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IN SITU TREATMENT OF CHLORINATED VOLATILE ORGANIC HYDROCARBONS BY FRACTURE-EMPLACEMENT OF A MICRO-IRON/CARBON AMENDMENT
Skog, J., D. Swift, J. Rothermel, R. Starr, G.H. Bures, and J. Moreno. REMTECH 2009: The Remediation Technologies Symposium, Banff, AB, Canada, 14-16 Oct 2009. Environmental Services Association of Alberta, Edmonton, AB (Canada), 25 slides, 2009

An in situ pilot remediation project was carried out on behalf of the U.S. Army Corps of Engineers (Omaha District) at the F.E. Warren Air Force Base in Colorado. The pilot featured an innovative application of drilling, fracture emplacement, treatment, and geophysical technologies to mitigate impacts from chlorinated solvents. The former missile site complex is underlain by silty sandstone bedrock sediments affected by trichloroethene (TCE) >2,000 ug/L and associated VOCs. Pilot tests of biotic and abiotic in situ chemical reduction (ISCR) were conducted to evaluate technology performance prior to developing the proposed remedy. Two pilot test areas (source area and dissolved plume) were selected to evaluate ISCR for reducing TCE concentrations to less than maximum contaminant levels. The pilot involved the emplacement of over 100 tons of EHC(tm), a micro-iron/complex-carbon treatment amendment, into deep bedrock sediments to attain optimal distribution throughout the contaminant plume, including beneath the former Launch and Service Building. A total of 206,000 lb of EHC(tm) was emplaced at 9 locations within the test areas. Hydraulic fracturing was conducted in redrilled boreholes to deliver the amendment slurry at 5-ft increments between depths of 35 to 55 ft in bedrock. Between 6,000 and 32,000 lb of the amendment was emplaced at each borehole in a biodegradable, linear protein gel slurry that carried the amendment in a uniform suspension. Up to 6,400 lb of EHC(tm) was delivered into each fracture. Tiltmeter geophysics was used to verify the final distribution and geometric configuration of the micro-iron fractures. Field observations and tilt response showed that the radius of fracture emplacement in the bedrock was up to 60 ft, with a typical fracture overlap of 30 to 50%. Following placement of the amendment, physical, chemical, and microbiological processes combined to create very strong reducing conditions that stimulated chemical and microbiological dehalogenation of the contaminants. Groundwater quality monitoring is underway to evaluate groundwater redox conditions, EHC(tm) longevity, geochemical parameters, contaminant and degradation byproducts, and microbial quantification of Dehalococcoides to determine the viability of the native microbial populations and evaluate whether bioaugmentation is warranted. http://www.remtech2008.com/remtech/2009/pdf/09-Bures.pdf



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