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Home My WebLink AboutCT 14-11; CARLSBAD BOAT CLUB & RESORT; WATER QUALITY TECHNICAL REPORT; 2006-06-01WATER QUALITY TECHNICAL REPORT CARLSBAD BOAT CLUB 4509 Adams Street Carlsbad, CA EXCEL ENGINEERING 440 State Place Escondido, CA 92029 (760) 745-8118 RCE #45629 Exp. 12/31/06 For: Carlsbad Boat Club 4509 Adams Street Carlsbad, CA 92008 June,2006 DEC 1 9 20\4 JIii .. -... ,. .. JIii ,. 11111 ,. -,. 1111 ,. -.. .. ,. .. f1IIII JIii .. .. ,. Ill ,. 11a ,. .. .. I ... TABLE OF CONTENTS 1. INTRODUCTION .............................................................................................................. 1 2. PROJECT DESCRIPTION ....................................................................... 1 Topography and Land Use .................................................................... 1 Watershed ..................................................................................... 2 Post-Construction Storm Water ............................................................ .3 Conditions of Concern ....................................................................... 4 3. POLLUTANTS AND CONDITIONS OF CONCERN .......................................... 5 Treatment' Control BMP Selection Matrix ............................................... .5 Anticipated and Potential Pollutants Table ....... : ........................................ 6 Drainage Pattern ............................................................................... 8 Water Qualiy ......................... -.......................................................... 8 Environmental Analysis, Hydrology/Water Quality ..................................... 8 Concerns of Receiving waters .............................................................. 9 Beneficial Uses .............................................................................. 10 Impaired Body of Water .................................................................... 10 4. STORMWATERBESTMANAGEMENTPRACTICES .................................... 10 Site Design BMP's ......................................................................... 11 Source Control BMP's ...................................................................... 11 Project Specific BMP's ........................................................... : ......... 12 S. PROJECT BMP PLAN IMPLEMENTATION ................................................ 12 Recommended Post-Construction BMP Plan Option ................................. 12 Operation and Maintenance Plans ........................................................ 13 Maintenance Responsibility .................................. ; ............................ 13 ,. - 41111 -,. .. ... .. 11111 .,., .. .. -.. ,. .. .. .. .. .. APPENDICES 1. Storm Water Requirements Applicability Checklist 2. Vicinity Map 3. Site Control BMP's 4. Source Control BMP's 5. Drainage Study 7. Drainage Map ... Ill .. .. .. --.. .. .. - JIii -.. Ill 'JIii .. .. JIil .. ,. .. JIii .. .. .. ,. i ... 1. INTRODUCTION This Water Quality Technical Report (WQTR) was prepared to recommended project Best Management Practice (BMP) options that satisfy the requirements identified in the following documents: City of Carlsbad -Storm Water Standards Manual; County of San Diego Watershed Protection, Storm Water Management and Discharge Control Ordinance (County Ordinance); Standard Specifications for Public Worlcs Construction; NPDES General Permit for Storm Water Discharges Associated with Construction Activity; and San Diego County NPDES Storm Water Pemiit. Specifically, this report includes the following: Project description and location with respect to the Water Quality Control Plan for the Carlsbad Boat Club. BMP design criteria and water quality treatment; Recommended BMP options for the project; BMP device information for the recommended BMP options; Operation, maintenance, and funding for the recommended BMPs; 2. PROJECT DESCRIPTION The existing site is approximately 1.0 acre in size, with approximately 0.10 acre being within the tidal zone. The existing residence/boat club structure is to be removed. In its place will be a new 3 story boat club and time share with under ground parking for vehicles and small boats. Three floors will be visible from the Lagoon and only one floor will be visible from Adams Street. The site will be accessed from Adams Street via a driveway, which starts out at 5% and at its steepest point reaches 19%. • I • The land currently has a large residential structure which is being used for boat club purposes. The majority of the site drains southerly into the Agua Hedionda Lagoon without any treatment. There is a little storm runoff that flows onto the property from the west and east. This runoff will not be allowed to cross onto the subject property. It will not be diverted and will reach its final destination, which is the Agua Hedionda Lagoon. · Site looking north Toe proposed storm drain for this project will tie into a proposed detention facility consisting of four 27-inch CMP's , which wiHprovide 314 cubic feet of storage for the proposed development. -2 - Site looking northeast Runoff will exit the site from three points. The first point is from the boat ramp located on the east side of the property. This outlet will discharge the runoff-generated from the pedestrian walkways and the boat ramp area. The second point will be from the location of the club house and boat dock area, the majority of this area is sand. The third area is the main storm drain system which will detain and treated runoff before discharge into the Agua Hedionda Lagoon. This storm drain services the rooftops, hardscape, and landscaped areas .. When the site is fully developed with structures, landscaping and sidewalks. There will be an increase in the runoff generated. However, since the difference in impervious surfaces only increases from 57% to 63% the differential run-off is minor. Pre construction runoff was calculated to be 3.94 cfs. The post construction runoff was calculated to be 4.25 cfs; an approximate 0.3 lcfs increase in runoff. Additionally the site will no longer be discharging untreated run-off into the Agua Hedionda Lagoon. The onsite soil consists of an upper loose and compressible alluvium of silty, gravelly sand. This soil type is categorized as moderately well drained and the run-off is low and erosion hazard is slight. There are no rock outcroppings on site. -3 - Looking east along the lagoon. All runoff from this project will ultimately proceed southerly and into the Agua Hedionda Lagoon. According to the 1998 303d lis(published by the San Diego Regional Water Quality Control Board, the Agua Hedionda Lagoon is an "impaired water body''. Pre-and post-construction BMPs are mentioned in this report for this project and will be detailed in the project's future SWPPP. Currently in City of Carlsbad runoff from building roofs, driveways, patios, sidewalks, streets, and alleys, etc. is characterized as low, intermittent, seasonal flow and poor water quality. Water quality is degraded by urban runoff. The greatest, and generally only, flow occurs during the winter months. · · -4- .. .. .. ,. - JIii -.. .. ,. - -.. .. -... .. .. .. .. .. .. ... : ,. .. .. ... ... -.. ' 3. POLLUTANTS AND CONDITIONS OF CONCERN As shown on the "Storm Water Requirements Application Checklist" (Appendix 1) this project is subject to the "Priority Project Permanent Storm Water BMP Requirements." Per table 2 (Page 7 of this report), this project falls into the following project categories: 1) Attached Residential Development 2) Restaurants 3) Hillside Development over 5,000 square feet The anticipated and potential pollutants generated by this type of development include: • Sediment • Nutrients • Trash and debris • Oil, Grease and Heavy Metals • Oxygen demanding substances • Bacteria and Viruses • Pesticides Per the 303D list, the Agua Hedionda Lagoon is impaired by bacteria and sedimentation/siltation . Therefore, these will be a pollutant of primary concern, with the remaining pollutants being of secondary concern . A review of table 4 (next page), "Structural Treatment Control BMP Selection Matrix", indicates infiltration basins and filtration are the only treatment controls BMP for bacteria and Viruses to achieve a high to medium removal efficiency . For this project our primary treatment BMP will be filtration in regards to our pollutant of primary concern. This offers a medium removal efficiency for sediments. This BMP also treats all secondary pollutants with a high to medium removal rating . There will be two variations of filtration used on this project; one will be the sedimentation time used in the proposed detention facility and the other will be a gravel and sand strip on the west side of the driveway (see detail below) . -. -.· .• .•..... '. •·'.· .. · .· .. _·:. :, ·. . . The sand filter captures and treats the design runoff in a two part system, first a straining area, then a filter bed. The straining area collects large sediment and prevents these objects from clogging the filter bed. The sand bed then strains the water, removing soluble and particulate pollutants. The treated water is conveyed through the perforated pipes and into an underground detention facility which allows more filtration and sedimentation before final controlled discharge into the Agua Hedionda Lagoon .5. .. ... -.. ,,. -.. ... .. ,. .. .. .. ... ,,. ... .. .. .. , .. .. .. .. .. .. ... .. Table 4. Treatment Control BMP Selection Matrix Pollutant of Treatment Control BMP Categories Concern Biofilters Detention Infiltration Wet Ponds or Drainage Filtration Hydrodynamic Basins Basins<1> Wetlands Inserts Separator Systems<1> Sediment M H H H L H M Nutrients L M M M L M L Heavy Metals M M M H L H L Organic u u u u L M L Compounds Trash and Debris L ·H u u M H M Oxygen Demanding L M M M L M L Substances Bacteria u u H u L M L Oil and Grease M M u u L H L Pesticides u u u u L u L (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 Sources: Guidance Specifying Management Measures for Sources ofNonpoint Pollution in Coastal Waters (1993), National Stormwater Best Management Practices Database (200 l ), and Guide for BMP Selection in Urban Developed Areas (200 l ) . -6- .. .. ... 11111 ,,. -.. .. .. .. .. .. .. .. - ,,. .. ... 1111 .. .. .. ... .. Table 2. Anticipated and Potential Pollutants Generated by Land Use Type General Pollutant Categories Priority Project Heavy Organic Trash Oxygen Oil and Bacteria Categories Sediments Nutrients Metals Compounds and Demanding Grease and Pesticides Debris Substances Viruses Detached Residential X X X X X X X Development Attached Residential X X X p(l) p(2) p X Development Commercial Development> 100, p(l) p(I) p(2) X p(S) X p(3) p(S) 000 ft.2 Automotive Repair X X(4)(S) X X Shops Restaurants X X X X Hillside Development X X X X X X >5,000 ft.2 Parking Lots p(I) p(l) X X p(l) X p(I) Streets, Highways X p(l) ·x x<4J X p(SJ X and Freeways 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 ifland use involves food or animal waste products . (4) Including petroleum hydrocarbons. (5) Including solvents . ·7- .. ... ... ... - ... ... .. ... ... .. .. ,,. ... -,. ... ... -.. .. .. 11111 .. ... .. .. Drainage Pattern Runoff from the site would ultimately flow into the Agua Hedionda Lagoon. Therefore, the proposed project would not result in an alteration of the course or flow ofrain waters, nor is it anticipated exposing people or property to water-related hazards, such as flooding. Impacts associated with flood hazards would not be significant. Impacts of the proposed Boat Club project on local water resources may include an overall reduction in polluted urban runoff into the Agua Hedionda Lagoon. Approximately 57 percent of the site is currently covered by impervious surfaces. The site will become approximately 63 impervious once developed. Impacts associated with surface runoff would be less than significant. Drainage patterns within the project area would not be modified; therefore, no significant impact would occur . Water Quality The quality of water coming from the proposed new Boat Club site would be enhanced when compared to the use of the existing Boat Club site. Consistent with the Regional Water Quality Control Board's (RWQCB) San Diego Urban Runoff Municipal Permit, the proposed project would ensure that appropriate measures to control pollutants from the new development would occur. Such measures include, but would not be limited to, the incorporation of runoff collection and treatment such as filter strips and on.;site detention prior to its release from the site. The use of these devices would reduce the amount of polluted or contaminated water released into the Agua Hedionda Lagoon. Environmental Analysis, Hydrology/Water Quality Currently there are no mechanical devices on site to process the runoff, which result in runoff going straight into the Agua Hedionda Lagoon without preliminary treatment. Based on this discussion, impacts associated with water quality for the life of the proposed project would be less . than significant. -8- .. .. -1111 -.. .. .. -.. .. -.... .. -.. .. .. ... .. -.. .. .. ... .. .. .. .. .. Concerns in Receiving Waters The Carlsbad Boat Club project is located adjacent to the Agua Hedionda Lagoon. According to the 1998 303d list published by the Regional Water Quality Control Board, the Batiquitos Lagoon (Carlsbad Water Shed HU 904) is an "impaired water body." The sections below provide the beneficial uses and identification of impaired water bodies within the project's hydrologic area. Beneficial Uses The beneficial uses of the inland surface waters and the groundwater basins inust not be threatened by the project. Tables 1 and 2 list the beneficial uses for the surface waters and groundwater within the project's hydrologic area TABLE 1. BENEFICIAL USES FOR INLAND SURFACE WATERS · TABLE 2. BENEFICIAL USES FOR GROUNDWATER Carlsbad Watershed (HU 904) Notes for Tables 1 and 2: Ex: Excepted from Municipal E: Existing beneficial use P: proposed beneficial use N: Not a beneficial use IND -Industrial Services Supply: includes use of water for industrial activities that do not depend primarily on water quality including, but not limited to, mining, cooling water supply, hydraulic conveyance, gravel washing, fire protection, or oil well re-pressurization . NA V -Navigation: Includes uses of water for shipping, travel, or other transportation by private, military, or commercial vessels. RECl -Contact Recreation: Includes use of water for recreational activities involving body contact with water where ingestion of water is reasonably possible. These uses include, but are not limited to, swimming, wading, water-skiing, skin and SCUBA diving, surfing, white water activities, fishing, or use of natural hot springs. · -9- .. ... .... .... ,,.. ... ... .. .... -.. .. .. .. 1111 ,,. ... , .. REC2 -Non-Contact Recreation: Includes use of water for recreation involving proximity to water, but not normally involving body contact with water where ingestion of water is reasonably possible. These uses include, but are not limited to, picnicking, sunbathing, hiking, camping, boating, tide pool and marine life study, hunting, sightseeing, or aesthetic enjoyment in conjunction with the above activities . COMM -Commercial and Sport Fishing: Includes the uses of water for commercial or recreational collection offish, shellfish, or other organisms including, but not limited to, uses involving organisms intended for human consumption or bait purposes. BIOL -Preservation of Biological Habitats of Special Significance: Includes uses of water that support designated areas or habitats, such as established refuges, parks, sanctuaries, ecological reserves, or Areas of Special Biological Significance (ASBS), where the preservation or enhancement of natural resources requires special protection . EST -Estuarine Habitat: Includes uses of water that support estuarine ecosystems including, but.not limited to, preservation or enhancement of estuarine habitats, vegetation, fish, shellfish, or wildlife ( e.g., estuarine mammals, waterfowl, shorebirds) . WILD -Wildlife Habitat: Includes uses of water that support terrestrial ecosystems including but not limited to, preservation and enhancement of terrestrial habitats, vegetation, wildlife, (e.g., mammals, birds, reptiles, amphibians, invertebrates), or wildlife and food sources . RARE-Rare, Threatened, or Endangered Species: Includes uses of water that support habitats necessary, at least in part, for the survival and successful maintenance of plant or animal species established under state or federal law as rare, threatened or endangered. MAR -Marine Habitat: Includes uses of water that support marine ecosystems including, but not limited to, preservation or enhancement of marine habitats, vegetation such as kelp, fish, shell~sh, or wildlife ( e.g., marine mammals, shorebirds). MIGR -Migration of Aquatic Organisms: Includes uses of water that support habitats necessary for migration, acclimatization between fresh and salt water, or other temporary activities by aquatic organisms, such as anadromous fish. 1111 SHELL -Shellfish Harvesting: Includes uses of water that support habitats suitable for the collection of filter-feeding shellfish (e.g., clams, oysters and mussels) for human consumption, commercial, or sport purposes. -1111 ... .. ... .. Impaired Water Bodies Section 303(d) of the Federal Clean Water Act (CWA, 33 USC 1250, et seq., at 1313(d)), requires States to identify and list waters that do not meet water quality standards after applying certain required technology-based effluent limits (impaired water bodies). The list is known as the Section 303( d) list o{ impaired waters. 4. STORM WATER BEST MANAGEMENT PRACTICES The Storm Water Standards Manual requires the implementation of applicable site design, source. control, project-specific, and structural treatment control BMPs . ... ,.. ... ,,. ... .. Site Design BMP's The following BMP's are considered in the project design process: 1. Reduce impervious surfaces especially in the boat ramp area (see appendices 3), 2. Sand filtration for treatment of 85th percentile flows (see appendices 3), -.. 3. A detention facility to allow reduction in runoff and provide sedimentation treatment, · 111 4. A cross gutter at the entry of the new Carlsbad Boat Club preventing offsite pollutants 11111 migrating onto the site, 1111 5. Well landscaped slopes to reduce erosion, see bio retention (see appendices 3), .. .. .. -.. .. ... - ... ... ... .. .. - ... .. .. .. .. .. Wherever possible, the use of impervious surfaces was limited to walkways around buildings, boat ramp and the parking area. In addition, the use of efficient landscaping incorporated in the area design to assist in the filtration and reduce the runoffs contamination with sediments, nutrients, heavy metals and to some extent oils and grease . Source Control BMP's The following BMP's were considered in the project design process: 1. Spill prevention and control (see appendices 5), 2. Trash storage (see appendices 5), 3. Include storm drain stenciling and signage (see appendices 4), 4. · Include properly designed outdoor material and trash storage areas (see appendices 4), 5. Parking lot sweeping (see appendices 4), 6. Inlet trash barrier cleaning (see appendices 4), 7. Professional landscape maintenance (see appendices 4), 8. Efficient irrigation, and Integrated pest management principles (see appendices 4), 11. Prompt removal and disposal of trash waste and debris from open areas. An appendix 5 contains all of the pertinent information relative to the Source control BMP' s listed above. However, item eleven requires that the Carlsbad Boat Club maintenance staff will implement a source control best management practice that requires the daily trash removal from the facilities grounds and beach area. This will eliminate the "washing away" of any debris into the Agua Hedionda Lagoon during a storm event. -II • .. .. ,,. ... .. .. ,,. ... .. .. ,,. ... .. .. .. .. ,,. .. .. .. .. .. ... .. .. .. Project-specific BMPs The Storm Water Standards Manual requires specific BMPs for this project. The following are incorporated into the design: 5. PROJECT BMP PLAN IMPLEMENTATION This section identifies the recommended BMP options that meet the applicable storm water and water quality ordinance requirements. This includes incorporating BMPs to minimize and mitigate for runoff contamination and volume from the site. Note that BMPs other than those identified in the plan may be used during final engineering. The following sections address the use of construction-and post-construction BMPs . Recommended Post-Construction BMP Plan Option Since the site is geometrically constrained, it is not practical to create an above ground detention basin near the outfall. Long-term maintenance of a detention basin would also be problematic. This site proposes to detain the peak runoff and the 85th percentile flows with an underground detention facility. This will be designed for a gradual discharge to allow sedimentation and, if possible infiltration. Also, as a means of reducing the discharge of hydrocarbons and other debris into the Agua Hedionda Lagoon, the site drainage will be filtered by a sand filter. Runoff from the roofs will also be directed through the detention/sedimentation facility before discharge into the Agua Hedionda Lagoon. Additionally the sites underground detention system will serve as "settlement area for any debris in the runoff and provide for possible infiltration, however, we are not counting this for the purposes of this report . • Collection of debris in the catch basin • Treatment of roof run-off • Detention area for predevelopment runoff release • 12 - ... ... ... -... .. ... .. ,. ... ... .. ,. - .... .. ... .. ... .. ... - .. .. Operation and Maintenance Plan and Maintenance Responsibility As a contract for the City of the long-term maintenance requirements of proposed BMPs and a description of the mechanism that will ensure ongoing long-term maintenance. The maintenance or the parking and enclosed trash areas and sweeping of the rooftop and maintaining of the mechanical BMPs are the responsibility of the Carlsbad Boat Club. These items will be included in the annual maintenance activities for the facility . Name of Project: Carlsbad Boat Club Owner: Carlsbad Boat Club 4509 Adams Street Carlsbad, CA 92008 • 13 • -.. ,.. .. ,,. ... .. .. ... ... ,,. .. ,,,,, ... ,.. -.. 1111111 .. .. .. ,.. .. .. .. ... ... ,.. ... APPENDIXl Storm Water Requirements Applicability Checklist STORM WATER REQUIREMENTS APPLICABILITY CHECKLIST Section 1. Permanent Storm Water BMP Requirements: If any answers to Part A are answered "Yes," your project is subject to the "Priority Project Permanent Storm Water BMP Requirements," and "Standard Permanent Storm Water BMP Requirements" in Section Ill, "Permanent Storm Water BMP Selection Procedure" in the Storm Water Standards manual. If all answers to Part A are "No," and any answers to Part Bare "Yes," your project is only subject only to the Standard Permanent Storm Water BMP Requirements. If every question in Part A and Bis answered "No," your project is exempt from permanent storm water requirements. P rt A D t P . "t P . ct P t St W BMP R t a . e ermine rioricy roJe ermanen orm ater eau remen s. . Does the project meet the definition of one or more of the priority project categories as defined Yes No in the Storm Water Standards (Appendix I)?* 1 . "Detached residential development of 10 or more units" ✓ 2. "Attached residential development of 10 or more units" ✓ 3. "Commercial development greater than 100,000 square feet" ✓ 4 . "Automotive repair shop" ✓ 5. "Restaurant" ✓ 6 . "Steep hillside development greater than 5,000 square feet" ✓ 7. "Project discharging to receiving waters within Water Quality Sensitive Areas" ✓ 8. "Parking lot" greater than or equal to 5,000 ff or with at least 15 parking spaces, and potentially ✓ exposed to urban runoff 9. "Streets, roads, highways, and freeways" that would create a new paved surface that is 5,000 ✓ square feet or greater 10. "Significant redevelopment" over 5,000 ft ✓ • Refer to the definitions section in the Stoffll Water Standards for expanded definitions of the priority project categori_es . Umited Exclusion: Trenching and resurfacing work associated with utility projects are not considered priority projects. Parking lots, buildings and other structures associated with utility projects are priority projects if one or more of the criteria in Part A is met. If all answers to Part A are "No•, continue to Part B . d Part B: Determine Stan ard Permanent s torm Wt R a er equ1remen ts . Does the project propose: Yes No 1 . New impervious areas, such as rooftops; roads, parking lots, driveways, paths and sidewalks? ✓ 2. New pervious landscape areas and Irrigation systems? ✓ 3 . Permanent structures within 100 feet of any natural water body? ✓ 4. Trash storage areas? ✓ 5 . Liquid or solid material loading and unloading areas? ✓ 6 . Vehicle or equipment fueling, washing, or maintenance areas? ✓ 7. Require a General NPDES Permit for Storm Water Discharges Associated with Industrial Activities ✓ (Except construction)?* 8 . Commercial or industrial waste handling or storage, excluding typical office or household waste? ✓ -14- ... .. ... 11111 .. ... .. ... .. .. 11111 ... .. ... .. .. .. Does the project propose: Yes No 9. Any grading or ground disturbance during construction? ✓ 10. Any new storm drains, or alteration to existing storm drains? ✓ *To find out If your project is required to obtain an Individual General NPDES Permit for Storm Water Discharges Associated with Industrial Activities, visit the State Water Resources Control Board web site at, www.swrcb.ca.gov/stormwtr/industrial.html. Section 2. Construction Storm Water BMP Requirements: If the answer to question 1 of Part C is answered "Yes," your project is subject to Section IV, "Construction Storm Water BMP Performance Standards," and must prepare a Storm Water Pollution Prevention Plan (SWPPP). If the answer to question 1 is "No," but the answer to any of the remaining questions is "Yes," your project is subject to Section IV, "Construction Storm Water BMP Performance Standards," and must prepare a Water Pollution Control Plan (WPCP). If every question in Part C is answered "No," your project is exempt from any construction storm water BMP requirements. If any of the answers to the questions in Part C are ''Yes," complete the construction site prioritization in Part D, below. P rt C D t . C t f Ph St W t R t a . e ermine ons rue 10n ase orm a er equ1remen s . . Would the project meet any of these criteria during construction? Yes No 1. Is the project subject to California's statewide General NPDES Permit for Storm Water Discharges ✓ Associated With Construction Activities? 2. Does the project propose grading or soil disturbance? ✓ 3. Would storm water or urban runoff have the potential to contact any portion of the construction ✓ area, including washing and staging areas? 4. Would the project use any construction materials that could negatively affect water quality if ✓ discharged from the site (such as, paints, solvents, concrete, and stucco)? Part D: Determine Construction Site Priority In accordance with the Municipal Permit, each construction site with construction storm water BMP requirements must be designated with a priority: high, medium or low. This prioritization must be completed with this form, noted on the plans, and included in the SWPPP orWPCP. Indicate the project's priority in orie of the check boxes using the criteria below, and existing and surrounding conditions of the project, the type of activities necessary to complete the construction and any other extenuating circumstances that may pose a threat to water quality. The City reserves the right to adjust the priority of the projects both before and during construction. [Note: The construction priority does NOT change construction BMP requirements that apply to projects; all construction BMP requirements must be identified on a case-by-case basis. The construction priority does affect the frequency of inspections that will be conducted by City staff. See Section IV. 1 for more details.on construction BMP requirements.] □ A) High Priority . . 1) Projects where the site is 50 acres or more and grading will occur during thewet season 2) Projects 5 acres or more and tributary to an impaired water body for sediment by the most current Clean Water Act Section 303(d) list (e.g., Penasquitos watershed) 3) Projects 5 acres or more within or directly adjacent to or discharging direcHy to a coastal lagoon or other receiving water within an water quality sensitive area 4) BJ Projects, active or inactive, adjacent or tributary to sensitive water bodies Medium Priority 1) Capital Improvement Projects where grading occurs, however a Storm Water Pollution Prevention Plan (SWPPP) is not required under the State General Construction Permit (i.e., water and sewer replacement projects, intersection and street re-alignments, widening, comfort stations, etc.) 2) Permit projects in the public right-of-way where grading occurs, however SWPPPs are not required, such as installation of sidewalk, substantial retaining walls, curb and gutter for an entire street frontage, etc . -15- .. ... ... .. .. ... □ CJ .. -... .. , .. ... ... ... .. .. .. -.. -.. - :1111 ... .. -... ... ... .. : .. .. -.. .. .. .. .. 3) 1) 2) 3) Permit projects on private property where grading permits are required (i.e., cuts over 5 feet, fills over 3 feet), however, Notice Of Intents (NOls) and SWPPPs are not required . Low Priority Capital Projects where minimal to no grading occurs, such as signal light and loop installations, street light installations, etc . Permit projects in the public right-of-way where minimal to no grading occurs, such as pedestrian ramps, driveway additions, small retaining walls, etc. Permit projects on private property where grading permits are not required, such as small retaining walls, single-family homes, small tenant improvements, etc . -16- APPENDIX2 Vicinity Map -17 - 9 R -~ .... 2002 CWA SECTION 303(d) LIST OF WATER QUALITY LIMITED SEGMENT Agua Hedionda Creek SAN DIEGO REGIONAL WATER QUALITY CONTROL-BOARD 90431000 Total Dissolved Solids Urban Runoff/Storm Sewers Unknown Noopoint Source Unknown point source Low 7 Miles Approved by USEPA: J11ly2003 ~.-,.\'.'lt~~~~l'!.:W""*~~'ii':"!~a.~~Mi~~-l::'i::m-!{~~(:.:!"'2~.:';:11~-z?.?.<:":~'j;i~"l--.;"t:i::t.:!'2"'";~}''· .......... -. , . ., }:, ~ :•·· :.:.•.;·,r~;~r-·::.;,..;;'iZ;;\\;.;,~{i;;,~.m:~~:::i:":r:·:,:~li•~·~:,;, -~~t ·-'{!'\ .;.,·,_, 'l-f-!7{~~~:• . .,.·~;;..;-.. -~~-';~...,.'t.': '•N~'i:.:·~·: .... _;:'";·".': ..... ·-:-..... :-~.::.. ·:·.'t~..:.-'.:.'7:::::.-~-:-:.;:' -~:· :.:.:.-':''.., .... , ... -::-.. ·: -·: .. :> 9 E Agua Hedionda Lagoon 90431000 Bacteria Indicators Low 6.8 Acres Nonpoint/Point Source Sedimentation/Siltation Low 6.8 Acres Nonpoint/Point Source ~.mllfam'~~~a!llr•~~~-s:s~a~~~.J!c"..;;•.~i~X:~!1~.L~~~a.~~-i!.:$~m~,1l?J. · .. •}!,;;!yf.f;~~"'..,~'£it\':'..,:"'!re;;;$~;.'.\t',.~r;t::l"'.'&-:~,-::is.i:t~;;?:;i-t:G-;r~--'.:~:.f"-.;l\1,':'.-!,f,;1.tf'c'~~t."n.f;;.~~~~t-~=r,r~,iJ'F..t':--3,;'].~:'.:'h~:,~"t,J.\;.:?'·,~y,~·;, .. Q• .i-/.c..•~:-~·~3"'\-;;,'.t?,iff~~.fXh..,.::j:.'. 1~::~.:at.:··'.'.':.:•:•":~:~.~FI: ;-: ~ 1··~ .,..,1:.;_•~ ...... ~,r,, 9 R Aliso Creek 90113000 Bacteria Indicators Phosphorus Urban Runoff/Storm Sewers Unknown point source Nonpoint/Point Source Impairment located at lower 4 miles. Toxicity Urban Runoff/Storm Sewers Unknown Nonpoint Source Unknown point source Urban Runoff/Storm Sewers Unknown Nonpoint Source Unknown point source Medium 19 Miles Low 19 Miles Low 19 Miles ·:-;~~~J::!;:::::w::!tl:"":::·~1r.'f.~.]!.~H,~;~~~~~1:'..tr,:t.:;i:~~9.-;.:.t.:"~';t:·;f'•-=t~ .. ~, . ...,.:'!..'..;yj;Y'';,';~~;, .. ,._;:2~~~10,:?-::~·:;'!':7;"•···· .. .;..~.· ·-..,-:, ~ ~•, • • ~ -•;:: .c· • ·,'..:.•. -•~ _ ,., •• ~ .• ·r.-·,<r . ..-,: .... .r;t.t.:..:,:;-.; •. -.~,:.,_\_":..." _.;t.!~:..t'.'·•.:-..' ', .-, . ·.• •. ;· __ . ,,,. ~• •. ; •:.;;.:.:,4:.,?:;;.-r.~..,...L.,.,:..,.'s:l:..C: · •.' ,·•. · · 9 E Aliso Creek (mouth) 90113000 Bact.eria Indicators Medium 0.29 Acres Non point/Point Source -~ ... 1L"'":v~1'RTT\!B~J8:W~~~~~T:.Z"?-.;""'1!£:!.:?'.~'i'\•:,'5,"lt,.'"t",!P'/-1~rr.g;:,~--~~i.I,ii6.--1;~.2:"J?f'="'..:... .. ,."-:,"\:'t.,:;;~..,;·;csn,.,.. ...• ~_-•·•.-.· ::•s·'....:.·~· ~···.-:~.·.~~~-: ... ·-,. ... ?-0:"'.r;,'1'r~0I .•. -.....,c,1'A(,.,N'l'\1,.;tf;"'t"C"8\t,..f·t-'"·\~-•-..,_:.~~-·:·.._.~_,1_:.,,,. .~~~7-..·r-,,~, ......... ,":'•_ .. ·.,.:: .. ~ 9 E Buena Vista Lagoon 90421000 Bacteria Indicators Low 202 Acres Nonpoint/PointSource Nutrients Low 202 Acres Estimated si=e of impairment is 150 acres located in upper portion of lagoon. Nonpoint/Point Source Sedimentation/Siltation Medium 202 Acres . • .•. ~·i~··•; Nonpoint/Point Source l'i1P.:..~~:W~1"Nl~~~~~S:-i'~~~~~~-.:n.~1f~~~~~~.$'~·&~~::~_;1.~:;r.,.~~l'!e~-t.j~~~'1:>:j';'~_;;.~z.~~~~'W'la.fi.!'.Cl~t1$~~~~~-ii~~~~t.~~~~~-~W.~ii::t~'.t.:,·~'t;·¼~"1:(~~\vt:, Page 1 o/16 APPENDIX3 Site Control BMP's ARMORTEC Concrete Erosion Control Systems ARMORFLEX• Armorflex mats consist of machine compressed cellular concrete blocks of a unique interlocking shape which are made up into mats for easy handling on-site. The blocks arl:l cabled longitu- dinally by means of galvanized steel aircraft or polyester cables. ARMORFLEX FEATURES Factory Made and Assembled Sophisticated purpose-built machinery gives consistent quality and eco_nomic production. Quality Concrete Specification 4000 psi concrete • sulphate-resistant to ensure durability • excellent freeze and thaw · resistance Up to 20 Percent Open Area Permits free drainage of ground- water thus preventing a destabiliz- ing build up of back-pressure behind the revetment. Closed-cell Block Flow Efficiencies Designed with open cir closed cell blocks, Armorflex provides the ideal combination of unit weight and surface roughness. The Armorflex Manning Rough- ness Coefficient, n, has a value ranging from 0.026 to 0.034, depending on the block used. Vegetation The open cells of Armorflex pro- vide the perfect environment for vegetation. Grass and small shrubs The open cell structure of Armor- flex concrete revetment systems nurtures plant life, providing quicker growth and more stable revegetation. can penetrate the filter, providing an attractive, permanent anchor for the system. When vegetation is not desired, install Arrnorflex with closed cells or fill open cells with stone. Access Armorflex is free of dangerous projections, so pedestrians, animals, vehicles and boats all have convenient, safe access to the water. Stability Serving as an articulated mattress, Armorflex provides continuous erosion protection against the destructive forces of water. The proper Armorflex class is determined by the design hydraulic conditions to which it will · be subjected. · Flexibility Armorflex blocks are interconnect- ed by flexible cables, providing · articulation between adjacent blocks. Block walls are designed with beveled relief to allow for flex- ibility in all directions . .. / . \\ ··· ..... )<~ \ ~'lj -.. __ _ !-1aq:....,("' / \ ' Permeability When placed on filter fabric or a conventional graded filter, the per- meability of the revetment system relieves hydrostatic pressure in the subgrade. The system's capability for soil retention ., OPEN-CELL BLOCK CLOSED-CELL BLOCK -A-TOPV!f.W ENOVIEW SIDE VIEW prevents leaching of subsoils through the installation. ' . ' 9 ''/!~~-· ' ,, -~ ..• ~' ( RESEARCH AND DESIGN Since 1980, Armortec has initiated and·participated in a wide range of research projects to evaluate the performance of Armorflex, includ- ing the following: 1. Tetratech model tests - California, U.S.A. 2. Leylstad field trials, Netherlands -Rijkswaterstaat Directorate of the Zuiderzee Projecti 1982. Armorflex Block Specifications (Typical Values) Nominal Gross Concrete · Specific Compressive Dimensions Areal Block Weight•• Open Block Weight Strength Maximum In. Block Area Class lbs./cu. It .. lbs./sq. in. Absorption A B C sq. It. lbs. lbs./sq.lt. % S-Class 30S 130-150 4000 121bs./cu.ft. 13.0 11.6 4.75 o:9s 31-36 32-37 20 Open Cell 50S 130-150 4000 12 lbs./cu. ft. 13.0 11.6 6.0 0.98 45-52 45-53 20 S-Class 45S 130-150 4000 12 lbslcu. ft. 13.0 11.6 4.75 0.98 39-45 40--45 10 Closed Cell 55S 130-150 4000 12 lbslcu. ft. 13.0 11.6 6.0 0.98 53-61 54-62 10 40 130-150 4000 12 lbs./cu. It. 17.4 15.5 4.75 1.77 62-71 35-40 20 Open 50 130-150 4000 12 lbs.ICU. It.· 17.4 15.5 6.0 1.77 81-94 46-53 20 Cell 60 130-150 4000 12 lbslcu. ft. 17.4 15.5 7.5 1.77 99-113 56-64 20 70 130-150 4000 12 lbs./cu. ft. 17.4 15.5 9.o• 1.77 120-138 68-78 20 45 130-150 4000 12 lbs.lcu. It. 17.4 15.5 4.75 1.77 78-89 43-50 10 Closed 55 130-150 4000 12 lbs./cu. It. 17 .4 15.5 6.0 1.77 94-108 53-61 10 Cell 75 130-150 4000 12 lbslcu. ft. 17.4 15.5 7.5 1.77 120-138 68-78 10 85 130-150 4000 12 lbs./cu. ft. 17.4 15.5 9.o• 1.77 145-167 82-95 10 • Block height may vary by approximately o.s• based on local manufacturer's capabilities. . •• Block weight may vary by 2% based on the specific gravity of locally available aggregate mat'erial. 3. Wave Attack Tests, Report No. M1910 -Delft Hydraulics Laboratory, 1982. 4. Hartel Canal Trials -Rotterdam Public Works Department and Delft Soil Mechanics Laboratory. 5. River Waal Breakwaters, Arnhem -Rijkswaterstaat, 1983. 6. "Design of Reinforced Grass Waterways," CIRIA Report 116, 1987 7. "Minimizing Embankment Damage During Overtopping Flows,'' FHWA Report-RD-88- 181 prepared by Simons, Li and Associates, Inc., November 1988. 8. "Hydraulic Stability of Articulated Concrete Block Revetment Systems During Overtopping Flow," FHWA Report-RD-89-199 prepared by Simons, Li and Associates, Inc., July 1989. Research Proven Performance Armortec has carried out exten- sive research into wave and open channel flow conditions on Armorflex in the United States and the Netherlands. Design manuals and computer programs are available to assist in the proper Armorflex block selection for your hydraulic conditions. Design recommendations can thus be made on the basis of specific , research data and sound engi- neering pririciples. Please call Armortec Corporation for design manuals and software. ARMORFLEX INSTALLATION Armorflex arrives on-site as a system of factory-assembled mats. These articulating mats con- sist of interlocking blocks held together by cable. Armorflex is placed on a site specific geotextile which has been placed on a pre- pared subgrade using conventional construction equipment. Delivery & Unloading Mats are supplied on 40-foot trailers, up to 1600 square feet per truck. Delivery can be phased so that mats can be off-loaded directly from the road vehicles onto the prepared subgrade, if the site layout permits. Laying Mats Mats can be handled with a lifting beam, which picks up mats from both ends. Anchorage The mats may slide on the geo- textile fabric until the system set- tles and seats. Temporary anchor- age can be achieved by driving wood stakes on two-inch centers along the top of the mat. Permanent anchorage can be achieved by connecting the mat . cables to patented anchors such as "Helix" or "Duckbill". Finishing Mats subject to wave attack should be blinded with a sand/gravel mixture. Above normal waterline mats may be topsoiled and seed- ARMORFLEX MATS WOVEN GEOTEXTILE GROUND ANCHOR ed to give a "green" effect. ARMORFLEX APPLICATIONS Channel lining River Bank Protection Drainage Ditch Lining Pipeline Protection Boat Ramps Reservoir Slope Protection Lake Shoreline Protection Bridge Abutment Protection Dikes and Levee Protection Dam c·rests and Spillways Weirs and Overflow Channels Disclaimer The infonnation presented herein will not apply to every installation. Dimensions and quantities shown are approximate only and will vary as a result of site conditions and installation procedures. No warranty or guarantee expressed or implied is made regarding the perfor- mance of any product, since the manner of use and hand/Ing are beyond ARMORTEC 3260 Pointe Parkway, Suite 200 Norcross, Georgia 30092 (770) .409-9002; (800) 305-0523 Fax (770) 662-5819 1,.. ·- .. ,,. ti. .. Media Filter Description Storm.water media filters are usually two-chambered including a pretreatment settling basin and a filter bed filled with sand or other absorptive filtering media. .As stormwater flows into the first chamber, large particles settle out, and then finer particles and other pollutants are removed as stormwater flows through the filtering media in the second chamber. There are currently three manufactt.trers of stormwater filter systems. Two are similar in that they use cartridges of a standard size. The cartridges are placed in vaults; the number of cartridges a function of the design fl.ow rate. The water flows laterally (horizontally) into the cartridge to a centerwell, then downward to an underdrain system. 'The third product is a flatbed filter, similar in appearance to sand filters. California Experience There are currently about 75 facilities in California that use manufactured filters. Advantages . ■ Requires a smaller area than standard flatbed sand filters, wet ponds, and constructed wetlands. ■ There is no standing water in the units between storms, minimizing but does not entirely eliminate the opportunity for mosquito breeding. ■ Media capable of removing dissolved pollutants can be selected ■ One system utilizes media in layers, allowing for selective removal of pollutants. ■ The modular concept allows the design engineer to more closely match the size of the facility to the d~ign storm. Limitations ■ .As some of the manufactured filter systems function at higher fl.ow rates and/or have larger media than fonnd in flatbed filters, the form.er may not provide the same level of performance as standard sand filters. However, the level of treatment may still be satisfactory. ■ .As with all filtration systems, use in catchments that have significant areas of non-stabilized soils can lead to premature clogging. J a1ucry 2003 callfcrnla Stormwater BMP Handbod< New Development a1d Redevelopment WWW .coomphendbooks. com MP-40 Design Considerations ■ Design Storm ■ MediaType ■ Maintenance Requirement Targeted Constituents li1 Sediment li1 Nutrients li1 Trash li1 Metals Bacteria li1 Oil and Grease li1 Organics Removal ~tlveness See New Development and Redevelopment Hancbook-Section 5. 1 of3 ,.. 11111 ,,... ,,,.. .. ... ... ,,. --.. ,,,. ... .. ,. ... .. ,. .. .. Jllll .. -.. ,.. Ill ,,. ... ,,.. lllr MP-40 Media Filter Design and Sizing Guidelines There are currently three manufacturers of stormwater filter systems . Filter System A This system is similar in appearance to a slow-rate sand filter. However, the media is cellulose material treated to enhance its ability to remove hydrocarbons and other organic compormds. The media depth is 12 inches (30 cm). It operates at a very high rate, 20 gpm/ft:2 at peak flows. Normal operating rates are much lower assuming that the stormwater covers the entire bed at flows less than the peak rate. The system uses vortex separation for pretreatment As the media is intended to remove sediments (with attached pollutants) and organic compounds, it would not be expected to remove dissolved pollutants such as nutrients and metals unless they are complexed with the organic compounds that are removed. Filter System B: It uses a simple vertical filter consisting of 3 inch diameter, 30 inch high slotted plastic pipe wrapped with fabric. The standard fabric has nominal openings of 10 microns. The stormwater flows into the vertical filter pipes and out through an underdrain system. Several units are placed vertically at 1 foot intervals to give the desired capacity. Pretreatment is typically a dry extended detention basin, with a detention time of about 30 hours. Stormwater is retained in the basin by a bladder that is automatically inflated when rainfall begins. This action starts a ti.mer which opens the bladder 30 hours later. The filter bay has an emptying time of 12 to 24 hours, or about 1 to 2 gpm/ft:2 of filter area. This provides a tot.al elapsed time of 42 to 54 hours. Given that the inedia is fabric, the system does not remove dissolved pollutants. It does remove pollutants attached to the sediment that is removed . Filter System C: The system use vertical cartridges in which storm water enters radially to a center well within the filter unit, flowing downward to an rmderdrain system. Flow is controlled by a passive float valve system, which prevents water from passing through the cartridge until the water level in the vault rises to the top of the cartridge. Full use of the entire filter surface area and the volume of the cartridge is assured by a passive siphon mechanism as the water surface recedes below the top of the cartridge. A balance between hydrostatic forces assures a more or less equal flow potential across the vertical face of the filter surface. Hence, the filter smface receives suspended solids evenly. Absent the float valve and siphon systems, the amount of water treated over time per unit areain a vertical filter is not constant, decreasing with the filter height; furthermore, a filter would clog unevenly. Restriction of the fl.ow using orifices ensures consistent hydraulic conductivity of the cartridge as a whole by allowing the orifice, rather than the media, whose hydraulic conductivity decreases over time, to control fl.ow. The manufacturer offers several media used singly or in combination (dual-or multi-media). Tot.al media thickness is about 7 inches. Some media, such as fabric and perlite, remove only suspended solids (with attached pollutants). Media that also remove dissolved include compost, zeolite, and iron-infused polymer. Pretreatment occurs in an upstream unit and/or the vault within which the cartridges are located Water quality volume or fl.ow rate ( depending on the particular product) is determined by local governments or sized so that 85% of the annual runoff volume is treated. Construction/Inspection Considerations ■ Inspect one or more ti.mes as necessary during the first wet season of operation to be certain that it is draining properly. 2 of3 Cal lfornla Stormwater BMP Handbook New Develq:,ment and Redevelopment www.cabmphancbooks.com Ja,uary 2003 1111"' ... ,,. ,,,. .. ,.. .. ,,. -.. ... ,,. -.. ... ... ... .. .. .. ... .. ,. ... .. .. ... ,. .. .. ... Media Filter MP-40 Performance The mechanisms of pollutant removal are essentially the same as with public domain filters (TC -40) if of a similar design. Whether removal of dissolved pollutants occurs depends on the media Perlite and fabric do not remove dissolved pollutantE, whereas for examples, zeolites, compost, activated carbon, and peat have this capability . As most manufactured filter systems function at higher flow rates and have larger media than found in flatbed filters, they may not provide the same level of performance as standard sand filters. However, the level of treatment may still be satisfactory. Siting Criteria There are no unique siting criteria . Additional Design Guidelines Follow guidelines provided by the manufacturer. Maintenance ■ Maintenance activities and frequencies are specific to each product .Annual maintenance is typical. ■ Manufactured filters, like standard filters (TC-40 ), require more frequent maintenance than most standard treatment systems like wet ponds and constructed wetlands, typically annually for most sites . ■ Pretreatment systems that may precede the filter unit should be maintained at a frequency specified for the particular process . Cost Manufacturers provide costs for the unitE including delivery. Installation costE are generally on the order of 50 to 100 % of the manufacturer's costs . Cost Considerations ■ Filters are generally more expensive to maintain than swales, ponds, and basins . ■ The modularity of the manufactured systems allows the design engineer to closely match the capacity of the facility to the design storm, more so than with most other manufactured products . References and Sources of Additional Information Minton, G.R., 2002, Stormwater Treatment: Biological, Chemical, and Engineering Principles, RP A Press, 416 pages . Ja,uary 2003 California Stormwater BMP Handbook New Development a,d Redevelopment www.cabmphaidbooks.com 3 of3 Flo-Gard™ Trash & Debris Guard The Flo--Gard™ Trash & Debris Guard is often the only practical option to filter stormwater leaving sites with little fall from a parking surface, through a parkway culvert to curb and gutter outfall. It is designed to remove debris and has an optionai Fossil Rock pouch for hydrocarbon removal. · Based on site conditions, the flow capacities shown may be derated by a safety factor of 0.50 to 0. 75 to account for severe debris buildup between maintenance cycles. Specifications: Model Width Height Depth (In FIitered Flow Bypass (In) · (In) Cap. (cfs) Cap. (cfs)* FG-TDG24 24 6 0.75 0.45 0.62 FG-TDG36 36 6 0.75 0.67 0.94 FG-TDG42 42 6 0.75 0.78 1.10 FG-TDG48 48 6 0.75 0.89 1.26 FG-TDG60 60 6 0.75 1.11 1.58 *Approximate -may vary with location and debris loading between maintenance Questions? Contact Kristar at (BOO) 579-8819. 09/04 I A I 0 0 0 ..... I I 0 () lt- ..--B 0 I Mounting •slide" bracket Gasket -------FRO NT VIEW ~ Sediment screen (8 mesh) I ~---------~C Security bolt / TOP VIEW ·j APPLICATION CHART . NOTES: MODEL NO. A FG-TDG24 32.00" FG-TDG36 44.00' FG-TDG42 50.00' FG-TDG48 56.00" FG-TDG60 68.00" FG-TDG-CUST As req'd s · C 6.00" .75" 6.00" .75" 6.00" .75" 6.00" .76" 6.00" .75" As retj'd 1. All metal components shall be constructed from stainless steel . (Type304). . 2. FloGard™Trash and Debris Guard shall be mounted to the face of curb, across the drain opening. Mounting brackets shall be secured to the face of curb using two 3.-'8" x 2-1f2" stainless steel expansion anchors and tamper resistant bolts. 3. Mounting brackets shall oo supplled with tamper resistant stainless steel security bolts: 4. Refer to application chart for standard heights and widths for FloGard™Trash and Debris Guard. Custom sizes are available upon request . 5. FloGard™Trash and Debris Guard Is supplied with a removable (8 mash) sediment screen. Alternate size sediment screens may be specified to retain the particle size anticipated for each speclrlc site. 6. FloGard™Tl'ash and Debris Guard may be specified with Fossll Rockr"' filler medium pouch for the col)ectlon qf oil and grease. 7. FloGard™Tl'ash and Debris Guard should only be used on sites that Incorporate a comprhenslve maintenance program that Includes regular cleaning and sweeping. TYPICAL INSTALLATION Parkway Culvert FRONT VIEW SIDE VIEW FLOGARD"' TRASH & DEBRIS GUARD KriStar tnlerprises, Inc., Santa Rosa, CA (800) 579-8819 FRONT VIEW 0 0 ' -~ Bolt to face of curb TOP VIEW Screen 0 0 0 Absorbent Pouch Tethering Clip · FLO-GARD™ TRASH & DEBRIS GUARD KriStar Enterprises, Inc., Santa Rosa, CA (800) 579-8819 .06/04 FRONTVIEW 0 0 0 0 0 0 .SIDE VIEW ... · .. ·.,q :: .. · .. ·-~ := .. v·:. • v. ·.: v·:.. . . '.\si-• ::·.·. P'.·'·.'I·· :>. P'..'·.'I·· ::-.-. P'.\si -· ::-.-. P'.":..'I·· · .. ·.I".·'. 'I··::·.·."'.·: .'I··::,... I".'·.'!··:>. P'. '·.'!·· ::-.-. P'.\si--::·.·. ~--'·.'I••::·.·. P'.\si-· ::· .. . ·. ·.v .·. ·v· ,:_-y ·· .. · .. · Optional Absorbent Pouch FLO-GARD™ TRASH & DEBRIS GUARD (Parkway Culvert Installation) J<riStar Enterprises, Inc., Santa Rosa, CA (800) 579-8819 06,'()4 Site Design & Landscape Planning SD-10 Description Design Objectives 0 Maximize Infiltration 0 Provide Retention 0 Slow Runoff 0 Minirrize lrrpervious Land Coverage Prohibit Durrping of lrrproper Materials Contain Pollutants Collect and Convey Each project site possesses unique topographic, hydrologic, and vegetative features, some of which are more suitable for development than others. Integrating and incolJX)rati.ng appropriate landscape planning methodologies into the project design is the most effective action that can be done to minimize surlace and groundwater cont.a.mi.nation from stormwater. Approach Landscape planning should couple consideration of land suitability for urban uses with consideration of community 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 Appropriate applications include residential, commercial and industrial areas planned for development or redevelopment. Design Considerations Design requirements for site design and landscapes planning should conform to applicable standards and specifications of agencies with jurisdiction and be consistent with applicable General Plan and Local Area Plan policies. Jmua-y 2003 Callfcrnla Stormwater BMP Handoook New Development md Redevelcpment www.cci:Jmphmdbooks.com 1 of 4 Ilia ,,. .. ,. .. ,,.. ,,.. ,,.. .. ,,. ... . ,.. .. ,. .. .. ... ,.. ... ,. .. SD-10 Site Design & Landscape Planning Designing New Installations Begin the development of a plan for the landscape unit with attention to the following 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 comm.unity 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-prone soils, fonndation 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 area, 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 La.ndscape 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 nndisturbed condition. ■ Limit clearing and grading of native vegetation at a site to the minimum amonnt 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 tnlerant plants. ■ Promote natural vegetation by using parking lot islands and other landscaped areas . ■ Preserve riparian areas and wetlands . Maxi.mi:ze Natural Water Storage and Infiltrati.on Opporhm.ities Within the La.ndsoo:pe Unit ■ Promote the conservation of forest cover. Building on land that is already deforested affects basin hydrology to a lesser extent th.an converting forested land Loss of forest cover reduces interception storage, detention in the o:rganic forest floor layer, and water losses by evapotranspiration, resulting in large peak nm.off increases 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 2 of 4 California Stcrmwater BMP Hmdbook New Development and Redeveloi::,nent www .abmphancbod<s.com Jmuary 2003 ... ,,. ... ,,. -... ,,. .. .. ..., ,,. ... .. ... .. ... ,,. .. Site Design & Landscape Planning SD-10 regulations to discourage the clearing, filling, and channelization of these features. Utilize them in drainage networks in preference to pipes, culverts, and engineered ditches. ■ Evaluating infiltration opportmrities 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 surlaces or a potential to produce relatively contaminated runoff away from groundwater recharge areas. Protection of Slo-pes and Channels dwing Landscape Design ■ Convey nmoff 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 reaching existing natural drainage systems . ■ Stabilize temporary and permanent channel crossings as quicldy as possible, and ensure that increases in nm-off velocity and frequency caused by the project do not erode the channel. ■ Install energy dissipaters, such as riprap, at the outlets of new storm drains, culverts, 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 surf ace, 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, or geo-grid stabilization are other alternatives. ■ Consider other design principles that are comparable and equally effective. Redeveloping Existing Installations Various jurisdictional storm.water 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 swfaces. The definition of II 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 . Ja1ua-y 2003 Gallfornla Stormwater BMP Handbook New Development a-\d Redevelq:,ment www .ccbmphcndbooks. ccm 3of4 ,.. ,,. .. ,,,. ... ... ... ,,.. .. ,.. .. ... Ilia, ... ... .. ,,. ... SD-10 Site Design & Landscape Planning Redevelopment may present significant opportunity to add features which bad 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 already existing infrastructure, opportunities should not be missed to maximize infiltration, . slow nm.off, reduce impervious areas, disconnect directly connected impervious areas. Other Resources A Manual for the Standard Urban Stormwater Mitigation Plan (SUS MP), Los Angeles County Department of Public Works, May 2002. · Stormwater Management Manual for Western W asbington, 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 C.o\lllty of Orange, Orange Connty Flood Control District, and the Incorporated Cities of Orange County, Draft FebruaIY 2003. · Ventura Countywide Technical Guidance Manual for Storm water Quality Control Measures, July2002 . 4of4 Callfornla Stormwater BMP Handbook New Development and Redeveloi:ment WNW. cabmphancbooks.com January 2003 Efficient Irrigation SD-12 Design Objectives @ Maximize lnfillratim @ Provide Retention @ Slow Runoff Mininize lrrpervious Land Coverage Prohibit Durrping of Irr-proper Materials Contain Pollutants Collect and Convey Description · ·· ~- Irrigation water provided to landscaped areas may result in excess inigation water being conveyed into storm water drainage systems. Approach Project plan designs for development and redevelopment should include application methods of inigation water that minimize runoff of excess inigation water into the stonnwater conveyance system. Suitable Applications Appropriate applications include residential, commercial and industrial areas planned for development or redevelopment. (Detached residential singl~family homes are typically excluded from this requirement.) Design Considerations Designing Newinstallations The following methods to reduce excessive inigationrunoff should be considered, and · incorporated and implemented where determined applicable and feasible by the Permittee: ■ Employ rain-triggered shutoff devices to prevent inigation 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 inigation times (for short cycles), etc. · Jff1ua-y 2003 Callfcmla Stormwater BMP Handbook New Developmerit ff1d Redevelcpmerit www .c<i>mphandbooks. can 1 of2 · ,. .. ,,. ... ,,. ,,. .. ,,. ,,. .. ,,,. ,,. ,,. 111111 ... 111111 ,,. .. ,,,. .. SD-12 Efficient 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 inigation 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 grmmd 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 nm.off. .Redeveloping Exuiting 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 smfaces. 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 Storm.water Mitigation Plan (SUS MP), 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 Connty, February 14, 2002. Model Water Quality Management Plan (WQMP) for C.01.lll.ty of Orange, Orange Colm.ty Flood Control District, and the Incorporated Cities of Orange County, Draft February 2003. Ventura Countywide Technical Guidance Manual for Storm.water Quality C.Ontrol Measures, . July2002 . 2 of2 California Stormwater BMP Ha1dbook New Development and Redevelopment www.cabmphandbooks.com January 2003 ... ... ,,. ... .... ,,. ... ,,. .. ... .. .. .. ... ... ,.. Outlet Protection/Velocity Dissipation Devices jss-1oj Standards and Specifications Maintenance and Inspection ■ There are many types of energy dissipaters, with rock being the one that is represented in the figure on Page 3. Please note that this is only one example and the RE may approve other types of devices proposed by the contractor. ■ Install riprap, grouted riprap, or concrete apron at selected outlet. Riprap aprons are best suited for temporary use during construction. ■ Carefully place riprap to avoid damaging the filter fabric. ■ For proper operation of apron: Align apron with receiving stream and keep straight throughout its length. If a curve is needed to fit site conditions, place it in upper section of apron. If size of apron riprap is large, protect underlying filter fabric with a gravel blanket. ■ Outlets on slopes steeper than 10% shall have additional protection. ■ Inspect temporary measures prior to the rainy season, after rainfall events, and regularly (approximately once per week) during the rainy season. ■ Inspect apron for displacement of the riprap and/or damage to the underlying fabric .. Repair fabric and replace riprap that has washed away. ■ Inspect for scour beneath the riprap and around the outlet. Repair damage to slopes or underlying filter fabric immediately. ■ Temporary devices shall be completely removed as soon as the surrounding drainage area has been stabilized, or at the completion of construction . • Caltrans Stenn Water Quality Handbooks Section 3 Outlet ProtectlonNelocity Dissipation Devices SS-10 2of3 IN6itn, Construction Site Best Management Practices Manual March 1, 2003 ... ... ... ... ... ,,,.. ... ,,,. ,.. ... ... ... 11111111 ,,. .. , ... ... Outlet ProtectionNelocity Dissipation Devices A w Pipe Diameter mm 300 450 600 Filter PLAN VIEW NTS A 1.2 W (min) Pipe outlet to well defined channel Key in 150-230 mm, ______ La_____ (6-9 in.) recommended SECTION A-A NTS for entire perimeter. _[ 1.5 dia. rock ll;;:;JII-(max), placed I 311~ at 150 mm 1-111-'-'-'111--. . d th T min. ep Discharge Apron Length, La Rip Rap m3/s m Dso Diameter Min mm- 0.14 3 100 0.28 4 150 0.28 3 150 0.57 5 200 0.85 7 300 1.13 8 400 0.85 5 200 1.13 8 200 1.42 8 300 1.70 9 400 For larger or higher flows, consult a Registered Civil Engineer ,.. Source: USDA -SCS .. ... .. .. • lliHiiin, Caltrans Storm Water Quality Handbooks Construction Site Best Management Practices Manual March 1, 2003 Section 3 Outlet ProtectlonNelocity Dissipation Devices SS-10 3of 3 ,.. ... ,,,. ,.. ... ,,. ... \ ... ,,. '111111 ,,. .... ... ,,,. .. ... 1111111 ... - ... ... ... Policy on the Use of Hydrodynamic Separators to Achieve Compliance with NPDES Provision C.3 Donald P. Freitas Program Manager Hydrodynamic separators, when used as a sole method of stormwater treatment, do not meet the "maximum extent practicable" requirement for stormwater treatment effectiveness with regard to compliance with NPDES Provision C.3 in Contra Costa . The following types of facilities, if sized and designed as described in the Stormwater C.3 Guidebook, can meet the "maximum extent practicable" standard for stormwater treatment effectiveness: · • Swales, planter boxes, bioretention areas, and other facilities using filtration through soil or sand (sized according to the flow-based criterion). • Dry wells, infiltration trenches, infiltration basins, and other facilities using infiltration to native soils (sized according to the volume.:.based criterion). • Extended detention basins, constructed wetlands or other facilities using settling (sized according to the volume-based criterion, with a detention time of 48 hours). Hydrodynamic separators, including vortex separators and continuous deflection separators ("CDS units"}, are substantially less effective than any of the above-listed facilities for removing stormwater pollutants of concern. This difference in effectiveness can be inferred by comparing design criteria and mode of operation and by analyzing the relative capability of each type_ of facility to remove small particles. The difference in effectiveness can also be validated by reviewing available results of laboratory and field tests. Experience to date has shown swales, planter boxes, bioretention areas, or other effective treatment facilities can be successfully applied to Contra Costa development sites. Lack of space, in itself, is not a suitable justification for using a less effective treatment device since uses of the site and the site design can be altered as needed to accommodate a swale, planter box, bioretention area, or other effective BMP. In most cases, effective BMPs can be fit into required landscaping setbacks, easements, or other unbuildable areas . Hydrodynamic separators can be used to remove trash and coarse sediment from stormwater upstream of detention basins or other treatment facilities designed to remove pollutants of concern to the maximum extent practicable. Installations of hydrodynamic separators are subject to the Provision C.3.e requirements for operation and maintenance verification. Planned inspection and maintenance of hydrodynamic separators must be documented in a Stormwater Treatment Facilities Operation and Maintenance Plan prepared in accordance with Appendix F of the Stormwater C.3 Guidebook . Each installation should be coordinated with the Contra Costa Mosquito and Vector Control District prior to final design. · (11/16/2005) 255 Glacier Drive, Martiaez, CA 94553-4897 • Tel: (925) 313-2360 Fax (925) 313-2301 • E-mail: mleanwater@pw.co.contra-mta.ca.us Program Participants: Antioch, Brentwood, Clayton, Cancard, Danville, El Cerrito, Hercules, Lofayett,, Martinez, Moraga, Oakley, Orinda, Pinole, Pfftsburg, Pleasant Hill, Richmond, San Pablo, San Ramon Walnut Creek, Contra Costa Counly and Contra Costa Counly Flood Control & Water Conservation District ,,,,. ... ,,. ,,. ... ,·,,. .... ,,,,. ... ,,. ,,. 111111"' .. ,,. ... ,,. ... ,,,,. ... ... ... ... .. TECHNICAL MEMORANDUM To: C.3 Planning /Permitting Work Group and C.3 Technical Work Group From: Dan Cloak Subject: Use of Hydrodynamic Separators to Achieve C.3 Compliance Date: 3 November 2005 Introduction Provision C.3 (Water Board, 2003) of the stormwater NPDES permit requires Contra Costa municipalities to make stonnwater treatment measures, source control measures, and site design measures a condition of approval for new development and significant redevelopment projects so that pollutant discharges are decreased to the maximum extent practicable. Some applicants for planning and zoning approvals have proposed installing hydrodynamic separators including continuous deflective separators, or "CDS units," to achieve compliance with the treatment requirements. In addition, manufacturers' representatives of these devices have communicated with municipal staff and have stated the devices meet the "maximum extent practicable" criterion. The C.3 Planning/Permitting Work Group and C.3 Technical Work Group requested technical review and preparation of draft guidance on the use of hydrodynamic separators to comply with Provision C.3. The guidance will be incorporated into the next. edition of the Contra Costa Stormwater C.3 Guidebook. Hydrodynamic Separators USEPA (1999a} describes hydrodynamic separators as "flow-through structures with a settling or separation unit to remove sediments." The separators depend on the energy from flowing water; no outside power source is needed. They can be located beneath parking lots or streets. USEPA (1999a) identifies and describes the following specific brands of hydrodynamic separator: !/IS Continuous Deflective Separator (CDS units) iJ Downstream Defender™ Ill Stonnceptor® ti Vortechs™ Additional brands of hydrodynamic separator are identified in Caltrans (2004a). CDS units use a fine screen to separate solids from water. Flow is directed tangentially to the screen to prevent blocking or clogging . Settleable solids accumulate in a containment sump. Floating material circulates at the water surface until the water level drops (Wong, 1997) . 1 of9 ... ... ,.. ... ,.. ... ... ... ... ... .. ,.. ,,.,. ... ... ... ... ,,,. ... ... ... ,.. ,. ... ,.. ,.. ... Hydrodynamic Separators 3 November 2005 Vortechs separators use swirling motion inside a chamber, and a baffled outlet, to encourage settling of solids (Vortechnics, 2004). Other brands have similar features and mode of operation, although designs differ. Pollutants of Concem and Particle Sizes Provision C.3 specifies neither the pollutants to be removed nor the effectiveness of treatment. Provision C.3.d does provide criteria for sizing treatment facilities . Finding 7 of the Water Board's February 19, 2003 Order adding Provision C.3 (Water Board, 2003) provides examples of the types of pollutants the Board intends treatment facilitiel;l to capture: . .. PAHs which are products of internal combustion engine operation and other sources; heavy metals, such as copper from brake pad wear and zinc from tire wear; dioxins as products of combustion; mercury resulting from atmospheric deposition; and natural-occurring minerals from local geology. Finding 7 states further: All of these pollutants, and others, may be deposited on paved surfaces and roof-tops as fine airborne particles, thus yielding stormwater runoff pollution that is unrelated to the particular activity or use associated with a given new or redevelopment project. However, Dischargers can implement treatment control measures, or require developers to implement treatment control measures, to reduce entry of these pollutants into storniwater and their discharge to receiving waters. The Water Board is also preparing TMDLs for mercury and PCBs and a water quality attainment strategy (WQAS) for copper and nickel. Airborne particles derive from chemical conversion of gases in the atmosphere and from windblown dust. The latter particles are larger, with a peak in the size distribution (by mass) at around 10 µm diameter. The size distribution falls off to near zero at around 100 µm (DEFRA, 2001). USEPA (1999b) has developed a generalized particle size distribution to be used in modeling air deposition from industrial sources. In the distribution, eighty-seven percent of total mass is associated with particles smaller than 15 µni . As small airborne particles gather on impervious surfaces and are subsequently transported in runoff, they tend to agglomerate to form larger particles or may also become attached to larger particles eroded by the flow of water. Therefore, pollutants derived from very small particles in air deposition may be associated with somewhat larger particles in runoff entering a treatment device. In sediment suspended in urban runoff, the distribution of particle sizes is variable. It has been noted that sampling equipment may fail to capture larger particle sizes, creating an inherent bias in the particle size distribution (KLI, 2002). Studies by USEPA (summarized in Rinker Materials, 2004) show 80-90% of total suspended sediment mass is in particles smaller th~ 100 µm . Some data from other sources show larger particle sizes predominating. 2of9 .. .. , .. ---- 11111 .. ... - .. ... - ... .. -.. ... .. .. -.. .. .. Hydrodynamic Separators 3 November 2005 The difference in results may be in part due to different characteristics of the tributary area sampled. Runoff from highways or open spaces seems more likely to include larger particles, which may be derived from automobiles, decomposing pavement, and run-on from unpaved areas, when compared to particles in runoff from rooftops, parking lots, and low-volume streets, which mostly originate from air deposition. Site design guidance in the Contra Costa Stonnwater C.3 Guidebook (CCCWP, 2005) emphasizes techniques to separate landscaped and pervious areas by creating "self-retaining areas." This would tend to reduce the likelihood of finding substantial amounts of larger-sized particles in the runoff from impervious areas that reaches treatment facilities . In sum, Provision C.3 aims to control the transport of toxic pollutants associated with very fine particles deposited by air deposition and windblown dust on paved areas and rooftops. This can be accomplished by facilities capable of removing particles in a range from sub-micron to 100 µm (Rinker Materials, 2004). Urbonas (2003) suggests that an effective BMP should be capable of removing particles smaller than 60 µm. Relative Treatment Effectiveness Provision C.3.d specifies alternative ways to determine the runoff flow or volume·that facilities must be designed to treat without bypassing or overflowing. To comply with Provision C.3, this runoff flow or volume must be treated to remove pollutants to the "maximum extent practicable," which is the standard for control of runoff pollutants established by the Clean Water Act. In this context, "maximum extent practicable" means less-effective treatment may not be substituted when it is practicable to provide more- effective treatment. Independent assessments of the performance of stormwater treatment devices either evaluate the application of engineering principles used in the design of the device (rational evaluation) or evaluate samples of device effluent, sometimes with comparison to influent samples ( empirical evaluation). Rational Evaluation Salvia (2000) categorized treatment devices as gravizy separators or filters and evaluated.manufacturers' claims by comparing the design of the proprietary devices with generally accepted engineering design procedures and criteria for the treatment of stormwater or wastewater. In water and wastewater treatment engineering, settling columns are typically used to determine the design settling rate for waters to be treated. Studies cited by Schueler (1987) using settling columns indicate that 60-70% of sediments in urban runoff settle out within 6 hours, and the remaining sediment may take as much as two days to settle. The California Stormwater BMP Handbooks (CASQA, 2003) recommend a 48- hour detention time for stormwater treatment detention basins . 3 of9 .. .. ... ... ' ,,,. .. ,.: ... .. .. .. --... ... -.. -.. .. .. 1111 .. ... lilll ... Hydrodynamic Separators 3 November 2005 Using the CASQA methodology, a 48-hour settling time, and typical Contra Costa rainfall patterns, a settling basin suitable for treating runoff from a completely impervious area would require a basin volume of approximately 3000 cubic feet per acre (CCCWP, 2005). By comparison, the manufacturers of hydrodynamic separators propose their devices can.effectively treat runoff within a substantially smaller volume. The flow patterns and settling dynamics of hydrodynamic separators are poorly understood. It is not established that hydrodynamic separators can remove very small particles in a shorter detention time than is required for quiescent settling basins. Public environmental agencies are evaluating these claims empirically . Swales, planter boxes and bioretention areas use filtration through a bed of granular media-the Stormwater C.3 Guidebook specifies a sandy loam-to remove particles from stormwater. In deep-bed filtration, water transports particles via settling, diffusion, and hydrodynamics into the interstices of between media granules. The particle then attaches to the medium by electrostatic interactions, chemical bridging, or adsorption (Weber, 1972). The effectiveness ofremoval is governed by the surface application rate and the size of the media. The Guidebook (CCCWP, 2005) specifies a sandy loam with an infiltration rate of five inches per hour and a depth of 18 inches, allowing at least two to three hours for removal to occur . In a sand filt~r, particles accumulate in deeper layers of the filtration media, increasing head loss and eventually causing breakthrough and loss of filter effectiveness if the filter is not periodically backwashed (Weber, 1972). In a biologically active soil filter, the action of bacteria, . insects, and earthworms are believed to promote agglomeration of soil particles with the soil media, maintaining the porosity of the media and, over time, increasing, maintaining or restoring the soil's ability to absorb additional pollutant particles. Because of the multiple mechanisms at work, and the absorptive capacity of the soil, it is expected that effluent from a soil filter will contain very low levels of particulates . Neither filtration nor settling will remove all dissolved pollutants consistently and effectively. Biological filters may remove some dissolved pollutants through ion exchange and absorption. On the other hand, some dissolved constituents, such as nitrogen and phosphorous, may be released from the soil filtration medium. Effluent concentrations may sometimes exceed influent concentrations, particularly in the startup phase of operation . Empirical Evab.tations In the last few years, public agencies have begun to independently evaluate performance claims. Empirical evaluations of treatment BMP effectiveness are hampered by the following: ~ Different target constituents. Total suspended solids (TSS) is typically used as a stand-in for pollutants of concern because data are available and because the concentration of some pollutants tends to be roughly proportional to TSS. However, measurement of TSS is subject to anomalies and also may not be proportional to concentrations of some pollutants of concern. 4of9 ... ... ... ... ... -... ... ... ... .. .... ... ... :1111 1111 ,. "' JIii .. ... Hydrodynamic Separators 3 November 2005 ~ No standard for lww to measure performance. Percent removal of load or concentration, calculated from measurements of influent and effluent, is the most typical measure. However, using this measure, higher influent concentrations tend to produce higher percent removals. Effluent concentration alone has been proposed as a better indicator of performance (Urbonas, 2003) . ll'l Differing qualities and characteristics of influent. Urban runoff influent varies with location, from one event to the next, and during events. Treatment results obtained under different conditions may not be fairly comparable. II Different flow rates. Stormwater flows are highly variable. Published test results may reflect high pollutant removals achieved at very low flow rates. Manufacturers of hydrodynamic separators have varying claims regarding the effectiveness of treatment. The manufacturers of CDS units claim only " ... an ability to capture and retain solids larger than 100 µm ... " (Francis, 2005, emphasis added). Hydro International claims their Downstream Defender can achieve 80% removal of a 50 µm mean particle size sand at specified rates of flow (Washington Department of Ecology, 2005). The Vortechs system, at specified rates of flow, claims a 64% removal of coarse silt particles, ranging from 38 µm to 75 µm, in laboratory studies (New Jersey Department of Environmental Protection, 2005). In each case, public agencies have requested additional information and tests to determine whether claimed removal rates reflect the distribution of particle sizes actually typical of stormwater or to verify the flow rates used are reasonable. Reports of the effectiveness of biofilters include data from "wet" swales and filter strips, where the primary modes of treatment are settling and contact with vegetation, rather than filtration through soil. Data from the National Stormwater BMP Database presented by Urbonas (2003) show typical effluent concentrations near 10 mg/L, well below that produced by hydrodynamic devices . Bioretention facilities using soil filtration to treat stormwater are believed to be considerably more effective than "wet" swales and are capable of producing effluent nearly free of lead, with removal rates of 98-99% (Hsieh and Davis, 2003; Center for Watershed Protection, 2000). It is likely similar results can be achieved for other heavy metals and for hydrophobic organic pollutants such as PCBs. Technical Feasibility and Operability The Caltrans (2004b) BMP Retrofit Pilot Study provides the most current, comprehensive, and regionally applicable information based on actual construction and operation of a variety of treatment BMPs. CDS units were the only hydrodynamic separators tested by Caltrans. They were highly successful at removing gross pollutants but no significant reduction in suspended solids was observed. Because they are efficient at capturing vegetation, excessive maintenance frequency _may be required to avoid clogging of units installed where there is substantial leaf fall. Mosquito breeding was repeatedly observed at the two CDS installations monitored by Caltrans, as it was for the multi-chambered treatment train (MCTT) and wet pond installations. To implement the 5 of9 ,.. ,,. .. ,,. .. -.. - , .. ... - ,.. .. .. -,,,. Hydrodynamic Separators 3 November 2005 southern California trash TMDL, Caltrans is developing non-proprietary designs for devices that remove gross pollutants (Caltrans, 2004c). Agency personnel have expressed concern that hydrodynamic separators, because they are in underground vaults identified only by manhole covers, could become "out of sight, out of mind," and not be adequately maintained. Given the relatively small number of installations, this concern can only be evaluated by anecdotal experience. Urbonas (2003) recalls inspecting a number of underground oil and grease traps in Denver. Despite being subject to maintenance agreements, nearly all the traps had not been maintained for years. Some had manhole covers overlain with asphalt paving . Coats In their compilation of fact sheets attached to the Storm Water Treatment BMP Technology Report, Caltrans (2004b) rates all hydrodynamic separators as having low costs and low effectiveness compared to a detention basin. Luksic (2002) cites the initial cost of the smallest concrete CDS unit, capable of serving a 25-acre catchment, as $13,200, with a cost for each clean-out service of $300 to $400. By comparison, a detention basin serving 25 acres of impervious area should have a volume of 1.75 acre-feet (CCCWP, 2005). Using the formula in CASQA (2003), the construction, design, and permitting cost a basin can be estimated at $63,700. CASQA (2003) estimates the cost of maintaining a detention basin at $3,100 per year, mostly for mowing and other vegetation management. CASQA (2003) cites construction costs for bioretention areas at $3 to $4 per square foot. Using the sizing criteria in CCCWP (2005), adequate treatment of runoff from 25 acres of impervious area would require 1 acre of bioretention area; therefore construction costs would be roughly $150,000. However, the landscape amenity provided by a bioretention area should also be considered when comparing costs. Costs of maintenance may be the same as landscape covering the same area. Summary and Conclusions The following types of facilities, if sized and designed as described in the Storm.water C.3 Guidebook (CCCWP, 2005), can meet the "maximum extent practicable" standard for stormwater treatment effectiveness: ~ Swales, planter boxes, bioretention areas, and other facilities using filtration through soil or sand (sized according to the flow-based criterion). m Dry wells, infiltration trenches, infiltration basins, and other facilities using infiltration to native soils (sized according to the volume-based criterion). 111 Extended detention basins, constructed wetlands or other facilities using settling (sized according to the volume-based criterion, with a detention time of 48 hours). Hydrodynamic separators, including vortex separators and continuous deflection separators ("CDS units"), are substantially less effective than any of the above-listed facilities for removing stormwater pollutants of 6 of9 ,.. ,,. .. -.. ,,,. - .. , .. : ,. ,,,. ,·,,. .. ... ,,. Hydrodynamic Separators 3 November 2005 concern. This difference in effectiveness can be inferred by comparing design criteria and mode of operation and analyzing the relative capability of each type of facility to remove small particles. The difference in effectiveness can also be validated by reviewing available results of laboratory and field tests. Experience to date has shown swales, planter boxes, bioretention areas, or other effective treatment facilities can be successfully applied to Contra Costa development sites. lack of space, in itself, is not a suitable justification for using a less effective treatment device since uses of the site and the site design can be altered as needed to accommodate a swale, planter box, bioretention area, or other effective BMP. In most cases, effective BMPs can be fit into required landscaping setbacks, easements, or other unbuildable areas. Operation and maintenance of hydrodynamic separators is more costly and more prone to problems than maintenance of swales, planter boxes, bioretention areas, detention basins, infiltration trenches, and other effective treatment facilities. Separators require frequent maintenance, are .prone to clogging, and are more likely to promote mosquito breeding than any other treatment device except (possibly} constructed wetlands. Hydrodynamic separators have lower initial cost; however, higher maintenance costs over the life of the project substantially reduce and may eventually overcome this initial cost advantage. Costs of effective treatment facilities may be higher than for hydrodynamic separators, but are not likely to be so high as to threaten the economic feasibility of a development project. Because practicable alternatives are capable of providing more effective treatment of stormwater pollutants of concern, hydrodynamic separators do not meet the "maximum extent practicable" requirement for stormwater treatment effectiveness as that requirement applies to compliance with Provision C.3 in Contra Costa. Hydrodynamic separators can be used to remove gross pollutants (trash and coarse sediment} from stormwater upstream of detention basins or other treatment facilities designed to remove pollutants of concern to the maximum extent practicable. Installations of hydrodynamic separators are subject to the Provision C.3.e requirements for operation and maintenance verification. Each installation should be coordinated with the Contra Costa Mosquito and Vector Control District prior to final design. References Cited Caltrans. 2004a. California Department of Transportation, Division of Environmental Analysis. Storm Water Treatment BMP New Technology Report,. November 2004. SW-04-069.04.02. Caltrans. 2004b. BMP Retrofit Pilot Program Final Report. January 2004. CTSW-RT-01-050. Caltrans. 2004c. "Gross Solids Removal Pilot Studies," July 6, 2004 update. http://www.dot.ca.gov/hq/env/stormwater/ongoing/gsrd pilot study/i ndex.htm 7of9 ,,. ,., ... - .. .. .. ! ,.. ,_ ,.. ,,. ,,. ,,. - - ... ,,. ,.. .. Hydrodynamic Separators 3 November 2005 CASQA. 2003. California Association of Stonnwater Quality Agencies. California Stormwater BMP Handbook: New Development and Redevelopment. Chapter 5. www.cabmphandbooks.org Center for Watershed Protection. 2000. "Comparative Pollutant Removal Capability of Stormwater Treatment Practices." Article 64 in The Practice of Watershed Protection. Center for Watershed Protection, Ellicott City, Maryland. www.cwp.org CCCWP. 2005. Contra Costa Clean Water Program. Stormwater C.3 Guidebook, Second Edition. www.cccleanwater.org DEFRA. 2001. Department for Environment, Food, and Rural Affairs, United Kingdom. Expert Panel on Air Quality Standards. Size Distribution and Chemical Nature of Airborne Particles. Francis, Scott. 2005. "CDS C.3 Compliance," August 29, 2005 memorandum to Mario Camorongan, City of Concord, CA. CDS Technologies, Morgan Hill, CA. · KLI. 2002. Kinnetic Laboratories, Inc., in cooperation with EOA Inc. Joint Stormwater Agency Project to Study Urban Sources of Mercury, PCBs, and Organochlorine Pesticides. (Year 2) www.scvurppp.org Luksic, Rachel. 2002. "An Update of the 1999 Catch Basin Retrofit Feasibility Study Technical Memorandum." Santa Clara Valley Urban Runoff Pollution Prevention Program. Hsieh, Chi-Hsu and Allen P. Davis. 2003. "Multiple-Event Study of Bioretention for Treatment of Urban Storm Water Runoff." Diffuse Pollution Conference, Dublin 2003. New Jersey Department of Environmental Protection. 2005. "Conditional Interim Certification Findings: Vortechs® Stonnwater Treatment System by Vortechs, Inc." Rinker Materials, Inc. 2004. "Particle Size Distribution (PSD) in Stormwater Runoff." Info Series, June 2004. Salvia, Samantha. 2000. "Application of Water Quality Engineering Fundamentals to the Assessment of Stormwater Treatment Devices." Santa Clara Valley Urban Runoff Pollution Prevention Program. Scheuler, Thomas R. 1987. Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban BMPs. Metropolitan Washington Council of Governments. Urbonas, Ben. 2003. "Effectiveness of Urban Stormwater BMPs in Semi- Arid Climates." Presented at the regional conference on: Experience with Best Management Practices in Colorado. April, 2003. USEPA. 1999a. United .States Environmental Protection Agency. Storm Water Technology Fact Sheet: Hydrodynamic Separators. EPA 832-F-99- 017. September 1999. USEPA. 1999b. Screening Level Ecological Risk Assessment Protocol, Chapter 3: Air Dispersion and Deposition Modeling . Vortechnics. 2004. Vortechs System Fact Sheet. www.vortechnics.com Washington Department of Ecology, 2005. "General Use Level Designation for Pretreatment (TSS) Pilot Use Level Designations for Basic (TSS) and Oil Treatment for Hydro lnternational's Downstream Defender®. Updated June 1999. 8 of9 ,,. h, ... ,.. .. .. -,,. ... ,,. ,.. .. ,,. .. ,.. -,... - 1111 ,,. -,. .. .. Hydrodynamic Separators 3 November 2005 Water Board. 2003. California Regional Water Quality Control Board for the San Francisco Bay Region. "Contra Costa Countywide NPDES Municipal Stormwater Permit Amendment." Order No. R2-2003-0022. www.waterboards.ca.gov Weber, Walter J. 1972. Physicochemical Processes for Water Quality Control. Wiley-Interscience, New York . Wong, Tony H.F. 1999. "Continuous Deflective Separation: Its Mechanism and Applications." Department of Civil Engineering, Monash University, Australia 9 of9 Fitst d1 fom · for Storrriwcrter Treatment $ysfefus . parts: B(;.[sins By Gary R. Minton It has been 25 years since the first community in the United States established the requirement for the post-development treatment of stormwater from new developments. Since then, local, regional, and state governments have published many manuals and · handbooks identifying acceptable treatment systems (structural best management practices, or BMPs) and design criteria. Initially, few of these design criteria were supported by laboratory or field research. Absent such data, engineers were forced to use best professional judgment in choosing design criteria. With numerous studies completed over the past two decades, it is timely to reexamine some of these criteria. Furthermore, our treatment strategy is rapidly evolving. The focus has been the general removal of pollutants using total suspended solids (TSS) as the surrogate for all pollutants. However, there has been a recent shift to consider specific pollutants. Some states now emphasize the removal of total phosphorus (e.g., Virginia, Washington, New York); total nitrogen (e.g., Maryland, North Carolina); and dissolved metals (e.g., Washington) iri particular situations. With this more complex management strategy, a particular design criterion may differ depending upon the targeted pollutant. This article is the first of a four-part series on design criteria. The first three articles consider three generic types of treatment systems: basins, fine-media filters, and vegetated swales and strips. The fourth article is devoted to the removal of dissolved pollutants. Differences in design criteria to target specific pollutants are also examined. I ·, I . Table 1 provides design criteria for basins from representative manuals and handbooks. Design criteria related to size and configuration are discussed for extended detention ponds and vaults, wetponds and vaults, and constructed wetlands in their many variant forms. On the East Coast, the initial focus was on extended detention ponds, in some cases modified flood control facilities. These basins were expected to be empty after each storm. For many jurisdictions, the basic type has evolved to include some form of wet pool, either covering the entire bottom area or just a small pool, called a micropool, at the outlet. In contrast, on the West Coast, the starting point was wet basins, expected to retain stormwater between storms. However, some manuals now include an extended detention layer in the design. Convergence of concepts appears to be occurring, although the perspective differs. On the East Coast the perspective focuses on extended detention basins with wet pools; on the West Coast, on wet basins with an extended detention layer. Basin Volume In this first article, basin volume is considered with respect to the removal of sediment and attached pollutants such as metals and nutrients. The last article of this series considers the volume required to achieve a significant removal of dissolved pollutants. 0.45 The volume of extended detention basins is commonly defined by specifying the depth of runoff to retain and treat. Initially, the specification was 0.5.inch, based on a philosophy of capturing the "first flush" of pollutants. It was reasoned that the majority of pollutants are present in the first 0.5 inch of runoff. Some jurisdictions began to state a management goal of capturing and treating "X" percent.of the volume of stormwater over · time, typically 85% -90%. This led to an increase in runoff depth to 1 inch or more, as indicated in Table 1. With a volume capture goal of 85% -90%, the relevance of first flush becomes problematic. Not commonly recognized is that the sizing of an extended detention basin involves two questions: the depth of runoff to divert and the volume of the basin. These are two separate but related questions. It is common to assume that the volume of the basin is equal to the design depth of runoff that is to be diverted to achieve the management objective. However, for many jurisdictions, the volume of the basin must be larger than, not equal to, the runoff depth that is to be diverted. Why? It is important to recognize that some stormwater might at times remain in the basin as the next storm arrives. Hence, how much larger the basin must be depends on two factors: the design drawdown time and the interevent time, or the time between runoff events. The required basin volume increases as the interevent time decreases and as the specified drawdown time at . brimful increases. The above effects are understood from the work of Guo and Urbonas (1996) and related articles. Their methodology solves directly the relationship between the management goal and the size of the basin for a particular climatic region. The concept is illustrated in Figure 1. They proposed that the selected basin volume be equal to the maximized water-quality capture volume (WQCV), shown in Figure 1. The WQCV is defined as the point on the curve where an incremental increase •in the storm volume captured and treated begins to decrease significantly with the incremental increase in basin volume. At the WQCV, the amount of stormwater captured over time is on the order of 80% -95%, depending on the community, and is therefore close to the management goal of many communities. The normalized WQCV in Figure 1 is all events divided by a value of runoff depth equal to the 99.5 percentile runoff depth for each community. Normalization allows comparison between communities. FIGURE 1. Portrayal ot the Concept of Guo and Utbonas (1996) 1 0.9 ti e ;J 0.8 +--~~·Plc::----+----·¼----tc----! @-(.) 0.7 -t-,~"'.'1--+-"-""'ll >-l o,s +--+---+-- § 0.5 -t-r--.r+--- ~ 0.4 +-1----.... ----.:.,,..---+----~---1 Q . t: 0.3,4-1.---4-e o.2 +-. r---~~ tr. 0.1 ,+,f........-,,,,,..,_-+----+----+-----1---.......-1 0 sp; e;_..---4----;..----4----....J...---....,i 0 0.2 OA 0.6 0.8 1 NormaJized Water-Quality Capture Volume Representative results from Guo and Urbonas (1996) are presented in Table 2. Here the volume of the basin is specified as a multiple of the depth of the mean annual runoff event. The mean annual runoff event is the total annual runoff divided by the total number of runoff events (Driscoll et al. 1989). For example, assume a community has a·. mean annual storm runoff depth of 0. 7 inches and a sizing ratio of 2. The volume of the extended detention basin is 1.4 inches times the tributary area and the runoff coefficient. TABLE 2 Maximized Detention Volume Ratio for Various Cities a, b . '.. . ... ,.... .. . ... -. -.. --· . . .. -·· . . •.. . . . .. -· . ~ . ., ·-..... Drawdown J Boston CincinnaU _ Denver Seattle lra~pa_ j Sacramento j ASCE 12 hours I 1.67 j 1.13 1 1.21 0~ 1.65 .. _ _ 1.00 __ ~ 1'.31 _ 24 hours j 1. 79 j 1.46 -_ 1.36 1.34 1. 76 _ _ _ 1.50 _ _ _ j 1.58 48 hou~~~l._2-89 _J ___ · ~~~~-J~-1A9] 2.29 1.95-J ~-2.31·-.. T ~96~~ a. J. Guo and B. Urbonas 1996 b. Based on 95% impervious surface ........... -· Table 2 shows the incremental effect on basin volume of increasing the drawdown time at brimful from 12 to 48 hours. It shows that increasing the drawdown time increases the required volume for the basin. This point is typically not recognized. Why must the volume be increased? Because the longer the drawdown time the more likely there will be stormwater in the basin when the next storm arrives. The effect differs significantly between communities. The incremental effect is minor for Boston, Tampa, and Denver. ,,. ... ,,. ... .... ,,,. .. ,,,,,. .. ,,,. .. ,.. -,. ,,. - .. ,... Conversely, it is significant for Seattle and Sacramento where the interevent times are relatively short during the wet season. For a given community, the aggregate volume of water captured over time is the same irrespective of the drawdown time specified at brimful. But the basin must be larger with greater design drawdown times. The ratios in Table 2 do not account for infiltration or evaporation. For the specified storm depths presented in Table 1, the ratio of volume of the basin to the runoff volu_me of the mean annual event (VbNr) ranges from 1.5to 3. While the ratios lie within the vicinity of the WQCV values suggested in Table 2, it is unlikely values currently specified in many manuals that are the most appropriate for their regions. This is because, as noted previously, it is commonly assumed that the volume of the basin is equal to storm depth to be diverted. Also presented in Table 2 are national values (ASCE 1998) based on the work of Guo. Given the substantial climatic differences between regions, apparent in Table 2, using average national values may result in either an undersized or oversized facility depending on the community. Other methods for determining the WQCV have been proposed, such as the California Stormwater Quality Association (CASQA 2003); Goforth-et al. (1983); King County (1998); Nix et al. (1983); Pitt, R. (2000); and Roesner et al. (1991). These methods have not been compared to ascertain whether they provide outcomes similar to Table 2. It is likely dissimilar results will be found. A professional dialogue is needed to ascertain the most appropriate method. For that reason, this author is not suggesting the approach by Guo and Urbonas (1996). Rather, it is presented to make the point that interevent time, the selected drawdown time, and the selected management objective interrelate to affect the design volume of a basin. As such, the selection of the drawdown time and the management objective are not separate decisions. With respect to wet basins, Table 1 indicates that it is common practice to specify a volume that is the same as that specified for extended detention basins. Some manuals · specify a larger volume. However, it is intuitive that a wet basin can be smaller than an extended detention basin if the desired removal efficiency or effluent concentration of TSS is the same. This is because additional settling occurs in wet basins between storm events. A synthesis of data of wet basin performance, Figure 2 suggests a VbNr of 1 is sufficient (Strecker 2003). Figure 2 plots effluent concentration as a function of the VbNr. The plot indicates little further reduction in the effluent concentration beyond a ratio of 1. Comparison of Figure 2 to Table 1 suggests that communities oversize wet pool basins if sediment and attached pollutants are the ·only objective. The data in Figure 2 reflect what is settling from the stormwater and the growth of plankton algae. Hence, TSS do not approach zero even with large basin volumes. It was previously observed with extended detention basins that maximization of the removal of particulate metals and nutrients likely requires a larger basin than if TSS r~moval is the sole objective. This may also be the case for wet basins. Hence, a VbNr on the order of 1.5 may be desirable. ,,.. ,,. I .... JIii ,,,,,. ... ,. .... ,,. ... ,.. ,.. .. -,,. .... ,,. ... ,,. ... ,. ... .,,,,.. FIGURE 2. VbNr Ratio and Effluent TSS (Strecker 2003) 50 f 0 40 0 0 0 30 0 0 0 0 0 0 -· ___________ ....__..._... ____ _ 0 1 2 3 4 . 5 6 7 8 · 9 10 Permanent Pool Volume (watershed meters} With respect to the West Coast perspective, the question arises as to the benefit of placing an extended detention layer atop a wet pool. Most manuals suggest splitting the design volume in half: half wet pool and half extended detention layer. A few suggest increasing the design volume to add an extended detention layer. The relative benefits of this approach are discussed later in this article. Drawdown Time Drawdown time is the time required to empty an extended detention basin or layer from brimful, the el~vation of overflow. As noted previously, the design drawdown time at brimful affects the size of an extended detention basin; its specification is therefore important. Table 1 presents a significant range of drawdown times, from 24 to 72 hours at brimful. The first recommendation for drawdown time was 40 hours at brimful, averaging 24 hours for all events (Grizzard et al. 1987). The recommendation was derived from a field study of one converted flood control detention pond and laboratory column tests. The ,,,.. ,,.. .. ... ',,. ,,,.. .. ',,,,. .,,,. ... I ,,.. .,,. ... ,,,. laboratory studies showed little additional removal of TSS beyond a settling time of six to 24 hours depending on the initial TSS concentration. A more recent study of a field basin (Keblin et al. 1998) found negligible improvement in TSS reduction at drawdown times in excess of 24 hours. As settling velocity distributions of sediment in stormwater can vary regionally because of varying soil types, the appropriate drawdown time may also vary regionally. For example, in New England, where a significant fraction of the sediment may be deicing sand, a lower drawdown time is likely needed than in the Pacific Northwest to achieve the same performance goal. Other pollutants need to be considered. Generally, metals and phosphorus associate primarily with the fine sediments, necessitating relatively longer drawdown times to achieve high removal of the particulate forms. The work of Keblin et al. (1998) suggests that achieving the highest practical removal efficiency of particulate metals may be twice that of only the sediment. It appears that the average drawdown time should be at least 24 hours. However, 48 hours is likely prudent in most regions. This results in drawdown times at brimful on the order of 40 to 72 hours. There is little reason not to specify a greater drawdown time in communities, such as Boston, where the effect on basin volume is minor. If the effect of the qecision is significant, as with Seattle and Sacramento, local studies of the relationship between performance and drawdown time should be conducted. This suggests that the analysis of the relationship between drawdown time at brimful and basin volume needs to be extended beyon~ 48 hours. The above discussion is relevant to extended detention basins that dry completely between storms. However, most manuals now encourage inclusion of some form of permanent wet pool. This raises the question as to whether very long drawdown times are necessary. One manufactured product, the StormVault, uses the combined wet pool/extended detention layer configuration. It appears to provide satisfactory treatment with a drawdown time at brimful of only six hours. The contribution of the wet pool to performance is likely significant. Drawdown Rate Although drawdown time has been in use for two decades, it is not necessarily the correct design criterion. The more appropriate criterion may be the drawdown rate; that is, the rate at which the water level drops in the basin. Consider two basins, identified as A and 8, both with the same design volume and drawdown time at brimful. They differ in that Basin A has an average depth at brimful one-third that of Basin B. Hence, Basin A has three times the surface area of Basin B. It follows that the average drawdown rate of Basin A is one-third that of Basin B. As a consequence, Basin A removes particles that are much smaller, with lower settling velocities, than Basin B. Conceptually, the perspective is to recognize that all particles with settling velocities greater than the fall rate of the water will reach the bottom of the basin before the water exits the basin. The slower the fall rate, the smaller the particle that reaches the bottom. The fall rate in an extended detention basin is akin to the hydraulic loading rate (HLR). The HLR is expressed as cubic feet per second per square foot of basin surface area. It will be noted that the units of cfs/ft2 are also ft/sec: the units of the settling velocity of a particle. -The relevance of the HLR has been recognized in water and wastewater treatment for a century (Hazen 1904) and is the basis for sizing sedimentation basins (AWW A 1990; F ') \ Metcalf and Eddy 1991 ). Its appropriateness has also been recognized for stormwater treatment (Small and DiToro 1979; USEPA, 1986; Dorman et al. 1996). Is there a benefit of specifying drawdown rate rather than time? Table 2 suggests it depends upon the community. The advantage of specifyin_g the drawdown rate is that the needed drawdown time and therefore basin volume decreases with a shallower basin, compensating for the larger area required of a shallower basin. For example, assume the local jurisdiction selects a drawdown rate of 0.15 ft/hr. For a basin with a depth of 7 .2 feet, the drawdown time is 48 hours at brimful. If a depth of 3.6 feet is selected, the drawdown time need only be 24 hours. According to Table 2, the required basin volume is only about 5% less for Boston and Cincinnati, 10% for Denver and Tampa, but approximately 40% for Seattle and Sacramento. What is the appropriate drawdown rate? Figure 3 summarizes information for several studies of extended detention basins. The data are from facilities in California, Maryland, North Carolina, Virginia, and Texas. Shown is the effluent concentration versus drawdown rate. Basing the choice of drawdown rate on effluent concentration may be more valid than efficiency, because efficiency tends to be lower at lower influent concentrations. However, effluent concentration is not independent of influent concentration, complicating the analysis. FIGURE 3.. Effluent TSS Concentration as Related ·to Average orawdown Rate at Brimful 140 120 20 0 0.00 0.50 1.00 1.50 2.00 Drawdown Rate (ft/hr} As the data are scattered, the appropriate drawdown rate is not readily obvious. Some of the scatter is due to highly varying median influent concentrations. It is also noted that the performances observed in each study reflect drawdown rates that are much lower than that at brimful because most storms in each study did not fill the respective basin. Given the scatter in Figure 3, one might conclude we should continue to use drawdown .... .. .. ... 11111 ,,. .. .. ,,. .. ... ,,,. ,- '-- time. However, to be fair, if the abscissa in Figure 3 were plotted against drawdown time, a similar scatter would be found. It would be just as difficult to 'select a drawdown time from such a scatter. Figure 3 suggests that below 0.30 ft/hr, the incremental benefit is problematic. Based on the work of Keblin et al. (1998) previously cited, this value should be halved to 0.15 ft/hr to achieve the maximum practical removal of attached pollutants . This value represents the average drawdown rate from brimful The size of particle that settles faster than a drawdown rate of 0.15 ft/hr is about 5 to 15 microns, depending on water temperature and the specific gravity and shape of the particle. However, particles smaller than this size range will be found on the bottom of the basin for two reasons. First, during all events the fall rate is for much of the time less than the average rate at brimful. Secondly, the stormwater as it enters the basin is thoroughly mixed vertically. As a consequence, many particles less than the 5-to 15- micron range reach the bottom before the basin empties because they are close to the bottom as they enter the basin. Is detention time irrelevant? Drawdown rate is relevant to particles that are discrete. That is, as they fall, coagulation does not occur when two particles make contact. Silts and sands are discrete suspensions, whereas clays coagulate given sufficient time. By convention, clay particles are smaller than 5 microns. Hence, at a drawdown rate of 0.15 ft/hr, much of the clay suspension might not reach the bottom before the basin empties unless it coagulates into larger particles. It is possible at influent sediment concentrations less than about 50 mg/L the clay fraction is significant, in which case time for coagulation may be important. Grizzard et al. (1986) found at these low concentrations it took on the order of 48 hours to reach a percent removal similar to that achieved in only two hours when the initial TSS concentration was on the order of 100 mg/L. Thi~ suggests extended time is needed for coagulation at very low initial concentrations. However, it is questionable as to whether high .levels of performance are relevant at such low initial concentrations. Some manuals specify a drawdown time of 24 hours for the average condition, but this average condition is not typically defined. Regardless, it is likely thateven with this specification, clays have insufficient time to satisfactorily coagulate. Hence, there may be an inherent limitation for extended detention basins if clay is a significant fraction of the incoming sediment. As such the benefit of a wet pool becomes apparent. The long residence time between runoff events provides sufficient time for the clay to coagulate in the wet pool and to reach the bottom of the basin. These issues again point to the importance of understanding local conditions and influent concentrations when selecting an appropriate drawdown rate. Length-to-Width Ratio The purpose of specifying a length-to-width (L/W) ratio is to improve hydraulic efficiency by reducing short-circuiting and dead zones. With respect to wet basins, hydraulic efficiency is defined as how well fresh stormwater exchanges with older water in the basin. Table 1 indicates a large range in design values. Specifying an L/W ratio for extended detention basins is likely unnecessary as these basins operate essentially as fill-and-draw systems. The constricted outlet tends to force incoming stormwater into all areas of the basin. A comparison of six extended detention basins in which the L/W ratio varied from 3 to 10 found no difference in performance (Caltrans 2004). Whether performance is affected by ratios in the range of 1 to 3 is unknown. ,,.. .... ,,. .. ,. ... .. ,.. ,,,. .. ,,. .. ,,. 111111 ,,,. .. - ,,. 11111 ,,. .. While a high L/W ratio may maximize hydraulic efficiency, it may also create a geometry that is difficult to fit into many developments. Furthermore, excessively narrow basins may induce the resuspension of sediments because of greater throughput water velocities. The experience from wastewater treatment is to have substantial L/W ratios, on the order 10 to 20 or greater depending on the unit operation (e.g., sedimentation, chlorination). Such high L/W ratios are not necessary in stormwater systems because the rate of inflow is generally lower relative to the basin volume than in wastewater systems . One study of the relationship between the UW ratio and hydraulic efficiency suggests a ratio above 2 provides little additional benefit. Figure 4 is an interpretation of Walker (1998). It shows the effect of increasing the UW ratio on hydraulic efficiency. Figure 4 suggests modest benefit of incremental increases of the ratio above 2. It also suggests the appropriate L/W ratio likely differs with the size of the basin as defined by the VbNr value. For basins with large VbNr values a L/W ratio of 2 is likely satisfactory. If the VbNr of wet basins is on the order of 1 as recommended in this article, the UW ratio should be greater, perhaps 3 to 4. The storm intensity common to the region may also be relevant to this decision. In the Southeast, with high-intensity storms, the incremental benefit of increasing the L/W ratio is likely greater than the Pacific Northwest with its mild storms. This difference is suggested by contrasting the results of Persson et al. (1999) and Persson (2000) to Walker ( 1996). In the former studies significant benefit was found up to a ratio of 5. However, these studies were conducted at higher flow rates. FIGURE 4. Effect of Length-to-Width Ratio on Water Volume Exchange (after Walker 1998) 1 0.9 O.& -c::, ! 0.1 ~ 0.6 = 0.5 Q) E 0.4 ::J 0.3 ~ 0.2 0.1 ~ Storm 0.5 of pond votume Storm VOIUm8 equal to pond VOIOOle 0'----""---------------0 2 4 L/W Ratio 6 8 Poor hydraulic efficiency has been found not to be an issue with poorly configured large wet basins with VbNr values on the order of 10 (Pitt 2000). This is not likely the case with smaller VbNr ratios. Baffles were added to a pond with a VbNr of about 1.5, increasing the L/W from 1.5 to 4.5 (Mathews et al. 1997). A significant improvement in hydraulic efficiency was observed. ,,.. '- ... ... ,,. - ,. .. Illa ,.. An L/W ratio of 1 is likely valid for small wet basins if an extended detention layer is included on top of the wet pool. Restricting the outlet causes stormwater to "back into" areas that would otherwise be dead zones such as corners or areas of dense vegetation. The designer may be allowed the flexibility of using either a wet pool only with a large L/W ratio, or a combination extended detention/wet pool with a smaller L/W ratio to meet site constraints. For pure extended detention basins a L/W ratio of 1 is likely sufficient. As with the L/W ratioi the benefits of an extended detention layer may differ with the climatic region: The concept may be most beneficial in the Southeast with its short, high- intensity storms and high rates of inflow. In contrast, the concept may be of less benefit on the West Coast where average storm intensities are much less. The above discussion does not take into consideration the potential adverse effects of thermal or density (from deicing salts) stratification on hydraulic and therefore performance efficiency. The effect of stratification is poorly understood. Thermal stratification reduced the detention time of a small wet basin by half (Timmins et al. 1999). The significance of stratification to performance is unknown, as is the effect of the energy of incoming .storms to temporarily destratify the basin. One study concluded that summer storms abetted stratification due to the incoming stormwater being higher in temperature than the pond water (McBean and Burn 1983). Stratification should not reduce performance during storms. As established above, performance is a function of hydraulic loading rate, which remains the same irrespective of stratification. However, stratification reduces the exchange of fre~h stormwater with water present in the basin. As a consequence, stratification in effect reduces performance between storms with respect to fine sediments and dissolved pollutants. Increasing the L/W ratio might decrease the potential for stratification by increasing flow velocities within the basin. Subsurface discharge to the lower half of the wet pool and/or entrance baffles might have a greater mitigating effect than a large L/W. A final note of interest is that in the study cited above, thermal stratification occurred in the top 10 inches of the wet pool. This suggests that the common recommendation (Table 1) to limit the maximum depth to avoid stratification may not be effective. More studies on this subject are needed. Multiple Ponds or Cells Several manuals suggest incorporating multiple cells, either as separate basins in series or by separation of one basin into two or more cells with a berm extending above the water surface. Multiple cells can significantly increase space requirements. The purported benefit is more effective treatment. However, there are no data substantiating this claim. Some conceptual designs like that shown in Figure·s may result in poorer performance than one basin of equal volume. While aesthetically pleasing, multi-ponds with irregular shapes increase short-circuiting and dead zones. This decreases hydraulic efficiency and, as a consequence, performance efficiency. An extended detention layer may minimize this effect. I ,.. ... .... ... ,,. -,,,. .. ,,.. -,,,. ... ,,,. .. ... ,.. ... .. FIGURE· $. A Conceptual Design for Constr\toted Wet~ends Vegetation Coverage For wetponds, a shallow safety bench of 10 to 15 feet in width is commonly recommended. The benches become covered by emergent vegetation. For wetlands, manuals usually specify a depth regime that results in vegetation coverage on the order 60% -85% of the surface area. Concepts of vegetation configurations are frequently included in manuals (Figure 5). Depending on its degree and location, emergent vegetation may enhance or degrade hydraulic efficiency and therefore performance efficiency. If the basin is configured so as to produce an open area down the middle of the basin, hydraulic efficiency and therefore performance is reduced. Water, finding the path of least resistance, moves through the center of the basin, with little exchange with "old" water in the densely vegetated areas along the sides of the basin (Persson et al. 1999). In shallow marsh wetlands, low-flow channels may have a similar effect. As the wetland ages, a pattern of uneven plant densities may create channels of less resistance, decreasing hydraulic efficiency. A more appropriate configuration might be open fore-and after bays with a shallow intermediate marsh area and no low-flow channel. To use less space, the intermediate area could be of wetpond depth. The interface between the central area and_ the fore-or after bays can be a berm, but with the top below the water and covered by emergent vegetation. This berm configuration could more evenly spread incoming water across the lateral cross-section of the pond. Alternatively, as previously noted, an extended detention layer might compensate for the adverse effects of fringe vegetation on hydraulic efficiency. Sediment Storage The common criterion is to either add 1 foot of depth or increase the basin volume by 20% above that calculated for performance. The added cost is not trivial. However, once construction of the development is complete, the accumulation rate of sediment is ,.. - ,,.. 111111 .... .. .. ,,. -... ,,.. -,,,. ... ,,. .. ,,. .. .... .. ... .. ,,. ,.. .. modest, on the order of 0.25 to 0.5 in/yr. Furthermore, most of the incoming sediment settles in the forebay. It is suggested that this requirement be eliminated, particularly if a forebay is inherent to the design. Furthermore, a more cost-effective alternative to the earthen forebay might be a large standard manhole, a small manufactured wet vault (e.g., Stormceptor), or a vortex separator. Even if the initial cost is greater, the life-cycle cost might be lower given the greater ease of maintenance of these devices . Final Observations The discussion suggests that wet basins and extended detention basins are not separate types but opposite ends of the same type. A continuum exists between the two extremes, depending on the climate of the particular region and the design volume. The discussion further suggests that extended detention basins should perform as well as wet basins, although they must be larger to achieve similar performance with respect to the removal.of sediment and particulate pollutants. As previously noted, particles as small as 5 to 10 microns should be readily removed at current drawdown rates . However, performance studies suggest otherwise, as implied in Figure 3. TSS in the effluent of wetponds are typically on the order of 1 O ·to 20 mg/L, whereas they are on the order of 20 to 40 mg/L for extended detention basins. This discrepancy is due in part to wetponds having volumes equal to or greater than those of extended detention basins (Table 1 ). It may also be due in part to the likely inability to induce the coagulation of clay even with a specified drawdown time for small storms. Design aspects other than volume and drawdown time might contribute to a less-than- expected performance for extended detention basins. The most likely reasons are adverse inlet and outlet conditions. Resuspension of previously deposited sediment and erosion may occur in the inlet area during the infrequent high-intensity storms if energy dissipation is insufficient. Resuspended clays might have insufficient time to re- coagulate and as a result exit during these events. The more likely candidate for subpar performance is the outlet structure. In a water or wastewater basin, exiting water is gathered along an effluent weir that extends the width of the oasin. This minimizes approach velocities to the weir. By contrast, the outlet structures of extended detention basins are very small relative to their end-cross sections. As a consequence, stormwater "rushes" toward one relatively small point in the basin. Approach velocities near the outlet are excessive relative to the settling velocity of silts and clays, and even fine sand. The effective HLR in the vicinity of the outlet is substantially greater than the nominal HLR of the basin. Sediments that should be removed based on the nominal HLR, or drawdown rate, are lost through the outlet. This condition is exacerbated if the bottom around the outlet is bare, allowing for erosion at the high approach velocities. While wet basins also have narrow outlets, the effect is less severe. With wet basins the water exiting each storm is "old" water that is relatively clear of fine sediments, given the retention time between storms . One or a combination of design elements may mitigate the effect of small outlet structures. Several outlet risers tied to an exit manifold may help. However, the issue of clogging very small orifices arises. A shallow wet pool or micropool at the outlet may counter the effect of excessive approach velocities by preventing scouring of accumulated sediments at the bottom of the basin in the vicinity of the riser structure (Fennessey and Jarrett 1997). Some have found that withdrawal at the surface improves performance (Ward et al. 1979; Millen et al. 1997) whereas others have not (Keblin et al. ',,. - ,,. .. .. ,,. -i,,,. ... 1998). Spacing, size, and the location of perforations on the riser may affect performance (Ward et al. 1979). However, another study found no significant difference in performance between a single bottom orifice and a perforated vertical riser (Fennessey and Jarrett 1997). It is possible that while the riser configuration reduces approach velocities, the reduction may not be sufficient to significantly affect performance. Certainly, however, a riser structure with a series of vertically placed holes should reduce erosion and/or resuspension in the immediate vicinity of the outlet. A cone of gravel around the bottom of the outlet structure has been found to significantly improve performance (Engle and Jarrett 1995). More studies on this issue are needed. Basins sized as suggested here should be able to meet the general criterion of 80% removal of TSS, a specification of most manuals. They should also be able to meet the specification of 40% removal of the total phosphorus (TP) inasmuch as 75% -90% of the phosphorus is typically bound to the sediments. Meeting the goal of 40% removal of nitrogen is less certain given that it is more soluble than phosphorus. These questions are considered in the fourth article of this series. It is common to specify a minimum drainage area, under the thesis that a base flow of water into the basin is needed to keep a permanent pool. This limits the use of wet basins for larger areas, on the order of at least 10 to 25 acres depending on the region. The concern is that the wet basin will not fully function without water. This is not the case. There is no need for the basin to "work" between storms. Pollutants migrate to the bottom as water evaporates and into the soil with infiltration. Allowing the pond to dry may reduce mosquito problems. Infiltration is good for the hydrologic cycle. However, drying may solubilize some pollutants, which might be lost in subsequent storms. If the removal target is solely TSS and attached pollutants, this is no concern. Even if dissolved pollutants are of concern, the pond or wetland fills with the next storm, at which time the solubilized pollutants likely renew attachment to inorganic and organic sediments. Constructed wetlands can withstand extended periods of dryness without harm to the vegetation. Specifications as to the maximum length of dryness to avoid this problem may be prudent and will vary with the climatic region and vegetation species. It is also important to recognize that a constant base flow can reduce the performance with some pollutants. One study found a negative net removal of phosphorus (Oberts 1997). Removal during storms was offset by loss ln base flows during dry periods . The concepts discussed in this article are also relevant to manufactured basins such as Stormceptor, BaySaver, EcoStorm, and Stormvault. Regardless of how they may be configured, they are essentially wet vaults. Summary The data suggest wet basins can be smaller than currently specified. They also can be smaller than extended detention basins if the sole objective is the reduction of sediment and attached pollutants such as metals, pesticides, and nutrients. In most situations this "basic" level of treatment is likely sufficient. A dead storage volume equal to the runoff of the mean annual event<that is, a VbNr of 1 to 1.5<is likely adequate for wet basins. A larger volume may be necessary where significant removal of dissolved pollutants is also desired. This aspect is considered in the four:th article of this series. To achieve reasonably equivalent performance, extended detention basins must be larger than wet basins with a VbNr on the order of 2 to 2.5, depending on the region. ,,.. ,,,. ... ,,. ... ... ,.. ,,. ... ... ,.. ... ,,,. ... .. ,.. ... ... ,,,. .. ,,,.. The specification of volume must also take into consideration the specified drawdown time at brimful and the interevent time for the locality. A longer specified drawdown time and shorter interevent time requires a larger basin volume to achieve the same management objective with respect to the aggregate volume of water treated over time. The effect of infiltration and evaporation could be included in this analysis. Drawdown rate rather than drawdown time is the correct design criterion for extended detention basins. In some regions, in particular the West Coast, recognition of drawdown rate as the correct criterion results in more cost-effective sizing. Current data suggest the specification for the average drawdown rate from brimful be on the order of 0.15 ft/hr. Although there is considerable uncertainty with this specification, the same uncertainty exists with the current specification for drawdown time. Regardless, even if changing from drawdown time to rate has little effect on basin volumes for much of the nation, the use of drawdown rate will ensure that field studies gather the appropriate information that has been lacking in most previous studies . Drawdown time may be relevant to the extent that clay is a significant fraction of the incoming sediment. Local studies are needed to ascertain the relevance of clay as are more studies on the relationship between time, coagulation, and settling. The data suggest, however, that the issue of clay might not be the most significant factor in what appears to be less-than-expected performance of dry basins. There may be an inherent limitation of extended detention basins to perform as well as wet basins irrespective of the drawdown rate or time. Design aspects other than volume and drawdown time must be considered, in particular the outlet structure. Modifications to current outlet design specifications are needed to reduce approaching velocities and the potential for resuspension and/or erosion in the vicinity of the outlet. The limitations of these basins can be mitigated through the inclusion of a wet pool. However, at some point the question arises as to what is being designed:. an extended detention basin with a wet pool or a wet basin with an extended detention layer. It follows that at some point the relevance of an extended detention layer becomes problematic. The length-to-width ratio is an important design parameter for wet basins, but it is probably not particularly relevant to extended detention basins. A ratio on the order of 2. to 4 is likely sufficient for wet basins. The appropriate ratio depends on the selected VbNr and general rainfall intensity. A ratio of 1 is likely sufficient for extended detention basins. Oddly configured basins or basins with varying bathymetry adversely affect hydraulic efficiency and therefore performance efficiency. The adverse effect of such configurations can be reduced by increasing the size of the system and/or by including an extended detention layer. However, as these relationships are little understood, it is advisable to carry out the appropriate studies before imposing such requirements. Care must be taken with emergent vegetation. Depending on location and density, emergent vegetation can be counterproductive. Vegetation along the sides of a wet basin, with open water down the center, reduces hydraulic efficiency. This can be countered by lateral berms with emergent vegetation and/or an extended detention layer. The significance of this observation is greater in regions with high-intensity storms such as the Southeast. ,,. ... ,,,. .... ,,. ... ... ... ,,,. ... : ,,. .. ,,. ... ... ,,. .. .. ,,,. ,,. .. ,,. .. ,... Additional laboratory and field studies are needed to better define the significance of the observations and recommendations made in this article. Being aware of the relevant design criteria and how their selection may affect performance leads to studies in which the most relevant characteristics of performance are evaluated such as hydraulic efficiency, water level fluctuations, and the size distributions of incoming and outgoing sediments . References American Society of Civil Engineers (ASCE), 1998, "Urban Runoff Quality Management," Manual and Report of Engineering Practice 87, Reston, VA. American Water Works Association (AWWA), 1990, Water Quality and Treatment, F.W. Pontius (ed), McGraw-Hill, New York, NY . Barrett, M., 1999, "Complying with the Edwards Aquifer Rules: Technical Guidance on Best Management Practices," Texas Natural Resource Conservation Commission, Austin, TX. California Department of Transportation (Caltrans), 2004, "BMP Retrofit Pilot Program, Final Report," CTSW-RT-01-050. California Stormwater Quality Association (CASQA), 2003, "Stormwater Best Management Practice Handbook," New Development and Redevelopment. Dorman, ME, M.E. Hartigan, J.P. Steg, and T.F. Quasebarth, 1996, "Retention, Detention, and Overland Flow for Pollutant Removal from Highway Stormwater Runoff," FHWA-RD-095, US Federal Highway Administration, McLean, VA . Driscoll, E, G.E. Pelhegyi, E.W. Strecker, and P.E. Shelly, 1989, "Analysis of Storm Event Characteristics for Selected Rainfall Gauges Throughout the United States," prepared for USEPA . Engle, B.W ., and A.R. Jarrett, 1995, "Sediment Retention Efficiencies of Sedimentation Filtered Outlets," Trans. Amer. Soc. Agri. Engrs, 38, 2,435. Fennessey, L.A., and A.R. Jarrett, 1997, "Influence of Principal Spillway Geometry and Permanent Pool Depth on Sediment Retention of Sedimentation Basins," Trans. Amer. Soc. Agri. Engrs., 40, 1, 53 . Goforth, G.F., J.P Heaney, and W.C. Huber, 1983, "Comparison of Basin performance Modeling Techniques," J. Environ. Engr., 109, 5, 1082 . Grizzard, T.J., 1987, "Final Report: London Commons Extended Detention Facility Urban BMP Research and Demonstration Project," Virginia Tech University, Occoquan Watershed Monitoring Laboratory, Manassas, VA. Grizzard, T.J., C.W. Randall, B.L. Weand, and K.L. Ellis, 1986, "Effectiveness of Extended Detention Ponds in Urban Runoff Quality<lmpact and Quality Enhancement," B. Urbonas and L.A. Roesner (eds), American Society of Civil Engineers, New York, NY. Guo, J., and B. Urbonas, 1996, "Maximized Detention Volume Determined by Runoff Capture Ratio," J. Water Res. Plan. and Manage., 122, 1, 33. ... ... .... ... 111111 ... ,,,. ... ,,,. 11111 ,.. ... ... ,,. ... ... .. ... ,.. -,,. Hazen, A., 1904, "On Sedimentation," Trans. Amer. Soc. Civil Engr., 53, 45. Keblin, M.V., M.E. Barrett, J.F. Malina, and R.J. Charbeneau, 1998, "The Effectiveness of Permanent Highway Runoff Controls: Sedimentation/Filtration Systems," Research Report 2954- 1, Center for Transportation Research, University of Texas, Austin, TX. King County, 1998, Surface Water Design Manual, Department of Natural Resources, Seattle, WA. Mathews, R.R., W.E. Watt, J. Marsalek, A.A. Crowder, and B.V.C. Anderson, 1997, "Extending Retention Times in a Stormwater Pond with Retrofitted Baffles," Water Qual. Res. J. Canada, 32, 1 73. McBean, E.A., and D.H. Burn, 1983, "Thermal Modeling In Urban Runoff and the Implications to Stormwater Pond Design," in International Symposium on Urban Hydrology, Hydraulics and Sediment Control, University of Kentucky, Lexington, KY . Metcalf and Eddy Inc., 1991, Wastewater Engineering: Treatment, Disposal, Reuse, McGraw-Hill, New York, NY. Millen, J.A., A.R. Jarrett, and J.W. Faircloth, 1997, "Experimental Evaluation of Sedimentation Basin Performance for Alternative Dewatering Systems," Trans. Amer. Soc. Ag. Engrs., 40, 1087 Minton, G.R., 2002, Stormwater Treatment: Biological, Chemical, and Engineering Principles, RPA Press, Seattle, WA, www.stormwaterbook.com . Nix, S.J., J.P. Heaney, and W.C. Huber, 1983, "Analysis of Storage/Release Systems in Urban Stormwater Quality Management: A Methodology," 1983 International Symposium on Urban Hydrology, Hydraulics and Sediment Control, University of Kentucky, Lexington, KY . Oberts, G., 1997, Lake McCarrons Wetland Treatment System-Phase Ill Study Report," Metropolitan Council of the Twin City Areas, St. Paul, MN. Persson, J., N.L. Somes, and T.H. Wong, 1999, "Hydraulic Efficiency of Constructed Wetlands and Ponds," Water Sci. Tech., 40, 3, 291 . Persson, J., 2000, The Hydraulic Performance of Ponds of Various Layouts, Urban Water, 2, 243. Pitt, R., 2000, "The Design and Use of Detention Facilities for Stormwater Management Using DETPOND," University of Alabama . Raasch, G.E., 1979, "Urban Stormwater Detention Sizing Technique, in International Symposium on Urban Storm Runoff," University of Kentucky, Lexington, KY. Roesner, L.A., Burgess, E.H. and Aldrich, J.A., 1991, "Hydrology of Urban Runoff Quality Management," Proceedings of the 18th National Conference on Water Resources Planning and Management, Symposium on Urban Water Resources, New Orleans, LA . Small, M.J., and D.M. Ditore, 1979, "Stormwater Treatment Systems," J. Environ. Engr., 105, 3, 557. ,.. ... ,,.. ., ,.. ,,.. ... ,,,. ,,,. ... ... ,,. ... ,,. .. ,.. ... --.. Strecker, E., 2003, presentation to the Independent Science Panel regarding its review of the technical adequacy of the State of Washington Stormwater Management Manual for Western Washington. Timmins, K., T.L. Koob, M.E. Barber, and D. Yonge, 1999, ''Thermal Stratification Impacts on Wetpond Performance," International Water Resources Engineering Conference, ASCE, Seattle, WA. USEPA, 1986, "Methodology for Analysis of Detention Basin for Control of Urban Runoff Quality," USEPA 440/5-87-001, Washington, D.C. Walker, D.J., 1998, "Modeling Residence Time in Stormwater Ponds," Ecol. Engr., 10,247 . Ward, A.O., C.T. Haan, and B.J. J3arfield, 1979, "Prediction of Sediment Basin Performance," Trans. Amer. Soc. Ag. Engrs., 22,1, 126. Whipple Jr., William, Hunter, Joseph V., 1981, "Settleability of Urban Runoff Pollution," J. Water Pollution Control Federation, Vol. 53, No. 12, pp. 1726 -1731. Gary Minton, Ph.D., P.E., is an independent consultant on stormwater treatment with Resource Planning Associates. He is author of the book Stormwater Treatment: Biological, Chemical, and Engineering Principles (www.stormwaterbook.com). Part 2: Fine-Media Filters By Gary R. Minton SW November/December 2004 This is the second of a four-part series examining design criteria for stormwater treatment systems. In the first of this series (Storrnwater, November/December 2004, sw 0411 revisiting.htmD. basins were the focus. Now we shift our focus to fine-media filters, which are filters that use fine-grained media similar to those used for potable water treatment. The concept of using fine media for stormwater treatment was first adopted by the City of Austin, TX, in the late 1970s. The most commonly used medium is sand, although other media are discussed in this article. Not considered in this article are manufactured stormwater filters, which commonly use coarser media. Since communities in the United States first began requiring post-development treatment of stormwater from new developments 25 years ago, local, regional, and state governments have published many manuals and handbooks identifying acceptable treatment systems (structural best management practices) and design criteria. As noted in part 1 of this series, few of the criteria were initially supported by laboratory or field research, and engineers relied on their best professional judgment in choosing design criteria. In light of the many studies completed in the past 20 years, it is time to reexamine some of these criteria. In addition, treatment strategy is evolving from a focus on the general removal of pollutants using total suspended solids (TSS) as the surrogate for all pollutants to a more recent trend to consider specific pollutants. Some states now emphasize removal of total phosphorus, total nitrogen, and dissolved metals in certain situations. A particular design criterion can vary depending on which pollutant is targeted. Table 1 provides design criteria for fine-media filters from representative.manuals and handbooks. Sand filters are a commonly used treatment system in Texas and the Chesapeake Bay area, and are particularly attractive for the removal of sediment (TSS or suspended sediment concentration) and attached pollutants. They can be expected to give consistent performance irrespective of the size of the storm and flow rate, unlike many other systems such as swales and vortex separators. They also may provide · relatively consistent effluent quality with respect to TSS and attached pollutants, irrespective of the variation in influent concentration (Caltrans 2004). Despite these advantages, sand filters are rarely used outside the two areas mentioned above. This likely occurs for two reasons: First, sand filters can be fairly large, particularly if the available head is modest given site topographic constraints. The second concern is maintenance. This article discusses how the selection of design criteria directly affects surface area and maintenance frequency. Alternative criteria are suggested that may result in wider use of fine-media filters. a. At influent TSS less than 100 mg/L, the requirement is effluent of 20 mg/L. b. The incremental increases in loading is to be reduced by 80%. The goal of other manuals is usually 80% reduction in the concentration or loading of TSS for the water that ts treated up to and including the design storm irrespective of the predeveloped concentration or loading. c. No specific goal is established; rather, removal expectations are provided for each type of system, ranging from 10% to 65%. d. Capture and treat the complete volume of 80% of the storms, i' representing small and moderate-size storms, while treating a portion of the larger storms. e. For 100% impervious surface. In most manuals, maximum storm depth captured or sizing storm decreases with increase in previous surface fraction. With the exception of Washington, the volume treated by the sand filter is the same as the volume calculated for an extended detention basin. f. Varies with the extent of the development of the site prior to the current development. g. Implied in the sizing equation. Pretreatment It is common practice to pretreat stormwater before it enters the filter bed. The objective is to reduce solids loading on the filter bed, thereby extending the time between necessary maintenance events. Subsurface filters commonly use a wet vault chamber separated from the filter bed by a common wall. The most common pretreatment method for surface filters is an extended detention basin. Wetponds are used where in some cases the filter is actually the outlet berm of the pond and not a separate unit. Flow- through grass swales have also been employed. However, wetponds and grass swales may not be the most appropriate choice for pretreatment given the potential for clogging of the filter bed-from algae in the case of ponds and eroded sediment in the case of swales. However, no problems have been published in this regard. Media Type and Size Distribution As previously mentioned, sand is the most commonly used filter medium. Mixtures of sand and a second medium are used, although infrequently. The objective is the removal of dissolved pollutants. Added media in full-scale facilities have included peat (for removal of metals), activated carbon (organics), calcite (phosphorus), and iron filings (phosphorus). There has been laboratory-or pilot-scale experimentation with dolomite (phosphorus) and soybean hulls (metals). An alternative is to coat the sand with an oxide of iron, manganese, or aluminum to remove dissolved metals. The size distribution commonly specified today is ASTM (American Society of Testing and Materials) C33. This is the specification for fine aggregate for use in·concrete. Its ready availability reduces the cost. It is, coincidently, fairly similar to the specification of sand for water treatment. Early manuals had a simple specification of "0.20 to 0.40 and fines are acceptable." It is believed that this specification has caused premature clogging of sand beds, sometimes through the entire depth of the bed. Media Depth Initially, the City of Austin specified a depth of 36 inches, mimicking the depth commonly used in potable water treatment. It was soon changed to 18 inches, likely because of the recognition that almost all of the removal of TSS and attached pollutants occurs on or near the surface of the bed. Substantial media depths are used in potable water treatment given the need to consistently and reliably meet a very strict potable water standard. Such a standard, less than one unit of turbidity, is not required of stormwater treatment. Table 2. Effect of Media Depth The relevance of media depth relates to the area required of the filter to pass the design event. The greater the depth of the media, the greater the surface area of filter required to meet the specified drawdown time as shown in Table 2. Eighteen inches is taken as the standard with a unit area of one. Reducing the media depth from 18 to 6 inches reduces the required area of the filter by about 50%. Conversely, a filter depth of 36 inches increases the filter area by about 30%. How the relationships in Table 1 wer.e produced is presented later in this article. Sand filters with 18 inches of media appear to perform more effectively than other stormwater treatment systems, in particular extended detention basins and swales. Therefore, some may consider it acceptable to reduce the depth of the media in a sand filter even if performance degrades somewhat. One study (Amini 1996) found that . increasing the media depth from 6 to 12 inches, the maximum depth evaluated in this study, increased the removal efficiency of TSS by only 5%. A study of bacteria removal found little improvement with media depths above 12 inches (Bellamy et al. 1985). In a recently completed study (Caltrans 2004), several sand filters with 18 inches of media · performed substantially better than a single filter that had only 12 inches, with mean effluent concentrations of about 6 and 12 mg/L, respectively. However, 12 mg/L is acceptable. While the results of these studies are inconsistent, they do indicate that shallower bed depths are acceptable in most situations, certainly 12 inches and possibly 6 inches. A depth of 6 to 12 inches is likely impractical with large filters where mechanical methods are used to maintain the filter bed. Heavy equipment could damage the underdrain system. But it may be acceptable for small filters, less than a few hundred square feet, where cleaning by hand occurs. Also, more frequent cleaning may be feasible with small filters. Alternatively, where 18 inches is specified, the depth of the design storm could be reduced, commensurate with the higher efficiency of sand filters over other treatment technologies (Barrett 1999, King County 1998). A shallow filter bed. is likely acceptable where the objective is the removal of TSS and attached pollutants. It may not be appropriate if the objective is the removal of dissolved species. Removal of dissolved pollutants is discussed in the last of this series of articles. Hydraulic Conductivity Sometimes referred to as the coefficient of permeability or the filter factor, hydraulic conductivity describes the ability of water to pass through media: Its value is inherent to the particular medium, its size distribution, and sediment accumulation. Hydraulic , .. i conductivity is not to be confused with the infiltration rate, which is the actual rate of flow through the filter. Confusion occurs as both have the same units (feet or inches per hour or per day). The filtration rate increases with the depth, or head, of water above the filter bed, whereas the hydraulic conductivity is unaffected by head. Hydraulic conductivity, however, decreases with the accumulation of sediment. Specified design values have ranged from 1.8 to 3.5 feet per day. The effect of its selection is shown in Table 3. The more conservative value of 1.8 feet per day increases the filter area by about 90%, a significant increase. Table a. :Effect of Design Hydraulic Conductivity What does the selected hydraulic conductivity represent? The hydraulic conductivity of clean sand is on the order of 2 to 5 feet per hour. The values in Table 3 are 5%-10% of clean sand. These values therefore represent a filter almost totally clogged: the time to clean the filter. If the filter .is not cleaned promptly, the management goal of treating, for example, 90% of the stormwater over time, is not met The greater the selected hydraulic conductivity the smaller the filter area, but the more frequent the maintenance. The value chosen is arbitrary within a_ reasonable range, and represents the tradeoff between filter area and the frequency of maintenance. In effect, its sele,ction represents a tradeoff between initial construction costs and long-term maintenance costs. Elevation Drop Tab le 4. Effect of Water Depth Note: 18 in of media, 4-ft water depth A major limitation in the use of fine-media filters is the available elevation drop-that is, the difference in the elevations of the development and of the public drainage system to which the development discharges. -Table 4 illustrates the effect of the available _ maximum water depth over the top of the filter, called the head. As the head increases, the surface area of the filter decreases. · Hence, the feasibility of fine-media filters increases with increasing head. However, the · decrease in filter surface area corresponds with the required frequency of cleaning. It should also be noted that reducing the bed depth also reduces the elevation drop required of the site, and therefore the potential feasibility of a fine-media filter. · Drawdown Time The design drawdown time affects the size of the filter. Therefore, its specification is important. Table 1 presents a significant range of 24 to 48 hours. Drawdown time affects filter area by its definition of Q, the average .. ,,.. ... ... 111111 ... .. .. ... -.. ... -... --.. -.. -.. - ---- filtration rate during the design storm. The greater the allowed drawdown time, the lower the filtration rate and therefore the smaller the filter area. Avoiding anaerobiosis in the filter bed is the common reason given as to why a maximum drawdown time must be specified. Bacteria attached to the filter media consume dissolved oxygen as they use organic matter and ammonia in the incoming stormwater. The concern is that under anaerobic conditions, dissolved phosphorus and metals previously removed may be released. An additional benefit from specifying a · drawdown time may be to inhibit the excessive growth of bacteria that might clog the filter. Drying of the filter bed between storms inhibits growth . The relationship between drawdown time and either anaerobiosis or excessive bacteria growth has not been established. Nor has the significance of pollutant release been defined. Whether release occurs depends on the mechanism of removal. A possible mechanism of dissolved phosphorus removal is sorption/precipitation to ferric oxide present on the surface of the sand. Under anaerobic conditions, ferric iron changes to ferrous, disassociating the complex and releasing the pollutants. One study found a constant anaerobic condition in the bottom of the filter (Shapiro 1999). The conditions of the study are likely the most extreme that will be faced. The filter had a media depth of 36 inches and a typical drawdown time of 72 hours. Furthermore, it was located in a region With long·storms and short interevent times, conducive to creating anaerobic conditions. Finally, irori filings were added to the sand to promote the removal of dissolved phosphorus. The transformation of the filings under anaerobic conditions appears to have caused sand particles to bind. The filter was found to be constantly anaerobic in the bottom 24 inches. However, despite this condition the filter removed on the order of 50% of the dissolved phosphorus as well as dissolved metals. All of the removal was likely occurring in the upper 12 inches of media that remained aerobic . If nitrogen removal is the objective, a temporary anaerobic condition is desirable . Bacteria change ammonia to nitrate in the presence of dissolved oxygen, but the net reduction of nitrogen is zero. Other bacteria under anaerobic conditions change the nitrate to nitrogen gas. The ideal operation is for the upper area of the filter to be aerobic and the lower area to be anaerobic. Specification of the drawdown time is therefore a function of the pollutant-removal objective, the interevent time between storms, and the time needed for the filter to dry. If the objective includes dissolved phosphorus and/or metals, a low drawdown time, perhaps on the order of 24 hours, is appropriate. If not, 72 hours may be satisfactory. A long drawdown time may also be desirable if nitrogen removal is the management objective . An alternative to a "tight" drawdown time may be to incorporate aluminum into the sand. Aluminum oxides may be an effective remover of dissolved phosphorus and/or metals (Minton 2002). Unlike ferric oxide complexes, aluminum oxide/phosphorus/metal · complexes will not disassociate under anaerobic conditions . Determining the Filter Bed Area and Live Storage Volume -I ... -... ,,,. .. -.. -.. ... - ... --.. ---- - ------ --~·. . . . .. . -·-· •=--··--·-~7 Equation 1. Ql I A. '" . '·'· . A}? ·+ 'J) I J~W• · . l Wber,z; I A ,, ace.i of fihet 1 ,. fil~ct media depth <l "' maximum water dq)tb abtwe the upptr sum«:e of filter Ht ,,, h:,·<iroulic couductivity Q ,., a,~n.'lge filnation rnte at prjmfuJ '" wo..,,t V « H)lum~ Qf ibe ®~ ¢Vffl\ D,,1 z· druwdo>A<n dme Manuals employ the same equation (Equation 1) for sizing the filter bed area, although the specific form of the equation varies with the units used. The average filtration rate is equal to the runoff volume of the design event divided by the drawdown time at brimful. For example, assume a design runoff depth of 1 inch. The volume of runoff is the multiple of 1 inch, the drainage area, and the runoff coefficient. If a 48-hour drawdown time is selected, the average filtration rate, Q, is half that if the drawdown time is 24 hours. Hence, Equation 1 states that a drawdown time of 48 hours requires a filter area that is half that for a 24-hour drawdown time . Previous observations in this article about the relationship between bed depth, hydraulic conductivity, drawdown time, available water depth, and filter surface area are understood with the examination of Equation 1. Hence, the selection of the values for the key design criteria must be considered as a whole, paying particular attention to the effect of these decisions on maintenance frequency . It is important to recognize that the available live storage volume above the filter itself is usually less thah the volume of the design event to be captured and treated. Commonly, the pretreatment unit provides the additional live storage volume. In effect, while a longer specified drawdown time deceases the filter area and the volume above it, it does not decrease the total storage volume that is required . Furthermore, Equation 1 fails to consider the combined effect of the interevent time and the choice of drawdown time on the potential for some stormwater to be present in the treatment system when the next storm arrives. This aspect was discussed in the first article of this series with respect to extended detention basins. Similarly, the interrelated effects of interevent time and drawdown time should be considered when specifying sizing criteria for the total live volume of the combined pretreatment-filter system. One manual recognizes this point (CASQA 2003). A fine-media filter can be viewed as an extended detention basin with a system of underdrains rather than orifices. Counterbalancing this relationship is the recognition that the actual hydraulic conductivity is greater than the design hydraulic conductivity through much of the maintenance cycle. The only proper way to define the filter area and the live storage volume is through · continuous simulation with a program that recognizes the gradual change in hydraulic conductivity as solids accumulate in the filter. A complementary methodology sizes the area of the filter based on solids accumulation, thereby relating_filter area to the desired maintenance cycle (Lenhart 2000, Minton 1995 and 2002, Urbonas 1999). There are two key elements to this approach: The first is the loading rate of sediment (TSS) to the filter, as pounds or kilograms per year. The second element is the amount of sediment that accumulates on the filter before the design hydraulic conductivity is reached, as pounds per square foot or kilograms per square meter. ""' ... ' .. ... .... ... ... ,.. ... -.. - .. JIii -,,.. JIii ---.. - .. .. - Equations 2 and 3 express the methodology. Equation 2 considers concentration. The analysis can also be based on annual unit loading-that is, pounds per acre or kilograms per hectare of drainage area per year (Minton 2002) . Equation a. Lr .,,, kQ(T s.~l 1-Er,> ~ TsS<:i) Where: Lf '" the aecurnu!akd loadii1g per year i.n the filt~t mewll (lb/yr or ~giyr) Q "" annual runoff volume ftti/yr or m1iyr) 'fs.s;, "" mean concenuntkm ofTSS in stormwater{mg/L) T 159 .., mean cm,c-.L·ntrnlion ofTSS tn dlluem (mg/L} k. "' tnetric eooversion facttir 0·' I for ~1eufo, 62All.OOO,OOO for rmp.erial Equation a. L,M A"' -r;:-~ The solids-accumulation method explicitly considers the desired maintenance frequency . The area of the filter is calculated with both the flow and solids-accumulation methods. The larger area is selected. Alternatively, the selection of the filter area is based on Equation 1. Equations 2 and 3 are then used to specify the maintenance frequency for the particular development. A regulatory agency could assume the same sediment concentration or unit loading for each type of land use. It could then specify maintenance frequency as a function of the maximum water depth over the filter. This relationship recognizes that as the available water depth increases, the filter area decreases, and in turn the maintenance frequency increases. Finally, the two methods can be contrasted to determine the appropriate values for the drawdown time, hydraulic conductivity, and media depth for a particular climatic region. Published data suggest that design hydraulic conductivity is reached at approximately 0.25 to 0.50 pounds of sediment per square foot of filter area (1.2 to 2.4 kg/m2) (Clark and Pitt 1999, Keblin et al. 1996, King County 1996, Shapiro 1999, Urbonas 1999). More field studies are needed. Final Observations Maintenance costs may be reduced, while performance is enhanced, by placing a suitable geofabric on the sand surface. The geofabric may extend the length of the maintenance cycle (Graham et al. 1994). Its replacement after clogging with most of the removed sediment may ease maintenance time and therefore costs. This approach is suggested for small filters, particularly if the media depth is reduced to between 6 and 12 inches. JIIIII ... ,,,.. ... -- -.. ... ... -,.. - """' -.. --.. ,,,,,. ... ,.. Field inspection during construction is particularly important with fine-media filters. Care must be taken in the selection and protection of fine media when located onsite, and before placement in the filter bed. The hydraulic condition of the filter must be checked if the filter was used during construction of the development. It is likely that fine-media filters are more attractive in regions with low annual rainfall. There are two reasons: The first is the unattractiveness of treatment systems that rely on · water to sustain their performance, such as wet basins and flow-through swales. Secondly, in drier climatic regions the amount of sediment reaching the filter is less over the typical year than in wet climatic regions. Hence, the maintenance frequency will likely be less than in wetter climates. Anecdotal information suggests that vigorous surface vegetation extends the maintenance cycle. The author knows of one sand filter in the Pacific Northwest in which a thick gmwth of grass was intentionally promoted. Although over five years old, the filter surface has never had to be cleaned. Other filters in the same area have required semi- annual maintenance. Sediment likely accumulates in the grass rather than the surface of the sand. Vegetation is known to enhance the infiltration capacities; more studies are needed on this question. Promotion of surface vegetation may be particularly attractive in wetter climates where filters experience a higher annual solids loading and longevity of agricultural soils (Minton 2002). Some manuals suggest that fine-media filters not be used for drainage areas in excess of 10 acres (Table 1 ). However, sand filters are serving much larger areas without issue. The author is familiar with a dual-filter system that serves a residential area of 250 acres. Washout of accumulated fine particles that are toxic has been observed under laboratory conditions (Clark and Pitt 1999). Whether this occurs under field conditions is· not known. Summary The effect of the choices of key design criteria, their interrelationship, and their combined effect on filter area and maintenance frequency must be considered. There is no one appropriate value for the hydraulic conductivity. The value that is selected should be based on the desired frequency of maintenance, with consideration to the effect on filter surface area. Where the objective is the removal of sediment and attached pollutants, a media depth of 12 inches and possibly as little as 6 inches is likely sufficient in most situations. While performance will be less with the shallower bed depth, the effluent concentrations will be similar to that produced by other treatment systems such as basins and swales. A shallower bed depth allows for a smaller filter surface area. A shallower bed depth also reduces the elevation drop required of the design. However, a smaller filter area, whether from a reduction in the bed thickness or by the greater available elevation drop, may result in unacceptable frequency of maintenance, · particularly in wetter climates. The selection of the drawdown time may differ depending on the pollutant-removal objective, but should take into consideration interevent time particularly in wet climates with frequent storms. It would be prudent to use both the flow and solids-accumulation methods to determine the filter area. More studies are needed on the relationship between solids accumulation and hydraulic conductivity, and the effect of surface vegetation on the maintenance cycle . JIii" ... ,,. ... .,.. ,.. 11111 .... I ... ... -.. -- ,,. -,., .. ... References Amini, F. 1996. Effect of filter thickness on sand filter performance. Water Qua/ Res J Canada 31, 4,801. Barrett, M. 1999. Complying with the Edwards Aquifer rules: Technical guidance on best management practices. Austin: Texas Natural Resource Conservation Commission . Bellamy, W.D., G.P. Silverman, D.W. Hendricks, and G.S. Logsdon. 1985. Removing Giardia cysts with slow sand filtration. J Amer Water Works Assn 77, 2, 52 . California Department of Transportation (Caltrans). 2004. BMP retrofit pilot program, final report, CTSW-RT-01-050. California Stormwater Quality Association {CASQA). 2003. Stormwater best management practice handbook, new development and redevelopment. Clark, S. and R. Pitt. 1999. Stormwater treatment at critical areas, evaluation of filtration media for stormwater treatment. US Environmental Protection Agency, EPA/600/R-00/010. Graham, N.J.D., T.S.A. Mbwette, and L. DiBernardo. 1994. Fabric protected slow sand filtration: A review. In Slow sand filtration, eds. M.R. Collins and M.J.D. Graham. Denver: American Water Works Association. Keblin, M.V., M.E. Barrett, J.F. Malina, and R.J. Charbeneau. 1998. The effectiveness of permanent highway runoff controls: Sedimentation/filtration systems, research report 2954-1. Austin: Center for Transportation Research, University of Texas. King County. 1996. Determination of infiltration rates and hydraulic conductivity for various sand filter media. Seattle. King County. 1998. Surface water design manual. Seattle: Department of Natural Resources. Lenhart, J. 2000. A suggested methodology for the preliminary evaluation of storrnwater filtration systems. Portland, OR: Stormwater Management Inc . Minton, G.R. 1995. Stormwater treatment by media filtration. Short course, University of Washington, Professional Development Program. Minton, G.R. 2002. Stormwater treatment: Biological, chemical, and engineering principles 416 pages. Seattle: RPA Press . Shapiro and Associates and the Bellevue Utilities Department. 1999. Lakemont storm water treatment facility monitoring report. Bellevue, WA. Urbonas, B. 1999. Design of a sand filter for stormwater quality enhancement. Water Environ Fed 71, 1,102. Gary Minton, Ph.D., P.E., is an independent consultant with Resource Planning Associates in Seattle, WA. He is author of the book Stormwater Treatment: Biological, Chemical, and Engineering Principles. I ,.. ,,.. .. ,,,.. ... 11111 ,,. ... .. JIii .. ,... .. -.. .. .... APPENDIX4 Source Control BMP's I' I Spill Prevention and Control Standard Symbol BMP Objectives o Soil Stabilization o Sediment Control o Tracking Control o Wind Erosion Control • Non-Storm Water Management • Materials and Waste Management Definition and These procedures and practices are implemented to prevent and control spills in a Purpose manner that minimizes or prevents the discharge of spilled material to the drainage system or watercourses. · Appropriate This best management practice (BMP) applies to all construction projects. Spill Application control procedures are implemented anytime chemicals and/or hazardous substances are stored. Substances may include, but are not limited to: ■ Soil stabilizers/binders. ■ Dust Palliatives. ■ Herbicides. ■ Growth inhibitors. ■ Fertilizers. ■ Deicing/anti-icing chemicals. ■ Fuels. ■ Lubricants. ■ · Other petroleum distillates. To the extent that the work can be accomplished safely, spills of oil, petroleum products, substances listed under 40 CFR parts 110, 117, and 302, and sanitary and septic wastes shall be contained and cleaned up immediately . • t1ilbiiiii Caltrans Storm Water Quality Handbooks Constructlo.n Site Best Management Practices Manual March 1, 2003 Section 8 Spill Prevention and Control WM-4 1 of 4 ,,. ..., ,,. ,,.. .. ,,. .. ,,,. ... ,,,,,.. Ila ,,. - ,,,. --.. ,.. .. -... 411 .. .. ,.. .. ... ,,. Spill Prevention and Control Limitations ■ This BMP only applies to spills caused by the contractor. ■ Procedures and practices presented in this BMP are general. Contractor shall identify appropriate practices for the specific materials used or stored on-site. Standards and Specifications ■ To the extent that it doesn't compromise clean up activities, spills shall be covered and protected from storm water run-on during rainfall. • lbHitiir, ■ Spills shall not be buried or washed with water. ■ Used clean up materials, contaminated materials, and recovered spill material that is no longer suitable for the intended purpose shall be stored and disposed of in conformance with the special provisions . ■ Water used for cleaning and decontamination shall not be allowed to enter storm drains or watercourses and shall be collected and disposed of in accordance with BMP WM-10, "Liquid Waste Management." ■ Water overflow or minor water spillage shall be contained and shall not be allowed to discharge into drainage facilities or watercourses. ■ Proper storage, clean-up and spill reporting instruction for hazardous materials stored or used on the project site shall be posted at all times in an open, conspicuous and accessible location. ■ Waste storage areas shall be kept clean, well organized and equipped with ample clean-up supplies as appropriate for the materials being stored. Perimeter controls, containment structures, covers and liners shall be repaired . or replaced as needed to maintain proper :function . Education ■ Educate employees and subcontractors on what a "significant spill" is for each material they use, and what is the appropriate response for "significant" and "insignificant" spills. ■ Educate employees and subcontractors on potential dangers to humans and the environment from spills and leaks . ■ Hold regular meetings to discuss and reinforce appropriate disposal procedures (incorporate into regular safety meetings). ■ Establish a continuing education program to indoctrinate new employees. ■ The Contractor's Water Pollution Control Manager (WPCM) shall oversee and enforce proper spill prevention and control measures . Caltrans Storm Water Quality Handbooks Construction Site Best Management Practices Manual March 1, 2003 Section 8 Spill Prevention and Control WM-4 2of4 ,.. ... ,.. ,,.. JIIII ... - -.. ,,.. ... ,.. ,111111 .. .. ,.. ... ,. .... ... ,,. ... ,,,. ... Spill Prevention and Control • 11:tivan, Cleanup and Storage Procedures ■ Minor Spills -Minor spills typically involve small quantities of oil, gasoline, paint, etc., which can be controlled by the first responder at the discovery of the spill . -Use absorbent materials on small spills rather than hosing down or burying the spill. -Remove the absorbent materials promptly and dispose of properly. -The practice commonly followed for a minor spill is: -Contain the spread of the spill. Recover spilled materials . -Clean the contaminated area and/or properly dispose of contaminated materials. ■ Semi-Significant Spills -Semi-significant spills still can be controlled by the first responder along with the aid of other personnel such as laborers and the foreman, etc. This response may require the cessation of all other activities . Clean up spills immediately: -Notify the project foreman immediately. The foreman shall notify the Resident Engineer (RE). Contain spread of the spill. If the spill occurs on paved or impermeable surfaces, clean up using "dry" methods (absorbent materials, cat litter and/or rags). Contain the spill by encircling with absorbent materials and do not let the spill spread widely. If the spill occurs in dirt areas, immediately contain the spill by constructing an earthen dike. Dig up and properly dispose of contaminated soil. -If the spill occurs during rain, cover spill with tarps or other material to prevent contaminating runoff. Caltrans Stonn Water Quality Handbooks Construction Site Best Management Practices Manual March 1, 2003 Section 8 Spill Prevention and Control WM-4 3of4 ,,. ,. .. ,.. .. .. , .. .. ,.. .. ,,. -,,. .. .. ,,.. .. ... .. -.. ,,. .. ... ,. Spill Prevention and Control ■ Significant/Hazardous Spills -For significant or hazardous spills that cannot be controlled by personnel in the immediate vicinity, the following steps shall be taken: -Notify the RE immediately and follow up with a written report. Notify the local emergency response by dialing 911. In addition to 911, the contractor will notify the proper county officials. It is the contractor's responsibility to have all emergency phone numbers at the construction site. Notify the Governor's Office of Emergency Services Warning Center, (805) 852-7550. -For spills of federal reportable quantities, in conformance with the requirements in 40 CFR parts 110,119, and 302, the contractor shall notify the National Response Center at (800) 424-8802. -Notification shall first be made by telephone and followed up with a written report. The services of a spills contractor or a Haz-Mat team shall be obtained immediately. Construction personnel shall not attempt to clean up the spill until the appropriate and qualified staff have arrived at the job site . -Other agencies which may need to be consulted includ.e, but are not limited to, the Fire Department, the Public Works Department, the Coast Guard, the Highway Patrol, the City/County Police Department, Department of Toxic Substances, California Division of Oil and Gas, Cal/OSHA, RWQCB, etc. · Maintenance and ■ Verify weekly that spill control clean up materials are located near material ,. lbllnini, Inspection storage, unloading, and use areas . ■ Update spill prevention and control plans and stock appropriate clean-up materials whenever changes occur in the types of chemicals used or stored onsite. Caltrans Stenn Water Quality Handbooks Construction Site Best Management Practices Manual March 1, 2003 Section 8 Spill Prevention and Control WM-4 4 of4 ,... ,. ... ,,.. .. ... ,,.. -.. ,,. .. ,,. ... ... ... ,,. ,,,. ... ... ... Trash Storage Areas Description Trash storage areas are areas where a trash receptacle (s) are located for use as a reposi.to:ry for solid wastes. Storm.water nm.off 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 ne·arby storm drain inlm, channels, and/or creeks. Waste handling operations that may be sources of stormwater pollution include dumpsters, litter contra~ and waste piles. Approach This fact sheet contains details on the specific measures required to prevent or reduce pollutants in stormwater nm off associated with trash storage and handling. Preventative measures including e~closures, containment structures, and impervious pavements to mitigate spills, should be used to reduce the likelihood of contamination. Suitable Applications SD-32 Design Objectives Maximize Infiltration Provide Retention Slow Runoff Minimze lrrpervious Land Coverage Prohibit Durrping of lrrproper Materials 0 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 excluded from this requirement.) Design Considerations Design requirements for waste handling areas are governed by Building and Fire Codes, 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 h~dledin accordance with.legal requirements 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. The 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 aronnd the area(s) to avoid nm-on. This might include berming or grading the waste handling area to prevent nm-on of stormwater. ■ Make sure trash container areas are screened or walled to prevent off-site transport of trash. Jaiuary 2003 California Stormwater BMP Handbod< New Developmffit aid Redevelopment www .ccbmphaidbooks.coo, 1 of2 ,,. ,,. .. .. : ,.,,. ; :· ... .... ... ,,. ... ,,. .. 1111' .. ,,,,. ... SD-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 smface 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 E;risting Installations Various jurisdictional storm.water management and mitigation plans (SUSMP, WQMP, etc.) define "redevelopment'' in terms of amonnts of additional impervious area, increases in gross floor area and/ or exterior construction, and land disturbing activities with structural or impervious smfaces. The definition of" redevelopment'' must be consulted to determine whether or not the req~ments for new development apply to areas intended for redevelopment. If the definition applies, the steps outlined nnder "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. Maintenance 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. H 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 Co1ro.ty, Port of San Diego, and Cities in San Diego Connty, February 14, 2002. · Model Water Quality Management Plan (WQMP) for Connty of Orange, Orange Connty Flood Control District, and the Incorporated Cities of Orange County, Draft Febru.a:cy 2003. Venttn'a Conntywide Technical Guidance Manual for Stormwater Quality Control Measures, July2002. 2 of2 Callfornla Stormwater BMP Ha,dbook New Development and RedeveloJ:(l1ent www.cabmphandbooks.com Ja,uary 2003 · Pervious Pavements Description SD-20 Design Objectives 0 Maximize lnfiltratiai 0 Provide Retention 0 Slow Runoff 0 Minirrize lrrpervious Land Coverage Prohibit Durrping of I fll)roper 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 structure 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 m10btrusive 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 lID.derlying 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 offers · 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 infrastructme 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, commercial and industrial applications are possible. The use of permeable 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: · Ja,ucry 2003 California Stormwater BMP Handboci< New Developmmt a,d Redevelq:,ment www.citirripha,dbooks.am 1 of 10 . ,. ,. •• ,,. ,,,. -,,.. ... .. ,,. ... ,,,. .. ... .. ,,,. ... ... ... ,,. ... ,,.. SD-20 Pervious Pavements ■ Permeable pavement can become clogged if improperly installed or maintained. However, this is cormtered 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 surlaces are CWTently not considered suitable for adoptable roads due to the risks associated with failure on high speed roads, the safety implications of ponding, and disruption arising from reconstruction. ■ When using rm-lined, infiltration systems, there is some risk of contaminating grormdwater, depending on soil conditions and aquifer suscepti"bility. However, tlris risk is likely to be small b_ecause 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 higher risk of abrasion and damage than solid blocks . Design Considerations Designing New Installations If the grades, subsoils, drainage characteristics, and grormdwater conditions are suitable, permeable paving may be substituted for conventional pavement on parking areas, cul de sacs and other areas with light traffic. Slopes should be flat or very gentle. Scottish experience has shown that permeable paving systems can be installed in a wide range of gronnd conditions, and the flow attenuation performance is excellent even when the systems are lined The suitability of a pervious system at a particular pavement site will, however, depend on 1he loadiilg criteria required of the pavement Where the system is to be used for infiltrating drainage waters into the ground, the vulnerability of local grormdwater sources to pollution from the site should be low, and the seasonal high water table should be at least 4 feet below the smface. Ideally, the pervious smface should be horizontal in order to intercept local rainfall at source . On sloping sites, pervious smfaces 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, the following criteria should be considered: · ■ The subgrade should be able to sustain traffic loadmg 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 rmder the influence of traffic. This is controlled by the horizontal tensile stress at the base of these layers. 2 of 10 California Stormwater BMP Ha,dbook New Development and Redevelop-nent www .ccbmphancbooks.com Ja,uary 2003 ,,,,. ,,,.. ,,,,. ... .. ... ,,,. ... ,,,.. ,. 111111 ... ... - ,.. -,.. ... ... ,,,.. Pervious Pavements SD-20 There is no current 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 conventional materials that are dense and relatively impermeable. The stiffness of the materials must therefore be assessed. ■ Water is present within the construction and can soften and weaken materials, and this must be allowed for. ■ Existing design methods assmµe full friction between layers. Any geotextiles or geomembranes must be carefully specified to minimize loss of friction between layers. ■ Porous asphalt loses adhesion and becomes brittle as air passe~ 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 unbmm.d layers does not occur . Positioning a geotextile near the surface of the pervious construction should enable pollutants to be trapped and retained close to the surface of the construction. 1his has both advantages and disadvantages. The main disadvantage is that the filtering of sediments and their associated pollutants at this level may hamper percolation of waters and can eventually lead to surface ponding. One advantage is that even if eventual mainteruince 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 st:ruct:m-e allows for its release over time. It is slowly transported in the stormwater to lower levels where chemical and biological processes may.be operating to retain or degrade pollutants. The 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 in contact with water for a large part of the time, the strength and dmability of the aggregate particles when saturated and subjected to wetting and drying should be assessed ■ A uniformly graded single size material cannot 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 material with a high swf ace friction. In pollution control terms, these layers represent the site of long 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. In · general, this means that materials should create neutral or slightly alkaline conditions and they should provide favorable sites for colonization by microbial populations. Jaiuuy 2003 Gallfornla Stormwater BMP Handbook New Development aid Redevelopment www .ca:>mphaidbooks.arn 3 of10 ,,,. ... ,,. ,,. ,,. ,,,. ... ... ... ,,. ... ,,.. ... ... .. ,,,. ,,,. ,.. ,,,. SD-20 Pervious Pavements· Construction/Jnspection Consi.derations ■ Permeable surfaces can be laid without cross-falls or longimdinal 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 operation, as one of the last items to be built, on a development site. Landscape development should be completed before pavement construction to avoid coutaroination by silt or soil from this source. ■ Surfaces draining to the pavement should be stabilized before construction of the pavement ■ Inappropriate construction equipment should be kept away from the pavement to prevent damage to the smface, sub-base or sub-grade. Mai.ntenance Reqicirements 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 · surface. The factors to be considered when defining maintenance requirements must include: ■ Typeofuse ■ Ownership ■ Level of trafficking ■ The local environment and any contributing catchments Smdies in the UK have shown satisfactoiy operation of porous pavement systems without maintenance for over 10 years and recent work by Imbe et al. at 9th ICUD, Portland, 2002 describes systems operating for over 20 years without maintenance. However, performance under surh regimes could not be guaranteed, Table 1 shows typical recommended maintenance regimes: 4of 10 California Stormwater BMP Hcndbook New Development and Redevelopment www.cabmphancbooks.com Jcnuary 2003 ,,. .. ,.. .. ,.. .. .. ,,. 11111 ,,. :--... '11111 ,,,. .. ... .. ,,. Pervious Pavements SD-20 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 beingwashed onto pavement • Vacuum clean surface 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) I■ Inspect outle:ts Annual • If routine cleaning does not restore infiltration rates, then . reconstruction of part of the whole ofa pervious surface maybe 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) extent of the blockage. Maximum 15-20 years ■ Surface materials should be lifted and replaced after brush cleaning. Geotextiles may need complete replacement ■ Sub-surface 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 all construction and drainage costs are taken into account (Accepting that the porous asphalt itself is a more expensive smfacing, the extra cost of which is offset by the savings in underground pipework etc.) (Niemczynowicz, et al:, 1987) Table 1 gives US cost estimates for capital and maintenance costs of porous pavement;s (Landphair et al., 2000) Redeveloping E.l:isting Installations Various jurisdictional storm.water 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. Jcnucry 2003 California Stormwater BMP Handbook New Development end Reclevelq:,ment www.ccbmphcndbooks.com 5 of10 ,,. ... .. ! ,,. ... , .. ,,. ,,. ... ,.. ... ,,. ... ,.. ... ,,. ... ... .. JIii ... ,,. .. ,,. ... SD-20 Additional Information Cost Considero.tions Pervious Pavements 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 accotm.t. (Accepting that the porous asphalt itself is a more expensive surlacing, the extra cost of whicli is offset by the savings in undergrotm.d pipework etc.) (Niemczynowicz, et al., 1987) Table 2 gives US cost estimates for capital and maintenance costs of porous pavements (Landphair et al., 2000) 6 of 10 California Stcrmwater BMP Hmdbook New Development and Redevelopnent www.ccbmphandbooks.com Jmuary 2003 r 1 r 1 r 1 r 1 r 1 r 1 r 1 r 1 ~ 1 r 1 r 1 r 1 , 1 r 1 r 1 r 1 r 1 r 1 r 1 Pervious Pavements Table 2 Engineer's Esti.mate for Porous Pavement ltlm IJdl Prh:1 ~IQ( QA-..1 Vfllll' Aen\'\'S ~rjiing. ,l>Y $2.0(J 1104 Ptvin9 SY $1$.0(). 212 E~ CY li:l6(J 2U1 Fllwr FJol:ri:: sv $1.15 '700 s«in•Fill r:t'( ,$~.00 :201 Sn CY 17.01:1 100 SilJhlWel EA $300.00 2 Seeding LF S0.05 844 CheckDam PY 136.00 0 Tot.l~neo.. ~--·~·~ for20Y•rs MUI Uds hiu C:7clal/ Qmlal.1 v-Ac:reWS &,ll_.plng Ill,; ~-W e 1 IIYNl!ing I'd.;; ~-W 6 1 lllS1)(;iC'llOft MH $20.00 5 5 Deet:,,Clt.-n N:, $450.00 0;$ 1 TOC.IAnn.,.11 -~· ...... Janua-y 2003 Porous Pavement Tatal Qllant.Z. Tola QNM,3 Aer.eWS ~ws $1,;a;J6 12081 $2,411 1$12 . $4,02$ 42,4. :sa..ose 636 $124 ~ $1.451 604 $805 1400 $U1C 2000 $3,21$ ~, $$,44a:I 8()4 17CO 2CO $1,400 300 1600 3 S900 4 U2 1288 SG-4 1832 SC 0 &O 0 tlo.tOS $19,$21 $SO$ .. Annual Maintenance EXPense Taal Q.9ant..1 TDW Q--.3 ~N! \\-"S A.~"'S Sl,WV 2 ~UUQ 3 i1.~ :2 ~.coo 3 $1(10 5 $100 5 $226 2 $450 3 $3,-u ~.792 California StCX"mwater BMP Hmdbook New Development and Redevelopment www .ca:imphancbod<s.com SD-20 'r.tal Q\lani.. Tulal Q....-.S Telal AereW5 A,:qWS U.t;J2A ::U19 $4,~8 :5020 ff,040 $12,084 84a S18,11:2 1000 $20,1..te .$2.1141 ~IXI lo'52,lil02 1001) ~.629 ·$2.300 28,00 $3,220 3$00 $11., 1.&() $SIM-I aoe $12,Gff 100& $1e,12(! $2.1-00 400 12,800 5011 $3,600 $1,200 7 $2,100 7 $2,100 $97 2576 $129 S.220 $161 $0 0 go 0 so $2t,tl$ $4(1.~ ~.7til $1,jtt $2,008 $2,4to 'Itial Quaol.4 Total Quaat.5 Total. A~WS: Al~'W'S ~JxXt 4 $8,Wl,I 5 $7,~ $4,.500 4 <1ie,tl00 5 $7,000 $100 5 $100 5 $10() .$675 u $878 ., S1,12S $11,o$1 $1$,il,83 $19,ffi) 7 of 10 ,,,. .... ,,,. ,,. ' 11111 ,,,. -,.. .. .. ,,,. ,,. -.. ... .. ,,. ... ,,,. .. ... ... ,,,. .. ,,. -... --,,. SD-20 Pervious Pavements Other Resources Abbott C.L. and Camino-Mateos L. 2001. In situ performance monitoring of an infiltration drainage system and.field testing of current design procedwes. Journal CIWEM, 15(3)1 pp.198- 202. Construction Industry Researcl:i and Information .Association (CIRIA). 2002. Source Control using Constructed Peruious Surfaces C582, London, SW1.P 3AU. Construction Industry Researcl:i and Information .Association (CIRIA). 2000. Sustainable urban drainage systems -design manual.for Scotland and Northern Ireland Report C521, London, SW1.P 3AU . Construction Industry Researcl:i and Information .Association (CIRIA). 2000 C522 Sustainable urban drai.nage systems -design manual.for England and Wales, London, SWl.P 3AU. Construction Industry Researcl:i and Information As&>ciation (CIRIA). RP448 Manual of good prad:icefor the design, oonstrud:ion and mai.ntenance of infiltration drainage systems/or storm.water runoff control and disposal, London, SWlP 3AU. Dierkes C., Kuhlmann L., Kandasamy J. & Angelis G. Pollution Retention Capability and Maintenance of Permeable Pavements. Proc 9th International Conference on Urban Drainage, Portland Oregon, September 2002. Hart P (2002) Permeable Paving as a Storm.water Source Control System. Perper presented at Scottish Hydraulics St:udy Group 14th Annual seminar, SUDS. 22 March 2002, Glasgow. Kobayashi M., 1999. Stormwater runoff control in Nagoya City. Proc. 8th Int Conf. on Urban Storm Drainage, Sydney, Australia, pp.825-833 . Landphair, H., McFalls, J ., Thompson, D., 2000, Design Methods, Selection, and Cost Effectiveness of Stormwater Quality Structures, Texas Transportation Institute Researeb. Report 1837-1, College Station, Texas. Legret M, Colandini V, Effects of a porous pavement with reservior strucutre on runoff water:water quality and the fate of heavy metals. Laboratoire Central Des Ponts et Chaussesss Macdonald K. & Jefferies C. Performance Comparison of Porous Paved and Traditional Car Parks. Proc. Pirst National Conference on Sustainable Drai.nage Systems, Coventry June 2001 . Niemczynowicz J, Hogland W, 1987: Test of porous pavements performed in Llllld, Sweden, in Topics in Drainage Hydraulics and Hydrology. BC. Yen (Ed.), pub. Int Assoc. For Hydraulic Research, pp 19-8o. · Pratt C.J. SUSTAINABLE URBAN DRAINAGE -A Review of published material on the perlormance 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 8 of 10 California Stormwater BMP Ha1dbook New Development and Redevelopment www.cromphancbooks.com Ja1uary 2003 ,,. ... ,,. ... ,,,. ... ,,. ... ... ... ... ,,. ... ,,. ... .. ... -,,,. ... 111111 ... .. ,.. ... .. .. Pervious Pavements SD-20 22,Construction Industry Research and Information .Association, London, SWl.P 3AU; 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 Contro~ retrofitting and combined sewer technology, Ed H.C. Torno, ASCE, ISBN o87262 7594, 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 Porous Car Park Proc. Pi-rst: National. Conference on Sustai.nable Drai.nage Systems, Coventry Jwte 2001 . Wild, T. C., Jefferies, C., and D'Arcy, B.J. SUDS in Scotland -the Scottish SUDS database Report No SR( 02)09 Scotland and Northern Ireland Forum for Environmental Research; Edi.nburg h. In preparation August 2002. Jcnua-y 2003 Callfornla Stormwater BMP Handbook New Development and Redevelcpment www.cwmphcndbooks. CXJl'Tl 9 of10 ,,. .. .,,. ,,.. ... ,.. ... ,,. .. i ,,.. ,,. ... .. : ,,,,. ... ... ,,. ... ,,. .. .... ,,. ,,,,. .. SD-20 Pervious Pavements Schematics of a Pervious Pavement System 10 of 10 California Stcrmwater BMP Hcndbook New Develq:iment and Redevelopment www.aomphancbooks.com Jcnuary 2003 Storm Drain Signage SD-13 Design Objectives· Maximize lnfillratioo Provide Retention Slow Runoff Mini rrize I rrpervi OLIS Land Coverage @ Prohibit Durrping of lrrproper Materials Contain Pollutants Collect and Convey Description -~·----- 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 nmoff 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 boimdaiy 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 prcij ect 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 Janua-y 2003 California Storrhwater Blv1P Handboci< New Development and Redevelopment www.ccbmphandbooks.com 1 of 2 SD-13 Storm Drain Signage -DRAINS TO OCEAN" and/or other graphical icons to discourage illegal dumping. ■ Post signs with prohibitive language and/or 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 sign.age 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 surlaces. If the prqj ect 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 maintain the legibility of placards or signs. Placement ■ . Sign.age 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 Examples ■ 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 ~an Diego Cmm:ty, 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 Februmy 2003. Ventura Countywide Technical Guidance Manual for Stormwater Quality Control Measures, July 2002. 2 of2 California Stormwater BMP Handbook New Develcpment and Redevelo~ent WWW. cabmphanchoci<s.oom January 2003 I \ Outlet ProtectionNelocity Dissipation Devices lss-101 Standard Symbol BMP Objectives • Soil Stabilization . • Sediment Control o Tracking Control o Wind Erosion Control o Non-Storm Water Management o Materials and Waste Management Definition and These devices are placed at pipe outlets to prevent scour and reduce the velocity Purpose and/or energy of storm water flows. Appropriate ■ Applications. These devices may be used at the following locations: Outlets of pipes, drains, culverts, slope drains, diversion ditches, swales, conduits or channels. Outlets located at the bottom of mild to steep slopes. Discharge outlets that carry continuous flows of water. Outlets subject to short, intense flows of water, such as flash floods. Points where lined conveyances discharge to unlined conveyances. ■ This BMP may be implemented on a project-by-project basis with other BMPs when determined necessary and feasible by the Resident Engineer (RE). Limitations . ■ Loose rock may have stones washed away during high flows. ■ Grouted riprap may break up in areas of freeze and thaw. ■ If there is not adequate drainage, and water builds up behind grouted riprap, it may cause the grouted riprap to break up due to the resulting hydrostatic pressure . • tl1ltTriM Caltrans Storm Water Quality Handbooks Construction Site Best Management Practices Manual March 1, 2003 Section 3 Outlet ProtectionNelocity Dissipation Devices SS-10 1 of 3 Water Conservation Practices Standard Symbol BMP Objectives o Soil Stabilization o Sediment Control o Tracking Control o Wind Erosion Control • Non-Storm Water Management· o Materials and Waste Management Definition and Water conservation practices are activities that use water during the construction of · Purpose a project in a manner that avoids causing erosion and/or the transport of pollutants off site. Appropriate ■ Applications Water conservation practices are implemented on all construction sites and wherever water is used. ■ Applies to all construction projects. Limitations ■ None identified. Standards and ■ Keep water equipment in good working condition. Specifications • lbHiwi, ■ Stabilize water truck filling area. ■ . Repair water leaks promptly. ■ Vehicles and equipment washing on the construction site is discouraged. ■ · A void using water to clean construction areas. Do not use water to clean pavement. Paved areas shall be swept and vacuumed. _ ■ Direct construction water runoff to areas where it can infiltrate into the ground. ■ Apply water for dust control in accordance with the Standard Specifications Section 10, and WE-1, "Wind Erosion Control." ■ Report discharges to RE immediately . Caltrans Stonn Water Quality Handbooks Construction Site Best Management Practices Manual March 1, 2003 Section 7 Water Conservation Practices NS~1 1 of 2 ... .. ... ... ... ... ... ... ... ... - .... ... ... .. .. ... ... ... ... ... ,.. .. .. ... ... ... ... ,.. ... ... ... Water Conservation Practices Maintenance and ■ Inspect water equipment at least weekly. • l1iltmn, Inspection ■ Repair water equipment as needed . Caltrans Stonn Water Quality Handbooks Construction Site Best Management Practices Manual March 1, 2003 Section 7 Water Conservation Practices NS-1 2of2 ... ... ... 11111 ... .. ... llr, .... ... ... . ,.. ... - .. ... ... - ,,.. ... ,,.. .. APPENDIXS Drainage Study .. ,.. .. , ... ,. ... - - ... ... .. ,,.,. ,.. .. CARLSBAD BOAT CLUB DRAINAGE STUDY June, 2006 Robert D. Dentino RCE #45629 Exp. 12/31/06 EXCEL ENGINEERING 440 State Place Escondido, CA 92029 (760) 745-8118 ,. 11111 ... ... .. ... ... ,,. Ill - ,_ I ',,,.. ... ,.. ,,. 11111 .. 11111 11111 TABLE OF CONTENTS Summary .................................................................................................................. · ............. . Vicinity Map ......................................................................................................................... . APPENDICES 1 2 San Diego Countyisopluvial Chart 100-Year, 6-Hour ................................................... A Tables and Charts for run-off coefficients and times of concentration ................................. B On-site Detention Calculations .............................................................................. C Existing Condition Hydrologic Calculations for the 100-Year Storm Event ............................... D Developed Condition Hydrologic Calculations for the 100-Year Storm Event ........................... E . Hydraulic Calculations ....................... · ........................................................................................... F 85 th Percentile Calculations ........................................................................................................... G Hydrology Map .......................................................................................... Pocket ,,. -,,. ,,,. ,,. ,.. ,.. 1111 .. JIii' .... 111111 ... -.. ,,.. JIIIII 111111 ,.. JIii ,.. .. .. HYDROLOGY Summary This 1.02-acre project (APN 206-200.06) is located on the south side of Adams Street, east of the intersection with Highland Drive in the City of Carlsbad. Topographically the site slopes to the south towards the Agua Hedionda Lagoon. Very little runoff enters the site from the adjacent property to the west. Existing Condition This project is adjacent and north of the Agua Hedionda Lagoon, which serves a final repository of an enormous drainage basin that serves parts San Diego North County, including Carlsbad and San Marcos. The final step after the Agua Hedionda Lagoon is the Pacific Ocean. The current site is approximately 57% impervious. Using table 3-1, in Appendix B, a prorated C value of 0.67 is obtained for soil type D and an impervious percentage of 57%. The current storm waters are partly absorbed onsite and the remainder flow southerly towards the Agua Hedionda Lagoon. There currently exists a large residential structure that serves as the Boat Club's meeting and administrative facilities. The parcel is lightly vegetated and a large portion of the site is paved with very weathered asphalt. There are no storm drain facilities on-site and the run-off from storm events sheet flows into the beach at the south end of the property and into the Lagoon. The current site generates approximately 3.94 cfs in a 100-year storm event. Developed Condition The existing residence/boat club structure is to be removed. fu its place will be a new 3 story boat club and time share with under ground parking for vehicles and small boats. Three floors will be visible from the Lagoon and only one floor will be visible from Adams Street. The site will be accessed from Adams Street via a driveway, which starts out at 5% and at its steepest point reaches 19%. The proposed site is approximately 63% impervious. Using table 3-1, in Appendix B, a prorated C value of 0:70 is obtained for soil type D and an impervious percentage of 63%. The runoff generated by a 100-year storm event has.been calculated to be approximately 4.25 cfs, an increase of .31 cfs. This runoff will be collected in an on-site storm drain system and allowed to infiltrate and to settle debris & hydrocarbons before discharging into the Agua Hedionda Lagoon. Additionally the project will be detaining the additional 0.31 cfs, generated by the new development, before treating it and discharging into the Agua Hedionda Lagoon Watershed The watersheds were analyzed using the 2003 San Diego County Hydrology Manual. 1 ""' ... : ,... '-' Pre-Development ,.. Pre-development Condition, as described in the Hydrology Calculations, is 0.90 acres and • contributes 3.94 cfs (100-year) in pre-development conditions. This runoff drains directly to the Agua Hedionda Lagoon ,... ,,,. : ,.. i,.. .... i j 11111 1 ; ,. i ' .. f//1111' JIii' ... .. ,.. ,,... .. ,,,.. Post-Development Area "A" (Hydrology Map, Pre-development Conditions), as described in the Hydrology Calculations, is 0.13 acres and contributes 0.58 cfs (100-year) in post-developed conditions. This runoff drains directly to the proposed curb inlet located on the west side of the driveway. Area "B", as described in the Hydrology Calculations, is _.08 acres and contributes 0.38 cfs (100- year) in the post-developed condition. This runoff drains directly to the proposed curb inlet located on the east side of the driveway . Area "C" is .11 acres and contributes .35 cfs (100-year) in the post-developed condition. This runoff drains directly to the proposed curb inlet located at the end of the driveway. Area "D" is .18 acres and contributes 0.83 cfs (100-year) in the post-developed condition. This runoff is flow southerly along the east property line and onto and into the Agua Hedionda Lagoon. This runoff passes through pedestrian concrete walkways and boat ramp area. Subsequently no hydrocarbons or pollution is picked up in its flow. Area "E" is .11 acres and contributes 0.48 cfs (100-year) in the post-developed condition. This will across the club house patio area and onto the beach. More than 50% of the square footage of area "E" is the beach it's self. This area contributes the least to any possible pollution of the Agua Hedionda Lagoon. Area "F" is 0.29 acres and contributes L65 cfs (100-year) in the post-developed condition. This runoff will flow to roof drains and to the storm drain system located in the driveway on the west side of the project. This water then confluences with the runoff from areas "A", "B" and "C" and will be processed through a CDS unit before any discharge into the Agua Hedionda Lagoon . All runoff from this project will· ultimately proceed southerly and into the Agua Hedionda Lagoon. According to the 1998 303d list published by the San Diego Regional Water Quality Control Board, the Agua Hedionda Lagoon is an "impaired water body''. Pre-and post- construction BMPs are mentioned in the Water Quality Technical Report for this project and will be detailed in the project's future SWPPP. 2 ! l I Not to Scale VICINITY MAP 3 r i. APPENDIX A County of San Diego 2003 Isopluvials 100-Y ear Rainfall Event -6 Hour & 24 Hour r; i: f'I v I": l:f' ,,_·1-. k ""' •1._y.~ -~ ,. I~ ~ ]'Ii I' r, ·T- "' , .f•. , .. "' .. -1 •• I I .1.. JI~ I\ I J;' . ~: ~ ~ . . I 1 I I, ~ I I.I I " --.----: --l ., ... -~._1• ~ t, :0 ~ ·n .. •' .. ... •. J..Jo",1 r, ·-111 ·1·111, '; County of San Diego · Hydrology Manual Rainfall Isopluvials 100 Year Rainfall Event-6 Hours lsopluvlal (1nches) l- ~fs ,._._.~,..,.-~·..,.,._._,..,.. ~ S1iiGIS We t=-&::r.:Sl::'I :)qp_,(~r.-=.! I +N i:.-.=::::=.'°=-:=,~a::=-°'~MIJTTJ,lc,,.,,.....~,.,wll"IICUM~ c.,,.w.a...,..,,.,.......,..., ,....,._ ___ ..._ ..... u,cwa~ ................. _ .. -....i ..... - --.......... "ar,MD,l,,a. ,..,......_ ............................. .. ,..-........,..,..._......_ ...... 3 0 ~ 3 Miles i ~ II". ,. I, I I ..., .ii :tfl.."' "'' fTµ ~ ,'1'/1 .. •r I ◄ "1 ... ior• ii.. 1! l"f;lt·I-I:i-.l ~H:! l'-1 l~I I l"·l 1-. ~r-•J 1-.1i·,·-i..1111 r·i:i •. ... I I 1• , 1-..r, e"II. •.1-:. ~ I.. 1-.ljl"• -~~ ,? , •·.r•. r:i ,J\ :i: LI I [ I I I I I I •'ll I\ ~"! I I IT I Y'I r-runt'' l"I : ~\I• ,1,· I& .-Pl•'• -1' -•--1", ' ~~ I ~1tt1ffflffl §l~k'tTn .~ ~ 1~ ii 111111 ~~rf.tm Id 11 II ~ ... .W (., i,,, 111111111111111111111111111111W] r.J ·-1.0 ~ ::,. n R• .•I l•1 ... IJi• ,,. •I~' K j: fl 1€1' "' ,.,. e bc-l~ •.I J' i....- ··••l•-f Vl.-r·,- " ~ :I', \f"• " ..... 1-- 1 .. -••◄• .... "" ·1·-~·•· :c r;p County of San Diego Hydrology Manual Rainfall Isopluvials 100 Year Rainfall Event -24 Hours lsopllNial (Inches) DPW -c-GIS ~ S:tiGIS ..,._..,,..,. .... -----We t'....:::.0 :l~•<:...U:.<! + "'9~.,..,.,,.,.~w,MN,lfTO,#ff...,,.,,,..llO'Ma& OA.....-»,~MITWOTLMTmlO. ,.-.,-.um~ QIIW90WffMUfY .... l'ffl,aN,olll,,,wmc:u..M~ ~ ...... ,. ..... ~ ,,.....,_ ............... --~ ........ ........ .,_ ..... _ . .,.... ....... ............. .,....,,... .. .,._ ....... ....,__ .... _..._......., .... ,...,...,....."',.__.,_....., 3 0 ~ 3 MIias I ,,... ... ,,,. ,,,. .... ,,,,. .. , ,,. ... ... .. ,,. .. ... ... .. ,,. -.... .. , ,,,. ... ... : ,,. .. ,,. .. ,,,,. .. APPENDIXB Tables and Charts for run-off coefficients and times of concentration r, r 1 r 1 r Ir,, 1 r, r 1 r 1, 1 r 1 r 1 r, r 1 r1 r1 r 1 r1 r1 San Diego County Hydrology Manual Date: June 2003 Table 3-1 Section: Page: RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use I Runoff Coefficient "C" Soil T~e NRCS Elements Coun Elements %IMPER. A B Undisturbed Natural Terrain (Natural) Permanent Open Space O* 0.20 0.25 Low Density Residential (LDR) Residential, 1.0 DU/A or less 10 0.27 0.32 Low Density Residential {LDR) Residential, 2.0 DU/A or less 20 0.34 0.38 Low Density Residential {LDR) Residential, 2.9 DU/A or less 25 0.38 0.41 Medium Density Residential (MDR) Residential, 4.3 DU/A or less 30 0.41 0.45 Medium Density Residential {MDR) Residential, 7 .3 DU/ A or less 40 0.48 0.51 Medium Density Residential (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54 Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 High Density Residential (HDR) Residential, 24.0 DU/A or less 65 0.66 0.67 High Density Residential (HDR) Residential, 43.0 DU/A or less 80 0.76 0.77 Commercial/Industrial (N. Com) N~ighborhood Commercial 80 0.76 0.77 Commercial/Industrial (G. Com) General Commercial 85 0.80 0.80 · Commercial/Industrial (O.P. Com) Office Professional/Commercial 90 0.83 0.84 Commercial/Industrial (Limited I.) Limited Industrial 90 0.83 0.84 Commercial/Industrial (General L) General Industrial .95 0.87 0.87 C 0.30 0.36 0.42 0.45 0.48 0.54 0.57 0.60 0.69 0.78 0.78 0.81 0.84 0.84 0.87 3 6 of26 D 0.35 0.41 0.46 0.49 0.52 0.57 0.60 0.63 0.71 0.79 0.79 0.82 0.85 0.85 0.87 *The values associated with 0% impervious may be used.fqr direct calculation of the runoff coefficient as descnbed in Section 3.1.2 (representing the pervious runoff coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity. Justification must be given that the atea will remain natural forever (e.g., the area is located in Cleveland National Forest). DU/A= dwelling units pel'. acre NRCS = National Resources Conservation Service 3-6 ,,,.. .. ,,. ,,.. .. ,. ! ... ,.. .. .. , .. 1111 ,,,. .. i,. ',. ,,,. .. ,,. .. ,,. ... ,,,. .. San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 12 of26 Note that the Initial Time of Concentration should be reflective of the general land-use at the upstream end of a drainage basin. A single lot with an area of two or less acres does not have a significant effect where the drainage basin area is 20 to 600 acres. Table 3-2 provides limits of the length (Maximum Length (LM)) of sheet flow to be used in hydrology studies. Initial Ti values based on average C values for the Land Use Element are also included. These values can be used in planning and design applications as described below. Exceptions may be approved by the "Regulating Agency'' when submitted with a detailed study. Table 3-2 MAXIMUM OVERLAND FLOW LENGTH (LM) & INITIAL TIME OF CONCENTRATION (T1) Element* DU/ .5% 1% 2% 3% 5% 10% Acre LM Ti LM Ti LM Ti LM Ti LM Ti LM Ti Natural 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 100 6.9 LDR 1 50 12.2 70 11.5 85 10.0 100 9.5 100 8.0 100 6.4 LOR 2 50 11.3 70 10.5 85 9.2. 100 8.8 100 7.4 100. 5.8 LOR 2.9 50 10.7 70 10.0 85 8.8 95 8.1 100 7.0 100 5.6 MDR 4.3 50 10.2 70 9.6 80 8.1 95 7.8 100 6.7 100 5.3 MDR 7.3 50 9.2 65 8.4 80 7.4 95 7.0 100 6.0 100 4.8 MDR 10.9 50 8.7 65 7.9 80 6.9 90 6.4 100 5.7 100 4.5 MOR 14.5 50 8.2 65 7.4 80 6.5 90 6.0 100 5.4 100 4.3 HDR 24 50. 6.7 65 6.1 75 5.1 90 4.9 95 4.3 100 3.5 HDR 43 50 5.3 65 4.7 75 4.0 85 3.8 95 3.4 100 2.7 N.Com 50 5.3 60 4.5 75 4.0 85 3.8 95 3.4 100 2.7 G.Com 50 4.7 60 4.1 75 3.6 85 3.4 90 2.9 100 2.4 O.P./Com 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 Limited!. 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 General 1.· 50 3.7 60 3.2 70 2.7 80 2.6 90 2.3 100 1.9 . *See Table 3-1 for more detailed description 3-12 ,,. ,,. ... ... : ,. ... ... .. ,,. .. ' .. ... ,,,. .. Ill ,,. .. ,,. ... ,,. ... . ........ ········-·-.......... · . . . ,.. ... ,,. ... .. ,,. ,,,. ... ... ,,. ... ,,. - ,,. ... ,.. .. ,. .. .. ,,,,. ... ,,,,. 1111 APPENDIXC Detention Facilities Calculations ,... ._ Required Detention: ,.. The required retention for the site was determined from the San Diego County Hydrology ._ manual formula for volume as follows: ,,,.. Volume = C*P6* A .. ,,,. .. ,. .. ,,.. - , .. ,.. .. ... ,.. ... ,,,. .. .. .. ,.. .. ,.. .. Where: Volume= volume of runoff (acre-inches) P6 = 6-hour precipitation (inches) C = delta of runoff coefficient A = area of watershed Volume= 0.03(2'.8)(0.90) = 0.0756 acre-inches Volume= 276 cubic feet of required detention. Check of 85th Percentile rainfall volume: =2.8 =0.03 =0.90 The 85th percentile volume (see 85th percentile calculations) has been calculated as follows: Q=0.64 cfs Duration of 10 minutes Volume=Q*D Volume=(0.64cfs)*(10 min)(60 sec) V=384 cubic feet Volume = 384 cubic feet of required detention. Using four 20-foot long, 30-inch CMP for storage . Area of30-inch CMP = 4.91 square feet A 20-foot section will yield 98 cubic feet Four 20 foot sections will provide 392 cubic feet, which is more than what is required. We will have 1.02% storage capacity for detention. .. ... ,,,. .. ,.. 11111 ... .. .,. ... ... - -.. ... 111111 ... .. ... 11111 .... -.. ,,.. ,. - APPENDIXD Pre-developed Hydrologic Calculations for the 100-Year Storm Event Onsite ,,. ... ,,,. ... ,,. ... ... , .. ,,. -,,,. ... ... ... ,,,. .. ,,. ... .. ... ... i .. .. ,,.. ... ,,. ... **************************************************************************** RATIONAL METHOD HYD~OLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 2003 HYDROLOGY MANUAL (c) Copyright 1982-2003 Advanced Engineering Software (aes) Ver. 1. SA Release Date: 01/01/04 License ID 14 62 FILE NAME: CBC.DAT TIME/DATE OF STUDY: 16:22 5/18/2006 ------------------------------------------------·--------------------------. USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: 2003 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 100.00 6-HOUR DURATION PRECIPITATION (INCHES) = 2.800 SPECIFIED MINIMUM PIPE SIZE(INCH) = 10.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED NOTE: ONLY PEAK CONFLUENCE VALUES CONSIDERED .95 **************************************************************************** FLOW PROCESS FROM NODE 1.00 TO NODE 2.00 rs CODE= 22 >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< SOIL CLASSIFICATION rs "D" RURAL DEVELOPMENT RUNOFF COEFFICIENT= .6700 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) 3.230 *CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED. TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.559 SUBAREA RUNOFF(CFS) = 4.90 TOTAL AREA(ACRES) = 1.12 TOTAL RUNOFF(CFS) 4.90 ===================-===--------------------------=-------------------------. END OF STUDY SUMMARY: PEAK FLOW RATE(CFS) = TOTAL AREA(ACRES) = 4.90 1.12 Tc(MIN.) = 6.40 ===========================-===----========================================= END OF RATIONAL METHOD ANALYSIS (0.22 ACRES OF THIS RUN-OFF IS COMIMG FROM OFF-SITE, WHICH AMOUNTS TO A TOTAL OF 0.96 CFS . THEREFORE THE TOTAL RUN-OFF GENERATED FROM 0.90 ACRES rs 3.94 CFS. ... .. ... ... ,.. ... ,. .. ,.. I,- , ... ,,. ... ... .. ... ... ... 'jlllllll ... .. .. .. ,,. ... APPENDIXE Developed Hydrologic Calculations for the 100-Year Storm Event ... ... ... ... .. ., ... .. ,,. ... ,,. .. ... .. • ... .. 11111 :,.. ... ... ... ,. .. ***********************************************************~**************** RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 2003 HYDROLOGY MANUAL (c) Copyright 1982-2003 Advanced Engineering Software (aes) Ver. 1.5A Release Date: 01/01/04 License ID 1462 FILE NAME: CBCF.DAT TIME/DATE OF STUDY: 16:36 5/18/2006 USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: 1985 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 100.00 6-HOUR DURATION PRECIPITATION (INCHES) = 2.800 SPECIFIED MINIMUM PIPE SIZE(INCH) = 10.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED NOTE: ONLY PEAK 90NFLUENCE VALUES CONSIDERED .95 **************************************************************************** FLOW PROCESS FROM NODE AREA "A" 1.00 TO NODE 2.00 IS CODE= 21 >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< SOIL CLASSIFICATION IS "D" COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT= .7000 INITIAL SUBAREA FLOW-LENGTH= 170.00 UPSTREAM ELEVATION= 55.00 DOWNSTREAM ELEVATION= 19.50 ELEVATION DIFFERENCE= 35.50 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) 2.131 *CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED. TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.559 SUBAREA RUNOFF(CFS) .58 TOTAL AREA(ACRES) = .13 TOTAL RUNOFF(CFS) .. 58 **************************************************************************** FLOW PROCESS FROM NODE 2.00 TO NODE 4.00 IS CODE= >>>>>COMPUTE PIPEFLOW TRAVELTIME THRU SUBAREA<<<<< >>>>>USING USER-SPECIFIED PIPESIZE<<<<< 4 ================-=====-=---=--------.--------------------------------------- DEPTH OF FLOW IN 12.0 INCH PIPE IS 1.3 INCHES PIPEFLOW VELOCITY(FEET/SEC.) 4.8 UPSTREAM NODE ELEVATION= 16.00 DOWNSTREAM NODE ELEVATION= 15.50 FLOWLENGTH(FEET) = 18.00 MANNING'S N = .011 GIVEN PIPE DIAMETER(INCH) = 18.00 NUMBER OF PIPES 1 PIPEFLOW THRU SUBAREA(CFS) .58 TRAVEL TIME (MIN.) = . 06 TC (MIN.) = 6. 06 ... ',,. .. ... ,,,. - .. ,,,. ... ,.. Illa ... .. .... .. ... .. ... -.. 11111 - 11111 ... .. .. .. **************************************************************************** FLOW PROCESS FROM NODE FLOW IN PIPE 4.00 TO NODE 4.00 IS CODE= >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< 1 -------.----------------------------------=-----------==-=---=-=-=====------ TOTAL NUMBER OF STREAMS= 3 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE: TIME OF CONCENTRATION(MIN.) 6.06 RAINFALL INTENSITY(INCH/HR) = 6.51 TOTAL STREAM AREA(ACRES) = .13 PEAK FLOW RATE(CFS) AT CONFLUENCE= .58 **************************************************************************** FLOW PROCESS FROM NODE AREA "B" 3.00 TO NODE 4.00 IS CODE= 21 ----------------------------------------------------------·----------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< .----------------------------------------------------------------------===== SOIL CLASSIFICATION IS "D" COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT= .7000 INITIAL SUBAREA FLOW-LENGTH= 235.00 UPSTREAM ELEVATION= 50.00 DOWNSTREAM ELEVATION= 19.50 ELEVATION DIFFERENCE= 30.50 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) 2.936 *CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED. TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 100 YEAR RAINFALL INTENSITY(INCH/HOUR) 6.559 SUBAREA RUNOFF(CFS) TOTAL AREA(ACRES) = .38 .08 TOTAL RUNOFF(CFS) .38 **************************************************************************** FLOW PROCESS FROM NODE 4.00 TO NODE 4.00 IS CODE= 1 -------------------. ---------------------------·---.------------------------ >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< =================--------------------=----------=======-==================== TOTAL NUMBER OF STREAMS= 3 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 2 ARE: TIME OF CONCENTRATION(MIN.) 6.00 RAINFALL INTENSITY(INCH/HR) = 6.56 TOTAL STREAM AREA(ACRES) = .08 PEAK FLOW RATE{CFS) AT CONFLUENCE= .96 **************************************************************************** FLOW PROCESS FROM NODE AREA "F" ROOF AREA 5.00 TO NODE 6.00 IS CODE= 21 >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< ===========================--------========================================= SOIL CLASSIFICATION IS "D" INDUSTRIAL DEVELOPMENT RUNOFF COEFFICIENT= .8700 (DUE TO ROOF) INITIAL SUBAREA FLOW-LENGTH= 140.00 ... ... ,,,. ... ,,. .. : ' ... i,.. I ,,.. r .. ,,.. .. .... ... .. .. .. .... ... .. ... .. ,. .. ... UPSTREAM ELEVATION= DOWNSTREAM ELEVATION 50.00 49.00 ELEVATION DIFFERENCE 1.00 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) 3.574 TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.559 SUBAREA RUNOFF{CFS) 1.65 TOTAL AREA(ACRES) = .29 TOTAL RUNOFF(CFS) = 1.65 **************************************************************************** FLOW PROCESS FROM NODE PIPE FLOW 6.00 TO NODE 4.00 IS CODE= >>>>>COMPUTE PIPEFLOW TRAVELTIME THRO SUBAREA<<<<< 3 »>»USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 10.000 DEPTH OF FLOW IN 10.0 INCH PIPE IS 1.8 INCHES PIPEFLOW VELOCITY(FEET/SEC.) 9.2 UPSTREAM NODE ELEVATION= 16.00 DOWNSTREAM NODE ELEVATION= 15.50 FLOWLENGTH(FEET) = 10.00 MANNING'S N .011 ESTIMATED PIPE DIAMETER(INCH) 10.00 NUMBER OF PIPES PIPEFLOW THRO SUBAREA(CFS) 1.65 TRAVEL TIME(MIN.) = .02 TC(MIN.) 6.02 1 **************************************************************************** FLOW PROCESS FROM NODE 4.00 TO NODE 4.00 IS CODE= >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< >>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<< 1 ==========================--=======---======-=============================== TOTAL NUMBER OF STREAMS= 3 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 3 ARE: TIME OF CONCENTRATION(MIN.) 6.02 RAINFALL INTENSITY(INCH/HR) = 6.55 TOTAL STREAM AREA(ACRES) = .29 PEAK FLOW RATE (CFS) AT_ CONFLUENCE = 1. 81 ** CONFLUENCE DATA ** STREAM RUNOFF Tc INTENSITY NUMBER (CFS) (MIN.) (INCH/HOUR) 1 .58 6.06 6.515 2 .38 6.00 6.559 3 1. 65 6.02 6.546 RAINFALL INTENSITY AND TIME OF CONCENTRATION CONFLUENCE FORMULA USED FOR 3 STREAMS. ** PEAK FLOW RATE TABLE ** STREAM RUNOFF Tc INTENSITY NUMBER (CFS) (MIN.) (INCH/HOUR) 1 2.56 6.00 6.559 2 2.60 6.02 6.546 3 2.56 6.06 6.515 AREA (ACRE) .13 .08 .29 RATIO ... ,,.. .. ... .... ... ,, ... ... ... .. ... .. ... .. ... ... , .. ... .. .. j ... ... Ill ,,,. .. ... ... ... COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS: PEAK FLOW RATE (CFS) 2. 60 Tc (MIN. ) = 6.02 TOTAL AREA(ACRES) = .50 **************************************************************************** FLOW PROCESS FROM NODE PIPE FLOW 4.00 TO NODE 8.00 IS CODE= >>>>>COMPUTE PIPEFLOW TRAVELTIME THRO SUBAREA<<<<< 3 >>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< --------==--=====---====-----------========-=---=------=-------=--========== ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000 DEPTH OF FLOW IN 12.0 INCH PIPE IS 2.1 INCHES PIPEFLOW VELOCITY(FEET/SEC.) 11.2 UPSTREAM NODE ELEVATION= 15.50 DOWNSTREAM NODE ELEVATION= 8.00. FLOWLENGTH(FEET) = 90.00 MANNING'S N .011 ESTIMATED PIPE DIAMETER(INCH) 10.00 NUMBER OF PIPES PIPEFLOW THRO SUBAREA(CFS) 2.60 TRAVEL TIME (MIN.) = .13 TC (MIN.) .= 6 .15 1 **************************************************************************** FLOW PROCESS FROM NODE 8.00 TO NODE 8.00 IS CODE= 1 >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< -=========================------------===-=-----------------------========== .TOTAL NUMBER OF STREAMS = 2 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE: TIME OF CONCENTRATION(MIN.) 6.15 RAINFALL INTENSITY(INCH/HR) = 6.45 TOTAL STREAM AREA(ACRES) = .50 PEAK FLOW RATE(CFS) AT CONFLUENCE= 2.60 **************************************************************************** FLOW PROCESS FROM NODE AREA "C" 7.00 TO NODE 8.00 IS CODE= 21 >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< =============================-----=-=---=----------.--------------========== SOIL CLASSIFICATION IS "D" COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT= .7000 INITIAL SUBAREA FLOW-LENGTH= 195.00 UPSTREAM ELEVATION= 38.00 DOWNSTREAM ELEVATION= 10.25 ELEVATION DIFFERENCE= 27.75 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) 2.593 *CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED. TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.559 SUBAREA RUNOFF(CFS) = .35 TOTAL AREA(ACRES) = .11 TOTAL RUNOFF(CFS} .35 **************************************************************************** FLOW PROCESS FROM NODE 8.00 TO NODE 8.00 IS CODE= 1 >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< ... ,,.. ... .... ... ... ... ... ... ... .. .. ... ... .. ... ... .. 11111 .. .. .. .. .. ... ... 111111 .. 111111 ,. ... >>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<< TOTAL NUMBER OF STREAMS= 2 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 2 ARE: TIME OF CONCENTRATION(MIN.) 6.00 RAINFALL INTENSITY(INCH/HR) = 6.56 TOTAL STREAM AREA(ACRES) = .11 PEAK FLOW RATE(CFS) AT CONFLUENCE= .59 ** CONFLUENCE DATA** STREAM RUNOFF NUMBER (CFS) 1 2.60 2 . 35 Tc (MIN.) 6.15 6.00 INTENSITY ( INCH/HOUR) 6.454 6.559 AREA (ACRE) .50 .11 RAINFALL INTENSITY AND TIME OF CONCENTRATION RATIO CONFLUENCE FORMULA USED FOR 2 STREAMS. ** PEAK FLOW RATE TABLE ** STREAM RUNOFF Tc INTENSITY NUMBER (CFS) (MIN.) (INCH/HOUR) 1 2.91 6.00 6.559 2 2.94 6.15 6.454 COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS: PEAK FLOW RATE(CFS) 2.94 Tc(MIN.) = 6.15 TOTAL AREA(ACRES) = .61 **************************************************************************** FLOW PROCESS FROM NODE PIPE FLOW 8.00 TO NODE 9.00 IS CODE= >>>>>COMPUTE PIPEFLOW TRAVELTIME THRU SUBAREA<<<<< 3 >>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< =======================-===----==-=====~==================================== ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000 DEPTH OF FLOW IN 12. 0 INCH PIPE IS 2 .1 INCHES PIPEFLOW VELOCITY(FEET/SEC.) 27.4 UPSTREAM NODE ELEVATION= 7.50 DOWNSTREAM NODE ELEVATION= 7.00 FLOWLENGTH(FEET) = 5.00 MANNING'S N .011 ESTIMATED PIPE DIAMETER(INCH) 10.00 NUMBER OF PIPES PIPEFLOW THRO SUBAREA(CFS) = 2.94 TRAVEL TIME(MIN.) = .00 TC(MIN.) 6.15 END OF STUDY SUMMARY: PEAK FLOW RATE(CFS) = TOTAL AREA(ACRES) = 2. 94 . 61 Tc(MIN.) = 6.15 1 ========----=----------------------------------.-------===================== END OF RATIONAL METHOD ANALYSIS ,,,. ... ... .. ... ... ... .. Ill 1111 .. '1111 ... 1111 ' .. .. .. 1111111 111111 1111111 ... .. , .. Ill 111111 1111111 ,. .. 111111 1 Ill .. **************************************************************************** RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 2003 HYDROLOGY MANUAL (c) Copyright 1982-2003 Advanced Engineering Software (aes) Ver. 1.5A Release Date: 01/01/04 License ID 1462 AREA "D" FILE NAME: CBCF2.DAT TIME/DATE OF STUDY: 16:38 5/18/2006 USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: 1985 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT (YEAR) = 100 .. 00 6-HOUR DURATION PRECIPITATION (INCHES) = 2.800 SPECIFIED MINIMUM PIPE SIZE(INCH) = 10.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED NOTE: ONLY PEAK CONFLUENCE VALUES CONSIDERED .95 **************************************************************************** FLOW PROCESS FROM NODE 10.00 TO NODE 11.00 IS CODE= 21 >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< ==========================---===========-==-================================ SOIL CLASSIFICATION IS "D" COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT= .7000 INITIAL SUBAREA FLOW-LENGTH= 290.00 UPSTREAM ELEVATION= 50.00 DOWNSTREAM ELEVATION= ELEVATION DIFFERENCE= 6.00 44.00 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) 3.096 *CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED. TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.559 SUBAREA RUNOFF(CFS) = 0.83 TOTAL AREA(ACRES) = .18 TOTAL RUNOFF(CFS) 0.83 =====================------------------------------=-------------=-----===== END OF STUDY SUMMARY: PEAK FLOW RATE(CFS) = TOTAL AREA(ACRES) = 0.83 .18 Tc(MIN.) = 6.00 ============================================================================ END OF RATIONAL METHOO ANALYSIS ,.. ... ',.. .. r -... ,.. .. .. Ill .. i ,,. I - '1111 .. ... ,. .. .. .. 1 .. ... ,. .. .. **************************************************************************** RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 2003 HYDROLOGY MANUAL (c) Copyright 1982-2003 Advanced Engineering Software (aes) Ver. 1.5A Release Date: 01/01/04 License ID 1462 AREA "E" FILE NAME: CBCF2.DAT TIME/DATE OF STUDY: 16:38 5/18/2006 USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: 1985 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 100.00 6-HOUR DURATION PRECIPITATION (INCHES)= 2.800 SPECIFIED MINIMUM PIPE SIZE(INCH) = 10.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED NOTE: ONLY PEAK CONFLUENCE VALUES CONSIDERED .95 *****************************~******************~**************i************ FLOW PROCESS FROM NODE 12.00 TO NODE 13.00 IS CODE= 21 >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< ============================-====-===============--===--===--=============== SOIL CLASSIFICATION IS "D" COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT= .6700 (50% OF AREA IS SAND) INITIAL SUBAREA FLOW-LENGTH= 260.00 UPSTREAM ELEVATION= 11.00 DOWNSTREAM ELEVATION= 6.00 ELEVATION DIFFERENCE= 44.00 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) 3.096 *CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED. TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.559 SUBAREA RUNOFF(CFS) = 0.48 TOTAL AREA(ACRES) = .11 TOTAL RUNOFF(CFS) 0.48 ============================-----=------------------------------------------ END OF STUDY SUMMARY: PEAK FLOW RATE(CFS) = TOTAL AREA(ACRES) = o~s1 .11 Tc(MIN.) = 6.00 =--====-==============·===================================================== END OF RATIONAL METHOD ANALYSIS ... :.., ,. ... -... JIii I JIii I._ i ,,,. ! I , .. ',,. .. ... ,111111 .. ,,.. .... 1111 )1111 Ill .. 1111 ... ... APPENDIXF Hydraulic Calculations ... .. ,.. .. .. - Carlsbad Boat Club Onsite Drainage Calculations The purpose of these calculations is to show that the two curb inlets along the westerly driveway . are adequately sized and will intercept the run off generated by a 100-year storm event. Below are the calculations for the curb inlets. The site is drained from the curb inlets via 12-inch and 10" SCH-40 PVC at slope that varies between 2%and 2.6%. The pipe flow table below verifies that the proposed pipes carrying the runoff can convey the flow generated by a 100-year event in open channel flow. l,. CURB INLET CALCULATIONS: CHECK INLET LENGTH .. SEE TABLE ON THE FOLLOWING PAGE FOR CURB INLET LENGTH CALCULATIONS ,,. ..., Per figure 7-832.9A (following page) and using a flow of0.58 cfs & a slope of 19% the required inlet length is 3.5 feet. Use a standard curb inlet with an opening of 4.0 feet ,. 111 PIPE FLOW CALCULATIONS: • CHECKPWEFLOW CIRCULAR PIPE CAP A CITY CHECK ... DIAMETER No.OF MANNING FLOW· DEPTH SLOPE VELOCITY (FT) PIPE (ill (cfs) (ffi (%) (FT/SEC} 1.0 1 0.011 0.58 0.21 2;00 4.83 1.0 I 0.011 2.60 0.46 2.00 7.33 ... 0.83 1 0.011 1.65 0.32 2.60 -7.22 I.. RIP-RAP SIZING CALCULATIONS: .. Per figure 19.7 (following pages) and using exit velocity of 7.33 fps the required rip-rap sizing i.. should be No. 2 backing rock approximately 1.0 feet thick with a l" aggregate base and filter • fabric .... ... ... .. ... ... .. :,.. ... .. ,,.. .. -.. ... .. .. .. .. .. .. I NOTES 0.060 0.050 0.040 P.030 0.025 +-= . LL 0.020 ....... .+-= LL I. Q) "CJ 0 '- 0.015 (!) 0.010 t... o.oo, Q) -0.001 -:::, 0.007 C!) o.oo, 0.005 0.004 0.003 ., ' . Figure 7-832.9A Avgvst, 19.U Using a gutter depression and interceptfng the entire flow g. LEGEND Solid Lines -• 0.10' gutter depression Dash Lines --a0.25' gutter depreulon L• Lenoth of Op~nlno · · I \ , i \ \ l. ' \ i \ \\ \ \ \~ \ \\ \ \\ \ J \ \ \, \ \' \ ~ \ \\ ·\ ' ~ ' .. \ •, \ \ ~ \" ~ o&. ~ . 1 ,. \\ I .\ .... '.\ \ CAUTION This chart•applies anly to side op111ings · · .. paralleling Iha dlrec:tlon of the intercepted flow It Is based on 1.5:percent· pavement cross slope and th~ gutter depressian cross• slope as shown in (Fig.7-832.IOA ). . \ . \ -' . , \ .. . \ \ ~ , \ . \ ~ .\ \ \ I \, 1 ' 1 \ \\ \· \ \ . \. \\ \ \ .\ \ \ , ' . .. ,, ,. ~ I \ ~- \ . (" .. \ • \ . ~ \ \~--\ \ \ \ . ' 1 \ .... , . \ \ .... ~ \ .-'\ 1 . .... .. ' _, • r-I \ \ . \\ .\ ~, .\ :a\ . q_\ ~, ~ UI ' ,. . ·,\. . \ \\ . \J , ~ \ ~ "·. .\ ' \ \ I ~ I \ \ ' \ \ \ ·I ' . I \ \ \ ' . \ \ \ .1 , \ ' \ \ , . \ \ ' \ \ ~ \ \ ' \ II I I \ \ \ \ ' \ ~ . · . \ \\' ' \ ' I ' \ \ \ \ , . . . . \ '' ' \ • ' , ' \ \ ·. \ , ' 1 \ \ . \ \ o.ooz .Q.l 0.4 0.5 0.6 0.1 0.11 o., 1.0 ,., 2.0 i., 3.0 4.0 5.0 6.0 8.0 10.0 Capacity -Cubic Feet per Second I ... ... ·. - .,. ... ------···---· •200-t.6. I Select-Ion of Rlprap and Fllter- Blankef Material ... ... ,.. .. ... -- .,. ... .. ... .. ... -... --.. ... -- -.. --------.. ,,,. ,,,,. .. ,. ~FROM: -SPECIAL PROV/5lONS .-f<EG,lONAL STD. SPeC.S. ( 1982) 200-1.6 . Stone for Rlorap Cp. 69) Add: "The lndl.vldual classes· of rocks used In s_lope protec-tlon shall conform to the following: PERCENTAGE U.RG::R lli-\N* ct.ASSES Rock t/2. 1/4 No. 2 No. 3 Sizes 2 Ton I Ton Ton Ton Backing Backing , 4 Ton 0-5 2 Ton 50-100 0-5 , 1 Ton 95-100 50-100 0-5 J 1 /2 Ton --50-100 0-5 1 /4 Ton 95-100 --50-100 200 lb 95-100 -75 lb 95-100 0-5 25 lb 25-75 o-s 5 lb 90-tOO 25-75· 1 lb 90-100 •The amount" of mater I a I sma I I er thai the sma I I est size-listed In the table for any class of rock slope protect-Ion shall not ·exceed the percentage limit Filter Blanket. (3) Upper Layer-Cs) Op-t-. 1 Opt. 2 VeJ. Rock Rlprap Sec. Sec. Lo-.er Ft/Sec Class . Thick-200 400 Opt. 3 Layer C 1) (2) ness "T" C4) (4) (5) (6) No. 3 Back- 6-7 Ing .6 3/16" C2 0.G. - No. 2 Back- 7-8 I.rig: 1.0 1/4" Bj D.G. - Fae- 8-9.5 Ing 1. 4 3/8" --. O.G~ - 3/4", 1 1/2" 9.5-11 Llg_ht 2.0 1/2" -· P.a. - ' 3/4", 1/4 1 1/.2" 1 t-t3 Ton 2.7 3/4" -P.a. Sand .. ·>· 1·' 3/4", 1/2 1 1/i" 13-15 Ton 3. 4 1" -P.a. Sand 15-17 1 Ton 4.3 1 1/2" -Type B Sand 17-20 2 Ton ~ 5.4 2" -Type l!. Sand Practical use of this table Is limited 1o sltua-t-lons where "T" Is less than o. Average veloclfy In pipe or bo-t-tom velocity Jn energy d lss lpator, wh lchever Is greater. . · · C2> .If desired ,:lprap and fl lter blanket class Js __ . ·--~~_av.al ~able, U9' ~ext larger class • · i I I s-t-ed In the tab I e determ l_ned on a we-I ghi" bms I :s. Compl lance with the percentage I lmlt shown In the +able tor al I other sizes of the Individual pieces of any_ c I ass of rock s I ope protect-I on sha II be de- term I ned by i"he rai"lo of the number of lridlvldual p I eces I arger than the sma I I es1-s I z:e I I sfed In the tab le for that cl ass. (3) Flit-er blanket thickness,. I Foat or "T", ·w_hlch-' ever Is less.. · · (4) ~tandard Speclflca-t-lons for Publ le Works Con- struction. • (5J . o.G. '".Disintegrated Granite, 1 M-1 to J.O 11,f,1 P,8 ... Processed "Mlscel laneous Base- Type B . "' Type. B bedd Ing mater I a I , Cm In linum 75%, crushed particles, JOOS passing 2 t/2" sieve, 10% passing 1" sieve) .(6) Sand 75% retained on 1200 sieve. FIGURE __ L9.7. III. 304 .. .. ... ... .. .... I .... .. ,,.. .. ... --:,:: ·e .. c::, .. 0 0 N B 2D or 'l'N (min.) Dor W -i -- Enf!MII (ty.p.) D · • Pipe Oiamtttr W • Bottom Width of Chinn■! .ST (min.) t ,,.. Flow · ! 1111 ,,.. -,.. .. , ... .. .. -, .. .. ',,. .. i ... .. ' _11111 \ , .. .. .. 0 Concratl Chann1I 6" wida slot PLAN 0 or W . ·_. ·. : . ,; " ,:;,-. ½ 20 ar TH SECTION 8-B -.5 ..§. .... ~ -•. Filtlr Blanltat ·=/: ~-•: :_--c=-··· Sill, Clas:s 420-C-2000 Concr■ta . SECTION A-A iNOTES:· '1. Plans shall ~fy: . Al Rock cfm and thicltnm m . B) Filtar material. number of iayers and thickness. 2. Rip l'.JP shall be eith■r quarry stone or broltan eoncr■ta (if shown on th1t plam.) Cobbles are not acceptable. 3. Rip rap shall be •placed over a_ filter blanket which: may be lith■r gi:anular m1t1rial or plastic filtar cloth. · . 4. Set standard special provisions for selection of rip r.ap l!'ld filt■F bl1nk•t. . 5. Rip rip enenJY dimpators shall b, designated as either Type 1 or Type 2. Tvi,. 1 shall b1 with-concretl sill: Type 2 shall bt without sm. FIGURE 19.<o ,I .. , . .. MCO-lllOlD IT TN( SAM DIEGO ', , .. I' HGIOH&. ST°'!'DA~DS CQPtfTU Ill au../d~ ,tJ-=.m$ c--• N·r r '*' o-RIP RAP ~.._----~ . ._ ~~~:~iG D-40.1 ENERGY DISSlPATOR --------------------•--I II. 303 . SAN DIEGO REGIONAL STANDARD DRAWiNG R1vjsion By . Approm Dau . Sill, 'filtar 11'(.;a. 11,-rr. ... ... .... ... .... ... .... , .. ... .. ... ... .. , ... ... .. ,,. .. APPENDIXG g5th Percentile Calculations ... i .. ... ... ... ,. .. - ,,. .. ,. :-.. .. ,.. .. ,,,. 1111 San Diego County Hydrology Manual Date: June 2003 3.1.3 Rainfall Intensity Section: Page: 3 7 of26 The rainfall intensity (I) is the rainfall in inches per hour (in/hr) for a duration equal to the Tc for a selected storm frequency. Once a particular storm frequency has been selected for design and a Tc calculated for the drainage area, the rainfall intensity can be determined from the Intensity-Duration Design Chart (Figure 3-1 ). The 6-hour storm rainfall amount (P 6) and the 24-hour storm rainfall amount (P24) for the selected storm frequency are also needed for calculation of I. P6 and P24 can be read from the isopluvial maps provided in Appendix B. An Intensity-Duration Design Chart applicable to all areas within San Diego County is provided as Figure 3-1. Figure 3-2 provides an example of use of the Intensity-Duration Design Chart. Intensity can also be calculated using the following equation: I = 7.44 p 6 D-0.645 Where: P6 = adjusted 6-hour storm rainfall amount (see discussion below) D = duration in minutes (use Tc) Note: This equation applies only to the 6-hour storm rainfall amount (i.e., P6 cannot be changed to P24 to calculate a 24-hour intensity using this equation). The Intensity-Duration Design Chart and the equation are for the 6-hour storm rainfall amount. In general, P6 for the selected frequency should be between 45% and 65% of P24 for the selected frequency. If P6 is not within 45% to 65% of P24, P6 should be increased or decreased as necessary to meet this criteria. The isopluvial lines are based on precipitation gauge data .. At the time that the isopluvial lines were created, the majority of precipitation gauges in San Diego County were read daily, and these readings yielded 24-hour precipitation data. Some 6-hour data were available from the few recording gauges distributed throughout the County at that time; however, some 6-hour data were extrapolated. Therefore, the 24-hour precipitation data for San Diego County are considered to be more reliable . 3-7 ,. .. ,,. .. ,.. .. ... 85th PERTENTILE FLOWS The chart is included in this report, immediately following this page. The isopluvial for the site has· a "P" value of 0.60 inches per hour (in/hr) for a storm. Flow for the 85th percentile storm would amount to: I=7.44(P)(D)"-0645 Where: !=Intensity P=0.60 D= 10 minutes 1=7.44(06.0)(10)"-0.645 . ,,,. I=l.01 in/hr -r,.. : ,. .. . ,,.. ... -... -.. ! .. i , .. - .. .. ,.. ,,,. Q=C*I*A Where: C=0.70 · I=l.01 A=0.90 Q=(0.70)*(1.01 )*(0.90) Q=0.64 cfs The run-off generated from the 85th percentile storm will be treated by three mechanical methods: 1) Roof drains will be passed through a mechanical cleaning device to remove organics and hydrocarbons . 2) The run-off generated on the paved surfaces and landscape areas will pass through a gravel and sand filter before entering the curb inlet. 3) Run-off that has been filtered will then proceed through the storm drain system and be allowed to settle and have additional filtration before discharging into the lagoon . ,,. .. ,,.. 11111 ,,.. .. ... - 1111 -.. ,. .. ,,,. ... ,,,. ... ... ... ,,. .. ,.. .. ,,. - APPENDIX6 Drainage Map ---- I I I I I I I I I I I I I I I I I I I I I I I I 1 ---- 50 =---==-Ja __ ____JJ.. __ ___,, 0 \ \ I I .. ---------=----c_;:· =_;_~ I \ --- ---+------------ 0 JO 0 • • ---. 0 ------------ I I I I I I I I I I I I I I I I I I I I I -L I 0 X I 10 I \ --·L\ ------~---------~--10---i ~o~~~~J===~~j~.~~=·:::::· ~~~~-~=-~='~'~ I I I I I I I - I I I I - l ----------------- -------- I I . . I I I r--__,, ; \ \ -------\ I I I I I o 0--rs_ 0 I I I I ~::::~~;J-_:::::::__y::---___::::::;;. I I I I I I I I I I I I I I I AREA! · HIGH POI/Ill -55 L0/11 POINT-6 , ACRES-!.12 (j) NOOE NUMBER PRE -OEVEL OPMENT ORA/NACE AREA MAP