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Seven soil samples were submitted for hydraulic conductivity tests to Sierra Testing Laboratories in 1996. One sample of the Modesto channel deposit was collected from boring GT-4 at a depth of 45 feet, 6 feet above the base of the channel. This boring is located in the axial (deepest) part of the channel. The sampled consisted of fine-to-coarse- grained sand with small pebbles. The vertical hydraulic conductivity of the sample was 1.2 X 10"2 cm/sec, which is indicative of high permeability. At the time the sample was collected,the water depth was 67 feet in the monitor wells (13 feet below the bottom of the boring). However, the sample at the base of the channel deposit (51 feet) was saturated but the sample of the underlying silt bed (54 feet) was only moist to damp. This indicates that water at the base of the channel deposit was "perched" above the silt bed. A grab water sample was collected with a hydropunch from this perched zone, and the laboratory reported a diesel concentration of 1,730,000 ppb in the sample. The other hydrologic unit that lies within the zone of interest and is known to have moderate to high permeability is a sand bed that lies at the top of the Riverbank Formation below the post-Riverbank soil horizon. In some borings, the top of this sand bed is near 60 feet and the upper several feet of are weathered, cemented, and hard, due to soil formation. In others, evidence of soil formation was not observed and the sand is fine grained or poorly sorted at the top but grades rapidly downward to loose,coarser-grained sand. Three samples of the upper part of this sand at a depth of 65 feet were tested for hydraulic conductivity in 1996 from borings GT6, GT-8, and GT-9. The vertical conductivity ranged from 1.8 x 10'3 cm/sec to 9.8 x 10"5 cm/sec. This indicates that the sample from the Modesto channel was 10 to 100 times more permeable than the samples from the Riverbank Formation. This bed varies in thickness above an erosional base, which is at a depth of approximately 70 feet in GT-11 but may be deeper in other places. No samples from the lower part of this bed were tested for hydraulic conductivity. There are several possible reasons for the lower permeability of the Riverbank samples, including: 1) they were collected from the upper portion of the channel (fluvial sand bodies generally become finer grained upward as the channel is abandoned); 2) permeability may have been reduced by post-depositional soil formation; 3) primary differences in the Modesto and Riverbank depositional systems (i.e. channel hydraulics, geometry, flow regime, etc.); or 4) differences in primary mineralogy and susceptibility to post-depositional weathering (the Modesto sand contains unaltered lithic grains and is fresh and loose, whereas the Riverbank sand appears to be more quartzose and less feldspathic, suggesting that these less stable minerals have been altered to clay or dissolved during sediment diagenesis,reducing the original permeability. No samples from sand beds lower in the Riverbank Formation were submitted for hydraulic conductivity testing, although it is known from drilling that this sand is coarser grained and less weathered than sand near the top of the formation, which suggests that it is probably also more permeable. Samples were not tested because these beds were interpreted as being below the zone of soil contamination. Several samples from GT-3 and GT-11 were submitted for diesel analysis, and concentrations ranged downward from 3.4 ppm to below