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t') R - - - - - 7-Eleven Store#20632 . Quarterly Groundwater Monitoring Report (1Q2004) April 21, 2004 Page 2 Current Quarter Analytical Data (See Figure 3 and Table 1) Maximum TPHg Concentrations MW-4R, 4,500 Hg/L Maximum Benzene Concentrations MW-4R, 310 pg/L Maximum MtBE Concentrations MW-7, 25,000 /L Maximum TBA Concentrations MW-7, 56,000 pg/L BACKGROUND Initial site assessment activities were executed in accordance with directives from SJCEHD (Fluor Daniel GTI 1997) The assessment concluded that soil impacted with gasoline appeared restricted to a limited area surrounding the underground storage tank (UST) pit and underlying the fuel dispensers The USTs were replaced as part of 1998 upgrading requirements Concurrent with limited overexcavation, several days of high-volume dewatering occurred as part of construction activities, which also served as a short-term remediation event Additional lateral and vertical assessment of dissolved methyl-tert-butyl ether (MtBE) and hydrocarbons was conducted through 2002 There are currently seven onsite monitoring wells In April 2002, three onsite monitoring wells (MW-4R, MW-6, and MW-7), two dual-nested sparge/vent • wells (SPV-1 and SPV-2) and a vertical delineation soil boring (SB-1)were installed at the site On April 22, 2002, a soil vapor extraction (SVE) test was performed at the site Vapor was extracted from MW-4R, MW-7, SPV-1, and SPV-2 Low influent vapor concentrations and poor vacuum response in observation wells were documented during the test An air sparge test in SPV-1 increased the dissolved oxygen concentration from 0 5 to 2 4 milligrams per liter(mg/L) in SPV-1 In April 2003, 7-Eleven, Inc upgraded the product lines at the site Benzene, total petroleum hydrocarbons as gasoline (TPHg), and MtBE were reported at maximum concentrations of 0 019 milligrams per kilogram (mg/kg), 4 7 mg/kg, and 0 60 mglkg, respectively, in soil samples collected beneath the product lines and fuel dispensers MONITORING AND SAMPLING PROCEDURES The depth to water was measured in monitoring wells MW-1, MW-2, MW-3, MW-4R, MW-5, MW-6, and MW-7 from the top of casing (TOC) using a water level indicator to within 0 01 feet bgs Dissolved oxygen readings were also collected from each well using a YSI Model 550A dissolved oxygen meter equipped with a down hole sensor Well purging and sampling equipment was thoroughly cleaned prior to purging and sampling each well The sampling procedure for each well included measuring the water level and checking for the presence of liquid-phase hydrocarbons (LPH), using either an electronic indicator and a clear Teflon® bailer or an oil-water interface probe Wells not containing LPH were purged of approximately three casing volumes of water (or to dryness) using a submersible pump or bailer The equipment and purging methods used for the current sampling event are noted on the field data sheets included in Attachment A During purging, temperature, pH, and electrical conductivity were monitored in order to document that these parameters were stable prior to collecting samples After purging, water levels were allowed to recover to 80% of the original levels prior to collection of the water sample Groundwater samples were collected using a disposable Teflon® bailer, placed into appropriate Environmental Protection Agency (EPA) approved containers, labeled, logged onto 20632 04-1Q Report doc SECQR International Incorporated