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i -w- r t 630 Based on San Joaquin County Flood Control and Conservation District Equal Water Elevation Levels Maps for spring of the years 1975, 1984, and 1985 the seasonal high groundwater levels for this site have been less than 33' below grade. Water levels typically fluctuate 5-10 feet in a given yearly cycle. is Using data collected by WaterWork, the groundwater gradient is approximately 0.002 ft/ft or 11.08 ft/mile in an easterly direction (Figure 3). a. 2.7 Proximity of private, municipal and Irrigation wells: Domestic and irrigation wells located within a one-half mile radius of the subject site are shown on the well location map (Figure 4) . There are seven existing � } monitoring wells on the subject property. gxcundwater 3.0 INVESTIGATION METHODS AND PROCEDURES �». 3.1 Soil contamination i Figr 5 shows the orientation of two geological cross sections throughout the site r, (Figures 6 & 7). The crass sections (Figures b & 7) depict predominantly clay soils above 18' and in the interval 28' to 45' below grade. These clayey soils have very low permeability and are not amenable to soil remediation by vapor extraction. From approximately 18-28 feet the sediments are relatively sandy with varying amounts of fines. These sediments would be expected to vary in permeability from low to moderate and are also poor �{ candidates for vapor extraction. Due to the inability to treat soils in-situ, excavation extending to a total depth of 38' was utilized for soil remediation (Figure 8). Soil borings and sidewall samples have shown_ that the A; existing excavation has encompassed the lateral extent of soil contamination. The sample locations are shown on �., Figure 8 and the analytical results are summarized on Table 1. A three dimensional profile of soil hydrocarbon levels �r beneath the site can be. constructed using the analytical j rc suli;s obtained fr©mso- borings and pit wall,/floor samples. Using this data, the concentration of total petroleum hydrocarbons as gasoline (TPHG) have been contoured on Figures 9, 10 and 11 for the intervals 0-22 feet below grade, 22-33 feet below grade and below 33 feet, respectively. Where a boring was sampled.__at.- more......than- one- point . _in..an`interval the results were averaged. 3 r: