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UST SYSTEM REMOVAL REPORT 7-ELEVEN STORE NO. 17334, 4501 N. PERSHING AVENUE, STOCKTON, CA 95207 Introduction March 3, 2023 v:\1858\active\185851132\05_report_deliv\deliverable\reports\2023_rpt_17334_ust.docx 1.2 MTBE, and TPHg concentrations in groundwater were detected in GP4 at concentrations of 9,100 micrograms per liter (µg/L), 100,000 µg/L, and 150,000 µg/L, respectively. In September and November 1997, FDGTI supervised the drilling and installation of four onsite groundwater monitoring wells (MW-1, MW-1A, MW-2, and MW-3) and one offsite groundwater monitoring well (MW-4) to depths ranging from 35 to 40 feet below ground surface (bgs). The maximum benzene and TPHg concentrations in soil were detected in MW-1A-25’ at 0.39 mg/kg and 43 mg/kg, respectively. MTBE was detected in four soil samples at concentrations ranging from 0.12 mg/kg to 8.1 mg/kg. Maximum concentrations of benzene, MTBE, and TPHg were detected in the groundwater sample collected from MW-1 at 1,200 µg/L, 14,000 µg/L, and 15,000 µg/L, respectively. In August 1998, FDGTI supervised the destruction of monitoring wells MW-1 and MW-1A via over-drilling, as they were located adjacent to the USTs that were to be removed. Approximately 750 cubic yards of soil were excavated from the new tank excavation to accommodate the installation of two new double-wall steel 10,000-gallon USTs. In September 1998, FDGTI supervised the removal of the USTs, vent lines, and dispenser islands from the site. Six soil samples were collected, one from each end of each UST. Benzene was not detected in any of the samples collected beneath the USTs. TPHg was detected in sample TNK-3S at a concentration of 4,300 mg/kg. The maximum MTBE concentration was detected in sample TNK-1N at 1.3 mg/kg. In December 1998, IT Corporation supervised the drilling and installation of one dual-nested groundwater monitoring well (MW-5A and MW-5B) to a depth of 40.5 feet bgs. The maximum TPHg concentration was detected in MW-5-30' at 236 mg/kg. Benzene was detected in two soil samples at concentrations of 0.0043 mg/kg and 0.0192 mg/kg. The maximum MTBE concentration was detected in MW-5-25' at 3.17 mg/kg. The maximum benzene, TPHg, and MTBE concentrations in groundwater during the fourth quarter 1998 groundwater sampling event were detected in MW-5A at 10,400 µg/L, 88,600 µg/L, 17,200 µg/L, respectively. In April 2002, The Shaw Group, Inc. (Shaw) supervised the drilling of one vertical delineation soil boring (SB-1) to a depth of 50 feet bgs and two double-nested soil vapor extraction/air sparge (SVE/AS) wells (SPV-1 and SPV-2) to depths of 30 feet bgs. Benzene and MTBE were not detected in any of the soil samples submitted for analysis. TPHg was detected in SPV-1@30' at a concentration of 3.9 mg/kg. A grab groundwater sample was collected from SB-1 at 50 feet bgs using a Hydropunch sampler. Benzene, TPHg, and MTBE were detected in the groundwater sample at concentrations of 28 µg/L, 7,100 µg/L, and 67 µg/L, respectively. In May 2002, SVE testing was conducted at the site to evaluate the radius of vapor extraction influence and vadose- zone volatile organic vapor generation potential. Extraction was conducted for a period of 3 hours on well SPV-2, 1 hour on well MW-5A, and approximately 3 hours on well SPV-1. Five soil vapor samples were collected during the testing. The maximum benzene concentration was detected in the vapor sample collected from well MW-5A at 18 µg/L. The maximum TPHg concentration was detected in the vapor sample collected from SPV-1 at 2,300 µg/L. The maximum MTBE concentration was detected in the vapor sample extracted from SPV-2 at 140 µg/L. The SVE radius of influence was estimated to be approximately 30 to 35 feet. In April 2003, SECOR International Incorporated (SECOR) supervised the removal and replacement of the fuel dispensers and associated piping. SECOR collected two soil samples underneath fuel dispensers and two soil samples under the fuel lines under the direction of the EHD. Benzene and TPHg were not detected in any of the soil samples submitted for analysis. MTBE was detected in one soil sample at a concentration of 0.012 mg/kg.