPs are comprised of the following BMPS: • Design Outdoor Material Storage Areas to Reduce Pollution Introduction • Design Trash Storage Areas to Reduce Pollution Introduction • Use Efficient Irrigation Systems and Landscape Design • Provide Storm Water Conveyance System Stenciling and Signage 1. DESIGN OUTDOOR MATERIAL STORAGE AREAS TO REDUCE POLLUTION INTRODUCTION This Source Control BMP entails placing any and all potentially hazardous materials that have a potential to contaminate urban runoff in storage areas on site that are enclosed in structures such as, but not limited to, cabinets, sheds, or other similar structures that prevent and contain with rain, runoff, or spillage. In addition, secondary structures such as berms, dikes, or curbs will be utilized out side of the storage structure to further prevent contamination. The storage areas shall be paved with a sufficiently impervious material to contain leaks and spills, and shall have a roof or awning to minimize direct contact with precipitation within the secondary containment area. Because the project does not proposed any material storage areas this Source Control BMP will not be utilized. 2. DESIGN TRASH STORAGE AREAS TO REDUCE POLLUTION INTRODUCTION This Source Control BMP entails designing trash storage areas to reduce pollution introduction. Trash Storage Areas shall be paved with an impervious surface, designed not to allow runoff from adjoining areas, screened or walled to prevent off-site transportation of tra~h, and contain attached lids on all trash containers that protects them from precipitation. Alternatively, the trash enclosure can contain a roof or awning to minimize direct contact with precipitation. The project will utilize this Source Control-BMP by designing and building the tra~h storage areas according to the City of Carlsbad Standard Drawing GS-16 and in accordance with CASQA SD-32: Trash Enclosures. These areas will be paved with an impervious surface, graded to drain away from the enclosure, and screened and walled to prevent off-site transport of trash. Trash containers will contain attached lids that exclude rain to minimize direct precipitation. A copy of each of these is provided in Appendix G. 3. USE EFFICIENT IRRIGATION SYSTEMS AND LANDSCAPE DESIGN -1 - STORM WATER MANAGEMENT PLAN ROBERTSON RANCH P.A. 22 This Source Control BMP entails employing rain shutoff devices to prevent irrigation during precipitation and this requires all landscaping aspects to be designed per the Carlsbad Landscape Manual. The proj ect will utilize this Source Control BMP by having the landscaping designer utilize the applicable City of Carlsbad Landscape Manual and any other applicable City of Carlsbad Standards. In addition, site irrigation will also be designed in accordance with CASQA SD-IO: Site Design and Landscape Planning. A copy of this has been provided in Appendix G. 4. PROVIDE STORM WATER CONVEYANCE SYSTEM STENCILING AND SIGNAGE This Source Control BMP entails providing storm drain conveyance system stenciling and signage. This shall be done by providing concrete stamping, porcelain tile, insert permanent marking or approved equivalent as approved by the City of Carlsbad, of all storm drain conveyance system inlets and catch basins within the project area with prohibitive language (i.e. "No Dumping - I Live Downstream') satisfactory to the City Engineer. In addition, signs shall be posted and prohibitive language and/or graphical icons, which prohibit illegal dumping at public access points along channels and creeks within the project area, trailheads, and parks shall be used. The project will utilize this Source Control BMP by utilizing CASQA SD-13: Storm Drain Stenciling. A copy of this is provided in Appendix G. -2- • • Site Design & Landscape Planning 5D-10 Description De~ign Objectives ~ Maximize Infiltration ~ Provide Retention ~ Slow Runoff o Minimize Impervious Land Coverage Prohibit Dumping of Improper Materials Contain Pollutants . Calfeet and Convey Each project site possesses unique topographic, hydrologic, and vegetative features, some of which are more suitable for development than others. Integrating and ilicorporating appl'opliate landscape planning methodologies into the project design is the most effective action that can be done to minimize sUlface and groundwater contamination from stormwater. Approach Landscape planning should couple consideration ofland suitabili1;yfor urban uses with consideration of communi1;y goals and projected growth. Project plan designs should conserve natural areas to the extent possible, maximize natural water storage and infiltration opportunities) and protect slopes and channels. Suitable Applications Appl'Opliate applications include residential, commercial and indushial areas planned for development or redevelopment. Design Considerations Design requirements for site design and laudscapes planning should conform to applicable standards and specifications of agencies with jurisdiction and be consistent with applicable General Plan and Local Area Plan policies . January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com ('ALlrotlNIAsrlJlt',l'NA H:t< Q~? t~}:n"'\-h<;4~(.""":·1 1'>.1 h>':\:. 10f4 SD-l0 Site Design & Landscape Planning' '."1_ #¥'#WMiw".!. W • Designing New Installations • • Begin the development of a plan for the landscape unit with attention to tbe fonowing general principles: • Formulate the plan on the basis of clearly articulated community goals. Carefully identify conflicts and choices between retaining and protecting desired resources and community growth. • Map and assess land suitability for urban uses. Include the following landscape features in the assessment: wooded land, open unwooded land, steep slopes, erosion-pi'one soils, foundation suitability, soil suitability for waste disposal, aquifers, aquifer recharge areas, wetlands, floodplains, surface waters, agricultural lands, and various categories of urban land use. When appropriate, the assessment can highlight outstanding local or regional resources that the community determines should be protected (e.g., a scenic are~ recreational area, threatened species habitat, farmland, fish run). Mapping and assessment should recognize not only these resources but also additional areas needed for their sustenance. Project plan designs should conserve natural areas to the extent possible, maximize natural water storage and infiltration opportunities, and protect slopes and channels. Conserve Natural Areas during Landscape Planning If applicable, the following items are required and must be implemented in the site layout during the subdivision design and approval process, consistent with applicable General Plan and Local Area Plan policies: • Cluster development on least-sensitive portions of a site while leaving the remaining land in a natural undisturbed condition. • Limit clearing and grading of native vegetation at a site to the minimum amount needed to build lots~ allow access, and provide fire protection. • Maximize trees and other vegetation at each site by planting additional vegetation, clustering tree areas, and promoting the use of native and/or drought tolerant plants. • Promote natural vegetation by using parking lot islands and other landscaped areas. • Preserve riparian areas and wetlands. Maximize Natural Water Storage and Infiltration Opportunities Within the Landscape Unit • Promote the conservation of forest cover. Building on land that is already deforested affects basin hydrology to a lesser extent than converting forested land. Loss of forest cover reduces interception storage, detention in the organic forest floor layer, and water losses by evapotranspiration, resultingjnlarge peak l'UllOffincreases and either their negative effects or the expense of countering them with structural solutions. • Maintain natural storage reservoirs and drainage corridors, including depressions, areas of permeable soils, swales, and intermittent streams. Develop and implement policies and 2of4 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com JanuarY ~003 Site Design &. Landscape Planning 5D-l0 AHA p a-M+g: Me regulations to discourage the clearing; filling, and channelization of these features. Utilize them in drainage networks ill preference to pipes, culverts, and engineered ditches. • Evaluating infiltration opportunities by referring to the stormwater management manual for the jurisdiction and pay particular attention to the selection criteria for avoiding groundwater contamination, poor soils, and hydrogeological conditions that cause these facilities to fail. If necessary, locate developments with large amounts of impervious surfaces or a potential to produce relatively contaminated runoff away from groundwater recharge areas. Protection of Slopes and Channels during Landscape Design • Convey runoff safely from the tops of slopes. • Avoid disturbing steep or unstable slopes. • Avoid disturbing natural channels. • Stabilize disturbed slopes as quickly as possible. • Vegetate slopes with native or drought tolerant vegetation. • Control and treat flows in landscaping and/or other controls prior to l'eachirig existing natural drainage systems. • Stabilize temporary and permanent channel crossings as quickly as possible, and ensure that increases in run-off velocity and frequency caused by the project do not erode the channel. • Install energy dissipaters, such as riprap, at the outlets of new st01111 drains, culvelts, conduits, or channels that enter unlined channels in accordance with applicable specifications to minimize erosion. Energy dissipaters shall be installed in such a way as to minimize impacts to receiving waters. • Line on-site conveyance channels where appropriate, to reduce erosion caused by increased flow velocity due to increases in tributary impervious area. The first choice for linings should be grass or some other vegetative surface, since these materials not only reduce runoff velocities, but also provide water quality benefits from filtration and infiltration. If velocities in the channel are high enough to erode grass or other vegetative linings, riprap, concrete~ soil cement, Ol' geo-grid stabilization are other alternatives. • Consider other design principles that are comparable and equally effective. Redeveloping Existing Installations Various jurisdictional st0l111water management and mitigation plans (SUSMP, WQM;P, etc.) define "redevelopment" in terms of amounts of additional impervious area, increases in gross floor area and/or exterior construction, and land disturbing activities with structural or impervious surfaces. The definition of" redevelopment" must be consulted to detennine whether or not the requirements for new development apply to areas intended fOl' redevelopment. If the definition applies, the steps outlined under "designing new installations" above should be followed. January 2003 California stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 30f4 SD-I0 Site Design &. Landscape. Planning ce Redevelopment may present significant opportunity to add features which had not previously been implemented. Examples include incorporation of depressions, areas of permeable soils, and swales in newly redeveloped areas. While some site constraints may exist due to the status of ah-eady existing infrastructure, opportunities should not be missed to maximize infiltration, slow runoff, reduce impervious areas, discOlmect directly cOlmected impervious areas. Other Resources A Manual for the Standard Urban Stormwater IVIitigation Plan (SUSMP), Los Angeles Coun,ty Department ofPubIic Works, May 2002. Storm water Management Manual for Western Washington, Washington State Department of Ecology) August 2001. Model Standard Urban Storm Water Mitigation Plan (SUSMP) for San Diego County, Port of San Diego, and Cities in San Diego County, February 14, 2002. Model Water Quality Management Plan (WQMP) for County of Orange, Orange County Flood Control District, and the Incorporated Cities of Orange County, Dl'aft February 2003. Ventura Countywide Technical Guidance Manual for Stormwater Quality Control Measures, July 2002. 4of4 California stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com ]clOuary .2003 • • • Roof Runoff Controls Rain Garden Description Various roof runoff controls are available to address stormwater 50-11 Design Objectives ,f Maximize Infiltration ,f Provide Retention ,f Slow Runoff Minimize Impervious Land Coverage Prohibit Dumping of Improper Materials ,f Contain Pollutants Collectand Convey that drains off rooftops. The objective is to reduce the total volume and ra~e of runoff from individual lots, and retain the pollutants on site that may be picked up from roofing materials and atmospheric deposition. Roof runoff controls consist of directing the roof runoff away from paved areas and mitigating flow to the storm drain system through one of several general approaches: cisterns or rain barrels; drywells or infiltration trenches; pop-up emitters, and foundation planting. The first three approaches require the roof runoff to be contained in a gutter and downspout system. Foundation planting provides a vegetated strip under"the drip line of the roof. Approach Design of individual lots for single-family homes as well as lots for higher density re~idential and commercial structures should consider site design provisions for containing and infiltrating roof runoff or directing roof runoff to vegetative sw:ales or buffer areas. Retained water can be reused for watering gardens, lawns, and trees. Benefits to the environment include reduced demand for potable water used for irrigation, improved stormwater quality, increased groundwater recharge, decreased runoff volume and peak flows, and decreased flooding potential. Suitable Applications Appropriate applications include residential, commercial and industrial areas planned for development or redevelopment. Design Considerations Designing New Installations Cisterns or Rain Barrels One method of addressing roof runoff is to direct roof downspouts to cisterns or rain barrels. A cistern is an above ground storage vessel with either a manually operated valve or a permanently open outlet. Roof runoff is temporarily stored and then released for irrigation or infiltration between storms. The number of rain January 2003 California Stormwater BMP Handbook New Development and Redevelopment- www.cabmphandbook.com 1 of 3 • SD-11 Roof Runoff Controls barrels needed is a function of the rooftop area. Some low impact developers recommend that every house have at least 2 rain barrels, with a minimum storage capacity of 1000 liters. Roof barrels serve several purposes including mitigating the first flush from the roof which has a high volum~, amount of contaminants, and thermal load. Several types of rain barrels are commercially available. Consideration must be given to selecting rain barrels that are vector proof and childproof. In addition, some barrels are designed with a bypass valve that filters out grit and other contaminants and routes overflow to a soale-away pit or rain garden. "If the cistern has an operable valve, the valve can be closed to store stormwater for irrigation or infiltration between storms. This system requires continual monitoring by the resident or grounds crews, but provides greater flexibility in water storage and metering. If a cistern is provided with an operable valve and water is stored inside for long periods, the cistern must be covered to prevent mosquitoes from breeding. A cistern system with a permanently open outlet can also provide for metering stormwater runoff. If the cistern outlet is significantly smaller than the size of the downspout inlet (say 1/4 to 1/2 inch diameter), runoff will build up inside the cistern during storms, and will empty out slowly after peak intensities subside. This is a feasible way to mitigate the peak flow increases caused by rooftop impervious land coverage, especially for the frequent, small stormS. Dry wells and Infiltration Trenches Roof downspouts can be directed to dry wells or infiltration trenches. A dry well is constructed by excavating a hole in the ground and filling it with an open graded aggregate, and allowing the water to fill the dry well and infiltrate after the storm event. An underground connection from the downspout conveys water into the dry well, allowing it to be stored in the voids. To minimize sedimentation from lateral soil movement, the sides and top of the stone storage matrix can be wrapped in a permeable filter fal;>ric, though the bottom may rema~n open: A "perforated observation pipe can be inserted vertically into the dry well to allow-for inspection and maintenance. In practice, dry wells receiving runoff from single roof downspouts have been successful over long periods because they contain very little sediment. They must be sized according to the amount of rooftop runoff received, but are typically 4 to 5 feet square, and 2 to 3 feet deep, with a minimum of I-foot soil cover over the top (maximum depth of 10 feet). To protect the foundation, dry wells must be set away from the building at least 10 feet. They must be installed in solids that accommodate infiltration. In poorly drained soils, dry wells have very limited feasibility. Infiltration trenches function in a similar manner and would be particularly effective for larger roof areas. An infiltration trench is a long, narrow, rock-filled trench with no outlet that receives stormwater runoff. These are described under Treatment Controls. Pop-up Drainage.Emitter Roof downspouts can be directed to an underground pipe that daylights some distance from the building foundation, releasing the roof runoff through a pop-up emitter. Similar to a pop-up irrigation head, the emitter only opens when there is flow from the roof. The emitter remains flush to the ground during dry periods, for ease oflawn or landscape maintenance. 2 of 3 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbook.com January 2003 Roof Runoff Controls 50-11 Foundation Planting Landscape planting can be provided around the base to allow increased opportunities for stormwater infiltration and protect the soil from erosion caused by concentrated sheet flow coming off the roof. Foundation plantings can reduce the physical impact of water on the soil and provide a subsurface matrix of roots that encourage infiltration. These plantings must be sturdy enough to tolerate the heavy runoff sheet flows, and periodic soil saturation. Redeveloping Existing Installations Various jurisdictional stormwater management and mitigation plans (SDSMP, WQMP, etc.) define "redevelopment" in terms of amounts of additional impervious area, increases in gross floor area and/or exterior construction, and land disturbing activities with structur3.I or impervious surfaces. The definition of" redevelopment" must be consulted to determine whether or not the requirements for new development apply to areas intended for redevelopment. If the definition applies, the steps outlined under "designing new installations" above should be followed. Supplemental Information Examples • City of Ottawa's Water Links Surface -Water Quality Protection Progra:m • City of Toronto Downspout Disconnection Program • City of Boston, MA, Rain Barrel Demonstration Program Other Resources Hager, Marty Catherine, Stormwater, "Low-Impact Development", January/February 2003. www.stormh20.com . Low Impact Urban Design Tools, Low Impact Development Design Center, Beltsville, MD. wwvv.lid-stormwater.net Start at the Source, Bay Area Stormwater Management Agencies Association, 1999 Edition January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbook.com 3 of 3 -Efficient Irrigation 5D-12 Design Objectives ~·""·m"'li\l(O~ \:1 ~CWI __ ,"=_' __ _ .t Maximize Infiltration -.t Provide Retention .t Slow Runoff Minimize Impervious Land Coverage Prohibit Dumping of Improper Materials Description Contain Pollutants Collect and Convey Irrigation water provided to landscaped areas may result in excess irrigation water being conveyed into stormwater drainage systems. - Approach Project plan designs for development and redevelopment should include application methods of irrigation water that minimize runoff of excess irrigation water into the stormwater <;!onveyance system. . Suitable Applications Appropriate applications include residential, commercial and industrial-areas planned for development or redevelopment. (Detached residential single-family homes are typically excluded from this requirement.) Design Considerations Designing New Installations The following methods to reduce excessive irrigation runoff should be considered, and incorporated and implemented where determined applicable and feasible by the Permittee: • Employ rain-triggered shutoff devices to prevent irrigation after precipitation. • Design irrigation systems to each landscape area's specific water requirements. • Include design featuring flow reducers or shutoff valves triggered. by a pressure drop to control water loss in the event of broken sprinkler heads or lines. • Implement landscape plans consistent with County or City water conservation resolutions, which may include provision of water sensors, programmable irrigation times (for short cycles), etc. January 2003 California Stormwater BMP Handbook . New Development and Redevelopment www.cabmphandbooks.com 1 of 2 • 50 ... 12 Efficie~t Irrigation • Design timing and application methods of irrigation water to minimize the runoff of excess irrigation water into the storm water drainage system. • Group plants with similar water requirements in order to reduce ·excess irrigation runoff and promote surface filtration. Choose plants with low irrigation requirements (for example, native or drought tolerant species). Consider design features such as: Using mulches (such as wood chips or bar) in planter areas without ground cover to minimize sediment in runoff Installing appropriate plant materials for the location, in accordance with amount of sunlight and climate, and use native plant materials where possible and/or as recommended by the landscape architect Leaving a vegetative barrier along the property boundary and interior watercourses, to act as a pollutant filter, where appropriate and feasible Choosing plants that minimize or eliminate the use of fertilizer or pesticides to sustain growth • Employ other comparable, equally effective methods to reduce irrigation water runoff. Redeveloping Existing Installations Various jurisdictional stormwater management and mitigation plans (SUSMP, WQMP, etc.) define "redevelopment" in terms of amounts of additional impervious area, increases in gross floor area and/or exterior construction, and land disturbing activities with structural or . impervious surfaces. The definition of " redevelopment" must be consulted to determine whether or not the requirements for new development apply to areas intended for redevelopment. If the definition applies, the steps outlined under "designing new' installations" above should be followed. Other Resources A Manual for the Standard Urban Stormwater Mitigation Plan (SUSMP), Los Angeles County Department of Public Works, May 2002. ModelBtandard Urban Storm Water Mitigation Plan (SUSMP) for San Diego County, Port of San Diego, and Cities in San Diego County, February 14, 2002. Model Water Quality Management Plan (WQMP) for County of Orange, Orange County Flood Control District, and the Incorporated Cities of Orange County, Draft February 2003. Ventura Countywide Technical Guidance Manual for Stormwater Quality Control Measures, July 2002. 2 of 2 California Stormwater BMP Handbook New Development ·and Redevelopment www.cabmphandbooks.com January 2003 Storm Drain Signage Description SD ... 13 Design Objectives Maximize Infiltration . Provide Retention Slow Runoff Minimize Impervious Lahd Coverage ./ Prohibit Dumping of Improper Materials Contain Pollutants Col/ect and Convey Waste materials dumped into storm drain inlets can have severe impacts on receiving and ground waters. Posting notices regarding discharge prohibitions at storm drain inlets can prevent waste dumping. Storm drain signs and stencils are highly visible source controls that are typically placed directly adjacent to storm drain inlets. Approach The stencil or affixed sign contains a brief statement that prohibits dumping -of improper materials into the urban runoff conveyance system. Storm drain messages have become a popular method of alerting the public about the effects of and the prohibitions against waste disposal. Suitable Applications Stencils and signs alert the public to the destination of pollutants discharged to the storm drain. Signs are appropriate in residential, commercial, and industrial areas, as well as any other area where contributions or dumping to storm drains is likely. Design Considerations Storm drain message markers or placards are recommended at all storm drain inlets within the boundary of a development project. The marker should be placed in clear sight facing toward anyone approaching the inlet from either side. All storm drain inlet locations should be identified on the development site map. Designing New Installations The following methods should be considered for inclusion in the project design and show on project plans: • Provide stenciling or labeling of all storm drain inlets and catch basins, constructed or modified, within the project area with prohibitive language. Examples include "NO DUMPING - January. 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 1 of 2 5D-13 Storm Drain Signage 'DRAINS TO OCEAN" and/or other graphical icons to discourage illegal dumping. • Post signs with prohibitive language and/o.r graphical icons, which prohibit illegal dumping at public access points along channels and creeks within the project area. Note -Some local agencies have approved specific signage and/or storm drain message placards for use. Consult local agency stormwater staff to determine specific requirements for placard types and methods of application. Redeveloping Existing Installations Various jurisdictional stormwater management and mitigation plans (SUSMP, WQMP, etc.) define "redevelopment" in terms of amounts of additional impervious area, increases in gross floor area and/or exterior construction, and land disturbing activities with structural or , impervious surfaces. If the project meets the definition of "redevelopment", then the requirements stated under" designing new-installations" above should be included in all project design plans. Additional Information Maintenance Considerations • Legibility of markers and signs should be maintained. If required by the agency with jurisdiction over the project, the owner/operator or homeowner's association should enter into a: maintenance agreement with the agency or record a deed restriction upon the property title to maintaiJ?-the legibility of placards or 'signs. (. Placement • Signage on top of curbs tends to weather and fade. • Signage on face of curbs tends to be worn by contact with vehicle tires and sweeper brooms. Supplemental Information Ex.amples • Most MS4 programs have storm drain signage'programs. Some MS4 programs will provide stencils, or arrange for volunteers to stencil storm drains as part of their outreach program. Other Resources A Manual for the Standard Urban Stormwater Mitigation Plan (SUSMP), Los Angeles County Department of Public Works, May 2002. ' Model Standard Urban Storm Water Mitigation Plan (SUSMP) for San Diego County, Port of San Diego, and Cities in San Diego County, February 14, 2002. Model Water Quality Management Plan (WQMP) for County of Orange, Orange County Flood Control District, and the IncOlyorated Cities of Orange County, Draft February 2003. Ventura Countywide Technical Guidance Manual for Stormwater Quality Control Measures, July 2002. ' 2 of 2 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 (. c. Trash Storage Areas Description Trash storage areas are areas where a trash receptacle (s) are located for use as a repository for solid wastes. Stormwater runoff from areas where trash is stored or disposed of can be polluted. In addition, loose trash and debris can be easily transported by water or wind into nearby storm drain inlets, channels, and/or creeks. Waste handling operations that may be sources of stormwater pollution include dumpsters, litter control, and waste piles. Approach This fact sheet contains details on the specific measures required to prevent or reduce pollutants in stormwater runoff associated with trash storage and handling. Preventative measures including enclosures, containment structures, and impervious pavements to mitigate spills, should be used to reduce the likelihood of contamination. Suitable Applications . SO-32 Design Objectives Maximize Infiltratiol) Provide Retention Slow Runoff Minimize Impervious Land COverage Prohibit Dumping of Improper Materials .t Contain Pollutants Collect and Convey Appropriate applications include residential, commercial and industrial areas planned for development or redevelopment. (Detached residential single-family homes are typically e:lFcluded from this requirement.) Design Considerations Design requirements for waste handling areas are governed by Building and Fire Cpdes, and by current local agency ordinances and zoning requirements. The design criteria described in this fact sheet are meant to. enhance and be consistent with these code and ordinance requirements. Hazardous waste should be handled in accordance with legal requireme-nts established in Title 22, California Code of Regulation. Wastes from commercial and industrial sites are typically hauled by either public or commercial carriers that may have design or access requirements for waste storage areas. T4e design criteria in this fact sheet are recommendations and are not intended to be in conflict with requirements established by the waste hauler. The waste hauler should be contacted prior to the design of your site trash collection areas. Conflicts or issues should be discussed with the local agency. Designing New Installations Trash storage areas should be designed to consider the following structural or treatment control BMPs: • Design trash container areas so that drainage from adjoining roofs and pavement is diverted around the area(s) to avoid run-on. This might include berming or grading the waste handling area to prevent run-on of stormwater. • Make sure trash container areas are screened or walled to prevent off-site transport of trash. January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 1 of 2 • SO-32 Trash Storage Areas • Use lined bins or dumpsters to reduce leaking of liquid waste. • Provide roofs, awnings, or attached lids on all trash containers to minimize direct . precipitation and prevent rainfall from entering containers. . • Pave trash storage areas with an impervious surface to mitigate spills. • Do not locate storm drains in immediate vicinity of the trash storage area. • Post signs on all dumpsters informing users that hazardous materials are not to be disposed of therein .. Redeveloping Existing l11$tallations Various jurisdictional stormwater management and mitigation plans (SUSMP, WQMP, etc.) define "redevelopment" in terms of amounts of additional impervious area, increases in gross floor area and/or exterior construction, and land disturbing activities with structural or impervious surfaces. The definition of" redevelopment" must be consulted to determine whether or not the requirements for new development apply to areas intended for redevelopment. If the definition applies, the steps outlined under "designing new installations" above should be followed. Additional Information Maintenance Considerations The integrity of structural elements that are subject to damage (i.e., screens, covers, and signs) must be maintained by the owner/operator. Mai:o.tenance agreements between the local agency and the owner/operator may be required. Some agencies will require maintenance deed restrictions to be recorded of the property title. If required by the local agency, maintenance agreements or deed restrictions must be executed by the owner/operator before improvement plans are approved. ." Other Resources A Manual for the Standard Urban Stormwater Mitigation Plan (SUSMP), Los Angeles County Department of Public Works, May 2002. Model Standard Urban Storm Water Mitigation Plan (SUSMP) for San Diego County, Port of" San Diego, and Cities in San Diego County, February 14, 2002. Model Water Quality Management Plan (WQMP) for County of Orange, Orange County Flood Control District, and the Incorporated Cities of Orange County, Draft February 2003. Ventura Countywide Technical Guidance Manual for Stormwater Quality Control Measures, July 2002. 2of2 California Storm water BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 c. STORM WATER MANAGEMENT PLAN ROBERTSON RANCH P.A. 22 Section 7.0 TREATMENTCONTROLBMWS Where identified in Table 1 of the City Standards, and after site design and source control BMPs have been incorporated into the project design, treatment control BMPs may then be utilized. 1. TREATMENT CONTROL BMW DESIGN STANDARDS Treatment Control BMPs shall be designed to infiltrate, fllter, ancVor treat runoff from the project footprint per Table 3: Numeric Sizing Treatment Standards. A copy of Table 3 is provided in Appendix C. There are four guidelines that need to be followed for Treatment Control BMPs: • All Structural Treatment Control BMPs shall infiltrate, fllter, and/or treat the required runoff volume or flow prior to discharging to any receiving water body supporting beneficial uses. • Multiple post construction Structural Treatment Control BMPs for a single priority project shall collectively be designed to comply with the numeric sizing treatment standards. • Shared BMPs shall be operational prior to the use of any dependent development or phase of development. The shared BMPs shall only be required to treat the depen,dent developments or phases of development tha1 are in use. • Interim storm water BMPs that provide equivalent or gr~ater treatment than is required may be implemented by a dependant development until each shared BMP is operational. If interim BMPs are selected, the BMPs shall remain ip. use until permanent BMPs are operational. 2. TREATMENT CONTROL BMW SELECTION All projects classified as Priority Projects in the City of Carlsbad shall select a single or combination of treatment control BMPs from the categories listed in Table 4: Structural Treatment Control BMPs Selection Matrix. A copy of Table 4 is provided in Appendix C. This selection matrix will determine the most efficient removal BMP for the pollutants of concern from the project site. The most efficient device or combination of devices shall be utilized to maximize pollutant removal. 3. POLLUTANTS OF CONCERN Based on the above fmdings for the proposed site usage the project has the following pollutants of concern: ' • Sediment (Anticipated) -1 - c. STORM WATER MANAGEMENT PLAN ROBERTSON RANCH P.A. 22 • Nutrients (potential by use) • Heavy Metals (Anticipated) • Organic Compounds (Anticipated) • Trash & Debris (Anticipated) • Oxygen Demanding Substances (Potential by use) • Oil & Grease (Anticipated) • Pesticides (potential by use) The other pollutants of concern have not been accounted for because the project landscaping will be designed and installed per the City of Carlsbad Landscape Manual and will incorporate efficient irrigation, pest resistant species, and incorporate drought resistant native species of planting. 4. STRUCTURAL TREATMENT CONTROL BMP SELECTION Based on the pollutants of concern present from the project site and the removal efficiencies listed in Table 4: Structural Treatment Control BMP Selection Matrix, the Structural Treatment Control BMP with the most efficient removal efficiencies for the project are as follow~ (listed most to least efficient): • Vegetated'Swale • Bioretention (see Appendix J for sizing, calculations) • Filter Inserts • Pervious Pavement Based on the above mentioned removal efficiencies and limited space on site, the project shall incorporate a combination of biofilters and drainage inserts on site. Higher removal efficient structural treatment control devices could not be used on site due to the limited space to accommodate their proper design and implementation. 5. TREATMENT CONTROLBMPINFORMATION Based on the above mentioned removal efficiencies, the project shall incorporate Suntree Technologies Inlet Basket System (or approved equivalent) and Bioclean Environmental Services, Inc (or approved equiValent) products in the proposed locations shown on the Preliminary Storm Water Management Plan Exhibit in Appendix J. 6. STRUCTURAL TREATMENT LIMITED ,EXCLUSIONS No Structural Treatment Limited Exclusions apply to this project as defined in the City Standards. -2- STORM WATER MANAGEMENT PLAN ROBERTSON RANCH PA 22 • Section 7.0 Table 2: Anticipated and Potential Pollutants Generated by Land Use Type General Pollutant Categories Project Categories Sediments Nutrients Heavy Organic Trash Oxygen Oil Bacteria . Pesticides • ~. Metals Compounds & Demanding & & Debris Substances Grease Viruses Detached Residential X X X X X X Development Attached Residential X X X p(l) p(2) p(1) Development Commercial Development p(1) pCl) p(2) X pCS) X p(3) > 100,000 ft2 Automotive X X(4)(S) X X Repair Restaurants X X X X Hillside . Development . <5, 000 ft2 X X X X X Parking Lots p(1) p(1) X pCl) X Streets, Highways, & X p(l) x X X(4) X pCS) X Freeways Notes: X = Anticipated p = Potential (1) A potential pollutant if landscaping exists on-site. . (2) A potential pollutant if the project includes uncovered parking areas. (3) A potential pollutant is land use involves food or animal waste areas. (4) Including petroleum hydrocarbons. (5) Including solvents. Source: City of Carlsbad Public Works Department Standard Urban Storm Water Mitigation Plan Storm Water Standards (2008, page 8) X X t. ,- pCS) - X pCl) STORM WATER MANAGEMENT PLAN ROBERTSON RANCH PA 22 {. SECTION 7.0 • Table 3: Numeric Sizing Treatment Standards Volume 1. Volume-based BMPs shall be designed to mitigate (infiltrate, filter, or treat) the volume of run-off produced from a 24-Hour 85th percentile storm event, as determined from Isopluvial maps cont~ned in the County of San Diego Hydrology Manual. Flow 2. Flow-based BMPs shall be designed to mitigate (infiltrate, filter, or treat) the maximum flow ,rate of run-off produced from a rainfall intensity of 0.2 inch of rainfall per hour for each hour of a storm event. Source: City of Carlsbad Public Works Department Standard Urban Storm Water Mitigation Plan Storm Water Standards (2008, page 14) . STORM WATER MANAGEMENT PLAN ROBERTSON RANCH PA 22 '. SECTION 7.0 Table 4: Structural Treatment Control BMP Selection Matrix Treatment Control BMP Catef(ories Pollutant Of Biofilters Detention Infiltration Wet Ponds Drainage Concem Basins Basins (1) or Inserts Wetlands Sediment M H H H L Nutrient L M M M L Heavy M M M H L Metals Organic U U U U L Compounds Trash & L H U U M Debris Oxygen L M M M L Demanding Substances Bacteria U U H U L Oil & M M U U L Grease Pesticides U U U U L Notes: (1) Including trenches and porous pavement. (2) Also known as hydrodynamic devices and baffle boxes L: Low removal efficiency M: Medium removal efficiency H: High removal efficiency U: Unknown removal efficiency Filtration Hydrodynamic Separator Systems (2) H M M L H L M L H M M L ,M L H L U L Sources: Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters (1993), National Stormwater Best Management Practices Database (2001), and Guide for BMP Selection in Urban Development Areas (2001). Source: City of Carlsbad Public Works Department Standard Urban Storm Water Mitigation Plan Storm Water Standards (2008, page 15) - Drain Inserts Description Drain inserts are manufactured filters or fabric placed in a drop inlet to remove sediment and debris. There are a multitude of inserts of various shapes and configurations, typically falling into one of three different groups: socks, boxes, and trays. The sock consists of a fabric, usually constructed of polypropylene. The fabric may be attached to a frame or the grate of the inlet holds the sock. Socks are meant for vertical (drop) inlets. Boxes are constructed of plastic or wire ·mesh. Typically a polypropylene ''bag'' is plac~d in the wire mesh box. The bag takes the form of the box. Most box products are one box; that is, the setting area and filtration through media occur in the same box. Some products consist of one or more trays or mesh grates. The trays may hold different types of media. Filtration media vary by manUfacturer. Types include polypropylene, porous polymer, treated cellulose, and activated carbon. . California Experience The number of installations is unknown but likely exceeds a thousand. Some users have reported that these systems require considerable maintenance to prevent plugging and bypass. Advantages • Does not require additional space as inserts as the drain inlets are already a component of the stand~d drainage systems. • Easy access for inspection and maintenance. • AI; there is no standing water, there is little concern for mosquito breeding. • A relatively inexpensive retrofit option. Limitations Performance is likely significantly less than treatment systems that are located at the end of the drainage system such as ponds and vaults. Usually not suitable for large areas or areas with trash or leaves than can .plug the insert. Design and Sizing Guidelines Refer to manufacturer's guidelines. Drain inserts come ap.y many configurations but can be placed into three general groups: socks, boxes, and trays. The sock consists of a fabric, usually constructed of polypropylene. The fabric may be attached to a frame or the grate of the inlet holds the sock. Socks are meant for vertical (drop) inlets. Boxes are constructed of plastic or wire mesh. Typically a polypropylene ''bag'' is placed in the wire mesh box. The bag takes the form of the box. Most box products are January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com MP-52 Design Considerations • Use with other BMPs • Fit and Seal Capacity within Inlet· Targeted· Constituents .t Sediment .t Nutrients .t Trash .t Metals Bacteria .t Oil and Grease .t Organics Removal Effectiveness See New Development and Redevelopment Handbook-Section 5. 1 of 3 MP-52 Drain Inserts one box; that is, the setting area and filtration through media occurs in the same box. One manufacturer has a double-box. Stormwater enters the first box where setting occurs. The stormwater flows into the second box where the filter media is located. Some productS consist of one or more trays or mesh grates. The trays can hold different types of media. Filtration media vary with the manufacturer: types include polypropylene, porous polymer, treated cellulose, and activated carbon. Construction/Inspection Considerations Be certain that installation is done in a manner that mal<:es certain that the stormwater enters the·unit and does not leak around the perimeter. Leakage between the frame of the insert and the frame of the drain inlet can easily occur with vertical (drop) inlets. Performance Few products have performance data collected under field conditions. Siting Criteria It is recommended that inserts be used only for retrofit situations or as pretreatment where other treatment BMPs presented in this section area used. Additional Design Guidelines Follow guidelines provided by individual manufacturers. Maintenance Likely require frequent maintenance, on the order of several times per year . . Cost • The initial cost of individual inserts ranges from less than $100 to about $2,000. The cost of using multiple units in curb inlet drains varies with the size of the inlet. • The low cost of inserts may tend to favor the use of these systems over other, more effective treatment BMPs. However, the low cost of each unit may be offset by the number of units that are required, more freque~t maintenance, and the shorter structural life (and·therefore replacement) . References and Sources of Additional Information Hrachovec, R., and G. Minton, 2001, Field testing of a sock-type catch basin insert, Planet CPR, Seattle, Washington Interagency Catch Basin Insert Committee, Evaluation of Commercially-Available Catch Basin Inserts for the Treatment of Stormwater Runoff from Developed Sites, 1995 Larry Walker Associates, June 1998, NDMP Inlet/In-Line Control Measure Study Report Manufacturers literature Santa Monica (City), Santa Monica Bay Municipal Stormwater/Urban Runoff Project - Evaluation of Potential Catch basin Retrofits, Woodward Clyde, September 24,1998 2 of 3 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 Drain -Inserts MP-52 Woodward Clyde, June 11, 1996, Parking Lot Monitoring Report, Santa Clara Valley Nonpoint Source Pollution Control Program. January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 3 of 3 (. Vegetated Swale 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. TIley are designed to treat runoff through filtering by the vegetation in the channel, filtering through a subsoil matrix, andj 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 pmt 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. TIlese swales were generally effective in reducing the volume and mass of pollutants in runoff. Even in the areas where the rumual rainfall was only about 10 inchesjyr, 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 TSS 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 CalifornIa stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com TC-30 ~;;I ~ Design Considerations • Tributary Area . • A~a Required • Slope • Water Availability ~:==~ I Targeted ConstituentS ~. 0 Sediment ~ 0 'Nutrients • 0 Trash • 0 Metals ... 0 Bacteria • 0 Oil and Grease ~ 0 Organics ... Legend (Removal Effectiveness) , • Low • High ... Medium CAUWRl';1A 1>WR.\1WA'I'!;}l {.H)ld.H'Y l\.".1!·{)(·Ji(H(,~~":: lof13 "" TC-30 Vegetated Swale • • Roadside ditches should be regarded as significant potential swalejbuffer strip sites and should be utilized for this purpose whenever possible. Limitations • Can be difficult to avoid channelization. • May not be appropriate for industrial sites or locations where spills may occur • Grassed swales cannot treat a very large drainage area. Large areas may be divided and treated using multiple swales. • A thick 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 not properly maintained. • In some places, their use is restricted by law: 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 • Flow rate based design determined by local requirements or sized so that 85% 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 2/3rds the'11eight of the grass or 4 inches, which ever is less, at the design u"eatment rate. • Longitudinal slopes should not exceed 2.5% • Trapezoidal channels are normally recommended but other configurations, such as parabolic, can also provide substantial water quali1yimprovement and may be easier to mow than designs with sharp breaks in slope. • Swales constructed 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 oflow growing, plants that thrive under the specific site, climatic, and watering conditions should be specified. Vegetation whose growing season colTesponds 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 Manning's Equation using a value of 0.25 for Manning's 11. 2of13 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 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 ship. • Use a roller on the sod to ensure that 110 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 aftel" the first rainfall of the season. Performance TIle 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, it is known that check dams, slight slopes, permeable soils, 'dense grass cover, increased contact time, and smaIl stol"m events all contribute to successful pollutant removal by the swale system. Factors decreasing the effectiveness of swales include compacted soiis, short runoff contact time, large storm events, frozen groundJ short grass heights, steep slopes, and high l11110ff velocities and discharge rates. Conventional vegetated swale designs have achieved mixed results in removing particulate pollutants. A study performed by the Nationwide Urban Runoff Prograql (NURP) monitored three grass swales in the Washington, D.C., area and found no significant improvement in urban l1llloff quality for the pollutants analyzed. However, the weak performance of the~eswales 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 11 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 fOI" removing soluble nutrients. The effectiveness of vegetated swales can be enhanced by adding check dams at approxiniately 17111eter (so foot) increments along their length (See Figure 1). 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 channel 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 1). The data suggest relatively high removal rates for some pollutants, but negative removals for some bacteria1 and fair performance for phosphorus. JanualY 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com S'of13 TC-30 Vegetated Swale Table 1 Grassed swale pollutant removal efficiency data Removal Efficiencies (% Removal) Shldy TSS. TP TN N03 Metals Bacteria 'I)'Pe Caltl'ans 2002 77 8 67 66 83-90 -33 . dryswaIes Goldberg 1993 67.8 4·5 -31-4 42-62 -100 grassed channel Seattle Metro and Washington 60 45 --25 2-16 -25 grassed channel ~epal'tment of Ecology 1992 Seattle Metro and Washington 83 29 --25 46-73 -25 grassed channel Department ofEeoIogy, 1992 Wang et al., 1981 80 ---70-80 -dryswale - Dorman et aI., 1989 98 18 -45 37-81 -dryswale Harper, 1988 87 83 84 80 88-90 -dryswaIe Kercher et al., 1983 99 99 99 99 99 -dryswale Harper, 1988. 81 17 40 52 37-69 -wetswale Koon, 1995 67 39 -9 -3Sto6 -wetswale While it is difficult to distinguish between different designs based on the small amount of aV8.11able data, grassed channels generally have poorer removal rates than wet and dry swales, although some swales appear to export soluble phosphorus (Harper, 1988; Koon, 1995), It is not clear why swales export bacteria. One explanation is that bacteria thrive in the warm swale soils. . Siting Criteria The suitability of a swale at a site will depend on land use, size of the area serviced, soil type, slope, imperviousness of the contributing watershed, and dimensions and slope of the swale system (Schueler et al'1 1992). In general, swales can be used to serve areas ofless than 10 acres, with slopes 110 greater than 5 %. Use of natural topographic lows is en,couraged and natural drainage courses should be regarded as significant local resources to b~ kept in use (Young et al., 1996). Selection Cr-itePia (NCTCOG, :1.993) • Comparable performance to wet basins • Limited to treating a few acres • Availability of water during dry periods to maintain vegetation • Sufficient available land area Research in the Austin area indicates that vegetated conh'ols are effective at removing pollutants even when dormant. Therefore, irrigation is 110t required to maintain growth during dry periods, but may be necessary only to prevent the vegetation from dying. 40f 13 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 Vegetated Swale TC-30 • The topography of the site should permit the design of a channel with appropriate slope and cross-sectional area. Site topography may also dictate a need fOl' additional structuralcont;ols. 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 terrace the swale and reduce the slope to within acceptable limits. The use of clleck danlS 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 S~ttle, Washington (Seattle Metro and Washington Department ofEcology11992), and is not well supported. Analysis of the data collected in that study indicates tIlat 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 criteli~ for swales is needed. Substantial pollutant removal has also been observed for vegetated controls designed solely for conveyance (Barrett et aI, 1998); consequently, some flexibility in the design is warranted. Many design guidelines recommend that grass be frequently mowed to maintain 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 of Design Recommendations 1) The swale should have a length that provides a minimum hydIaulic re$idence time of at least 10 minutes. The maximum bottom width should not ~xceed 10 feet unless a dividing berm is provided. The depth of flow should not exceed 2/3l'ds the height of the grass at the peak of the water quality design stonn intensity. The channel slope should not exceed 2.5%. . 2) A design grass height of 6 inches is recommended. 3) Regardless of the recommended detention tiIne1 the swale should be not less than 100 feet in length. 4) The width of the S'wale should be determined using Manning's Equation1 at the peak of the design storm, using a Manning's n of 0.25. 5) The swale can be sized as both a treatment facility for the design stonn 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 3=1 (H:V). 6) Roadside ditches should be r~arded as significant potential swalejbuffer 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 clogging. 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, close-growing, water-resistant grasses. If possibl~, divert runoff (other than necessary inigation) during the period of vegetation January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 50f13 • 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 during drought conditions, reseeding of bare areas, and clearing of debris and blockages. Cuttings should be removed from the channel and disposed in a local composting 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 channel. 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 it is not, reseed as necessmy. Any standing water removed during the maintenance operation must be disPQsed to a sanitary sewer at an approved discharge location. Residuals (e.g., silt, grass cuttings) must be disposed in accordance with local or State requirements. Maintenance of grassed swales mostly involves maintenance of tlle grass or wetland plant cover. Typical maintenance activities are. summarized below: • Inspect swales at least twice annually for erosion, damage to 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 swal~ should be checked for debris and litter, and areas of sediment accumulation. • Grass height and mowing frequency may not have a large impact on pollutant removal Consequently, mmving may only be llecessary once or twice a year for safety or aesthetics or to suppress weeds and woody vegetation. • Trash tends to accumulate in swale areas, pru.ticularly along highways. The need for litter removal is determined through periodic inspection, but litter should always be removed prior to mowing. • Sediment accmnulating near culverts and in channels should be removed when it builds up to 75 mm (3 in.) at any spot, 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. 6of13 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 • • Vegetated S1A!ale Cost ConstJouction Cost TC-30 Little data is available to estimate the difference in cost between various swale designs. One study (SWRPC, 1991) estimated the 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 otb,eJ," practices. A more realistic estimate would be a total cost of approximately $0.50 per ft.2., which compares favombly witll other storm water management practices . January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com "7 of 13 ,'. I.4iiiii ' .• TC-30 Table 2 Swale Cost Estimate (SEWRPC, 1991) Unit COst Component Unit Extent low Moderate High low Mobiliuition I Swala 1 $101 $214 $441 $107 OemobWzation·Ughi Site Preparatioo CI9aring~ ................ /Jaa 0.5 $2,200 $3,800 $5,400 $1,100 Grubblng' .........•..•. AJ:%a 0.25 $3,800 $5.200 $6,600 $950 General Excavatlorfl ............ Yd3 372 $2.10 $3.70 $5.30 $781 lAver and TnlQ ........ Ydl 1.210 $020 $0.35 $).50 $242 Sites Development Salvaged Topsoil yeP 1,210 $0.40 $1.00 $1.60 $4S4 Saed. and Mulehf .. Sod9 ..•.•....•..•......... Yd' 1,210 $1.20 $2AO $3.60 $1,452 Subtotal ~~ -~. -.. $5.116 Contingencias Swals 1 25% 25% 25% $1,219 Total .-----$6.395 Source: (SEWRPC, 1991) Note: Mobilimtion/dsmobUlzation refers to the organiZStioo and plannfhg involved in establishing a vsgeiailva svmfe. a Swate has a tlottom width of 1.0 footl a top Widthof10 feet with 1:3 side slopes, and a 1,OO()"foot length. \) Area cleared = (top width + 10 feet) x swale length. ~ Area grubbed = {top width x swale length}. dVolume excavated = (0.61 x top width x swale depth) x swale length (parabolic cross-section), Q Area tilled = (top wIdth + S(swate deptlf) x swale length (parabolic cross-section). 3{top Width) ~ r Area seeded = area cleared x 0.5. . a Area sodded = area cleared x 0,£. 8 of 13 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com • .Vegetated Swale Total Cost Moderate HIgh $274 $441 $1,900 $2,700 $1,300 $1,650 $1,376 $1.972 $424 $605 $1,210 $1,936 $2,904 $4,356 $9,358 $13,660 $2,347 $$.415 $11135 $17.075 . January 2003 • Vegetated Swale ,.~. 1-, Table 3 Estimated'Maintenance Costs (SEWRPc.. 1991) Component UnUCost lawn Mowing $0.85 11,000 ft21 mowing General Lawn Care $9.00/1,000 WI year Swals Debris and Utter $0 .10 flinear foot I year Removal Grass Rssaeding with $O.30/yd2 Mutch and Fertilizer Program Administration and $0.151 Unear foot I year, Swate Inspection plus $251 Inspection Total ~. --.... _--._ .... January 2003 SwaleSlze (Depth and Top Width) , 1.5 Foot Depth1 One. a·Foot Depth~ 3.-Foot Foot Bottom Width. Bottom WIdth; 21.,Foot 10..footTop Wldth Top Width $).14 I Hnearfoot $0.21 I linear foot $O.18/linearfoot $0.28 I linear foot iEO.10 flinearfoot $0.10 I linear foot $0.01 IIlnea r foot $0.01 I linear foot $).15 I linear foot $0.,5 I linear foot $0.531 linear fcot $; 0.15 I IinoaT foot california Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com TC-I, comment Lawn maintenanCG area=(lop widlt! + 10 feet} x length. Movi eight times per year Lawn maintenanCG area = (top wid1h + 10 fem) 11: leng1h - Araa t9vagaf:i.!t0d 4lqIJals 1 % oflawn rna int0n ance a rea PIll r year Inspect four times pel' year - 9 of 13 • , • TC-30 Vegetated Swale Maintenance Cost Caltrans (2002) estimated the e:A'Pected annual maintenance cost for a swale with a tributary 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 costs 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 K, Walsh, Patrick M., Malina, Joseph F., Jr., Charbeneau, Randall J 1 1998, "Performance of vegetative controls for b.-eating highway runoff," ASCE Journal of Environmental Engineering, Vol. 124, No. 11, pp. 1121-1128. Brown, W., and T. Schueler. 1997. The Economics ofStorInwater 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 of StorInwater Filtering Systems. Prepared for the Chesapeake Research Consortium, Solomons, MD, and USEPA Region V, Chicago, IL, by the Center for Watershed Protection, Ellicott City, MD. . Colwell, Shanti R, Horner, Richard R, and Booth, Derek B., 2000. Characterization of Performance Predictors and Evaluation of Mowing Practices in Biofiltration Swales. Report to King County Land And Water Resources Division and others by Center for Urban Water Resources Management, Department of Civil and Environmental Engineering, University of Washington,Seattle,Wi\ Dorman, M.E., J. Hartigan, RF. Steg, and T. Quasebarth. 1989. Retention, Detention and Overland Flow for Pollutant Removal From Highway Stormwater Runoff. Vol. 1. FHWi\jRD 89/202. Federal Highway Administration, Washington, DC. Goldberg. 1993. Dayton Avenue Swale Biofiltration Study. Seattle Engineering Department, Seattle, W A. Harper, H. 1988. Effects of Storm water Management Systems on Groundwater Quality. Prepared for Florida Department of Environmental Regulation, Tallahassee, FL, by Environmental Research and Design, Inc., Orlando, FL. Kercher, W.C., J.C. Landon, and R Massarelli. 1983. Grassy swales prove cost-effective for water pollutioll control. Public Works, 16: 53-55. Koon, J. 1995. Evaluation of Water Quality Ponds and Swales in the Issaquah/East Lake Sammamish Basins. King County Surface Water Management, Seattle, WA, and Washington Department of Ecology, Olympia, WA Metzger, M. K, D. F. Messer, C. L. Beitia, C. M. Myers, and V. 1. Kramer. 2002. The Dark Side Of Stormwater Runoff Management: Disease Vectors Associated With Structural BMPs . Stormwater 3(2): 24-39.0akland, P.H. 1983. An evaluation of storm water pollutant removal 10 of 13 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 (. Vegetated Swale TC-30 through grassed swale treatment. In Proceedings of the International Symposium of Urban Hydrolo[Jl), Hydraulics and Sediment Control, Lexington, KY. pp. 173-182. Occoquan Watershed Monitoring Laboratory. 1983. Fmal Report: Metropolitan Washillgton Urban Runoff Project. Prepared for the Metropolitan Washington Council of Governments, Washington, DC, by the Occoquan Watershed Monitoring LaboratOlY, Manassas, VA. Pitt, R, and J. McLean. 1986. Toronto Area Watershed Management Strategy Study: Humber River Pilot Watershed Project. Ontario Ministry of Environment, Toronto, ON. Schueler, T. 1997. Comparative Pollutant Removal Capability of Urban BMPs: A reanalysis. Watershed Protection Techniques 2(2):379-383. Seattle Metro and Washington Department of Ecology. 1992. Biojiltration Swale Performance: Recommendations and Design Considerations. Publication No. 657. Water' Pollution Control Department,Seattle,WA. Southeastern Wisconsin Regional Plamling 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, Stormwater Fact Sheet: Vegetated Swales, Report # 832-F-99-006 http://www.epa.gov lowm/mtb/vegswale.pdf, Office of Water, Washington DC. Wang, T., D. Spyridakis, B. Mar, and R. Horner. 1981. Transport, Deposition and Control of Heavy Metals in Highway Runoff. FHWA-WA-RD-39-10. University of Washington, Department of Civil Engineering, Seattle, WA. Washington State Department of Transportation, 1995, Highway Runoff Manual, Washington State Department of Transportation, Olympia, Washingt?n. Welborn, C., and J. Veenhuis. 1987. Effects of Runoff Controls on the Quantity and Quality of Urban Runoffin Two Locations inAustin, TX. USGS Water Resources Investigations Report No. 87-4004. U.S. Geological Survey, Reston, VA Youse!, Y., M. Wanielista, H. Harper, D. Pearce, alldR Tolbelt.1985. BestManagement Practices: Removal of Highway Contaminants By Roadside Swales. University of Central Florida and Florida Department of Transportation, Orlando, FL. Yu, S., S. Barnes, and V. Gerde. 1993. Testing of Best Management Practices for Controlling Highway Runoff. FHWAfVA-93-R16. Virginia Transportation Research Council, Charlottesville, VA. Infonnation ResoUJ"ces Maryland Department of the Environment (MDE). 2000. Maryland Stormwate,. Design Manual. 'Wvvw.mde.state.md.us/environment/wma/stounwatermanual. Accessed May 22, 2001. Reeves, E. 1994. Performance and Condition of Biofilters in the Pacific Northwest. Watershed Protection Techniques 1(3):117-119. . January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 11 ofi3 TC-30 Vegetated Swale . . (. Seattle Metro and V\Tashingtoll Department of Ecology. 1992. Biofiltration Swale Peiformance. c. Recommendations and Design Considerations. Publication No. 657. Seattle Metro and Washington Department of Ecology, Olympia, WA USEPA 1993. Guidance Specifying Management Measures fol' Sources oJNonpoint Pollution in Coastal Waters. EPA-840-B-92-002. U.S. Environmental Protection Agency, Office of Water. Washington, DC. Watershed Management Institute (W:MI). 1997. Operation, Maintenance7 and Management 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 Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 • • Vegetated Swale IMP ZSDSW W'i. ! Qi E • Natation: I ProvIde for!£OOf pNIC:Ciion. 1. =-I.Olnglft of lIwall.\ hl1p~Ulltlml)llt IlfClI per <:ll{!ck dam (ft) (b) DlmellSloJl:Jf View of SWllle IIl1P(lllt)dmclIt al'Cli. 1)5 ;:; O~ptl\ <)f clI"r;k dom {fI} s.s '" Bottom 1OlplI<)t S\"I\llo {tUft} W ;:; Top Width of !1heclc dam (Hj Wp = Bottom width <)f chOll!! dllm{ft) ll&l :Ratio tlf liortzellltaf to wrtiCllI Cilalllll.;m 5\111\\0 sid!) slupc (lilt!} Janua*y 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com TC-30 13 of 13 • • Multiple System Fact"Sheet Description A multiple tI'eatment system uses two or more BMPs in series. Some examples of multiple systems include: settling basin combined with a sand filter; settling basin or biofilter combined with an infiltration basin or trench; extended detention zone on a wet pond. California Experience TIle research wetlands at Fremont, California are a combination of wet ponds, wetlands, and vegetated controls. Advantages • BMPs that are less sensitive to high pollutant loadings, especially solids, can be used to pretreat runoff for sand filters and infiltration devices where the potential for clogging exists. • BMPs which target different constituents can be combined to provide tI'eatInent for all constituents of concern. • BMPs which use different removal processes (sedimentation, filtration, biological uptake) can be combined to improve the overall removal efficiency for a given constituent. • BMPs in series can provide redundancy and reduce the likelihood of total system failure. Limitations • Capital costs of multiple systems are higher than for single devices. • Space requirements are greater than that required for a single technology. Design and Sizing Guidelines Refer to individual treatment control BMP fact sheets. Performance • Be aware that placing multiple BMPs in series does hot necessarily result in combined cumulative increased performance. This is because the first BMP may already achieve part of the gain normally achieved by the second BMP. On the other hand, picking the right combination can often help optimize performance of the second BMP since the influent to the second BMP is of more consistent water quality, and thus more consistent performance, thereby allowing the BMP to achieve its highest performance . January 2003 california Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com TC-60 Design Consif;lerations • Area Required • Slope • Water Availability • Hydraulic Head • Environmental Side-effects ",; Targeted Consti"tuehtS ,- o Sediment -o "Nutrients - o Trash -o Metals -o Bacteria A o Oil and Grease -o Organics - leg~nd (Removal EffectiveneSs) T· -Low -High A Medium CAI.w()!!N1ANDR}~WA'TI?R t:(ti~!1~l.~ i '; ;"~~:;'I.!;'" ~ ) t {.(l . ..;,: 1 of 2 TC-60 Multiple System Fact Sheet When addressing. multiple constituents through multiple BMPs, one BMP may optimize removal of a particular constituent, while another BMP optimizes removal of a different constituent or set of constituents. Therefore, selecting the right combination ofBMPs can be very constructive in collectively removipg multiple constituents. Siting Criteria Refer to individual treatment control BMP fact sheets. Additional Design Guidelines • When using 1:\'\1"0 or more BIYIPs in series, it may be possible to reduce the size of BMPs. • Existing pretreatment requirements may be able to be avoided when using some BMP combinations. Maintenance Refer to individual treatment control BMP fact sheets. Cost Refer to individual treatment control BMP fact sheets. Resources and Sources of Additional Information Refer to individual treatment control BMP fact sheets. 20f2 California stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com ,. January 2003 • , • Pervious Pavements Description 5D-20 Design Objectives Ii:l Maximize Infiltration Ii:l Provide Retention Ii:l Ii:l Slow Runoff Minimize Impervious Land Coverage Prohibit Dumping of Improper Materials Contain Pollutants Collect and Convey Pervious paving is used for light vehicle loading in parking areas. The term describes a system comprising a load-bearing, durable surface together with an underlying layered stl1lcture that temporarily stores water prior to infIltration or drainage to a controlled outlet. The surface can itself be porous such that water infiltrates across the entire surface of the material (e.g., grass - and gravel surfaces, porous concrete and porous asphalt), or can be built,up of impermeable blocks separated by spaces and joints, through which the water can drain. This latter system is termed 'permeable' paving. Advantages of pervious pavements is that they reduce runoff volume while providing treatment, and are mlObtrusive resulting in a high level of acceptability. Approach Attenuation of flow is provided by the storage within the underlying structure or sub base, together with appropriate flow controls. An underlying geotextile may permit groundwater recharge, thus contributing to the restoration of the natural water cycle. Alternatively, where infiltration is inappropriate (e.g., if the groundwater vulnerability is high, or the soil type is unsuitable), the surface can be constructed above an impermeable membrane. The system off~rs . _ a valuable solution for drainage of spatially constrained urban areas. Significant attenuation and improvement in water quality can be achieved by permeable pavements, whichever method is used. The surface and subsurface infrastructure can remove both the soluble and fine particulate pollutants that occur within urban runoff. Roof water can be piped into the storage area directly, adding areas from which the flow can be attenuated. Also, within lined systems, there is the opportunity for stored runoff to be piped out for reuse. Suitable Applications Residential, c01ll1llercial and industrial applications are possible_ The use of penneable pavement may be restricted in cold regions, arid regions or regions with high wind erosion. There are some specific disadvantages associated with permeable pavement, which are as follows: January 2003 California stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com CALIt\llt)\;IIl.SflJ1NW"rEll (~t']q ,~Tt [\"':-;0 ... ·: ~':.,'! ~ ... '~~ lof 10 5D-20 Pervious Pavements (e . Permeable pavement can become clogged if improperly installed or maintained. However, this is countered by the ease with which small areas of paving can be cleaned or replaced when blocked or damaged. • Their application should be limited to highways with low traffic volumes, axle loads and speeds (less than 30 mph limit), car parking areas and other lightly trafficked or non- trafficked areas. Permeable srufaces are cru'rently not considered suitable for adoptable roads due to the risks associated "vith failure on high speed roads, the safety implications of ponding, and disruption arising from reconstructioIl. • When using un-lined, infiltration systems, there is some risk of contaminating groundwater, depending on soil conditions and aquifer susceptibility. However, tIns risk is likely to be sma~ because the areas drained tend to have inherently low pollutant loadings. • The use of permeable pavement is restricted to gentle slopes. • Porous block paving has a hlgher risk of abrasion and damage tllan solid blocks. Design Considerations Designing New Installations If ilie grades, subsoils, drainage characteristics, and groundwater conditions are· suitable, permeable paving may be substituted for conventional pavement on parking areas, cul de sacs and oilier areas with light traffic. Slopes should be flat or velY gentle. Scottish experience has shown that permeable paving systems can be installed in a wide range of grO'lmd conditions, and the flow attenuation pelformance is excellent even when the systems are lined. The suitability of a pervious system at a palticular pavement site will, however, depend on the loading criteria required of the pavement. Where the system is to be used for infiltrating drainage waters into the ground, the vulnerability oflocal groundwater sources to pollution from the site should be low, and the seasonal hlgh water table should be at least 4 feet below the surface. Ideally, the pervious surface should be horizontal in order to intercept local rainfall at source. On sloping sites, pervious sUlfaces may be terraced to accommodate differences in levels. Design Guidelines The design of each layer of the pavement must be determined by the likely traffic loadings and their required operational life. To provide satisfactory performance, ilie following criteria should be considered: • The subgrade should be able to sustain traffic loading without excessive deformation. • The granular capping and sub-base layers should give sufficient load-bearing to provide an adequate construction platform and base for the overlying pavement layers. • The pavement materials should not crack of suffer excessive rutting under the influence of traffic. This is controlled by the horizontal tensile stress at the base of these layers. 2 of 10 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 • , • Pervious Pavements There is no cUl'rent structural design method specifically for pervious pavements. Allowances should be considered the following factors in the design and specification of materials: • Pervious pavements use materials with high permeability and void space. All the current UK pavement design methods are based on the use of cOllventionalmateriais that are deilse and relatively impermeable. The stiffness oftlle materials must therefore be assessed. • "'Vater is present within the construction and can soften and weaken materials, and this must be allowed for. • Existing design methods assume full friction between layers. Any geotextiles or' geomembranes must be carefully specified to minimize loss offrictioll between layers. • Porous asphalt loses adhesion and becomes brittle as air passes through the voids. Its durability is therefore lower than conventional materials. The single sized grading of materials used means that care should be taken to ensure that loss of finer particles between unbound layers does not occur. ' Positioning a geotextile near the surface of the pervious consh"Uction should enable pollutants to be trapped and retained close to the sUlface of the construction. This hru:; both advantages and disadvantages. TIle main disadvantage is that the filteling of sediments and their associated pollutants at this level may hamper percolation of waters and can eventually lead to sUlface poneling. One advantage is that even if eventual maintenance is required to reinstate infiltration, only a limited amount of the construction needs to be disturbed, since the sub-base below the geotextile is protected. In addition, the pollutant concentration at a high level in the structure allows for its release over time. It is slowly transported in thestormwater to lower levels where chemical and biological processes may be operating to ret~ or degrade pollutants. TIle design should ensure that sufficient void space exists for the storage of sediments to limit the period between remedial works. • Pervious pavements require a single size grading to give open voids. The choice of materials is therefore a compromise between stiffness, permeability and storage capacity. • Because the sub-base and capping will be ill contact with water for a large part of the time, the strength and dUl'ability of the aggregate particles when saturated and subjected to wetting and drying should be assessed. • A uniformly graded single size material calIDot be compacted and is liable to move when construction traffic passes over it. This effect can be reduced by the use of angular crushed rock matelial with a high SUlface frictioll. In pollution control terms) these layers represent the site oflong term chemical and biological pollutant retention and degradation processes. The construction· materials should be selected, in addition to their structural strength properties, for their ability to sustain such processes. hI general, this means that materials should create neutral or slightly alkaline conditions and they should provide favorable sites for colonization by microbial populations . January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 30f10 ~. SD-20 Pervious Pavements Constructionjlnspecb.:on Considerations • Permeable surfaces can be laid 'without cross-falls or longitudinal gradients. • The blocks should be lain level • They should not be used for storage of site materials, unless the surface is well protected from deposition of silt and other spillages. • The pavement should be constructed in a single operatioll, as one of the last items to be built, on a development site. Landscape development should be completed before pavement construction to avoid contamination by silt or soil from this source. • Surfaces draining to the pavement should be stabilized before construction of the pavement. • Inappropl'iate construction equipment should be kept away from the pavement to prevent damage to the sUlface, sub-base or sub-grade. Maintenance Requirements The maintenance requirements of a pervious surface should be reviewed at the time of design and should be clearly specified. Maintenance is required to prevent clogging of the pervious sUlface. The factors to be considered when defining maintenance requi~'ements must include: • Typeofuse •' • Ownership ~. ' • Level of trafficking • The local environment and any contributing catchments Studies in the UK have shown satisfactory operation of porous pavement systems with<;>ut maintenance for over 10 years and recent work by Imbe et al. at 9th ICUD, Portland, 2,002 describes systems operating for over 20 years without maintenance. However, performance under SUcll regimes could not be guaranteed, Table 1 shows typical recommended maintenance regimes: 4ofl0 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 • •• • Pervious Pavements 5D-20 ew Table 1 Typical Recommended Maintenance Regimes Activity Schedule ~ Minimize use of salt or grit for de-icing ~ Keep landscaped areas well maintained Ongoing • Prevent soil being washed onto pavement • Vacuum clean smiace using commercially available sweeping machines at the following times: -End of winter (April) 2/3 x per year -Mid-summer (July / August) -After Autumn leaf-fall (November) • Inspect outlets Annual ~ If routine cleaning does 110t restore infiltration rates, then reconstruction of part of the whole of a pervious smface may be required. • The surface area affected by hydraulic failure should be lifted for inspection of the internal materials to identify the location and As needed{infrequent)· eAi:ent of the blockage. Maximum 15-20-years ~ Smface materials should be lifted and replaced after brush cleaning. Geotextiles may need complete replacement . ~ Sub-smface layers may need cleaning and replacing. ~ Removed silts may need to be disposed of as controlled waste. Permeable pavements are up to 25 % cheaper (or at least no more expensive than the traditional forms of pavement construction), when an construction and drainage costs are tak~n into account. (Accepting that the porous asphalt itself is a more expensive surfacing~ the extra cost of which is offset by the savings in underground pipe work etc.) (Niemczynowicz, et aI., 1987) Table 1 gives US cost estimates for capital and maintenance costs of porous pavements (Landphair et al., 2000) Redeveloping Existing Installations Various jurisdictional stormwater management and mitigation plans (SUSMP 7 WQMP, etc~) define "redevelopment" in terms of amounts of additional impervious area, increases in gross floor area andlor exterior construction, and land disturbing activities with structural or impervious surfaces. The definition of" redevelopment" must be consulted to determine whether or not the requirements for new development apply to areas intended for redevelopment. If the definition applies, the steps outlined under "designing new installations" above should be followed . January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com SofiD SD-20 Pervious Pavements • Additional Information Cost Considerations • • Permeable pavements are up to 25 % cheaper (or at least no more expensive than the traditional forms of pavement construction), when all construction and drainage costs are taken into account. (Accepting that the porous asphalt itself is a more expensive suTIacing, the extra cost of which is offset by the savings in underground pipework etc.) (Niemczynowicz, et ru.., 1987) Table 2 gives US cost estimates for capital and maintenance costs of porous pavements (Landphair et ai, 2000) 6of10 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 i ,~. Pervious Pavements • Table 2 Engineer's Estimate for Porous Pavement Item lJaib .Pri~ ~5' QPIlt.l Year Ac:t'eWS Gtadil'lS sy $2-00 604 Paying SV $1~f.(1(} 212 IExeava1ion cy $3.00 201 iFIIt(1t' Fabric SY $1.15 700 $tQn$Fill Cy $1$.1l0 201 $;)n(i cy $1-00 i(tO $ightWf)1 EA $300.00 2 S~din9 IF $(tQ$ 644 Ch«;kOam cy $'$tl.(JO I) T()lal ~km Co_ CQn~.nCQ$t$.Amo~ fer 2,0 YOfli'S It~m 11mb Prif;e Cyd~f Qqnt.l Year Ac:t'I!W5 SW$8plng AC $250.00 G 1 Wa$'hing PC $2(10.00 6 1 In$P.eCtlon MH .$2tJ.* ~ $ ~Ctean At; $4$0.00 0.5 1 TotalAnnual ~C$ ExpeMt January 2003 Porous Pavtmtent 'rota) Qupt.t ToW Qqat.3 Aer~WS ACRWS. $1.,2{)8 1209 $2,41$ 1812 $4~i)2S 424 4IS,O$6 $36 $124 400 $1,451 6Q4 ~O$ 1401') $1,610 2(lOO $3,216 403 $6,44$ 604 $100 200 $1,.400 aoo $600 3 $000 4- $32 12$$ $G4 1&32 $0 0 $0 I) $1O,t05 $1&,_ $605 $9$$ Annual Maintenance Expense T~ Qupf.l To'" Q--. •• 3 A~I'e'WS Ael'l!W5 $1,qOI) :2 Q.OQ() 3 $1,500 2 $3.000 3 IiCD $ $100 $ $225 2 $450 3 $3,960 $7;192 california Stormwater BMP Handbook . New Development 8!1d Redevelopment www.cabmphandbooks.com 'n:Ital Qu;uat.4 Tc)llf A~I'e'WS $3,624 2419 $4,~a $U.OfU 84$ S,16;.12 $2.174 aO{l $2.902 $2.$00 2800 $3.220 $9.1)$4 806 $12.8$6 $2.100 400-$2,800 $1.200 i $2,,100 $97 2576 $129 $0 tl $0 $2~61t $«1,1$8 $t~t $2JlO8 Thtlil Qupt.4 1'.,llt A~re-WS $4,500 " $a.OOQ 14.500 4 $6.000 $100 li-$100 $$7$ 3.$ $376 $11,6$1 $1$,433 Qt,tallt.5 A(l'e\YS :a02li 1000 1(108 :aMt) 1(JOS eO!) ., :am 0 QttanMi . A4;:RWS (} I) () 5 • 50-20 Total $6,040 $20.140 $3,629- $4.140 $16.128 $3.0041 $2,1(ftl • $161 $0 .,m $2,49f Total $7,50(1 $1.590 $100 $1,125 $19,374) 7 of 10 c. SD-20 Pervious Pavements Other Resources Abbott C.L. and Comino-Mateos L. 2001. In situ performance monitoring of an infiltration drainage system andfield testing of current design procedures. Journal CIWEM, 15(3)~ PP.198- 202. Construction Industry Research and Information Association (CIRIA). 2002. Sow'ce Control llsing Constructed Pervious Surfaces C582, London, SWIP 3Ao. Construction Industry Research and Information Association (CIRIA). 2000. Sustainable urban drainage systems -design manual for Scotland and Northern Ireland Report C521~ London~ SWIP3AU. Construction Industry Research and Information Associatioh (CIRIA). 2000 C522 Sustainable urban drainage systems -design manualfor England and Wales .. London, SWIP 3AU. ConstI'uction IndustlY Research and Information Association (CIRJA). RP 448 Manual oj good practice for the design} construction and maintenance ofinfiltratioll drainage systemsfor stormwater runoff control and disposal, London, SWIP sAU. Dierkes C., Kuhlmann L., Kandasamy J. & Ange1is G. Pollution Retention Capability and Maintenance of Pel' me able Pavements. Proc 9th International Conference on Urban Drainage, Portland Oregon, September 2002. Hart P (2002) Permeable Paving as a Stormwater Source Control System. Paper presented at Scottish Hydraulics Study Group 14th Annual seminar, SUDS. 22 March 2002, Glasgow. Kobayashi M., 1999. Stonl1water runoff control in Nagoya City. Proc. 8 th Int. Conf. on Urban Storm Drainage, Sydney, Australia, PP.825-833. Landphair, H., McFalls, J., Thompson, D., 2000, Design Methods, Selection1 and Cost Effectiveness of Stonnwater Quality Structures, Texas Transportation Institute Research Report 1837-11 College Station) Texas. Legret M, Colandini V, Effects of a porous pavement with l'eservior sh'Ucutre on runoff water:water quality and the fate of heavy metals. Laboratoire Central Des Ponts et Chaussesss Macdonald K & Jefferies C. Pelformance Comparison of Porous Paved and Traditional Car. Parks. Proc. First National Conference on Sustainable Drainage Systems~ Coventry June 2001. Niemczynowicz J, Hogland W, 1987: Test of porous pavements performed in Lun~ Swede~ in Topics in Drainage Hydraulics and Hydrology. BC. Yen (Ed.), pub. Int. Assoc. For Hydraulic Research1 pp 19-80. Pratt C.J. SUSTAINABLE URBAN DRAINAGE - A Review of published material on the performance of various SUDS devices prepared for the UK Environment Agency. Coventry University, UK December 2001. Pratt C.J., 1995. Infiltration drainage -case studies of UK practice. Project Report 80f 10 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 Pervious Pavements SD-20 (. 22,Construction Industry Research and Information Association~ London, SWIP gAU; also known as National Rivers Authority R&D Note 485 Pratt. C. J., 1990. Permeable Pavements for Stormwater Quality Enhancement. In: Urban Stormwater Quality Enhancement -Source Control, retrofitting and combined sewer teclmology, Ed. H.C. Torno, ASCE, ISBN 0872627594, pp. 131-155 Raimbault G., 1997 French Developments in Reservoir Structures Sustainable water resources I the 21st century. Malmo Sweden SchlUter W. & Jefferies C. Monitoring the outflow from a P01'OUS Car Park Froc. First National Conference on Sustainable Drainage Systems, Coventry June 2001. Wlld, T.e., Jefferies, C., and D'Arcy, RJ. SUDS in Scotland -the Scottish SUDS da.tabase Report No SR( 02)09 Scotland and Northern Ireland Forumfor Environmental Research;, Edinburgh. In preparation August 2002. c. " January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com ·90flO (. 5D-20 Pervious Pavements 10 of 10 ~ :6-... -! . , , <, "i' t> ~ } t 1-. , {It) Pervfoul! pavement ulled tOfliitil.nuallllll {b) Pervious pavement used fot inftlll1tt!on Schematics of a Pervious Pavement System california storm water BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 Bioretention Description , The bioretention best management practice (BMP) functions 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, poneling area, organic layer or mulch layer, planting soil, and plants. The runoffs velocity is reduced by passing over or through buffer strip and subsequently distributed evenly along a poneling area. Exfiltration of the stored water in the bioretention area planting soil into the underlying soils occurs over a period of days. California Experience None documented. Bioretention has been used as a stormwater 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 storm water 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. limitations • The bioretention BMF is not recommended for areas with slopes greater than 20% or where mature tree removal would January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com T'C-32 Design Considerations' • Soil for Infiltration • Tributary Area • Slope • Aesthetics • Environmental Side-effects Targeted Constituents ~- ""0 Sediment -o 'Nutrients • o Trash -o Metals -o Bacteria -o Oil and Grease - o Organics - leglitnd (Removal Effectiveness) ., • LoW -High .. Medium CAIJl'\;)~MJ\ Sf;)Jo.lWA tHI Qth\trf~t ~<\S"5(f.({f.."tt~~':\. lof8 (I.. 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 rmioff. • In areas where the native soil permeability is less than 0.5 in/hI' 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 completelywithln 72 hours. • Approximately 1 tree or slullb per 50 ft2 ofbioretention area should be included. • Cover area with about 3 inches of mulch. Construction/Inspection Considerations Bioretention aJ.'ea should not be established until contributing watershed is stahilized. 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 sUliaces. 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 covel', 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, witll woody plants locking up these nutrients through the seasons. Microbial activity within the soil also contributes to the removal of nitrogen and organic matter. Nitrogen is removed by nitrifying and denitrifying 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 20fB California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com january 2003 Bioretention TC-32 \e aerated. Sedimentation occurs in the swale or ponding area as the velocity slows and solids fall out of suspension. The removal effectiveness ofbioretention has been studied during field and laboratory studies conducted by the University of Maryland (Davis et al, 1998). During these experiments, synthetic storm water runoff was pumped through several laboratory and field bioretention areas to simulate typical storm events in Prince George's 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,Zn1 Pb) 93-98% TKN 68-80% Total Suspended Solids 90% Organics 90% BacteIia 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 al, 1998). The microbial activity and plant uptake occurring in the bioretention area win likely result in higher removal rates than those determined for infiltration BMPs. Siting Criteria Bioretention BMPs are generally used to treat stormwater from impervious surfaces at commercial, residential, and industrial areas (EP.A, 1999). Implementation ofbioretention 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 illlets 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 effectively minimize sediment loading in the treatment area, bioretention only should be used in stabilized drainage areas. January 2003 California stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 30f8 TC-32 Bioretentio.n (. Additional Design Guidelines The layout of the bioretentiol1 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 backfilled and used as the planting soil, thus eliminating the cost of importing planting soil The use ofbioretention may not be feasible given an unstable sun-ounding soil stratum, soils with clay content greater than 25 percent, a site \1\~th 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 oll-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 lllay 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 bioretentioll 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 minimunl 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 natwal 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 are,as in urban settings typically are unable to tolerate. The preferred width is 25 feet (7.6 meters), with a length of twice the width. Essentially, any facilities wider thap 20 f~et (6.1 meters) &.hould 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 72 hours. A restriction on the type of plants that can be used may be necessru:y due to some plants' water intolerance. Furthermore, if water is left standing for longer than 72 hours mosquitoes and other insects may strut to breed. TIle 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 loarns, loamy sands, or loams. The pH of the soil should range between 5.5 and 6~5, where pollutants such as organic niu'ogen and phosphorus can be adsorbed by the soil and microbial activity can tlomish. Additional requirements for the planting soil include a 1.5 to 3 percent organic content and a maximum 500 ppm concentration of soluble salts. 4of8 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com ]qnuary 2003 • Bioretention TC-32 Soil tests should be performed for evelY 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 (10.1 centimeters) deeper than the bottom of the largest root ball and 4 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 recOlmnended 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 (1000 per acre). For instance, a 15 foot (4.6 meter) by 40 foot (12.2 meter) bioretention area (600 square feet or 55.75 square metel's) would reqUire 14 trees and shrubs. The shrub-to-tree ratio should be 2:1 to 3:1. 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 my conditions should be used ip, the'bioretention area. The designer should assess aesthetics, site layout, and maintenance requirements when selecting plant species. Adjacent nOll-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. Regiollallandscaping 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 th~ 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 damagingfl.ows if they are placed away from the path oftlIe 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 ofthe trees and Slll'Ubs, the ground cover and/or mulch shoUld be established. Ground cover such as grasses or legumes can be planted at the beginning of fue growing season. Mulch should be placed immediately after trees and shrubs are planted. Two to 3 inches (5 to 7.6 em) 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 New Development and Redevelopment www.cabmphandbooks.com 50f8 TC-32 Bioretenti'on (e 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 (EP.A, 1999). Diseased vegetation should be treated as needed using preventative and low-toxic measUres to the extent 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 meaSID'es to restate 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 110t 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 evelY two to three years, although spot mulching may be sufficient when there are random void areas. Mulch replacement should be done prior to the start of the wet season. New Jersey's Deprutment of Environmental Protection states in their bioretention systems standards that accumulated sediment and debris removal (especially at the inflow point) will normally be the prinlary maintenance function. Other potential tasks include replacement of dead vegetation, soil pH regulation, erosion repair at inflow points, mulch replenishment, unclogging the underdrain, and repaiIing 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 witlrin 5-10 years of construction (LID, 2000). ,Cost Conso'uction Cost Construction cost estimates for a bioretention area are slightly greater than those for the required landscaping for a new development (EPA, 1999). A general rule of thUlllb (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 rrulge between $10 to $40 per square foot, based on the need for control structures, CID'bing, storm drains and underdrains. Retrofitting a site typically costs more, averaging $6,500 per bioretention area. Th~ higher costs are attributed to the demolition of existing concrete, asphalt, and existing stI'Uctill'es 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 $111,600. In any bioretention ru'ea 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 treatm.ent (due to the increased llumber 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. 60f8 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 Bioretention TC-32 Perhaps of most importance, however, the cost savings compared to the use of traditional structllrhl storlllwater conveyance systems makes bioretention areas quite attractive financially. For example, the use ofbioretention 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 Oliginally planned (Rappahanock,). 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 b~ comparable to those of typical landscaping required for a site. Costs beyqnd the normal landscaping fees will include the cost for testing the soils and may include costs for a sand bed and planting $oil. 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, ArizQna. Davis, A.P., Shokolihian, M., Sharma, H. and Minami, C., "Laboratory Study of Biological Retention (Bioretention) for Urban Stormwater Management," Water Environ. Res.; 73(1), 5-14 (2001). Davis, AP., Shokouhian, M., Sharma, H., Minami, C., and Wmogradoff, D. "Water Quality Improvement through Bioretention: Lead, Copper, and Zinc1" Water Environ. Res., accepted for publication, August 2002. - Kim, H., Seagren, E.A., and Davis, A.P., "Engineered Bioretention for Removal of Nittate from Stormwater Runoff," WEFTEC 2000 Conference Proceedings on CDROM Research Symposillm~ Nitrogen_ Removal, Session 19, Anaheim CA, October 2000. Hsieh, C.-h. and Davis, A.P. "Engineering Bioretention for Treatment of Urban Stonllwater Runoff," Watersheds 2002, Proceedings on CDROM Research Symposiwn, Session 15, Ft. Lauderdale, FL, Feb. 2002. Prince GeOl'ge's County Department of Environmental Resources (PGDER), 1993. Design Manual for Use of Bioretenflon in Stormwater Management. Division of EnvirOnniental Management, Watershed Protection Branch. Landover, MD. U.s. EPA Office of Water, 1999. Stormwater Technology Fact Sheet: Bioretention. EPA 832-F- 99-012. Weinstein, N. Davis, AP. and Veeramachaneni, R. "Low Impact Development (UD) Stormwater Management Approach for the Control of Diffuse Pollution from Urban Roadways," 5th International Conference DiffuseJNonpoint Pollution and Watershed Management Proceedings, C.S. Melching and Emre Alp, Eds. 2001 International Water Association January 2003 Californfa Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 7of8 TC-32 6" ·PIPE1NS"GRAVEl JACKeT Schematic of a Bioretention Facility (MDE, 2000) SofS California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com Bioretenti·on STONE DIAPHRA~M GRAVEI.CURTAIN DRAIN OVERFLOW PLAN VIEW January 2003 Section 6 Long-term Maintenance of BMPs 6.1 Introduction The long-term performance of BMPs hinges on ongoing and proper maintenance. In order for this to occur detailed maintenance plans are needed that include specific maintenance activities and frequencies for each type of BMP. In addition, these should include indicators for assessing when "as needed" maintenance activities are required. The fact sheets included in this volume contain the basic information needed to develop these maintenance plans, but municipalities and other regulatory agencies also need to identify the responsible party and potentially to address funding requirem~nts. The following discussion is based primarily on data developed by Horner et al. (1994) and information available at http://www.stormwatercenter.net/ 6.2 Critical Regulatory Components Critical regulatory components identified by Horner et al. (1994) include: • Regulations should officially designate a responsible party, frequently the development site owner, to have ultimate responsibility for the continued maintenance of stormwater facilities. This official designation provides the opportunity for appropriate preparation and budgeting prior to actually assuming responsibilities. It also facilitates enforcement or other legal remedies necessary to address compliance or performance problems once the facility has been constructed. • Regulations should clearly state the inspection and maintenance requirements. Inspection and maintenance requirements should also comply with all applicable statutes and be based on the needs and priorities of the individual measure· or facil.ity. A olear presentation will help owners and builders comply and inspectors enforce requirements. • Regulations should contain comprehensive requirements for documenting and detailing maintenance. A facility operation and maintenance manual should be prepared containing accurate and comprehensive drawings or plans of the completed facility and detailed descriptions and schedules of inspection and maintenance. '-• The regulations should delineate the procedure for maintenance noncompliance. This process should provide informal, discretionary measures to deal with periodic, inadvertent noncompliance and formal and severe measures to address chronic noncompliance or performance problems. In either case, the primary goal of enforcement is to maintain an effective BMP -the enforcement action should not become an end in itself. • Regulations should also address the possibility of total default by the owner or builder by providing a way to complete construction and continue maintenance. For e:x:ample, the public might assume maintenance responsibility. If so, the designated public agency must be alerted and possess the necessary staffing, equipment, expertise, and funding t<;> assume this responsibility. Default can be addressed through bonds and other performance January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 6-1 Section 6 Long-term Maintenance of BMPs guarantees obtained before the project is approved and construction begins. These bonds can then be used to fund the necessary maintenance activities. • The regulations must recognize that adequate and secure funding is needed for facility inspection and maintenance and provide for such funding. 6.3 Enforcement Options A public agency will sometimes need to compel those responsible for facility construction or maintenance to fulfill their obligations. Therefore, the maintenance program must have enforcement options for quick corrective action. Rather than a single enforcement measure, the program should have a variety of techniques, each with its own degree of formality and legal weight. The inspection program should provide for nonconforming performance and even default, and contain suitable means to address all stag~s. Prior to receiving construction approval, the developer or builder can be forced to provide performance guarantees. The public agency overseeing the construction can use these guarantees, usually a performance bond or other surety in an amount equal to some fraction of the facility's construction cost, to fund maintenance activities. Enforcement of maintenance requirements can be accomplished through a stormwater maintenance agreement, which is a formal contract between a local government and a property owner designed to guarantee that specific maintenance functions are performed in exchange for permission to develop that property (http://www.stormwatercenter.net/). Local governments benefit from these agreements in that responsibility for regular maintenance of the BMPs can be placed upon the property owner or other legally recognized party, allowing agency staff more time for plan review and inspection. 6.4 Maintenance Agreements Maintenance agreements can be an effective tool for ensuring long-term maintenance of on-si~e BMPs. The most important aspect of creating these maintenance agreements is to clearly define the responsibilities of each party entering into the agreement. Basic language that should be incorporated into an agreement includes the following: 1. Performance of Routine Maintenance Local governments often find it easier to have a property owner perform all maintenance according to the requirements of a Design Manual. Other communities require that property owners do aesthetic maintenance (Le., mowing, vegetation removal)'and implement pollution prevention plans, but elect to perform structural maintenance and sediment removal themselves. 2. Maintenance Schedules Maintenance requirements may vary, but usually governments require that all BMP owners perform at least an annual inspection and document the maintenance and repairs performed. An annual report must then be submitted to the government, who may then choose to perform an inspection of the facility. 6-2 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 Section 6 Long~term Maintenance· of BMPs 3. Inspection Requirements Local governments may obligate themselves to perform an annual inspection of a BMP, or may choose to inspect when deemed necessary instead. Local governments may also wish to include language allowing maintenance requirements to be increased if deemed necessary to ensure proper functioning of the BMP. 4. Access to BMPs . The agreement should grant permission to a local government or its authorized agent to enter onto property to inspect BMPs. If deficiencies are noted, the government should then provide a copy of the inspection report to the property owner and provide a timeline for repair of these deficiencies. 5. Failure to Maintain In the maintenance agreement, the government should repeat the steps available for addressing. a failure to maintain situation. Language allowing access to BMPs cited as not properly maintained is essential, along with the right to charge any costs for repairs back to the property .. ~. owner. The government may wish to include deadlines for repayment of maintenance costs, and provide for liens against property up to the cost of the maintenance plus interest. 6. Recording Of The Maintenance Agreement An important aspect to the recording ofthe maintenance agreement is that the agreement be recorded into local deed records. This helps ensure that the maintenance agreement is bound to the property in perpetuity. Finally, some communities elect to include easement requirements into their maintenance agreements. While easement agreements are often secured through a separate legal agreement, recording public access easements for maintenance in a maintenance agreement reinfor:ces a local government's right to enter and inspect a BMP. Examples of maintenance agreements include several available on the web at: http://www.stormwatercenter.net/ 6.5 Public Funding Sources If local agencies are willing to assume responsibility for stormwater BMPs, it is essential to identify the long-term funding sources. Several of these are described below: General Tax Revenues Tax revenues are an obvious source of funding, particularly for the long-term inspection and maintenance of existing runoff and drainage facilities. The benefits and protection to the public from continued safe and effective operation of the facility justifies using revenues from general funds. To use tax revenues, particularly from a general fund, the inspection and maintenance program must annually compete with all other programs included in the government's annual operating budget. This inconsistent and unreliable funding makes securing a long-term financial January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 6~3 ~. Section 6 Long-term Maintenance of BMPs commitment to inspection and maintenance difficult and subject to political pressures. Nevertheless, tax revenues remain a popular funding source because the collection and disbursement system is already in place and familiar. Utility Charges Using utility charges to fund inspection and maintenance is a somewhat recent application-of an already established financing technique. In addition, several municipalities and counties throughout the country have runoff management, drainage, and flood control authorities or districts to provide residents with runoff related services. Using utility ch~rge financing has several advantages. By addressing only runoff needs and benefits, utility funding avoids competing with other programs an:d needs. Utility funding also demonstrates a direct link between the funding and the services it proVides. This approach can require an entirely new operating system and organization that needs legal authorization to exi~t, operate, and assess charges~ The effort requ~ed to create such an entity can deter many, although the continued success of established authorities and growth of new ones have done much to allay concerns over the effort required. In a runoff utility, the user charges are often based on the need for serVices rather :than the benefits derived from them. While charges are based on actual costs to inspect and maintain runoff facilities and measures within the service area, the assessed rate structure should relate to site characteri~tics. These include property area size, extent of impervious coverage, and other factors with a direct and demonstrable effect on runoff. To be fair, the rate structure should also . remain simple and understandable to the ratepayer. To finance the stormwater utility in Prince William County, Virginia, residential and nonresidential owners of developed property pay based on the amount of impervious area (rooftops, paved areas, etc.) on their property. Residents pay $10.38 billed twice a year ($20.76 total annual fee) for detached singe-family homes. Town home and condominium oWners will pay $7.785 billed twice a year ($15.57 total annual fee). Nonresidential property owners pay $0.84 per 1,000 ft2 of impervious area per month. Fee adjustments or credits may be available if a stormwater management system is already in place. The fee will be on the real estate bills. Fees for the stormwater utility in Austin, Texas are higher with residential users billed $5.79jmo, while commercial users pay $94.62jmoj acre of impervious cover. These fees cover not only maintenance of existing BMPs, but also capital improvement projects related to the drainage infrastructure .. Permit Fees Collecting permit fees to finance runoff inspection and maintenance is a long standing funding procedure. Most governmental entities local, county, and state can establish and collect fees and other charges to obtain operating funds for programs and services. Many inspection servi,ces, most notably the construction inspection of both ESC measures and permanent drainage and runoff management facilities, are financed at least in part through fees collected by permitting agencies. Unlike taxes or some utility charges, inspection costs are borne by those who need them; 6-4 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com January 2003 Section 6 Long-term Maintenance of BMPs The permit fee collection program should have a demonstrable link to the runoff management or drainage systems. The public agency should demonstrate a direct link between the permit fees collected and the permitted project one method is using dedicated accounts for individual projects and facilities. Finally, the rate structure should reflect site characteristics such as area size or imperviousness that directly relate to the measure or facility by affecting runoff or erosion. Dedicated Contributions Public agencies at times have used developer contributions to fund long-term facility maintenance. This approach is particularly appropriate in single-family residential subdivisions, where numerous individual property owners served by a single runoff facility can result in confusion over who has maintenance responsibility. . The exact funding technique depends on many factors, including community attitude and knowledge, economic and political viability, and program needs and costs. Some techniques, including permit fees and dedicated contributions, may be more appropriate for short-term activities, such as construction inspection. Others utility charges and specialized tax revenues may apply to all phases of an inspection and maintenance program but require considerable effort and special legal authorization to operate. January 2003 California Stormwater BMP Handbook New Development and Redevelopment www.cabmphandbooks.com 6-5 STORM WATER MANAGEMENT PLAN ROBERTSON RANCH P.A. 22 • Section 8.0 • '--. CONSTRUCTION STORM WATER BMPS Based on the size of the project site the City of Carlsbad will require that a separate document be prepared. If the project site is less then one acre then the project will require a Water Pollution Control Plan. If the project site is one acre of more then a Storm Water Pollution Prevention Plan will be required. Since the project has a disturbed area more than one acre a SWPPP will be required. Construction BMPs..and any applicable design standards can be found in this separate document. IMPLEMENTATION & MAINTENANCE REQIDREMENTS Once the City of Carlsbad approves all the project BMPs, the applicants and the City Project Managers must ensure proper implementation of the selected BMPs. ill order to accomplish effective implementation and maintenance the City of Carlsbad may require that some sort of Permanent BMP Maintenance Agreement be entered into. This WIll be at the discretion of the City of Carlsbad Staff. ill the event that a Permanent BMP Maintenance Agreement is required by City Staff, the following items will need to be . addressed: 1. OPERATION AND MAINTENANCE PLAN The applicant shall include and Operation & Maintenance Plan (O&M), prepared satisfactory to the City, with the approved maintenance agreement, which describes the designated responsible party to mange the storm water BMPs, employee's training program and duties, operating schedule, maintenance frequency, routine service schedule, specific maintenance activities (including maintenance of storm water conveyance system stamps), copies of resource agency permits, and any other necessary activities. At a minimum, maintenance , agreements shall require the applicant to provide inspection and servicing of all permanent treatment BMPs on an annual basis. The project proponent or City- approved maintenance entity shall complete and maintain O&M forms to document all maintenance requirements. Parties responsible for the O&M plan shall retain records for at least 5 years. These documents shall be made available to the City inspector upon request at any time.. ill addition, CASQA Section 6: Long-term Maintenance of BMPs shall be utilized as guide. A copy of this is provided in Appendix H. 2. ACCESS EASEMENT/AGREEMENT If a permanent BMP requires access for maintenance, ,as part of the O&M plan, the applicant shall execute and record an access easement or agreement that shall be binding on the under lying land throughout the life of the project in favor of the party responsible for maintenance, until such time that the permanent treatment BMP requiring access for maintenance is removed or replaced. The City shall approve any changes to the permanent BMPs, O&M plans, or access agreements . The agreement shall include a provision that gives the City the right, but not the -1 - • STORM WATER MANAGEMENT PLAN ROBERTSON RANCH P.A. 22 obligation to perform the maintenance. The party responsible for BMP maintenance will pay the City for any and all costs uncured by the City for maintaining any BMPs. The agreement will provide a cost recovery provision in favor of the City satisfactory to the City Attorney. -2 - STORM WATER MANAGEMENT PLAN ROBERTSON RANCH PA 22 • Section 9.0 \' '. t Please see drainage study titled "Drainage Study for Robertson RanchPA 22" by O'Day Consultants date November 5, 2009 on file. I -----I -~. \ \ ~4 ~.<\ \ / .-1\ . \ \ I I \ \ \ \ \ Lor 7 PER MAp 15808 NOTE II £LEC TRDMC DA TA RLES ARE FOR REFERENCE ONL Y AND ARE NDT TO. BE USED FOR HDRIZDNTAL DR VERTlCAL SURVEY CDNTRDL ©2009 O'Oay Consultants, Inc. 98-080ciil:9}, 0.R. \ \ SIl8-8ASlN AIi'£4 AI 0.45 AC A2 0.62 AC Bl 0.59 AC 82 0.21 AC B3 0.29 AC 84 0.17 AC 85 0.17 AC B6 0.44 AC 87 0.09 AC B8 0.57 AC 89 0.82 AC ,. 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JOB NO.: 011014 S 2710 LOKER AVENUE WEST CML ENGINEERING ENGINEER OF WORK SUITE 100 CARLSBAD, CAUFORNIA 92010 PlANNING 760-931 -7700 PROCESSING DATE: Fax: 760-931-8680 ODAYIIODAYCONSULTANTS.COM SURVEYING GEORGE O'DAY RCE: 32014 G: \011014\0114yswmp-a.dwg Feb 09, 2010 4: 40pm Xrefs: 0114BMAP; 0114BSTR; 01 14BUTL; 01 14BGrd-cc7; 011 4tp-g-cc7; 01147utl; 0114AMAP; 0114fema; 0114Ygrd-a; 0114ymap