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S E C 0 R <br /> 7-Eleven Store#32262 <br /> • Quarterly Groundwater Monitoring Report (1Q2004) <br /> May 12, 2004 <br /> Page 2 <br /> Current Quarter Analytical Data (See Figure 2 and Table 1) <br /> Maximum Benzene Concentrations Not Detected, <0 50 to <200 IL <br /> Maximum TPHg Concentrations Not Detected, <50 to <20,000_pglL _ <br /> Maximum MtBE Concentrations MW-5, 110,000 p g/L <br /> Maximum TBA Concentrations MW-5, 2,500 pg/L <br /> BACKGROUND <br /> In 1997, Fluor Daniel GTI conducted Phase I and Phase II assessments at the site, consisting of soil <br /> borings and grab groundwater samples No detectable concentrations of petroleum hydrocarbons, <br /> polynuclear aromatic hydrocarbons, or pesticides were found on-site A Phase 1 addendum was <br /> submitted by IT Corporation on September 27, 1999 <br /> Under the direction of a SJCEHD representative, ten soil samples were collected on May 2 and 3, <br /> 2003, beneath the product lines (L1 through L4 on Figure 4) and dispensers (D1 through D6) at <br /> depths between 3 5 feet and 4 5 feet below ground surface (bgs) The soil samples collected did not <br /> contain total petroleum hydrocarbons as gasoline (TPHg) or benzene, toluene, ethylbenzene, or total <br /> . xylenes (BTEX) above laboratory reporting limits Maximum reported concentrations of MtBE and t <br /> tent-butyl alcohol (TBA) were 4 5 milligrams per kilogram (mglkg) and 12 mg/kg, respectively (D1- <br /> 4 0') <br /> Due to the presence of petroleum hydrocarbons and fuel oxygenates in soil and groundwater <br /> beneath the site, SECOR submitted an Underground Storage Tank Unauthorized Release with the <br /> (Leak)/Contamination Site Report to the SJCEHD and the Central Valley Regional Water Quality <br /> Control Board <br /> i <br /> During fuel line and dispenser upgrade activities on May 3, 2003, SECOR personnel collected grab <br /> water samples (W1 and W2) from two tank pit observation wells (TP-1 and TP-2) Depths to bottom <br /> of wells TP-1 and TP-2 were measured between 11 feet and 12 feet bgs MtBE, TBA, and tert-amyl <br /> methyl ether (TAME) were reported at concentrations up to 510,000 micrograms per liter (PglL), <br /> 79,000 ug/L, and 1,500 ug/L, respectively During dewatering activities, approximately 199,090 <br /> gallons of impacted water and a calculated estimate of 243 8 pounds of MtBE were removed from <br /> the tank pit excavation Concentrations of MtBE, TBA, and TAME in water samples collected <br /> following dewatering activities were significantly lower than pre-UST removal and tank pit dewatering <br /> activities (Table 2) <br /> Due to contamination found in the soil and groundwater during upgrade activities and the discovery <br /> of air bubbles between the UST and outer lining, the SJCEHD required 7-Eleven to remove and <br /> replace the three USTs on-site On May 29, 2003, two 10,000-gallon USTs and one 15,000-gallon <br /> double-walled fiberglass UST were removed from the excavation and disposed of off-site <br /> On June 2, 2003, nine soil samples (T1-10' through T9-140') were collected from native soil <br /> adjacent to and underlying the middle and ends of the three USTs The soil samples contained <br /> maximum concentrations of TPHg (2 2 mglkg, T2-10'), benzene (0 007 mg/kg, T8-10'), MtBE (36 <br /> • mg/kg, 1-10'), and TSA (52 mg/kg, T3-10') Based on soil analytical results, the highest <br /> concentrations of petroleum hydrocarbons in soil appeared to be located in the northwestern corner <br /> of the UST pat <br /> 32262 04-10 Report doc SECOR International incorporated <br />