NRMRL NATIONAL RISK MANAGEMENT RESEARCH LABORATORY GROUND WATER AND ECOSYSTEMS RESTORATION RESEARCH PRB Strategies and Performance Monitoring for Remediation of Inorganic Contaminants Background A permeable reactive barrier (PRB) is a zone of granular reactive material that extends below the water table to intercept the flow of contaminated ground water. As organic or inorganic contaminants pass through a PRB, they are ideally reduced to non-hazardous compounds or immobilized to less soluble or less toxic forms. Research is focused on assessing the geochemical, hydrogeological, and microbiological factors that govern the performance and functioning of PRBs. Understanding these factors is necessary in order to predict the longevity of PRB systems, conduct economic analyses, and to optimize the implementation of this ground water cleanup technology for a wide variety of hazardous compounds. Objectives As of 2002, the oldest zero-valent iron PRB systems were about 10 years old. In order to reach the best possible technology-selection decisions and to optimize PRB design parameters for ground water cleanup at contaminated sites, information is needed to identify the site-specific factors that govern continued PRB performance. Two PRB systems installed in 1996 (one at the U.S. Coast Guard Support Center, Elizabeth City, North Carolina; the other at the Denver Federal Center, Lakewood, Colorado) have been extensively monitored to track and evaluate system behavior through time. Approach This project includes both field and laboratory research components. Detailed performance monitoring data on full-scale PRBs installed to treat contaminated ground water have been collected at two different sites. The PRBs investigated in this project are among the oldest full-scale systems available for study and provide an opportunity to analyze the performance of systems with more than 5 years of field history. In addition, the PRBs examined here have contrasting design and hydrogeochemical characteristics that are useful for gaining insight about the factors that govern PRB longevity and long- term performance. waste PRB „ - v- ^——J El treated water ------- Geochemical studies include conventional low-flow ground water sampling and analysis, and solid-phase characterization investigations. Laboratory batch and column tests using reactive media are conducted to determine the effectiveness of reactive materials, such as zero-valent iron to treat a variety of hazardous substances. Contaminant-removal mechanisms will be identified in careful water chemistry, geochemical modeling, and solid-phase characterization studies. Accomplishments Wilkin, R.T. and M.S. McNeil. (2003). Laboratory Evaluation of Zero-Valent Iron to Treat Water Impacted by Acid Mine Drainage. Chemosphere, 53, 7: 715-725. Wilkin, R.T., R.W. Puis, and G.W. Sewell. (2003). Long-Term Performance of Permeable Reactive Barriers Using Zero- Valent Iron: Geochemical and Microbiological Effects. Ground Water, 41: 493-503. Paul, C., M. McNeil, F. Beck, P. Clark, R. Wilkin, and R. Puis, R. Capstone Report on the Application. Monitoring, and Performance of Permeable Reactive Barriers for Ground Water Remediation: Volume 2. Long-Term Monitoring of PRBs: Soil and Ground Water Sampling (PDF) (145 pp, 5.07 MB) (EPA/600/R-03/045b) August 2003 - Abstract Wilkin, R.T. and Puis, R.W. Capstone Report on the Application. Monitoring, and Performance of Permeable Reactive Barriers for Ground Water Remediation: Volume 1. Performance Evaluations at Two Sites (PDF) (156 pp, 23.6 MB) (EPA/600/R-03/045a) August 2003 - Abstract Furukawa, Y., J. Kim, J. Watkins, and R. Wilkin. (2002). "Formation of Ferrihydrite and Associated Corrosion Products in Permeable Reactive Barriers of Zero-Valent Iron." Environmental Science and Technology, 36: 5469-5475. Wilkin, R.T., Su, C., Ford, R.G., and Paul, C.J. (2005). Chromium removal processes during groundwater remediation by a zerovalent iron permeable reactive barrier. Environmental Science and Technology, v. 39, p. 4599-4605. Wilkin, R.T., Acree, S.D., Beak, D.G., Ross, R.R., Lee, T.R., and Paul, C.J. (2008). Field application of a permeable reactive barrier for treatment of arsenic in ground water, EPA Report, EPA/600/R-08/093, 88 pp. He, Y., Wilson, J.T., and Wilkin, R.T. (2008). Transformation of reactive iron minerals ina permeable reactive barrier (biowall) used to treat TCE in groundwater. Environmental Science and Technology, v. 42, p. 6690-6696. Lee, T. R. and Wilkin, R. T. (2010). Iron hydroxy carbonate formation in zerovalent ironpermeable reactive barriers: Characterization and evaluation of phase stability. Journal of Contaminant Hydrology, in press. Investigators Robert Puis Richard Wilkin U.S. EPA Ground Water and Ecosystem Restoration Division Ada, Oklahoma 74820 580-436-8874 Collaborators Federal Tri-Agency Research Initiative (Department of Defense, Department of Energy) Naval Research Laboratory ------- |