Geophysical characterization, redox zonation, and contaminant distribution at a groundwater surface water interface

Three transects along a groundwater/surface water interface were characterized for spatial distributions of chlorinated aliphatic hydrocarbons and geochemical conditions to evaluate the natural bioremediation potential of this environmental system. Partly on the basis of ground penetrating radar measurements, a conductive sediment layer was detected from the shore out to at least 300 m offshore which exhibited gradients in redox pairs and contaminant profiles. The cis-Dichloroethene and 1-chloroethene were predominant in the presence of elevated methane and ferrous iron concentrations and depressed sulfate and aquifer solids-bound iron concentrations. The shallow monitoring points were generally hypoxic to aerobic and exhibited values of specific conductance reflective of near-shore lake water, indicating reoxygenation of the contaminant plume due to wave infiltration. The barge transect yielded trace contaminant concentrations and showed evidence of sulfate reduction, These analyses contributed to the understanding of processes affecting contaminant fate and transport at near-shore mixing zones.