Conducted demonstration projects for bioremediation technologies treating chlorinated organic constituents in the groundwater and soil at Dover Air Force Base

BACKGROUND: The Remediation Technology Development Forum (RTDF) for Bioremediation of Chlorinated Solvents Work Group has conducted demonstration projects for bioremediation technologies treating chlorinated organic constituents in the groundwater and soil at Dover Air Force Base, Delaware. The RTDF is a consortium of industries and government agencies working together to access and pilot bioremediation technologies to clean-up soil and groundwater contaminated with chlorinated solvents such as trichloroethene (TCE). One project utilized accelerated anaerobic in-situ bioremediation to promote the anaerobic biodegradation of TCE and cis-1,2-dichloroethene (cDCE) in the groundwater. Laboratory and field studies by RTDF members, including Dr. Lee, had shown that the native microorganisms in this area of the site are only capable of biodegrading TCE to cDCE, and not further to vinyl chloride (VC), ethene, or ethane. Because other areas of the site show evidence for the complete dechlorination of TCE, it was decided to try a pilot at the Dover Air Force Base. Terra Systems, Inc. was responsible for the operation and maintenance of the accelerated anaerobic in-situ bioremediation system. In addition, Terra Systems, Inc. operated a successful demonstration project for co-metabolic bioventing of TCE and 1,1,1-Trichloroethane in the vadoze zone of another area at the Dover Air Force Base for RTDF.

ACTION TAKEN: A 60 foot long by 40 foot wide recirculating pilot with three injection and three extraction wells was established in one area of the Dover Air Force Base and has been fed lactate and nutrients alternately. TCE was degraded to cDCE in the pilot after nine months once reducing conditions were achieved in the aquifer as a result of the lactate additions. No further degradation of the cDCE was observed, consistent with the laboratory treatability studies. At this time, it was decided to bioaugment with a dechlorinating enrichment culture isolated from a site in Florida. Under the direction of Dr. Lee, 350 liters of the culture were grown up and added to the center injection well in the pilot area. Three months after the bioaugmentation, dechlorination of the cDCE to VC and ethene was observed. Over 99.5% of the TCE and cDCE within the center leg of the pilot cell was degraded to ethene. The dechlorinating culture has moved with the groundwater throughout the entire cell. Treatment of the contaminated groundwater without recirculation was successful in degrading the chlorinated solvents. A minimum of 10 mg/L of organic carbon was needed to support complete dechlorination. Batch weekly additions of substrate supported dechlorination and provided an adequate distribution of substrate while avoiding biofouling of the injection well.

EFFECTIVENESS: This was the first successful demonstration of bioaugmentation to completely degrade chlorinated ethenes. It opens up the possibility for treatment of many sites where the native microbial population is not capable of completely biodegrading the chlorinated solvents. The accelerated anaerobic bioremediation process is being scaled-up to treat one of the source areas at Dover Air Force Base.

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