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S E C 0 R
<br /> 7-Eleven Store#32262
<br /> Quarterly Groundwater Monitoring Report (1Q2004)
<br /> May 12, 2004
<br /> Page 3
<br /> Between June 3 and July 9, 2003, three new double-walled fiberglass USTs (one 15,000-gallon UST F
<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, sod 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 TPA the new well was constructed with 6-inch diameter PVC that
<br /> was screened from 10 feet to 15 feet bgs
<br /> Following the completion of UST replacement activities, future remediation lines, which consisted 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 /> 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-6D at concentrations ranging from 0 0079 mg/kg to 9 5 mg/kg TBA was detected in MW-5 and
<br /> MW-6D at concentrations ranging from 0 010 mg/kg to 2 2 mg/kg Sod samples collected from MW-
<br /> 1 through MW-5, and MW-6D, did not contain TPHg, BTEX, DIPS, EtBE, 1,2-DCA, or EDB above
<br /> laboratory reporting limits
<br /> MONITORING AND SAMPLING PROCEDURES
<br /> The depth to water was measured in monitoring wells MW-1 through MW-5 and MW-6D from top of
<br /> casing (TOC) using a water level indicator to within 0 01 feet bgs Dissolved oxygen readings were
<br /> also collected from the wells using a YSI Model 550A dissolved oxygen meter equipped with a down
<br /> hole sensor
<br /> Well purging and sampling equipment was thoroughly cleaned prior to purging and sampling the
<br /> well The sampling procedure for the well included measuring the water level and checking for the
<br /> presence of liquid-phase hydrocarbons (LPH), using either an electronic indicator and a clear
<br /> Teflon® bailer or an oil-water interface probe Wells not containing LPH were purged of
<br /> approximately three casing volumes of water (or to dryness) using a submersible pump or bailer
<br /> The equipment and purging methods used for the current sampling event are noted on the field data
<br /> sheets included in Attachment A During purging, temperature, pH, and electrical conductivity were
<br /> monitored in order to document that these parameters were stable prior to collecting samples After
<br /> purging, the water level was allowed to recover to 80% of the original levels prior to collection of the
<br /> water sample Groundwater samples were collected using a disposable Teflon bailer, placed into
<br /> appropriate Environmental Protection Agency (EPA) approved containers, labeled, logged onto
<br /> chain-of-custody documents, and transported on ice to a California state-certified laboratory Copies
<br /> of the field notes have been included in Attachment A
<br /> GROUNDWATER SAMPLE ANALYSES AND RESULTS
<br /> The groundwater sample collected from MW-1 through MW-5 and MW-6D were analyzed for the
<br /> presence of TPHg, BTEX, and fuel oxygenates MtBE, TBA, diisopropyl ether (DIPE), ethyl-tert-butyl
<br /> ether (EtBE), and tert-amyl-methyl ether (TAME) using EPA Method 8260B 1,2-dichloroethane and a
<br /> 1,2-dibromoethane were also analyzed using this method The certified laboratory analytical report
<br /> and chain-of-custody documentation are presented as Attachment B
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<br /> 32262 04-1 Q Report doc SECOR International Incorporated
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