Frequently Asked Questions

Table of Contents

Where is the Topock Compressor Station?
What is the history of chromium use at the Topock Compressor Station?
What is chromium, and why should I be concerned about it?
Has the Colorado River been affected?
Am I affected by the contaminated groundwater?

Where is the Topock Compressor Station?

Pacific Gas and Electric Company's (PG&E) Topock Compressor Station (Station) is located in eastern San Bernardino County 12 miles southeast of Needles, California, along the Colorado River. The Topock Project Site (Site) includes the Station property, as well as the area overlying the plume and the properties that contain the Interim Measures facilities. The nearest communities are Moabi Regional Park, California (1 mile northwest of the Station); Topock, Arizona (one-half mile east, across the Colorado River); and Golden Shores, Arizona (5 miles to the north).

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What is the history of chromium use at the Topock Compressor Station?

PG&E's Station compresses natural gas before transporting it through pipelines to central and northern California. From 1951 to 1985, PG&E used hexavalent chromiumHexavalent chromium is a form of chromium. Chromium is a metal naturally found in rocks, soil, and the tissue of plants and animals. Hexavalent chromium can be found naturally at low concentrations, but it is also used in industrial products and processes and is a known carcinogen. On May 28, 2014, the California Department of Public Health adopted a new California drinking water standard at 10 parts per billion for hexavalent chromium. to prevent rust in its cooling towers. From 1951 to 1964, untreated wastewater from the cooling towers was discharged into percolation beds in Bat Cave Wash, a normally dry wash next to the Station. Beginning in 1964, PG&E treated the wastewater to remove hexavalent chromium. The treated wastewater was discharged into Bat Cave Wash until 1968, and subsequently was discharged into an onsite injection well. Over time, PG&E installed a series of lined evaporation ponds for wastewater disposal. In 1985, PG&E stopped using the chromium-based additive and switched to a phosphate-based solution. In 1996, PG&E entered into a Corrective Action Consent AgreementA voluntary agreement between a lead agency and responsible party in which the company commits to investigate the nature and extent of contamination at and surrounding a site governed by RCRA, and to take corrective action. with the California Department of Toxic Substances ControlThe department within the California Environmental Protection Agency in charge of the regulation of hazardous waste from generation to final disposal. DTSC oversees the investigation and cleanup of hazardous waste sites. (DTSC) to investigate and clean up the hexavalent chromium contamination at the Site.

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What is chromium, and why should I be concerned about it?

Chromium is a naturally occurring metal found in rocks, soil, and the tissue of animals and plants. It is present in the environment most commonly in two different forms: hexavalent chromium and trivalent chromium. Hexavalent chromium is the toxic variety; it is considered a human carcinogen when inhaled. It is also highly soluble; therefore, it is easily transported in groundwaterWater beneath the Earth’s surface that flows through soil and rock openings (aquifers).. Trivalent chromium, on the other hand, is considered an essential nutrient and is relatively harmless. It is insoluble and tends to bind to the soil; thus, it does not travel readily in the environment. Hexavalent chromium can be converted into trivalent chromium under certain geochemical conditions.

The California drinking water standard, which is a legal mandate based on health and other considerations, is currently set at 50 parts per billionA unit of measure used to describe levels or concentrations of contamination. One part per billion is the equivalent of one drop of contaminant in one billion drops of water. for total chromium (which includes both hexavalent chromium and trivalent chromium). The California drinking water standard for hexavalent chromium, established on July 1, 2014, is 10 ppb.

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Has the Colorado River been affected?

Water from the Colorado River has been sampled either monthly or quarterly since 1997. River sampling results consistently indicate that the river is not affected by chromium from the Topock plume. Water contained within sediments from different locations along the river have been sampled, and results also indicate that the sediment is not affected by chromium from the Topock plume. Monitoring of surface (river) water will continue. There are several "slant" wells on the California and Arizona shorelines that extend under the river and are positioned to monitor (sample) groundwater from 150 feet below the river. To date, samples from these "slant" wells have not detected hexavalent chromium.

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Am I affected by the contaminated groundwater?

The groundwater containing hexavalent chromium is in an area that is not currently used for drinking or other purposes. Hexavalent chromium is no longer used by PG&E at the Station, and has not been for many years. In addition, under the Interim Measures directed by DTSC, PG&E has been actively controlling the potential movement of the hexavalent chromium plume by extracting the contaminated groundwater at key locations to keep the direction of flow of the plume away from the Colorado River.

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