Technology:
In Situ Bioremediation
- A 500 ft wide biobarrier (biologically reactive groundwater flow-through biobarrier) installed downgradient of the source zone in the mixed MTBE-BTEX dissolved plume
- Biobarrier comprised of two different bioaugmented plots (oxygenated and seeded with two MTBE-degrading cultures), and two different types of biostimulated plots (one aerated and one oxygenated)
- Seeding done using two cultures: MC-100 microbial culture and also a MTBE-degrading isolate identified as SC-100 (Rhodococcus aetherovorans)
- Aeration/oxygenation system consisted of 21 modules; each module with a satellite gas injection tank and 6 solenoid valves, connected to the gas injection wells; Injection wells screened at 14-15 ft bgs for shallow wells and 18-20 ft for deep wells; Air used for oxygenation
- Over 400 wells installed; 225 for monitoring and 175 for gas injection.
- Monitoring wells were screened over 4-ft intervals
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Cleanup Authority:
California Regional Water Quality Control Board (CARWQCB)
Contacts:
Karen Miller
NFESC
kmiller@nfesc.navy.mil
Paul C. Johnson, Ph.D,
Arizona State University
paul.c.johnson@asu.edu
Cristin L. Bruce, Ph.D,
Arizona State University
cristin.l.bruce@asu.edu |
Contaminants:
MTBE, BTEX and TBA
- Dissolved MTBE plume 5,000 ft long and 500 ft wide
- MTBE concentrations ranging from 1,000 µg/L to 10,000 µg/L and BTEX concentrations about 1,000 µg/L in the vicinity of the source zone soils
- TBA concentrations approximately 1,000 µg/L |
Waste Source:
Leaking Underground Storage Tanks (USTs) from the Naval Exchange service station located on-site |
Type/Quantity of Media Treated:
Groundwater
- The shallow aquifer of interest is unconfined and the depth to ground water is approximately 8 ft bgs, varying seasonally to about a foot
- Minor amounts of gravel and fill material
- Unconsolidated clay, silt, and sand to 30 ft bgs, and a clay aquitard at approximately 20 ft bgs |
Purpose/Significance of Application:
- To install and operate a full-scale MTBE biobarrier across a mixed MTBE-BTEX dissolved plume and to assess the reductions in MTBE and BTEX concentrations achieved over time, and effectiveness of air delivery to the treatment zone |
Regulatory Requirements/Cleanup Goals:
MTBE, BTEX, and TBA concentrations - <10 µg/L |
Results:
- MTBE concentrations in groundwater exiting the treatment system were below the cleanup goal of 10 ug/L within 7 months of operation
- Downgradient benzene concentrations reached the cleanup goal by December 2000 (prior to start of bioaugmentation)
- TBA concentrations measured in March 2002 were below the cleanup goal
- The aeration/oxygenation system achieved dissolved oxygen levels above 4 mg/L |
Cost Factors:
- Biobarrier installation costs totaled approximately $307,200, and included $186,519 for air and oxygen delivery system, $29,716 for field laboratory, and $90,964 for culture injection
- Annual O&M costs were $77,843 per year, and included $19,000 for oxygen generator O&M, $44,400 for sampling and analysis, and $14,443 for utilities |
Description:
The Naval Exchange service station at Naval Base Ventura County in Port Hueneme, CA, contained USTs that leaked MTBE-containing gasoline between September 1984 and March 1985. The leak resulted in contamination of soil and groundwater at the site, and caused a mixed MTBE-BTEX plume measuring 5,000-ft long and 500-ft wide to develop. Laboratory and pilot field testing of in situ bioremediation were carried out at the site in 1998, with addition of oxygen and MC-100 microbial culture. The success of these tests prompted a large field demonstrationof the technology using a 500-ft wide biobarrier containing MC-100 and another MTBE-degrading isolate, SC-100, for in situ bioremediation of the mixed MTBE-BTEX plume.
The biobarrier was installed down-gradient of the source zone and began operation in September 2000. It consisted of two different bioaugmented plots (oxygenated and seed with MC-100 and SC-100), and two different types of biostimulated plots (one aerated and one oxygenated). Biostimulation began in September 2000, and bioaugmentation began in December 2000. Approximately 225 wells were used for regular performance monitoring on a monthly to quarterly basis for dissolved oxygen (DO), MTBE, and BTEX, and 175 wells were used for gas injection. The operation ended in December 2002.
The results showed that the biobarrier was able to reduce effluent MTBE concentrations to below the cleanup goal of 10 µg/L within 7 months of operation. Concentrations of benzene were reduced to the cleanup goal using bioaugmentation alone. Biostimulation was not required for the reduction of benzene levels to acceptable levels. The biobarrier system was able to reduce TBA concentrations to the cleanup goal by March 2002. The aeration/oxygen system was successful in achieving dissolved oxygen levels above 4 mg/L the level determined necessary to stimulation and support aerobic degradation. The biobarrier installation costs were $307,200, with the annual O&M costs being $77,843. A lesson learned from this demonstration is that biostimulation (aeration only) was successful where the influent MTBE concentration was as high as 1,000 µg/L, and that biostimulation could be a viable option at some sites. |
