Study finds lower chromium background
HINKLEY • A University of California, Davis statistician completed a study showing a lower level of background chromium in Hinkley wells than previously disclosed.
Central in the dispute over groundwater contamination in Hinkley has been the level of chromium that was already there — and thus, was not caused by pollution from Pacific Gas and Electric Company.
The Lahontan Regional Water Board asked UC Davis statistician Neil Willits to analyze data from PG&E’s 2007 study of background levels of chromium — a study that some Hinkley residents disputed because it sampled more drinking wells than the water board had asked for. Willits found that background levels were 2.5 parts per billion, not the current standard of 3.1 parts per billion.
One resident had gathered a petition arguing that PG&E’s study was flawed because some of the extra samples could have come from areas where natural levels were higher. A peer review of the 2007 study raised similar concerns.
As a result, the water board ordered the new analysis of a smaller amount of wells from the original study. That came back with lower measurements.
While the report provides ammunition for critics of PG&E’s 2007 study, it is unclear what practical effect it will have on the continued groundwater cleanup in Hinkley.
The water board has already voted to define the naturally occurring background level of chromium in Hinkley at 3.1 parts per billion. Changing that number would make it more difficult for PG&E to clean up the area and could delay the cleanup.
“Do they want to change that at this point?” Kemper said. “Staff is saying, it’s too early to tell.”
The water board plans to release an environmental impact report next month showing in detail what would be involved in a long-term water cleanup effort, Kemper said.
While Willits’ report found significantly different results than PG&E’s study, the earlier peer review questioned the accuracy of sampling from drinking wells in the first place. Monitoring wells can provide more precise data about contamination levels at specific depths of the aquifer, Kemper said.
PG&E spokesperson Jeff Smith said the utility was committed to determining the correct level of background contamination.
“It’s certainly valuable input that this additional study was done,” Smith said, adding that the utility believed a more accurate way to determine the background level would be to obtain new data.
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