SITE INFORMATION AND CORRESPONDENCE_CASE 2

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was terminated before PID readings decreased to zero. One area in the northwest corner was deepened to 23 feet and disclosed groundwater contamination. PID readings showed the south wall to be clean. It was decided to deepen the excavation in that area and work to the north, backfilling with pea gravel to prevent the loose cross-bedded fluvial sand at 8 to 12.5 feet (Appendix A) from caving further. A de-watering well was installed to 24 feet in the southeast corner and pumped into a 7,500 gallon surface tank. Later lab analysis showed this water to be non detect (ND) for BTEX, TPH- gas and TPH-diesel. Neither water sample was analyzed for 8240 GCMS, by direction of San Joaquin County Health Department personnel, as amended by addendum Number One, Item 5. An area of approximately 20 by 35 feet at the south end was deepened to 23 feet (Figure 3). Two floor samples at 23 feet were taken and analyzed by an on-site mobile laboratory. Results showed the south wall and adjacent floor to be clean, but contamination was detected to the north. Because of groundwater contamination, (Table 1), the high de-watering volume, and the district's budget restraints it was decided to limit the remainder of the vertical excavation to the water table (16 feet), and remediate the groundwater at a later date. Excavation continued to the north and west of the original tank removal site down to the water table. PID readings and visual inspection noted high contamination below the fuel island pumps (between Tanks 2 & 3), and the former Tank 1 area (Figure 7). Sufficient samples were obtained, under the direction and supervision of San Joaquin County Health Department personnel, from the walls and floor to define the residual contamination at the end of the remedial excavation attempt (Figure 3, Tables 1 & 2). Uncontaminated overburden was stockpiled to the southeast of the site (Figure 2), sampled (ND), and replaced at approximately the same elevation during backfilling. Contaminated soil was trucked to the northeast of the property (Figure 1) near the railroad tracks and stored on visqueen for later treatment. Measurements and calculations estimate 1,600 cubic yards of soil are stockpiled. Figures, Appendices, and Tables can be found in the attachments.