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ATHE <br /> STs rE,e,M <br /> _ . ,. : 01 <br /> February 13, 1996 <br /> San Joaquin County Alton Project No. 30-0136 <br /> Public Health Services <br /> Environmental Health Division <br /> 445 North Joaquin Street, P.O. Box 388 <br /> Stockton, California 95201-0388 <br /> ATTN: MS. MARY MEAYS <br /> SITE: FORMER MOBIL, BULK PLANT 04-343 <br /> 500 EAST GRANTLINE ROAD <br /> TRACY, CALIFORNIA <br /> RE: REQUEST FOR GROUNDWATER SAMPLING REDUCTION AND WELL <br /> ABANDONMENT <br /> • Dear Ms. Meays: <br /> On behalf of Mobil Oil, Alton Geoscience respectfully requests to reduce the frequency of <br /> groundwater monitoring and sampling of Monitoring Wells AW-1 through AW-4, AW-7, and <br /> AW-10 from quarterly to annually, at former Mobil Station 04-343, located at 500 East Grantline <br /> Road in Tracy, California (Figure 1). Alton also requests that Monitoring Wells AW-5, AW-6, <br /> .AW-8, AW-9, AW-11, and AW-12 be eliminated from the monitoring and sampling program <br /> and abandoned. <br /> Low to non-detectable dissolved-phase hydrocarbon concentrations have been detected in <br /> Monitoring Wells AW-1, AW-2, AW-4, AW-7, and AW-10 since June 1992 (see Table 1), In <br /> addition, AW-3 has contained only dissolved-phase diesel concentrations which have not migrated <br /> downgradient. Due to these factors, Alton Geoscience requests that frequency of monitoring and <br /> sampling of Monitoring Wells .AW-1 through AW-4, AW-7, and AW-10 be reduced from <br /> quarterly to annually. <br /> Based on continued low and non-detectable dissolved-phase diesel, gasoline and benzene <br /> concentrations during the past three years, Alton requests that Monitoring Wells AW-5, AW-6, <br /> AW-8, AN'J-9, AW-11, and AW-12 be abandoned. Monitoring Wells AW-1, AW-3, and AW-10 <br /> will act as a sufficient monitors of onsite hydrocarbon dissolved-phase concentrations, while AW- <br /> 7 will sufficiently monitor any down-gradient migration of dissolved-phase hydrocarbons. <br />• <br /> 30A Lindbergh Avenue <br /> Livermore,California 94550 <br /> (510)606-9150•FAX(510)606-9260 <br />