STUDY OF ARSENIC IN GROUNDWATER AND ALONG A REDOX GRADIENT

Landfills around the world and in the United States are often sites of extensive groundwater contamination. Shepley’s Hill landfill in Devens, Massachusetts is a landfill with widespread arsenic contamination caused by the highly reducing environment within the landfill. One possibility for arsenic mobilization is based on the assumption that the arsenic occurs naturally in the surrounding glacial strata around the landfill and is mobilized by the reduction of the host ferric (hydro)oxides from Fe(III) to Fe(II). The groundwater at Shepley’s Hill landfill has highly elevated concentrations of arsenic, ranging from near background (less than 10 ppb As) in some places to as high as 10,000 and above near the underlying basal glacial till beneath the landfill bottom. The main objective of this study is to test if there are transport mechanisms of arsenic in the groundwater other than dissolved arsenic. Several sequential filtration experiments between 8 microns and 50 nanometers were carried out on groundwater samples from the site to quantify how much, if any, of the total arsenic is dissolved and how much, if any, is attached to a suspended colloidal fraction in the solutions. Total arsenic analyses were performed on the filtered samples using Hydride Generation Atomic Fluorescence Spectrometry to determine arsenic concentrations in the filtrates. Preliminary results show that most of the arsenic in the studied samples from this site is in the form of complete dissolution and near none is in the form of attached fraction on the surfaces of suspended colloidal particles. Other part of the study includes experimental determination of arsenic partition coefficients between ferric (hydro)oxides and groundwater and analyzing the speciation of arsenic to better constrain the possible transport mechanisms of arsenic at this site.