State health authorities have proposed a tough new drinking-water standard for perchloroethylene, or PCE, a suspected cancer-causing solvent found in trace amounts in dozens of water supply wells in the San Fernando and San Gabriel valleys.
The standard would cut in half the allowable level of PCE, which has been found in more water wells in California than any other industrial chemical. Under the proposed new limit of 2 parts of PCE per billion parts of water, the number of local wells shut down because of pollution would increase, along with the costs of ground water monitoring and cleanup.
Roughly 30 of 115 San Fernando Valley wells and 41 of 250 San Gabriel Valley wells are at or above the present PCE limit of 4 p.p.b. Another 15 or so San Fernando Valley wells and about 18 San Gabriel wells usually test at or above the 2 p.p.b. limit.
The tougher PCE limit would not necessarily curtail use of the wells, which still could provide water for blending with cleaner supplies as long as the water served to customers does not exceed the 2 p.p.b. limit.
But the proposed limit would make it harder for utilities to comply with the standard because it would reduce the number of PCE-tainted wells that could be pumped without topping the limit. Blending, an inexpensive solution, would become less realistic as a long-term strategy under the new standard, which would apply more pressure on utilities to choose between treating their wells or abandoning vital ground-water supplies.
The California Department of Health Services has scheduled a July 13 public hearing in Sacramento on the PCE standard, and proposed limits on 13 other contaminants found in water supplies in various parts of the state. New standards could be adopted by the end of this year.
Pete Rogers, chief of the water supply branch for the state health department, acknowledged that PCE poses only a small cancer hazard under present limits. But he said the risk can be lowered, adding that there is no reason to "condone even . . . minor risks if there's something we can do about it."
Patty Prickett, a member of the Community Work Group--a citizens panel that monitors ground-water cleanup efforts in the San Fernando Valley--applauded the proposed standard. After years of being buffaloed by big water utilities, said Prickett, the health department "is beginning to take their regulatory authority seriously."
But utility officials--including those with the Los Angeles Department of Water and Power--questioned the need for a more stringent standard. They said the standard could lead to less healthy water if barely tainted ground water is replaced by surface water that has higher levels of trihalomethanes, a group of suspected cancer-causing compounds. That's because the trihalomethane standard is fairly weak, allowing a higher theoretical risk of cancer than that posed by PCE.
"We're going to point out some of the inconsistencies" in the proposal, said Duane Georgeson, the DWP's assistant general manager for water.
PCE is used to dry-clean clothes and degrease metal, and formerly was used to decaffeinate coffee. Due to spills and leaks, PCE has seeped through the ground. Although not very toxic, there is concern that continuous exposure through drinking water could raise the risk of cancer.
About 80 DWP wells extending from North Hollywood southeast past Griffith Park provide about 15% of the city's water supply. The water mainly is blended in reservoirs and served to customers in the Hollywood-Central City-East Los Angeles areas. Glendale, Burbank, the Crescenta Valley County Water District and the city of San Fernando also rely on ground water, but all of them except San Fernando have problems with their wells.
Water from more than one-fourth of 115 San Fernando Valley wells exceeds the present PCE limit, and water from about half exceeds the standard for trichloroethylene, or TCE, a similar industrial solvent.
Burbank's PCE and TCE problem is so severe that the city is not pumping any of its 10 wells and is buying all of its water from the Metropolitan Water District. Los Angeles and Glendale have shut down their most polluted wells and are mixing water from other wells with surface supplies in reservoirs and delivery lines to dilute PCE and TCE to acceptable levels. The Crescenta Valley district, which serves customers in Glendale, La Crescenta and La Canada Flintridge, also blends its well water.
The proposed 2 p.p.b. limit represents about a drop of PCE in 6,500 gallons of water--or about two or three drops in a swimming pool.
1 in 1 Million
At that concentration, state health officials estimate that at most one extra cancer would occur among 1 million people who drank such water for a lifetime. In other words, each person's chance of getting cancer would go up by no more than one chance in a million.