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PROPANE BIOSTIMULATIOIN BARRIER DEMONSTRATED IN MTBE-CONTAMINATED GROUND WATER
Citation:
AzadpourKeeley**, A. PROPANE BIOSTIMULATIOIN BARRIER DEMONSTRATED IN MTBE-CONTAMINATED GROUND WATER. IN: Propane Biostimulation Barrier Demonstrated in MTBE-Contaminated Ground Water, (8):4-5, (2003).
Impact/Purpose:
The demonstration was undertaken to determine whether biodegradation is reducing intrinsic methyl tert- iary butyl ether (MTBE) in ground water to concentrations below state criteria.
Description:
The U.S. EPA's National Risk Management Research Laboratory (NRMRL) and U.S. Navy recently completed a technology demonstration at the Naval Base Ventura County (NBVC) in Port Hueneme, CA. The demonstration was undertaken to determine whether biodegradation is reducing intrinsic methyl tert- iary butyl ether (MTBE) in ground water to concentrations below state criteria. Fifteen ground-water sampling events were conducted over a 38-week period. Analysis of intrinsic MTBE, deuterated MTBE (d-MTBE), daughter products, and geochemical parameters demonstrated that the technology did not meet the State of California's treatability criteria (below 5 g/L).
The demonstration occurred in June 2001-March 2002 at the NBVC National Environmental Technology Test Site, where 10,800 gallons of fuel were released into ground water between 1984 and 1985. The resulting ground-water plume consists of approximately 9 acres of BTEX and 36 additional acres of MTBE contamination. The plume extends approximately 4,500 feet downgradient from the release site. Pre-treatment data indicated MTBE concentrations reaching 5,000 g/L in the selected demonstration area, which is located mid-way downgradient along the MTBE plume.
Geology at the site consists of unconsolidated sediment composed of sands, silts, clays, and minor amounts of gravel and fill material. A shallow, perched, unconfined aquifer is the uppermost water-bearing unit. It comprises an upper, 8- to 10-ft silty-sand unit, an underlying 12- to 15-ft fine- to coarse-grained sand unit, and a basal clay layer. The water table is located 6-8 feet below ground surface, with a saturated aquifer thickness of 16-18 feet (reflecting 1-2 feet of seasonal variation). Pre-demonstration study showed little ground-water flow other than in the bottom portion of the aquifer.
The demonstration tested the ability of propane biostimulation barrier technology to stimulate cometabolism through the injection of oxygen, propane, and MTBE-degrading bacteria into the aquifer. Exogenous propane oxidizing bacteria Rhodococcus ruber strain ENV425 was used to seed the aquifer at the onset of the demonstration. Oxygen and propane were intermittently sparged into the aquifer using separate sparge points at a total rate of approximately 1- to 10-pounds/day and 0.1- to 0.5- pounds/ day, respectively.
Deuterated MTBE and ground-water tracers (bromide and iodide) were used to determine the technology's efficacy. The ratio of tracers between downgradient transects provided evidence of MTBE dilution and degradation, while d-MTBE ratios served as a tracer of anthropegenic MTBE. Critical evidence of biodegradation was provided by measurement of d-MTBE daughter products.
