A permeable reactive barrier (PRB) of zero-valent iron is helping to clean up groundwater at a former uranium and vanadium ore processing mill at Monticello, Utah. LM managed remediation of tailings and tailings-contaminated material at this site. Cleanup of the mill site is regulated under the Comprehensive Environmental Response, Compensation, and Liability Act.
Arsenic, molybdenum, nitrate, selenium, uranium, and vanadium are contaminants of concern in groundwater at the site. An Interim Record of Decision designated emplacement of a PRB hydraulically downgradient of the mill site to remove these contaminants. Results of both laboratory and field treatability studies were used to help design the PRB and its reactive material components. The Accelerated Site Technology Deployment Program within DOE's Office of Science and Technology funded design, installation, and initial monitoring of the PRB.
An extensive monitoring network was installed during summer 1999 to evaluate the performance of the PRB. The PRB has been effective in reducing contaminant concentrations. Concentrations of arsenic, selenium, uranium, and vanadium are reduced to nondetectable levels on the downgradient side of the PRB. In addition, concentrations of molybdenum and nitrate are reduced to near nondetectable levels. As expected, concentrations of iron increase as groundwater passes through the PRB. Concentrations of iron exiting the wall are lower than expected (based on the treatability studies) and are well within an acceptable risk range.
The Variation in Hydraulic Conductivity Over Time at the Monticello Permeable Reactive Barrier document describes the hydraulic behavior of the PRB since its installation, based primarily on results of three separate rounds of slug tests and routine water-level monitoring.
The Alternatives for Mending a Permeable Reactive Barrier at a Former Uranium Milling Site: Monticello, Utah, report evaluates seven technologies that might be used to mend areas where groundwater mounding upgradient from the PRB occurs. The report also includes laboratory results from one possible mending option, injection of ferrous iron. Results suggest that all seven alternatives are nearly cost competitive.
DOE and the U.S. Environmental Protection Agency are conducting additional investigations of rejuvenation and performance assessment. Results of portions of this investigation are provided in Final Report Phase II: Performance Evaluation of Permeable Reactive Barriers and Potential for Rejuvenation by Chemical Flushing, U. S. Environmental Protection Agency Region 8 Support and Final Report: Rejuvenating Permeable Reactive Barriers by Chemical Flushing, U.S. Environmental Protection Agency, Region 8 Support.