ARCHIVED REPORTS_XR0009152 - Laserfiche WebLink

Home Browse Search

Third Quarter 2002 Monitoring and Sampling Report 2 7-Eleven, Inc Store No 17334 4501 North Pershing Avenue Stockton,CA October 29 2002 Groundwater monitoring and sampling has been ongoing at the Exxon site since 1987, and conducted at the Cardlock and Shelf 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 grade (bg) In 1990 to 20 feet bg 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 site (Fluor Daniel GTI, 1997) Soil samples were collected from the borings at depths of 15 to 22 feet bg Six borings (GP-1 through GP-6)were drilled beneath the three ' 10,000-gallon USTs at the site as required by the SJCPHS prior to tank lining permit approval 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) TPH-G was not 1 detected in any of the soil samples collected The highest MTBE concentration was reported in sample GP-1 @ 15 feet at 0 91 mg/kg (EPA Method 8260) The highest dissolved benzene, TPH-G, and MTBE concentrations In groundwater samples were reported in sample GP-4 at 9,100 micrograms per liter(µg/L), 150,000 µg/L, and 84,000 pg/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 bg (Figure 2) Soil samples were collected during drilling at 5-foot-depth intervals from 5 feet bg to total depth In addition, the areas of well MW-1 and MW-2 were sampled continuously from 15 feet bg to total depth A total of twenty-three soil samples collected from the soil borings were submitted for laboratory analysis The groundwater monitoring wells were constructed of 2-inch-diameter Schedule 40 poly-vinyl-chloride (PVC) casing with flush threads, and 0 020-inch-slot well screen Wells MW-1, MW-2, 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 ' On August 14, 1998, monitoring wells MW-1 and MW-1A were abandoned, as they were located adjacent to the USTs that were removed on August 25, 1998 On August 25, 1998, approximately 200 cubic yards of soil 1 were excavated from the new tank pit to accommodate the Installation of two new double-wall steel 10,000- gallon USTs, and samples were collected at depths of up to 14 feet bg below/adjacent to the tanks/islands and lines (Fluor Daniel GTI, 1998) ' On December 17, 1998 a double-nested groundwater monitoring well (MW-5)was installed to a depth of 40 feet bg (Figure 2) Each well segment is constructed of two 2-inch diameter Schedule 40 PVC casings with flush threads and 0 020-Inch-slot well screen The deep well (MW-5B) is screened from 38 to 40 feet bg The shallow well (MW-5A) is screened from 13 to 33 feet bg 1 17334023 QMR DOC