Worried that South Bay water supplies may be more vulnerable to pollution than previously believed, local, state and federal officials are launching a broad assessment of underground water contamination in the region.
A federal report completed in June suggests that there may be major gaps in a natural underground layer of silt and clay that was presumed to prevent pollutants from reaching the deep aquifers that provide most of the drinking water in the South Bay.
In response, officials from a range of government agencies are pooling geologic, hydrologic and pollution test data and evaluating it jointly to determine whether to accelerate ground-water cleanup efforts in the region.
Participants--including officials from the federal Environmental Protection Agency, the state Department of Health Services and the Regional Water Quality Control Board--hope to complete an initial assessment by May.
"We feel this new information is important, but feel we have to confirm it," said Julia Bussey, a hazardous materials specialist with the state Department of Health Services. "If it turns out to be correct, then we would have significant cause for concern."
Prompting the interagency action is an EPA report dated June 30 based on evidence from monitoring wells drilled within a two-mile radius of a former rubber manufacturing complex north of Del Amo Boulevard, between Vermont and Normandie avenues.
A test well near Torrance High School revealed a break in a thick layer of silt and clay that separates the near-surface Gage aquifer from the Lynwood and Silverado aquifers, from which most South Bay drinking water is drawn.
Officials said that although no South Bay drinking water wells have been contaminated, they consider the EPA study disturbing on two counts.
For one, it showed that pollutants that seeped from disposal pits at the World War II-era rubber complex have a relatively clear path to the deep aquifers, located about 200 feet underground.
The complex, started under U.S. government contract by Shell Oil, Dow Chemical Co., U.S. Rubber, Goodyear Tire & Rubber and Firestone in 1942, leaked contaminants that include cancer-causing benzene, toluene and xylene, according to the EPA.
It is not known how far underground the pollutants have traveled, officials said. But in view of the new information on geology in the area, the so-called Del Amo site--now being investigated by the state--may be placed on the federal Superfund list of priority cleanup projects, they said.
Meanwhile, other nearby sources of potential ground-water pollution will have to be reexamined soon for leaks, the officials said. Among them is the Torrance landfill. Paul La Courreye, EPA manager of the Del Amo site study, said that if Torrance's former dump were located above a solid aquitard--the name for the silt and clay layer--there would be far less urgency in checking it for leaks.
"The Torrance landfill is a well-done landfill," La Courreye said, referring to the anti-pollution steps taken when the dump was closed. "But it's in the wrong place."
A broader worry raised by the new EPA study is the possibility that the clay and silt layer underlying the South Bay's upper aquifer may be absent elsewhere in the region, officials said.
Shallow ground-water contamination from polluters ranging from dry cleaners to oil refineries is already extensive in the South Bay. And some industrial contaminants already have entered the upper aquifer, mostly near oil refineries.
Officials have long believed that the aquitard was continuous throughout the region, a solid barrier preventing pollutants from fouling the deep aquifers.
"This investigation kind of blows a hole in that theory," La Courreye said. "It indicated that the safety net we thought was there may not exist."
J. T. Liu, an engineer with the Regional Water Quality Control Board, said: "It wasn't good news at all. . . . It is kind of a warning to us."
It is this potential for a larger water contamination problem that prompted the interagency group to begin its comprehensive assessment of the South Bay's underground pollution, officials said. Led by the state Department of Health Services, the group began meeting in August.
In the first stage of the study, information on hydrology, geology and underground pollution will be pooled and used to develop a computer model that can gauge the risk to the South Bay's deep aquifers.
Although new testing may have to be performed, individual agencies have accumulated a great deal of important data already as part of their routine regulatory work, state officials said.
Among the information turned up so far, for instance, is evidence of another gap in the aquitard detected in Carson near the point where Sepulveda Boulevard crosses the Dominguez Channel, they said.
Contained in apparently overlooked test well data at the Regional Water Board, the evidence is potentially significant because three refineries and a tank farm are located near the Carson test well site.
Bussey said she could not say when the interagency group will be able to determine whether more cleanup efforts are needed.
Cleanup work usually involves the extraction and treatment of tainted water from shallow ground-water basins or aquifers, and the treatment or removal of contaminated soil.
Officials pointed out that they are already pursuing such projects vigorously at numerous hazardous waste sites in the South Bay. But the recent EPA report, they acknowledged, has created a new climate.
La Courreye, speaking from his office in San Francisco, said: "It has made the level of urgency go up for all agencies with any doings down there."
CROSS-SECTION OF TORRANCE STUDY AREA
EPA tests conducted in Torrance recently revealed a gap in the natural silt and clay layer separating the near-surface Gage aquifer and two deeper aquifers, the Silverado and Lynwood, from which most of the South Bay's drinking water is drawn. Experts say the finding is worrisome because it indicates that the clay and silt layer, called an aquitard, may not be as effective as they assumed in shielding the deep aquifers from underground pollution.
SOURCE: ENVIRONMENTAL PROTECTION AGENCY