The agency that supplies Stockton, Calif., with most of its drinking water has discovered contamination from an unlikely source: its own water treatment plant, according to Recordnet.com.
In late October 2008, the Stockton East Water District detected carbon tetrachloride (CCl4) in water that had already been treated, and later concluded that the chemical came from chlorine tanks used to purify water at the district's plant on Main Street east of Stockton, the website reported.
The public was not notified because the district considered the risk minor, said Kevin Kauffman, general manager of Stockton East. California health officials agreed that immediate notification was not necessary.
The chemical was detected at a level that exceeds state standards but is lower than a more relaxed federal standard. The highest readings, Kauffman said, were 1.2 or 1.3 parts per billion.
"It's such a minor risk, it's not noticeable," Kauffman said.
Even so, one entity that supplies Stockton with water is increasing the amount of water pumped from the ground and decreasing the amount of water taken from Stockton East.
The water is safe since officials are using groundwater to dilute the tainted surface water, said Ross Moilan, district manager for California Water Service Co., which delivers water to 42,000 homes and businesses in central and south Stockton. CalWater conducted its own tests and detected the chemical "at or below" the state standard, Moilan said.
"There's nothing to be alarmed about," Moilan said.
The city of Stockton conducted its own tests and didn't find any CCl4, Municipal Utilities Department Deputy Director Bob Granberg said.
Officials were alerted to the contamination when a Stockton East employee drove a pickup truck into a canal upstream of the treatment plant, and the water was tested for fear that gasoline, oil or other substances had contaminated the water.
Although the tests found nothing related to the accident, the CCl4 was discovered in water that had already been treated at the plant.
Investigations showed that the chemical, a chlorine byproduct, escaped into the water in relatively high concentrations as one-ton chlorine gas tanks approached empty.
As a temporary solution, officials have changed how they use the tanks. Switching to liquid chlorine might be a permanent solution, Kauffman said.
"We really want to guarantee it won't happen" in the future, he said.