Technology:
In situ bioremediation
- A pilot study was performed using a mixture of molasses, biologically inoculated solution (supernatant), and tap water was injected into the subsurface
- The full-scale system used 91 temporary injection points, installed to 24 ft bgs with a Geoprobe
- Molasses injection events were performed in April 1997 and February 1998, which involved a mixture of water, molasses, and a small amount of supernatant
- During the first injection event, each injection point received 25 gallons of molasses, 1 gallon of supernatant, and 125 gallons of water
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Cleanup Authority:
State voluntary cleanup program
Site Contact:
Not identified
| EPA Remedial Project Manager:
Eugene Dennis
U.S. EPA Region 3
1650 Arch Street (3HS21)
Philadelphia, PA 19103-2029
(215) 814- 3202
E-mail: dennis.eugene@epa.gov |
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Contaminants:
TCE, hexavalent chromium
- Concentrations of TCE reported as high as 12,000 æg/L |
Waste Source:
Electroplating operations |
Type/Quantity of Media Treated:
Groundwater
- Site geology consists of interbedded sand and clay units
- Depth to groundwater is approximately 3.5 to 8 ft
- Groundwater velocity is estimated at approximately 60 ft per yr |
Purpose/Significance of Application:
Bioremediation of a site contaminated with both chlorinated solvents and hexavalent chromium |
Regulatory Requirements/Cleanup Goals:
- The pilot study was performed to determine if TCE degradation and metal precipitation could be enhanced by an in situ reactive zone - Cleanup goals for the full-scale application were not identified |
Results:
- The average TCE concentration in on-site wells has decreased by 99% (3,040 æg/L in April 1995 to 4 æg/L in October 1998) during bioremediation
- The trends for TCE degradation products (cis-1,2-DCE and VC) indicate that TCE has been reductively dechlorinated to ethene under the engineered anaerobic conditions; initial cis-1,2-DCE and VC concentrations increased following the first reagent injection, but declined as shown in the October 1998 groundwater monitoring results
- The average concentrations of total chromium and hexavalent chromium in the injection area have been reduced by approximately 98% and 99%, respectively |
Cost Factors:
- The overall project cost was approximately $400,000
- No further information was provided about the components of this cost, such as a breakdown of capital or operations and maintenance (O&M) costs |
Description:
Metal plating operations were conducted at a manufacturing facility located in Emeryville, California (actual site name confidential) from 1952 until 1989. Investigations conducted at the site found groundwater to be contaminated with chlorinated solvents, primarily TCE, and hexavalent chromium. From August 1995 to February 1996, the site owner conducted a pilot study of anaerobic reductive dechlorination to evaluate its potential as a groundwater remedy under a state voluntary cleanup program. Based on the results of the pilot test, a full-scale system was installed and is operating at the site.
The injection of molasses reagent solution created conditions favorable for the reduction in TCE, DCE, VC, and chromium concentrations in the subsurface. During an 18-month period of full-scale operation, average concentrations of TCE were reduced by 99%, from more than 3,000 ug/L to 4 ug/L, and average concentrations of Cr+6 also were reduced by 99%. The pilot study showed that the rate of reductive dechlorination could be enhanced with the use of an injected molasses solution.
The use of molasses injection was shown to create an anaerobic reactive zone in an 18-month period where concentrations of TCE, DCE, and hexavalent chromium were reduced. According to the PRP contractor, this technology was shown to save substantial resources when compared to pump and treat. |
