Year Established: 2013 Start Date: 2013-03-01 End Date: 2014-02-28
Total Federal Funds: $18,000 Total Non-Federal Funds: $36,015
Principal Investigators: Rebecca Neumann, Jennifer Jay
Abstract: Arsenic contaminated groundwater negatively impacts the health of millions worldwide, including those who live in Washington State. Given the prevalence and negative health consequences of arsenic-contaminated groundwater, it is important to develop robust arsenic remediation strategies. In-situ arsenic removal from groundwater by induced microbial sulfate reduction, either with or without the addition of zero-valent iron (ZVI), is a promising remediation strategy. It works by injecting the appropriate microbial substrates into the subsurface, creating biogeochemical conditions that favor the formation of minerals that incorporate arsenic during precipitation or create surfaces upon which arsenic adsorbs. While numerous laboratory studies have documented the ability of induced sulfate reduction to remove arsenic from solution, adoption of the technique remains low, reflecting the sparse number of field-based applications, a deficiency of direct evidence regarding arsenic sequestration mechanisms, and a lack of testing focused on the long-term stability of the treatment. The objective of the proposed project is to advance understanding of the long-term sustainability of arsenic removal from groundwater following field-scale application of induced microbial sulfate reduction with ZVI. Washington State has one of the few field applications of induced microbial sulfate reduction. The WA Department of Ecology has overseen application the technique (with ZVI) as permeable reactive barriers (PRB) to remediate the leading edges of a groundwater arsenic plume emanating from a former landfill near Tacoma. The effort has decreased and maintained low arsenic concentrations within the PRB for a 2-year period. Despite the apparent success of the applied remediation strategy, many questions remain, which the site manager from the Department of Ecology wants answered to help him make decisions about maintaining the PRBs and expanding the remediated area. Namely: -What is the arsenic sequestration mechanism in the PRBs? -What is the capacity of the PRBs to scavenge arsenic out of contaminated groundwater as it flows through the remediated zones? -Does the sequestered arsenic get re-mobilized when it is exposed to ambient, uncontaminated groundwater? We will work to answer these questions by, 1) conducting laboratory column experiments on sediment already collected from a PRB at the site. We will pump groundwater collected from the PRB, a high arsenic aquifer area, and an uncontaminated aquifer area through the sediments at rates faster than that occurring in the field. The approach will allow us to both expedite and study the biogeochemical processes involved with arsenic scavenging and/or re-mobilization. And, 2) Performing solid-phase speciation analyses (sequential extractions, x-ray flouresence (XRF), and x-ray adsorption spectroscopy (XAS)) on the collected sediments, both before and after the column experiments. The collected data will clarify the arsenic sequestration mechanisms acting in the field, and will highlight the mineral phases involved with arsenic scavenging or arsenic remobilization stimulated during the column experiments. Collectively, the efforts will provide direct evidence of the long-term stability of in-situ microbial induced sulfate reduction as a strategy for removing arsenic from groundwater. Results will not only help inform future cleanup and monitoring strategies at the studied site, but will fill a crucial gap that currently exists for this remediation technology namely, an assessment of the stability and performance of a field-based application. Our study will be a key test of this promising arsenic remediation technology, and could, if results are favorable, support wider adoption of the strategy. Ultimately, a successful in-situ remediation scheme will help reduce human exposure to arsenic and achieve compliance at cleanup sites, both globally and within Washington State.