Boating cause of Donner gasoline contamination
The level of gasoline contamination at Donner Lake appears to be associated with boating activity, according to a preliminary study released by the University of California at Davis.
The study, which initially was designed to measure the impact from a leaking fuel pipeline, narrows the range of possible causes of water pollution to carbureted two-cycle marine engines.
Concern over emissions from two-cycle engines led the Tahoe Regional Planning Agency this year to phase out the engines at Lake Tahoe by June, 1999. Two-stroke engines discharge a fourth of their fuel unburned.
In the preliminary report, researchers with the university’s Tahoe Research Group said levels of a controversial fuel additive increased during the summer boating season at Donner Lake, exploding over the busy Fourth of July weekend.
Monitoring tests showed average levels of methyl tertiary butyl ether or MTBE to be just a 10th of a part per billion in April, before the boating season began at the 5,936-foot altitude lake. But MTBE levels climbed steadily as boating activity increased at the lake, reaching 2 ppb just prior to the Fourth of July weekend.
Over the three-day weekend, the fuel additive increased a dramatic six-fold, to 12 ppb, representing the addition of 565 pounds of MTBE into the lake over the weekend, the report concluded.
The study appears especially significant because it appears to discount most other possible causes of the pollution, said John Reuter, the director of the Lake Tahoe Interagency Monitoring Program, who led the research effort.
“Other traditional ways MTBE can come in didn’t happen,” Reuter said.
“The increase is most likely the result of increased fuel exhaust into Donner Lake from two-cycle engine watercraft since rainfall and urban runoff was negligible at this time, and since stream flow was nearing its seasonal minimum,” the report concluded.
In addition, Donner Lake has no fueling station where spills could occur, said Jennifer Boehm of the Truckee-Donner Recreation and Parks District.
Bob Fortino, the General Manager for the Donner Lake Water Co., said his company is planning the final stages of a treatment facility to protect the water.
“Our engineers are looking at the chemicals from the jet skis and there may be a way to treat those chemicals, but we’re not sure yet,” Fortino said.
According to Fortino, the chemicals are
not yet effecting the drinking water supply, and he wants to keep it that way.
“Donner Lake is our drinking water source and it must be protected, but we also don’t want to interfere with the business and recreational activities if at all possible.”
The UCD study was not intended initially as a study of the impact of recreational boating. Monitoring began following the March 1 discovery of leaking gasoline from a Santa Fe pipeline in the Summit Creek watershed above Donner Lake. The Tahoe Research Group began testing the lake’s water at three locations, and at nine different depths, on March 26.
Since then, the group has taken 460 samples on 12 occasions, with the water analyzed by Alpha Analytical, Inc. of Sparks, Nev.
Researchers do not believe the pipeline leak was responsible for the MTBE increase in the lake, because at no time did they find high levels of the gasoline additive in the creeks flowing into the lake.
Over the last six months, the research group found MTBE in concentrations ranging from .09 to 12.1 ppb, with the additive distributed uniformly through the lake’s top 35 feet. Levels remained low below that level, where temperature differences minimized any mixing.
The report calculated the total amount of MTBE in the 102,000-acre-foot lake at 45-65 pounds at the beginning of the season, rising to 250 pounds by July 1 and increasing sharply to 815 pounds shortly after the Fourth of July weekend.
Still to be determined, Reuter said, is how long the fuel additive, which is a suspected carcinogen, will last in the lake. Levels have been dropping slowly since the summer peak, with an apparent half-life of 120-150 days.
Testing will continue to see how much of the additive remains in the lake after cooler temperatures cause the water in the 230-foot deep lake to mix in the fall and again in the spring, if the lake freezes over the winter.
Peak MTBE levels found at Donner Lake were below state and federal standards for drinking water, although they approached the taste and odor threshold.
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The Tahoe Institute for Natural Science on Wednesday announced the release of its latest Tahoe Nature Activity Book.