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SS No. 6348 , Tracy <br /> PIER, 1/31/92 <br /> In July, 1991, Mittelhauser Corporation commenced <br /> Phase II investigation of the property, including installing <br /> four monitoring wells and additional borings to delineate <br /> potential contamination. During drilling, a gasoline product <br /> line and a pressurized natural gas line were ruptured at the <br /> two-foot depth near the southeast corner of the station <br /> building. Although the pressurized natural gas expelled the <br /> contents of the product line into the air, approximately one <br /> gallon of gasoline later dripped into the soil due to a <br /> malfunctioning blend valve. Soil contaminated by this <br /> release was excavated down to a clean surface. A confirmation <br /> sample was taken of this surface and neither gasoline (TPHg) <br /> nor BTEX was detected. A release report was filed with RWQCB. <br /> PRELIMINARY ACTIVITIES <br /> Prior to drilling , a work plan describing the <br /> proposed activities and a health and safety plan were submitted <br /> to the San Joaquin County Department of Public Health <br /> Services. That Department then issued a permit to install the <br /> borings and wells. Underground Service Alert was notified. <br /> FIELD ACTIVITIES <br /> On July 8 and 9 , 1991 , Mittelhauser personnel <br /> supervised the drilling by Cache Creek Drilling Company of four <br /> eight-inch diameter borings using truck-mounted hollow stem <br /> auger equipment. These borings were drilled to a depth of <br /> approximately 21 feet and were converted to two-inch diameter <br /> monitoring wells, designated as MW-1, MW-2, MW-3 and MW-4 . <br /> Groundwater, which was encountered in the monitoring <br /> wells at approximately 12 feet below ground level , later <br /> stabilized in the monitoring wells at a depth of approximately <br /> 11 feet below ground level. <br /> Four additional borings drilled on July 10, 1991 are <br /> designated B-1, B-2 , B-3 , and B-4 . Also that day a boring was <br /> hand-augered to the 10 foot depth in the service bays to <br /> identify any fluid leakage associated with the automotive <br /> hydraulic hoist and interior sumps. This boring is designated <br /> as B-5. <br /> On July 16 and 18, 1991, Mittelhauser returned to the <br /> site to bore an additional seven holes, designated as B-6 , B-7 , <br /> B-8 , B-9 , B10 , B-11, and B-12 . Monitoring well and boring <br /> locations are shown on Figure 2 . <br /> • -3- <br />