Paul Smitherman C.T. Hess Charles W. Culbertson Robert G. Marvinney Yan Zheng Qiang Yang 2014 In greater Augusta of central Maine, 53 out of 1093 (4.8%) private bedrock well water samples from 1534 km² contained [U] >30 μg/L, the U.S. Environmental Protection Agency’s (EPA) Maximum Contaminant Level (MCL) for drinking water; and 226 out of 786 (29%) samples from 1135 km² showed [Rn] >4,000 pCi/L (148 Bq/L), the U.S. EPA’s Alternative MCL. Groundwater pH, calcite dissolution and redox condition are factors controlling the distribution of groundwater U but not Rn due to their divergent chemical and hydrological properties. Groundwater U is associated with incompatible elements (S, As, Mo, F, and Cs) in water samples within granitic intrusions. Elevated [U] and [Rn] are located within 5–10 km distance of granitic intrusions but do not show correlations with metamorphism at intermediate scales (100−101 km). This spatial association is confirmed by a high-density sampling (n = 331, 5–40 samples per km²) at local scales (≤10^–1 km) and the statewide sampling (n = 5857, 1 sample per 16 km²) at regional scales (10²–10³ km). Wells located within 5 km of granitic intrusions are at risk of containing high levels of [U] and [Rn]. Approximately 48 800–63 900 and 324 000 people in Maine are estimated at risk of exposure to U (>30 μg/L) and Rn (>4000 pCi/L) in well water, respectively. application/pdf 10.1021/es405020k en American Chemical Society Uranium and radon in private bedrock well water in Maine: geospatial analysis at two scales article