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First Quarter 2002 Monitoring and Sampling Report 2 7-Eleven Inc Store No 17334,4501 North Pershing Avenue, Stockton,CA April 22,2002 ' on evaluations of site assessment and feasibility testing needs and access-related drilling conditions Results and specific assessment steps will be submitted under separate cover ' Geolo IH dro Bolo 9Y Y g 9Y 1 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 below ground surface (bgs), followed by interbedded clayey silt and silty fine sand to maximum exploratory drilling depths ' ranging from 35 to 40 feet bgs The depth to groundwater in MW-9 has ranged from 30 feet bgs in 1990 to 20 feet bgs in 1996 Depth to ' groundwater for the current quarter ranged between 15 59 to 16 72 feet below grade 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 4000 feet downgradient of the site The nearest crossgradient/upgradient water supply well is of unreported status ' and lies about 1,500 feet away Other wells within 2000 feet of the site are not in hydraulic communication with shallow groundwater at the site ' 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, and the resulting data was used to prepare a potentiometric surface map (Attachment 1, ' Figure 2) Based on the potentiometric surface map, groundwater flow is toward the northeast at an approximate gradient of about 0 005 foot per foot, consistent with historic measurements Groundwater ' monitoring results for the quarter and historical monitoring results are presented in Tables 1 and 2, respectively (Attachment 2) Field data sheets are included in Attachment 3 I ' Monitoring Well Sampling and Analytical Results Quarterly groundwater samples were collected after purging at least 4 well-casing volumes of groundwater ' from each monitoring well, unless the well was purged dry The groundwater samples were collected using disposable bailers Groundwater samples were placed in analysis-specific containers with analysis- 17334Q21 QMR DOC 1