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S E C 0 R 7-Eleven Store#17334 Quarterly Groundwater Monitoring Report (1Q2005) April 18, 2005 Page 2 Groundwater Flow Direction and Gradient Northeast @ 0 005 foot per foot _(Figure 2) Current Quarter Analytical Data (See Figure 3 and Table 1) Maximum TPHg Concentrations MW-5A, 20,000 /L Maximum Benzene Concentrations MW-5A, 860 lag/L Maximum MtBE Concentrations MW-5A, 120 lag/L _ Maximum TBA Concentrations MW-5A, 580 fag/L _ BACKGROUND SJCEHD files show that there are three underground storage tank (UST) sites with documented releases located near 7-Eleven Site No 17334 the Cardlock Gasoline Station at 4555 N Pershing Avenue (100 feet east and crossgradtent of the site), a Shell Service Station at 4445 N Pershing Avenue (crossgradtent of the site), and an Exxon Service Station at 4444 N Pershing Avenue (crossgradtent of the site) Exxon's well MW-9 is located adjacent to the 7-Eleven site property boundary The Cardlock facility was reportedly under investigation for diesel contamination, and received no further action in December 1997 Available SJCEHD records show the Cardlock facility did not conduct • analysis for methyl-tert-butyl ether (MtBE) or other oxygenates The Shell site, according to available information, is due to receive regulatory agency closure shortly 2 Groundwater monitoring and sampling has been ongoing at the Exxon site since 1987, and conducted at the Cardlock and Shell sites since 1992 In 1988, Exxon installed a 30-foot- deep groundwater monitoring well, MW-9, approximately 10 feet east and 10 feet south of 7-Eleven's tank pit The depth to groundwater in MW-9 has ranged from 30 feet below ground surface (bgs) in 1990 to 20 feet bgs in April 1996 On February 20, 1997, Fluor Daniel GTI supervised the advancement of four angled and three vertical geoprobe borings (GP-1 through GP-7) at the subject site (Fluor Daniel GTI, 1997) Borings GP-1 through GP-6 were drilled beneath the three 10,000-gallon USTs In addition, groundwater grab samples were collected from borings GP-3, GP-4, and GP-7 Benzene was detected in soil sample GP-4 @ 17 feet at a concentration of 0 0095 milligrams per kilogram (mg/kg) Total petroleum hydrocarbons as gasoline (TPHg) was not detected above laboratory reporting limits in any of the soil samples collected The highest MtBE concentration was reported in sample GP-1 @ 15 feet at 0 91 mg/kg The highest dissolved benzene, TPHg, and MtBE concentrations in groundwater samples were reported in sample GP-4 at 9,100 micrograms per liter (ug/L), 150,000 ug/L, and 84,000 ug/L, respectively From September 23 through November 26, 1997, Fluor Daniel GTI supervised the drilling of five groundwater monitoring wells (MW-1, MW-1A, MW-2, MW-3, and MW-4) to depths ranging from 35 to 40 feet bgs (Figure 2, Table 3) On August 14, 1998, monitoring wells MW-1 and MW-1A were destroyed, as they were located adjacent to the USTs that were removed on August 25, 1998 On August 25, 1998, 17334 05-1Q Report doc 5ECOR International Incorporated