California’s water threatened by MTBE

Leaks of the petrol additive MTBE from nearly 1,200 underground tank sites threaten the drinking water supply of millions of Californians, state records show.


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An investigation by The San Francisco Chronicle newspaper says that in the city’s Bay Area alone, 251 leaking tank sites pose risk of contaminating public wells with methyl tertiary-butyl ether (MTBE), and that the oxygenate has already reached 48 wells in public water systems serving hundreds of thousands of people, forcing closures or expensive treatment. The analysis, which used data from the State Water Resources Control Board and the state Department of Health Services, does not include tens of thousands of private wells in California and hundreds of thousands nationwide, which are not regulated by public agencies and may not be tested for MTBE, unless nearby leaking underground tanks cause concerns.

The 1,189 underground tank sites leaking MTBE lie within 1,000 feet of public supply wells or on vulnerable drinking water aquifers, state records show. There are an additional 1,729 leaking tank sites farther away from drinking water wells that also pose a concern, the newspaper says. More than 2,500 public drinking water systems that serve 30.5 million people, or 90% of California’s population, have been sampled for MTBE. Of the 8,311 groundwater sources sampled, 48 contained MTBE, while of 595 surface water sources tested, 26 contained the fuel additive.

Statewide, Los Angeles County has the greatest number of leaking tanks, with 16, centered in Santa Monica, Glendale and Burbank, followed by eight each in San Diego County and El Dorado County, which has problems with water contamination in Lake Tahoe. In 1999, recognizing that Santa Monica and South Lake Tahoe had lost crucial wells to MTBE, Governor Gray Davis issued an executive order phasing out the additive by 2003 (see related story).

Last year, a report revealed that leaks of MTBE from underground storage tanks could contaminate as many as 9,000 community water wells in 31 states (see related story).

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