The California Department of Toxic Substances Control (DTSC) along with the Department of Interior (DOI), are the lead governmental agencies responsible for the site investigation and cleanup and oversee PG&E's actions to protect the Colorado River and to clean up soil and groundwater contamination in the vicinity of its Topock Compressor Station (Station). Environmental investigation and groundwater monitoring has been under way at the Topock Site (Site) since 1997. The plume of affected groundwater (containing mainly hexavalent chromium) lies mostly beneath federally owned lands. DTSC has required PG&E to take actions, called Interim Measures, to prevent any movement of the plume toward the Colorado River. Under Interim Measures, PG&E has been extracting and treating groundwater at the site since March 2004. PG&E has completed two volumes of the RCRA Facility Investigation/Remedial Investigation (RFI/RI) report for the Site and has conducted additional studies to help evaluate cleanup options and technologies. These studies include: a river sediment Pore Water Study, a series of sediment core testing studies, a Groundwater Background Study, In-situ Pilot Tests at two site locations, and groundwater characterization by slant borings. In 2009, PG&E is conducting additional groundwater characterization in an area located east/southeast of the compressor station, known as the East Ravine.

Long-term cleanup options for contamination in groundwater at the Site are being evaluated as part of a Corrective Action Process under the Resource Conservation and Recovery Act (RCRA), and the Comprehensive Environmental, Response, Compensation, and Liability Act (CERCLA), will be summarized in the final Corrective Measures Study/Feasibility Study (CMS/FS) report, which will incorporate the input of stakeholders (including agencies and tribal governments) on the draft CMS/FS.

The agencies provided oversight of the first phase of soil investigation in addition to overseeing groundwater investigations. The first phase of soil investigation in areas outside of the Station was completed in 2008. Additional investigations may be required after data analysis is complete.

DTSC is coordinating with multiple state and federal agencies and stakeholders who meet regularly as part of a Consultative Workgroup (CWG). The CWG, established by DTSC in March 2000, consists of agencies and entities that have an interest in protecting the Colorado River and the surrounding environment. In addition, DTSC has conducted extensive outreach to the public and governmental representatives, including federal, state, county, and city elected officials and staff and tribal government leaders and staff. To view the map of current groundwater monitoring locations click on the map on this page. To view the most recent plume maps based on quarterly groundwater data, visit the RCRA Facility Investigation page or the Groundwater and River Monitoring page.