Arsenic and uranium occurrence in private wells in Connecticut, 2013–18—A spatially weighted and bedrock geology assessment

The U.S. Geological Survey, in cooperation with the Connecticut Department of Public Health, conducted a study to determine the presence of arsenic and uranium in private drinking water wells in Connecticut. Samples were collected during 2013–18 from wells completed in 115 geologic units, with 2,433 samples analyzed for arsenic and 2,191 samples analyzed for uranium. The study concluded four major findings.

• In a spatially weighted analysis of groundwater samples collected from more than 2,000 private wells in bedrock aquifers in Connecticut, 3.9 percent of collected samples contained arsenic concentrations greater than the U.S. Environmental Protection Agency’s (EPA) maximum contaminant level (MCL) of 10 micrograms per liter (µg/L), and 4.7 percent of collected samples contained uranium concentrations greater than the EPA MCL of 30 µg/L.
• Of the 2,433 water samples collected and analyzed from bedrock aquifers in Connecticut, 4.2 percent (102) contained arsenic concentrations at greater than 10 µg/L, and of the 2,191 water samples collected and analyzed from bedrock aquifers in Connecticut, 5.4 percent (118) contained uranium concentrations greater than 30 µg/L.
• Uranium concentrations greater than or equal to 1 µg/L are relatively ubiquitous across the State of Connecticut, with these concentrations present in 44.9 percent of the State, according to spatially weighted statewide-scale proportion analysis.
• Of the 115 geologic units studied, 44 had at least one sample with arsenic or uranium concentrations that exceeded the respective constituent’s EPA MCL.