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section A-B) This zone is distinguished by exceptionally low friction ratio (Rf), ranging from 0 3 to 0 6 % in the lower portion in some borings (e g CPT-1, 42-54 feet) This low ratio is due to a combination of the low sleeve friction (fs) (lack of clayey, cohesive sediment) and the high cone bearing (qt) (due to the presence of gravel and coarse sand) The friction ratio rises to approximately 2% upward through the zone, which corresponds to the upward-fining texture of this sand body as described in previous reports Overlying and underlying the Modesto Channel are finer-grained stratigraphic units that are characterized by lower cone beartng, higher sleeve friction and pore pressure, and higher friction ratio Over most of the site the upper zone is relatively uniform in thickness (30 feet) but the lower zone varies from more than 30 feet in CPT-6 to as little as 5 feet in CPT-1 This is due to erosion at the base of the Modesto Channel The lower zone has been referred to as the Modesto Aquitard, and it represents the initial fine-grained deposition of glacial outwash during the glacial stage that succeeded the Riverbank interglacial stage (soil-fonriing episode) Foot-by-foot calculations of the permeability by Gregg In-Situ yield values of 10"5 cm/sec or less for the aquitards and values of 10"2 to 104 cm/sec for the Modesto Channel (Appendix A) These values are in excellent agreement with those determined by ASTM lab methods, as reported in the 1996 Problem Assessment Report Two sand bodies can be correlated within the Riverbank Formation in the site area, and a third body may be present in the deepest borings (CPT-1 and GT-11, cross section D-E) The upper body labeled 1" Riverbank Channel, is fairly uniform in thickness (10 feet or less), but it thins and apparently pinches out south of the Gillies-Bardot property Iine and is not present in CPT-5 (cross section A-B) It is thickest in GT-6, and appears to be eroded slightly into the underlying aquitaid in . this well (cross section F-G) The lower sand body, labeled 2"d Riverbank Channel, is thicker than the upper one and also varies more from north to south Both of these channel deposits have higher friction ratios than the Modesto Channel and exhibit less upward increase in this ratio, primarily due to their lower cone bearing (indicating that these sand bodies are finer-grained, contain less gravel, and do not fine upward as much as the Modesto Channel) The aquitard that separates these two channels has very high sleeve friction (8-15 tons/f,2), whereas other units have sleeve friction values of 1-6 The high sleeve friction may tori espond to the presence of cement (hardpan) in this aquitard Extremely low permeabilities (10-15 cm/sec) were calculated in several CPT borings (Appendix A) Little is known about the possible 3`d Riverbank Channel It is recognized primarily in GT-11, where fine-to-medium-grained sand was sampled from 110 to 120 feet This bed may in fact be older than the Riverbank Formation, because it is overlain by red clay that records an earlier soil- forining event It is worth noting that pore pressure increases below the 2nd Riverbank Channel and sleeve fraction is also higher and more variable than above it, while cone bearing is somewhat lower Based on these parameters, Gregg In-Situ interpreted this sediment to be finer-grained than the material above it(Appendix A) 3.2 Depth to Groundwater Table 1 provides all depth-to-groundwater measurements and calculated groundwater elevations The depth increased throughout much of 2003, but rose slightly between September and December 4