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The study, which involved more than 850 leaking
underground fuel tanks in the Los Angeles area, suggests that expanded
use of MTBE alternatives may pose as much of an environmental threat
as their predecessor. The solution, the researchers say, is to stop
the leaks before they start by designing better storage tanks.
Bans on the use of MTBE are scheduled to go into
effect Jan. 1 in California, Connecticut and New York. Seventeen other
states, as well as Chicago, Ill., and Reno, Nev., are considering
restrictions or bans on MTBE, citing concerns that it can leak from
gasoline storage tanks and contaminate drinking water supplies.
In the greater Los Angeles area there are more than
1,100 gas stations with leaking underground fuel tanks, according to
the report. The researchers analyzed data from groundwater samples
taken at 868 of these facilities, measuring the concentration of each
oxygenate, such as MTBE, and examining the "plume length" — the
distance that leakage travels. Chemicals diffuse at different rates
through soil, so knowing the distance traveled gives an indication of
the potential threat to drinking water supplies.
The 1990 Clean Air Act Amendments require that
gasoline formulations contain oxygen to help them burn more completely,
reducing harmful tailpipe emissions of ozone, a major component of
smog. Methyl tertiary-butyl ether (MTBE) is an oxygenate commonly
added to gasoline to meet the federal standards.
"Several other fuel oxygenates with similar
properties are present in formulations supplied to gasoline stations,"
says Tom Shih, D. Env. (doctorate in environmental science and
engineering), an environmental scientist with the California
Environmental Protection Agency. "However, unlike MTBE, there is
virtually no research on the environmental behavior of these
alternative fuel oxygenates."
Without a better understanding of these chemicals,
there is a risk of repeating the MTBE problem, he says.
Shih and his colleagues at the EPA and the
University of California, Los Angeles, investigated the extent of
groundwater contamination beneath gas stations, automotive shops and
other sites with leaking underground fuel tanks in the Los Angeles
area. 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
common contaminant; it was detected at 82.5 percent of the 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: "Clearly it is more costly to have a leak occur and
remediate the environmental impact than to prevent the release in the
first place." The average cost of site investigation and cleanup
ranges from $100,000 to $1 million. "With proper design, it is
entirely possible to have underground fuel tanks that don't leak,"
Shih says.
The high number of leaking tanks just in the Los
Angeles area 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. |
