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7-Eleven Store #20632
<br /> . Quarterly Groundwater Monitoring Report (102003)
<br /> June 13, 2003
<br /> Page 2
<br /> al
<br /> Current Quarter Analytical Data (See Figure 3 and Table 1)
<br /> Maximum TPHg Concentrations MW-3, 1,300 ug/L
<br /> Maximum Benzene Concentrations Not Detected, <0 50 to<100 ug/L
<br /> Maximum MtBE Concentrations MW-7, 56,000 ug/L
<br /> Maximum TBA Concentrations MW-4R, 170,000 ug/L�
<br /> BACKGROUND
<br /> Initial site assessment activities were executed in accordance with directives from (SJCEHD)
<br /> requirements (Fluor Daniel GTI, Additional Site Assessment and Corrective Action Work Plan,
<br /> January 8, 1997) The assessment concluded that soil impacted with gasoline appeared restricted to
<br /> a limited area surrounding the underground storage tank (UST) pit and underlying the fuel
<br /> dispensers The USTs were replaced as part of 1998 upgrading requirements Concurrent with
<br /> limited overexcavation, several days of high-volume dewatering occurred as part of construction
<br /> activities, which also served as a short-term remediation event
<br /> Additional lateral and vertical assessment of dissolved methyl-tert-butyl ether (MtBE) and
<br /> hydrocarbons has been conducted There are currently seven site-related monitoring wells Most
<br /> recent assessment activities include the installation of three onsite monitoring wells (MW-4R, MW-6,
<br /> and MW-7) in April 2002, along with two dual-nested sparge/vent wells, SPV-1 and SPV-2, and a
<br /> vertical delineation soil boring, SB-1
<br /> MONITORING AND SAMPLING PROCEDURES
<br /> The depth to water was measured in monitoring wells MW-1, MW-2, MW-3, MW-4R, MW-5, MW-6,
<br /> and MW-7, from top of casing (TOC) using a water level indicator to within 0 01 feet bgs Dissolved
<br /> oxygen readings were also collected from each well using a YSI Model 550A dissolved oxygen meter
<br /> equipped with a down hole sensor
<br /> Well purging and sampling equipment is thoroughly cleaned prior to purging and sampling each well
<br /> The sampling procedure for each well includes 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 are purged of approximately
<br /> three casing volumes of water (or to dryness) using a submersible pump or bailer The equipment
<br /> and purging methods used for the current sampling event are noted on the field data sheets included
<br /> in Attachment A During purging, temperature, pH, and electrical conductivity are monitored in order
<br /> to document that these parameters are stable prior to collecting samples After purging, water levels
<br /> are allowed to recover to 80% of the original levels prior to collection of the water sample
<br /> Groundwater samples are collected using a disposable Teflon° bailer, placed into appropriate EPA-
<br /> approved containers, labeled, logged onto chain-of-custody documents, and transported on ice to a
<br /> California state-certified laboratory Copies of the field notes have been included in Attachment A
<br /> GROUNDWATER SAMPLE ANALYSES AND RESULTS
<br /> The groundwater samples collected from MW-1, MW-2, MW-3, MW-4R, MW-5, MW-6, and MW-7
<br /> were analyzed for the presence of total petroleum hydrocarbons as gasoline (TPHg), benzene,
<br /> toluene, ethyl benzene, and total xylenes (BTEX), and fuel oxygenates MtBE, tert-butyl alcohol
<br /> • (TBA), dusopropyl ether (DIPE), ethyl-tert-butyl ether (EtBE), and tert-amyl-methyl ether (TAME)
<br /> using EPA Method 8260E The certified laboratory analytical report and chain-of-custody
<br /> documentation are presented as Attachment B
<br /> 20632 03-10 Report SECOR Intemational Incorporated
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