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An Evaluation of BMP Removal Efficiency in the Kensico Reservoir Watershed

This study evaluates the effectiveness of 45 BMP structures in improving water quality in the Kensico Reservoir watershed. The study examines the removal efficiency of 5 selected BMPs for turbidity, total suspended solids, total phosphorus, and fecal coliform. The results show consistent removal of TSS and total phosphorus, while fecal coliform removal varies depending on the BMP type.

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An Evaluation of BMP Removal Efficiency in the Kensico Reservoir Watershed

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

  2. 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. 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. 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

  5. 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%

  6. 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 %

  7. 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%

  8. 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%

  9. Summary of Monitored Storm Events

  10. 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

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

  12. Paired Comparisons of Influent and Effluent Event Mean Concentrations

  13. BMP Removal Efficiencies

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

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

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

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

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

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

  20. 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

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