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Foothill Sanitary Landfill Preliminary Closure Plan Revision #1 May 6, 1994 III . PRELIMINARY CLOSURE COST ESTIMATES Closure costs are calculated for the closure situation when closure costs will be the most expensive. The maximum extent of the landfill that will ever require closure at any given time is estimated to be when the existing 80 acres needs final cover, the first 20 acre module has already been lined and partially filled, and the next module has been partially excavated for soil. The existing landfill does not have a liner, so the cost estimates for closure are divided into two sections. The existing 80 acre closure cost is based on the prescriptive standard of a two. foot foundation layer, one foot clay barrier layer (1 x 10-5) , and one foot vegetative layer. The closure for the 20 acre lined module will be based on the subtitle 0 requirement that the final cover must meet or exceed the performance of the bottom liner installed. Such a liner will consist of a two foot foundation layer, a two foot clay barrier layer with a permeability of 1 x 10''' cm/sec or less, a layer of geosynthetic liner material, and a one foot vegetative layer. Other items of closure cost such as fencing, revegetation, etc. are also included as closure costs. FINAL COVER EXISTING 80 ACRES Final cover will consist of 2 feet of foundation layer cover (sandy to silty material) , a 1 foot low-permeability barrier layer (silty material mixed with imported clay) , and a 1 foot vegetative layer (sandy to silty material) . One foot of the foundation layer will have already been placed prior to closure. 'Therefore, only one foot of additional soil will be needed to complete the foundation layer for the existing 80 acres. SOIL REQUIREMENTS 80 ACRE EXISTING Foundation layer = 129 , 067 c.y. Clay cover = 129 , 066 c.y. Vegetative cover = 129 . 066 c.v. Totals 387 , 199 c.y. 19