MTBE found to be airborne; Contaminates air-stripper well
It’s not just in the water. The South Tahoe Public Utility District has found small amounts of the controversial fuel additive MTBE in the air coming into a stripping tower used to clean drinking water.
Tests revealed that water going into the tower had no detections of MTBE, while water coming out was contaminated at 0.2 parts of the additive per billion parts water. Air tests received last week show air pulled into the tower contained 1.6 parts per billion of MTBE.
“We tested a small stream of air for 10 hours,” said Dawn Forsythe, STPUD information officer. “We don’t know if it was at high levels like 6 or 7 parts per billion for a small period of time then at non-detectable levels – or whether it was a steady stream at that level. We just don’t know. But over a 10-hour period, that’s the average.”
The district closed its Clement well in January, the 13th of the district’s 34 wells to be closed because of the additive. The circumstances surrounding this one, however, were mysterious.
It was the only well still pumping water through the air-stripping tower, which was installed in the early 1990s to treat a contamination plume of the cleaning solvent PCE – tetrachloroethylene.
The district’s nearby Tata Lane well, which is contaminated by MTBE, pumped water through the tower last year, and the stripper successfully treated the water for several months. However, MTBE levels increased in the well, and small traces were coming through the stripper. The Tata Lane well was closed in July.
Until January, the Clement well’s water came out with no traces of MTBE. District officials were confused as to where the MTBE was coming from in January and conducted tests on the air coming into the tower. Now that the district knows where the contamination is coming from, the first action officials will make is to do more testing.
“We’re going to repeat the test, and it will be up to the board whether to keep the well shut off,” Forsythe said. “It has been their policy not to serve any water with MTBE.”
The situation poses new problems for South Shore.
“One thing that makes air different from a groundwater plume is when you test it you know where it’s at and how much is there. With the air, how do you really know if it’s there every day and how much? There’s no way to manage MTBE in the air,” Forsythe said.
David Spath, chief of the California Department of Health Service’s Division of Drinking Water and Environmental Management, said a similar situation has recently developed near Los Angeles within the last month.
“This is sort of a new phenomenon. We’ve just found out about a situation near Los Angeles where the groundwater being treated had multiple contaminants but no MTBE. The contaminants were being stripped out, but MTBE was popping up (when the water came out) at levels up to 6 parts per billion,” Spath said.
“You’ve come across it there just as we have. It’s a little disconcerting. We’re going to have to look at it closely,” he added.
MTBE – methyl tertiary butyl ether – is a gasoline additive comprising significant portions of California gasoline. It is classified by the U.S. Environmental Protection Agency as a possible cancer-causing agent and has a turpentine-like taste and odor. While most state and federal action levels for the additive are above 15 parts per billion, California has a taste and odor threshold of 5 parts per billion.
While theoretically MTBE and other contaminants should be burned off while automobiles are running, Spath said, traces of them are released from automobile exhaust. In the atmosphere, MTBE’s behavior isn’t much different from in the groundwater.
“MTBE in the air is MTBE in the water,” Spath said.
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