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I - rea(ogicaf7echnits 2w. Page 5 1 Well Installation Report City of Escalon Project No. 750.2 r.x . January 30,2001 3.2 Geology and Field Observations The following section discusses the subjective field observations and geology documented during this investigation based on the interpretations of the field geologist. • The dominant soil type in the upper 75 feet of subsurface geologic soils investigated is I!, sand, with fine to coarse-grained texture. Varying amounts of silt and silty sand were encountered from borehole to borehole. • A couple laterally discontinuous clay lenses were encountered in a few of the boreholes. • Heaving sand was encountered at 75 feet in many of the boreholes. • A thick clay layer was encountered starting at 95-feet in SB-101 and continues to at least 11.5-feet. 1 • Groundwater was encountered at 60-63 feet. The capillary fringe did not appear to } extend up very far above the water table. The soil was generally moist from the surface ` to the groundwater interface. • None of the borings showed field evidence of contamination. 3 See Appendix B, Boring Logs for more inforination. 4.0 CONCLUSIONS AND RECOMMENDATIONS Based on our interpretation of the data collected over the course of this subsurface investigation, GTI has reached several conclusions. These conclusions are based on the premise that the data we considered, although incomplete, are representative of actual site i conditions. We acknowledge that there may be undiscovered conditions, which would upon their consideration, change our interpretation and thus our conclusions. Our recommendations are based on our knowledge of site conditions, and on the state and limitations of subsurface investigative technology. 4.1 Conclusions ill Geological Technics Inc., taking into consideration the data obtained from this investigation and from the data compiled during previous soil and groundwater investigations and the regular groundwater monitoring events, makes the following conclusions: 1. The soil plume is defined laterally by non-detects in MW-2, MW-3, MW-4 and MW-5. + 2. The soil plume is defined vertically by non- detects in MW-101. L3. The soil plume appears to be quite small in aerial extent, approximately 60'(W-E) by 70' (N-S); however, it is deep and contains high levels of petroleum hydrocarbons. 4. This area has been shown to be in the zone of influence for a soil vapor extraction system as proposed in the work plan dated October 31, 2000. } ..` Note: Further discussion of plume definition and site features are presented in the Remedial Action Plan — Revised, that will be submitted shortly.