Chromium 6 — the toxic chemical that made Erin Brockovich famous four years ago through a motion picture — has surfaced as an issue again related to Pacific Gas and Electric Co.’s natural gas transmission system at the Arizona-California border.

It has raised safety concerns about the nearby Colorado River water supplies that 21 million people in the southern half of California depend upon. The controversy drew front-page news coverage in the Los Angeles Times on March 6.

PG&E’s gas utility officials and others expressed confidence that the ongoing efforts will be successful in preventing any contaminated water supplies from getting into the Colorado River near Topock, AZ, where a major PG&E natural gas transmission pipeline picks up interstate supplies from the Southwest.

The center of the concerns is the long-ago disposed of quantities of water containing Chromium 6 that the utility used from 1951 through 1969 as a means of preventing corrosion and mold in water cooling towers at its isolated gas pipeline receiving station along the Colorado River. An underground plume estimated to be 108 million gallons of tainted water that had been dumped untreated in percolation beds for 18 years is now threatening the river, causing the local regional water district in Southern California to sound the alarm bells.

An environmental engineer with the Los Angeles-based Metropolitan Water District (MWD) confirmed in the Times report that the plume has moved underground past the last sentry well, about 125 feet from the river water. (Although Chromium 6 if inhaled is a known cancer-causing chemical, its danger in drinking water is debated among scientists who have not established a danger level in terms of its concentrations.)

According to the Times‘ report, the concentrations detected around the PG&E gas utility facilities have ranged from “non-detectable to more than 100 parts/billion (ppb) in recent weeks.” The mass of the plume near Topock measures more than 12,000 ppb, and the maximum legal contaminant level is 50 ppb, the MWD engineer said in the news report.

While noting that no traces of Chromium 6 have been found in the river water, the California toxic substance control department director was quoted as saying the state views the situation “very seriously,” and that is why it is pushing PG&E’s utility to do more pumping to accelerate removing the contaminated water.

Beginning last Monday, PG&E’s removal program will begin taking 20,000 gallons of groundwater daily from three extraction wells at Topock, trucking the contaminated water away to a toxic waste disposal site. The state officials said they are confident this pumping will move the Chromium 6-tainted groundwater away from the river supplies.

The pumping and trucking is part of a short-term remediation, but MWD is pushing for a long-term solution that would require a 2,000-foot-long, 150-foot-deep underground barrier at the leading edge of the contaminated water. That is still being negotiated between the state and the utility.

The situation arising at the border natural gas pipeline juncture is similar to the compressor station PG&E maintains in the Southern California high desert town of Hinkley, near Barstow, CA, that was first uncovered as a potential problem in 1987.

It was the focus of the “Erin Brockovich” movie and a $333 million settlement with local residents in that town. In both Topock and Hinkley, Chromium 6-tainted water used in cooling towers was dumped in unlined evaporation ponds where it percolated down into the groundwater.

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