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<br /> Second Quarter 2002 Monitoring and Sampling Report 2
<br /> 7-Eleven, Inc Store No 17334,4501 North Pershing Avenue, Stockton CA July 29,2002
<br /> ' Groundwater monitoring and sampling has been ongoing at the Exxon site since 1987, and conducted at
<br /> the Cardlock and Shell sites since 1992 In 1988 Exxon installed a 30-foot-deep groundwater monitoring
<br /> ' well, MW-9, approximately 10 feet east and 10 feet south of 7-Eleven's tank pit The depth to groundwater
<br /> in MW-9 has ranged from 30 feet below grade (bg) in 1990 to 20 feet bg in April 1996
<br /> ' On February 20, 1997, Fluor Daniel GTI supervised the advancement of four angled and three vertical
<br /> geoprobe borings (GP-1 through GP-7) at the site Soil samples were collected from the borings at depths
<br /> of 15 to 22 feet bg Six borings (GP-1 through GP-6)were drilled beneath the three 10,000-gallon USTs
<br /> at the site as required by the SJCPHS prior to tank lining permit approval In addition, groundwater grab
<br /> samples were collected from borings GP-3, GP-4, and GP-7 Benzene was detected in soil sample GP-4
<br /> ' @ 17 feet at a concentration of 0 0095 milligrams per kilogram (mg/kg) TPH-G was not detected in any
<br /> of the soil samples collected The highest MTBE concentration was reported in sample GP-1 @ 15 feet at
<br /> 0 91 mg/kg (EPA Method 8260) The highest dissolved benzene, TPH-G, and MTBE concentrations in
<br /> groundwater samples were reported in sample GP-4 at 9,100 micrograms per liter(µg/L), 150,000 µg/L,
<br /> and 84,000 µglL, 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 to 40
<br /> feet bg (Figure 2) Soil samples were collected during drilling at 5-foot-depth Intervals from 5 feet bg to
<br /> total depth In addition, the areas of well MW-1 and MW-2 were sampled continuously from 15 feet bg to
<br /> total depth A total of twenty-three soil samples collected from the soil borings were submitted for
<br /> ' laboratory analysis The groundwater monitoring wells were constructed of 2-inch-diameter, Schedule 40
<br /> poly-vinyl-chloride (PVC) casing with flush threads, and 0 020-inch-slot well screen Wells MW-1, MW-2,
<br /> ' MW-3, and MW-4 are screened from 13 to 33 feet bg, and well MW-1A is screened from 38 to 40 feet bg
<br /> On August 14, 1998, monitoring wells MW-1 and MW-1A were abandoned, as they were located adjacent
<br /> to the USTs, which were removed on August 25, 1998 On August 25, 1998, approximately 200 cubic
<br /> yards of soil were excavated from the new tank pit to accommodate the installation of two new double-wall
<br /> steel 10,000-gallon USTs A total of four soil samples were collected from the new UST excavation Soil
<br /> samples NTP-W-14' and NTP-E-14'were collected at a depth of 14 feet bg from the floor of the
<br /> excavation Samples SW-E-6' and SW-N-6' were collected from the side wall of the northeast corner of
<br /> the new tank pit excavation On July 17, 1998, Fluor Daniel GTI personnel collected six soil samples from
<br /> ' the floor of the UST excavation, from beneath each end of the three USTs at a depth of approximately 14
<br /> feet bg
<br /> On December 17, 1998, a double-nested groundwater monitoring well (MW-5)was installed to a depth of
<br /> 40 feet bg Each well segment is constructed of two 2-inch diameter Schedule 40 PVC casings with flush
<br /> threads and 0 020-Inch-slot well screen The deep well (MW-5B) is screened from 38 to 40 feet bg The
<br /> • shallow well (MW-5A) is screened from 13 to 33 feet bg
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<br /> ' 17334Q22 QMR DOC
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