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.
Drinking water is one exposure route. These federal datasets also cover St Lawrence County, NY.
The EPA places St Lawrence County, NY in Zone 2 - a moderate-risk category, with a predicted average indoor radon level between 2 and 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
67% of homes in St Lawrence County, NY were built before 1980, and 35% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in St Lawrence County, NY averages 5.9 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
Across 35 public water systems serving St. Lawrence County, NY with EPA lead testing on record, 4 (11.4%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 4.2 ppb. 5 water systems serving St. Lawrence County, NY carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Stage 1 Disinfectants and Disinfection Byproducts Rule | 2 |
| Surface Water Treatment Rule | 1 |
| Lead and Copper Rule | 1 |
| Total Trihalomethanes (TTHM) | 1 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.