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%d <br /> STATE OF CALIFORNIA PETE wILSON, Governor <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— <br /> CENTRAL VALLEY REGION = - <br /> 3443 ROUTiER ROAD, SUITE A <br /> SACRAMENTO, CA 95827-3098 a`m <br /> PHONE: (916) 361-5600 <br /> FAX: (916) 361-5686 <br /> RECEN <br /> JUL 31 1!,99 <br /> 30 July 1991 'ENVIRONMENTAL HEALTH <br /> PERMIT✓SERVICES <br /> Ms. Mary Meays <br /> San Joaquin County Environmental Health <br /> l P:O-: Box 2009:. <br /> Stockton, CA 95201 <br /> FORMER CHEVRON #9=7780, 3245 EAST- FREMONT STREET, STOCKTON, SAH JOAQUIN COUNTY <br /> I have reviewed the file for this site and a recent "Quarterly Ground Water <br /> Monitoring Report" dated 4 -June 1991, prepared by Alton Geoscience. Chevron's <br /> cover letter to the 4 June` 1991 report requested closure consideration. <br /> The depth. to ground water has increased about 35 feet since the investigation <br /> began in 1987 from about 4W feet in 19$7 to about 75 feet .in April 1991. The <br /> three original- wells, installed by Groundwater Technology in 1987, contained <br /> significant"ground water contamination the last time they were sampled in <br /> February 1988:; The three wells were dry since .February 1989 and have since <br /> been destroyed' du.e to the poor condition of the tops of the. wel-ls. EA <br /> Engineering installed four monitoring wells in 1988, the deepest of the wells <br /> was 65 feet. At that time,.;one-:of the wells contained significant ground <br /> water contamination, two contained low levels of contamina•ton, =and the fourth <br /> contained non-.detectable levels., Al-1 of these wells have been dry since <br /> September 1989 but are in good condition and were not destroyed. EA installed <br /> two more wells. in August 1990 which have had non-detectable levels of <br /> contamination 'since they were installed. Well EA-6 is near the-former tank <br /> pit, the apparent source of contamination. <br /> Our file does °not contain any information`'`from Blaine Technical Services, who <br /> removed the tanks and collected'.the soi'-1 samples from :the excavation. The <br /> dimensions of :the pit, especially the final depth, are not clear from the <br /> information we do have. Sample .#218- was collected at. 18 feet and contained <br /> 1100 ppb TPH as gasoline, however, it is not clear whether this was a bottom <br /> sample and whether this contamination was left in place or: the excavation <br /> continued. Sample #3 was collected at .14 feet, but again, .it is- not clear <br /> whether this was a side sample and whether it was left in place or the <br /> excavation- continued. <br /> Based on the non-detectable levels of ground water contamination and the 35 <br /> foot drop in the water elevation, it .appears that ground water contamination. <br /> may no longer ,be present, however, it i,s probable that soil contamination does <br /> remain in place. I recommend that. Chevron collect .at least two more rounds of <br /> A <br />