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i GeologicaC7ecFuiics Inc. Page 2 City of Escalon Project No. 750.3 February 26,2001 L1.1 Site Geology and Field Observations The following section discusses the subjective field observations and geology documented ! L during this investigation based on the interpretations of the field geologist. L ! • `The dominant soil type in the upper 75 feet of subsurface geologic soils investigated is sand, with fine to coarse-grained texture. • Varying amounts of silt and silty sand were encountered from borehole to borehole. • Laterally discontinuous clay lenses were encountered in a few of the bofeholes. • Heaving sand was encountered at 75 feet in several of the boreholes. - •L A thick clay layer was encountered starting at 95-feet in SB-101 and continues to a depth of at least 115-feet. _ The lithology of the site is illustrated in cross section Figures 3 and 4. Refer to Figure 2 for cross section location. 1.2' Site Hydrology Four groundwater sampling/monitoring events have been completed for the investigation- April 18, July 14, September 1, and December 1, 2000. The average groundwater elevation on December 1, 2000 was about 56 feet above MSL, which corresponds to about 62 feet below ground surface. This depth is consistent with the previous events. Groundwater gradients calculated for the events indicate that groundwater flows to the west-northwest at gradients ranging 0.0023 — 0.0025 ft/ft. This data is summarized in Table 1, Appendix A. Historical groundwater directions and gradients are presented in Figure 5: Groundwater Gradient Rose Diagram. For the December 1, 2000 event, the vertical gradient was calculated for the MW-1/MW- 101 pair. The vertical gradient was negative (a downward direction) and an order of magnitude greater then the horizontal gradient of the water table wells(Table 6).- 1.3, Contaminant Distribution/Mass Balance Calculations Tables 1 & 2 contain soil and groundwater analytical data compiled to date. The extent of TPH-G, BTEX and MTBE in soil are illustrated in Figures 6a, 6b, and 6c for the following C depths: • 0—25' (Zone 1) • 25' — 50' (Zone 2 • 50' —65' (Zone 3) The contour line depicting the extent of the contamination in these illustrations is halfway Y between confirmed detect versus non-detect sampling points. The concentration depicted for each point is the average for each sample/boring — i.e., averaged vertically in the zone profile. The extent of TPH-G, BTEX and MTBE in groundwater is illustrated in Figure 7 utilizing the data from the 12/1/00 sampling event and the 2/12-23/99 hydropunch sampling event. a L