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GeoSyntec Consultants <br />topographic map will serve as the base map for any future differential settlement <br />measurements made during the post -closure maintenance period. <br />3.4.2.2 Final Cover Materials <br />The proposed final cover system for the closure of the unlined WMU B area is the <br />prescriptive design for solid waste landfills outlined in §21090 of Title 27. A drainage <br />layer will be added on the steeper 2H:1 V slopes to meet slope stability requirements. <br />The prescriptive final cover is shown on Figure 3-2, and consists of (from top to <br />bottom): <br />• Grass mixture and organic layer for erosion control <br />• 1 -foot thick vegetative layer <br />• Geocomposite drainage layer (for 2:1 V side slopes only) <br />• 1 -foot thick compacted clay liner (hydraulic conductivity of 1 x 10-6 cm/s or <br />less) <br />• 2 -foot thick compacted soil foundation layer <br />Soil materials used for the construction of the final cover will be obtained from on- <br />site excavations for the construction of other WMUs, or existing soil stockpiles. The <br />geocomposite drainage layer will be purchased from a geosynthetic manufacturer. A <br />list of required materials and estimated volumes/areas are shown on Table 3-1. <br />On-site soils will be used to construct the foundation layer over the future 3H:1 V <br />waste slopes. The soil will be placed as an intermediate soil cover at the same time as <br />waste placement. An approximately 1 to 2 -ft thick soil foundation layer is currently in. <br />place over the existing waste slopes. Forward will verify the soil thickness on these <br />slopes and, if necessary, will place additional on-site soils to meet the minimum 2 -ft <br />thickness. Existing vegetation will be cleared and grubbed prior to placing additional <br />soil. The southwest corner of the existing south slope will be flattened to 2H:1 V as <br />shown on Figure 3-1 by placing additional soil. This work will be performed by <br />Forward prior to final waste acceptance. The foundation layer will be compacted to a <br />minimum relative compaction of 90% (ASTM D1557). <br />0 J:\ALLIED\FORWARD\CLOSUREPLAN\REPORT 3-5 99.11.30 <br />