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ENVIRONMENTAL INVESTIGATION REPORT L INVESTIGATION REPORT Unocal Service Station No 5886 n No 5886 2701 West March Lane L ine Stockton,California Delta Project No D095-066 195-066 ' Page 6 4 1 4 Unauthorized Release Reports removal of the crushed rock and backfill, the canopy areas were sampled Five soil On August 8, 1995, Unocal submitted an Underground Storage Tank Unauthorized Release (Leak) ollected from each of the canopy areas and submitted to Sequoia for chemical analyses ' Contamination Site Report (URR, form HSC 05) to the SJCEHD This report was submitted following Itlons and chemical analyses requested were performed at the direction of SJCEHD Soil verbal notification to SJCEHD on August 4, 1995 At SJCEHD's request, Delta prepared and submitted )llected from the base of each sidewall and the base of each excavation The location of an additional Unauthorized Release Report dated August 24, 1995 are presented in Figure 4, Canopy Footing Soil Sample Locations ' 4 2 Canopy Footing Backfilling. Removal of Drain Rock, and Soil Sampling iopy Footing Soil Sample Analytical Results Following the soil sampling of the canopy footings, they were backfilled by Earth Systems Engineering e was submitted under chain-of-custody documentation to Sequoia for analyses of TPH ' Group of Tracy, California A layer of filter fabric was placed at the bottom and approximately four to TPH as diesel using EPA Method $015 Modified and BTEX using EPA Method 8020, five feet of 314 inch drain rock was used to bring the bottom to approximately four to five feet below naIytical results did not report benzene in any sample above the laboratory's limits of surface grade (bsg) A second layer of filter fabric was placed over the drain rock and the remaining area iluene and ethylbenzene were reported separately in soil samples at 0 0052 was backfilled and compacted with clean imported fill ,ram (mg/kg) and 0 059 mg/kg, respectively Concentrations of total xylenes were sample at 0 0055 mg/kg Detectable concentrations of TPH as gasoline and TPH as On August 18, 1995, Delta submitted a Work Plan for Corrective Action and a subsequent Addendum to )rted in some samples and are presented in Table 3, Canopy Footing Sample Results Work Plan for Corrective Action, dated August 23, 1995 to perform confirmation soil sampling as laboratory analytical reports and chain-of-custody documentation are presented in requested by SJCEHD on August 15, 1995 Approval of the proposed work was received in a letter dated August 23, 1995, from the SJCEHD ).Debris Sampling On September 22, 1995, approximately 30 cubic yards of crushed rock and 30 cubic yards of imported 95, Delta collected soil samples from construction debris/soil generated at the site during ' backfill were removed from the area of the former northern and southern canopy footings and stockpiled ties Four Boll samples were collected per approximately every 100 cubic yards of sail on-site Approximately 10 cubic yards of the crushed rock was reused (following confirmation with into one sample by the laboratory prior to chemical analyses The soil samples were ' SJCEHD) in the base of the two pits due to the potential infiltration of ground water The remaining i as gasoline, TPH as diesel, and BTEX using the previously described methods TPH crushed rock and backfill material was stockpiled on-site and sampled for disposal BTEX were not reported above the laboratory's limits of detection from any sample ' ions (2 4 mg/kg to 9 2 mg/kg) quantified as an unidentified hydrocarbon >C 10 were Stockpiled soil was sampled on September 27, 1995, as per the requirements outlined in SJCEHD letter the TPH diesel analyses Sequoia verbally indicated that although the samples were ' dated August 23, 1995, and the methods described in Appendix B Following characterization and t a fresh diesel standard, the chromatograms were not similar to diesel and may have authorization from the SJCEHD, the soil was transported to Forward Landfill for disposal A copy of ve of traces of asphalt or plant debris A tabulation of the analytical results are presented the landfill authorization is included in Appendix D ;opies of the laboratory reports and chain-of custody documentation are presented in RPT160 STS RPTI60 S7S