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<br /> 7-Eleven Store #32262
<br /> Work Plan for Additional Site Assessment and Interim Remediation
<br /> March 19, 2004
<br /> Page 2
<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 The soil samples contained
<br /> maximum concentrations of TPHg (2 2 mg/kg, T2-10'), benzene (0 007 mg/kg, T8-10'), MtBE (36
<br /> mg/kg, 1-10'), and TBA (52 mg/kg, T3-10') (Table 1) Based on soil analytical results, the highest
<br /> concentrations of petroleum hydrocarbons In soil appear to be located in the northwestern corner of
<br /> the UST pit
<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 to
<br /> 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 polyvinyl
<br /> chloride (PVC) pipe that Is screened from 10 feet to 15 feet bgs (Table 3)
<br /> Following the completion of UST replacement, remediation piping consisting of two 2-Inch diameter
<br /> and one 1-inch diameter PVC lines was Installed and stubbed up In the well box for TP-1 The
<br /> remediation piping was installed along the west side of the USTs, extending approximately 90 feet
<br /> south of TP-1 and stubbed up adjacent to the air/water service area
<br /> On October 15-17, 2003, six groundwater monitoring wells (MW-1 through MW-5, and MW-6D) were
<br /> installed at the site MtBE was detected in soil samples collected from MW-2, MW-3, MW-5, and
<br /> MW-61D at concentrations ranging from 0 0079 mg/kg to 9 5 mg/kg (Table 1) TBA was detected In
<br /> MW-5 and MW-6D at concentrations ranging from 0 010 mg/kg to 2 2 mg/kg (Table 1) Soil samples
<br /> collected from MW-1 through MW-5, and MW-6D, did not contain TPHg, BTEX, dllsopropyl ether
<br /> (DIPE), ethyl-tent-butyl ether (EtBE), 1,2-dichloroethane (1,2-DCA), or ethylene dibromide (EDB)
<br /> above laboratory reporting limits
<br /> During quarterly monitoring and sampling in the fourth quarter 2003, the groundwater flow direction
<br /> was toward the north-northwest at a gradient of 0 004 feet per foot (Figure 3) MtBE was reported In
<br /> groundwater samples collected from MW-2 (1,700 ug/L), MW-3 (95 ug/L), MW-4 (1 9 ug/L), MW-5
<br /> (120,000 ug/L), and MW-6D (270 ug/L) (Figure 4 and Table 2) TBA was reported in MW-5 at a
<br /> concentration of 15,000 ug/L TPHg, BTEX, DIPE, EtBE, 1,2-DCA, and EDB were not detected
<br /> above laboratory reporting limits In groundwater samples from MW-1 through MW-5, and MW-6D A
<br /> groundwater hydrocarbon concentration map Is presented as Figure 4
<br /> Adjacent Leaky Underground Storage Tank Sites
<br /> SECOR reviewed SJCEHD files to obtain information related to leaky underground storage tanks
<br /> (LUFT) sites located near the subject site A total of four LUFT sites were found during the file
<br /> review
<br /> • 2420 Grant Line Road, Grant Line Food and Gas,
<br /> • 2375 Grant Line Road, Shell Gasoline Station,
<br /> 32262 offsite well install and interim remediation workplan doc SEGOR International Incorporated
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