ABSTRACT: MTBE in groundwater has been shown to travel over 1,000 feet downgradient from its source in several comprehensive field studies conducted across North America. The biodegradability of MTBE is examined by summarizing all the significant literature on the subject and by detailing the findings of recent field investigations of MTBE transport. In Orange County, California, the persistence of MTBE is analyzed and statistical representations of source variability are presented. Regional and far field transport of MTBE in groundwater sourced from underground gasoline storage tanks are summarized in comprehensive tables of frequency and plume length. Estimates of source mass and duration allow for comparison of associated plume size. The conclusion reached after reviewing all the available literature on MTBE is that its biodegradability seems slight and the size of the plumes are surprisingly large. Intrinsic or natural attenuation remedies for MTBE merit close scrutiny.

The issue of MTBE persistence in groundwater has been one of the most important topics of discussion in the remediation industry during the past year. MTBE biodegradability in groundwater is unclear and misunderstood due to the lack of applied research on the fundamental mechanisms of biodegradation. There are reports of an MTBE plume of over three miles in length (MacDonald, 1998) and due to its reported lack of any significant biodegradability, a significant regulatory problem indeed. The municipalities charged with public water supply sourced by groundwater are very concerned and the proposed action level for MTBE in groundwater is 35 µg/L (a possible carcinogen). Reported concentrations from groundwater monitoring wells of MTBE range from 10,000 to 50,000 µg/L on the high end (pure phase solubility approximately 51 million µg/L) are not uncommon. The petroleum industry is exploring alternatives and funding additional research.