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Phillips 66 Company 2 T Stag n#1205,16470 Cam Street Lathrop,CA Febru 19 2 2 In July1998, one Geoprobe TM boring was advanced to a depth of 40 feet below ground • surface (bgs) downgradient (north) of the former UST excavation Laboratory analysis of soil reported maximum concentrations of TPHg and MtBE of 1,900 ppm(GP-1-10') and 0 31 ppm (GP-140'), respectively Laboratory analysis of groundwater reported concentrations of TPHg and MtBE of 52,000 ppb and 61 ppb, respectively (PEG, 1999) From August through September 1998, IT Corporation (IT) drilled and installed four groundwater monitoring wells (MW-1 through MW-4) to approximate depths of 26 to 28 feet bgs During the installation of well MW-4, the drill auger broke through a city of Lathrop water main releasing approximately 600,000 to 1,000,000 gallons of water Laboratory analysis of soil reported maximum concentrations of TPHg and MtBE of 6,800 ppm (MW-3-16') and 7 2 ppm (MW-2-1 F), respectively Laboratory analysis of groundwater reported maximum concentrations of TPHg and MtBE of 29,000 ppb (MW-1) and 4,000 ppb (MW-2), respectively (PEG, 1999) In December 2000, IT drilled and installed five groundwater monitoring wells (MW-5 through MW-9) to approximate depths of 24 feet bgs Laboratory analysis of soil reported maximum concentrations of TPHg and MtBE of 473 ppm (MW-9-10') and 0 119 ppm (MW-6-20'), respectively Laboratory analysis of groundwater reported maximum concentrations of TPHg and MtBE of 72,000 ppb (MW-6) and 750 ppb (MW-6), respectively (IT, 2001) In March 1999, IT performed a Sensitive Receptor Survey and reported 12 wells within a • 1/2-miles radius of the site The closest wells to the site are approximately 0 15-mile west/southwest (upgradlent) of the site The nearest downgradient wells are located approximately 0 3 northeast of the site (IT, 2001) Groundwater monitoring has been performed since August 1998 Fourth Quarter 2001 groundwater monitoring reported high concentrations ( 10,000 ppb) of TPHg in wells MW-1, MW-5, MW-6, MW-7, and MW-9 The highest concentrations of benzene and MtBE were 780 ppb (MW-7) and 660 ppb (MW-6) Groundwater flow was to the northeast with a gradient of approximately 0 001 ft/ft Depth to groundwater ranged from 12 50 (MW-9) to 14 32 (MW-3) feet bgs (GR, 2001) PROPOSED SCOPE OF WORK Task 1 --Pre-Event Activities Prior to conducting the DPE event, SECOR will submit a letter of notification to the San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD) SECOR will also prepare a site-specific Health and Safety Plan (HASP) The HASP is required by the Occupational Health and Safety Adrrvmstration (OSHA) "Hazardous Waste Operations and Emergency Response" guidelines (29 CFR 1910 120), and by California Occupational Health and Safety Administration (Cal-OSHA) "Hazardous Waste Operations and • Emergency Response" guidelines (CCR Title 8, Section 5192) The Health and Safety File TOSCO112051MTS11205-5-Day DPE Work Plan doe