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1 S <br /> Ile 27 October 2004 <br /> AGE-NC Project No 96-0254 <br /> Page 8 of 10 <br /> ' The nearest surface water feature to the site is the Stanislaus River,located approximately five miles <br /> south of the site First encountered ground water is not used for drinking or irrigation, although all <br /> ground water in the State of California is considered to be of potential beneficial use Results of the <br /> Investigation were reported in the AGE-prepared Well Survey, dated 20 April 2000 <br /> 7.0 SITE CONCEPTUAL MODEL <br /> Based on the data collected to date from soil borings and ground water monitoring wells, AGE has <br /> developed a site conceptual model for the release,migration and distribution of the contaminants in <br /> the subsurface as described below <br /> ' Release(s)of petroleum hydrocarbons occurred from the on-site gasoline USTs,the diesel UST and <br /> the least at the shallow fuel dispensers Once released to the subsurface,the contaminants migrated <br /> vertically Into the sand near the water table at the site <br /> STRATIGRAPHY ' <br /> Silty sand was encountered from surface grade to approximately 30 feet west and east of the former <br /> ' diesel UST, while silty sand and interbedded silty clay was encountered south and north of the <br /> former diesel UST from depths of 15 to 30 feet bsg A clay to clayey silt layer was encountered at <br /> the base of the former diesel UST area from a depth of 20 to 25 feet bsg A sand layer was <br /> encountered south of the UST at a depth of 20 feet and under the UST at a depth of 25 feet bsg Silt <br /> and coarse sand were encountered from a depth of 30 feet to 45 feet bsg,while clay or silty clay was <br /> observed in deep borings B7 to B9 at 45 feet bsg <br /> Boring logs are attached as Appendix A Lines of cross sections are shown on Figure 2 Stratigraphic <br /> cross sections are presented on Figure 4 <br /> PETROLEUM RELEASE SOURCE <br /> Release(s)of petroleum hydrocarbons occurred from the on-site gasoline USTs,the diesel UST and <br /> the fuel dispensers The UST removal samples Indicated TPH-d from the diesel UST and fuel from <br />' the dispensets, while MTBE only was detected itt soil sample c,olloctud from the former gasoline <br /> UST common excavation on the southern portion of the site xmr- iows +ZAP' dil l aay <br /> 1 saI i lAsples bra �C. o", VT <br />' Once released to the subsurface, the contaminants migrated vertically Into the sand near the water <br /> table at the site The dominant ground water flow direction has been north to northwest, causing the <br /> Advanced GeoEnvironmental,Inc <br />