Aerobic Degradation at Site 19, Edwards Air Force Base, California

Site Name:

Edwards Air Force Base

Location:

California

Period of
Operation:

February 5, 1996 to April 1, 1997

Cleanup
Type:

Field demonstration

Vendor:

Not Applicable

Technology:
In Situ Bioremediation; Aerobic Degradation
- Two 8-in diameter, PVC treatment wells installed approximately 24 m deep and spaced 10 m apart; equipped with submersible pumps
- Each treatment well screened in both the upper (15 m) and lower aquifers (10 m)
- Groundwater recirculation - one well withdrew water from the upper aquifer and discharged it into the lower aquifer, while the other well withdrew water from the lower aquifer and discharged it into the upper aquifer creating a bioreactive treatment cell
- Initial flow rate - 38 liters per minute (L/min)
-Operation included groundwater pumping, pulsed addition of toluene, and addition of dissolved oxygen (DO, as gaseous oxygen) and hydrogen peroxide (H2O2)
- An area of 480 m2 (0.12 acres) was monitored using 20 monitoring wells
- The demonstration included five phases, during which time the operating parameters were varied: pre-operational studies (days 0 - 33); establishment of a toluene-degrading consortium (days 34 - 55); pre-steady-state operation (days 56 - 136); steady-state operation (days 145 - 271); and balanced flow operation (days 317 - 444)

Cleanup Authority:
CERCLA

EPA RPM:
Richard Russell
U.S. EPA Region 9
75 Hawthorne Street, SFD-8-1
San Francisco, CA 94105
(415) 744- 2406
e-mail: russell.richard@epa.gov

Air Force Project Manager:
David Steckel
AFFTC/EMR
5 East Popson Avenue, Building 2650A
Edwards Air Force Base, CA 93524- 1130
(805) 277-1474
fax: (805) 277-6145
e-mail: david.steckel@edwards.af.mil
Principal Investigator:
Dr. Perry McCarty
Stanford University
Department of Civil
and Environmental Engineering
Stanford, CA 94305-4020
(650) 723-4131
fax: (650) 725-9474
e-mail: mccarty@ce.stanford.edu

Contaminants:
Chlorinated Solvents
- Primary contaminant in groundwater- trichloroethene (TCE)
- Levels as high as 1,150 ug/L found in the groundwater; average TCE concentration in the upper and lower aquifer of 680 and 750 ug/L, respectively
- No 1,1-DCE found at the site prior to the demonstration

Waste Source:
Equipment cleaning and solvent degreasing operations

Type/Quantity of Media Treated:
Groundwater
- Volume of water in test area - 1,160 m3
- Volume of water pumped - 12,132 m3 from upper to lower aquifer; 16,063 m3 from lower to upper aquifer
- Groundwater contaminant plume of approximately 53 acres
- Two relatively homogeneous aquifers - upper, unconfined aquifer is 8 m thick, and separated by a 2 m aquitard from the lower confined aquifer; lower, confined aquifer is approximately 5 m thick and lies above weathered bedrock

Purpose/Significance of Application:
Field demonstration of in situ bioremediation using groundwater recirculation wells to remediate TCE in a two aquifer system

Regulatory Requirements/Cleanup Goals:
- The objectives of the field demonstration included evaluate the effectiveness of in situ bioremediation to treat TCE in groundwater and to collect data for potential full-scale application at the site
- Specific remedial goals were not established for the demonstration

Results:
- The system was found to be technically feasible for remediation of TCE in a two aquifer system
- TCE concentrations were reduced by 97.7%, from levels of up to 1,150 µg/L to 27 µg/L
- The average reduction of TCE during steady-state operation (days 145 - 271) was 87% in the upper aquifer bioactive zone and 69% in the lower aquifer adjacent to treatment well T1 discharge screen
- The average reduction of TCE during balanced flow operation (days 365 - 444) was 86% and 83% in the upper and lower aquifer bioactive zones, respectively
- No information was provided about potential degradation products from this demonstration

Cost Factors:
- The total cost for the demonstration at Edwards AFB was $337,807, including $323,453 in capital costs and $14,354 in O&M costs

Description:
Edwards Air Force Base covers approximately 301,000 acres, is located on the western portion of the Mojave Desert, about 60 miles north of Los Angeles, and is used for aircraft research and development. From 1958 through 1967, rocket engines were maintained in facilities at the site. Spent TCE from maintenance operations was disposed at Site 19, a 53 acre area on the west side of Rogers Dry Lake. The resulting groundwater contaminant plume extends approximately 3,200 ft down-gradient from the source area. The site was added to the National Priorities List in August 1990. A Record of Decision (ROD) had not been signed for this facility at the time of this report.

Site 19 at Edwards Air Force Base was selected for a field demonstration to evaluate in situ bioremediation for the treatment of groundwater contaminated with TCE. The system used for the demonstration consisted of two treatment wells screened in both the upper and lower aquifers. One treatment well was used to withdraw water from the upper aquifer and discharged it into the lower aquifer, while the other treatment well was used to withdraw water from the lower aquifer and discharge it into the upper aquifer. This process recirculated the water between the two aquifers creating a bioreactive treatment cell. Treatment system operation included the pulsed addition of toluene, and the addition of dissolved oxygen and hydrogen peroxide (H2O2). The demonstration included steady-state and balanced flow operation. The results of the field demonstration showed that in situ bioremediation using groundwater recirculation was technically feasible for remediating TCE in a two aquifer system. TCE concentrations were reduced by 97.7%. The average reduction of TCE during steady-state operation was 69% to 87% in the lower and upper aquifer bioactive zones, respectively. The average reduction of TCE during balanced flow operation was 83% and 86% in the lower and upper aquifer bioactive zones, respectively. Prevention of well clogging was found to be an important operational concern for application of this technology. In this demonstration, site operators used well redevelopment and addition of hydrogen peroxide to control clogging.