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In Situ Bioremediation Via Horizontal Wells

by Terry C. Hazen, Westinghouse Savannah River, Technology Cent, Aiken, United States,
B. B. Looney, Westinghouse Savannah River, Technology Cent, Aiken, United States,
M. Enzien, Westinghouse Savannah River, Technology Cent, Aiken, United States,
M. M. Franck, Westinghouse Savannah River, Technology Cent, Aiken, United States,
C. B. Fliermans, Westinghouse Savannah River, Technology Cent, Aiken, United States,
C. A. Eddy, Westinghouse Savannah River, Technology Cent, Aiken, United States,



Document Type: Proceeding Paper

Part of: Engineering Hydrology

Abstract:

The U.S. Department of Energy, Office of Technology Development, has been sponsoring full-scale environmental restoration technology demonstrations for the past 3 years. The Savannah River Site Integrated Demonstration focuses on 'Clean-up of Soils and Groundwater Contaminated with Chlorinated VOCs'. In order to optimize resources the project is simultaneously evaluating and testing a large number of drilling, monitoring, characterization, and remediation technologies developed by SRS, other DOE sites, national labs, industry and universities. During fiscal year 1992 alone, more than 44 different technologies were tested at the site. The principal remediation technology being tested during 1992 was in situ bioremediation. In situ air stripping was the first remediation technology demonstrated at the test site during 1990 using parallel horizontal wells (one below the water table and one above the water table). This first very successful demonstration provided the impetus and the characterization and monitoring data to serve as an excellent control for the in situ biostimulation demonstration. Several laboratories including our own had demonstrated the ability of methanotrophic bacteria to completely degrade or mineralize chlorinated solvents, and these bacteria were naturally found in soil and aquifer material. Thus the test consisted of injection of methane mixed with air into the contaminated aquifer via a horizontal well and extraction from the vadose zone via a parallel horizontal well. This configuration has the advantage of simultaneously stimulating methanotrophic activity in both the groundwater and vadose zone, and inhibiting spread of the plume. Groundwater was monitored biweekly from 13 wells for a variety of chemical and microbiological parameters. Groundwater from wells in effected areas showed increases in methanotrophs of more than 1 order of magnitude every 2 weeks for several weeks after 1% methane in air injected was started. Simultaneous with the increase in methanotrophs was a decrease in water and soil gas concentrations of trichloroethylene and tetrachloroethylene. Two of wells declined in TCE/PCE concentration in the water by more than 90% to below 2 ppb. All of the wells in the zone of effect showed significant decreases in contaminants in less than 1 month. Four of five vadose zone piezometers (each with 3 sampling depths) declined from concentrations as high as 10,000 ppm (vol/vol) to less than 5 ppm in less than 6 weeks. The fifth cluster also declined by more than 95%. A variety of other microbial parameters increased with methane injection indicating the extent and type of stimulation that had occurred.

Subject Headings: Field tests | Wells (water) | Injection wells | Vadose zone | Mitigation and remediation | Bacteria | Pollutants

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