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<br /> S E C 0 R
<br /> 7-Eleven Store #32262
<br /> Site Assessment Report
<br /> December 12, 2003
<br /> Page 2
<br /> ether (MtBE) and tert-butyl alcohol (TBA) were 4 5 milligrams per kilogram (mg/kg) and 12 mg/kg,
<br /> respectively(D1-4 0') (Table 1)
<br /> During fuel line and dispenser upgrade activities on May 3, 2003, SECOR personnel collected grab
<br /> water samples (W1 and W2) from two tank pit observation wells (TP-1 and TP-2, Figure 2 and 3)
<br /> Depth to bottom of wells TP-1 and TP-2 were measured between 11 feet and 12 feet bgs MtBE,
<br /> TBA, and tert-amyl methyl ether (TAME) were reported at concentrations up to 510,000 micrograms
<br /> per liter (ug/L), 79,000 ug/L, and 1,500 ug/L, respectively (Table 2) Prior to UST removal and tank
<br /> pit dewatering activities, grab groundwater sample W1 was collected from tank pit observation well
<br /> TP-1 During dewatering activities, approximately 199,090 gallons of impacted water and a
<br /> calculated estimate of 243 8 pounds of MtBE were removed from the tank pit excavation
<br /> Concentrations of MtBE, TBA, and TAME in water samples collected following dewatering activities
<br /> were significantly lower than pre-UST removal and tank pit dewatering activities
<br /> Due to contamination found in the soil and groundwater during upgrade activities and the discovery
<br /> of air bubbles between the UST and outer lining, the SJCEHD required 7-Eleven to remove and
<br /> replace the three USTs on-site On May 29, 2003, two 10,000-gallon USTs and one 15,000-gallon
<br /> double-walled fiberglass UST were removed from the excavation and disposed off-site
<br /> On June 2, 2003, nine soil samples (T1-10' through T9-140') were collected from native soil
<br /> adjacent to and underlying the middle and ends of the three USTs (Figure 2) The soil samples
<br /> contained maximum concentrations of TPHg (2 2 mg/kg, T2-10'), benzene (0 007 mg/kg, T8-10'),
<br /> MtBE (36 mg/kg, 1-10'), and TBA (52 mg/kg, T3-10') (Table 1) Based on soil analytical results, the
<br /> highest concentrations of petroleum hydrocarbons in soil appear to be located in the northwestern
<br /> corner of the UST pit
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<br /> Between June 3 and July 9, 2003, three new double-walled fiberglass USTs (one 15,000-gallon UST
<br /> and two 10,000-gallon USTs) were installed Associated product piping, dispenser pans, and turbine
<br /> sumps were also replaced, and the vent line slope was modified In order to accommodate the new
<br /> USTs, soil and pea gravel were excavated from the original tank pit, which expanded the UST pit
<br /> slightly to the south
<br /> During UST removal activities, tank pit observation points TP-1 and TP-2 were removed During the
<br /> installation of the new USTs, a new tank pit observation point was installed in place of the former
<br /> location of TP-1 Referred to as TP-1, the new well was constructed with 6-inch diameter PVC that
<br /> is screened from 10 feet to 15 feet bgs (Table 3)
<br /> Following the completion of UST replacement activities, future remediation lines, which consist of
<br /> two 2-inch diameter and one 1-inch diameter PVC lines, were stubbed up in the well box for TP-1
<br /> The remediation piping was installed along the west side of the USTs, extending approximately 90
<br /> feet south of TP-1 and stubbed up adjacent to the air/water service area
<br /> SOIL BORING, SAMPLING, AND WELL INSTALLATION
<br /> Permitting/Site-Specific Health and Safety Plan/Utility Clearance
<br /> Well installation permits for MW-1 through MW-5, and MW-6D, were obtained from the SJCEHD
<br /> • prior to installation of the wells (Attachment A)
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<br /> 32262 Assessment Report SECOR International Incorporated
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