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Extended Site Characterization Report., 7500 West Eleventh Street, Tracy, CA, Page 27 interpretation of the data available from logs of push-probe and well borings along Section C-C' (Figure 11), strongly suggests the presence of the same stratum of sands and silts at similar depths to those at which this stratum of permeable materials was encountered in borings along Section A-A'. A similar zone of sand and silt is seen on Section B-B' on Figure 10. (However, along that section, which passes through MW-2 in the west and MW-4 in the east, there is a distinct discontinuity in the sand facies in the -3 and MW-3. )icivnit of borings PP Beneath the sand stratum found in a zone between some 10 ft. and 25 ft. BGS, there is another clay zone that appears to be continuous over the whole area explored; its top is at depths varying between approximately 25 ft. and 28 ft. BGS. Where borings were drilled to sufficient depth (i.e., on the 7500 West Eleventh Street property itself) that clay layer was found to have a thickness of some 10 ft. It is underlain by another sand stratum in a zone between approximately 28 ft and 33 ft. BGS. Beneath that sand lies a third clay stratum with a thickness of about 5 ft., and beneath that, with its top approximately 35 ft. BGS, is a thick sand stratum down to at least the maximum depth of exploration (50 ft. BGS). The stratigraphy described above is typical of the alluvial fan upon which Tracy and the surrounding area is situated. Based on pump tests that SJC has conducted in similar strata at other locations in Tracy, it is estimated that the clays and silty clays beneath the 7500 West Eleventh Street site ' have a hydraulic conductivity on the order of 10-4 to 10-6 cm.lsec., while the silts and sands have permeabilities in the range of 101 to 10-2 cm./sec. (The San Joaquin Company Inc. 1994.) �` sic