Superfund Research Program
Mobilization of Anthropogenic As in Groundwater
Project Summary (2006-2011)
This project is being conducted using field studies at two Superfund sites. Both sites are contaminated with arsenic (As), and are undergoing active groundwater treatment through the period of this investigation. The Vineland Chemical Company (ViChem) site in southern NJ, experienced dispersal of at least hundreds of tons of waste As over five decades into surface soils, aquifer formations, groundwater, and surface waters. Stream, lake, and estuary sediments far downstream from the original arsenical herbicide and fungicide production facilities were also affected. The recharge dynamics of this altered flow regime are being examined by analyzing samples collected from monitoring wells for tracers present in the environment and to relate behavior of As and other redox sensitive species to those changes. A series of sediment cores in Union Lake are being collected and analyzed to reconstruct the history of As migration downstream, and to estimate the proportion of As sediment inventory mobilized upward towards the sediment surface. A similar set of groundwater measurements, directed at elucidating controls on As behavior, are being conducted at the Winthrop (ME) Landfill site. Sources of As to this strongly reducing plume are unresolved, but mobilization from surrounding natural soils appears to be a significant possibility, suggesting that similar As plumes could occur at many other landfills. The hydrogeology at the Winthrop site is very complex due to the large spatial variability in hydraulic conductivity. The groundwater flow regime is being constrained by employing geophysical survey techniques (ground penetrating radar and resistivity). Arsenic mobilization processes are being studied by following the geochemical evolution along a flow path underneath the landfill and by tracing the compositions of a plume of re-injected water labeled with SF6. These studies are contributing to a better understanding of the processes affecting As transport under different geochemical conditions ranging from oxidizing to highly reducing.