Abstract
This chapter focuses on a permeable reactive barrier (PRB), which was installed at a site near Monticello, Utah, in June 1999 to remediate contaminated groundwater at a former uranium-processing mill. Laboratory and field column tests were used to evaluate reactive materials and zero valent iron (ZVI) was selected for the installation, as it effectively removes various contaminants such as arsenic, molybdenum, nitrate, selenium, uranium, and vanadium present in the groundwater at this site and is also available in large quantities at low cost. The PRB is 31 m long and contains 251 metric tons of ZVI and the installation includes slurry walls that direct contaminated groundwater in an alluvial aquifer through the PRB. The PRBwas keyed at least 0.3 m into impermeable bedrock and after 1 year of operation, effluent from the PRBcontinued to meet regulatory concentration goals for all contaminants. Low iron (Fe) concentrations in effluent from the PRB contrasted with high Fe concentrations in effluent from column tests, which is explained by the longer residence times in the PRB that led to higher pH values and precipitation of Fe(OH)2. Groundwater mounded immediately upgradient of the PRB, which resulted partly due to a reduction in the width of the alluvial aquifer because of the impermeable slurry walls, and possibly due to a zone of decreased permeability caused by steel sheet pile installation during PRB construction. Results of tracer tests and downhole flow measurements suggest that groundwater was flowing though the PRB at nearly the average linear design velocity of 5.7 m per day.
Published Version
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