SPATIAL ASSOCIATIONS BETWEEN ARSENIC IN GROUNDWATER, SEDIMENTS, BEDROCK, AND AGRICULTURAL LANDUSE IN NEW ENGLAND

Arsenic concentrations in 1572 public-supply bedrock-groundwater wells, 1597 stream-sediment samples, and 1274 unmineralized bedrock samples are used to (1) map the occurrence and distribution of arsenic in the surface environment throughout New England and (2) measure the spatial associations between these data and other information on geologic units and land-use features in the region. Ten percent of the public-supply bedrock wells in New England exceed the new EPA arsenic standard of 10 mg/L. Possible sources of arsenic include weathering of rocks and applications of arsenical pesticides that were commonly used on apple, blueberry, and potato crops from the 1920s to 1960s in New England. The distribution of bedrock groundwater wells with elevated arsenic has a strong positive spatial correlation with (1) the Coastal Maine and the Central Maine-New Hampshire geologic provinces, (2) calcpelite bedrock in the Central Maine-New Hampshire geologic province, (3) volcanic and sulfidic schist bedrock in the Coastal Maine geologic province, and (4) elevated stream sediment and rock arsenic geochemistry. Arsenic concentrations in bedrock wells do not correlate with past agricultural landuse. Compositions of stream sediments, which integrate both natural and anthropogenic arsenic sources, have a strong positive correlation with groundwater chemistry, bedrock geology, and rock chemistry and a weaker positive correlation with past agricultural landuse. Although spatial correlation is not sufficient to demonstrate cause-and-effect, the spatial statistics favor rock-based arsenic as the dominant source of arsenic in stream sediments and groundwaters. The distribution of bedrock geology features at the geologic province and lithology group level closely match the areas of elevated arsenic in rocks, stream sediments, and groundwater.