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• Foundation Layer: A minimum two-foot thick layer of soil placed <br /> immediately over the entire surface of the last lift of refuse. This layer shall <br /> have the appropriate engineering properties, so as to provide a relatively <br /> unyielding surface upon which to place and compact the low-hydraulic- <br /> conductivity layer. <br /> • Low-Hydraulic-Conductive Layer: A minimum one-foot thick layer of clean <br /> low-hydraulic-conductivity soil containing no waste or leachate placed over <br /> the foundation layer. The low-hydraulic-conductivity (or low through-flow <br /> rate) soils shalf be placed on top of-thin foundation layer and compacted to <br /> attain a hydraulic conductivity, which is the lesser of either; <br /> - 1 x 10,6 cm/sec. <br /> - The hydraulic conductivity'of anybottom`liner system or underlying <br /> natural geologic materials. <br /> • Erosion Resistant Layer: A minimum one-foot thick layer of soil containing <br /> no waste or leachate placed on top of all portions of the low-hydraulic <br /> conductivity layer. Vegetation root depths must not exceed the topsoil layer <br /> thickness. Vegetation is to be replanted, as needed, to provide effective <br /> erosion resistance. <br /> The final cover should be designed to allow for minimal maintenance. The final <br /> grading design for areas flatter than 5:1 (horizontal:vertical) shall have a gradient <br /> of at least three percent, to prevent ponding°and accommodate settlement. <br /> Federal Final Cover Prescriptive Design Standard <br /> The minimum final cover standards for the Forward Landfill, as outlined in the <br /> closure criteria of 40 CFR, Subpart F, Section 258.60, include: <br /> • A cover with-a permeability less thanorequal to the hydraulic-conductivity of <br /> any bottom liner system or natural-sub-soils present, or a permeability no <br /> greater than-1 x 195 cm/sec, whichever is less. The barrier layer shall consist <br /> of a minimum 18 inches of earthen material. <br /> • A cover which minimizes erosion of the final cover by the use of an erosion <br /> resistant layer that contains a minimum six inches of earthen material and is <br /> capable of sustaining native plant growth. <br /> Forward Landfill jTD 5-6 <br /> L:\AI li ed\2000.193\Reports\fi naljtd:Sec-5.0:08/22/01 <br /> BRYAN A_STIRRAT A ASSOCIATES <br />