Salty Water in Madison, Wisconsin

Studies have shown that chlorides released into United States’ watersheds are accumulating and increasing over time, with potential impacts to aquatic life and drinking water. In the watersheds of Madison, Wisconsin, much of the chloride can be attributed to use of road salt for deicing during the winter season, but wastewater treatment plant effluent is another contributor. The Madison Metropolitan Sewerage District (District) is faced with the significant challenge of reducing the concentration of chloride in the discharge from the Nine Springs Wastewater Treatment Plant (NSWTP), in order to comply with the expected Water Quality Based Effluent Limit of 395 mg/L.The District has implemented several initiatives to identify and reduce the sources of chloride to the NSWTP. The District also evaluated available technologies and costs for removal of chloride from the NSWTP wastewater, including source water softening to eliminate the need for home softeners, and treatment of the NSWTP effluent.This paper describes the assessment of chloride sources to the NSWTP, ongoing District initiatives to reduce chloride contributions, alternatives considered for both source water softening and wastewater effluent treatment, and the results of a Triple Bottom Line assessment for evaluating and comparing compliance strategies.