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UST Closure Report November 10,2000 6425 Pacific Avenue Project No.3954 Stockton,Califcmia Page 1 1.0 Site Location and Description The Mason Center L.L.C. property ("the Site") is located at 6425 Pacific Avenue, in Stockton, California (Figure 1). The Site is owned by Lincoln Center Properties L.L.C. and was formerly operated as a gas station by Wickland Oil Company and Exxon USA Corporation. At present, Mason Center L.L.C. is redeveloping the site for use as a gas station and mini-mart. Three 10,000-gallon underground storage tanks (USTs) will be removed from the Site. These USTs will be replaced with two 20,000-gallon USTs. The topography on and around the Site is relatively flat and covered with pavement. The regional topography slopes very gently to the west. The surface elevation at the Site is approximately 12 feet above mean sea level. Reportedly, groundwater in monitoring well PZ- 001A, located about 30 feet north of the gas station property, is approximately 30 feet below grade (bg) (pers com, Farr Associates, October 3, 2000). The Site is located within the Lincoln Center Shopping Center, operated by Sims-Grupe Management Corp., Inc. 2.0 UST Removal and Disposal Wickland Oil Company installed the three double-walled fiberglass 10,000-gallon USTs in 1998. All three tanks failed a pressure test in August 2000. On November 1, 2000 these USTs were removed under a permit from the San Joaquin County Environmental Health Division (SJC- EHD). A copy of the UST Closure Permit from San Joaquin County is included in Appendix A. Mr. Kent Miller, City of Stockton Deputy Fire Marshal, observed measurement of the lower explosive limit(LEL) and oxygen concentrations in all tanks. Ms. Letitia Briggs of the SJC-EHD was present during removal of the USTs. W.A. Craig, Inc. destroyed the USTs onsite under the supervision of the City of Stockton Fire Department. W.A. Craig also transported and disposed of the USTs as non-hazardous solid waste at the Forward Landfill in Stockton on November 2"d and 3rd, 2000. Certification that the USTs were free of flammable vapors prior to removal is provided in Appendix B. Weigh tickets from Forward Landfill for the disposal of the USTs are included in Appendix C. 3.0 Soil Sampling and Analysis Methods and Procedures A work plan describing methods and procedures to collect soil samples beneath the three USTs was prepared and submitted to the SJC-EHD on October 6, 2000. The workplan was required because pea-gravel in the UST backfill at depths up to 25 feet bg. Due to the depth of the pea- gravel, native soil samples could not be collected with an excavator. After the USTs were removed, the excavation was backfilled to within 4 feet of surface grade. On November 3, 2000, a hydraulically operated drilling rig was used to collect native soil samples beneath the former USTs. Precision Sampling Inc. of Richmond California, a C-57 licensed contractor, provided the XD-1 hydraulic drilling rig and operators. Mr. Tim Cook of W.A. Craig, Inc. supervised drilling and sampling activities. Ms. Letitia Briggs of the SJC-EHD was present to observe sampling activities. \\Tom\&Central Project File\3954 Mason Stockton\UST Closure Report\UST Closure ReportAcc