Fifty to 70 city drinking-water wells eventually could become contaminated if the spread of toxic trichloroethylene isn't stopped, Water Director Gene Cronk told the City Council yesterday.
Two city wells and four wells belonging to Hughes Aircraft Co. have been closed because of unacceptably high levels of the industrial solvent.
Cronk said he can't estimate, beyond saying "a few years," how long it might take for contamination to spread to as many as 70 of Tucson's 300 wells. He said the problem needs to be dealt with quickly before it gets out of hand.
Tests indicate the cancer-causing chemical is moving at about one mile per month through the underground aquifer.
"No one is doing anything about it," he said.
Cronk said he hopes to have an answer by the end of the month from the Arizona Department of Health Services on his proposal for high-capacity pumps to be installed in the area around Hughes and Tucson International Airport to remove contaminated water from the ground and filter out its pollutants.
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The pumps could draw 1 billion gallons of water a day. The water would be filtered through activated charcoal, then allowed to sink back into the ground, he said.
The pumping might have to go on permanently, he said.
Last week he estimated the coast of the drilling, pumping and filtering at $400,000 for the first year. Thereafter, the cost would be $100,000 a year for replacing the charcoal, he said.
Cronk said that if he doesn't have an answer from the state within 30 days, he will ask the city to undertake the project itself.
Yesterday, he described the progression of trichloroethylene since its discovery in March as "the worst possible scenario."
Not only is the chemical spreading rapidly in the direction of other city water supplies, he said, but the degree of contamination is increasing.
Cronk said later his remarks were precautionary, rather than a response to an actual emergency.
He said the effects of trichloroethylene on humans are unknown, but he wants to act fast because he doesn't want to take any chances.
"There's no reason to panic," he said.
As the contamination migrates toward other city wells, it is being diluted to safe levels, he said.
The city is basing its decision on whether to shut down wells on a California standard that 5 parts per billion on trichloroethylene in water could cause cancer. There are no state or federal standards for the chemical.
At 5 parts per billion, he said, tests show the water is still reasonably safe. He compared the risk to that of smoking two packs of cigarettes in a lifetime.
But he said he is worried because the most recent tests on some of the Hughes wells showed contamination levels of more than 2,100 parts per billion.
He said he is also concerned about delays in the investigation by the state and the federal Environmental Protection Agency of where the contamination is coming from and what to do about it.
It takes between two and three months from the time samples are taken until the results are returned, he said. A state official said last week the investigation should be completed by February.
Right now, he said, the problem is in a small area and could be dealt with, but by the time the state and federal agencies are ready to act it will be much more difficult to clean up.
To assist in monitoring the problem, the council approved shifting $23,000 in the Water Department budget to allow for hiring of an analytical chemist.
The water director also warned that existing city laboratory facilities may be inadequate and the city may have to invest about $30,000 in a portable lab.