ARCHIVED REPORTS_REMEDIAL ACTION DOCUMENT

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REMEDIATION COMPLETION REPORT-LATHROP DEHYDRATOR STATION 3.0 FIELD ACTIVITIES The top four feet of material(approximately 250 cubic yards) excavated from the agricultural field east of the property fence was stockpiled to the north of the excavation and along the eastern side of the fence for later reuse.Two composite samples (samples 90Stockl &90Stock2)were taken from the stockpiled native agricultural soil and analyzed for TPH-d, TPH-mo and TPH-g/BTEX to confirm that the material was free of petroleum hydrocarbons. No petroleum hydrocarbons or BTEX were detected above reporting limits in either sample. 3.6 Verification Sampling Verification soil samples were collected from the bottom and side walls of the excavation area and analyzed to document soil conditions prior to backfilling.The goal of the excavation was to remove,to the extent feasible within site constraints,soil containing petroleum hydrocarbon concentrations above the preliminary remedial cleanup goals.These goals are 10 mg/kg for TPH-g,100 mg/kg for TPH-d,1,000 mg/kg for TPH-mo,and non- detect for BTEX (not applicable if TPH-d and TPH-g are below their respective criteria), based on the Leaking Underground Fuel Tank models and the RAD (CH2M HILL 2003). Approximate locations of verification samples were determined by overlaying a 20-foot- square 0-footsquare grid system onto the excavation area.Actual sample locations were determined in the field by the field geologist to sufficiently characterize the excavation boundaries (Figure 4).Sample identifications were assigned based on the location and depth of the sample, and the order in which the samples were collected.Soil samples were analyzed for TPH-g and BTEX (EPA Methods 5030 and 8260) and TPH-d and TPH-mo (EPA Methods 8015 and 3550 Modified)by an on-site mobile laboratory (Mobile Chem Labs,Inc.).To ensure that high quality data were obtained,field and laboratory quality assurance/quality control (QA/QC) protocols were used. Sampling activities are summarized below and results of analytical testing are included in Tables 1 and 2.The approximate locations of verification samples are illustrated on Figure 3. A total of 31 soil samples were collected from the excavation during construction.The samples comprised the following: • 24 final verification samples(17 were collected from the perimeter side walls and 7 were taken from the bottom of the excavation). Analytical results are presented in Table 1. • 7 over-excavation samples (used to identify localized areas where further excavation was warranted).Two of the over-excavation samples (sampled at 8.5 feet bgs and 10 feet bgs)were not analyzed because neighboring samples collected at greater depths indicated low or no detectable levels of contamination. Analytical results are presented in Table 2. Analytical reports and chain-of-custody documents are included in Appendix D. Highlights of the results are summarized below: • 18 of the 24 final verification samples indicated concentrations that were below their respective preliminary remedial cleanup goals. SFOILATHROPCOMPLETIONREPORT 12-1.04.DOC 8