Stable isotopic study of groundwater arsenic contaminated plume at Shepley's Hill Landfill
2014
In the northeast United States, arsenic (As)
contamination in groundwater is frequently associated with
historical landfill leachate plumes. Based on the history of
Shepley's Hill Landfill (SHL) 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. Past
geochemical investigations proved the presence of high levels of As
in groundwaters within and around the SHL region. A total of 114
samples were collected from the SHL region and analyzed for their
hydrogeochemistry and isotopic signature. Since the isotopic ratios
of aD and a18O can potentially be influenced by the mobilization
process of As, this study attempts to identify any correlations
between the stable isotopic ratios and the hydrogeochemistry of SHL
waters. The results of the groundwater hydrogeochemical analysis
show multiple relationships between metal concentrations and As
concentration levels, typical of groundwater undergoing redox
reactions. The result of the stable isotope analysis show
significant fractionation of stable isotope ratios away from the
meteoric water line. However, the role of strong redox gradients
and various redox ladder reactions involving water did not produce
a significant correlation with the isotopic fractionations present
within different zones of the landfill. In most cases, the
fractionations stand independent of the increase/decrease in As
concentration and can be attributed to either unrelated chemical
reactions within groundwater or evaporation.
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