Steam Injection Into Fractured Bedrock at Loring Air Force Base Introduction to the Problem Hundreds of contaminated sites exist where most or all of the subsurface contamination resides in fractured bedrock. Due to the complexity of the hydrogeologic systems in fractured bedrock, few types of remediation have been attempted. Background Over 450 drums that contained spent solvents were disposed of in the Loring Air Force Base quarry. Ground water sampling below the buried drums revealed ground water contamination from leaking drums. The contamination consisted of mostly tetrachloroethene (PCE). A research project was undertaken on steam injection remediation in fractured rock. Objectives • Determine whether steam injection can be used to heat fractured bedrock • Determine whether steam injection can enhance the recovery of volatile contaminants from fractured limestone • Evaluate changes in rock and ground water concentrations due to the steam injection • Evaluate horizontal and vertical migration of contaminants from the treatment zone during steam injection • Evaluate the use of electrical resistance tomography and borehole radar tomography to track steam/heat fronts in fractured limestone Approach Site characterization activities, including sampling of rock to determine contaminant concentrations, discrete interval transmissivity testing, and discrete interval groundwater sampling, was carried out and interconnectivity testing was performed. Based on all of the characterization data, a steam injection, extraction, and monitoring system was designed and constructed. Steam injection was initiated in September 2002 and continued for approximately 80 days. Concurrently, vapors and ground water were extracted and analyzed. After steam injection was complete, three rounds of post-treatment ground water samples and post-treatment rock chip samples were taken. Accomplishments Steam injection rates were lower than initially anticipated due to low permeability of the fracture network. However, effluent sampling during the steam injection showed that aqueous and vapor-phase concentrations increased, starting about three weeks after steam injection was initiated. Although effluent concentrations continued to increase throughout the 80 days of the steam injection, steam injection had to be stopped due to lack of sufficient funding. If remediation had been completed, it appears that significant additional recoveries would have been possible. Ground water concentrations in the area that received the most steam were reduced in the post treatment The National Risk Management Research Laboratory's mission is to advance scientific and engineering solutions that enable EPA and others to effectively manage current and future environmental risks. NRMRL possesses unique strengths and capabilities and is dedicated to providing credible technological information and scientific solutions that support national priorities and protect human health and the environment. ------- samples. However, in other areas concentrations increased. The post-treatment rock chip samples seem to show an overall decline in contaminant concentrations in the rock. Ground water sampling indicates vertical and hydraulic migration did not occur. The characterization and steam injection data were evaluated to determine the usefulness of different types of characterization data for remediation in fractured rock. Final Report Steam-Enhanced Remediation Research for DNAPL in Fractured Rock. Loring Air Force Base. Limestone. Maine (PDF) (2ii pp. 16.5 mb (EPA/540/R-05/010) August 2005 - Abstract Principal Investigators Eva Davis U.S. EPA Ground Water and Ecosystem Restoration Division Ada, Oklahoma 74820 580-436-8548 Collaborators Maine Department of Environmental Protection Queens University SteamTech Environmental Services University of California-Berkeley U.S. EPA Region 1 U.S. Geological Survey The National Risk Management Research Laboratory's mission is to advance scientific and engineering solutions that enable EPA and others to effectively manage current and future environmental risks. NRMRL possesses unique strengths and capabilities and is dedicated to providing credible technological information and scientific solutions that support national priorities and protect human health and the environment. ------- |