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STREAM INJECTION INTO FRACTURE BEDROCK AT LORING AFB
Citation:
Davis*, E L., G. Heron, AND S. Carroll. STREAM INJECTION INTO FRACTURE BEDROCK AT LORING AFB. Presented at Battelle 4th Int'l. Conference, Monterey, CA, May 24 - 27, 2004.
Impact/Purpose:
To inform the public.
Description:
The Quarry at the former Loring Air Force Base in Limestone, Maine, was used for the disposal of drums containing spent chlorinated solvents, mainly tetrachloroethene (PCE). After closure of the base, surface geophysics were used to locate the drums, and they were removed. Subsequent sampling of the fractured bedrock and groundwater in the area where drums had been removed revealed the presence of PCE DNAPL. Due to the difficulties associated with remediating DNAPLs in fractured bedrock, a Technical Impractability (TI) wavier was granted for the groundwater. However, with funding provided by the Air Force Base Conversion Agency, the Maine Department of Environmental Protection, and the USEPA ORD, a research project was initiated in 2001 on the use of steam injection to recover DNAPL from the fractured limestone.
During the summer of 2001, boreholes were drilled based on the existing knowledge of contaminant distribution and extent in the subsurface. Cores from these boreholes were used to obtain rock chip samples that were extracted with methanol and analyzed for volatile organic solvents. Transmissivity measurements were made in each of the boreholes on 10 foot intervals, and groundwater samples were obtained from select intervals. During the summer of 2002, interconnectivity testing was performed between the boreholes. Based on the information gathered on contaminant distribution, transmissivity distribution, and interconnectivity, a steam injection, extraction and monitoring system was designed and built. Steam injection was initiated in September 2002.
Steam injection rates were limited due to low transmissivity, and thermocouples and electrical resistance tomography used to monitor steam movement in the subsurface showed only moderate temperature increases. Initially concentrations in the effluent vapor and groundwater decreased, as is expected during pump-and-treat or soil vapor extraction operations. However, after approximately three weeks of operation, effluent concentrations began to increase, and they continued to increase throughout the rest of the project. Steam injection was halted when funding ran out after 83 days of steam injection.
The first round of post treatment groundwater samples were obtained in May 2003, and post treatment rock cores were obtained in July 2003. This presentation will present a summary of the results of the pre-treatment characterization, the strategy for steam injection, extraction, and monitoring, and the results in terms of contaminants recovered and comparisons of pre- and post treatment groundwater and rock concentrations.