Assessment of Sustained Impacts from the Kingston Fossil Plant Coal Ash Spill on Surface Water and River Sediments in Eastern Tennessee

In December 2008, the failure of a coal ash retention pond at the Kingston Fossil Plant contaminated the Emory River, Clinch River and Watts Bar Reservoir with toxic metals. Despite an extensive cleanup effort, further leaching of toxic metals from river sediments remains a cause of concern. In spring 2016, new water and sediment samples were collected from seven contaminated and three uncontaminated portions of the river systems for trace metal and H-C-O-S-N isotopic analyses. In the water column, the trace metals were below detection limit (<0.002 mg/L) and only Mn (0.11-0.29 mg/L) slightly exceeded the EPA human health guideline (0.05 mg/L) in two locations. However, the concentrations of As and Cd within the river sediments (3.5-10.9 and 0.7-2.2 mg/Kg, respectively) exceeded the sediment quality guidelines (8.2 mg/kg and 1.2 mg/kg, respectively). While no other trace metals (Cr, Cu, Ni, Pb, Zn) surpassed the established toxicity guideline levels, they were in highest concentrations further away from the spill location. This suggests important metal fluxes to the river sediments from other anthropogenic sources and/or bedrock dissolution. In the most contaminated sediment layers, the δ³⁴S [sulfur isotopic value] was the highest (+4 to +11‰ [per mil]) reflecting that of combusted coal (+9 to +12‰). Using sulfur isotopes, it was determined that the remaining coal ash is currently buried by at least ~5 cm thick layer of younger sediments. The measured low δ³⁴S values of elemental S (-3.5 to +1.1‰), acid-volatile sulfides (-2.7 to +1.1‰) and chromium-reducible sulfides (-6.9 to +1.3‰) in the uncontaminated sites suggest that microbial sulfate reduction is active in the studied rivers. However, the role of this process appears to be minor/negligible in the bio-immobilization of trace metals from coal ash spill. Other natural processes such as dilution, sedimentation, and dissolution of carbonate bedrock are more important in decreasing trace metal fluxes and burial of coal ash contaminants over time. It is evident that in addition to the 2008 coal ash spill these river systems continue to be negatively impacted by other metal contaminants from industry, mining, etc., thus continued research on the potential for toxicity in the Kingston region is necessary.