Uranium Occurrence and Arsenic Variability in Private Well Water in Southeast New Hampshire

Uranium, derived from geologic sources, is a frequently occurring contaminant in groundwater in New England’s bedrock aquifers. While recent studies have helped to quantify the presence of arsenic in New England’s fractured rock aquifers, less is known about the distribution of uranium in these aquifers. The goal of this ongoing study is to characterize the occurrence and analyze the spatial distribution of uranium in private well water through randomized sampling of private wells in southeastern New Hampshire. In addition, the study examines temporal variability in arsenic, since the majority of wells used in this study were also sampled 10 years ago as part of an arsenic occurrence and distribution study in the same area. To date, approximately 225 samples have been analyzed for arsenic, iron, manganese, lead, and uranium. Samples were collected and submitted by private well owners in the study area. Initial uranium occurrence results show that about 47% of wells had detectable (> 1 ug/L) concentrations of uranium, but less than 2% of the samples exceeded the U.S. Environmental Protection Agency’s (EPA) Maximum Contaminant Level (MCL) of 30 ug/L for uranium. Comparisons of field-filtered samples to unfiltered samples, which were collected for a subset of wells, showed little variability in concentrations for arsenic, lead, and uranium, indicating that these analytes were fully dissolved in the groundwater. Comparisons between arsenic measurements from 2002 and 2012 show similar concentrations: 19% of samples were above the MCL of 10 ug/L in 2002, compared to 17% in 2012. However, individual wells showed slightly more variability: only 80% of samples with arsenic greater than 10 ug/L in 2002 were still above 10 ug/L in 2012.