TRACE ELEMENTS IN DAN RIVER SEDIMENTS AFTER THE 2014 COAL ASH SPILL

On February 2, 2014, an estimated 82,000 tons of coal ash and 27 million gallons of contaminated water were released into the Dan River from a coal ash retention pond at the Duke Energy Steam Station in Eden, NC. Coal ash contains elevated concentrations of trace elements, some of which are toxic, prompting a concern that the ash spill could adversely impact human, aquatic, and environmental health.

The objective of this study was to examine trace element signatures in the Dan River sediment over space and time. Sediment samples were collected by our research group and the Virginia Department of Environmental Quality at up to 10 locations in the Dan River over a two-year period. The samples were digested and analyzed for trace elements using ICP-MS. We used correlation analysis to examine patterns and potential relationships in the geochemical data. Results illustrated strong positive correlations of several trace elements, including As, Cd, Cr and Pb, with Fe. These correlations suggest a geochemical association, likely adsorption, of these elements on Fe-bearing minerals or mineral coatings. In addition, we examined data for outliers as potential indicators of coal ash inclusion in sediment. For example, although As showed a strong positive correlation with Fe along one linear trend, there were 7-8 samples that were enriched with As with respect to Fe, suggesting a coal ash concentration in those sediment samples. We compared the concentration data to the Freshwater Sediment Threshold Effects Limit (TEL). Results of the comparison show TEL exceedances for one sample for As and 25% of the samples for Cr. There were no TEL exceedances for Pb, although several samples in 2014 came close. We are continuing to conduct additional statistical analyses and comparison with background samples to evaluate relationships between trace element concentrations in sediment and the coal ash spill, natural sources of trace elements, and other human influences.