THE OCCURRENCE AND DISTRIBUTION OF HEXAVALENT CHROMIUM IN GROUNDWATER ACROSS NORTH CAROLINA

Potential groundwater contamination from coal ash ponds is a current public health concern in North Carolina. One of the suspected contaminants is chromium, particularly toxic hexavalent chromium. A recent study on hexavalent chromium in groundwater from the Piedmont aquifers of North Carolina finds that hexavalent chromium is more prevalent in local groundwater than previously thought due to geogenic sources from water-rock interactions, especially in groundwater from aquifers associated with mafic rocks. In order to further evaluate the geochemical (pH, redox state) and hydrogeological (depth) factors that control the occurrence of hexavalent chromium in groundwater, this project generates a dataset of private, public, and monitoring wells across the Mountain, Piedmont, and Coastal regions of North Carolina to investigate the scope and origin of hexavalent chromium in groundwater. A total of 285 water samples were collected and analyzed for major and trace elements, including hexavalent chromium. The data show that hexavalent chromium is the predominant species of dissolved chromium in groundwater. Geospatial and statistical analyses provide evidence for higher concentrations of hexavalent chromium in shallow and oxic groundwater, particularly in the Piedmont aquifers associated with mafic rock formations. We identified several “hot spots” areas in the Piedmont area with private and public wells containing hexavalent chromium of up to 25 and 5 parts per billion, respectively. In contrast, groundwater from aquifers associated with sedimentary formations in the coastal area have typically low hexavalent chromium. Our results indicate that most hexavalent chromium is likely naturally occurring (geogenic) and ubiquitous in groundwater from the Piedmont region in eastern U.S., which could pose health risks to residents in the region who consume well water as a major drinking water source.