Jim Steinberg, Staff Writer
Posted: 01/08/2012 06:03:56 AM PST

HINKLEY – The water agency supervising the clean-up of chromium 6 groundwater contamination here has asked Pacific Gas and Electric Co. to provide more scientific details on the study it did to determine the naturally occurring background level.

The request follows critical reports from three independent scientists recruited to evaluate the 2007 study which determined the Hinkley area has a naturally occurring chromium 6 level of 3.1 parts per billion.

Determining the background level is “critically important” because it sets the bar for how far PG & E has to go to return the Hinkley’s groundwater to its original condition, said Jeff Smith, a PG & E spokesman.

In the 1950s and 1960s, PG & E used the cancer causing chemical chromium 6, also known as hexavalent chromium, to prevent rust and algae buildup in its Hinkley cooling towers.

The chemical, widely used before its cancer-causing properties were known, was discharged into unlined ponds and from there entered the groundwater.

Late last year it was revealed that the plume grew a mile in 2011, a rate that surprised geologists and engineers at the Lahontan Regional Water Quality Control Board.

Traditionally the plume has migrated northward at about a foot per day.

Laurie Kemper, assistant director of the water agency, said that the staff is first pursuing some of the questions raised by Stuart Nagourney, an adjunct professor of chemistry at The College of New Jersey.

Nagourney, in his critique of the background study, raised many technical questions on the detection methods used in the background study, which was paid for by PG & E.

He said these analytical data, and the decisions about how they were arrived, directly impact the conclusions of the study.

Kemper said that in formulating its questions, her agency consulted with a scientific laboratory it uses to analyze water samples.

Kemper said that the decision was made to pursue the issues raised by Nagourney first, in order to determine “if we can trust the data in the study.”

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