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STATE OF CALIFORNIA-Environmental Protectic ?ncy PETE WILSON,Govemor <br /> CALIFORNIA REGIONAL WATER QUALITY CONTP.QL BOARD <br /> CENTRAL VALLEY REGION <br /> 3443 Routier Road,suite A <br /> Sacramento,CA 95827-3098 r .� <br /> PHONE:(916)255-3000 4. <br /> FAX:(916)255-3015 r, <br /> U AM P/F <br /> 22 November 1995 <br /> Mr. Darrell Klingman <br /> Pacific Gas and Electric Company <br /> 3400 Crow Canyon Road <br /> San Ramon, CA 94583 <br /> SOIL AND GROUND WATER INVESTIGATION, PACIFIC GAS AND ELECTRIC <br /> COMPANY, LATHROP GAS DEHYDRATOR STATION, SAN JOAQUIN COUNTY <br /> I have reviewed the 29 September 1995 Ground Water Investigation Report for the Pacific Gas and <br /> Electric Company(PG&E) site in Lathrop. A significant amount of work has been done to characterize <br /> the lateral extent of soil and ground water contamination at the site. Petroleum contamination in the <br /> shallow unsaturated soils is limited to the area around the former reboiler unit, although the lateral extent <br /> of contaminated soils closer to the water table (approximately 10 feet below the ground surface) is <br /> greater. Ethylene glycol soil contamination also is limited to the immediate area around the former <br /> reboiler unit. Ground water sampling shows that the lateral extent of total petroleum hydrocarbons as <br /> gasoline (TPHg) and kerosene is defined with concentrations up to 9,100 and 47,000µg/1, respectively. <br /> Ethylene glycol was not detected during the first round of ground water sampling. <br /> I agree with PG&E's recommendation that quarterly ground water monitoring be implemented to <br /> evaluate the temporal and spatial contaminant concentration trends and biological breakdown of <br /> contaminants. PG&E believes intrinsic bioremediation is taking place, but the monitoring parameters do <br /> not show this clearly. Ethylene glycol should continue to be analyzed in samples from monitoring well <br /> MW-1. By 30 January 1996, please submit your next quarterly ground water sampling report. Based <br /> on the review of this report, the Board may require active ground water remediation. <br /> A remediation plan needs to be developed to clean up the contaminated soils near the former reboiler <br /> unit. These soils apparently are a continuing source of ground water contamination in MW-1 in which <br /> concentrations of TPI-Ig and benzene have increased dramatically since the first sample taken in January <br /> 1993. By 31 December 1995, please submit a detailed soil remedial action plan with a schedule to <br /> implement the work. <br /> If you hav y questions, you may call me at (916) 255-3077. <br /> Anee <br /> . WEISS <br /> ring Geologist <br /> JMW.jmw/lm <br /> cc: San Joaquin County Department of Public Health Services, Stockton <br />