STABLE ISOTOPES (δD AND δ18O) FRACTIONATION IN GROUNDWATER IN THE VICINITY OF AN ARSENIC CONTAMINANT LANDFILL PLUME IN CENTRAL MASSACHUSETTS

In the northeast United States, arsenic contamination in groundwater is frequently observed to be associated with historical landfill leachate plumes. Based on the history of Shepley’s Hill landfill in Devens, MA, solid waste disposal activities spanned nearly a century of landfilling with little or no documentation of when or what waste material was disposed. Standard geochemical investigations up until now have not been able to resolve the possible source(s), pathways and mechanism for the arsenic mobilization, which is the main focus of this study. Among the potential contamination sources of arsenic are the waste material deposits, the underlying unconsolidated glacial lake sequences, the presence of a peat layer, and/or the bedrock. This study proposes to use an unconventional approach of using stable isotopic ratios of groundwater from different zones of the landfill and comparing them with varying arsenic concentrations as a technique to delineate probable arsenic sources, the mobilization processes, and arsenic transport modes within the aquifer. The role of strong redox gradients and the various redox ladder reactions involving water are likely to create characteristic isotopic signatures. When juxtaposed with other groundwater composition data, these signatures might lead to a better understanding of the biogeochemical processes within and beneath the landfill waste pile and possibly aid in finding ways to correct the groundwater contamination.