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The liner system for the FL expansion has been designed to provide the required five-foot separation between refuse and current groundwater elevations. In the unlikely event that historic high groundwater levels occur and a 5-foot separation between historic high groundwater and refuse can not be maintained, an engineered alternative liner system is proposed for those areas where waste is discharged at or below an elevation 5 feet above estimated maximum high groundwater. This alternative system includes a subdrain system installed below the waste containment system (liner), and an additional foot of operations layer soil installed above the liner. The subdrain would prevent the potentiometric groundwater level from rising above the liner system by collecting the groundwater and draining it towards a sump from which it could be pumped and removed, and the 5 foot overall thickness of the liner system will therefore maintain a 5-foot separation between waste and groundwater. See Figure G for details of the proposed engineered alternative liner system. An engineered alternative final cover system is proposed for the FL expansion. This system is comprised of four feet of cover soil with a maximum permeability of 1.0E-06 centimeters per second (cm/sec). This proposed design is the same as that placed on the closed north slope of the original Austin Road Landfill. After nearly two years of moisture monitoring within this cover system, the performance of this cover has been shown to be equivalent to or better than that of a prescriptive cover system. The FL has received tentative approval of this cover system from the Central Valley Regional Water Quality Control Board, pending further moisture monitoring. See Figure G for details of the proposed engineered alternative final cover system. 5.2.2 WASTE CONTAINMENT SYSTEM FEATURES The proposed lateral expansion area will be developed with a similar waste containment system (i.e., liner, LCRS, and protective cover) as the existing waste containment system, as discussed in Section 4.1.1, with the addition of the engineered alternative system for historic high groundwater described in Section 5.2.1 above. 5.2.3 SITE CAPACITY/SITE LIFE PROJECTION ® The total remaining permitted airspace for the FL, as of February 16, 2007, is approximately 28.0 million cubic yards (mcy). The projected remaining Forward Landfill Project Description 5-3 BRYAN A.STIRRAT&ASSOCIATES ():\Allied\Forward\2007.0018 Lateral Expansion\Reports\Proj Descrip\021308 Final Proj Des\Sec 5.doc:2/13/2008)