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I Second Quarter 2002 Monitoring, Sampling, and Interim Remediation Report 3 7-Eleven, Inc Store No 20632 4627 DaVinci Drive Stockton,CA July 25,2002 Monitoring Well Sampling and Analytical Results Quarterly groundwater samples were collected after purging at least four well-casing volumes of groundwater from each monitoring well, unless the well was purged dry Prior to purging, dissolved oxygen (DO) levels were recorded in each well Groundwater samples were collected using disposable bailers Samples were placed in analysis-specific containers with analysis-specific preservative The samples were then sealed using Teflon septum caps, labeled with the fob identification number, and the sample number, date, time, and type of laboratory analysis required The samples were stored on ice and transported with a chain-of-custody record to a state-certified laboratory for analysis Groundwater samples were analyzed for BTEX and TPH-G using Environmental Protection Agency (EPA) methods 8021 B/modified 8015, and for oxygenates MTBE, TBA, DIPS, ETBE, and TAME using EPA method 82606 Dissolved benzene was detected at relatively low levels in two wells (MW-4R [320 micrograms per liter {dig/L)] and MW--5 [20 pg/L]) Dissolved MTBE was detected in all wells at concentrations ranging from 1 1 pg/L in well MW-6 to 22,000 pg/L in well MW-7 Quarterly and historical analytical results for groundwater samples are summarized in Tables 1 and 1A, respectively (Attachment 2) Selected dissolved constituents are plotted on Figure 2 Laboratory analytical reports are included in Attachment 4 Dissolved oxygen (DO) levels ranged from 0 8 milligrams per liter(mg/L) in well MW-1 to near 6 mg/L in the Faillah three new monitoring wells, indicating anaerobic (less than 2 0 mg/L) to aerobic conditions Furthest(new) downgradient well MW-7 contains 22,000 pg/L MTBE, additional lateral plume delineation is needed, and access requirements to install another well further downgradient are currently under l J negotiation with offsite private property owners New well installation is scheduled for third quarter 2002 pending successful access Purgewater Transportation and Disposal All purgewater generated during this quarterly monitoring and sampling event was stored onsite in 55-gallon Department of Transportation (DOT)-approved drums, pending characterization and proper Ddisposal at a licensed recycling facility Waste disposal documentation will be forwarded if requested aConclusion and Recommendations Additional delineation is recommended to proceed as soon as possible, followed by submittal of a recommendations for remedial action Site remediation (at least in the source area and/or within site boundaries) is recommended to commence by the start of early fourth quarter 2002 20632Q22 QMR DOC