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1 <br /> Third Quarter 2002 Monitonng Samphng,and Intenm Remediation Report 2 <br /> 7-Eleven Inc Store No 20632,4627 DaVinci Drive, Stockton,CA October 28,2002 <br /> GO Additional lateral and vertical assessment of dissolved MTBE and hydrocarbons has been conducted as <br /> required by the proposal to the SJCPHS There are currently seven site-related monitoring wells Most <br /> recent assessment activities Include the Installation of three onsite monitoring wells (MW-4R, MW-6, and <br /> MW-7) in April 2002, along with two dual-nested sparge/vent wells, SPV-1 and SPV-2, and a vertical <br /> delineation soil boring, SB-1 Additional offsite drilling on private property downgradient from the site Is <br /> planned for early 2003 <br /> Geology/Hydrogeology <br /> rXI <br /> The relatively flat site is located at an elevation of approximately 2 feet above mean sea level The site is <br /> underlain by Quaternary alluvial deposits Materials encountered during previous drilling at the site <br /> generally consisted of silts and clays to maximum exploratory drilling depths to 21 5 feet below grade (bg) <br /> Historically, groundwater has been encountered at depths ranging from 10 to 15 feet bg During the <br /> current sampling event, equilibrated depth to water ranged from 6 50 to 7 65 feet below top of casing <br /> (TOC) Historical groundwater flow has been to the south-southwest The potentiometric surface for the <br /> quarter is shown on Figure 2 <br /> Sensitive Receptors <br /> Previous reports indicate that there are no public water supply wells located within one mile downgradient <br /> of the site <br /> Groundwater Monitoring Data <br /> Before monitoring, the well caps were opened to allow the water In each well to stabilize to atmospheric <br /> pressure The DTW was measured to the nearest 0 01 foot from the top of the well casing using an <br /> interface probe <br /> A potentiometric surface map prepared using the quarterly groundwater elevation data is shown on <br /> Attachment 1, Figure 2 Based on the groundwater elevation data, groundwater flow is toward the south <br /> at an approximate hydraulic gradient of 0 002 foot per foot Monitoring data from the two recently installed <br /> monitoring wells MW-6 and MW-7 indicate that the groundwater flow direction is to the south Quarterly <br /> groundwater elevations for the quarter and historical monitoring results are presented in Tables 1 and 1A, <br /> respectively (Attachment 2) Field data sheets are included in Attachment 3 <br /> 1 <br /> 20632Q23 QMR DOC <br />