DNAPL Bioremediation-RTDF at Dover AFB, Area 6, Dover, Delaware

Site Name:

Dover Air Force Base


Dover, Delaware

Period of

May 1996 - March 1998


Field demonstration

In Situ Bioremediation
- Demonstration conducted in two phases - one stimulating indigenous microorganisms, one using bioaumentation with an imported culture of microorganisms
- Three injection and three injection wells; aligned perpendicular to groundwater flow with extraction wells spaced 60 ft from injection wells to create recirculation area
- Sodium lactate added on a 7-day cycle; nutrients (ammonium phosphate and yeast extract) pulsed fed

Cleanup Authority:
Not identified

RTDF Contact:
Dave Ellis
RTDF Steering Committee Chairperson
Telephone: (302) 892-7445
E-mail: david.e.ellis@usa.dupont.com
DOE Contacts:
Don Maiers
Principal Investigator
Telephone: (208) 526-6991
E-mail: dmi@inel.gov

Jim Wright
Subsurface Contaminants
Focus Area Manager
Telephone: (803) 725-5608
E-mail: jamesb.wright@srs.gov

- TCE,1,2-DCE
- 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

Waste Source:
Spills and disposal of solvent wastes from industrial operations at the site

Type/Quantity of Media Treated:
- Depth to groundwater - 10 to 12 ft
- Unconfined aquifer; hydraulic conductivity - 60 ft/day
- Total groundwater circulated during the demonstration - 2.7 million gal

Purpose/Significance of Application:
Demonstration of bioremediation to treat DNAPL in groundwater

Regulatory Requirements/Cleanup Goals:
No specific cleanup levels identified for the demonstration

- 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)

Cost Factors:
Estimated net present value of implementing ISB at Dover AFB - $596,000

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.