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• 7-Eleven Store #32262 Work Plan for Additional Site Assessment and Interim Remediation March 19, 2004 Page 3 • 2450 Toste Road, Former Curtiss Pontiac Buick, and • 2353 Taste Road,Tracy Marine and Sales Due to the proximity of the Shell and Grant Line Food and Gas Sites, their groundwater monitoring wells and the 7-Eleven groundwater monitoring wells were surveyed jointly and plotted on an aerial photograph included in Attachment B The well locations are also shown on Figure 5 Details related to the two adjacent sites are presented below • 2420 Grant Line Road — Grant Line Food and Gas The site is an active Valero gas station with eight monitoring wells MW-1 through MW-8 (Figure 5) Groundwater monitoring and sampling have been performed since at least 1994, according to Advanced GeoEnvironmental, Inc 's Quarterly Report, First Quarter 2003, dated May 21, 2003 (Attachment C) Depth to water onsite has ranged between approximately 8 and 10 5 feet bgs The groundwater flow direction at the site has been to the north-northwest for ten of the twelve monitoring events provided in the quarterly report The maximum concentration of dissolved MtBE was reported at 360 ug/L in well MW-8 located northeast of the underground storage tanks (Figure 5) • 2375 Grant Line Road — Shell Gasoline Station The site is an active Shell gas station • with four USTs and four groundwater monitoring wells (MW-1 through MW-4), which were installed in early 2003 Monitoring and sampling have been performed since February 2003 The site is located north (downgradient) of the 7-Eleven site across Grant Line Road Based on the 4th quarter 2003 groundwater monitoring report (Attachment C), the groundwater gradient at the site is northward In the fourth quarter 2003, maximum MtBE concentrations were reported in well MW-1, located north (downgradient) of Shell's USTs, at 2,900 Ng/L MW-4, located upgradient of Shell's USTs, contained 74,ug/L of MtBE (Figure 5) Due to greater distance of the Former Curtiss Pontiac Buick and the Tracy Marine Sales Sites from the 7-Eleven site, the well locations for the two sites were not posted on the aerial photo or on Figure 5 Cone penetrometer test (CPT) borings encountered discrete sand beds ranging from 5 to 10 feet thick at depths ranging from 15 to 65 feet bgs (Attachment C) GEOLOGIC AND HYDROGEOLOGIC SETTINGS Site Geology and Hydrogeology Based on the description of the soil samples collected from the 7-Eleven site, the lithology underlying the site is dominated by silt with minor amounts of gravel and clay, from ground surface to 17 feet bgs In MW-6D, silt, with minor amounts of sand and clay, was encountered from ground surface to total depth (51 feet bgs) As discussed above, CPT boring data collected from the Former Curtiss Pontiac Buick and the Tracy Marine Sales sites encountered discrete sand beds from 15 to 65 feet bgs Groundwater was observed at approximately 10 feet bgs No obvious low permeability, confining layer (clay or silt) was observed in the soil borings (Figures 6 and 7 and Attachment C) Geologic cross sections showing lithology beneath the 7-Eleven site are presented as Figures 6 and 7 Copies of the soil boring logs are included in Attachment C along with the cross sections from the Former Curtiss Pontiac Buick and the Tracy Marine Sales Sites Based on well monitoring data collected October 30, 2003, the groundwater flow direction from the 7- Eleven site is toward the north with a gradient of 0 004 feet per foot (ft/ft) (Figure 3) On the adjacent 32262 Offsite well install and interim remediation workplan doc SECOR International Incorporated