Water Environment Federation (WEF)

The Connecticut Nitrogen Trading Program: lessons learned and the challenges that remain to achieve the TMDL for Long Island Sound

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Courtesy of Courtesy of Water Environment Federation (WEF)

Long Island Sound’s (LIS) most pressing water quality problem is caused by over-enrichment of nutrients, specifically nitrogen, which leads to greatly reduced levels of dissolved oxygen in the bottom waters of western LIS. Primary sources of nitrogen include municipal wastewater treatment plant discharges (also known as publicly owned treatment works or POTWs), atmospheric deposition and runoff from urban, suburban and agricultural areas. POTWs are the principal source in Connecticut and are the subject of this paper.

The federal Clean Water Act requires that the state establish total maximum daily loads (TMDLs) for all water bodies that do not meet minimum state water quality standards, such as LIS. The TMDL establishes the maximum loading for nitrogen that LIS can assimilate without causing impaired water quality. A 64 percent reduction goal was set for Connecticut POTWs through a wasteload allocation process. The baseline loading from all 79 POTWs was established at 48,709 pounds per day. To meet the reduction goal, the baseline loading must be reduced by 30,935 pounds per day. This would result in a cumulative loading of 17,774 pounds per day as measured at the end of the discharge pipes (EOP) from the 79 POTWs. Nitrogen “trading” was identified as a mechanism for cost-effectively attaining the aggregate goal for Connecticut POTWs. The Nitrogen Trading Program, the first statewide watershed based trading program in the nation, has recently completed 5 successful years.

In the first 5 years, the nitrogen reduction program in Connecticut has reduced the total nitrogen load from the 79 POTWs by 15,500 pounds per day. This equates to approximately 50 percent of the needed reduction to achieve the TMDL. The Nitrogen Trading Program to date has provided a unique alternative compliance program where each community has been able to make their own decision for the level of treatment improvements needed to achieve the solution of a watershed based water quality problem. This paper will review the success of the first 5 years of the nitrogen trading program and explore the challenges that will need to be overcome to achieve the TMDL for LIS.

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