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S E C O R Mr Ed Ralston February 12, 2003 Page 2 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 boring samples reported maximum concentrations of 6,800 ppm TPHG in MW-3-16' and 7 2 ppm MtBE in MW-2-11' Groundwater samples collected from newly installed wells contained 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 samples reported maximum concentrations of TPHg and MtBE of 473 ppm (MW-9-10') and 0 119 ppm (MW-6-20'), respectively Groundwater samples collected from the newly installed wells 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 %2-miles radius of the site The closest wells to the site are located approximately 0 15 mile west/southwest (upgradient) of the site The nearest downgradient wells are located approximately 0 3 northeast of the site (IT, 2001) Groundwater monitoring has been performed at the site since August 1998 In the fourth Quarter 2002, groundwater samples contained concentrations of TPHg in excess of 10,000 ppb in wells MW- 1, MW-5, MW-7, and MW-9 The highest concentrations of benzene and MtBE reported at 240 ppb and 230 ppb, respectively Groundwater flow was to the east northeast with a gradient of �l approximately 0 001 ft/ft SCOPE OF WORK Between June 2002 and November 2002, SECOR performed three phases of off-site assessment at the site The Initial phase was conducted on June 5, 2002 and consisted of the advancement of five geoprobe borings (GP-1 through GP-5) Based on the soil and groundwater analytical results from GP-1 through GP-5, SECOR performed the second phase of offsite assessment on June 21, 2002 The second phase of off-site assessment consisted of four additional step-out geoprobe borings (GP- 6 through GP-9) The final phase of offsite assessment, conducted in November 2002, consisted of the Installation of six groundwater monitoring wells (MW-10 through MW-15) The purpose of the work was to delineate the lateral extent of petroleum hydrocarbon impact in soil and groundwater beneath the site As required by the Occupational Health and Safety Administration (OSHA) Standard "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), SECOR prepared a site-specific Health and Safety Plan (HASP) Prior to the commencement of fieldwork, the HASP was updated with appropriate field personnel and subcontractor information The field staff and contractors reviewed the HASP before beginning field operations at the site The completed scope of work Is discussed below • Permitting Prior to initiating work, SECOR obtained soil boring and well installation permits form SJCEHD and encroachment permits form the City of Lathrop SJCEHD soil boring and 11ConocoPhdiips\Tosco Marketmg112051Reports\AssmtRpt doc