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*410/ 14./ Di Salvo Truck Lines-Sal ` March 9, 1995 Page-9. above the reported laboratory detection limits in SP1, SP2 and SPA, and BTEX constituents were not law detected in SP1. BTEX constituents were not detected in the trip blank at or above the reported laboratory detection limits. 6. L Based on the laboratory analyses of the soil and groundwater samples collected from the site, the vertical extent of soil contamination extends to the capillary zone and the groundwater quality has been impacted by BTEX constituents and diesel. Laboratory analyses of soil samples collected from SPI 6. indicate the lateral extent of soil contamination above the groundwater has been fully investigated southeast of the former UST locations. Laboratory analyses of soil samples collected from SP3 and SP4 6 indicate soil contamination may not extend a significant distance beyond the locations of SP3 and SP4 northwest and west of the former UST locations. The estimated lateral extent of soil contamination L northwest, southeast and west of the former UST locations is shown in Figure 2, Appendix A. A chemical concentration map of groundwater samples collected from SPI, SP2 and SP4 is shown in Figure L 3, Appendix A. L7.0 RECOMMENDATIONS Based on the difficulty of in-situ remediation of Idiesel contaminated in soils containing a high Lpercentage of clay size particles, the estimated lateral extent of soil contamination at the site and the absence of buildings near the estimated extent of soil contamination, Condor recommends the existing L diesel contamination in the soil be investigated and removed by over-excavation. The estimated volume of soil to be removed, assuming an average over-excavation depth of 12.0 feet bgs, would be approximately 1,500 cubic yards. The estimated total volume of soil does not include the clean material used to backfill the former UST locations. L The over-excavation should be directed in the field based on PID measurements and visual Lobservations of the excavated soil and the physical limitations of the site. The over-excavation should proceed, as feasible, until laboratory analyses indicate non-detectable concentrations of diesel in soil Lsamples collected from the excavation sidewalls. The soil samples should be analyzed for, unless directed otherwise by SJCPHS,EHD, BTEX and TEPH using U.S. EPA and California approved methods under Lstrict quality assurance measures. The over-excavated soil suspected of hydrocarbon contamination should be transported to a disposal facility or placed on and covered with plastic sheeting to await disposal and/or i L L `� CONDOR