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HYDRAULIC CHARACTERIZATION FOR STEAM ENHANCED REMEDIATION CONDUCTED IN FRACTURED ROCK
Citation:
Novakowski, K., K. M. Stephenson, E L. Davis*, S. Carroll, AND G. Heron. HYDRAULIC CHARACTERIZATION FOR STEAM ENHANCED REMEDIATION CONDUCTED IN FRACTURED ROCK. Presented at Battelle Conference (4th International), Monterey, CA, May 24 - 27, 2004.
Impact/Purpose:
To inform the public.
Description:
Remediation of fractured rock sites contaminated by non-aqueous phase liquids has long been recognized as the most difficult undertaking of any site clean-up. This is primarily the result of the complexity of the fracture framework, which governs the groundwater flow pathways and the distribution of the LNAPL/DNAPL. Thus, as a part of a field-scale study of Steam Enhanced Remediation (SER) in a fractured rock setting, detailed characterization of the groundwater flow and potential steam flow pathways was conducted prior to the steam injection process. The objective of the hydraulic characterization was to identify the particular fracture features most likely to carry the majority of the hot water, steam, and contaminants between injection and extraction wells. A total of 28 injection, extraction and monitoring wells were constructed in an area approximately 30 by 45 m thought to be the primary location of a mixed LNAPL/DNAPL source. The NAPLs were distributed in inclined bedding plane fractures pervading the Cary Mills Limestone, at a quarry site located on the former Loring Air Force Base in northern Maine. The wells were diamond drilled to an average of 30 m depth and then hydraulically tested using a modified slug test method. The hydraulic testing was conducted using straddle packers having a variable packer spacing ranging from 3 to greater than 10 m. The results of the single well tests were then used to direct an interwell testing program in which more than 100 pulse interference tests were conducted. The pulse interference tests were conducted by measuring the pressure response between two boreholes in which specific permeable features had been isolated. Straddle packers having a spacing of 3 m were used to isolate the features in each borehole. Based on the results of the pulse interference testing and hydraulic head measurements, the site was separated into three areas having poor interconnection between each. A few well-connected, sub-horizontal fractures were identified in the eastern portion of the site whereas very little interconnection between boreholes was observed in the western portion of the site. This information was used to design the specific injection and extraction points for the SER program. During the steam injection, temperature was monitored in 27 boreholes around the site. The results of the heat transport were then compared to the results of the pulse interference tests to assess the value of the hydraulic characterization. Based on this comparison, it was determined that the pulse interference testing identified the major hot water carrying fracture features and was invaluable in determining the location of specific steam injection and water extraction zones. In the absence of this information, the efficiency of heat delivery would have been significantly compromised.