MULTIPLE CONTAMINANTS, MULTIPLE STANDARDS: GEOCHEMISTRY AND HEALTH IN NORTH CAROLINA GROUNDWATER QUALITY

North Carolina has the fourth largest population of private well users in the U.S., the majority of whom have never has their well water tested for trace metals. This is despite the fact that health relevant concentrations As, Cr, U, and V are all known to occur naturally in groundwater across the state. We investigated the geochemistry of 1494 groundwater wells across North Carolina and evaluated the effects of aquifer lithology and geochemical conditions on the occurrence of these elements in groundwater. The highest concentrations of all elements tended to be in groundwater from fractured crystalline rock aquifers in the central Piedmont Region, with extreme concentrations of U and As being particularly tied to particular geologies. Detectable concentrations of As were mostly found in suboxic groundwater, while U, V, and Cr (typically as the more toxic Cr(VI)) were mostly found in oxic groundwater. Arsenic and U were both more likely to be found in higher pH groundwater, probably reflecting desorption. Vanadium and Cr, however, were more likely to be found in lower pH groundwater, which may be a function of the relationship between pH and redox. It was not uncommon for individual wells to have more than one of these contaminants above health guideline levels, with V and Cr co-occurring particularly frequently. These co-occurrences may present additional risks to individuals relying on groundwater for drinking water. The lack of health data to inform recommendations regarding contaminant co-occurrence and health, as well as conflicting messages from government agencies about the risks presented by individual elements are just a few of the challenges in understanding potential health risks to individual well users. Though As, Cr, U, and V are ultimately geogenic in origin in most cases in NC, anthropogenic activities can have an impact on their concentrations in well water. More research is needed to understand how changes to groundwater recharge induced from climate change, groundwater withdrawal, and water contamination may impact groundwater quality. More detailed analysis of aquifer solids, better understanding of temporal trends, and depth/water table constrained data are just some of the possible ways in which geochemistry may help us better understand the future of water quality in the aquifers of the Eastern U.S.