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STEAM INJECTION INTO FRACTURED LIMESTONE AT LORING AIR FORCE BASE
Citation:
Davis*, E L., G. Heron, AND S. Carroll. STEAM INJECTION INTO FRACTURED LIMESTONE AT LORING AIR FORCE BASE. Presented at 2004 US EPA/NGWA Fractured Rock Conference, Portland, ME, September 13 - 15, 2004.
Impact/Purpose:
To inform the public.
Description:
A research project on steam injection for the remediation of spent chlorinated solvents from fractured limestone was recently undertaken at the former Loring AFB in Limestone, ME. Participants in the project include the Maine Department of Environmental Protection, EPA Region I, the Air Force, EPA's Office of Research and Development, and SteamTech Environmental Services. In addition, expert advise on characterization of fractured rock and steam injection was provided by researchers from Queen's University and the University of California at Berkeley. The primary objective of the project was to facilitate development of promising technologies for bedrock remediation while reducing the amount of mass remaining in the subsurface at this site.
The Quarry was located in the northwest corner of the former Loring AFB, and was used as a source of limestone gravel for the base, and at some time drums of spent chlorinated solvents from base operations were stored or disposed of there. During the 1990s, approximately 450 drums were removed from the upper tier of the Quarry. Subsequent investigation of the groundwater revealed concentrations of tetrachloroethene at levels that would indicate the presence of nonaqueous phase liquids (NAPLs). Other contaminants found in the groundwater included trichloroethene, carbon tetrachloride, and BTEX. Characterization of the fracture system indicated a very complex system with the presence of three different fracture systems as well as several faults. Fracturing within the treatment zone, however, was sparse. Groundwater flow is believed to be controlled by bedding plane fractures.
In Summer 2001, installation of a steam injection system aimed at the area where high levels of PCE and TCE were known to exist in groundwater in the fractured limestone was initiated. As boreholes were installed of the system, characterization of the contaminant distribution, the fracture system, and the hydrogeology was undertaken. Based on the results of the characterization activities, the injection and extraction system was redesigned, based on injecting steam into the relatively clean boreholes, and extracting contaminants from the most highly contaminated boreholes. Steam injection was initiated in September 2002 and continued for 80 days. Temperature distribution in the subsurface and the extraction rate of contaminants was monitored, and changes were made to the system to optimize the amount of steam injected into the system and the amount of contaminants recovered. After the funding for the research was exhausted and the injection terminated, extraction continued for an additional 7 days, and periodic temperature monitoring was continued for an additional 3 months. During the Summer of 2003, post-treatment groundwater and rock core samples were obtained and analyzed. Data is being compiled to describe heat flow in the fractured rock system, as well as the flow and transport of contaminants in the aqueous and vapor phase. This presentation will describe the design of the steam injection system and what was learned about steam and contaminant movement in fractured limestone during the steam injection.