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1 , 31 October 2005 AGE-NC Project No 03-1080 ' Page 8 of 10 TPH-g and TPH-d fractions would be mainly in the aliphatic fractions For the more conservative t fate and transport analysis, AGE elected to spread the TPH-g'and TPH-d concentrations equally across the aliphatic TPH spectrum,although aged TPH-g fractions should be localized in the higher, less-volatile portion of the TPH spectrum (see Appendix E, Appendix G) ' Utilizing RISC Workbench, AGE conducted a 100-year fate and transport study to analyze the, potential impact of contaminated soil and ground water at the dispenser D 1 location to any shallow ' ground water well located approximately_45 feet down-gradient of the dispenser location-The fate and transport model—used in the study was based on the site conceptual model soil profile of dominantly sandy silt/silty sand soil separated by an intervening 5-foot clayey silt and silt interval�- at 15 feet bsg (Figures 3 and 4} _The contaminant source is located in the vadose zone, since first- encountered ground water occurs at approximately 30 feet bsg AGE analyzed the fate of contaminant concentrations in soil beneath dispenser DI utilizing a vadose zone_contaminant transport model In this model,the mass of chemicals in the source is assumed to be leached to the water table due-o infiltration Default RISC Workbench values were selected for ' a sandy silt soil with an intervening silty claylaver Utilizing ground-water infiltration rate equations of Connor and others(107T,an averaged infiltration rate of 1 06 inch/year was calculated for sandy I silt-type soils,based on a City of Stockton average rainfall of L7 3 nches/year,the actual infiltration rate is probably considerably lower since the site is covered by asphalt and concrete Model parameters are provided in Appendix G ' The vadose zone fate and transport model predicts that there should not be any impact to ground water at the dispenser D1 location from the aged petroleum hydrocarbon-impacted soil (Table 5, ' Appendix G), there should be no impact to any down-gradient wells ' 8.0. SUMMARY AND CONCLUSIONS , Based upon a review of site assessment activities at the Lathrop Gas and Food Mart to date, AGE ' concludes • The general soil profile at the dispenser location consists dominantly of silty sand and sandy " ' silt, interbedded with finer-grained intervals of clays and silts at approximately 15 feet, 25 feet and 35 feet bsg (Figures 3 and 4) J • Ground water depths at the site have fluctuated between 30 feet and 35 feet bsg, ground water flow direction has generally been toward the northeast, although easterly and southwesterly flow directions have been recorded ' Contaminants of concern (CDCs) detected in soil at the dispenser location include TPH-g, TPH-d, ethylbenzene, xylenes, 1,2-DCA, and TBA at maximum concentrations of Advanced GeoEnvironmentai,Inc 1