St Lawrence County, New York: drinking water report. St. Lawrence County is New York's largest county by area, stretching across the northern border with…
St. Lawrence County is New York's largest county by area, stretching across the northern border with about 108,000 residents. Canton, Potsdam, Ogdensburg, and Massena are the main communities. The St. Lawrence River provides water to some systems, while others rely on groundwater. The county's remote character and harsh climate have not spared it from industrial contamination – the Massena area hosts one of the most concentrated clusters of Superfund sites in New York.
The General Motors Foundry, ALCOA, and Reynolds Metals all operated major facilities in Massena, creating a toxic legacy that includes PCBs, fluoride, and heavy metals. According to the EPA's 2024 Superfund status update, the GM Foundry site has documented PCB contamination in soil, groundwater, and the St. Lawrence River sediments. The ALCOA facility contributed fluoride and cyanide to the Grasse River, a St. Lawrence tributary.
PFAS adds to the contamination picture. The former Massena International Airport and military facilities in the area used AFFF. A 2024 NYSDEC investigation found PFAS at 19 ppt in monitoring wells near the airport. The Akwesasne Mohawk community, which spans the U.S.-Canada border adjacent to these industrial sites, has been disproportionately affected.
Massena-area residents near the industrial and Superfund sites face the highest exposure risk. Communities drawing from the St. Lawrence River benefit from the river's volume diluting localized contamination, but private well users near industrial areas need individual testing.
Check your water for available data. For PCBs, industrial metals, and PFAS, reverse osmosis at the kitchen tap provides the most comprehensive protection. Our water filter guide covers systems rated for industrial contaminant removal. Get your detailed report for local data, and visit our New York page for statewide context.