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Mining Plan <br />Reclamation will eventually obscure all the benches resulting in a fairly gentle, somewhat <br />undulating, north facing slope. <br />Overexcavation Hole: Much of this amended plan involves the creation of an <br />overexcavation Hole at the base of the quarry backwall. It is the rock that will be extracted from <br />this Hole (Area H) that makes the removal of undisturbed land from the mining plan possible. <br />Without this Hole the disturbance area of the existing quarry would be expanded about 25%. <br />The mining of this area will involve mining into the deposit to create a Hole up to I50 <br />feet below the expected reclamation surface. The methods to be used in raining the Hole will <br />be like the methods used elsewhere, with one exception. Bench configurations in this area need <br />not be modeled to produce a reclamation defined slope gradient. This is because the Hole will <br />be completely backfilled with waste produced by processing the limestone removed from this and <br />other areas. <br />The Hole will not daylight anywhere and therefore concerns over backfill compaction and <br />stability are not relevant. The backfill will be held in place by native rock that wilt form the <br />sides of the Hole and therefore the bacld-ill cannot go anywhere. <br />• The only real concern with this overexcavation is the effective increase in the height of <br />the quarry backwall. In effect, at maximum depth, the backwall of the quarry will be increased <br />by as much as 150 feet. After backfilling is done the quarry backwall will return to a height <br />similar to that anticipated in the existing approved plan. The concern therefore is about the <br />stability of the quarry backwall during the mining of the Hole itself. <br />This is primarily a safety issue that is outride the jurisdiction of the Colorado Mined Land <br />Reclamation Board, but does involve the reclamation of the site. That reclamation involvement <br />concerns the possibility that increasing the total quany backwall height could result in a major <br />collapse of the quarry backwall. If that did occur, it would undoubtedly destroy the carefully <br />designed bench reclamation to be implemented primarily th Area MV. <br />Several factors must be considered in assessing the stability issue of the Hole edge, <br />especially the west side of the Hole. First, is the past tendency of huge limestone blocks to slide <br />down the hill. Second, is the slight undercutting of the backwall that would occur because the <br />benched side slope of the Hole will be slightly steeper than the quarry backwall above the Hole, <br />especially in Area MV. Third, is the contribution of the steep dip angle of the limestone bedding <br />planes. And fourth, is the amount of the Hole that will be unbackfilled at any one time. Each <br />of these will be discussed below. <br /> <br />Pikeview Quarry Amendment Exhibit D Page 19 <br />