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S E C 0 7-Eleven Store #20632 Quarterly Groundwater Monitoring Report (4Q2005) January 20, 2006 Page 2 Groundwater Flow Direction and Gradient: South-Southwest @ 0.005 foot per foot (Figure 2) Current Quarter Analytical Data (See Figure 3 and Table 1) Maximum TPHg Concentrations MW-4R, 29,000 /L Maximum Benzene Concentrations MW-4R, 190 /L Maximum MtBE Concentrations MW-7, 7,600 pg/L Maximum TBA Concentrations MW-7, 26,000 /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 in groundwater from 0.5 to 2.4 milligrams per liter (mg/L). 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 mg/kg, respectively, in soil samples collected beneath the product lines and fuel dispensers. On June 18, 2004, SECOR submitted a work plan (WP) to the SJCEHD for the advancement of eight geoprobes for additional offsite assessment. The WP was approved by the SJCEHD in a letter dated July 6, 2004. The eight geoprobes were advanced on January 31, 2005. Analytical results for soil and groundwater samples collected were submitted in an offsite assessment report on May 18, 2005. MONITORING AND SAMPLING PROCEDURES . The depth to water was measured to within 0.01 feet bgs 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 20632 05-4Q Report.doc SECOR Intemational Incorporated