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

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

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)

3 Tasks ● Monitoring a minimum of 10 storm events at 5 selected BMPs, ● 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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5 BMP No.BMP Type Tributary Name Monitoring PeriodSampling Locations 12Retention Pond (Wet) - Surface Pond with Permanent Pool Malcolm Brook Inlets: 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) N Inlet: BMP13IN Outlet: BMP13OUT 57Sand filter with Layered Media None Inlet: BMP57IN Outlet: BMP57OUT 74Retention Pond (Wet) - Surface Pond with Permanent Pool E112007Inlets: E11N1, E11S1 Outlet: E11

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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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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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 – 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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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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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 Sep BMP 13—Wet Meadow Apr Oct BMP 37— Retention Pond Sep Sep BMP 57— Sand Filter Apr Oct

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

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

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

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

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.

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

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

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.

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

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

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