Arsenic concentrations in drinking water from 2273 households and in rock samples from 307 sites throughout the state of New Hampshire were studied to understand potential links between bedrock geology and arsenic concentration in drinking water, and to calculate arsenic exposure estimates for the New Hampshire population. Though it remains clear that most of the arsenic in New Hampshire drinking water is likely from bedrock sources, a simple correlation between arsenic concentration in rock samples and arsenic concentration in drinking water was not observed. A combination of the Eh–pH status of the groundwater in the aquifer and proximity to high concentrations of arsenic in bedrock are suggested to be the most likely controlling mechanisms statewide.
Utilizing the high sampling density of drinking water along with water source and population data from the 1990 and 2000 Census, maps of average arsenic exposure were plotted at the census tract level. Integrating exposure from all types of water sources — drilled bedrock wells, wells in surficial deposits, and municipal water systems — a comprehensive estimate of exposure to various arsenic concentrations was constructed. Domestic bedrock wells supply water to 120,000 households, with a median arsenic concentration of 1.9 μg/L, domestic surficial wells provide water to approximately 40,000 households with a median arsenic concentration of 0.15 μg/L, and municipal water systems provide water to 265,000 households with a median arsenic concentration of 0.41 μg/L. Above 0.61 μg/L, domestic bedrock wells supply the largest number of households with elevated concentrations of arsenic, while below this value; more arsenic is delivered via municipal water systems. While many studies focus on more readily available public water supply data, this study points out the importance of quantifying arsenic exposure from private water supplies, and provides a technique for correcting spatially variable water source parameters.