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' SOIL Exr-AVATION AND SUBSURFACE INVESTIGATION RESULTS REPORT 32 TCkay Street Lom Cahforrna ' A generalized cross section of the soil beneath the excavation and budding is shown on Figure 4 This figure indicates the subsurface consists primarily of sandy and clayey silts ' to a depth of 30 feet below grade An approximately 3-foot-thick silty sand layer was noted at a depth of approximately 24 feet A discontinuous sand layer was also reported from approximately 14 to 16 feet below grade ' 3.6 Analvfical Results: Soil Boring Samples A total of twelve soil samples were analyzed by Sparger for concentrations of TPH, as gasoline and diesel, and BTEX The analytical results are summarized in Table 3, and shown on Figures 4 and 5 The laboratory analytical reports and chain of custody forms are included in Appendix F TPH, as diesel, was detected only in the soil sample collected from the angled boring AB at a vertical depth of 14 5 vertical feet beneath the warehouse No detectable TPH, as gasoline, or BTEX were reported in this sample All other sod samples did not contain petroleum hydrocarbon concentrations above the practical quantitation reporting limits outlined in the "Tri-Regional Board Staff Recommendations for Preliminary Evaluation and Investigation of Underground Tank Sites" (August 10, 1990) I4.0 DISCUSSION AND RECOMMENDATIONS The investigation results indicate significantly impacted soil (greater than 100 ppm TPH, as diesel) has been removed from the site, except at a depth of approximately 8 to 15 feet beneath the warehouse building The excavation of this soil is not practical Aegis recommends no further action at the site based on the following factors • The impacted soil does not appear to extend vertically beyond approximately 15 feet below grade • Groundwater is documented to be present in the area at 50 to 60 feet below I grade • The subsurface soils beneath the impacted soil consist mainly of relatively impermeable materials (silts) r Analytical results indicated the presence of highly weathered, relatively insoluble r hydrocarbons None of the more mobile and soluble hydrocarbon constituents r (BTEX) were detected 1 The area is paved and beneath a building Very little water may be expected to t come in contact with the impacted soil 1 These considerations indicate the soil has low leaching potential and may be left in place without threatening groundwater 92-074A ERR 5-