STABLE ISOTOPE STUDY OF GROUNDWATER IN ARSENIC CONTAMINATION PLUME AT SHEPLEY'S HILL, DEVENS, MASSACHUSETTS

Out of 30,000 arsenic analyses conducted in the US, 10% have been observed to contain more than 10 ppb (maximum contaminant level established by the US EPA). In the northeast U.S., arsenic in groundwater is frequently observed to be associated with historical landfill leachate plumes with uncertain sources of arsenic and its pathways. Based on the history of Shepley’s Hill landfill in Devens, MA, the solid waste disposal activities spanned nearly a century of landfilling with little or no documentation of when or what waste material was disposed in this landfill. The possible source(s) and pathways of the arsenic contamination still remain unknown and 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, and/or the bedrock. In this study, currently in progress, we are exploring the possibility of using stable isotopic ratios of groundwater from different zones of the landfill and 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 which might lead to a better understanding of biogeochemical processes within and beneath the landfill waste pile and also ways to possibly correct the contamination of the aquifer.