Pacific Gas and Electric Company's (PG&E) Topock Compressor Station is located in eastern San Bernardino County, approximately 12 miles to the southeast of Needles, California, along the Colorado River. The nearest communities are Moabi Regional Park, California (one mile northwest); Topock, Arizona (one-half mile east, across the Colorado River); and Golden Shores, Arizona (five miles to the north, across the Colorado River).

In 1996, the California Department of Toxic Substances Control (DTSC) entered into an agreement with PG&E to fully investigate the nature and extent of hexavalent and total chromium contamination resulting from releases from the PG&E Topock Compressor Station in Needles, California. Under the terms of the agreement, PG&E is following an investigation and cleanup process governed by a federal law known as the Resource Conservation and Recovery Act (RCRA). Additionally, because some of the property affected by operations at the compressor station is owned by the United States Department of the Interior (DOI), DOI is overseeing remedial actions at the site pursuant to the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA). Due to the Topock Compressor Station's proximity to the Colorado River, ADEQ participates in investigation activities as they relate to the Colorado River and potential future impacts to Arizona's groundwater.

Arizona's Involvement in Current Groundwater Investigations

In 2005, ADEQ initiated a yearlong groundwater study in Arizona to assess whether there was a potential threat to human health from hexavalent chromium in the drinking water supplies for the Arizona communities of Topock and Golden Shores. At the time of the document review, the study concluded that there was no immediate threat to human health from use of groundwater for drinking water in Arizona. However, available information at the time did not allow ADEQ to completely assess potential long-term threats to the future water supply because the eastern extent of hexavalent chromium contamination in groundwater was not defined. As such, the study recommended the installation of groundwater monitoring wells in Arizona. The final report is available at ADEQ's Phoenix office and at the document repositories listed below.

In December 2006, PG&E entered ADEQ's Voluntary Remediation Program (VRP) in order to initiate a Colorado River investigation that would include the Arizona side of the river. PG&E submitted a work plan in March 2007 with the primary goal to define the eastern extent of the hexavalent chromium plume emanating from the Topock Compressor Station. The VRP approved the work plan in May 2007.

The well installations proposed in the work plan were completed in spring 2008. A total of three wells were installed, including a slant well beneath the Colorado River, a vertical well at the Havasu National Wildlife Refuge (HNWR), and a vertical well at the Topock Marina. As of December 2008, the slant well and the HNWR well have been non-detect for chromium and hexavalent chromium. The Topock Marina well has had low-level detections of chromium and hexavalent chromium, with a maximum of 4.38 parts per billion (ppb) of total chromium. Federal Safe Drinking Water Act, California Safe Drinking Water Act, and Arizona's Aquifer Water Quality Standard for total chromium is 100 ppb. At this time, there is no indication that the chromium concentrations identified in the Topock Marina Well are from a source emanating from the Topock Compressor Station.

Groundwater Monitoring Program and Surface Water Monitoring

In addition to these new groundwater well installations, the groundwater and Colorado River surface water monitoring activities that began in 1997 continue to this day. The current Groundwater Monitoring Program includes over 100 monitoring wells with quarterly sampling. Additionally, quarterly surface water samples are collected from 10 shoreline wells and nine river channel locations. To date, Colorado River sampling results consistently indicate that the river is not impacted by chromium.

At this time, USDOI and California DTSC continue to oversee the larger study area as part of the RCRA and CERCLA investigations. The VRP remains active as a stakeholder in these investigative activities and also continues to monitor the surface water data and quarterly sampling data obtained from all wells included in the Groundwater Monitoring Program.

Document Repositories

Arizona Department of Environmental Quality
ADEQ Records Center
Phoenix, Arizona 85007
(602) 771-4380
(602) 771-4389 - Fax

Golden Shores/Topock Library Station
13136 Golden Shores
Topock, Arizona 86436
(928) 768-2235

Lake Havasu City Library
1770 McCulloch Boulevard
Lake Havasu City, Arizona 86436
(928) 453-0718

California DTSC

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