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Working To Restore Nature The closest surface water to the site is Duck Creek, 113 of a mile to the southeast Mormon Slough is approximately 1 mile to the north The piezometric level of groundwater has been ' reported to be between 45 and 55 feet below the surface at the site (San Joaquin County Flood Control and Water Conservation District, 1989 data) Municipal wells typically seal off the first 100 to 250 feet because the upper zones of saturation do not meet quality standards or do not provide sufficient quantity to be developed, (Bulletin 146, California Department of Water Resources, 1967) Therefore, it is highly unlikely the fuel components at this site have affected or will affect drinking water supplies ' There is one supply well on the subject property All water for the site, including sinks and restrooms in the office, is supplied by the well The location of the supply well is shown on Figure 2 Well locations within a 112 mile radius of the site were requested from the Department of Water Resources A well, identified as 01N07E17M, is located approximately 400 feet east of the project site This well is screened from 144 to 176 feet below grade and tis not expected to be affected by activities associated with this tank closure INVESTIGATION HISTORY Soil Investigation - June 15, 1990 On June 15, 1990, RESNA personnel (formerly WaterWork) advanced two angled soil borings (ASB-1, ASB-2) beneath the existing tank The location and orientation of the borings are depicted on Figure 3 These borings were advanced at 45° from vertical and terminated beneath the longitudinal centerline of the tank approximately 5 feet beneath the tank bottom The results of the initial phase of investigation were presented in a report entitled, "Underground Fuel Tank Abandonment Contaminant Assessment Report," dated July 30, 1990 Analytical results of soil samples collected from Boring ASB-1 showed significant concentration ' of gasoline hydrocarbons at 15 5 and 21 feet along the boring length This corresponds to approximately 11 and 15 vertical feet below grade, at the fill end of the tank Laboratory analysis of soil samples collected from ASB-2 at the opposite end of the tank recorded very low levels of contamination The absence of significant contamination at this end of the tank indicates that soil contamination is localized at the fill end of the tank Soil contamination at the ' site is likely due to overspill during routine filling of the tank Laboratory results are summarized in Table l Analytical data sheets are included in Appendix I ' Soil and Groundwater Investigation - January 15-16, 1991 On January 15, and 16, 1991 to further define the vertical extent of contamination, two additional angle soil borings (BJJS-ASB1 and BJJS-ASB2) were advanced beneath the existing M 11500661REPORTb1WP-0794 FNL 2