A tiny desert town whose plight was made famous by the movie "Erin Brockovich" has seen a dramatic increase in the size of a toxic plume of chromium as it has spread to multiple groundwater wells.

Water regulators earlier this year discovered a well with increasing concentrations of the cancer-causing pollutant and now even more wells have been uncovered with elevated levels, said Lauri Kemper, assistant executive officer of the Lahontan Regional Water Quality Control board.

The water board on Monday ordered Pacific Gas & Electric to do additional groundwater monitoring at the site near Hinkley, about 120 miles northeast of Los Angeles.

"The more dispersed chromium continues to move," Kemper told The Associated Press on Tuesday. "Because of the widespread nature of the lower concentration chromium, it's difficult to capture the contamination."

The contamination was first publicized during a 1996 court case in which PG&E settled with more than 600 Hinkley residents for $333 million. Many sick residents blamed the contaminated water for their crippling health problems that included Hodgkin's disease and breast cancer.

Brockovich was a legal assistant when she uncovered that PG&E knowingly polluted the city's water supply. The subsequent 2000 movie, "Erin Brockovich," featured Julia Roberts and garnered the actress an Academy Award.

Tests showed the plume was spreading again in 2008, and PG&E took action that it thought had contained the contamination. Tests in March showed that it was growing again, and it is now more than two miles long and a mile wide.

Current chromium levels near Hinkley remain low enough not to violate current drinking water standards. But some studies have shown that long-term exposure to even low levels of the compound can contribute to health problems.

"This is a hazardous substance that is moving through people's wells," said resident Carmella Gonzalez. "I don't have unrealistic expectations of them cleaning it but they darn well ought to stop the migration."

A company spokesman said they are complying with the directives.

"There's nothing more important to us than making sure we do whatever is necessary to respond to any concerns," said Jeff Smith, a spokesman for PG&E.

Brockovich, who has continued to be involved in a variety of environmental causes, could not immediately be reached for comment.