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C,eologfcaI7eChnas Inc Page 3 ' In Situ Remediation Feasibility Study Project No 507 2 • September 20,2002 1 Sample Permeability Organics Density Porosity ' (cm/sec) % (dry) % MW-7 @ 20' 1 x 10E-7 2 1 995 4308 ' MW-10 @ 25' 1 x 10E-6 16 905 48 1S MW-10 @ 30' 9 x 10E-7 1 3 939 4624— MW-109 624MW-109 @ 75' 3 x 10E-6 20 825 5275 SB-6 @ 35' 2 x 10E-4 08 103 8 3842 The occurrence of predominantly fine grain units was confirmed as evident in the above table The clayey soils in the upper 20 ft of MW-109 contained prominent field evidence of contamination - odor and staining The 80-foot sample in MW-109 had a faint hydrocarbon odor, and the OVM detected 19 parts per million organic vapors The deeper soil encountered in SB-109 was a blue/grey to blue/green color so it was difficult to visually determine when dulling had progressed past the contamination 2.2 Hydrogeology of Site @ The historical groundwater directions and gradients are shown in Figure 3, Groundwater Gradient Rose Diagram The groundwater elevation data are summarized in Table 1, Appendix A Figures 5 and 7 illustrate the historical range of groundwater elevation on the cross sections Table 5 provides a summary of monitoring well construction The groundwater gradient is relatively flat and the direction of groundwater has vaned 1 during the course of the investigation As evident in Figure 3, groundwater had a strong bifurcated flow regime, trending predominantly to the southwest or north-northeast at approximately 180-degree direction reversal With the installation of wells MW-7 and ' MW-10 in May 2001, the direction had been to the east-northeast in four of five events The site is quite close to the San Joaquin River and tidal fluctuations may contribute to some of the observed changes in groundwater direction Vertical Groundwater Gradients Under vertical groundwater flow conditions, the water level in a monitoring well is a function of the length of the well screen and its depth or vertical position in the aquifer As with horizontal flow conditions, the diameter of the well or piezometer is immaterial The following procedure is used to calculate vertical groundwater gradient a Determine the vertical distance between the two measuring devices by the distance from ' the mid-point between the tap and bottom seal of the deep well (MW-109) and the mid- point between the groundwater elevation and the bottom seal in the shallow well (MW- 9) 0 Measure the head in both wells used in the calculations