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S E C 0 R k7-Eleven Store #32262 ~ Quarterly Groundwater Monitoring Report (2Q2004) August 18, 2004 • Page 2 e MW-6D Depth to Groundwater (DTW) 6 72 to 8 94 ft bgs Average Change in Groundwater Elevation Since Last Event 0 19 foot decrease Groundwater Flow Direction and Gradient Northwest @ 0 005 feet per foot (Figure 2) Current Quarter Analytical Data (See Figure 2 and Table 1) Maximum Benzene Concentrations Not Detected, <0 50 to <50 &L Maximum TPHg Concentrations Not Detected, <50 to <5,000 pg/L Maximum MtBE Concentrations MW-5, 30,000 pg/L Maximum TBA Concentrations Not Detected, <5 0 to <500 pg/L BACKGROUND In 1997, Fluor Daniel GTI conducted Phase I and Phase II assessments at the site, consisting of soil borings and grab groundwater samples No detectable concentrations of petroleum hydrocarbons, polynuclear aromatic hydrocarbons, or pesticides were found on- site A Phase I addendum was submitted by IT Corporation on September 27, 1999 Under the direction of a SJCEHD representative, ten soil samples were collected on May 2 and 3, 2003, beneath the product lines (L1 through L4 on Figure 4) and dispensers (D1 through D6) at depths between 3 5 feet and 4 5 feet below ground surface (bgs) The soil samples collected did not contain total petroleum hydrocarbons as gasoline (TPHg) or benzene, toluene, ethylbenzene, or total xylenes (BTEX) above laboratory reporting limits Maximum reported concentrations of MtBE and tert-butyl alcohol (TBA) were 4 5 milligrams per kilogram (mg/kg) and 12 mg/kg, respectively (D1-4 0') Due to the presence of petroleum hydrocarbons and fuel oxygenates in soil and groundwater beneath the site, SECOR submitted an Underground Storage Tank Unauthorized Release with the (Leak)/Contamination Site Report to the SJCEHD and the Central Valley Regional Water Quality Control Board During fuel line and dispenser upgrade activities on May 3, 2003, SECOR personnel collected grab water samples (W1 and W2) from two tank pit observation wells (TP-1 and TP-2) Depths to bottom of wells TP-1 and TP-2 were measured between 11 feet and 12 feet bgs MtBE, TBA, and tent-amyl methyl ether (TAME) were reported at concentrations up to 510,000 micrograms per liter (pg/L), 79,000 ug/L, and 1,500 ug/L, respectively During UST excavation dewatering activities, approximately 199,090 gallons of impacted water and a calculated estimate of 243 8 pounds of MtBE were removed from the tank pit excavation Concentrations of MtBE, TBA, and TAME in water samples collected following dewatering activities were significantly lower than pre-UST removal and tank pit dewatering activities (Table 2) • Due to contamination found in the soil and groundwater during upgrade activities and the discovery of air bubbles between the UST and outer lining, the SJCEHD required 7-Eleven 32262 04-2Q Report doc SECOR International Incorporated