USGS Scientists and the Hinkley Community Work to Define Natural Background Concentrations of Hexavalent Chromium in Groundwater

Pacific Gas and Electric discharged Cr(VI) from its compressor station into unlined ponds and created a plume in the aquifer. Determining what is “background” is an important part of the Lahontan Regional Water Quality Control Board’s process for defining what PG&E must do to rectify the situation.

The USGS was asked to answer the question: “What are the natural background concentration of Cr(VI) in Hinkley’s groundwater?" To address this issue, the USGS worked with community members as part of the scientific project. The goal was to make the scientific process transparent and reduce the level of conflict over background values.

The lead scientist, Dr. John Izbicki, understood that “background” meant different things to different stakeholders and created a “summative scale” tool everyone could use to determine which wells could be labelled as “background.” This tool was based on how geochemistry in the aquifer works and new data sets were collected that included measurements that indicated aquifer condition such as grain size of minerals and oxygen levels.

Working with the Community of Hinkley

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Map of Results

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VIDEO

View presentation of final results to the Lahontan Regional Water Quality Control Board.