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 on which are located the Interim Measures facilities. The nearest communities are Moabi Regional Park, California (one mile northwest of the Station); Topock, Arizona (one-half mile east, across the Colorado River); and Golden Shores, Arizona (five miles to the north).

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What is the history of chromium use at the Topock Compressor Station?
PG&E's Station compressed natural gas before transporting it through pipelines to central and northern California. From 1951 to 1985, PG&E used hexavalent chromium as an anti-corrosion agent 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 on-site 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 Agreement (CACA) with 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 (Cr6) and trivalent chromium (Cr3). Hexavalent chromium is the toxic variety; it is considered a human carcinogen when inhaled. It is also highly soluble, and therefore easily transported in groundwater. Trivalent chromium, on the other hand, is considered an essential nutrient and relatively harmless. It is insoluble and tends to bind to the soil; thus it does not travel readily in the environment. Hexavalent chromium is stable only under certain chemical conditions and may convert into trivalent chromium. However, trivalent chromium does not convert as readily to hexavalent chromium.

The California drinking water standard, which is a legal mandate based on health and other considerations, is currently set at 50 parts per billion (ppb) of total chromium (which includes both hexavalent chromium and trivalent chromium). There is no separate drinking water standard for hexavalent chromium.

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Has the Colorado River been affected?
Water from the Colorado River has been sampled quarterly since 1997 and monthly since November 2003. 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 no hexavalent chromium has been detected. Monitoring of surface (river) water will continue, and several new "slant" wells have been added on the California and Arizona shorelines. These wells extend under the river, and are positioned to monitor (sample) groundwater from 150 feet below the river bottom. 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 used for drinking or other purposes. Hexavalent chromium is no longer used at the Station. 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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