Arsenic occurrence in New Hampshire drinking water

Arsenic concentrations were measured in 992 drinking water samples collecte d from New Hampshire households using online hydride generation ICP-MS. The se randomly selected household water samples contain much less arsenic than those voluntarily submitted for analysis to the New Hampshire Department o f Environmental Services (NHDES). Extrapolation of the voluntarily submitte d sample set to all New Hampshire residents significantly overestimates ars enic exposure. In randomly selected households, concentrations ranged from <0.0003 to 180 mu g/L, with water from domestic wells containing significan tly more arsenic than water from municipal sources. Water samples from dril led bedrock wells had the highest arsenic concentrations, while samples fro m surficial wells had the lowest arsenic concentrations. We suggest that mu ch of the groundwater arsenic in New Hampshire is derived from weathering o f bedrock materials and not from anthropogenic contamination. The spatial d istribution of elevated arsenic concentrations (>50 mu g/L) correlates with Late-Devonian Concord-type granitic bedrock. Field observations in the reg ion exhibiting the highest groundwater arsenic concentrations revealed abun dant pegmatite dikes associated with nearby granites. Analysis of rock dige sts indicates arsenic concentrations up to 60 mg/kg in pegmatites, with muc h lower values in surrounding schists and granites. Weak acid leaches show that approximately half of the total arsenic in the pegmatites is labile an d therefore can be mobilized during rock-water interaction.