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Site Geology and Hydrogeology <br /> ' The borings made on the site indicate that material above <br /> ' approximately 9 to 10 feet is probably fill . The substantial <br /> difference in the geologic boring logs (Appendix A) and the piece <br /> of wire found in well M-2 at nine feet provide evidence that <br /> geologic material was imported. Because the groundwater level is <br /> ' approximately six-feet below ground surface, it is unclear <br /> whether the addition of fill material has disrupted normal local <br /> groundwater flow patterns. <br /> The water levels in the cased exploratory test holes and <br /> monitoring wells on the Tesoro site were measured on March 23, <br /> t1988. The water-level measurements and well elevations are given <br /> in Table 2 . Figure 2 shows the potentiometric surface of the <br /> water table on the Tesoro site. Based on the data, it can be <br /> t concluded that the predominant direction of groundwater flow on <br /> the Tesoro property is to the east-southeast . This finding is <br /> consistent with previous studies conducted for the Port of <br /> Stockton by Woodward Clyde & Associates . The data show that the <br /> Tesoro site is downgradient from the originally observed wet spot <br /> along the Southern Pacific pipeline right-of-way and Time Oil <br /> property boundary. <br /> Product Thickness Sampling Results <br /> Table 3 presents the results of hydrocarbon thickness mea- <br /> surements in the exploratory test holes. Floating hydrocarbon <br /> product has been measured only in test holes that border the Time <br /> Oil property and Southern Pacific pipeline right-of way. <br /> - 9 - <br />