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Long Island Sound Nitrogen

Hypoxia, or low dissolved oxygen (DO) caused primarily by excess nitrogen loading has been identified as the issue of greatest concern for water quality in Long Island Sound (LIS).

To address the excess nitrogen, and resulting DO problems, the Connecticut Department of Energy and Environmental Protection (CTDEEP) and New York State Department of Environmental Conservation (NYSDEC) developed A Total Maximum Daily Load Analysis to Achieve Water Quality Standards for Dissolved Oxygen in Long Island Sound (LIS TMDL) that outlines nitrogen reductions necessary to meet water quality standards in the Sound. The U.S. Environmental Protection Agency (EPA) approved the LIS TMDL in 2001.

The Long Island Sound TMDL Workgroup

The Connecticut River Nitrogen Project was a cooperative effort involving staff from NEIWPCC, the states of Connecticut, Massachusetts, New Hampshire, and Vermont, and EPA’s Region 1 and LIS offices. The Connecticut River Workgroup focused its efforts in better understanding nitrogen loading and transport from the Connecticut River watershed to LIS.

In 2010, the Connecticut River Nitrogen Project merged with the LIS TMDL Workgroup. Coordinated by NEIWPCC, the LIS TMDL Workgroup consists of representatives from the Sound’s five watershed states including staff from the CTDEEP, Massachusetts Department of Environmental Protection (MassDEP), New Hampshire Department of Environmental Services (NHDES), NYSDEC, and Vermont Department of Environmental Conservation (VTDEC). The workgroup also includes representatives from EPA’s Region 1, Region 2, and LIS office.

The LIS TMDL Workgroup was established to carry out the LIS TMDL’s phased implementation plan through a five-state watershed process. The plan includes commitments to reevaluate nitrogen reduction targets periodically and revise the LIS TMDL plan accordingly.

The LIS TMDL reevaluation process has been underway since adoption of the original LIS TMDL. The phased implementation plan schedule for the LIS TMDL calls for a reevaluation of the allocations based upon advances in monitoring, modeling, research, implementation, water quality criteria, and other factors. That reevaluation is currently supported by the Long Island Sound Study (LISS), a NEIWPCC program partner.

A future revision of the LIS TMDL may include updated nitrogen allocations for both lower basin sources (CT and NY) and upper basin sources (MA, NH, and VT).

Enhanced Implementation Plan for the Long Island Sound Total Maximum Daily Load

In 2012, the LISS Management Committee and the five watershed states approved a framework for the assessment of the LIS TMDL. This assessment is known as the Enhanced Implementation Plan for the Long Island Sound Total Maximum Daily Load. The plan contains three main elements:

  1. Continue implementation of nitrogen reductions from wastewater treatment plants (WWTPs). This includes continued upgrades and optimization work in the CT and NY portions of the watershed. This also includes capping WWTP nitrogen loads, monitoring nitrogen discharged from WWTPs, and the completion of nitrogen removal optimization studies at WWTPs in the MA, NH, and VT portions of the LIS watershed. Work on this element of the plan is ongoing.
  2. Complete a preliminary evaluation of current stormwater and nonpoint source control efforts with a goal of qualitatively assessing their adequacy for meeting the 2000 LIS TMDL load reductions for stormwater and nonpoint sources. This element of the plan has been completed (see next section for detail on the resulting report).
  3. Develop and implement a feasible tracking system to evaluate attainment of nitrogen load reductions from nonpoint source and stormwater best management practices. Work on this element of the plan is ongoing (see section on Tracking & Accounting of Nonpoint Source & Stormwater Best Management Practices below).

In 2019, NEIWPCC began to support a new work group, the Long Island Sound Study Nitrogen Coordination Work Group. The work group provides the opportunity for coordination between three ongoing Nitrogen reduction efforts:

  1. EPA has begun work on the Long Island Sound Nitrogen Reduction Strategy. The strategy uses existing data  to develop non-binding nitrogen loading threshold targets in several sub-watersheds. When complete, EPA will develop nitrogen loading allocations for each sub-watershed.
  2. New York has begun work on the Long Island Nitrogen Action Plan (LINAP), a multi-year initiative to reduce nitrogen in Long Island’s surface and ground water.
  3. Connecticut has developed its Second Generation Nitrogen Strategy.

The Nitrogen Coordination Work Group aims to connect leaders, develop shared goals and a technically sound path forward of the various reduction strategies/programs. NEIWPCC, as a regional interstate agency, is well positioned to support these coordination efforts.

The LIS TMDL Enhanced Implementation Plan Report

The report completed under part two of the Enhanced Implementation Plan for the Long Island Sound Total Maximum Daily Load is a preliminary and qualitative evaluation of the adequacy of current stormwater and nonpoint source nitrogen control efforts in achieving the LIS TMDL for DO. This qualitative analysis is based on (1) nitrogen loading trends, (2) changes in drivers of nitrogen loading, and (3) the scope and effectiveness of on-the-ground nonpoint source and stormwater nitrogen control efforts.

Each of the five watershed states completed a section of the report. NEIWPCC prepared the watershed synthesis section of the report, which serves as a synthesis and evaluation of TMDL-related implementation efforts at the state and watershed level. Elements of the report are linked below.

Low Cost Nitrogen Removal for WWTPs in MA, NH, and VT

This study, completed March 2015 by JJ Environmental, LLC, assessed the feasibility and cost-efficiency of installing low-cost biological nitrogen removal retrofits at select WWTPs in the upper LIS watershed (MA, NH, and VT).

Tracking & Accounting of Nonpoint Source & Stormwater Best Management Practices

This is a multi-phase effort to develop and implement a feasible tracking system that will allow for quantitative TMDL evaluations of the attainment of stormwater and nonpoint source nitrogen load reductions, as required by the TMDL. The first phase, completed April 2014 by WaterVision, LLC, involved evaluating existing tracking and accounting systems and making recommendations on the general framework for the LIS tracking system.

An Evaluation of Nonpoint Source Pollution Control Measure Tracking Systems for Long Island Sound [Phase I] Final Report (PDF)

Nutrient Trading in Long Island Sound

In 2020, NEIWPCC initiated an exploratory study into the opportunities and obstacles to expand water quality trading to further improve water quality and ecosystem health in the Long Island Sound watershed. Ultimately, the interdisciplinary team found that expanded water quality trading is unlikely to be an effective tool to meet water quality goals under current ecological, economic, and regulatory conditions.

View the project webpage to learn more.

For more information, contact Richard Friesner, PhD, coordinator of our Long Island Sound TMDL work group or the Nitrogen Coordination Work Group at