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r <br /> CHRONOLOGY <br /> FORMER UNOCAL 5421, <br /> 7303 PACIFIC AVE. STOCKTON <br /> SITE CODE: 1226123 <br /> APN: 077-360-21 <br /> 11/17/89 Three USTs removed under permit and inspection; one waste oil and 2 gasoline. Soil <br /> samples collected evidenced a gasoline release in the rank field in northeast quadrant of <br /> the parcel. <br /> 11/28/39 UAR completed and filed this date. <br /> 12/18/89 Site placed in the LOP for investigation and remediation. <br /> 12/05/89 Soil was removed/overexcavated from the fuel tank area to 26.5 feet BGS and <br /> confirmation samples collected. Piping trench samples were also collected to 17 feet <br /> BGS;sample P2(17) was the most contaminated(7200 ppm TPH-GAS, 170ppm <br /> Benzene). <br /> 12!10/90 Four groundwater monitoring wells(MW)were installed on-site. Groundwater results <br /> were positive for gasoline and BTEX. Water was approx. 59 feet BGS at this time. <br /> 06/05/92 On site septic with leach field closed;soil excavated and confirmation samples collected. <br /> 11/09/92 Seven additional soil borings were completed on-site to groundwater. <br /> 04/15i98 Dual-wall replacement USTs and piping installed in 1990 were removed this date:soil <br /> samples collected evidenced an unauthorized release of gasoline from this system. One <br /> soil sample under the USTs at 17 feet BGS had TPH-GAS concentrations as high as <br /> 25,000 ppm,270 ppm Benzene,and 170 ppm MTBE. UAR completed and filed this <br /> date. <br /> 04/21/98 The dual-wall UST excavation was deepened to 26 feet BGS and confirmation samples <br /> collected; residuals were TPH-GAS 24 ppm,Benzene .77 ppm. No MTBE was detected <br /> at .050 ppm. <br /> 07/09/98 EHD received the site Closure Report requesting site closure with no further action. All <br /> MWs are currently ND for gasoline and oxygenates with 230 ppb TPH-DIESEL in MW <br /> 1. Gasoline residuals do remain on-site in the soil in the vadose zone. <br /> 07/12/98 EHD prepared the site for CVRWQCB closure concurrence. <br /> Chron7303 <br />