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<br /> 7-Eleven Store#32262
<br /> Extended Groundwater Pumping Test and Oxygen Infection Feasibility Study
<br /> November 15, 2005
<br /> Page 2
<br /> During fuel line and dispenser upgrade activities on May 3, 2003, SECOR personnel
<br /> collected grab water samples (W1 and W2) from two tank pit observation wells (TP-1 and
<br /> TP-2) Depths to bottom of wells TP-1 and TP-2 were measured between 11 feet and 12
<br /> feet bgs MtBE, TBA, and tert-amyl methyl ether (TAME) were reported at concentrations
<br /> up to 510,000 micrograms per liter(pg/L), 79,000 ug/L, and 1,500 ug/L, respectively
<br /> During UST excavation dewatering activities, approximately 199,090 gallons of Impacted
<br /> water and a calculated estimate of 243 8 pounds of MtBE were removed from the tank pit
<br /> excavation Concentrations of MtBE, TBA, and TAME In water samples collected following
<br /> dewatering activities were significantly lower than pre-UST removal and tank pit dewatering
<br /> activities
<br /> Due to contamination found in the soil and groundwater during upgrade activities and the
<br /> discovery of air bubbles between the UST and outer lining, the SJCEHD required 7-Eleven
<br /> to remove and replace the three USTs on-site On May 29, 2003, two 10,000-gallon USTs
<br /> and one 15,000-gallon double-walled fiberglass UST were removed from the excavation
<br /> and disposed of off-site
<br />. On June 2, 2003, nine soil samples (T1-10' through T9-14 0') were collected from native
<br /> soil adjacent to and underlying the middle and ends of the three USTs The soil samples
<br /> contained maximum concentrations of TPHg (2 2 mg/kg, T2-10'), benzene (0 007 mg/kg,
<br /> T8-10'), MtBE (36 mg/kg, 1-10'), and TBA (52 mg/kg, T3-10') Based on soil analytical
<br /> results, the highest concentrations of petroleum hydrocarbons in soil appeared to be
<br /> located in the northwestern corner of the UST pit
<br /> Between June 3 and July 9, 2003, three new double-walled fiberglass USTs (one 15,000-
<br /> gallon UST and two 10,000-gallon USTs) were Installed Associated product piping,
<br /> dispenser pans, and turbine sumps were also replaced, and the vent line slope was
<br /> modified In order to accommodate the new USTs, soil and pea gravel were excavated
<br /> from the original tank pit, which expanded the UST pit slightly to the south
<br /> During UST removal activities, tank pit observation points TP-1 and TP-2 were removed
<br /> During the installation of the new USTs, a new tank pit observation point was installed in
<br /> place of the former location of TP-1 Referred to as TP-1, the new well was constructed
<br /> with 6-inch diameter PVC that was screened from 10 feet to 15 feet bgs
<br /> Following the completion of UST replacement activities, future remediation lines, which
<br /> consisted of two 2-Inch diameter and one 1-inch diameter PVC lines, were stubbed up in
<br /> the well box for TP-1 The remediation piping was installed along the west side of the
<br /> USTs, extending approximately 90 feet south of TP-1, and stubbed up adjacent to the
<br /> air/water service area
<br /> On October 15-17, 2003, six groundwater monitoring wells (MW-1 through MW-5, and MW-
<br /> 6D) were installed at the site MtBE was detected in soil samples collected from MW-2,
<br /> I W-Elevenl7-11 Stores1322621Reports132262 Pump Test and 02 Feasibildy 11-10-05 doc SECOR lntemational Incorporated
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