Arsenic Occurrence in New Hampshire Drinking Water

Arsenic concentrations were measured in 992 drinking water samples collected from New Hampshire households using online hydride generation ICP-MS. These randomly selected household water samples contain much less arsenic than those voluntarily submitted for analysis to the New Hampshire Department of Environmental Services (NHDES). Extrapolation of the voluntarily submitted sample set to all New Hampshire residents significantly overestimates arsenic exposure. In randomly selected households, concentrations ranged from <0.0003 to 180 μg/L, with water from domestic wells containing significantly more arsenic than water from municipal sources. Water samples from drilled bedrock wells had the highest arsenic concentrations, while samples from surficial wells had the lowest arsenic concentrations. We suggest that much of the groundwater arsenic in New Hampshire is derived from weathering of bedrock materials and not from anthropogenic contamination. The spatial distribution of elevated arsenic concentrations (>50 μg/L) correlates with Late-Devonian Concord-type granitic bedrock. Field observations in the region exhibiting the highest groundwater arsenic concentrations revealed abundant pegmatite dikes associated with nearby granites. Analysis of rock digests indicates arsenic concentrations up to 60 mg/kg in pegmatites, with much lower values in surrounding schists and granites. Weak acid leaches show that approximately half of the total arsenic in the pegmatites is labile and therefore can be mobilized during rock-water interaction.