DIFFERENTIATING WATERSHED-DERIVED SEDIMENTS FROM A DRINKING WATER TREATMENT RESIDUALS (DWTRS) DEPOSIT

Drinking water treatment residuals (DWTRs) are a common by-product of modern water treatment technologies and are often discharged under U.S. EPA regulations into local rivers and streams. Historically considered largely inert, these discharges are currently under increased scrutiny as sources of variety of non-conventional pollutants including both aluminum and iron salts, among others. Previous attempts to accurately delineate the contribution of DWTRs to suspected downstream deposits have been complicated by the mixing of DWTRs with watershed-derived sediments. This study of a probable DWTR deposit in Beaver Reservoir (northwest Arkansas) uses historical discharge records and in situ measurements (dual-frequency bathymetry, sediment probing, sediment coring) to delineate DWTR sediments from watershed-derived sources. Geochemical analyses of sediment cores confirmed the presence of unusually high aluminum (mean of 265,000 mg/kg) and iron (mean of 76,500 mg/kg) residuals which are 7.9 and 3.8 times background levels, respectively, along with the presence of other elevated trace metals including Cd, Cr, Cu, Mn, Ni, and Zn. Dual-frequency (28 kHz and 200kHz) bathymetric mapping and sediment probing show the distinctly non-uniform deposit in the cove and provide a volumetric estimate of in-place sediment. The total quantity of sediment in this cove is substantially greater than that observed in other coves of Beaver Reservoir that are not subject to DWTR discharge. Results from this study will further inform regulators and lead researchers toward a better understanding of the ultimate fate of these discharge residuals and provide a framework for future analysis and long-term monitoring.