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a , Project No 58100-06-18 June 21, 1995 Page 2 Placer Tractor Service Samples collected from native soil beneath the former gasoline/diesel fuel USTs indicated the presence of residual TPHg in soils at concentrations ranging from 2 2 to 3,700 mg/kg Soil analytical data relative to the UST removals is summarized in Table I Additional investigation was performed between April 1989 and March 1990 by WCC which consisted of the installation of five additional groundwater monitoring wells (MW-5 through MW-9) and the collection and chemical analysis of both soil and groundwater samples Soil analytical data indicated that TPHg was not detected in soil samples collected at depths ranging from approximately 5 feet to 55 feet below ground surface (bgs) at lateral distances ranging from 45 to 220 feet from the former USTs Analytical data also indicated the presence of TPHg in groundwater at concentrations ranging from 1 9 to 3 4 mg/l, respectively Alton Geoscience (Alton) installed three new groundwater monitoring wells (MW-10 through MW- 12) and drilled two soil borings (AB-1 and AB-2) in April 1992,and Environmental Assessors, Inc (EA) installed six monitoring wells (MW-13, MW-14, MW-16, MW-19, MW-20 and MW-24) and drilled four soil borings (SB-15, SB-17, SB-18 and SB-22) in October 1993 to complete characterization of site conditions Alton also performed a limited vapor extraction pilot test in September 1992 to evaluate the feasibility of using soil vapor extraction as a remediation alternative • The most recently completed groundwater monitoring event was performed by Nmyo and Moore (N&M) in May 1994, and consisted of the purging and sampling of wells MW-10 through MW-24 Wells MW-1 through MW-6 were dry in May 1994 due to declining groundwater elevation levels and could not be sampled Other work completed by N&M concurrent with the groundwater monitoring event included the abandonment of wells MW-1 through MW-8 and MW-10 These wells were abandoned due to the declining groundwater elevations In addition, wells MW-9, MW- 11, MW-13, MW-14, MW-16, MW-19, MW-20, and MW-24 were temporarily decommissioned by N&M by lowering the top of the well casings due to future planned onsite construction activities The locations of the former USTs, former and existing groundwater monitoring wells, and the current site improvements are depicted on Figure 2, Site Plan Historical soil and groundwater analytical data for the site are summarized in Tables II and III, respectively SUMMARY OF SITE CONDITIONS Utilizing the data acquired by WCC, Alton, EA and N&M as a basis, a summary of the soil and groundwater conditions beneath the site as of and/or prior to May 1994 is presented below • In 1987, the initial TPHg concentrations detected in groundwater beneath the site ranged from 154 mg/l to 231 mg/1 The depth to groundwater beneath the site in 1987 was approximately 40 feet bgs