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STATE OF CALIFORNIA-Environmental Protec, gency PETE WILSON,Governor <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD <br /> CENTRAL-VALLEY REGION '`�°F�F'""ti <br /> 3443 Routier Road,Suite A -- <br /> Sacramento,CA 95827-3096 <br /> PHONE:(916)255-3000 <br /> FAX(916)255-3015 , <br /> 12 May 1997 <br /> Ms. Linda Gonsalves <br /> Pacific Gas and Electric Company <br /> 375 North Wiget Lane, Suite 130 <br /> Walnut Creek, CA 94598-2412 <br /> RESULTS OF ADDITIONAL INVESTIGATION, PACIFIC GAS & ELECTRIC <br /> COMPANY, LATHROP GAS DEHYDRATOR STATION, SAN JOAQUIN COUNTY <br /> I have reviewed the 29 April 1997 Technical Report, Additional Groundwater Investigation for <br /> Pacific Gas &Electric's gas dehydrator sit-,in Lathrop. The report describes the latest phase of <br /> investigation which included drilling and installing four new groundwater monitoring wells and <br /> continued monitoring for contaminants and biodegradation parameters. <br /> It appears at this time that the mass removal rate of petroleum from the subsurface due to passive <br /> biodegradation is great enough to prevent the contamination from migrating. However, the new <br /> monitoring wells should continue to be monitored quarterly for at least one full year to confirm <br /> this hypothesis. The remaining wells can be monitored on a semi-annual basis. All of the samples <br /> should be analyzed for total petroleum hydrocarbons (TPH), benzene, toluene, ethylbenzene and <br /> xylene, and ethylene glycol compounds. Analyzing for biodegradation parameters can be <br /> discontinued. <br /> It may be a good idea to use the silica gel cleanup method on the samples prior to analyzing them <br /> for TPH. This would provide additional information regarding the extent of biodegradation in the <br /> subsurface. <br /> You next quarterly report is due by 30 October 1997. If you have any questions, you may.call <br /> me at (91 255-3077. <br /> J EL M. WEISS <br /> Associate Engineering Geologist <br /> JMW:jmw/lsb <br /> cc: San Joaquin County Department of Public Health Services, Stockton <br />