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PUBLIC PiEALTH SERACES N <br /> PFJ P <br /> ,oma <br /> SAN JOAQUIN COUNTY �o 2,: i <br /> ENVIRONMENTAL HEALTH DIVISION a i <br /> Ernest M. Fujimoto, M. D., M.P.H., Acting Health Officer <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 ; <br /> 209/468-3420 C CL1 <br /> BOB BOUST <br /> JUN 0 31997 <br /> UNOCAL <br /> 2000 CROW CANYON PL STE 400 <br /> SAN RAMON CA 94583 <br /> RE: 437 East Miner Ave SITE CODE: 1 1 81 <br /> Stockton CA 95202 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has <br /> reviewed information regarding your March 1997 telephone request for additional information <br /> and the "Work Plan to Install An Offsite Groundwater Monitoring Well" dated March 31 , 1997. <br /> PHS/EHD has prepared the following comments for your clarification and response. <br /> Aae of Release <br /> The "Soil Remediation Feasibility Study Work Plan" dated April 30, 1996 indicated that the site <br /> was an operating Unocal service station from 1922 until 1992. A site history of tank operations <br /> since 1967 was provided with information that three underground storage tanks, two 1,000 <br /> gallon gasoline and one 550 gallon waste oil, were removed from the southeast corner of the <br /> station in 1967; however no soil samples were collected at that time. The tanks which were <br /> subsequently installed, were placed further west, and these tanks were removed in January <br /> 1992. The tanks appeared rusted; however the product piping appeared to be in good <br /> condition. Four soil samples (UX-1 - UX-4) were collected from beneath the former gasoline <br /> tanks, one soil sample (UW-1) was collected from beneath the waste oil tanks and four samples <br /> (UT-1 - UT-4) were collected from the piping trenches. The results of the soil sampling <br /> indicated limited contamination in the piping area and was estimated to comprise 20 cubic <br /> yards. Based on the piping sample results, the site was placed into the Local Oversight Program <br /> and on the contaminated site list. <br /> On February 25, 1992, two soil samples (SL-1 - SL-2) were collected from beneath each of the <br /> hydraulic lifts and one soil sample (SOW-1) was collected from beneath the oil-water separator. <br /> Also, an additional waste oil tank was identified and subsequently removed on May 6, 1992 and <br /> one composite sample (UW-2A-B)was collected. <br /> On October 9, 1992, PHS/EHD requested additional investigation related to elevated metal <br /> concentrations detected. PHS/EHD re-issued the correspondence on November 12, 1992 to a <br /> new Unocal representative. <br /> On October 1, 1993, eight exploratory borings (U-A - U-H) were drilled and sampled. <br /> Petroleum hydrocarbons were only detected in samples collected from borings U-C and U-D <br /> which were located in the vicinity of the tanks which were reportedly removed in 1967. <br /> On January 3, 1994, PHS/EHD directed that a groundwater investigation be initiated based on <br /> the concentrations observed in samples collected from borings U-C and U-D. PHS/EHD also <br /> indicated that the horizontal and vertical extent of the contamination evidenced to date had not <br /> been determined. <br /> A Division of San Joaquin County Health Care services <br />