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The completed final cover for the unlined portion of the site will <br /> consist of the following: <br /> * A minimum 24 inch foundation layer of compacted soil <br /> placed over waste fill. <br /> * A minimum 12 inch clay barrier layer compacted to achieve <br /> a hydraulic conductivity of 1x10 cm/sec or less, placed <br /> over the foundation layer <br /> * A minimum 12 inch layer of vegetative cover soil placed <br /> over the clay barrier layer. <br /> The vegetative cover layer will be fertilized, as necessary, and <br /> seeded with moderately rooted, erosion-resistant vegetation native <br /> to the surrounding area. Vegetation that will germinate without <br /> irrigation and require minimum maintenance will be selected. Final <br /> cover slope and drainage details are shown on drawings 2 and 5 of <br /> the Preliminary Closure Plan (Appendix A) . Final cover for the <br /> lined future modules will be equal to the bottom liner as specified <br /> by new state regulations (Chapter 15, Article 5) and federal <br /> Subtitle D regulations. <br /> 13 . 2 SETTLEMENT <br /> The settlement of refuse fill, characteristic of all landfills, is <br /> affected by a variety of factors. These factors include (1) the <br /> types and moisture contents of refuse placed, (2) refuse density, <br /> (3) consolidation of the refuse under loads imposed by overlying <br /> fill, (4) biological decomposition, (5) chemical decomposition, and <br /> (6) moisture infiltration. <br /> The initial refuse density is estimated at about 1, 100 pounds per <br /> cubic yard. Further densification will occur from surcharge <br /> loading by successive lifts of refuse. Despite this densification <br /> process, refuse settlement after closure is estimated to range from <br /> 15 to 20 percent of the refuse thickness. This estimate is based <br /> on the method of preparation, effects of surcharging, estimated <br /> settlement during the active life of the landfill operation, refuse <br /> composition, and landfill settlement experienced at other sites <br /> with similar characteristics. <br /> The final surface grades are designed to accommodate drainage of <br /> the completed landfill after settlement and to minimize erosion of <br /> the final cover. To verify the integrity of the final cover as <br /> required by regulations, a program of periodic observation and <br /> maintenance will be established and maintained to provide reference <br /> points for future settlement measurements. <br /> 36 <br />