Superfund Research Program

Enhanced Remediation at U.S. Arsenic-Contaminated Sites

Project Leader: Benjamin C. Bostick
Co-Investigator: Steven N. Chillrud
Grant Number: P42ES010349
Funding Period: 2000-2021

Project-Specific Links

Final Progress Reports

Year:   2020  2016  2010  2005 

This project focuses on investigation of arsenic mobilization and transport at two Superfund sites, the first an old municipal landfill in Winthrop, ME and the second a chemical manufacturing plant in Vineland, NJ.  This year graduate student Alison Keimowitz, was lead author on 3 peer reviewed journal publications, completed her PhD dissertation which was focused on arsenic transport and fate issues at our study sites, and was awarded a Fulbright Fellowship.  The first manuscript, published in Applied Geochemistry, concludes that elevated groundwater arsenic concentrations at the Winthrop Superfund site are of natural origin, with arsenic being mobilized by the interaction of highly reducing landfill leachate with underlying sediment.  Approximately 35% of US Superfund sites where arsenic is a contaminant of concern involve landfills (EPA, 2005); improper disposal of arsenical wastes is probably responsible for this contamination at some fraction of these sites.  However, reducing conditions generally induced in groundwater by landfill leachate have the potential to mobilize arsenic at these sites as well as many old landfills.  The Simpson/Stute group followed up on investigations concerning the potential of old unlined landfills to be mobilizing arsenic with staff from Region 3 of the NYS Department of Environmental Conservation, including shared field and laboratory efforts on samples collected at several old landfills and one submitted collaborative manuscript.  This collaboration has focused on developing As/Fe ratios in iron flocs which commonly appear at surface seeps near landfills as a predictive tool of arsenic mobilization issues being present at a landfill.  Roughly ¾ of the old landfills investigated to date in Region 3 have elevated As/Fe ratios.

Additional fieldwork during the 2005 focused on collection of samples from the Vineland site for tracer measurements and for characterization of the potential for As mobilization in aquifer solids. The researchers collected 24 samples for SF₆ and ³H/³He on extraction and monitoring wells, which will allow them to determine groundwater ages for the aquifer underneath the site. The SF₆ analyses show a characteristic decrease of age as a function of depth. The tracer data set will allow the researchers to compare how the operating pump & treat system has influenced the groundwater flow regime by comparison with an earlier survey and eventually will be used as calibration target of the existing groundwater flow model that then is needed to determine locations of additional wells to ensure capture of the arsenic plume.  Preliminary characterization of the aquifer solids suggests that the vast majority of the arsenic is easily mobilizable. This is a promising preliminary result relevant to proposed field experiments focused on assessing feasibility of in situ mobilization of arsenic as a way to greatly enhance the pump and treat remediation of the site.