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' Pombo Property Soil & Groundwater Sampling • 2.3 Groundwater Sampling A travel blank, provided by the laboratory, accompanied the sample vials from the time they are picked up from the lab to the time they are delivered to the lab. This travel blank would have been analyzed only if all samples contained the same contaminants. ' All sampling equipment, including the stainless steel Geoprobe' screen point, used by sampling personnel, was disassembled and cleaned prior to commencement of sampling. These procedures were also used between each boring. The groundwater samples were analyzed or extracted within 14 days according t o their EPA methods. The samples were analyzed for Total Petroleum Hydrocarbons (gasoline), BTX&E (Benzene, Toluene, Xylene, and Ethyl Benzene) and the Oxygenated compounds by EPA Method 8260. Analysis was conducted by GeoAnalytical Laboratories. Laboratory analyses of the Organophosphate group ' and Chlorinated Pesticides, EPA Methods 622 and 608, were conducted on selected samples. Method 601 was used for the various refrigerants. e� ' 3.0 SITE CONDITIONS '. 3.1 Site Geology & Groundwater Occurrence The Pombo Ranch is located on the southwestern edge of the San Joaquin Delta. ' The shallow unconsolidated sediments present at Pombo Ranch are composed fine- grained overbank and coarse grained channel deposits sourced from Cretaceous and Tertiary rocks exposed in the Coast Range Mountains to the west. Soil boring logs are presented in Appendix B. The sediments encountered in the area of the above and underground fuel storage i' tanks (borings 1,2,3,4,5,and 7) are composed of tan silty plastic clays which grade into a tan very fine grained, well sorted, silty sand at approximately ten feet below grade. A coarse sand to pebble, very poorly sorted sand is present the base of borings B-5 and B-7, Imported fill (dark brown organic rich clay) possibly related to the removal of the underground storage tank was encountered in Boring B-3. Groundwater was encountered at depths of 8 to 10 feet below grade in the fine grained silty sand strata. Groundwater was encountered at depths greater than 10 feet where the silty clays were present at depths of ten feet or greater. This suggests that locally the water table is confined beneath the clay unit. The coarse sand ' encountered in borings B-5 and B-7 is probably a channel deposit and may form a preferential pathway for groundwater and contaminant movement. Boring B-6 located at the Truck and Trailer wash area encountered a well-sorted . silty sand overlying a dry firm silty clay. The presence of moisture in the upper sand unit suggests that a local perched zone is present. i1 ,' 4