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D.6.6 Construction <br />• Design criteria adopted for the initial disposal area <br />construction were to provide sufficient tailings storage to <br />reduce the rate of rise in the disposal area to below 14 <br />ft/year by the end of year 2. Two additional 15-ft lifts or <br />raises will be constructed on the lower embankment to raise <br />the tailings disposal area to the final elevation of 8,620 ft. <br />The bulk of all materials to be used in the construction <br />exist within the limits of the disposal area. Figure D.6.2 <br />shows the location from which material will be selectively <br />excavated for construction. The description and criteria <br />defining each material type are given on Table D.6-2. The cut <br />and fill operations will be concurrent during initial <br />construction while some temporary stockpiling of the materials <br />to be placed over the liner will be performed. Similarly, <br />placement of the material to be installed beneath the liner <br />• will be performed at locations where borrow •denudes this <br />material or it is lacking. <br />For the purposes of design, it has been assumed that the <br />first raise to 8,605 ft will be constructed when the tailings <br />reaches an elevation of 8,582 ft. Construction of the first <br />raise at this tailings elevation will ensure sufficient <br />freeboard to allow storage of PMF inflows with at least one <br />ft of residual freeboard. The final raise will be constructed <br />when the tailings elevation reaches 8,600 ft. <br />The northwestern perimeter embankment may be constructed <br />at any time prior to the tailings reaching an elevation of <br />8,615 ft. The northern perimeter embankment must be constructed <br />during Phase I to divert storm runoff away from the disposal <br />area. <br />1~J <br />{)-43 <br />