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1.0 INTRODUCTION <br /> This Preliminary Site Conceptual Model (PSCM) has been prepared by Thrifty Oil Co (Thrifty) <br /> ' to provide a detailed description of the extent of delineation of the soil and groundwater plume <br /> beneath the above-referenced site and surrounding area This PSCM was prepared based on a <br /> detailed review and compilation of data from historical and current assessment, remedial, and <br /> 1 monitoring activities conducted at the site The PSCM was requested by the San Joaquin County <br /> Environmental Health Department (SJCEHD) in a telephone conversation between Thrifty and <br /> the EHD on June 27, 2003, and was confirmed in a facsimile sent by Thrifty to the EHD dated <br />' June 27, 2003 <br /> The purpose of this PSCM is to construct a strategic framework for the effective and efficient <br />' implementation of environmental assessment and remediation activities associated with the <br /> petroleum hydrocarbon release beneath the site This strategic framework, which will be <br /> periodically updated as new data is collected, ultimately provides a comprehensive <br /> representation of the background of the release, the distribution of the release, sensitive receptors <br /> that may be potentially impacted by the release, and the potential effects of local <br /> geologic/hydrogeologic conditions on the distribution of the release <br />' 2.0 SITE DESCRIPTION <br /> Former Thrifty Oil Co Station#171 is located on the southeast corner of North Wilson Way, and <br /> East Harding Way in Stockton, California(Figure 1) This site is generally square and <br />' approximately 11,500 square feet in size Currently, the site maintains an existing kiosk <br /> structure in the central portion, three-associated pump islands dust south, also east and west of the <br /> structure, and three underground gasoline storage tanks east of the kiosk The three tanks each <br /> have the capacity of 10,000 gallons and store regular unleaded, unleaded plus, and premium <br /> unleaded gasoline The site is generally covered with asphalt, with concrete tank pad, pump <br /> islands, and concrete driveways located along both streets (Figure 2) <br />' 3.0 PREVIOUS SITE ASSESSMENT ACTIVITIES <br />' Previous site assessment and remedial work has been conducted at the site from 1987 to the <br /> present Tabulated soil and groundwater analytical data and boring logs from the assessment and <br /> monitoring activities are presented in Appendixes A, B, and C, respectively, and summarized <br />' below <br /> In December 1987, Hydrotech Consultants, Inc performed the initial site investigation at the <br />' site The investigation consisted of advancing four borings (B-1 through B-4) to depths of 20 <br /> feet below ground surface (bgs) adjacent to the underground storage tanks (USTs) Detectable <br /> concentrations of total petroleum hydrocarbons (TPH) were found only in the soil sample <br />' collected from boring B-4 at 10 feet bgs at 1,983 milligrams per kilogram (mg/Kg) <br />