GWEN IFILL: Now NewsHour science correspondent Miles O'Brien begins a two-part look at America's drinking water, and the regulatory system that is supposed to guarantee its safety.

His report is the result of a partnership with the Center for Public Integrity. It begins in the small desert town that made Erin Brockovich a household name.

ROBERTA WALKER, Resident of Hinkley, Calif.:Come on, you want some water? Want to get some water? Come on.

MILES O’BRIEN:Clean water is something most of us take for granted, but not Roberta Walker. She, her dogs, and her family drink spring water that is either bottled or trucked in, because where she lives, people can't drink the well water.

Welcome to Hinkley, Calif.

ROBERTA WALKER:This is bought out, this home on the right. This is all boarded up. So you can see how these are all boarded up.

MILES O’BRIEN:Yes.

Roberta drove me around town, what's left of it.

ROBERTA WALKER:There was a home here on the corner and that, of course, is gone.

MILES O’BRIEN:It is a ghost town?

ROBERTA WALKER:Yes. Yes.

MILES O’BRIEN:The steady decline of Hinkley is rooted here at a natural gas pipeline pumping station owned by the giant California utility Pacific Gas & Electric. In the 1950s and '60s, PG&E admits it dumped 26 tons of a coolant made of chromium 6 into unlined retaining ponds here. The chemical is toxic and causes cancer.

It leached into the soil and contaminated the aquifer, the drinking water in Hinkley. The Hollywood version of the story is writ large in the movie "Erin Brockovich" released in 2000. Julia Roberts won an Academy Award for her portrayal of the crusading legal assistant who forced PG&E into a $333 million dollar settlement with the residents of Hinkley in 1996.

But, for Roberta, there was no Hollywood ending.

So your house was right about here?

ROBERTA WALKER:Yes.

MILES O’BRIEN:PG&E did buy and raze her old home, as they did for many others here. So she built this place on the outskirts of town out of harm's way, or so she thought.

So far, PG&E has spent $700 million dollars trying to clean up the stubborn mess. But the plume of chromium 6-tainted water persists.

Sheryl Bilbrey is in charge of PG&E's remediation effort.

Why is it taking so long?

SHERYL BILBREY,Pacific Gas & Electric: It's a very complex project. We are highly regulated. There's a lot of interested parties. The other thing is, it's very important to us that we get it right.

MILES O’BRIEN:Recent testing shows there is still chromium 6 in the groundwater in Roberta Walker's neighborhood. It is less than it was in the bad old days, but Roberta is still girding to move once again, this time away from Hinkley.

Did you ever think you would ever have to deal with chromium 6 or PG&E again?

ROBERTA WALKER:Absolutely not. Absolutely not. In front of God and the world, they said they were going to clean it up.

MILES O’BRIEN:And?

ROBERTA WALKER:And they didn't. It was just—it's just a shocker.

MILES O’BRIEN:For the real-life Erin Brockovich, it was also an unwelcome surprise.

ERIN BROCKOVICH, Consumer Advocate: I thought it was being cleaned up. The state thought it was being cleaned up. The community thought it was being cleaned up. So here it is 10 years later, I'm not paying attention because I thought it was all being handled.

MILES O’BRIEN:And how are people finding you? Just through the social networking?

Brockovich is now an environmental activist on a larger stage, curating a crowd-sourced map of reported cancer clusters, which she says are largely linked to chromium 6-contaminated water nationwide.

ERIN BROCKOVICH:There's more and more mounting evidence or what chromium 6 does to the human health, what it does to the environment, what it does to the air. Every community that I deal with that has been exposed to chromium 6, they have the same health symptoms, they have the same problems.

MILES O’BRIEN:In 2010, a nonprofit advocacy organization, the Environmental Working Group, tested tap water in 35 U.S. cities; 31 of them were contaminated with chromium 6. Utility testing records show about 70 million Americans are drinking this tainted water.

With evidence mounting that chromium 6 may be more dangerous than once thought, the Environmental Protection Agency decided to revisit the drinking water standard for the chemical. The standard, 100 parts per billion, was set 20 years ago. It is 5,000 times greater than the California EPA's public health goal for chromium 6 in drinking water, .02 parts per billion.

Ann Mason is a senior director with the American Chemistry Council, which represents the chemical industry.

ANN MASON, American Chemistry Council: The people in the United States are drinking water that meets the EPA safe drinking water level.

MILES O’BRIEN:So, you—would you say categorically, it's OK? Everybody is safe?

ANN MASON:I would say if the drinking water meets the safe drinking water level, that EPA has set that level and that's the rule of the land as we see it right now.

MILES O’BRIEN:There is a lot of research that links chromium 6 in drinking water to cancer. In 2008, the National Institutes of Health weighed in with an eye-opening rodent study. It uncovered clear evidence that high doses of chromium 6 in drinking water cause cancer in rats and mice.

Heather White is executive director of the Environmental Working Group.

HEATHER WHITE,Environmental Working Group: We think the science is clear. There's been a lot more research that we have seen over the last decade that shows that there is a big cause for concern about drinking hexavalent chromium, whether it would be stomach cancer, whether it be liver damage, whether it be toxicity. There's even been studies that shows that it can have reproductive health effects.

JULIA ROBERTS, Actress: By the way, we had that water brought in special for you folks. It came from the well in Hinkley.

MILES O’BRIEN:After the "Erin Brockovich" movie in 2000, California lawmakers decided life should imitate art. They chartered a so-called blue-ribbon panel of scientists to help set a chromium 6 drinking water standard for the state.

One of the scientists on the panel was this man, Dennis Paustenbach. The NewsHour and the Center for Public Integrity learned the company he ran, ChemRisk, had been hired by Pacific Gas & Electric during the lawsuit. At the time, the most compelling scientific study that linked chromium 6 in drinking water to cancer came from China in 1987. It studied villagers in Liaoning Province who lived near a chromium ore smelter and drank tainted water for years.

The lead author, Dr. Zhang JianDong, found they had increased rates of stomach cancer. Acting on behalf of its client PG&E, ChemRisk paid Zhang to redo his study. Paustenbach offered this explanation before the California Senate.

DENNIS PAUSTENBACH, ChemRisk, Inc.: After he saw the questions that we raised about the analysis, he went back and examined and said, of course not. It can't be true. My original conclusions don't make sense.

MILES O’BRIEN:The revised study reversed the original conclusion that chromium 6 was the likely cause of the villagers' developing cancer.

Scientists at the California Environmental Protection Agency were skeptical and took a look at the underlying data themselves.

Allan Hirsch is with CAL/EPA.

MILES O’BRIEN:The original study itself, was it good science?

ALLAN HIRSCH, California Environmental Protection Agency: Well, our analysis which we completed in 2008 agreed with the original 1987 paper. And we found that the rates of stomach cancer in these five villages were significantly higher than stomach cancer rates in the overall province.

MILES O’BRIEN:The California EPA set its public health goal of .02 parts per billion in 2011. The next step, changing the drinking water standards, has not happened.

There's been a fair amount of study about hexavalent chromium over the years. Isn't the scientific jury in?

SHERYL BILBREY:I don't think so. There's a lot of scientists that are still debating that question. I think that's why the process has taken so long, from what I have read, both at EPA and at the state level. So, I think they're still trying to figure out exactly what is the right answer there.

MILES O’BRIEN:Back in Hinkley, I got tour of the massive PG&E cleanup project.

Kevin Sullivan is the engineer in charge.

KEVIN SULLIVAN, Pacific Gas & Electric: This barrier is about a half-mile-long.

MILES O’BRIEN:They are pumping ethanol into the ground, which converts chromium 6 into a more benign form of the chemical called chromium 3. They have also planted acres of alfalfa that is irrigated with the tainted water. The rich organic soil also makes the conversion.

So that is now chromium 3 in your hand.

KEVIN SULLIVAN:Exactly.

MILES O’BRIEN:There is so much alfalfa, the utility now owns a thriving dairy farm.

But since the ethanol injections began, a new problem seems to have surfaced. Residents have started reporting elevated levels of arsenic and manganese in their wells. PG&E says it occurs naturally and has always been there. Nevertheless, when Sullivan appears at community meetings here.

KEVIN SULLIVAN:These are concentrations of over 100, OK? And we wanted to cut that off right there.

MILES O’BRIEN:There is dirty water on the table and angry accusations in the air.

RICHARD JOHNSON,Resident of Hinkley, Calif.: The community is in an uproar right now. We are not just being poisoned by chromium. We got high arsenic levels, manganese. All this can lead you to believe that PG&E really don't give a crap about any one of you.

TERESA SHEEFTSALL,Resident of Hinkley, Calif.: I don't want to live here. I don't want my family here. I have no choice. No one will buy my home. Who wants to move into this?

MILES O’BRIEN:But Sullivan insists they are making progress.

KEVIN SULLIVAN:We have cleaned up like 54 acres. Now, I know that doesn't—believe me, I understand that if it is not your property, what have you done for me lately? But 54 acres is a lot of progress in terms of getting this cleaned up. We have a lot longer to go, but these are positive signs that we have been able to achieve in the last few years.

MILES O’BRIEN:But Sullivan says it will be at least another 40 years before they're done with the cleanup here. It seems nothing moves quickly when the wells are poisoned.

GWEN IFILL:In part two of his report on Friday, Miles takes a closer look at the Environmental Protection Agency's system for regulating toxic chemicals in the environment.

Online, we go behind the scenes in Hinkley, and you can also check out chromium levels in the water of 31 U.S. cities.