REVISED DRAFT SUBWATERSHEDS WASTEWATER PLAN EXECUTIVE SUMMARY “We are in a county that will no longer allow our water quality crisis to go unaddressed, but will come together to Reclaim Our Water” Suffolk County Executive Steve Bellone 2014 State of the County Suffolk County Department of Health Services August 2019 This document was prepared with funding provided by the New York State Department of Environmental Conservation as part of the Long Island Nitrogen Action Plan and by New York State Department of State under the Environmental Protection Fund. Subwatersheds Wastewater Plan • Executive Summary Table of Contents Executive Summary ......................................................................................................... 5 1.0 Introduction ................................................................................................................................................................. 5 1.1 Background ........................................................................................................................................................ 5 1.2 Wastewater Management in Suffolk County ........................................................................................ 7 1.3 Innovative/Alternative Onsite Wastewater Treatment Systems ................................................ 9 1.4 Sewage Treatment Plants and Sewering ............................................................................................ 13 1.4.1 Sewer Expansion Projects ........................................................................................................... 14 2.0 SWP Development .................................................................................................................................................. 14 2.1 Stakeholder Participation ......................................................................................................................... 14 2.2 Quality Assurance Project Plans ............................................................................................................. 16 2.3 Subwatershed Identification .................................................................................................................... 16 2.4 Groundwater Modeling .............................................................................................................................. 6 2.5 Nitrogen Load Estimation Methodology ............................................................................................. 22 2.5.1 Nitrogen Load from Sanitary Wastewater ........................................................................... 123 2.5.2 Nitrogen Load from Fertilizer ................................................................................................... 24 2.5.3 Nitrogen Load from Animal Waste .......................................................................................... 25 2.5.4 Nitrogen Load from Atmospheric Deposition .................................................................... 25 2.6 Existing Conditions Nitrogen Load Estimates .................................................................................. 25 2.6.1 Simulated Nitrogen Concentrations under Existing Conditions ................................. 26 2.6.2 Simulated Nitrogen Loads to Surface Waters ..................................................................... 26 2.6.3 Simulated Nitrogen Concentrations in Community Supply Wells ............................. 30 2.7 Subwatershed Characterization and Ranking .................................................................................. 31 2.7.1 Water Quality Database Development ................................................................................... 31 2.7.2 Surface Water Modeling and Residence Time Calculation ............................................ 32 2.7.3 Subwatershed Ranking Approach ........................................................................................... 33 2.8 Ecological Endpoints and Nitrogen Load Reduction Goals ......................................................... 40 2.8.1 Ecological Endpoint Identification .......................................................................................... 42 2.8.2 Nitrogen Load Reduction Goals ................................................................................................ 42 2.8.3 Reference Water Body Approach for Marine/Mixed Water Bodies.......................... 43 2.8.4 Stress-Response Relationship Approach for Mixed/Marine Water Bodies ........... 45 2.8.5 Comparison to Existing Guidance and Literature Values .............................................. 47 2.8.6 Nitrogen Load Reduction Goal Approach for Fresh Water Bodies and Coastal Ponds ............................................................................................................................................................... 47 2.8.7 Summary of Recommended Subwatershed-Specific Nitrogen Load Reduction Goals ............................................................................................................................................................................ 48 2.9 Wastewater Management Areas for Nitrogen Load Reduction to Surface Waters .......... 48 2.10 Near Shore Areas ........................................................................................................................................ 51 2.11 Groundwater and Drinking Water Priority Areas ........................................................................ 51 2.12 Integrated Subwatersheds Wastewater Priority Map ............................................................... 53 3.0 Evaluation of Wastewater Management Methods .................................................................................... 54 3.1 Alternative Cost-Benefit Analysis .......................................................................................................... 56 3.2 Geographic Cost-Benefit Considerations ........................................................................................... 57 ES -1 Subwatersheds Wastewater Plan • Executive Summary 3.3 Pilot Area Evaluations ................................................................................................................................. 59 3.4 Countywide I/A OWTS Alternatives Evaluation .............................................................................. 62 3.5 Sewering and Clustering Alternatives Evaluation .......................................................................... 65 3.5.1 Inventory of Existing Sewer Proposals in Suffolk County ............................................ 68 3.5.2 Wastewater Management Response Evaluation .............................................................. 69 3.5.3 Sewer Scenario Evaluation Findings and Recommendations ..................................... 69 3.6 Nitrogen Mitigation for Groundwater and Drinking Water Restoration and Protection 3.7 Summary of Overall Recommended Wastewater Management Strategy ............................ 7472 4.0 Predicted Benefits of SWP Implementation ................................................................................................ 75 4.1 Predicted Benefits of SWP Implementation on Surface Waters ............................................... 77 4.2 Predicted Benefits of SWP Implementation on Groundwater and Drinking Water ......... 79 5.0 Summary of SWP Recommendations ............................................................................................................. 82 5.1 Primary Program Recommendations ................................................................................................... 83 5.1.1 Recommended Revisions to the Suffolk County Sanitary Code ................................. 83 5.1.2 Detailed Recommendations for Phase I – Program Ramp Up ..................................... 84 5.2 Other Program Recommendations ........................................................................................................ 85 5.2.1 OSDS Upgrade Requirements for Home Elevation .......................................................... 86 5.2.2 Initial Recommendations to Address Contaminants of Emerging Concern ......... 86 5.2.3 Initial Recommendations to Address Sea Level Rise ...................................................... 86 5.2.4 Initial Recommendations to Address Phosphorus........................................................... 87 5.2.5 Initial Recommendations to Address Pathogens .............................................................. 89 5.2.6 Initial Recommendations to Address Upzoning................................................................ 89 5.2.7 Initial Recommendations to Address Open Space ........................................................... 89 5.2.8 Initial Recommendations to Address Transfer of Development Rights ................. 90 5.2.9 Initial Recommendations to Address Legacy Nitrogen and Other Nitrogen Mitigation Measures ................................................................................................................................. 90 ........................................................................................................................................................................... 91 5.3 Adaptive Management and Monitoring Plan ..................................................................................... 91 6.0 Recommendations for Further Evaluations ...............................................................................................