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1 <br /> Geofogicaf7echnics Inc. Page 3 <br /> F . City of Escalon <br /> Project No. 750.3 <br /> February 26,2001 <br /> The vertical distribution of contamination in the vadose zone is illustrated in Figures 3a and <br /> 4a. The vertical distribution of groundwater contamination is defined by the depth of the <br />} water table and the bottom of the well screen in deep well MW-101 (62 - 89 feet bgs). The <br /> bottom of well MW-101 was presented as the vertical extent due to the presence of TPH-G <br /> contamination in the well during the December 1, 2000 sampling event. <br /> Mass balance calculations for TPH-G in soil and groundwater are included in Table 4. The <br /> following assumptions were utilized in the calculations: <br /> • The average contaminant concentrations for soil zones 1 2 & 3 and the <br /> - groundwater <br /> plume, were derived by averaging TPH-G.data from within the zones (one half of the <br /> detection limit was used for ND values). <br /> ,,; • The area of each zone was calculated by the CAD software program, which was utilized <br /> I to draw the zones. <br /> Lrr • The volume of soil excavated from the UST and dispenser areas, 270 cubic yards (or <br /> '7290 cubic feet), was subtracted from the calculated volume of Zone 1. The excavation <br /> areas are illustrated in Figure 8. <br /> r • .,The density of soils was adapted from Watson and Burnett, 1995. <br /> L• • The porosity of the saturated zone (35%) was adapted from Driscoll, 1986. <br /> �� • The soil data from the UST and dispenser excavations are from Wright Environmental <br /> Services, Inc. report 12/30/98. <br /> r The estimated amount of TPH- G mass present in soil and groundwater is 4500 kg (1600 <br /> L gallons). <br /> i <br /> 2.0 FEASIBILITY STUDY <br /> The following discussion is intended to meet the requirements of CCR, Title 23, Div. 3, <br /> Chapter 16, 2725 (d)(2). Soil cleanup alternatives shall be evaluated first with a discussion <br /> C of water cleanup goals to follow in section 2.3. <br /> 2.1 Proposed Vadose Zone Cleanup Alternatives <br /> i Three cleanup alternatives have been considered during the course of this investigation- <br /> 0 Excavation and disposal of the impacted soils <br /> C, • Remediation by natural attenuation. <br /> r • Soil vapor extraction <br /> It is important to keep in mind that the contemplation and use of these methods has been <br /> influenced by factors including the removal of the former underground storage tanks <br /> fi (USTs) at the site and the City of Escalon's efforts to widen and regrade Escalon Avenue. <br /> f <br /> t <br /> i <br />