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Water Quality Management Program Staff Training

This training agenda outlines essential updates and changes to the Water Quality Management Program, focusing on the Best Management Practices (BMPs) for stormwater. It covers the rationale behind program changes, details on new BMPs, plan review processes, operation and maintenance plans, and specific design examples influenced by NPDES Phase 2 regulations. It emphasizes maximum feasible pollutant reduction, defines roles, and discusses treatment goals for developments that disturb more than 1 acre or add significant impervious surfaces, enhancing stormwater quality and compliance.

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Water Quality Management Program Staff Training

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  1. Water Quality Management ProgramStaff Training

  2. Agenda • Why is this change necessary? • Program rationale • Describe new BMPs • Plans review process • Operation and Maintenance Plan • Design examples

  3. NPDES Phase 2 regulations: • 6 Minimum Control Measures • Post construction storm water quality treatment • “…treat storm water to the maximum extent practicable…” • All new developments and redevelopments disturbing 1+ acres

  4. Steps Taken to Date: • Ordinance with post construction language • BMP storm water stakeholder group • BMP Manual revised • Ordinance revised • Developed plan review and permitting processes • Training

  5. Schedule • Effective date = March 31 • If plan has been platted and has approved SWMP, no additional storm water quality treatment required.

  6. About the program…

  7. Program rationale • Step 1: Define “Maximum Extent Practicable” (MEP) for Bowling Green. • Step 2: Establish how much treatment is enough. • Step 3: Develop a “doable” program.

  8. How the City Defines MEP: • Identify pollutant of concern (303d lists, TMDLs) • Establish pollutant load reduction goal • Based upon accepted research, other communities • No need to reinvent the wheel… • Develop design features and practices that work for the City • Treatment volume based on impervious surfaces • Consider local limitations (karst, groundwater table)

  9. Pollutant of Concern • Sediment or total suspended solids (TSS) • Available BMP research • Many other programs using TSS as pollutant of concern • KYR10000 – references 80% TSS reduction • Sediment is no. 1 pollutant in nation

  10. Impervious Cover • TSS loading is higher from impervious cover • Impervious cover…

  11. Sidewalks Roads Parking Driveways Buildings

  12. Establish treatment goals/limits • Water Quality Treatment required for sites that disturb 1 ac or more AND add 10,000ft2 or more new impervious surfaces • WQv = [(P Rv)(A)]/12 • Where, • WQv is the water quality treatment volume (ac-ft) • P is the average rainfall in inches, (in the case of Bowling Green, is 1.1 inches); • Rv is the volumetric runoff coefficient, which is: • Rv = 0.05 + 0.009(I), where I is the percent impervious cover; • and A is the area in acres • Set treatment goal based upon pollutant of concern…

  13. A “Doable” Program • Presumptive program: • IF you design as described in BMP Manual • IF you install per the approved plans • AND • IF you maintain the BMP per the Operation & Maintenance Plan • THEN • You are in compliance. • Discharge influent/effluent testing not required (for now…)

  14. BestManagement Practices • Mitigate storm water quality and quantity damages from development

  15. Ponds • Dry ponds • Outlet structure • Dry storage area • 60% TSS reduction

  16. Ponds • Wet ponds • Outlet structure • Permanent pool • 80% TSS reduction

  17. Ponds • Variations • Micropool • Extended detention • Multiple ponds • Pocket ponds

  18. Wetlands • Outlet structure • Shallow wet treatment area • Upland dry storage • Plants are key • Length of flow (residence time) key • 75% TSS reduction

  19. Bioretention areas • Outlet structure • Small storm & large storms • Dry treatment area • Depressed planting area • Specific soils • Under drain • 80% TSS reduction

  20. Open Channel Systems • Simple outlet system • Treatment area • Dry • good in most all land use applications • Underdrain system • Wet • Not well accepted in residential • Long wetland

  21. Sand filters • Many variations • Best suited for non-residential • Typically underground • Must receive drainage from only impervious surfaces

  22. Infiltration trenches • Limited application due to karst topography

  23. Manufactured BMPs • Treatment mechanisms different from non-manufactured BMPs • Must provide 3rd party testing to verify pollutant removal to get approved for use • Nashville has similar program – will use Nashville’s list of approved BMPs and reduction capabilities

  24. Summary table

  25. WQMPs • Trigger: 1 ac or more disturbance and 10,000 ft2 new impervious surfaces • Or part of a larger common plan of development • DPW is point of contact for info on WQMP • P&Z will have checklists and general info

  26. Conservation Subdivision • WQMP = • Clearly defined clearing limits • Total impervious surfaces for development cannot exceed 15% • Minimum lot sizes – 1 acre • Disconnected roof drains • Stabilized sinkhole basins • No additional WQ treatment required

  27. Hot Spot Landuses • Pretreatment required for following landuses: • Automotive Fueling Facilities • Automotive Repair Facilities • Restaurants with grease collection and disposal • Other landuses as determined to have a high potential of pollutant discharge into the MS4 as determined by the City Engineer • Typically, oil grease separators, hydrodynamic separators, etc.

  28. Asbuilt Certification • Need to verify • That BMP was installed per approved plans • That WQv treatment goals being met • Engineer and surveyor • Asbuilt must be approved before: • Bonds released (S/D) • CO issued (non-S/D)

  29. Maintenance • City to maintain BMPs in • residential areas • on public ROWs • Landowner to maintain all other BMPs • All BMPs • O&M Plan • Routine inspections • Annual inspection certification

  30. O&M Plan O&M Plan Lashlee Landings - Agreement - Location map - Schematics - Inspection checklists • Includes the following: • BMP Maintenance Agreement • Privately owned BMPs only • BMP location map • BMP schematics • BMP maintenance and inspection templates • Annual BMP report template • Recorded with the deed • Privately owned BMPs only

  31. Drainage Easement Bioretention #1 Detention Pond Bioretention #2 Drainage Easement Access Easement BMP Location Map

  32. Redbud, 10’ O.C Daylilies, 2’ O.C. 18” storage 2.5’ planting media Geotextile fabric 6” #57 stone 4” perforated plastic pipe BMP Schematics

  33. BMP Schematics

  34. BMP Inspection Checklists

  35. Residential Example: Lashlee Landing

  36. Site Data - 51 Single Family Lots Area = 38 ac. Impervious Area = 13.8 ac 36% 3 ac in roadway and driveways, 10.8 ac in roof tops WQv=[(P Rv)(A)]/12 Rv = 0.05 + 0.009(I) WQv = [1.1*(0.05+0.009*36)*38]/12 = 1.30 ac-ft Scenario 1: Wet pond = 80% TSS DA1, DA2, DA3 routed to pond Single Drainage Area

  37. Site Data - 51 Single Family Lots Area = 38 ac. Impervious Area = 13.8 ac 36% 3 ac in roadway and driveways, 10.8 ac in roof tops 2 drainage basins Each has to treat WQv; weighted TSS reduction goal Drainage Area (DA) 1 Area = 7.6 ac. Imp Area = 2.25 ac; I = 2.25/7.6 = 30.0% Drainage Area (DA) 2 Area = 30.4 ac. Imp Area = 11.55 ac; I = 11.55/30.4 = 38.0% WQv=[(P Rv)(A)]/12 Rv = 0.05 + 0.009(I) DA1 Rv = 0.05 + 0.009(30) = 0.32 WQv = [(1.1*0.32)*7.6]/12 = 0.22 ac-ft DA2 Multiple Drainage Areas Rv = 0.05+0.009(38) = 0.39 WQv = [(1.1*0.39)*30.4]/12 =1.09 ac-ft

  38. DA1 Rv = 0.05 + 0.009(30) = 0.32 WQv = [(1.1*0.32)*7.6]/12 = 0.22 ac-ft - 2 Dry WQ Swales - provides 0.11 ac-ft of WQv in each - Dry WQ Swales = 90% TSS reduction DA2 Rv = 0.05+0.009(38) = 0.39 WQv = [(1.1*0.39)*30.4]/12 =1.09 ac-ft - Wet pond - provides 1.09 ac-ft of WQv - TSS reduction = 80% %TSS = (7.6*90)+(30.4*80)/38ac = 82% TSS Therefore, site okay Multiple Drainage Areas

  39. Bioretention 80% TSS Dry Detention 60% TSS Flow Flow Treatment Train • When one BMP discharges into another • Discharge from upstream BMP will be “clean” so downstream BMP TSS reduction will be less effective TSS reduction = 80+60 – (80x60)/100 = 92%

  40. DA2 Bioretention areas to dry detention DA1 DA2 %TSS reduction = 80+60 – (80x60)/100 = 92% Dry Swales TSStotal = ([10ac x 60] + [15ac x 92] + [13ac x 90]) / 38 = 82.8% TSS Scenario 2: DA1 = Dry detention = 60% TSS DA1 = 10ac @60% TSS DA2 = 15ac @80% TSS then 60% (treatment train) DA3 = 13 ac @90% TSS

  41. Commercial Example:Creekwood Village

  42. Multi-family Dry regional detention facility Goal - Regional WQMP: Provide regional WQ BMPs Establish builtout imperviousness per lot Problem: Assume 15 acres, 40 lots w/80% imperviousness per lot, 1500 linear ft of roadway. What is WQv? What BMPs might work? Where? Creekwood Village S/D

  43. Regional WQMP Review against restrictions If above restrictions, require additional on lot treatment Individual WQMP Develop WQMPs as unit (lots 6-7) or separately Lots 6 and 7

  44. Drainage Easement Bioretention #1 Dry Pond Bioretention #2 Drainage Easement Access Easement Problem: Lot 7 – 0.67 ac total, 25% impervious cover Lot 6 – 1.1 ac total, 23% impervious cover Problem: What is the WQv? Does this WQMP meet the TSS reduction goal if developed as one WQMP?

  45. Questions and Discussion

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