Evaluation of the Treatment of Groundwater Arsenic at Mining and Industrial Sites Using Zvi and Bofs Permeable Reactive Barrie

Abstract: Permeable reactive barriers installed at a gold mine and at a chemical manufacturing facility have been effectively remediating arsenic contaminated groundwater since they were installed in 2002. At the mine site, the PRB is pilot scale and uses a reactive mixture consisting of zero valent iron filings and organic carbon derived from locally available wood chips. For experimental control the PRB is isolated from the surroundings by sheet pilings and As-contaminated groundwater from tailings at the mine is pumped through the reactive materials at controlled rates. For more than four years, As input at around 20 mg/L has been treated to <0.01 mg/L. At the chemical manufacturing site the PRB is full-scale and the reactive material is entirely granular basic oxygen furnace slag. This full-scale PRB consists of two parallel 600 m long trenches ~5 m apart and installed across the direction of groundwater flow to a depth of approximately 10.5 m, where it intercepts up to a meter of clay aquitard. Each PRB is approximately 0.6 m wide. For more than four years, As flowing into the PRB at 1-3 mg/L has been treated to <0.01 mg/L. The two PRB locations have very different groundwater chemistry and use dissimilar reactive materials, but both are providing high levels of As treatment. At the pilot scale PRB there is no indication that the level of As treatment is diminishing after four years of operation. The full-scale PRB locally shows signs of partial loss of reactivity in the upgradient PRB however, the downgradient PRB remains effective and a zone of low-As water now extends more than 6 m past the PRBs. The reactive materials from these PRBs have been tested to provide insight into the As removal mechanisms and factors that affect their performance.