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r I CAMBIA ® Table 1.Site Conceptual Model,Shell-branded Service Station,2494 East Fremont Street,Stockton,California i i 2 10 Preferential Pathways Analysis No analysis has been performed However, due to groundwater depth (a least 46 fbg), it is highly unlikely that any utility trenches would act as a preferential pathway for groundwater migration 2 11 Other Pertinent Issues Groundwater has risen significantly in the vicinity of the site since the 1970s Historical depth to water information for the area suggests groundwater levels may have been 70 to 80 fbg during the 1970s It appears that the release at this site may be an old release Since fuel oxygenates (most notably MTBE) have not been detected at significant concentrations at this site, this suggests the release occurred prior to the introduction of fuel oxygenates into gasoline In addition, since TPHg and BTEX have been detected at depths of 70 to 80 fbg, this suggests the release may have occurred when groundwater level was lower than it is today These components of gasoline have a specific gravity less than that of water and typically do not migrate downward 3 Rernediation Status 3 1 Remedial Actions Taken During the 1996 tank removal activities, approximately 15 cubic yards of soil were overexcavated from the UST pit, and 20 cubic yards of soil were overexcavated from the northestern dispenser island 3 2 Area Remediated The areas beneath the former USTs and dispensers 3 3 Remediation Effectiveness Unknown 4 Well and Sensitive Receptor Survey 41 Designated Beneficial Water Existing and potential beneficial uses include municipal and domestic Use water supply, agricultural supply, industrial service supply, and industrial process supply(CVRWOCB Basin Plan) 4 2 Shallow Groundwater Use A well survey conducted by Cambria in 2001 did not identify wells screened in shallow groundwater within a 2,000 foot radius of the site 4 3 Deep Groundwater Use A well survey conducted by Cambria in 2001 identified three water supply wells within a 2,000 foot radius of the site The closest well, which is located approximately 600 feet southeast of the subject site, is screened from 165 to 176 fbg 4 4 Well Survey Results A well survey conducted by Cambria in 2001 identified three water supply wells within a 2,000 foot radius of the site The closest well, which is located approximately 600 feet southeast of the subject site, is screened from 165 to 176 fbg A second well was identified that is 900 feet south of the site, and the third well is located approximately 1,950 feet west of the site 45 Likelihood of Impact to Wells It is unlikely TPHg and STEX have impacted water supply wells due to the limited extent of their plumes 1,2-DCA concentrations show significant attenuation between the suspected souce area and the southeast corner of the site, which suggest the plume likely does not extend far offsite i 0955 Page 3 of 4 Date Modified 8/14/2003