In the Lab

MTBE alternatives could pose similar threat to groundwater
Adding more fuel to the debate surrounding methyl tertiary butyl ether, a new study suggests that alternative fuel additives could be just as detrimental to groundwater as MTBE.

Bans on the use of MTBE went into effect Jan. 1 in California, Connecticut and New York, and 17 other states and two cities are considering restrictions or bans on the additive, citing concerns it can leak from gasoline storage tanks and contaminate drinking water supplies. (An MTBE "safe harbor" provision is stalling an energy bill in Congress as well.)

But a study published in the Jan. 1, 2004, issue of Environmental Science & Technology suggests that expanded use of MTBE alternatives may pose as much of an environmental threat as their predecessor.

"Several other fuel oxygenates with similar properties are present in formulations supplied to gasoline stations," says Tom Shih, D.Env., an environmental scientist with the California Environmental Protection Agency (Cal/EPA). "However, unlike MTBE, there is virtually no research on the environmental behavior of these alternative fuel oxygenates."

Shih and his colleagues at Cal/EPA and the University of California, Los Angeles, investigated the extent of groundwater contamination beneath more than 850 leaking underground fuel tanks at gas stations, automotive shops and other sites in the Los Angeles area. They analyzed data from groundwater samples, measuring the concentration of each oxygenate and examining the plume length.

The study focused on MTBE and four other additives with similar properties: tertiary butyl alcohol (TBA), tertiary amyl methyl ether (TAME), diisopropyl ether (DIPE) and ethyl tertiary butyl ether (ETBE).

"Except for ethanol, these oxygenates constitute the majority of the fuel oxygenates used in the United States," Shih says.

As the researchers expected, MTBE was the most commonly detected contaminant, found at 82.5 percent of the study sites. TBA was a close second at 61.1 percent, while the other three oxygenates were all detected at frequencies below 25 percent.

Combined with the data on plume lengths, the results indicate that TBA contamination is occurring at a scale similar to MTBE. And while the other compounds don't appear to pose a serious risk at the moment, their low occurrence rates could be a reflection of less-frequent use.

"All indications suggest that the alternative oxygenates would pose groundwater contamination threats similar to MTBE if their scales of usage were expanded," the researchers conclude.

The implication, according to Shih, is that replacing MTBE with other oxygenates could lead to a replay of the current problem with a different contaminant.

Some have proposed using ethanol as a substitute for MTBE. "Early indications suggest that ethanol may pose less of a threat to groundwater and drinking water resources," Shih says. But ethanol has a number of drawbacks: It is more expensive and scarce; it doesn't offer the same air quality benefits; it can't be mixed with gasoline and transported long distances; and the use of ethanol could cause a significant increase in the release of the respiratory irritant acetaldehyde, according to Shih.

The solution, Shih says, is to stop the leaks before they start. The average cost of site investigation and cleanup ranges from $100,000 to $1 million.

"Clearly it is more costly to have a leak occur and remediate the environmental impact than to prevent the release in the first place," he says. "With proper design, it is entirely possible to have underground fuel tanks that don't leak."

The high number of leaking tanks in the Los Angeles area alone hints at the size of the problem nationwide, according to Shih. He also says the leakage frequently occurs even at sites with upgraded double tanks. Shih advocates a complete redesign of the system, which would include more effective management and enforcement as well as high-tech leak detection techniques.

For more information on the study, go to Environmental Science & Technology's Web site at pubs.acs.org/journals/esthag.


This news item originally appeared in the May 2004 issue Environmental Protection, Vol. 15, No.3.

This article originally appeared in the 05/01/2004 issue of Environmental Protection.

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