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Final Progress Reports: Columbia University: Enhanced Remediation at U.S. Arsenic-Contaminated Sites

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

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Final Progress Reports

Year:   2020  2016  2010  2005 

Dr. Steve Chillrud and his team of researchers are investigating the geochemistry and remediation of arsenic associated with the Vineland Superfund site in southern New Jersey. This involves work on the site of a former arsenic herbicide manufacturing facility as well as downstream at a recreational lake impacted by site arsenic. Due to decades of improper chemical storage and disposal by Vineland Chemical, the site was extensively contaminated with arsenic. Despite nearly a decade of pump-and-treat remediation, groundwater arsenic concentrations can still be several hundred μg/L. Laboratory column experiments using contaminated Vineland aquifer solids have suggested that current aquifer cleanup strategies, relying on pump-and-treat to flush groundwater through the aquifer, could require hundreds of years, but the remediation time frame could be decreased substantially (to <5 years) by introducing oxalic acid to the system. The research group also conducted a pilot experiment where they injected oxalic acid and tracers into a very small portion (~50 m2) of the aquifer next to one of the large volume extraction wells. Approximately 3 kg of arsenic was successfully removed by the oxalic acid, similar in magnitude to the amount of solid phase arsenic within the small pilot area. Overall, the work suggests that addition of oxalic acid shows promise for accelerating treatment of a highly contaminated site, offering the potential to lower dramatically the As remediation timescale.

Activities over the last year have focused on additional laboratory measurements and experiments on samples from the Vineland Site, data analysis and manuscript preparations, and a series of meetings with the Vineland Site Managers (Environmental Protection Agency Region 2 and US Army Corps of Engineers) to plan future activities at the site. The researchers have been completing the analyses of samples collected as part of the spring/summer 2009 pilot experiment and samples collected from Union Lake. They have also developed a new method to integrate the use of microfocused synchrotron techniques with column transport experiments to simultaneously monitor grain-scale solid phase reactions and column scale transport in order to better understand As release and transport processes. Small column experiments (~4 cm long x 0.635 cm ID) were performed on the laboratory bench as well as in the synchrotron beamline. Microfocused synchrotron X-ray fluorescence (μSXRF) maps for As and Fe were collected at the same location in the columns (<1 mm2) before and during treatment with 10 mM oxalic acid. Based on μSXRF counts, between 79% and 83% of As was removed from the sediments by the oxalic acid treatment; these removal percentages agreed well with laboratory data based on integrating column effluent (88-95%). A smaller percentage of Fe was removed, 14-25% based on μSXRF counts; column effluent indicated 7-9% Fe removal. A combination of laboratory columns, μSXRF data, and geochemical models were used to investigate As release rates during oxalic acid treatment. A pore volume based As removal rate was used to create a PHREEQC 1-D transport model, which indicated that microscale processes can be predictive of the larger system.

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