1. An Evaluation of BMP Removal Efficiency in the Kensico Reservoir Watershed New York City Department of Environmental Protection 16-17 September 2008 Prepared by Prepared for 2008 NYWEA Watershed Science and Technical Conference and

2. 1 Presenters: Paul Muessig, Michael Powell, and Jon Trombino EA Science and Technology 3 Washington Center Newburgh, New York John Canning New York City Department of Environmental Protection Division of Drinking Water Quality Sutton Park Office 465 Columbus Avenue Valhalla, New York

3. 2 Introduction ● Acknowledgements – NYCDEP staff ● 45 BMP structures in Kensico Reservoir watershed to improve and maintain water quality ● Monitoring Plan and Quality Assurance Project Plan ● 5 BMPs selected for intensive monitoring ● 4 on perennial tributaries to Kensico Reservoir ● NYCDEP Kensico Laboratory processed all samples (turbidity, total suspended solids [TSS], total phosphorus, and fecal coliform)

4. 3 Tasks ● Monitoring a minimum of 10 storm events at 5 selected BMPs, 2000-2007 ● Precipitation, hydrologic, and water quality data compiled to Microsoft ACCESS ● Formatted and submitted to EPA/ASCE International BMP Database ● Evaluate removal efficiency of BMPs

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6. 5 BMP No.BMP Type Tributary Name Monitoring PeriodSampling Locations 12Retention Pond (Wet) - Surface Pond with Permanent Pool Malcolm Brook 2000-2002Inlets: MB-3, MB-4 Outlet: MB-1 37Retention Pond (Wet) - Surface Pond with Permanent Pool N52004Inlet: N51MAIN Outlet: N5-1 13Wetland - Basin without Open Water (Wetland Meadow Type) N12005-2006Inlet: BMP13IN Outlet: BMP13OUT 57Sand filter with Layered Media None2005-2006Inlet: BMP57IN Outlet: BMP57OUT 74Retention Pond (Wet) - Surface Pond with Permanent Pool E112007Inlets: E11N1, E11S1 Outlet: E11

7. 6 BMP 12—Retention Pond ● Wet retention with 2 inlets, forebay, and permanent micro-pool ● Design WSE 370 ft MSL; extended detention 380 ft MSL ● Perennial tributary to Kensico Reservoir ● Watershed – 91.4 acres ● Forested – 15.5 acres ● Residential – 32.2 acres ● Office park – 43.7 acres ● Slopes – generally < 8%

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13. 12 BMP 13—Wet Meadow ● Wet meadow extended detention, 1 inlet with 2 ft deep micro-pool ● Micro-pool WSE 420 ft MSL; extended detention 425 ft MSL ● Perennial tributary to Kensico Reservoir ● Watershed – 20 acres ● Forested – 3 acres ● Residential (1/3-acre lots) – 17 acres ● Slopes – 8-15 %

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17. 16 BMP 37—Retention Pond ● Wet retention basin, 1 inlet with permanent micro-pool and wet forebay ● Permanent pool 396 ft MSL; extended detention 398 ft MSL ● Watershed – 249 acres ● Low density residential – 180.5 acres ● Medium density residential – 12.6 acres ● Office park – 29 acres ● Institutional – 23.5 acres ● Forested – 3.4 acres ● Slopes – <8%

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22. 21 BMP 57—Sand Filter ● Multi-media layered sand filter ● Capture and treat runoff from 550 to 600 ft along Nannyhaggen Road ● Sedimentation chamber, filtration chamber (2 ft x 28.5 ft), overflow bypass weir ● Temporary storage, 5 ft over filtration bed ● Watershed – 2.3 acres ● Forested – 2 acres ● Paved road surface – 0.3 acres ● Slope – < 8%

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25. 24 Summary of Monitored Storm Events BMP Monitoring Period Number of Events Monitored Duration of Precipitation (hrs) Event Precipitation (in.) Events Exceeding Extended Detention Design Event BMP 12— Retention Pond Feb-2000 - Sep-2001 171-300.23 - 3.367 BMP 13—Wet Meadow Apr-2005 - Oct-2006 141-700.24 - 6.856 BMP 37— Retention Pond Sep-2002 - Sep-2004 191-430.50 - 5.0112 BMP 57— Sand Filter Apr-2005 - Oct-2006 111-500.24 - 2.318

26. 25 Field Methods ● ISCO 6700 Autosampler – timed and flow- weighted grab samples over duration of storm event at inlet and outlet weirs ● Continuous stage and discharge recording ● Precipitation record at Kensico Reservoir ● Hydrology staff selected 10 samples for analysis—4 each on rising and falling limb of hydrograph and 2 around peak

27. 26 Statistical Methods ● Paired comparisons between influent and effluent concentrations ● Efficiency ratios ● Comparison of influent and effluent probability curves

28. 27 Paired Comparisons of Influent and Effluent Event Mean Concentrations BMPN Method of Comparison Significant Reduction? BMP 12- Retention Pond TSS15t-testYes Turbidity17t-testYes Total phosphorus 15t-testYes Fecal coliform 16Wilcox Signed Rank Yes BMP 13- Wetland Meadow TSS13t-test on log- transforms No Turbidity13t-testYes Total phosphorus 13t-testYes Fecal coliform 13t-test on log- transforms Yes BMPN Method of Comparison Significant Reduction? BMP 37 Retention Pond TSS18Wilcox Signed Rank Yes Turbidity18Wilcox Signed Rank Yes Total phosphorus 17t-test on log- transforms Yes Fecal coliform 17t-testYes BMP 57 Sand Filter TSS10t-testYes Turbidity10t-test on log- transforms Yes Total phosphorus 8t-testYes Fecal coliform 10t-test on log- transforms No

29. 28 BMP Removal Efficiencies BMPParameterER BMP 12- Retention Pond TSS71% Turbidity55% Total phosphorus57% Fecal coliform52% BMP 13- Wetland Meadow TSSNot statistically significant Turbidity35% Total phosphorus29% Fecal coliform55% BMP 37 Retention Pond TSS78% Turbidity59% Total phosphorus50% Fecal coliform40% BMP 57 Sand Filter TSS79% Turbidity31% Total phosphorus73% Fecal coliformNot statistically significant

30. 29 BMP 12 Retention Pond Effluent Probability Plot for TSS Cumulative Frequency Concentration (mg/L) Good removal over influent concentrations >30 mg/L. Estimated irreducible concentration is 2 mg/L.

31. 30 BMP 37 – Retention Pond Effluent Probability Plot for TSS Cumulative Frequency Concentration (mg/L) Good removal with influent >10 mg/L. Irreducible Concentration = 10 mg/L

32. 31 BMP 57 - Sand Filter Effluent Probability Plot for TSS Cumulative Frequency Concentration (mg/L) Good removal over range of influent concentrations.

33. 32 BMP 12 - Retention Pond Effluent Probability Plot for Fecal Coliform Cumulative Frequency Concentration (cfu/100mL) For small storm events, BMP is actually a contributor. Some removal with influent concentrations >1,000 cfu/100mL.

34. 33 BMP 13 – Wet Meadow Effluent Probability Plot for Fecal Coliform Cumulative Frequency Concentration (cfu/100mL) Consistent removal (  50%) over range of influent concentrations.

35. 34 BMP 37 – Retention Pond Effluent Probability Plot for Fecal Coliform Cumulative Frequency Concentration (cfu/100mL) Removal with influent >20,000 cfu/100mL.

36. 35 Conclusions ● TSS  Consistent 70-80% removal (with exception of BMP 13 – Wet Meadow)  Removal of turbidity and total phosphorus is similar to TSS ● Fecal Coliform  Sand filter is ineffective  Retention ponds and wetland meadow remove  50% at high influent concentrations  Residual in retention ponds and wetland meadow may contribute at low influent concentrations