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"MMIRM IN Mr. R.W. Conlon 20W 50-4150 October 3, 1990 Page 14 4.0 SITE CONDITIONS 4.1 HYDROGEOLOGY The site is located on the northern edge of the San Joaquin Baain within the Great Valley of California. The Great Valley,also known as the Central Valley,is a nearly flat alluvial plain extending from the Tehachapi Mountains on the scuth to the Klamath Mountains on the north, and from the Sierra Nevada on the east to the Coast Ranges on the west. Geologically,the Gcaat Valley is a large,elongated, northwest trending,asymmetrical structural trough that has been filled with a thick sequFnce of sediment ranging in age from Late Jurassic to Recent. Recent alluvium and lake deposits cover most of the central lower parts of the valley. Generally,the valley is subdivided into two sub-bascis, the Sacramento and San Joaquin Basins,by the cross-valley Stockton fault, Drainage from the San Joaquin Basin is through the San Joaquin,River,which is approximately 1.5 miles south of the site. The sediments encountered during drilling operations consisted of interbedded slits and clays and in some wells a fine,unconsolidated sand was encountered at approximately 45 feet (Figures 7 and 8). During the drilling operations water levels within the borings rose 2 to 3 feet from the depth at which they were first encountered,indicating the water table beneath the site is semi-confined. Monitrwing wells were last gauged an June 14,1990 and the depth to water ranged between 35 and 36 feet below ground surf are,which is approximately five feet lower than levels measured a year ago. Groundwater monitoring data for June 14,1990 Is presented in Table 2. There is a mound in the water table centered around MW- 2 which indicates that the groundwater gradient is divergent from MW-2 in all directions across the site, as shown on trio potentiometric surface map (Figure 9). 4.2 SOIL SAMPLING RESULTS A total of 79 soil samples were sent to a State-certified laboratory for analysis. Fifteen samples contained detectable concentrations of hydrocarbon constituents ranging from 2 to 2,500 ppm TPF{-G. Nine samples contained detectable concentrations of benzene ranging from 1 to 11 ppm. Sample MW-5C contained 11 ppm TOG. Sample Ala-3E contained 0.4 ppm organic lead. Results from the laboratory analysis of soil are summarized in Appendix III and copies of laboratory reports are presented In Appendix 1V. GROUNDWATER TECHNOLOGY,INC. _J