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Geological?ecFinics i=. Page 5 Former Moresco Property Site Characterization Report Project No. 251.2 A, October 11, 1996 3.0 RESULTS OF INVESTIGATION The data collected during this investigation have been summarized in the following sections. 3.1 Site Geology The geology of the site has been evaluated by observing sediments recovered in split spoon samplers during the field investigation. Selected samples were submitted for geotechnical and geochemical evaluation. The site's geology is typical for shallow valley sediments consisting of sand with varying amounts of silt and clay. A thin gravel layer was encountered at 63 feet. For conceptual purposes we have identified at least four distinct sediment types occurring between the surface and 100 ft; clean sand, sand with fines, clayey silt/silty clay, and sandy gravel. Representative samples from each lithologic type except for the gravel were submitted for geotechnical testing. Not enough gravel was able to be recovered in a .� relatively undisturbed condition(basic requirement for accurate geotechnical testing). The purpose of the geotechnical testing was to identify site specific fate and transport characteristics for each lithologic unit. This site specific information including permeability, porosity, moisture, dry density will enhance mass balance calculations and the confidence of future fate and transport modeling. Selected samples of each lithologic unit were submitted for geochemical testing. The purpose of the geochemical testing was to identify site specific fate and transport attenuation characteristics for each lithologic unit. This site specific information including cation �. exchange capacity, total organic carbon, % organics, and the carbon-nitrogen-phosphorous ratio offers insight with respect to those parameters that might limit or promote contaminant attenuation by adsorption or biologic attenuation. The detailed boring logs are attached in Appendix B and a geologic cross section is presented in Figure 3_ *• 3.2 Site Hydrology The exact depth to groundwater at this site is not known at this time. However, on June 18, 1996 depth to groundwater was measured to be approximately 110 feet bgs in the domestic well. Construction details of this well are not known.. San Joaquin County Flood Control Maps for Spring 1986 (considered year of high water occurrence) show the depth to - — groundwater to be approximately 90 feet bgs. We suspect that regional groundwater flows to the southwest based on the contour lines of the Flood Control Maps. However, this may be altered by influence of the domestic well LW located 200 feet east of the former tank location.