MTBE: A real concern for South Lake Tahoe
The South Tahoe Public Utility District has a name for its pain.
It’s called MTBE.
A synthetic chemical oxygenate, MTBE is a gasoline additive which comprises 11 percent of the gasoline used in California. MTBE – methyl tertiary butyl ether – has been used in varying degrees throughout the United States since the late 1970s.
However, the federal Clean Air Act Amendments of 1990 required the use of oxygenated fuels in many areas of the country. California law does not mandate MTBE’s use, but because of the state’s oxygen content standards, it has become the additive of choice. The most common alternative, ethanol, is used in numerous states including Oregon, Nevada and Arizona. However, it currently cannot be used in California.
MTBE is given a lot of credit for helping reduce air pollution in the state. California’s “cleaner burning” gasoline has reduced levels of benzene – the most significant toxic component of auto emissions – by 50 percent, according to the U.S. Environmental Protection Agency. Overall toxicity of automobile exhaust has been reduced by 30 to 40 percent.
However, when gasoline leaks from tanks, spills onto the ground or leaks from watercraft, it has a less-than-positive effect on water.
Unlike other contaminants regulatory agencies traditionally have dealt with – such as benzene – MTBE is not absorbed into the soil. It breaks down much slower than other contaminants. Additionally, it permeates the ground at the same rate as water.
MTBE contamination has been discovered at thousands of sites throughout California.
MTBE-contaminated water smells and tastes like turpentine. It can be detected by people at very low levels of contamination and makes water undrinkable.
It has been found to cause cancer in rats and mice, and the U.S. EPA has classified it as a possible human carcinogen.
According to STPUD Information Officer Dawn Forsythe, the local utility district was one of the first agencies in the state to discover its MTBE problem. More MTBE problems likely will develop throughout California.
The district shut down its first two wells in September 1997. Ten of the district’s 34 wells are shut down now. Only three specifically were contaminated by MTBE, but the others were shut down as precautionary measures. Groundwater moves at a rate of a couple hundred feet per year. When a nearby well is pumping, the hydrologic effect pulls the groundwater – and MTBE – at up to three times the normal rate.
With six contaminant plumes coming from South Shore gas stations, the wells were shut down to avoid pulling MTBE toward them.
MTBE was first detected at the Tata Lane No. 4 well in February 1997. The well had an “air stripper,” which successfully treated the water. However, the MTBE levels increased, and traces of MTBE were found in the treated water. MTBE levels were below California standards, but STPUD shut the well down this July.
Arrowhead Nos. 1 and 2 in Meyers were the first to be closed. Specifically contaminated with MTBE, the wells are going to be destroyed – filled with cement grout – within a few months.
Another well is planned to be drilled near the same site. A 30-foot-thick aquitard – or non-porous layer of clay which is expected to inhibit the flow of groundwater and MTBE – lies between the aquifer used by the current contaminated wells and the new well. (See diagram.)
The district’s Paloma well, with a capacity of 2,500 gallons per minute, is operating at half capacity because the threat of pulling a nearby contaminant plume toward it.
Water usage restrictions have been in place since the end of July for STPUD’s 13,000 customers. When the busy summer season is over after Labor Day weekend, however, those restrictions likely will be lifted.
The STPUD board of directors has taken action to direct its staff to pursue the option of adopting a Groundwater Management Plan, which could give the board regulatory authority over the groundwater in its district.
Additionally, STPUD has started an MTBE-free campaign by encouraging residents to contact government officials about the threat to the Tahoe Basin.
Forsythe said STPUD now is working closely with the Lahontan Regional Water Quality Control Board and members of the EPA came to the South Shore last week to discuss the problem.
Forsythe said STPUD is “getting a handle on it,” but the district’s resources and workforce have been strained. With more than a 20-percent decrease in capacity in the district, STPUD employees are working hard to “get water to the right places at the right time.”
No MTBE has reached residents’ drinking water, but the contaminant still has created a major problem.
“We can’t get another water supply, so it becomes of utmost importance to protect what we do have,” she said.
Forsythe said the public has been helpful and supportive of STPUD’s fight.
“I know our guys are less strained by the public monitoring its water usage, and we are very grateful for the public support on making Tahoe MTBE-free,” Forsythe said. “For them to vocalize that and to see government reaction to that public outcry is gratifying.”
Forsythe encourages residents to contact her for more information on MTBE at (530) 544-6474, ext. 208.
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