In mid-December an employee at Aerojet General Corporation drew a water sample from a public well near the company's Irwindale, Calif., plant in the east San Gabriel Valley.
It was a routine check for any of the 129 chemicals the US Environmental Protection Agency (EPA) has flagged as potentially dangerous. "We weren't on any kind of hunt," Aerojet spokesman Floyd Brown says.
But the first sample turned up 600 parts per billion of trichlorethylene (TCE). The EPA limit for TCE, a synthetic chemical widely used as an industrial solvent, is 5 parts per billion. Recent tests have shown it to be carcinogenic and possibly harmful to humans in quantities much larger than were found near Irwindale and in an extensive search of the Los Angeles basin.
After Aerojet reported its TCE findings to the state Department of Health, a laborious search was conducted and unacceptable levels of TCE were found all over the basin. To date, 52 water wells have been closed.
Most of the wells checked in the San Gabriel Valley, 15 miles east of downtown Los Angeles, have been cleared. But enough traces have been found in different ground water systems in that valley and in other sections of the county -- Santa Monica to the west, Burbank to the north, Compton to the south -- so that officials know locating the source, or sources, will be difficult.
Officials working on the problem theorize that the pollution being found today is the result of misuse of TCE at least 15 years ago, before stringent regulations on handling and disposal were issued. Thus, the investigation will include a search of history books and property deeds to determine what industries operated in the area more than a decade or two ago.
"It's not going to be easy, unless we come up with one magic source," says Richard Harris, assistant executive officer of California's Regional Water Quality Control Board.
Finding a modern-day culprit is possible. But officials think the chances are slim that industry practices are still sloppy.
"It is a situation that needs to be investigated, but not one of total alarm, " says William R. Ree, senior sanitary engineer with the Los Angeles Department of Water and Power.
Officials are beginning to wonder about cleaning up the contaminated ground water, a job more difficult than removing pollution from surface sources. Beyond closing the wells, only a thorough study of the hydrology and geology in the affected cities will determine what approach to take.