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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
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