HEXAVALENT CHROMIUM, CR(VI), IN GROUNDWATER: AT THE INTERFACE BETWEEN SCIENCE, REGULATORS, STAKEHOLDERS, AND THE HINKLEY COMMUNITY (Invited Presentation)

The Pacific Gas and Electric Company (PG&E) Hinkley compressor station, in the Mojave Desert, 80 miles east of Los Angeles, California, is used to compress natural gas as it is transported through a pipeline from Texas to California. Between 1952 and 1964, cooling water treated with a compound containing Cr(VI) to prevent corrosion of machinery within the compressor station was discharged to unlined ponds and released to groundwater. In 1998, Cr(VI) contamination at the site resulted in a $333 million legal settlement, at the time the largest of its kind in US history, that gained notoriety in the movie “Erin Brockovich”. As late as 2015, the extent of anthropogenic Cr(VI) released from the Hinkley compressor station was uncertain. The USGS was requested by the Lahontan Regional Water Quality Control Board (RWQCB) to determine the extent of anthropogenic Cr(VI) in groundwater and to estimate scientifically defensible Cr(VI) background concentrations that will be used by the Lahontan RWQCB to manage cleanup at the site. Input to the study was provided by a Technical Working Group (TWG) composed of community members, the Lahontan RWQCB, the Independent Review Panel Manager, PG&E, and consultants for PG&E. To help Hinkley community members follow and participate in study progress, a summative scale was developed from data collected as part of this study. The scale consisted of eight questions that required binary (yes or no) answers for each sampled well. The questions provided (1) a transparent framework for data interpretation in which all stakeholders participated; (2) unbiased interpretation of data traceable to numerical measurements; (3) a framework in which geologic, hydrologic, and geochemical data could be interpreted collectively; and (4) a framework to consolidate different types of data into a simple, easy-to-understand format. This presentation describes collaboration with the TWG and the Hinkley community. Technical results of the study are available in Izbicki, 2023, https://doi.org/10.3133/pp1885.