In Situ Bioremediation at Gas Station, Cheshire, Connecticut

Site Name:

Gas Station, CT

Location:

Cheshire, CT

Period of
Operation:

October 1997 to March 1999

Cleanup
Type:

Full scale

Vendor:

Brian L. Clark, P.E.
Executive Vice President
Enzyme Technologies, Inc.
5228 NE 158th Avenue
Portland, OR 97230
Telephone: (503) 254-4331 x11
Fax: (503) 254-1722
E-mail: brianc@enzymetech.com

Technology:
In Situ Bioremediation
- In situ bioremediation using the Enzyme-Catalyzed In Situ Dissolved Oxygen Treatment (DO-IT) process; patented process uses a combination of proprietary multi-enzyme complexes (proteins that are extracted from living TPH-degrading bacterial cultures), and a consortium of total petroleum hydrocarbon (TPH) degrading bacteria, with supplemental oxygen; generates a concentration of dissolved oxygen in water of approximately 40 mg/L
- Existing horizontal air sparging trench and vertical vapor extraction wells were retrofitted and used as injection points; groundwater was extracted from an existing group of wells located down-gradient from the injection points; layout provided for both treatment and hydraulic control
- Oxygen-laden water was injected on a daily basis; nutrients, including nitrogen, phosphorus, and potassium, were dissolved in the injection water, and applied "as necessary"; information was not available about the amount of amendments added, or the dates for adding amendments.

Cleanup Authority:
RCRA UST (Connecticut LUST Program)

Project Contact:
David Lis, IEP
Apex Environmental
58H Connecticut Avenue
South Windsor, CT 06074
Telephone: (860) 282-1700
State Contact:
Alan Davis
Connecticut Dept. of
Environmental Protection
79 Elm Street
Hartford, CT 06106-5127
Telephone: (860) 424-3342

Contaminants:
MTBE, BTEX, TPH
- MTBE concentrations as high as 6,000 ug/L
- BTEX concentrations as high as 14,000 ug/L

Waste Source:
Leaks from an underground gasoline storage tank

Type/Quantity of Media Treated:
Groundwater
- Depth to groundwater is less than 10 feet below ground surface (bgs)

Purpose/Significance of Application:
Use of in situ bioremediation to treat MTBE in groundwater

Regulatory Requirements/Cleanup Goals:
- The cleanup criteria specified for groundwater at this site were MTBE - 70 ug/L, benzene - 1 ug/L, and TPH - 500 ug/L

Results:
- During the first 34 days of operation, MTBE concentrations in a well located within the center of the plume was reduced from approximately 6,000 ug/L to 1,600 ug/L (a 73% reduction) and from approximately 6,000 ug/L to 200 ug/L (a 97% reduction) in a downgradient well; BTEX concentrations were reduced by 93% from 14,000 ug/L to less than 1,000 ug/L
- Data available for BTEX and TPH after 12 months of operation showed a general decrease in concentrations (MTBE data were not provided)
- After 18 months of operation, the vendor reported that the cleanup criteria specified for this site for MTBE, benzene, and TPH were achieved; information about specific levels achieved was not provided

Cost Factors:
Information on the costs for use of in situ bioremediation at this site was not provided.

Description:
Releases from underground storage tanks (USTs) at an active gasoline service station located in western Connecticut resulted in contamination of groundwater at the site with MTBE and BTEX. Concentrations of MTBE and BTEX measured in groundwater at the site were 6,000 ug/L and 14,000 ug/L, respectively. The vendor estimated that 1,000 cubic yards of soil and groundwater at the site were contaminated as a result of the release. In the early 1990s, the USTs were removed and decommissioned. A groundwater extraction and treatment system and an air sparging/soil vapor extraction (SVE) system were installed to treat soil and groundwater at the site. In 1997, the groundwater treatment and air sparging/SVE systems were replaced with in situ bioremediation.

The DO-IT process applied at this site by retrofitting an existing horizontal air sparging trench and vertical vapor extraction wells were retrofitted as injection points for the oxygenated water, nutrients, and enzyme/bacterial consortium mixture. The vendor reported that the cleanup criteria specified for this site for MTBE, benzene, and TPH were achieved in approximately 18 months of treatment. According to the vendor, this was the first permitted in situ bioremediation project in the state of Connecticut. The relatively shallow depth to groundwater provided for a greater degree of contact between the oxygen, nutrients, and biological products with the contaminants of concern.