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H. Project Description LANDFILL DESIGN The design of the landfill is based on a preliminary conceptual design. If major changes to the preliminary conceptual design are implemented,subsequent environmental evaluation would be required. Design elements for the proposed horizontal and vertical expansion of the landfill include excavation,base liner,leachate collection,erosion control,surface water control,and landfill gas control . Excavation The applicant estimates that planned excavations at the proposed landfill and proposed borrow area north of the existing landfill would provide sufficient borrow soils for the construction of the soil components of the proposed base liner system, and provide sufficient material for daily, intermediate,and final covers for the proposed landfill. The base grading plan calls for excavation of approximately 1.9 million cubic yards(mcy)of soils. The proposed excavation and site preparation are shown in Figure U.3. The excavation for the creek realignment, floodplain and surface water detention facility would result in a total of 2 racy of soil. The conceptual design indicates that the proposed landfill expansion would require 6.3 mcy of soil materials in total,including approximately 1.8 racy of clays suitable for the liner and/or final cover, and approximately 4.5 mcy suitable for daily and intermediate cover. It was assumed that a 3:1 ratio of refuse to cover would be required. This is a more conservative estimate than the 4:1 ratio used to determine refuse capacity. Soils excavated during construction and suitable for the liner or covers would be stockpiled on site until needed. Some of the materials would be stockpiled on top of the existing landfill after it is properly closed. These stock piles would preload the existing landfill and maximize settlement prior to construction of the vertical expansion. It is also anticipated that preloading the landfill would squeeze out the leachate being collected by a leachate remediation system for the existing landfill. The remaining soils would need to be excavated from the borrow area,imported, and/or an alternative cover would be needed. The current landfill has a problem with applying daily cover during wet weather because of the difficulty of excavating soils. The operator has submitted an application to the California Integrated Waste Management Board(CIWMB)to use alternative daily cover material (ADC) (Wickes, 1993). In order to use ADC, the applicant would need to submit a request to the CIWMB and the Local Enforcement Agency(LEA)to implement a demonstration program. The request must contain detailed information on the type of ADC selected,an evaluation of the 111.7