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Manteca Unified School District ' 2901 E. Louise Ave., Lathrop, California Remedial Excavation Report Page 2 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 was and floor to define the residual contamination at the end of the remedial excavation attempt (Figure 3, Tables I & 2) Uncontaminated overburden was stockpiled to the southeast of the site(Figure 2), sampled(ND), and replaced at appro\imately 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 sod are stockpiled ' 31 Soil Sampling P g ' Soil samples were taken in 1" by 6" brass sleeves from relatively undisturbed soil Soil samples were collected from the floor and walls of the excavation with a backhoe or excavator The laboratory samples did not have head space and were immediately ' sealed in their liners using aluminum foil-lined caps The samples were then immediately delivered to the on-site State certified mobile laboratory, Sparger Technology, Inc, Sacramento, CA, or stored in a cooler with Blue Ice antil tuned over to lab personnel Soil samples collected for laboratory analysis were analyzed using method 3015 for ' TPH Diesel and TPH Gasoline, and methoa 8020 for BTEX Five (5) selected samples were collected, under the direction and supervision of San Joaquin County Health Department personnel, for 8240 GCMS analysis (Table 2) The 8240 analyses were done at the Sacramento laboratory Those samples were either taken by the 1