ARCHIVED REPORTS_REMEDIAL ACTION DOCUMENT

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REMEDIATION COMPLETION REPORT-LATHROP DEHYDRATOR STATION 3.0 FIELD ACTIVITIES • Benzene,toluene,ethylbenzene,and total xylenes were non-detect in all 24 final verification samples. • TPH-g and TPH-mo were also non-detect in all 24 final verification samples. • TPH-d was non-detect in 13 of the 24 verification samples.TPH-d was above the preliminary cleanup goal of 100 mg/kg in six of the 24 samples,with the highest concentration of 1,000 mg/kg in sample 90SW8-9.This side wall sample was an off-site location, taken at 9 feet bgs near the southeastern corner of the excavation).Samples 90SW18-8,90SW17-10,and 90SW13-9 (collected within approximately 15 feet on either side of sample 90SW8-9) contained TPH-d at concentrations of non-detect,530 mg/kg, and 92 mg/kg,respectively. 3.7 Backfilling The excavation was backfilled by placing three-quarter-inch subrounded drain rock from the base of the excavation(13 feet bgs)to approximately 6 feet bgs.A woven geotextile fabric was then placed over the drain rock.Class II aggregate base rock fill was placed in loose uncompacted 12-inch lifts and compacted to achieve a minimum 95 percent relative compaction per American Society for Testing and Materials (ASTM) standard ASTM D1557 (ASTM 1997). Two truck loads of bedding sand were brought in to place around the approximate 30 feet of exposed active gas lines. Backfilling continued with the Class 11 aggregate base to restore original site grades. The eastern portion of the excavation (east of the fenceline) was backfilled with three- quarter-inch drain rock from approximately 10 feet bgs to 3 feet bgs.Previously stockpiled agricultural soil was then placed from 3 feet bgs to the original grade. The results of the compaction testing are included in Appendix E. The top 3 feet of the eastern portion of the excavation where native soil was replaced was rolled and not tested because this area is outside the station and is for farmland use. 3.8 Final Site Grading and Restoration The station pad was restored by scraping/blading the ground surface with a loader scraper to create a nominal slope to the south to facilitate drainage toward the road drainage ditch. Three-quarter-inch surface drain rock was then placed across the Site to match existing station grades. Agricultural material was placed with a skip loader to match existing grades to the east of the fenceline. New permanent fencing and entry gate were installed to replace sections that were removed for construction activities. Figure 4 illustrates the final condition of the Site. Representatives of San Joaquin County inspected the Site,approved the final restoration and approved completion of the grading permit. Photographs of the Site construction activities are provided in Appendix B. SFOILATHROPCOMPLETIONREPORT 12-1-04.DOC 9