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S E C 0 R
<br /> 7-Eleven Store #17334
<br /> Quarterly Groundwater Monitoring Report (4Q2005)
<br /> January 20, 2006
<br /> Page 3
<br /> On August 14, 1998, monitoring wells MW-1 and MW-1A were destroyed, as they were
<br /> located adjacent to the USTs that were removed on August 25, 1998 On August 25, 1998,
<br /> approximately 200 cubic yards of soil were excavated from the new tank pit to
<br /> accommodate the installation of two new double-wall steel 10,000-gallon USTs, and
<br /> samples were collected at depths of up to 14 feet bgs below/adjacent to the USTs and
<br /> pump islands, and the product lines (Fluor Daniel GTI, 1998)
<br /> On December 17, 1998, a double-nested groundwater monitoring well (MW-5) was installed
<br /> to a depth of 40 feet bgs (Figure 2)
<br /> On April 3 and 4, 2002, soil boring SB-1 was advanced to a depth of 50 feet bgs, where a
<br /> grab groundwater sample was collected with a Hydropunch sampler (IT Corporation, 2002)
<br /> Two double-nested sod vapor extraction/air sparge SVEIAS wells (SPV-1 and SPV-2) were
<br /> also installed to 30 feet bgs Dissolved benzene, TPHg, and MtBE were detected in
<br /> groundwater samples from SB-1 @ 50' bgs, at concentrations of 28 µg/L, 7,100 gg/L, and
<br /> 67 µg/L, respectively
<br /> On April 4, 2003, two soil samples were collected under the fuel dispensers and two soil
<br /> samples were collected under the fuel lines northeast of the current UST pit Soil sample
<br /> L2-5 0' contained MtBE at a concentration of 0 012 mg/kg
<br /> MONITORING AND SAMPLING PROCEDURES
<br /> The depth to water was measured to within 0 01 feet bgs in monitoring wells MW-2, MW-3,
<br /> MW-4, MW-5A, and MW-513, from the top of casing (TOC) using a water level indicator
<br /> Dissolved oxygen concentrations were also measured in each well using a YSI Model 550A
<br /> dissolved oxygen meter equipped with a down hole sensor
<br /> Well purging and sampling equipment was thoroughly cleaned prior to purging and
<br /> sampling each well The sampling procedure for each well included measuring the water
<br /> level and checking for the presence of liquid-phase hydrocarbons (LPH), using either an
<br /> electronic indicator and a clear Teflon® bailer or an oil-water interface probe Wells not
<br /> containing LPH were purged of approximately three casing volumes of water (or to dryness)
<br /> using a submersible pump or bailer The equipment and purging methods used for the
<br /> current sampling event are noted on the field data sheets in Attachment A During purging,
<br /> temperature, pH, and electrical conductivity were monitored After purging, water levels
<br /> were allowed to recover to 80% of the original levels prior to collection of the water sample
<br /> Groundwater samples were collected using a disposable Teflon® bailer, placed into
<br /> appropriate EPA-approved containers, labeled, logged onto chain-of-custody documents,
<br /> and transported on ice to a California state-certified laboratory Copies of the field notes
<br /> are presented in Attachment A
<br /> GROUNDWATER SAMPLE ANALYSES AND RESULTS
<br /> The groundwater samples collected from MW-2, MW-3, MW-4, MW-5A, and MW-5B were
<br /> analyzed for TPHg, benzene, toluene, ethylbenzene, and total xylenes (BTEX), and fuel
<br /> 1' oxygenates MtBE, tert-butyl alcohol (TBA), diisopropyl ether (DIPE), ethyl-tert-butyl ether
<br /> 17334 05-4Q Report doc SECOR International Incorporated
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