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The Modesto Channel passes underneath the UST cavity and then turns eastward and trends almost N-S All borings planned for future drilling (GT-16 through GT-21) are expected to encounter this channel, and GT-16 and GT-20 should be close to its axis The 1St Riverbank Channel is oriented differently East of the UST cavity, it trends north-south, but its absence in CPT-5 indicates that it must curve westward before reaching that boring (Figure 7) The axis of the channel apparently passes between CPT-5 and the UST cavity, because the sand body is 15 feet tluck in GT-14 but thins to less than 10 feet in the vicinity of cavity Hence, the channel has a more sinuous geometry than does the overlying Modesto Channel As illustrated in the boring logs,the I` Riverbank aquifer fines upward from coarse-grained to fine- grained sand One sample collected from the base of the sand body in GT-8 at 65 feet had a hydraulic conductivity of 1 8 x 10"3 cm/sec (Figure 7) A sample of poorly-sorted sand at the same depth in GT-6 was tested at 9 8 x 10-5 cm/sec, and a sample of fine-to-medium-grained, well-sorted sand collected from the upper portion of the sand body in GT-9 at a depth of 60 feet yielded a hydraulic conductivity of 7 3 x 10-5 cm/sec This upward decrease in permeability is consistent with the grain-size trend Cone penetrometer data, such as those from CPT-2, also indicate that hc declines upward, from 102 cm/sec at 71 feet to 10-4 at 61 feet Hence, an average hydraulic conductivity for this aquifer might be 104 cm/sec, about two orders of magnitude less than that of the Modesto aquifer The trend of the 2nd Riverbank Channel is similar to that of the l" Riverbank Channel, but the axis is offset approximately 40 feet to the north (Figure 8) The axis of this channel is between those of the 1St Riverbank and Modesto channels (c f Figures 6 and 7) This deposit is thicker, exceeding 25 feet in both GT-2 and GT-3, coarser grained (consisting of several feet of sandy gravel in some borings), and more deeply incised into underlying deposits than either of the upper two aquifers None of the CPT bonngs were located in the thickest or coarsest portion of the 2nd Riverbank aquifer, but CPT-I and CPT-4 were located on either side of this axis where the sand body was 7-8 feet thick (Figure 4) Hydraulic conductivity calculations from the CPT logs yielded h, values of 10-3 to 10"5 cm/sec in this aquifer Presumably, h, is at least an order of magnitude greater in the center of this sand body (in the vicinity of GT-3 in Figure 4) The only sample from this channel deposit that was collected for hydraulic conductivity testing consisted of moderately well-sorted fine-to-medium-grained sand at 92 feet in the lower part of this sandibody in boring GT-13 This sample had an h, of 3 7 x 10-4 cm/sec (Appendix E) The maximum h, in this aquifer is probably comparable to that in the Modesto aquifer The 3`d Riverbank Channel was penetrated only in a few bonngs, but it appears to trend mostly east-west (Figure 9) Only three borings penetrated its full thickness, but the contours suggest that this deposit is less than 20 feet thick The isopach "thin" at boring CPT-1 could be interpreted to suggest that this channel was braided, with deeper channels separated by interchannel bars or overbank deposits Only one sample of this channel deposit was tested for hydraulic conductivity Sand to the lower part of this aquifer in GT-13 2s fine to medium grained and moderately sorted to well sorted, and has an hC value of 5 9 x 10"5 cm/sec (Appendix E) This agrees perfectly with calculated values of 5 x 10"5 cm/sec in sandy lenses from the CPT log in boring CPT-4, along the 6