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The state of California has examined dozens of alternatives for cleaning up toxic hexavalent chromium that seeped from a utility compressor station into groundwater in the Mojave Desert community of Hinkley, but a new report does not offer any recommendations.

The draft environmental impact report, made public this week, considered 36 alternatives to contain a plume of contamination that now stretches more than 5 miles long and 2 miles wide, but had no preferred option.

Each of the five final options selected have a trade-off, said Anne Holden, project manager at the Lahontan Regional Water Quality Control Board in South Lake Tahoe.

"As you increase the speed of cleanup, the environmental impacts increase," Holden said Wednesday, Aug. 22.

The quickest method would cause a loss of habitat for the threatened desert tortoise, lower groundwater levels in the project area and degrade water quality during treatment, according to the report. Under the five alternatives, cleanup would take 29 to 40 years. Ultimately, the water agency will choose a cleanup method.

The goal is to return the levels of hexavalent chromium, or chromium-6, to a maximum of 3.1 parts per billion; the chemical has been as high as 4,600 parts per billion at the core of the plume.

The chemical, made infamous by the 2000 movie "Erin Brockovich," spread from a Pacific Gas & Electric compressor station, where it was used in cooling towers and disposed of in unlined ponds in the 1950s and '60s. The chromium contaminated drinking water in Hinkley, a rural community of fewer than 2,000 people west of Barstow.

Hexavalent chromium is a highly reactive chemical that damages cells. The known health effects range from skin irritation to lung and stomach cancers. In the 1990s, hundreds of Hinkley residents claimed illnesses and other damages stemming from the contaminated water.

"Because the alternatives involved fundamental tradeoffs between different impacts, there is no objective way to determine a single environmentally superior alternative without making value judgments about different impacts," the report states.

The regional water board is holding meetings and soliciting public comments on the report through Oct. 19. The board is expected to choose a cleanup option in January.

PG&E already is using various techniques to clean up the contamination. But a new cleanup and abatement order is expected in late September, based on an expansion of the plume that was discovered in 2010.

The alternatives considered in the environmental report are: pumping contaminated groundwater and treating it or using it to irrigate alfalfa and other livestock crops, which changes the chemical to a less-toxic form as it moves through the soil; injecting ethanol or another food-grade carbon substance into the groundwater to neutralize the hexavalent chromium; or use subsurface water injection to create barriers of fresh water within the aquifer and deflect the contamination in another direction.

PG&E has spent millions of dollars on cleanup and earlier this year agreed to a $3.6 million settlement with the state, company spokesman Jeff Smith said. Half of the settlement will pay for a pipeline that will import water directly to Hinkley's school.

"We will be there until it is entirely cleaned up and the impacts of our past actions are cleaned up," Smith said. "There's nothing more important to us than it gets cleaned up and the community of Hinkley is made whole."

PG&E is delivering bottled water to some residents for drinking and cooking. At some homes, the company is installing ion exchange and reverse osmosis treatment systems and, at others, is drilling new domestic wells that tap deeper water that is not contaminated.

The draft environmental impact report for Hinkley groundwater cleanup is available online at www.waterboards.ca.gov/lahontan/

Public comments may be submitted through Oct. 19 to the Lahontan Water Board's South Lake Tahoe office, 2501 Lake Tahoe Blvd., South Lake Tahoe, CA 96150; or to Anne Holden at aholden@waterboards.ca.gov.

The regional water board will hold a meeting to discuss the environmental impact report at 6 p.m. Wednesday, Aug. 29, at the Hinkley School, 37600 Hinkley Road, Hinkley.