1988-04-08_REVISION - M1977342 - Laserfiche WebLink

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C~ Henderson Mine Permit X77-342 Technical Revision 414/88 Page 2 3. Soil Cover on Tailing The Henderson Reclamation Plan (1977) states that the ultimate tailing surface will be covered with 6-18 inches (12 inches average) depth of soil and vegetated with grasses, shrubs, and trees. We installed a soil-tailing test plot in September 1982 to observe the long-term effects that a soil-on-tailing reclamation procedure may have on the vegetative cover (Figure 1). The plot consists of twenty-four ten by ten foot cells filled with six, twelve, or eighteen inches of soil placed on three feet of tailing. The cells are separated by timbers. All cells were seeded with the present Climax seed mix at 50 pounds per acre and fertilized with 20-20-10 (N-P-K) at the rate of 100 pounds per acre. The plots have been in place for five growing seasons without any maintenance, and our observations are that the vegetative cover is ~ 4~~~ sustained satisfactorily on either the six, twelve or eighteen inch soil ~' •~s depth. We therefore request that the requirement in the plan that the 1,^°1 ,, ultimate tailing surface be covered with 6-18 inches (12 inch average) 6~~ depth of soil be revised to 3-9 inches (6 inch average) depth of soil. 4. Soil Stockpile Plan During the last five years Henderson has undergone some drastic modifications to its operation which have resulted in fluctuating production levels and subsequently fluctuating tailing deposition rates and amounts. This year the projected rate of production was reduced to a point where the present soil salvage and stockpile plan requires some revisions. We wish to revise the soil stockpiling plan so it corresponds with decreased mine production, decreased tailing deposition, and d,l.-..~ decreased soil cover requirements. Because the smaller tailing pond disturbs less land, more soil is available at a lower elevation for reclamation. These factors allow a much simpler and lower-cost approach to moving, storing, and replacing soil. In addition, construction costs for the perimeter access road and interceptor canal are dramatically reduced due to more favorable topography (i.e. not as steep). 4.1 Current Soil Stockpile Plan Previously the tailing deposition area was to have occupied 1,551 acres, reached the 8,900 foot contour on the upstream side of the basin, and required 2.5 million cubic yards of soil to be placed on the tailing to a depth of one foot at cessation of mining. Two stockpile areas, one at the northwest and one at the southeast ends of the tai_ting basin, were to have received 1.01 million cubic yards each wile 0.47 mi'I1ion cubic yards have already been stockpiled