In Situ Bioremediation
- Groundwater flow and three-dimensional transport models (MODFLOW and MT3D) were used in designing the pilot system
- The pilot system included three extraction or pumping wells and three injection wells, each screened to a depth of 38 to 48 ft bgs, and designed to operate as an isolated or "closed-loop" recirculation cell
- The pumping wells were operated at a combined rate of 3.75 gpm (1.25 gpm each), providing a residence time of about 60 days for groundwater from the deep zone of the aquifer
- The extracted groundwater was filtered, and substrate (sodium lactate) and nutrients (ammonia and phosphate) were injected into the combined groundwater stream downstream of the filter
- On June 5 and 20, 1997, an aqueous culture (from the DOE's Pinellas site in Largo, Florida; augmenting solution) was injected into the cell
|EPA Remedial Project Manager:|
R. Drew Lausch
U.S. EPA Region 3
1650 Arch Street
Philadelphia, PA 191103
Dr. David Ellis
Barley Mill Plaza 27-2234
P.O. Box 80027
Wilmington, DE 19880-0027
ITRC In Situ Bioremediation Technical Task Team Leader
California Environmental Protection Agency
Department of Toxic Substances Control
PO Box 806
Sacramento, CA 95814
- Concentrations in the pilot area before the test were PCE - 46 ug/L, TCE - 7,500 ug/L, cis-DCE - 2,000 ug/L, and vinyl chloride - 34 ug/L
Type/Quantity of Media Treated:
- The saturated portion of the formation consists of various sands and is about 38 feet thick
- The aquifer acts as one unconfined unit that includes three zones (approximately equal thickness) - an upper zone of fine sand (0 to 12 ft bgs), an intermediate zone of medium sand (12 to 25 ft bgs), and a deep zone also of medium sand (25 to 48 ft bgs)
- Groundwater is found in the intermediate and deep zones, starting at 10 to 12 ft bgs.
- Hydraulic conductivity was 60 ft/day and groundwater velocity 140 ft/yr
Purpose/Significance of Application:
The first successful bioaugmentation project using live bacteria from another site to treat TCE using reductive dechlorination
Regulatory Requirements/Cleanup Goals:
Pilot test goals:
1) demonstrate that TCE and PCE degradation can be stimulated in the deep portion of an aquifer;
2) confirm that degradation will proceed to nontoxic end products;
3) develop operation and cost data for a full-scale system; and
4) document the methodology used in the pilot system.
- During the first five months of operation, the concentration of TCE gradually decreased, cis-DCE showed a slight increase, and there was no increase for vinyl chloride or ethene, indicating that limited dechlorination was occurring
- For the first 90-days following bioaugmentation, TCE concentrations continued to decrease and DCE concentrations continued to increase; however, there was no evidence of vinyl chloride or ethene in the groundwater
- By March 1998, all TCE and DCE in the groundwater were converted to ethene and between 75 and 80% of the TCE and DCE had been recovered as ethene, indicating that the bioaugmentation was successful in destroying TCE by reductive dechlorination.
- From April 1998 through June 1999, the test was focusing on testing of parameters involved with technology scale up.
- Total capital costs were $285,563
- Total operating costs were $164,962 for the first three months of operation (through November 30, 1996) and $522,620 for the first fifteen months of operation (through November 30, 1997)
- According to the RTDF contact, a typical full-scale bioaugmentation system would cost substantially less than the system used in the pilot test at Dover
Dover Air Force Base (AFB), located in Dover, Delaware, is a 4,000 acre military installation that began operating in 1941. An estimated 23,000 cubic feet of waste, including solvents, waste fuels and oils, and a variety of other wastes, were disposed at the site from 1951 to 1970. Soil and groundwater at the base were found to be contaminated with volatile organic compounds, including TCE and PCE, and with heavy metals, including arsenic and cadmium. In March 1989, the site was listed on the National Priorities List. During a remedial investigation, "Area 6" was one of the areas at the base that was determined to have been contaminated with chlorinated solvents; a plume of VOCs was identified in groundwater in this area. Based on the results of that investigation as well as additional sampling, the area was selected for pilot testing of a bioaugmentation process. The remediation of Dover AFB is managed by EPA Region 3 and the Delaware Department of Natural Resources and Environmental Control. Interim RODs were signed in September 1995 that identify the following technologies for remediation at Dover: anaerobic reductive dehalogenation, cometabolic bioventing, and monitored natural attenuation. The pilot test was performed as part of the Bioremediation Consortium of the Remediation Technology Development Forum.
Data from the pilot test indicated that an extended period of time was required for the bacteria to exhibit functional dechlorination. At the start of bioaugmentation, lag periods of about 180 days between bioaugmentation and complete reduction of TCE and DCE to ethene were observed, including a 90-day lag period before vinyl chloride was first observed. Injection well plugging was a problem during the pilot test. Several methods were used to keep the wells unplugged including cleaning the well screens with wire brushes and pumping out residue from the screened interval, using hydrogen peroxide to clean the wells, and changing substrates from sodium lactate to lactic acid. Hydrogen peroxide proved the most effective technique for keeping the wells from clogging.