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17&,C�QDP1 ' gallons of impacted water and a calculated estimate of 243 8 pounds of MtBE were removed from the tank pit excavation Concentrations of MtBE, TBA, and TAME in water samples collected following dewatering activities were significantly lower than pre-UST removal and tank pit dewatering activities (Table 3) Due to contamination found in the soil and groundwater during upgrade activities and the discovery of air bubbles between the UST and outer lining, the SJCEHD required 7-Eleven to ' remove and replace the three USTs on-site On May 29, 2003, two 10,000-gallon USTs and one 15,000-gallon double-walled fiberglass UST were removed from the excavation and disposed of off-site On June 2, 2003, nine sod samples (T1-10' through T9-14 0') were collected from native soil adjacent to and underlying the middle and ends of the three USTs The soil samples ' contained maximum concentrations of TPHg (2 2 mg/kg, T2-10'), benzene (0 007 mg/kg, T8- 10'), MtBE (36 mg/kg, T1-10'), and TBA (52 mg/kg, T3-10') (Table 1) ' Between June 3 and July 9, 2003, three new double-wailed fiberglass USTs (one 15,000- gallon UST and two 10,000-gallon USTs) were installed Associated product piping, dispenser pans, and turbine sumps were also replaced, and the vent line slope was modified ' In order to accommodate the new USTs, soil and pea gravel were excavated from the original tank pit which expanded the UST pit slightly to the south During UST removal activities, tank pit observation points TP-1 and TP-2 were removed During the installation of the new USTs, a new tank pit observation point was installed in the same location as the former location of TP-1 Referred to as TP-1, the new well was constructed with 6-inch diameter PVC screened from 10 feet to 15 feet bgs (Table 2) ' Following the completion of UST replacement activities, future remediation lines, which consisted of two 2-inch diameter and one 1-inch diameter poly-vinyl chloride (PVC) lines, ' were stubbed up in the well box for TP-1 The remediation piping was installed along the west side of the USTs, extending approximately 90 feet south of TP-1, and stubbed up adjacent to the air/water service area ' On October 15-17, 2003, six groundwater monitoring wells (MW-1 through MW-5, and MW- 6D) were installed at the site (Table 2) Soil and groundwater laboratory analytical results ' are summarized in Tables 1 and 3, respectively and well construction details are included in Table 2 23 Supply Well Survey ' Department of Water Resources ' SECOR visited the Department of Water Resources (DWR) Central District office in Sacramento, California, to review copies of the Water Well Driller's Reports and identify water supply wells that located within a 2,000-foot radius of the site ' A review of the DWR well logs identified six wells located within a 2,000-foot radius of the • site (Figure 3 and Table 4) The well logs provided approximate location, age, and ' construction specifications of each well 32262 Assessment&Feasibility Report&SCM doc 2 September 30,2004 ' 77EL 32262 04 0502