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Second Quarter 2002 Monitoring, Sampling,and Interim Remediation Report 2 7-Eleven, Inc Store No 20632 4627 DaVmci Drive,Stockton CA July 25 2002 I Additional lateral and vertical assessment of dissolved MTBE and hydrocarbons was proposed to the SJCPHS as required The proposed scope of work Included the installation of a downgradient monitoring well, Installation of a replacement well for former well MW-4 (abandoned during tank removal), and a vertical delineation soil boring The scope of work was revised in the field (April 2002) due to access restrictions and addition of feasibility testing wells as approved by the SJCPHS Three monitoring wells (MW-4R, MW-6, and MW-7) were installed In April 2002 and were Included in the second quarter monitoring and sampling event In addition, two dual-nested sparge/vent wells, SPV-1 and SPV-2, and a vertical delineation soil boring, SB 1, were installed during the same field mobilization The revised scope of work will be detailed in the report of findings (in preparation) Geology/Hydrogeology The relatively flat site is located at an elevation of approximately 2 feet above mean sea level The site is underlain by Quaternary alluvial deposits Materials encountered during previous drilling at the site generally consisted of silts and clays to maximum exploratory drilling depths to 21 5 feet below grade (bg) Historically, groundwater has been encountered at depths ranging from 10 to 15 feet bg During the N current sampling event, equilibrated depth to water ranged from 6 02 to 7 30 feet below top of casing (TOC) Historical groundwater flow has been to the south-southwest The piezometric surface for the quarter is shown on Figure 2 a Sensitive Receptors Previous reports indicate that there are no public water supply wells located within one mile downgradient of 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 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 southwest at an approximate hydraulic gradient of 0 002 foot per foot Quarterly groundwater elevations 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 The potentiometric surface map does not include data for the new wells MW-4R, MW-6, and MW-7, as these wells were not yet surveyed when the map was prepared 20632Q22 QMR DOC