|Envirogen Propane Biostimulation Technology for In Situ Treatment of MTBE-Contaminated Ground Water, Innovative Technology Evaluation Report (152 pp, 2.44 MB) (EPA/600/R-02/092) November 2002
Methyl tertiary butyl ether (MTBE) has become the most widely used automobile fuel oxygenate, though in some areas, ethanol is used more often. As a consequence of fuel spills and leaking storage tanks, MTBE has become a ubiquitous and recalcitrant ground water contaminant.
In an attempt to demonstrate ground water remedial alternatives for MTBE, EPA and the U.S. Navy entered into a memorandum of understanding to conduct a demonstration of a treatment technology for MTBE in ground water. Technology vendors were chosen through an open solicitation, which requested proposals for MTBE treatment processes. Proposals were then selected using external and internal peer review. Envirogen was selected to demonstrate its propane biostimulation barrier technology as a mechanism to inhibit the migration of MTBE through ground water. The potential remedial action proposes the stimulation of co-metabolism by the injection of oxygen, propane, and MTBE-degrading bacteria into the aquifer.
The primary objective of the biostimulation technology evaluation was to determine whether biodegradation was occurring in a ground water test plot to a sufficient degree to reduce intrinsic MTBE to California's treatability criterion of 5 milligrams per liter or below. The evaluation was carried out using control and test plots, and primary and secondary analytes. There were 15 sampling events over a 38-week test period. An analysis of intrinsic MTBE, deuterated MTBE, daughter products, and geochemical parameters demonstrated that the technology did not meet California's treatability criterion.
The National Environmental Technology Test Site at the Ventura County Naval Base, Port Hueneme, California, is located approximately 70 miles northwest of Los Angeles. It is the site of a hydrocarbon release into ground water between September 1984 and March 1985 involving approximately 4,000 gallons of leaded and 6,800 gallons of unleaded premium gasoline. The resulting ground water plume consists of approximately 9 acres of benzene, toluene, ethylbenzene, and xylenes, and approximately 36 additional acres of MTBE contamination, extending approximately 4,500 feet downgradient from the site of the release.
The geology at the site consists of unconsolidated sediments composed of sands, silts, clays, and minor amounts of gravel and fill material. A shallow, semi-perched, unconfined aquifer is the uppermost water-bearing unit. Three depositional units comprise the shallow aquifer: an upper silty-sand, an underlying fine- to course-grained sand, and a basal clay layer. The cone penetrometer pushes indicate that the upper silty-sand unit ranges between 8 to 10 feet thick and the underlying sand is approximately 12 to 15 feet thick. The water table is generally encountered at depths 6 to 8 feet below ground surface, with seasonal fluctuations ranging between 1 and 2 feet, yielding a saturated aquifer thickness of 16 to 18 feet near the test area.
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