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important amounts of rain water and surface run• will not infiltrate <br />to flow along the base and it is proposed to do this when the pile is <br />• completed. Completion might not be for as much as 20 years after con- <br />struction begins and the technology of constructing low-permeability <br />layers can be expected to improve in that time. Therefore it is unwise <br />at this time to settle on a final method of reducing permeability or the <br />additive(s) to be used. The additive(s) to be used are expected to be <br />sponge-like so that it can retain water to be available to vegetation <br />on top of the pile, yet the material itself would be essentially imper- <br />vious so that only minute amounts of water could flow through. Such <br />materials available now are bentonite, peat, sawdust and other ground <br />up organic materials. <br />Wheii emplacement of the pile is completed and final configuration is at- <br />tained the horizontal areas will be prepared as indicated on Figure 7. The <br />• pile will be sloped slightly toward the center with a roughly 3-foot fall <br />between the edges and the center. The additive material will be then laid <br />on in sufficient thickness. It will be covered with additional mine run <br />rock laid on to be horizontal in a direction transverse to the pile but will <br />have the slopes shown on Figure 1 lengthwise of the pile. The additive <br />material will be covered to a depth of about 4 feet at the edges and about <br />7 feet in the center. The faces of the pile will be prepared in a similar <br />manner, with the additive material laid on and covered with about 4 feet <br />of mine run rock. The layer will not be thickened near the center of the <br />pile bu•t will be at constant depth across the width. <br />By laying the additive material on in this manner a natural channel-way will <br />be provided near the center of the pile for runoff flow, yet, because of the <br />• thickness of the rock above the additive layer and the low slope the flow <br />will spread over a wide area and its velocity will decrease so that erosion <br />will not occur. No water is expected to filter through the additive layer <br />-13- <br />