Chromium found in monitoring wells near Colorado River
PG&E has notified the California Department of Toxic Substances Control of detection of hexavalent chromium at a new groundwater monitoring well it recently installed as part of an ongoing remediation action it's undertaking near the Topock Compressor Station at the California-Arizona border, roughly midway between Needles, Calif., and Lake Havasu City, Ariz...
SAN FRANCISCO, Feb. 24, 2005, (PRNewswire-FirstCall) -- Pacific Gas and Electric Co. (PG&E) has notified the California Department of Toxic Substances Control (DTSC) of detection of hexavalent chromium at a new groundwater monitoring well it recently installed as part of an ongoing remediation action it's undertaking near Topock, at the California-Arizona border.
About 20 million people are served with Colorado River water in the two states via canals that cross the arid Southwest, with the vast majority of those users -- 16 million according to the Colorado River Water Users Association (www.crwua.org) -- in Southern California. This includes major metropolitan areas such as Los Angeles, Phoenix and San Diego.
As a result of this recent detection, DTSC has directed the utility to increase groundwater extraction rates and the frequency of monitoring at the site. PG&E immediately began complying with the DTSC directive.
A groundwater sample was drawn Feb. 14 from the new monitoring well and sent to a California-certified laboratory to be analyzed. The results indicated a hexavalent chromium concentration of 357 parts per billion (ppb). An additional sample was collected from this well Feb. 16, and the results from the certified laboratory confirmed the earlier results with a similar concentration of 354 ppb. The California drinking water limit for total chromium is 50 ppb.
No chromium contamination has been detected in the river. As a precaution, multiple samples were also taken on Feb. 16 directly from the Colorado River upstream and downstream of the new monitoring well, which lies roughly midway between Needles, Calif., and Lake Havasu City, Ariz. Test results of these samples confirm that hexavalent chromium is not present in the Colorado River. Since 1997, the company has included the Colorado River in its regular quarterly sampling program and the results show that hexavalent chromium has not been detected in any of our Colorado River samples.
Data from the new, 100-foot deep monitoring well will assist PG&E and DTSC in analyzing and remediating groundwater beneath its Topock Gas Compressor station. This new, 100-foot-deep monitoring well is at the same location that in January of 2004 produced a positive detection of hexavalent chromium of 111 ppb at an 80-foot depth, which resulted in the installation of the present extraction system. The extraction system has been operating since March 2004 and frequent field measurements show it has met the goal of maintaining hydraulic control of the plume.
Because the extraction system has maintained hydraulic control of the plume, the consensus of hydrogeologists working on this project is that the plume has been at the new sampling location at this deeper level, far lower than the river nearby, for some time, and has not recently migrated there. The new information is serving to better delineate the location of the existing plume and provides valuable information as the company works to implement additional interim and final remediation measures.
The absence of chromium in the shallow groundwater near the river is consistent with what has been found in other nearby wells at the site. The presence of decaying organic matter in the shallow floodplain sediments creates geochemical conditions that remove hexavalent chromium in that area from the groundwater.
For several months prior to the detection of chromium in the newly installed well, the extraction system had been operating at a rate of about 70 gallons per minute and had been successful at maintaining hydraulic control of the plume. At the direction of DTSC, PG&E increased the extraction rate to the current maximum possible rate of about 90 gallons per minute on Feb. 22 as a precaution. To date, the system has extracted more than 19 million gallons of contaminated groundwater. The company is currently constructing a treatment system on property recently purchased from Metropolitan Water District (MWD) to provide for extraction of groundwater at significantly higher rates and ensure continued capture of the groundwater plume during all river conditions. The expanded system will help ensure the groundwater in the area does not reach the Colorado River.
"Pacific Gas and Electric Company is fully committed to keeping hexavalent chromium out of the Colorado River," said Robert Harris, PG&E's vice president of environmental affairs. "The company is working diligently with the local, state and federal agencies and neighboring tribal sovereign nations to complete the expanded treatment system in an expedited timeframe to ensure the ongoing remediation of the groundwater near the Colorado River."
PG&E has been working cooperatively with local, state and federal regulators and other interested parties for several years to address and responsibly resolve the groundwater contamination issue. In March 2000, a Consultative Working Group (CWG) was formed to advise DTSC, the lead regulatory agency on this project. The CWG includes representatives from the Regional Water Quality Control Board, Metropolitan Water District, and numerous Department of Interior agencies.
The expanded treatment system is considered an interim measure to maintain hydraulic control the groundwater plume. PG&E is continuing to work with the DTSC, MWD and other interested parties to complete the full evaluation of the site and determine the most prudent long-term course of action to complete the groundwater remediation.
From 1951 until 1964, untreated wastewater from the station's cooling towers containing the corrosion-inhibitor hexavalent chromium was discharged into percolation beds in a dry wash near the plant. Beginning in 1964, the wastewater was treated to remove chromium and the treated water was disposed of by various methods over time, including the use of lined evaporation ponds and an injection well.