The Groundwater Resources Association of California (GRA), in conjunction with the Santa Clara Valley Water District, developed the Fifth Symposium in its Series on Groundwater Contaminants, "Biological Treatment of MTBE Contamination in Groundwater: Ex-situ and In-situ Challenges". The Symposium washeld at the DoubleTree Hotel in San Jose, California on October 17, 2002.

Methyl tert-butyl ether, MTBE, has been most commonly used as a fuel oxygenate in the last two decades because of its high octane level, low production cost, ease of blending with gasoline, and ease of transfer and distribution. With a significant increase in the rate of use in fuels since 1992, the detection of MTBE in environmental media has also increased. As a result, MTBE has received nationwide attention as a groundwater contaminant in recent years, especially in California due to highly publicized impacts to drinking water supply wells in Santa Monica and South Lake Tahoe. While MTBE was initially thought to be resistant to biodegradation in groundwater aquifers, this perception has changed dramatically in the last five years. Recent and ongoing studies indicate that MTBE is subject to biodegradation under a range of environmental conditions. In fact, a number of innovative treatment technologies that have been tested at bench-scale and pilot-scale levels and applied in the field rely exclusively on biologically-based principles for the removal of MTBE from contaminated media.

This Symposium showcased experts discussing recent reports of both ex-situ and in-situ MTBE bioremediation case studies. Speakers focused on the use of molecular, isotopic and other innovative tools for evaluating the success of in-situ bioremediation in the field, and the program provided information via a panel of speakers on the regulatory acceptance of bioremediation as a remedial action for MTBE. Speakers also discussed the potential for success of intrinsic biodegradation as a component of natural attenuation, and a panel of attorneys and regulators were invited to debate emerging issues related to MTBE during lunch.