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1 Third Quarter 2002 Monitoring and Sampling Report 3 7-Eleven, Inc Store No 17334 4501 North Pershing Avenue Stockton,CA October 29,2002 On April 3 and 4, 2002, soil boring SBA was advanced to a depth of 50 feet bg where a grab groundwater sample was collected by Hydropunch (IT Corporation, 2002) Two double-nested SVE/AS wells (SPV-1 and SPV-2)were also installed to 30 feet bg, and soil samples were collected at total depth in the borehole of each well The deep well segments were screened from 25 to 30 feet bg The shallow well segments were ' screened from 12 to 22 feet bg TPH-G was detected in a soil sample from SPV-1 at 30 feet bg MTBE was not detected in soil samples from either well boring Dissolved benzene, TPH-G, and MTBE were detected in groundwater samples from SBA @ 50' bg, at concentrations of 28 pg/L, 7,100 pg/L, and 67 pg/L, respectively ' Additional downgradient dissolved plume assessment is pending offsite private property access A workplan for additional site assessment will be submitted in early 2003 Geology/Hydrogeology The relatively level site is located at an elevation of approximately 8 feet above mean sea level The site is underlain by Quaternary alluvial deposits assigned to the Modesto Formation (Fluor Daniel GTI, Additional Site Assessment Report, January 15, 1998) Materials encountered during previous drilling at the site generally consisted of clayey silt and sandy silt to approximately 24 feet bg, followed by interbedded clayey silt and silty fine sand to maximum exploratory drilling depths ranging from 35 to 40 feet bg The depth to groundwater in MW-9 has ranged from 30 feet bg in 1990 to 20 feet bg in 1996 During the current sampling event, equilibrated depth to groundwater in sampled wells at the site ranged between 17 25 to 17 67 feet below top of casing (TOC) Seasonal water table fluctuations average 2 to 3 feet Historically, groundwater flow direction at the subject site and adjacent facilities has been to the northeast Sensitive Receptors Previous reports on sensitive receptors indicate that there are no public supply wells within 4,000 feet downgradient of the site The nearest crossgradient/upgradient water supply well is of unreported status and lies about 1,500 feet away Groundwater Monitoring Data Before monitoring, the well caps were opened to allow the water in each well to stabilize to atmospheric pressure The DTW was measured to the nearest 0 01 foot from the top of the well casing using an Interface probe ' A potentiometric surface map prepared using the quarterly groundwater elevation data is shown on Attachment 1, Figure 2 Based on the groundwater elevation data, groundwater flow Is toward the northeast at an approximate gradient of about 0 006 foot per foot, consistent with historic measurements Groundwater monitoring results for the quarter and historical monitoring results are presented in Tables 1 and 1A, respectively (Attachment 2) Field data sheets are included in Attachment 3 1 ' 17334Q23 QMR DOC