IMPLEMENTING A TMDL, WATER QUALITY STANDARD MODIFICATION AND NITROGEN TRADING TO ATTAIN HYPOXIA MANAGEMENT GOALS IN LONG ISLAND SOUND

The Connecticut Department of Environmental Protection (CTDEP), a partner in the EPA's National Estuary Program's Long Island Sound Study (LISS), faced an unusually difficult challenge to meet water quality goals for Long Island Sound (LIS). LIS is a large and complex waterbody whose waters are shared by Connecticut (CT) and New York (NY). Three other New England states are prominent in its 16,000 sq. mi. watershed. Fifteen years of monitoring, research and modeling preceded adoption of a CT-NY total maximum daily load (TMDL) analysis in 2001 and made it clear that, initially, both CT and NY would need to greatly reduce nitrogen loads to LIS to alleviate seasonal hypoxia that impacts the bottom waters of the western half of the Sound each summer. Additional actions in Massachusetts, New Hampshire and Vermont in the upper watershed were also recommended and a work team established to set goals for those states by 2004. Research has also shown that existing water quality standards for dissolved oxygen (DO), which were based on freshwater, coldwater species tolerances years ago, were probably both unattainable and unnecessarily high. As such, CTDEP has now experienced the rarity of co-writing a multi-state TMDL and concurrently revising its DO standard. Further, LISS discussions had identified nitrogen trading as a promising option for meeting the 64% nitrogen reduction goal for 79 municipal sewage treatment plants (STP) scattered throughout the state. In 2001, CT passed enabling legislation to create a Nitrogen Credit Exchange, and in 2002 a general permit for nitrogen was issued to the 79 STPs that set the stage for trading. The first year's annual trade was completed in 2003 based on 2002 STP performance and demonstrated the value of trading to accelerate management and save money. The aggregate nitrogen reduction achieved by the 79 STPs far exceeded expectations as denitrification projects were completed and plant operators maximized nitrogen removal to generate credits for sale or to minimize the number of credits they would need to purchase. The interaction of all these activities presents a unique case study demonstrating the value of detailed planning, sound use and judicious adjustment of regulatory tools, and the possibilities of water pollutant trading, to meet management goals.