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  • Pratt Institute: Sustainable Environmental Systems

    Calculating Gowanus Measuring the Storm and Wastewater Impacts of Rezoning

    Stewart Fisken

    5-14-2017

    Professors: Alec Applebaum and Jaime Stein

  • 1

    Contents

    Definitions/Abbreviations ................................................................................................. 2

    List of tables .................................................................................................................... 3

    List of Graphs .................................................................................................................. 3

    List of figures ................................................................................................................... 3

    Introduction ................................................................................................................... 4

    Thesis Statement and the Combined Sewer Problem ................................................. 4

    A Brief History of the Gowanus .................................................................................... 4

    Time to Act ................................................................................................................... 6

    Gowanus Canal Conservancy: The Environmental Stewards .................................... 11

    Project Scope .............................................................................................................. 14

    Wastewater and Stormwater in the Combined Sewer System ................................... 14

    The Gowanus Watershed .......................................................................................... 15

    Site Area: Boundaries of Analysis .............................................................................. 23

    Wastewater .................................................................................................................. 27

    Baseline Sewer System Theory ................................................................................. 27

    Creating the Residential Zoning District Wastewater Generation Model .................... 28

    Outputs: The results of the Wastewater Generation Model ....................................... 36

    Stormwater .................................................................................................................. 40

    RH-035 and Site Area Stormwater Runoff ................................................................. 40

    How Development Will Improve Stormwater Management ........................................ 42

    The Combined Impact ................................................................................................. 44

    Recommendations ...................................................................................................... 46

    Wastewater Reduction ............................................................................................... 46

    Stormwater Reduction ............................................................................................... 48

    Conclusion ................................................................................................................... 53

    Appendix ....................................................................................................................... 54

  • 2

    Definitions/Abbreviations

    CEQR: City Environmental Quality Review CSO: Combined Sewer Overflow CWA: Clean Water Act, 1972 DCP: Department of City Planning (New York City) DEP: Department of Environmental Protection (New York City) DEC: Department of Environmental Conservation (New York State) EIS: Environmental Impact Statement (New York City) EPA: Environmental Protection Agency (United States) GCC: Gowanus Canal Conservancy Lot area: The area designated by property lines and NYC Tax lots LTCP: Long Term Control Plan, from NYC DEP PLACES: Planning for Livability, Affordability, Community, Economic Opportunity and Sustainability. DCP neighborhood planning study process Rezoning area: Area undergoing study for rezoning, as designated by NYC DCP PLACES Study Site area: Area of drainage shed RH-035 being analyzed in this paper Stormwater: Water generated over land from a rain event Street area: The area of space taken up by the streets within the project area. Calculated by subtracting the total lot area from the total project area. Wastewater: black and grey water generated from a building, wastewater. WWTP: Wastewater Treatment Plant ULURP: Uniform Land Use Review Procedure

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    List of tables

    Table 1. RH-035 Land Use ............................................................................................ 26 Table 2. Model Assumptions and Given Data ............................................................... 31 Table 3. Median Building Characteristics of NYC Buildings Built after 2013 ................. 32 Table 4. Maximum Density Scenario ............................................................................. 34 Table 5. Zero Residential Development Wastewater Generation Scenario ................... 36 Table 6. Lowest Density Wastewater Generation Scenario .......................................... 37 Table 7. Equally Mixed Density Wastewater Generation Scenario ............................... 37 Table 8. Primarily Lower Density Wastewater Generation Scenario ............................. 38 Table 9. Primarily Higher Density Wastewater Generation Scenario ............................ 38 Table 10. Maximum Density Wastewater Generation Scenario .................................... 39 Table 11. 1.2" Rain Event Stormwater Generation of Site Area .................................... 42 Table 12. Pre Development 1.2” Rain Event Stormwater Generation of Lot Area ......... 43 Table 13. Post Development 1.2" Rain Event SW Generation Table ............................ 43 Table 14. Median vs Average Value Comparison for unit/sfLA Values ......................... 55

    List of Graphs

    Graph 1. Impacts on CSO of Increasing Baseline Flow in Sewer System ..................... 28 Graph 2. Development Impacts on Stormwater Generation .......................................... 41 Graph 3. Impacts on CSO Threshold from Residential Rezoning ................................. 45

    List of figures

    Figure 1. Owls Head and Red Hook Sewersheds ......................................................... 16 Figure 2. Gowanus Canal Drainage Shed ..................................................................... 17 Figure 3. Gowanus Canal Drainage Area Split between Two WWTPs ......................... 18 Figure 4. Gowanus drainage sheds .............................................................................. 20 Figure 5. Urban Stormwater Management Systems...................................................... 21 Figure 6. Combined Sewer Overflow (CSO) ................................................................. 22 Figure 7. NYC DCP PLACES Study Area ..................................................................... 24 Figure 8. Site Area ........................................................................................................ 25 Figure 9. The Model System ......................................................................................... 29 Figure 10. R9 Example Calculation ............................................................................... 34 Figure 11. Predevelopment Stormwater Flow ............................................................... 50 Figure 12. Post Development Stormwater Flow ............................................................ 51

  • 4

    Introduction

    Thesis Statement and the Combined Sewer Problem

    The Gowanus is under consideration for a rezoning process that could drastically

    change the environment of the neighborhood and impact the existing combined sewer

    system. This project examines the components that cause combined sewer overflow

    (CSO) discharges as well as how rezoning the Gowanus might impact the combined

    sewer system, and provides recommendations to address each component with the

    goal of reducing CSO discharges into the Gowanus Canal. The development of a

    metrics based model is used to quantify possible increases in wastewater entering the

    combined sewer system. Land cover and current stormwater management

    requirements are analyzed to calculate the potential impacts on stormwater generated

    and flows into the combined sewer system. The wastewater and stormwater impacts

    are combined to assess the total impact on the combined sewer system and

    recommendations are made to reduce the impacts of both wastewater and stormwater

    generation from new residential development within the anticipated Gowanus rezoning

    boundaries.

    A Brief History of the Gowanus

    The history of the Gowanus, the neighborhood and the canal, was expertly described in

    the book Gowanus: Brooklyn's Curious Canal written by Joseph Alexiou and published

  • 5

    in October 20151. The neighborhood of Gowanus is nestled between Park Slope and

    Carroll Gardens and cut through by the Gowanus Canal. Alexiou starts by going back to

    the 1600s when the area around the modern-day canal was a saltwater marsh

    surrounding the Gowanus Creek that quickly became famous for its giant oysters and

    agriculture as the dom