A lawsuit filed in 2017 said the city of Vacaville had failed to inspect or clean up polluted water it had piped in from wells near a former wood-processing plant. The Ninth Circuit initially OK’d the suit, but on Friday said the city cannot be held responsible.

A lawsuit accusing Vacaville of endangering its residents with tap water polluted with hexavalent chromium — the cancer-causing chemical made infamous in the film "Erin Brockovich" — was dismissed Friday by a federal appeals court, which said the city merely carried the water in its pipes and isn't responsible for contamination caused by others.

The city was sued in 2017 by the environmental group California River Watch, which said Vacaville had failed to inspect or clean up the water it had piped in from wells near a former wood-processing plant whose owners had dumped the chemical into the ground for many years.

The plant, operated by Wickes Forest Industries, was classified as a federal hazardous waste site in 1980. Groundwater samples several years later showed unsafe levels of hexavalent chromium, also known as chromium-6, the chemical that sickened hundreds of residents of a Mojave Desert town depicted in the Academy Award-winning 2000 docudrama. When the suit was filed, tests of Vacaville groundwater had shown 24 parts per billion of hexavalent chromium, while state law set a maximum level of 10 parts per billion.

The suit was initially dismissed by a federal judge in Sacramento but was revived last September by a panel of the Ninth U.S. Circuit Court of Appeals, which said in a 2-1 ruling that River Watch could try to prove that Vacaville had violated a federal hazardous waste law by transporting a known carcinogen through its water pipes. But in an unusual action, the panel then agreed to reconsider its decision, after receiving additional written arguments, and ordered dismissal of the suit in a 3-0 ruling Friday.

The federal law against transporting dangerous substances applies only to “the active movement of waste as part of the waste disposal process,” such as shipments to waste treatment and disposal sites, Judge Patrick Bumatay wrote. He said Vacaville was not responsible for creating the contamination or cleaning it up and cannot be held liable under the law merely because it “incidentally carries the waste through its pipes when it pumps the water to its residents.”

Bumatay, who had written the decision in September to reinstate the suit, was joined Friday was joined by Douglas Rayes, a federal judge from Arizona temporarily assigned to the Ninth Circuit who had also endorsed the previous decision.

Judge A. Wallace Tashima, who had voted to dismiss the case in September, disagreed with the majority’s reasoning Friday but endorsed the result, saying that if Vacaville could be held responsible for spreading the contamination, so could any homeowner, farmer, rancher or government agency that took water from a polluted source and provided it to others.

Jack Silver, a lawyer for River Watch, said the court created an unprecedented, narrow definition of “transportation” of hazardous substances to dismiss the suit. He said the organization has not decided whether to appeal.

While Vacaville officials have said they worked diligently to clean up water supplies to the city of 100,000, Silver said the water still has unsafe levels of hexavalent chromium, and experts retained by River Watch believe residents face above-normal risks of cancer and miscarriages. He also said Wickes Forest Industries and another company that operated a nearby wood-processing plant are no longer in business and cannot be sued.

Vacaville responded with a statement from its director of utilities, Curtis Paxton, saying the city was complying with all state and federal water quality requirements.

“The state is in the process of revisiting a potential drinking water regulation for Chromium 6,” Paxton said, and if addition treatment of water is required, “Vacaville will provide that treatment.”

Bob Egelko is a San Francisco Chronicle staff writer. Email: begelko@sfchronicle.com Twitter: @BobEgelko

Bob Egelko has been a reporter since June 1970. He spent 30 years with the Associated Press, covering news, politics and occasionally sports in Los Angeles, San Diego and Sacramento, and legal affairs in San Francisco from 1984 onward. He worked for the San Francisco Examiner for five months in 2000, then joined The Chronicle in November 2000.

His beat includes state and federal courts in California, the Supreme Court and the State Bar. He has a law degree from McGeorge School of Law in Sacramento and is a member of the bar. Coverage has included the passage of Proposition 13 in 1978, the appointment of Rose Bird to the state Supreme Court and her removal by the voters, the death penalty in California and the battles over gay rights and same-sex marriage.