Preliminary analysis is first to estimate problem nationwide
As many as 9,000 community water wells in 31 states may be affected by contamination from the gasoline additive methyl tert-butyl ether (MTBE) due to their proximity to leaking underground storage tanks, according to a new study. First added to gasoline to enhance octane and later in much larger amounts to reduce air pollution, MTBE has turned up in groundwater throughout the nation. Its foul smell and taste are apparent at very low concentrations (parts per billion).
The estimate is reported in the March 23 Web edition of the journal Environmental Science & Technology by researchers from the U. S. Geological Survey and the Oregon Graduate Institute of Science & Technology in Portland. The report will appear in the May 1 print edition of the journal, which is published by the American Chemical Society, the world's largest scientific society.
The data from the study is "generally representative of the entire nation," says USGS scientist John Zogorski, Ph.D., one of the study's authors. Approximately 90 million people in the United States obtain a portion of their drinking water from community water supply wells. The 9,000 wells identified in the study represent one-third of the wells in 31 states where information was suitable for analysis.
"Very large amounts of MTBE have been used in gasoline during the past 20 years and perhaps 250,000 leaking underground storage tank releases have contained MTBE," says Zogorski.
He notes that many tanks are "likely to have caused significant groundwater contamination. This, plus MTBE's tendency to migrate long distances, is the reason for concern and for completing more detailed assessments of these community wells as soon as possible."
To produce the preliminary estimate, the scientists combined information about the locations of leaking underground storage tanks and drinking water wells with information about the behavior of MTBE. "Because MTBE degrades slowly in groundwater, past MTBE-gasoline releases that reach groundwater will continue to threaten community water supply wells until at least the year 2010," Zogorski says.
"Our preliminary modeling analysis considered some of the important factors that should be helpful to the states and others in assessing the risk of MTBE contamination," says Richard Johnson, Ph.D., the study's lead author and a professor at the Oregon Graduate Institute. A complete analysis will require more information about groundwater movement, contaminant sources and water supply well pumping, he says.
One highlight of the modeling was the important effect of pumping rates at wells. "The more aggressively community water supply wells are pumped compared to the safe yield of the groundwater source, the more likely it is that contamination from MTBE-gasoline releases will cause a problem," according to Zogorski.
Several states plan to halt or reduce MTBE use. California, the only state permitted by the Clean Air Act to make its own regulatory decisions about MTBE, plans to ban the oxygenate in 2003. Maine has permission from U.S. Environmental Protection Agency to quit using MTBE if it can find other ways of meeting air quality goals. Likewise, New Jersey has EPA approval to stop using extra MTBE in gasoline during the winter.
About 21 billion gallons of MTBE were produced for use in gasoline in the United States between 1970 and 1998. The September 1999 Report of the U.S. Environmental Protection Agency's Blue Ribbon Panel on Oxygenates in Gasoline called for a substantial reduction on the future use of MTBE in reformulated gasoline because of growing concerns about groundwater contamination.
More than 50 research papers on MTBE and related issues will be presented during the national meeting of the American Chemical Society in San Francisco, Calif., March 26-30. Topics include the extent of MTBE contamination, risks to human health, the government's response, bioremediation and other cleanup methods, and alternatives to MTBE.
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