- Average TCE concentrations - 4,800 ug/L; average cis-1,2-DCE concentrations - 1,200 ug/L
- Estimated contaminant mass in demonstration area - 3.6 pounds
- During the first phase (indigenous microbes), no degradation beyond DCE was observed
- After an initial lag period of 90 days, the augmenting culture began transforming DCE to vinyl chloride and ethene
- At the end of the demonstration, complete degradation of chlorinated solvents to ethene occurred
- Complete dechlorination of solvents occurred first between the injection well and the nearest monitoring well (about 4 ft)
Spills and waste disposal practices from historic maintenance and repair operations at the Dover AFB in Delaware had resulted in the contamination of soil and groundwater at the site with solvents, including TCE, PCE, and DCE. The Remediation Technologies Development Forum (RTDF) sponsored a demonstration of in situ bioremediation (ISB) at a site located in Area 6 of the Dover AFB in Delaware. Average TCE, DCE, and PCE concentrations in groundwater at Area 6 were 4,800 ug/L, 1,200 ug/L, and 3 ug/L, respectively.
The ISB system used for the demonstration included injection and extraction wells, a nutrient/substrate injection system, and a groundwater monitoring system. The demonstration, performed between May 1996 and March 1998, included two phases - one involving the stimulation of indigenous microorganisms; one using bioaugmentation with a culture from Largo, Florida. While no degradation beyond DCE was observed during the first phase using indigenous microbes, the addition of the culture from Florida resulted in the complete degradation of solvents to ethene. Costs to perform ISB at Dover AFB were based on the cost of the demonstration. The estimated net present value of implementing ISB at Dover AFB was $596,000. Better mechanisms for effective distribution of nutrients and substrate into low permeability zones of an aquifer was identified as a future development need to facilitate implementation of ISB.