After a detailed study of the most widespread industrial contaminant in U.S. drinking water, the National Research Council will report today that evidence is growing stronger that the chemical causes cancer and other human health problems.

The 379-page report clears a path for federal regulators to formally raise the risk assessment of trichloroethylene, known as TCE, a step that has been tied up by infighting between scientists at the Environmental Protection Agency and the Defense Department.

California has some of the nation's worst TCE contamination, including vast tracts of groundwater in the San Gabriel and San Fernando valleys that are a drinking source for more than 1 million Southern Californians. The state's 67 Superfund sites with TCE contamination are clustered in Los Angeles and Santa Clara counties.

If the risk posed by TCE is significantly higher than previously thought, it could prompt lower limits for TCE in water, as well as stricter cleanups of hundreds of military bases and other polluted facilities. The contamination occurred because TCE, a chemical solvent, was widely dumped into the ground.

Already, some EPA offices are forcing tougher cleanups based on evidence that the chemical poses a greater-than-expected cancer risk.

The EPA attempted to issue a risk assessment in 2001 that found TCE to be two to 40 times more carcinogenic than previously thought, but that action was opposed by the Defense Department, the Energy Department and NASA. The Pentagon has 1,400 properties contaminated with TCE.

The Bush administration sent the matter to the National Research Council for study, based on military assertions that the EPA had overblown the risks. But the new report does not support that criticism.

"The committee found that the evidence on carcinogenic risk and other health hazards from exposure to trichloroethylene has strengthened since 2001," the report said.

The report urged federal agencies to complete their assessment of TCE risks as soon as possible "with currently available data," meaning they should not wait for additional basic research, as suggested by the Defense Department.

The report is to be formally released today by the National Research Council. An early copy was provided to The Times by the Natural Resources News Service, a Washington, D.C., nonprofit that investigates environmental issues. The authors of the study also briefed members of Congress on Wednesday.

"It is the strongest report on TCE that we have had," said Rep. Maurice D. Hinchey (D-N.Y.), whose district includes hundreds of homes that have air filtration systems to eliminate TCE vapors from the ground. "The fact that we have this TCE-laden drinking water used by millions of people is abominable."

Hinchey and others in Congress are demanding stronger cleanup standards and lower limits for the chemical in drinking water. Currently, the EPA allows 5 parts per billion; that could be lowered to as little as 1 part per billion for drinking water if the risk assessment sidetracked in 2001 is adopted, according to an analysis by the Air Force.

It would drive up cleanup costs by billions of dollars but potentially save thousands of lives, scientists say. The report's authors told Congress on Wednesday that they did not think the EPA should throw out its 2001 draft risk assessment and start over. Instead, they hope the TCE analysis can be completed within six months to a year.

Dr. Gina Solomon, an environmental health expert who served on a scientific advisory board that reviewed the original assessment, said the new report could have a profound effect on the issue.

"That is a very strong statement, a ringing endorsement of the EPA's 2001 draft risk assessment," said Solomon, an associate clinical professor of medicine at UC San Francisco and a staff scientist at the Natural Resources Defense Council.

Solomon said the report also rejected a key position of the chemical industry and Pentagon environmental experts that TCE was not dangerous at low levels of exposure.

Federal regulators should stick with the current scientific model that the cancer risk posed by TCE is proportional to the level of exposure, the National Research Council said.

In its report, the council found the evidence of TCE risk was greatest for kidney cancer, but not as high for liver cancer. It did not study other diseases that could be connected, including leukemia.

The report found merit in the Pentagon's criticism of EPA methodology on epidemiology, which is the study of how disease is distributed in the population. It called for a new survey of prior research.

The report from the National Research Council has been awaited by communities exposed to TCE across the country.

"We can't afford any more delays," said Jerry Ensminger, a former Marine drill sergeant who served at Camp Lejuene, where drinking water supplies were tainted. His daughter died at age 9 in 1976 from leukemia, which Ensminger blamed on TCE exposure.

Ensminger said he was heartened by the report's conclusions, but remained concerned about whether the government would move quickly to deal with the chemical contamination.

"I want to know why the Bush administration does not err on the side of life when it comes to the environment," he said.

© 2006 The Los Angeles Times