Aerobic Degradation at Moffett Naval Air Station, Mountain View, California

Site Name:

Moffett Site

Location:

Mountain View, California

Period of
Operation:

September 1986 to November 1988
(three seasons)

Cleanup
Type:

Field demonstration

Technology:
In Situ Bioremediation; Aerobic Degradation
- One extraction well and two injection wells used to create groundwater recirculation treatment cell
- TCE, cis- and trans-DCE, and VC injected into groundwater (regulatory approval obtained)
- Experiments conducted using native bacteria, methane addition, phenol and toluene addition, and hyfrogen peroxide addition; bromide tracer tests also performed

Cleanup Authority:
CERCLA

EPA RPM:
Roberta Blank
U.S. EPA Region 9
75 Hawthorne Street, SFD-8-1
San Francisco, CA 94105
(415) 744-2384
e-mail: blank.roberta@epa.gov
Principal Investigator:
Dr. Lewis Semprini
Oregon State University
Department of Civil, Construction,
and Environmental Engineering
202 Apperson Hall
Corvallis, OR 97331-2302
(541) 737-6895
fax: (541) 737-3099
e-mail: Lewis.Semprini@orst.edu

Contaminants:
Chlorinated Solvents
- 1,1,1-trichloroethane (TCA) and 1,1-dichloroethane (DCA) found in test zone; regulatory approval obtained for adding TCE, cis- and trans-DCE, and VC to the injected groundwater for demonstration

Waste Source:
Leaks and spills from aircraft and maintenance operations; disposal of waste in landfills

Type/Quantity of Media Treated:
Groundwater
- Test zone located in shallow, confined aquifer - 1.5 m thick; approximately 4 to 6 m bgs
- Hydraulic conductivity - 0.11 cm/sec; indigenous methanotrophic bacteria present in aquifer

Purpose/Significance of Application:
One of the earliest field demonstrations of aerobic in situ bioremediation under varying experimental conditions

Regulatory Requirements/Cleanup Goals:
- The objectives of the field demonstration included evaluating the performance of in situ biodegradation of chlorinated aliphatic hydrocarbons (CAHs) using native bacteria enhanced through addition of methane, toluene, and phenol
- Specific remedial goals were not established for this demonstration

Results:
- Methane addition was required for biodegradation of CAHs
- Removal rates for methane addition - TCE (20 - 30%), cis-DCE (45 - 55%), trans-DCE (80 - 90%), and VC (90- 95%); rate of TCE reduction remained relatively constant over three seasons of testing
- Use of phenol and toluene achieved higher percent removals of TCE (93 - 94%)
- Presence of 1,1-DCE was toxic to the transforming bacteria

Cost Factors:
Not provided

Description:
Moffett Naval Air Station, used for aircraft operations and maintenance, operated from 1933 to 1994, and is located 35 miles south of San Francisco in Santa Clara County. In 1994, the Navy ceased operations and the airfield was transferred to the National Aeronautics and Space Administration. Soil and groundwater at the site are contaminated with petroleum products and VOCs, including TCE and PCE. Moffett was selected for a field demonstration of aerobic biodegradation and a series of experiments were conducted to evaluate the performance of the technology in treating CAHs using native bacteria enhanced through addition of methane, toluene, and phenol.

Results showed that active use of methane in the treatment zone was required for biodegradation of CAHs, and that groundwater residence times in the treatment zone of 1-2 days resulted in biodegradation of TCE, DCE, and VC. The use of phenol and toluene achieved higher percent removals of TCE (93 - 94%) compared with use of methane (19%), and hydrogen peroxide was found to achieve TCE removals similar to those achieved using oxygen. While 1,1-DCE was partially transformed in the study with phenol, the transformation products were toxic to the transforming bacteria. Therefore, the use of this technology when 1,1-DCE is present may not be appropriate. Alternating pulsed addition of methane and oxygen helped to prevent biofouling in the area near the injection well. According to the researchers, the relatively low concentration of phosphate in the groundwater did not limit the biodegradation of CAHs at this site; other phosphate minerals may have dissolved in the groundwater to replenish this mineral as it was being removed by the bacteria. The results from the field experiments were found to be consistent with the results from batch soil column laboratory testing using aquifer solids from the test zones.