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1 0 • <br />September 11, 2000 <br />' 50441 <br />Mr. Vidal Pedraza Harding Lawson Associates <br />San Joaquin County Public Health Service <br />' Environmental Health Division (PHS/EHD) <br />Page 6 <br />' ETBE, and TAME were detected above the normal respective laboratory reporting limits. For the tank sand <br />stockpile composite sample (SP2A,B,C,D), TPHd was detected at a concentration of 4.6 mg/kg, whereas <br />TPHg, BTEX, and MTBE were not detected above normal method reporting limits. Lead was detected in all <br />' samples, with concentrations ranging from 12 to 26 mg/kg. <br />BACKFILL, COMPACTION, AND DISPOSAL ACTIVITIES <br />After receipt of the analytical results, the excavation was back-filled with the stockpiled native soils and <br />clean imported fill. This process proceeded in lifts of 0.5- to 1.0 -foot thick within the formed area shown in <br />' Plate 3 to a depth of approximately one -foot bgs. Lifts were compacted to approximately 90 percent relative <br />compaction with a hand-held compactor (whacker). Backfill materials consisted of clean native soil and <br />additional clean imported Class II aggregate base fill material as necessary. Compaction curves on the clean <br />native soil (HLA provided) and on the Class II aggregate base material (Granite Construction) were utilized <br />with a Troxel nuclear density gauge to assess adequate relative compaction. Copies of the compaction <br />curves and the compaction test results are included as Appendix B. Following completion of compaction <br />' testing, Newark Sierra contracted the placement of a concrete slab within the formed area shown in Plate 3. <br />The pieces of the three USTs and the stockpile of tank sand were properly manifested and transported to <br />' Forward Landfill in Stockton, California. Copies of the waste manifests, the Tank Closure Certification <br />form, and the PHS/EHD UST Disposition Tracking Records for the three tanks are included as Appendix C. <br />As previously discussed, no product was present in the USTs, no piping was present, and no rinseate was <br />' generated by the UST -cleaning process. <br />SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS <br />Based on the information and analytical results discussed above, HLA presents the following summary, <br />conclusions, and recommendations: <br />• The analytical results on the three UST -removal soil samples and on the composite sample of the <br />stockpiled native soil did not indicate the presence of detectable concentrations of any analytes above <br />normal respective reporting limits. <br />' • The analytical results on the composite sample from the tank -sand stockpile indicated a TPHd <br />concentration of 4.6 mg/kg. <br />' • No water was observed within the excavation at any time. <br />• The dismantled pieces of the three 500 gallon steel single -walled USTs (two whole and one partial) and <br />the approximately 10 cubic yards of sand from within the USTs (tank sand) were properly transported in <br />' accordance with environmental and transportation regulations and disposed of at Forward Landfill, in <br />Stockton, California. No piping was present when the USTs were discovered nor was any observed <br />during subsequent excavation and removal of the USTs. <br />' • No product was present in any of the USTs and no rinseate was generated during cleaning of the USTs. <br />• The excavation was appropriately back-filled, compacted, and then resurfaced with a concrete slab. <br />1 <br />