OHSU

Research focuses on MTBE leaks from underground fuel tanks

05/02/00

Portland, Ore. — A team of scientists from Oregon Graduate Institute of Science and Technology (OGI) and the U.S. Geological Survey (USGS) today gave the nation the best estimate yet on how extensive the potential contamination of the country's drinking water supplies may be from the spread of a fuel additive leaking from thousands of underground fuel tanks.

MTBE (methyl tert-butyl ether), a possible cancer-causing toxic chemical, is leaking from as many as 250,000 underground gasoline storage and fuel tanks in the United States, the team of investigators announced today. That assessment was made in a technical article posted today on the Web page of the American Chemical Society (ACS) based in Washington, D.C. The article will appear in the May issue of Environmental Science & Technology, an ACS publication.

The article was researched and written by two OGI scientists based in Beaverton and three USGS investigators based in Rapid City, South Dakota. The research is the best effort to date in determining the nationwide impact of underground discharges of MTBE - a chemical added to gasoline to make fuel burn more efficiently in internal combustion engines. In the quest to clean up the nation's air from auto pollution, thousands of community water supply systems have at least one leaking storage tank releasing gasoline containing MTBE within one kilometer of a drinking water well.

MTBE is one of several oxygenates, compounds containing oxygen, added to gasoline in the U.S. since the 1970s to boost octane and to reduce air pollution. The Clean Air Act mandated that additives such as MTBE be added to gas in areas where summer ozone and winter carbon monoxide concentrations exceed air-quality standards.

The OGI researchers are Rick Johnson, director of OGI's Center for Groundwater Research, and James Pankow, head of OGI's Department of Environmental Science and Engineering (ESE). The USGS team includes John Zogorski, David Bender and Curtis Price, all of the USGS National Water-Quality Assessment Program. The team of OGI scientists has developed expertise on MTBE because of research agreements over the last several years with the USGS, the Metropolitan Water District of Southern California and other agencies.

"The extent of MTBE use in gasoline is very large," says Johnson, lead author of the article. "In 1998, more than 10.5 million gallons per day (mgd) of MTBE were used in the U.S., with 4.2 mgd used in California alone."

"MTBE is being found with increasing frequency in the drinking waters of the nation," adds Pankow. Today's OGI-USGS article concludes that:

* Widespread sources identified. Because MTBE has been widely used as an additive since 1979, it is estimated that 250,000 of the known 385,000 leaking underground fuel tanks in the U.S. involve MTBE. The additive is very water-soluble and large concentrations are possible when gasoline containing MTBE is spilled into surface water or groundwater.

* Number of polluted wells unknown. The exact number of community water supply wells that will be affected by MTBE leaks is very difficult to predict. But the study estimates there are 9,000 community water supply wells in 31 states with at least one leaking underground storage tank site within one kilometer of the well.

* Pumping rate key to avoiding contamination. Pumping water from community water supply well systems at a fast rate increases the odds for contamination, the article concludes. Pumping at lower rates lowers the risk. The study investigated the manner in which the more aggressively a well is pumped to supply drinking water, the more likely it is that contamination from a nearby underground MTBE release will cause contamination of a well.

* More data needed. Significantly more data collection and research is needed to protect water supply systems from MTBE and other potential contaminants. The study concludes that better national information is needed regarding: 1) the nature and locations of underground MTBE sources; and 2) the hydrogeology and pumping practices for community wells. This information could be used to prepare clearer estimates of the scale of threats posed by MTBE to drinking water.

Technical background

1. MTBE dissolves easily from gasoline into groundwater, does not biodegrade quickly in groundwater and can move as easily as water itself though underground aquifers towards the community water supply wells that supply 90 million people in the U.S. with a portion of their drinking water.

2. The September 15, 1999 "Report of the Blue Ribbon Panel on Oxygenates in Gasoline" states that: 1) between 5 and 10 percent of community drinking water supplies in high MTBE use areas show at least detectable concentrations of MTBE; and 2) about 1 percent of those systems are characterized by levels of this slowly-degraded compound that are above 20 ug/L.

3. Maryland, New Hampshire, New York and California have set MTBE remediation "action levels" at or below 20 ug/L, and the U.S. Environmental Protection Agency (EPA) has set its advisory level for taste and odor at 20-40 ug/L.