Arsenic in Groundwater in Eastern New England: Occurrence, Controls, and Human Health Implications

In eastern New England, high concentrations (greater
than 10 μg/L) of arsenic occur in groundwater. Privately
supplied drinking water from bedrock aquifers often has
arsenic concentrations at levels of concern to human health,
whereas drinking water from unconsolidated aquifers is
least affected by arsenic contamination. Water from wells
in metasedimentary bedrock units, primarily in Maine
and New Hampshire, has the highest arsenic concentrationsnearly 30% of wells in these aquifers produce water
with arsenic concentrations greater than 10 μg/L. Arsenic
was also found at concentrations of 3−40 mg/kg in
whole rock samples in these formations, suggesting a
possible geologic source. Arsenic is most common
in groundwater with high pH. High pH is related to
groundwater age and possibly the presence of calcite in
bedrock. Ion exchange in areas formerly inundated by
seawater also may increase pH. Wells sampled twice during
periods of 1−10 months have similar arsenic concentrations
(slope = 0.89; r-squared = 0.97). On the basis of water-use information for the aquifers studied, about 103 000 people
with private wells could have water supplies with arsenic
at levels of concern (greater than 10 μg/L) for human
health.