Cometabolic Bioventing at Building 719, Dover Air Force Base, Dover Delaware

Site Name:

Dover Air Force Base


Dover, Delaware

Period of

- Propane acclimation period: December 1997 to April 1998
- Bioventing operation: May 1998 to July 1999


Field demonstration


Not Applicable

In Situ Bioremediation; Cometabolic Bioventing
- Test plot - approximately 30 ft long, 20 ft wide, and 10 ft deep with a volume of 4,500 ft3 of soil
- Three injection wells, screened to a depth of 10 ft bgs
- A blower and a mass flow controller were used to inject a mixture of air and propane (300 ppm in air) through the three wells at a rate of 1 cfm
- 13 soil gas monitoring points to monitor soil gas conditions throughout the demonstration. Each soil gas monitoring point was equipped with two gas probes (one at a depth of 4-5 ft and one at a depth of 8-9 ft bgs); an additional 11 "temporary" soil gas monitoring points were used during initial air permeability testing, and during system operation, to monitor soil gas.

Cleanup Authority:
CERCLA - Remedial Action

EPA Contact for Demonstration:
Dr. Gregory Sayles
U.S. EPA (mail stop 420)
26 W. Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7607
Fax: (513) 569-7105
Regulatory Contact:
Darius Ostrauskas
EPA Remedial Project Manager
U.S. EPA Region 3
1650 Arch Street (3HS50)
Philadelphia, PA 191103
(215) 814-3360

Chlorinated Solvents
- Maximum concentrations of chlorinated aliphatic hydrocarbons (CAHs) in soil found during site investigations were TCE (250 mg/kg); TCA ( 1,000 mg/kg); DCE (20 mg/kg)
- Estimated mass of CAH in test plot - 26 pounds ; TCA made up approximately 70% of the total estimated mass of contaminants
- Soil in the area is sand with varying amounts of clay, silt and gravel. Soil permeability is 1.9x10-7 to 7.0x10-8 cm2.

Waste Source:
Discharges to a drainage ditch and sanitary sewer; leaks from underground and above ground tanks

Type/Quantity of Media Treated:
Soil/ 450,000 lbs, based on an assumed density of 100 lbs/ft3

Purpose/Significance of Application:
Field demonstration of in situ cometabolic bioventing to treat chlorinated solvents in soill

Regulatory Requirements/Cleanup Goals:
The objectives of the pilot test included evaluating in situ cometabolic bioventing to treat chlorinated solvents in soil and to collect data for potential full-scale application of the technology at the site

- After 14 months of operation, concentrations of TCE, TCA, and DCE were reduced in the soil in the test area
- Reductions included TCE from >10 mg/kg to <0.25 mg/kg; TCA from >100mg/kg to <0.5mg/kg; and DCE from >20mg/kg to <0.25mg/kg

Cost Factors:
- Not provided

Dover Air Force Base (AFB), located in Dover, Delaware, is a 4,000 acre military installation that began operating in 1941. Building 719 is a jet engine inspection and maintenance shop where a variety of materials, including solvents and fuel, were used un base operations. Until the mid-1960s, wastes from the shop were discharged to a drainage ditch and sanitary sewer. During site investigations, leaking tanks were identified in the area to the northeast of the shop, and soil and groundwater at the site was found to be contaminated with chlorinated solvents. Dover AFB was listed on the National Priorities List in March 1989. As part of the interim ROD for the site, a pilot test of in situ cometabolic bioventing was conducted at Building 719 to evaluate the ability of the technology to remove CAHs. The test plot selected for the pilot study was an area contaminated with high concentrations of CAHs. Prior to the pilot test, laboratory tests were performed on soils from the test plot area to evaluate candidate substrates. Propane was selected because of its ability to stimulate cometabolic activity towards both TCA and TCE.

The bioventing system used for the pilot test included three injection wells, screened to a depth of 10 ft bgs, which was the lowest expected water table elevation. In addition, soil gas conditions were monitored throughout the demonstration using soil gas monitoring points. In situ cometabolic bioventing was successful in reducing CAH concentrations in test plot soil. After 14 months of operation, TCE and DCE were reduced to concentrations of less than 0.25 mg/kg, and TCA was reduced to concentrations of less than 0.5 mg/kg. According to the researchers for the pilot test, results of laboratory treatability testing identified propane as a useful cosubstrate for driving the cometabolism of TCE and TCA.