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1 <br />' Laboratory classification testing confirmed field descriptions. Testing focused on <br />fine-grained soils with potential use in landfill construction. Fine-grained soils de- <br />scribed in the field as clays and silts were classified by laboratory testing as CL <br />and ML by the Unified Soil Classification System. Sand content of fine-grained <br />' soils within 0- to 20 -foot -depth intervals was less than 5 to 50 percent. Silty sand <br />samples were found to contain between 39 and 47 percent fines (i.e., materials <br />passing No. 200 sieve). <br />Selected samples of soils from within the anticipated depth of site excavations <br />' were tested for compaction characteristics and remolded permeability to ascer- <br />tain the suitability of available on-site material for use as low -permeability liners <br />and final cover layer and in constructing retention structures. The permeability of <br />soils classified as ML and CL is shown on Table 8-1 and was determined to be <br />1 x 10-6 to 1 x 10-8 cm/sec when remolded at 95 percent relative compaction. A <br />complete discussion of laboratory soils testing is presented in Appendix B. <br />8.2 GROUND WATER <br />Most of the ground water used in eastern San Joaquin County is pumped from <br />units below the Riverbank and Turlock Lake Formations. Significant yields from <br />these formations are obtained only from scattered wells tapping discontinuous <br />sand and gravel layers. <br />A survey of wells within a 1 -mile radius of the site was conducted to establish lo- <br />cal ground -water conditions. Through area reconnaissance and review of Cali- <br />fornia Department of Water Resources records, 38 water -supply wells were lo- <br />cated. Specific well construction data were available only for 10 wells. These <br />data show that the cased depths for local wells range from 75 to 368 fe�t.dv- <br />erage 164 feet. <br />Most of the local wells are used for irrigation. Extensive irrigation and resulting <br />ground -water withdrawal began around 1907 and have increased steadily since. <br />As a result of pumping, ground -water levels have declined significantly over the <br />years. The water level in a well within 1 mile of the site has declined from an ele- <br />vation of 48 feet MSL in 1929 to -27 feet MSL in 1987. <br />' PJ9 9390219A.00W 37 Rev. 0 <br />July 19, 1989 <br />