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<br /> 7-Eleven Store#32262
<br /> Quarterly Groundwater Monitoring Report (3Q2004)
<br /> October 1, 2004
<br /> Page 3
<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 (Table 2)
<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
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<br /> On June 2, 2003, nine sod 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 /> MW-3, MW-5, and MW-6D at concentrations ranging from 0 0079 mg/kg to 9 5 mg/kg TBA
<br /> was detected in MW-5 and MW-6D at concentrations ranging from 0 010 mg/kg to 2 2
<br /> mg/kg Soil samples collected from MW-1 through MW-5, and MW-6D, did not contain
<br /> TPHg, BTEX, DIPE, EtBE, 1,2-DCA, or EDB above laboratory reporting limits
<br /> MONITORING AND SAMPLING PROCEDURES w
<br /> The depth to water was measured to within 0 01 feet bgs in monitoring wells MW-1 through
<br /> MW-5, MW-6D, MW-7 through MW-9, and TP-1 from the top of casing (TOC) using a water
<br /> level indicator Dissolved oxygen concentrations were also measured in the wells using a
<br /> YSI Model 550A dissolved oxygen meter equipped with a down hole sensor
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<br /> 32262 04-3Q Report doc SFCOR International Incorporated
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