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File No. 20-1008-48 KLEINFELDER January 3 , 1992 landfills, and thicker sections of near-surface silty sands encountered probably reflect the proximity to the break in slope. The landfill has yet to receive additional cap materials, including one foot of impermeable material overlain by approximately 1 foot of topsoil. This additional material, assumed to be an average of two to three feet, has been included in our stability analysis. In each instance, an attempt was made to drill through the bottom of the refuse and into the underlying basement material. In Boring B-3 this was not possible because of refusal due to the nature of the refuse met at approximately 30 feet. Underlying material generally consisted of medium dense to dense silty sands to depths explored of approximately 35 to 40 feet. Free groundwater was not encountered in any of the borings drilled for this investigation. According to the Spring 1990 Semi-Annual Groundwater Report published by the San Joaquin County Flood Control and Water Conservation District, the depth to groundwater at this site is over 100 feet. Due to the impermeable clay cap that is proposed to be constructed on top Amok of the landfill, we have assumed that rainwater will be diverted off the landfill site and into the excavated borrow area. We have assumed, for the purpose of this investigation, that appropriate maintenance procedures will be followed by the County to ensure that rainwater is not allowed to percolate into the landfill in the future. During the course of -our field investigation, our personnel encountered light to moderate concentrations of methane and hydrogen sulfide gases exiting from our test borings, and on several instances, our drilling was suspended until additional safety and detection equipment could be procured to continue with the drilling process. The above is a general summary of soil and groundwater conditions encountered in the test borings drilled. More detailed descriptions of the soils encountered in each boring are noted on the Logs of Borings. All soils have been classified according to the Unified Soils Classification System which is described on Plate A-2 of the appendix. LABORATORY TESTS Laboratory tests were performed on selected samples obtained from the exploratory borings in order to evaluate the moisture density and strength characteristics of the soils encountered. The tests performed consisted of Moisture Content and Dry Density • determinations and Unconfined Compressive Strength tests. Laboratory test results are noted on the Logs of Borings at Copyright 1992 KLeinfelder, Inc. Page 3 of 9