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borings, and the construction of two vapor extraction/inlet wells (W-7, W-8). During this l investigation unanticipated impacts were found to exist outside of the former tank bed. The data for this assessment is found in the document,Environmental Assessment Report, dated June 14, 1994. In December 1994, an additional site assessment was conducted by SECOR to verify the extent of _.- petroleum hydrocarbons in soil at the site. This investigation involved the drilling of five soil borings, and the construction of four groundwater monitoring wells (MW-1, MW-2, MW-3, and MW-4). The data for this assessment is contained in the document, Environmental_Investigation Report, dated May 4, 1995. 3.0 SCOPE OF WORK =� 3.1 Pre-field Activities Prior to conducting any Site activities,SECOR implemented a Site Specific Health and Safety Plan as required by 29 CFR 1910.120. The health and safety plan detailed field procedures regarding various potential health and safety hazards that may be encountered during site activities. All personnel contracted for the field investigation were required to review and understand this plan. SECOR obtained the necessary permits required by San Joaquin County Public Health Services, Environmental Health Division(PHS/EHD) for the installation of groundwater monitor wells. An off-site encroachment permit was obtained from the State of California-Department of ,F J Transportation (Caltrans). In addition, a utility clearance was conducted to safeguard that the -� drilling activities would not impact any subsurface utilities. The clearance involved retaining a private locating service for locating and marking underground utilities on and off-site. Underground .rj Service Alert (USA) was notified 48 hours before the drilling start date for clearing and locating public utilities off-site. t='1 3.2 Soil Borinus On July 15, 16, 17, 18, and 31, 1996,SECOR supervised the drilling of six soil borings at the site. C= The approximate location of these borings and other selected site features are shown on Figure 2: k<' Soil borings MW-5,MW-6,MW-7,MW-8, and MW-9,were advanced to a depth of approximately 100 feet bgs using a CME-75 drill rig equipped with 8.0-inch outside diameter hollow-stem augers -, operated by Mitchell Drilling Environmental Corporation of Rancho Cordova, California. Due to ` low clearance from overhead power lines, soil boring MW-10 was advanced to a depth of approximately 100 feet bgs using a limited access rig equipped with 8.0-inch outside diameter hollow-stem augers operated by West Hazmat Drilling Corporation of San Francisco, California. 3.3 Soil Sampling During drilling, all soil samples and drill cuttings were logged by the field geologist and described in accordance with the Unified Soil Classification System. In addition, all soil samples and drill cuttings were field screened for volatile organic compounds using a photoionization detector (PID) equipped with a 10.6 eV lamp calibrated to an isobutlyene standard. These readings and any subjective evidence of petroleum hydrocarbon were recorded on the boring logs (Appendix A). I ` Job No-10710-001-01 2 SECOR LOCKEFOKD.[NV OdaberQ 1996 I I I r