SITE INFORMATION AND CORRESPONDENCE

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The laboratory analysis indicate that no detectable concentrations of hydrocarbons,including benzene, toluene, ethyl benzene and total xylene, exist within the excavation area, at the reported laboratory detection limits. However, since the initial excavation activities were performed, a small localized area of discolored soil at the bottom of the excavation area has developed. Based upon the site work performed to date, LOF and Condor believe that the bottom of the excavation area is less than one foot above the groundwater surface. Therefore, the area of discoloration is likely due to capillary action from the zone immediately above the groundwater. Based upon the results of the laboratory analysis of the soil samples obtained from the excavation area side-walls and bottom, LOF and Condor believe that sufficient evidence exists which indicates that the soil impacted by the fuel oil release has been substantially removed. LOF and Condor recommend that the remaining area of discolored soil located at the bottom of the excavation area be removed prior to backfilling the excavated area. The location and boundary limits of the discolored soil area will be mapped in order to assist with the excavation and sampling control. The discolored soil will be removed until the area is determined to be visually clean and confirmed by field screening with an organic vapor analyzer (OVA). The excavation area will be backfilled upon verification with the OVA that the soils located in the discolored area have been removed. LOF and Condor believe that further site investigations and future remedial activities, if required, are not contingent upon the existing excavation area remaining open. LOF and Condor believe that the request to backfill the excavation area is justified because; 1) laboratory analysis indicate that the majority of the impacted soil in the area of the release has been removed, 2) the existing excavation area poses an unnecessary safety risk, and 3) an open conduit to the groundwater will be eliminated by backfilling the excavation area. Therefore, based upon the reasons stated above, LOF is requesting RWQCB's concurrence to remove the localized areas of stained soil from the bottom of the excavation area, and backfill the excavated area, as soon as possible. An on-site borrow area to supply backfill material for the excavation area has been evaluated. The borrow area is located approximately 2000 feet south of the release site at an unimproved area of the Lathrop facility property (Figure I). Soil samples were collected from the borrow area and analyzed for; 1) extractable petroleum hydrocarbons by Method 3550 TEPH, 2) benzene, toluene, ethyl benzene, and total xylene (BTEX) by Method 8020, and 3) TTLC / STLC concentrations of the priority pollutant metals. Soil samples from six locations were collected and managed following the methods described in the Work Plan. The six soil samples were composited to form two samples for laboratory analysis. Three individual samples were combined to form one composite sample. The laboratory analysis indicated no detectable concentrations of hydrocarbons or BTEX exist at the reported laboratory detection limits. The TTLC and STLC metal concentrations are summarized in the attached table (Table 1).