Technology:
In situ bioremediation
- A "two-zone" enhanced bioremediation process that used sequential anaerobic and aerobic biodegradation processes to degrade PCE and TCE; anaerobic conditions were used for eight months (through late July 1997), then changed to aerobic conditions
- The system was a groundwater recirculating cell that consisted of three injection wells and three extraction wells, and covered a surface area of approximately 10 ft by 20 ft; with wells screened from 13 to 20 ft bgs
- Nutrients and a carbon source were injected into the groundwater through the three up-gradient wells and extracted through the three down-gradient wells
- A relatively constant recirculating flow rate of 0.25 gpm was used along with an amendment injection rate of about four gallons per day (approximately 1% of the recirculating flow)
- Lactic acid was used in the anaerobic conditions, and ORC socks plus methane in aerobic conditions
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Cleanup Authority:
Not identified
Site Contact:
Not identified | Point of Contact:
Dr. Ronald Lewis
U.S. Environmental Protection Agency
26 W. Martin Luther King Dr.
Cincinnati, OH 45268
(573) 569-7856
lewis.ronald@epa.gov |
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Contaminants:
Chlorinated Solvents
- TCE, PCE; initial TCE levels were 12 mg/L |
Waste Source:
Manufacturing operations |
Type/Quantity of Media Treated:
Groundwater
- Soil at the Watertown site consists of about 13 ft of sand and gravel over approximately 7 ft of silty sand
- Depth to groundwater is approximately 8 ft bgs |
Purpose/Significance of Application:
Combined anaerobic/aerobic system for treatment of chlorinated solvents. |
Regulatory Requirements/Cleanup Goals:
- Purpose of the demonstration was to evaluate the use of a combined anaerobic and aerobic system for treatment of chlorinated solvent |
Results:
- After four to five months of operation of anaerobic operation, significant increases in DCE were observed along with decreases in TCE concentrations, indicating that reductive dechlorination was occurring; no significant increases in VC concentrations were observed until July 1997, 8 months after operations began
- By July 1997, TCE concentrations had been reduced from about 12 mg/L at the beginning of the demonstration to less than 1 mg/L and there was an overall reduction of about 80% in the mass of total VOCs
- During the aerobic phase, levels of DCE and vinyl chloride have started to decrease in the groundwater; in addition, DCE epoxide, a transient biodegradation product of aerobic degradation of DCE, was detected, indicating that aerobic VOC-degrading bacteria have been stimulated |
Cost Factors:
- The field-scale pilot study has incurred a cost of approximately $150,000 through November 5, 1997
- No estimates were provided about the projected costs for a full-scale system using this technology |
Description:
The Watertown site has been used since the late 1800's for a variety of operations, including a coal gas manufacturing plant, which ceased operations in the 1930's, and a metal plating shop, which ceased operations in 1990. The site is currently being used as a manufacturing facility for electric switch assembly. Soil and groundwater at the site are contaminated with chlorinated solvents, including TCE and PCE, from past operations and waste disposal practices. A field demonstration of the Two-Zone Plume-Interception Treatment Technology, developed by Harding Lawson Associates (HLA, formerly ABB Environmental Services, Inc.), was conducted at the Watertown site under the Superfund Innovative Technology Evaluation (SITE) program. The field demonstration is currently ongoing.
Under anaerobic conditions, TCE in groundwater was reduced by reductive dechlorination (from 12 mg/L to less than 1 mg/L) and there was an overall reduction of about 80% of the total VOC mass in one well. Data indicate that methanogenic conditions were not achieved during the anaerobic phase and most of the reductive dechlorination was attributed to sulfate-reducing bacteria. A period of about one month was required to establish aerobic conditions after ORC socks were placed in the wells. This lag time was attributed to the presence of residual carbon that had to be degraded before aerobic conditions could be established. Initial results indicate that VOC levels, primarily DCE and vinyl chloride, are decreasing. According to EPA, future applications should consider not starting in the winter, start when the anaerobic process can go quickly, use a higher level of lactate, and drive the oxidation potential down quickly. |
