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S ECC R
<br /> 7-Eleven Store#17334
<br /> Quarterly Groundwater Monitoring Report (102003)
<br /> • June 13, 2003
<br /> Page 2
<br /> Current Quarter Analytical Data (See Figure 3 and Table 1)
<br /> Maximum TPHg Concentrations MW-5A, 36,0000 ug/L
<br /> Maximum Benzene Concentrations MW-5A, 2,000 ug/L
<br /> Maximum MtBE Concentrations MW-5A, 460 ug/L
<br /> Maximum TBA Concentrations MW-4, 740 ug/L
<br /> BACKGROUND
<br /> SJCEHD files indicate that there are three underground storage tank (UST) sites with documented
<br /> releases located near 7-Eleven Site No 17334 the Cardlock Gasoline Station at 4555 N Pershing
<br /> Avenue (100 feet east and crossgradient of the site), a Shell Service Station at 4445 N Pershing
<br /> Avenue (crossgradient of the site), and an Exxon Service Station at 4444 N Pershing Avenue
<br /> (crossgradient of the site) Exxon's well MW-9 is located adjacent to the 7-Eleven site property
<br /> boundary The Cardlock facility was reportedly under investigation for diesel contamination, and
<br /> received no further action in December 1997 Available SJCEHD records indicate the Cardlock
<br /> facility did not conduct analysis for methyl-tert-butyl ether (MtBE) or other oxygenates The Shell
<br /> site, according to available information, is due to receive regulatory agency closure shortly
<br /> Groundwater monitoring and sampling has been ongoing at the Exxon site since 1987, and
<br /> conducted at the Cardlock and Shell sites since 1992 In 1988 Exxon installed a 30-foot-deep
<br /> groundwater monitoring well, MW-9, approximately 10 feet east and 10 feet south of 7-Eleven's tank
<br /> pit The depth to groundwater in MW-9 has ranged from 30 feet below ground surface (bgs) in 1990
<br /> to 20 feet bgs in April 1996
<br /> On February 20, 1997, Fluor Daniel GTI supervised the advancement of four angled and three
<br /> vertical geoprobe borings (GP-1 through GP-7) at the site (Fluor Daniel GTI, 1997) Borings GP-1
<br /> through GP-6 were drilled beneath the three 10,000-gallon USTs In addition, groundwater grab
<br /> samples were collected from borings GP-3, GP-4, and GP-7 Benzene was detected in sod sample
<br /> GP-4 @ 17 feet at a concentration of 0 0095 milligrams per kilogram (mg/kg) Total petroleum
<br /> hydrocarbons as gasoline (TPHg) was not detected above laboratory reporting limits in any of the
<br /> soil samples collected The highest MtBE concentration was reported in sample GP-1 @ 15 feet at
<br /> 0 91 mg/kg The highest dissolved benzene, TPHg, and MtBE concentrations in groundwater
<br /> samples were reported in sample GP-4 at 9,100 micrograms per liter (ug/L), 150,000 ug/L, and
<br /> 84,000 ug/L, respectively
<br /> From September 23 through November 26, 1997, Fluor Daniel GTI supervised the drilling of five
<br /> groundwater monitoring wells (MW-1, MW-1A, MW-2, MW-3, and MW-4) to depths ranging from 35
<br /> to 40 feet bgs (Figure 2, Table 3)
<br /> On August 14, 1998, monitoring wells MW-1 and MW-1A were abandoned, as they were located
<br /> adjacent to the USTs that were removed on August 25, 1998 On August 25, 1998, approximately
<br /> 200 cubic yards of soil were excavated from the new tank pit to accommodate the installation of two
<br /> new double-wall steel 10,000-gallon USTs, and samples were collected at depths of up to 14 feet
<br /> bgs below/adjacent to the USTs and pump islands, and the product lines (Fluor Daniel GTI, 1998)
<br /> On December 17, 1998, a double-nested groundwater monitoring well (MW-5) was installed to a
<br /> depth of 40 feet bgs (Figure 2)
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<br /> 17334 03 1 Q Report SECOR International incorporated
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