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Mining Plan • slope gradient, especially when benching is done, is of great concern when far greater changes in slope gradients have never produced stability problems elsewhere. Limestone Bedding Planes - Probably of more concern than average slope gradient is the cross cutting of bedding planes that occurs when mining this formation. The dip of the limestone is about 3:1 to the east, but the mining produces average gradients of about 1.5:1, and sometimes steeper. Furthermore, vertical walls created in the limestone cut across the bedding planes in the opposite direction from the steps. In effect, the method of mining takes a continuous bedding plane and chops it into small pieces, some of which are unsupported. This is the primary cause of bench decay previously discussed. This transformation occurs because the small, unsupported pieces tend to become separated from the underlying material and subsequently slide down to the surface of the next bench. This is apparently caused by rapid weathering. Figure MP-5 diagrammatically explains this process. This fragmentation of the bedding structure is actually advantageous th that it removes the possibility of major collapses. If collapse occurs, it is only small pieces that fall rather than • huge pieces as occurred when the clay slip zone was present. In effect, the fracturing of the bedding plane replaces large scale instability with very small scale instability that is far more easily managed. Dimensions of Hole Opening - As the Hole is created bacld'illing will occur behind the mining and into portions of the Hole that are completed (see Reclamation Plan, Exhibit E). This will be done for several reasons. First, the amount of waste stored on site for use in backfilling must be limited. Room available for waste storage is limited and therefore prompt backfilling must be done to avoid creating "mountains" of waste. Second, backfilling with waste will be needed to establish access roads in and out of the Hole. Thus, the need to easily remove the mined rock requires that backfilling be done and this will help limit the dimensions of the Hole that will be open at any one time. Third, it is not expected that any more than 1/4 of the total length of the west wall of the Hole will be unsupported by backfill (or unmined rock) at any one time. Thus, any large scale instability that might occur would be limited in scope simply because most of the west wall will either be supported by backfill or by native rock yet to be mined. • And fourth, to further support the wall, the backfill will be replaced at an angle across the Hole. Angled backfilling behind the mining will proceed as the Hole is excavated to the Pikeview Quarry Amendment Exhibit D Page 23