Geochemical Characterization of Beaver Reservoir Sediments Containing Drinking Water Treatment Residuals

Phillips Creek, a tributary of Monte Ne cove on Beaver Reservoir in northwest Arkansas, has been the discharge location of drinking water treatment residuals (DWTRs) from a local water utility for more than forty years. This permitted discharge, in addition to sediment fluxes resulting from rapid land cover change in the Monte Ne watershed, led to the formation of a localized deltaic deposit at the head of Monte Ne cove containing both DWTRs and watershed sediments. The objective of this study was to analyze the geochemical character of this deposit containing mixed-source sediments in conjunction with sediments from a nearby cove containing only watershed-derived sediments in an effort to evaluate the behavior of residuals in the aquatic environment and the effects on sediment geochemistry. A five-stage sequential extraction technique was performed on sediments from both coves and results show distinct geochemical variations between coves. Monte Ne sediments, containing mixed DWTR and watershed sediments, showed elevated total levels of Al, Cr, Cu, Fe, Mn, Ni, Zn when compared to background and regulatory guidelines, while Prairie Creek sediments showed elevated total levels of Ni, Pb, and Zn only. Fractionation results showed that Cu, Ni, Pb, and Zn levels in Prairie Creek are in more potentially mobile fractions than in Monte Ne, signaling a probable DWTR influence on metal availability. A proxy measurement of aging effects also showed only modest changes in the binding efficiency of residuals through time. This study represents one of a very few analyzing the effects of DWTRs on sediment geochemistry in a complex aquatic environment.