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Pacific Gas and Electric Company Research and Development <br /> 3400 Crow Canyon Road <br /> San Ramon,CA 94583, � <br /> .. g to z1f ... <br /> 510/866-5391 (; ' <br /> May 13, 1996 <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> i <br /> P.O. Box 388 <br /> Stockton, CA 95201-0388 <br /> RE: 'PG&E Tracy Service Center, 502 East Grant Line Road, Tracy, CA <br /> (Site Code 1407) <br /> Mr. Steve Sasson: <br /> In response to your letter dated April 8, 1996,PG&E sampled all groundwater monitoring <br /> wells at the site for MTBE. The laboratory detected MTBE.(29 ug/L) in-well 6W-2. MTBE <br /> was not detected in the samples collected from wells OW-],'OW-3, OW-4, OW-5, or OW-6. <br /> The detection limit was 5 gg/L.- <br /> Additionally,your letter.requested a mass balance of contaminants remaining in place. After <br /> reviewing all of the available data collected at,the11_site, prepared the enclosed estimate of. <br /> the mass of gasoline hydrocarbons that existed in the,subsurface when the site investigation <br /> was performed in 1987-8. The data supported'an estimate of approximately 129 pounds, or <br /> 22 gallons of gasoline in the subsurface At that time. <br /> Gasoline hydrocarbons were detected in well OW-2 (located within ten feet in the <br /> hydraulically downgradient direction of the former tank location)at an all time high of <br /> 1,700 pg/L°in 1989. Since that time,'gasoline hydrocarbon concentrations in well OW-2 <br /> have decreased until, beginning in February 1995,they were not detected. They remained at <br /> non-detectable concentrations for the following three consecutive quarters(except for <br /> benzene, which was detected during one event at a concentration of 0.7 gg/L). None of the <br /> other.six groundwater monitoring wells at the site(including three wells located <br /> hydraulically downgradient and within 60 to 80 feet of the former tank location)have ever <br /> produced water samples containing detectable concentrations of gasoline hydrocarbons, <br /> including BTEX. It should also be noted that,during the last year of groundwater <br /> monitoring, the water table was measured at or above levels recorded during previous year. <br /> At this point, we can only assume that, in'light of the historic groundwater data, either no. <br /> -gasoline hydrocarbons remain in the subsurface or some gasoline hydrocarbons remain but <br /> are too tightly bound to the soil.to affect the groundwater:' <br />