A $333m payout, an Oscar and now a final twist: was Erin Brockovich wrong?

She rode rode back into town for a second round in the battle against a polluting power giant that made her famous. But now Erin Brockovich may have to back up a little. Fresh scientific evidence has called her claims into question.

Nearly 15 years after the utility company Pacific Gas and Electric paid a $333m (£210m) out-of-court settlement to end claims that it had polluted the water in Hinkley, California, with chromium 6, a carcinogen, a new survey shows that the number of cancer cases there in 1996-2008 was not especially elevated. In fact, they were lower than would be expected.

The findings of the survey, conducted by John Morgan, a professor of epidemiology at Loma Linda University, California, are startling not least because they come just as the saga of Ms Brockovich and her battle with PG&E has burst back into life.

Last week she was at an emotional community meeting called in the wake of news that a new underground water plume containing chromium 6 had breached containment barriers and had begun to leach towards some homes. The discovery of the plume has been considered serious enough by PG&E that it offered to buy 100 homes from residents in the area to give them a chance to move elsewhere.

Its woes in Hinkley date back to the late Fifties when chromium-laced water it had used to clean cooling towers was disposed of in ponds that eventually began to leak into the groundwater. According to the survey there were 196 cases of cancer among residents in the area over the 12-year period of the study, a number that is lower than the 224 cases that would normally be expected.

Scores of different ailments were cited in the class-action suit that Mr Brockovich spearheaded, and not all were to do with cancer. Moreover, Professor Morgan did not in this survey study what kinds of cancers were occurring in Hinkley. But analysis of the data from the decade before 1996 that did identify different cancer types did not raise any red flags either.

"We didn't find a cancer excess in Hinkley and this is in fact our third survey," Professor Morgan said last night. "Whether that means that PG&E were had or not I am not qualified to say." But he reiterated that there was "no evidence of cancer excess".

If the survey would seem to be offering reassuring news, not everyone in Hinkley is ready to believe it. "Am I comforted by a survey that says there is no excess of cancer here when I know there is a carcinogen in the water supply?" responded Carmela Gonzalez, who has been closely involved in the battle with PG&E from the beginning. "No. I don't trust those numbers and I don't feel safe living in Hinkley. Who would?"

Nor does it seem that PG&E is inclined to use the survey to its advantage. "Regardless of what the statistics show, we know people there are concerned about their health, and that is why we are offering to buy properties in the area and why we are cleaning up the groundwater," said a spokesman, David Eisenhauer. Some in Hinkley consider the timing of the study's release suspicious and wonder if Mr Morgan is coming to the rescue of the company.

It is an implication he resents, however. He insists there is no link between the study and recent events in the area."I have dedicated my entire life to reducing cancer," he said. But he added that he understood their scepticism. "They feel taken advantage of and they are not trusting anyone at this point."