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Air Water Trade-Off?

Does cleaner air mean dirtier water? A key ingredient of California's reformulated gasoline has begun showing up in surface and groundwater around the state.

Methyl tert-butyl ether, or MTBE, an oxygenate meant to reduce vehicle emmissions, has been used in small quantities for years, but comprises approximately 11 percent by volume of the reformulated fuel mandated by the State of California last year. The additive travels quickly, does not degrade naturally and resists ordinary treatment. It has been found at low levels in groundwater and reservoirs throughout the Bay Area, including Anderson, Coyote and San Pablo Reservoirs. Suspected sources include leaking underground fuel tanks and pipelines, watercraft, and aerial deposition.

Although the U.S. EPA considers MTBE a possible carcinogen, little is known about the effects of the chemical on humans or the Estuary. "MTBE's presence is new and there are a lot of unknowns about it," says Sandy Oblonsky of the Santa Clara Valley Water District. The District recently began an MTBE monitoring program for wells, reservoirs and percolation ponds, and is planning another for stormwater. As of February, all water suppliers are required to monitor for MTBE.

The EPA currently has a health advisory for MTBE of 20 to 200 parts per billion in drinking water, while the California Department of Health Services has established an action level of 35 parts per billion. So far, MTBE levels found in Bay Area water have been well below these limits. In the meantime, some environmentalists suggest that an alternative oxygenate, such as ethanol, should be substituted immediately.

Ironically, says Julia May of Communities for a Better Environment, a recent study in Denver found that MTBE was not effective at reducing carbon monoxide. "It's toxic and it doesn't do what it's supposed to do," she says. According to the California Air Resources Board's Allan Hirsch, however, MTBE in gasoline was found to reduce carbon monoxide by approximately 10 percent in studies conducted in the winter of 1992-1993.

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