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1.0 INTRODUCTION BP Oil Company (BP Oil) retained Alisto Engineering Group (Alisto) to conduct an investigation at former BP Oil Site No. 11195, 16500 South Interstate 1-5, Lathrop, California. A site vicinity map is shown on Figure 1, and an expanded site plan is shown on Figure 2. 1.1 Purpose and Scope of Work The additional investigation was performed to assess the extent of petroleum hydrocarbons in the subsurface soil and groundwater. The scope of work was based on the requirements set forth in a letter from the San Joaquin County Environmental Health Division (SJCEHD) dated February 20, 1998. The work plan was prepared by Alisto (Alisto, 1998a) and approved by the SJCEHD on June 12, 1998 . The tasks performed for this assessment included the following: • Drilled and logged five soil borings and collected soil samples. • Installed Monitoring Wells MW-8 through MW-12 and destroyed Monitoring Well MW-7. • Surveyed top-of-casing elevations for Monitoring Wells MW-1 through MW-6 and MW-8 through MW-12 to establish a datum. • Developed Monitoring Wells MW-8 through MW-12 and collected groundwater samples from 11 monitoring wells at the site. • Submitted soil and groundwater samples for laboratory analysis. • Performed recovery testing to calculate hydraulic conductivity in each monitoring well. • Conducted a potential receptor survey and search of wells within a 1/2-mile radius of the site. • Evaluated data and analytical results. • Prepared this report presenting the results and findings of the above tasks. 1.2 Site Location and Description The site is a retail gasoline outlet located on the southwest corner of the intersection of Louise Avenue and Harlan Road,Lathrop, California, and is doing business as a Union 76-branded facility. There are three underground storage tanks (USTs) onsite: one 10,000-gallon, one 8,000-gallon, and one 6,000-gallon tank. All three USTs are single-wall fiberglass,installed in 1983. A 500-gallon, fiberglass used oil UST was formerly located west of the building with a remote fill line located in the service bay. The used off tank and remote fill line were removed in 1997. There is a septic tank and drain field in the southwest corner of the site. A potable water supply well near the northwest quadrant of the site,was destroyed in Jule 1998 (BP Oil, 1998). R/4160 1