In Situ Bioremediation
- Field demonstration conducted within MTBE plume, where MTBE was identified as the primary contaminant
- Three pilot tests were performed - release wells, release panel, and emplaced MTBE degraders (strain PM1, permeable trench); multi-level monitoring wells (screened at varying depths) were used for each test
- Release Wells - two, 8-inch diameter wells (RW1 and RW2) screened to 8 feet below ground surface (bgs); each well was equipped with an oxygen emitter
- Release Panel - consists of three layers of prefabricated stripdrain material, each layer 6 feet by 6 feet and about 1 inch thick; continuous lengths of 1/4 inch tubing woven around the internal supports; panel placed in a trench and backfilled with native soil and pea gravel. During operation, oxygen was cycled on and off to test the system.
- Emplaced MTBE Degraders - test area consisted of a section of pea gravel (1.5 ft wide, 1.5 ft long, and 12 ft deep); PM1 was injected in slurry form using three injection wells; solution was extracted from a well located downgradient
- Sulfur hexafluoride (SF6 ) was used as a tracer in each test
Dr. Douglas Mackay
University of Waterloo
744 Frenchman's Road
Stanford, CA 94305
Telephone: (650) 324-2809
Fax: (650) 324-2259
Telephone: (805) 606-2359
- MTBE plume extends about 1,700 feet downgradient
Leaks from gasoline storage tanks
Type/Quantity of Media Treated:
Purpose/Significance of Application:
Use of in situ bioremediation to treat MTBE in groundwater
Regulatory Requirements/Cleanup Goals:
Goal of field demonstrations is to study possible methods for stimulating aerobic in situ bioremediation of MTBE by increasing the concentration of dissolved oxygen (DO)
- No information about specific treatment goals was provided
Release Wells - No MTBE data were available for this pilot test. After 140 days of operation, DO concentrations were 2.5 mg/L in downgradient wells and a gradual buildup of SF6 in the release wells was observed. According to the researchers, this indicates that the emitters are working as expected.
- Release Panel - During the first "on" cycle (August 1999) DO concentrations were as high as 23 ug/L and MTBE concentrations were reduced from 417 ug/L to below the detection limit. Data from the end of the first "off" cycle (December 1, 1999) showed that once the oxygen supply was turned off, the DO concentrations decreased to low levels (1.2 ug/L), and MTBE concentrations increased to 427 ug/L. After the oxygen was turned "on" (December 14, 1999), MTBE concentrations began to decrease from 427 ug/L to 20 ug/L (as of December 29, 1999)
- Emplaced MTBE degraders - No performance data were available at the time of this report
Efforts are underway to develop projected costs for full-scale systems; however, no cost information was available at the time of this report.
Site 60 at Vandenberg Air Force Base (AFB) is the location of an abandoned service station. Leaks from gasoline tanks resulted in contamination of the groundwater with MTBE, BTEX, and other petroleum hydrocarbons. The MTBE plume extends approximately 1,700 feet downgradient from the source area, and the smaller BTEX/TPH plume, located within the MTBE plume, extends approximately 100 feet downgradient of the source area. A research project to study in situ bioremediation of MTBE has been underway at Vandenberg AFB since 1998. As part of this project, Site 60 is being used to study possible methods for stimulating aerobic in situ biodegradation of MTBE using native and non-native microbes. To achieve aerobic conditions in an otherwise anaerobic plume, researchers are studying the use of diffusive emitters to introduce oxygen into the subsurface.
Three pilot tests are underway at Site 60 to test in situ bioremediation of MTBE using release wells, a release panel, and emplaced MTBE degraders. Multi-level monitoring wells (screened at varying depths) are being used to monitor each of the pilot tests. For the pilot test of the release wells, no MTBE concentration data were available. However, DO concentrations in groundwater increased to 2.5 mg/L (after 140 days of operation). According to the researchers, these results indicate that the emitters are working as expected. For the pilot test of the release panel, data show that MTBE concentrations decrease when oxygen is provided to the groundwater ("on" cycle) and that MTBE levels increase when the oxygen source is discontinued ("off" cycle). According to the researchers, these data suggest that degradation of MTBE is dependent on oxygen release in the groundwater and also that treatment may easily be reestablished after there has been an interruption in the supply of oxygen to the groundwater. At the time of this report, performance data were not available for the emplaced MTBE degrader pilot test. The pilot tests are continuing at Vandenberg Site 60, with the most recent work focusing on the emplaced MTBE degrader pilot test. Additional investigations are underway to identify the MTBE-degrading microbes and to better understand enhanced aerobic intrinsic bioremediation of MTBE.