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II. Project Description functional properties of the ADC,a comparison of the properties of the ADC with corresponding properties of soil, and information on the site. If the request is approved, ADC could be used initially on an experimental basis and if,after the program is implemented,the LEA and CIWMB staff find that the material can function as a suitable daily cover, ADC could be used on a non- experimental basis. Base Liner Details of the base liner for the Austin Road Landfill are shown in Figure II.4. The purpose of the base liner is to contain leachate within the landfill so that it can be channeled and collected. For the horizontal expansion,the base liner would be placed upon the prepared excavation at the site. For the vertical expansion,the base liner would be placed upon the final cover of the existing landfill. From top to bottom,the typical base liner design includes an 18-inch operation/drainage layer,60 mil high density polyethylene(HDPE)liner, and a 24-inch compacted clay layer having permeability of 1 x 10-7 cm/sec. The base liner for the vertical expansion would be constructed approximately 30 years after the existing landfill is capped. The specific design for the vertical expansion would depend on the settlement of the existing landfill. The HDPE liner would serve both as an added barrier to protect groundwater and as a flow surface for leachate. The protective layer would serve as protection for the other liner components during the initial stages of landfilling activities. Other materials may be used in later phase developments,if the materials meet applicable regulations and performs equal to or better than HDPE. Groundwater varies between-48 feet to-12 feet mean sea level (MSL),with an average of-35 feet MSL in the expansion area(Kleinfelder, 1988). The maximum depth of the liner, not including the leachate collection trenches and sumps,is 20 feet MSL. This results in a minimum separation of 32 feet between the liner and groundwater. Leachate Collection The proposed landfill's leachate collection plan includes a drainage system,a leachate collection system, and a leak detection system. For purposes of this project,leachate is any liquid that has come in contact with or percolated through refuse. Any surface water run-off that.could have contacted solid waste or include leachate would be handled by the leachate collection system. 11.9