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PG&E's Toxic Plume Creeps Toward L.A. Water Supply

March 06, 2004|Marc Lifsher | Times Staff Writer

Pacific Gas & Electric Co. is poised to begin pumping polluted groundwater from under the Mojave Desert to stop the toxic chemical hexavalent chromium from seeping into the Colorado River and tainting the water supply of 18 million Southern Californians.

The chemical compound, made infamous by the 2000 movie "Erin Brockovich," is "on the brink of contaminating the Colorado River," the Metropolitan Water District of Southern California warned in a strongly worded Feb. 11 letter to state regulators.

"We ask that you take additional emergency action sufficient to protect a resource of such critical importance to California," the letter said.

The slow-moving toxic plume is emanating from land near PG&E's Topock natural gas compressor station, south of Needles on California's border with Arizona.

The utility used the chemical compound, also known as chromium 6, to control such things as corrosion and mold in water cooling towers at the isolated plant, which pushes natural gas along a pipeline from west Texas to the Los Angeles Basin. PG&E dumped the untreated wastewater in nearby percolation beds between 1951 and 1969.

The plume of at least 108 million gallons of chromium 6-tainted water is now threatening the river and causing alarm among experts at the Metropolitan Water District, which operates the Colorado River Aqueduct, a major source of Los Angeles' drinking water.

"The plume has moved past the last sentry well. It's thought to be 125 feet from the river," said Lisa Anderson, an environmental engineer at MWD's headquarters in Los Angeles.

Levels of chromium 6 in a monitoring well near the river have ranged from non-detectable to more than 100 parts per billion over the last few weeks, Anderson said. The mass of the plume, just a few hundred feet behind the leading edge, measures more than 12,000 ppb, and the maximum legal contaminant level for all types of chromium in drinking water is 50 ppb, she said.

Although chromium 6 is a known carcinogen when inhaled, scientists continue to debate whether the chemical represents a danger in drinking water, and at what concentration.

The Topock station plume is on course to reach the river at a point 42 miles upstream from water intakes for both the MWD's aqueduct and the Central Arizona Project, an agricultural and urban water delivery system. The water also is used by three other agencies in California, the Imperial Irrigation District, the Palo Verde Irrigation District and the Coachella Valley Water District.

The state Department of Toxic Substances Control stressed that it had so far found no traces of chromium 6 in the river. And both the department and PG&E, the utility arm of San Francisco-based PG&E Corp., said they were committed to keeping the chemical from reaching the Colorado River.

"We view the situation very seriously. That's why we're telling PG&E to start pumping," said Ed Lowry, director of the Toxic Substances Control Department. "This needs to be addressed now."

Lowry said he was confident that the chromium 6 migration could be halted through a combination of short- and long-term techniques.

Starting Monday, PG&E engineers will begin pumping more than 20,000 gallons a day of groundwater from three extraction wells at Topock and trucking it away for disposal at a toxic waste dump.

"We feel confident that the pumping will [move] the flow of any water with hex [chromium 6] away from the river," said Alfredo Zanoria, a state hydrologist who has worked on the PG&E Topock site since 1997.

MWD also is pushing for quick action by the state and PG&E on a longer-term strategy: construction of a 2,000-foot-long, 150-foot-deep underground barrier between the leading edge of the contamination plume and the river.

"We're supporting the initial pumping to control the plume, but we're urging the department to reach an agreement with PG&E requiring them to put in subsurface barriers," Anderson said.

Technical experts at the Department of Toxic Substances Control say they are unsure how fast the plume is traveling through the complex hydrology of the Mojave Desert.

"We don't believe the thing is moving toward the river at that vigorous of a pace," said Zanoria. He estimated the flow at no more than 3 feet a year.

But department director Lowry said he was taking no chances. He said he had directed PG&E to start the process of building the subsurface barrier, which could take 12 to 18 months for planning and construction. The cost of the project is not known but is a secondary consideration, "with this chemical this close to the river," Lowry said.

PG&E said it was evaluating the barrier proposal.

"It looks to be a promising technique, if it can be installed to work there," said Bob Doss, the company's chief environmental engineer.

The combination of pumping and possible construction of a barrier, no matter what the cost, are evidence that "PG&E's No. 1 priority has been and will always be the protection of the Colorado River and the ecosystem out there," Doss said.

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