2011-10-31_REVISION - M1976009HR (7)

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These benches still exist in one portion of the quarry. Subsequently, MSHA decided to apply different requirements for benching and producing those high - walled benches, although very stable, was no longer allowed. Benches are now produced in a similar ratio but with about half the dimensions of the large ones. Over the years, these tall benches have been watched closely to determine whether there are any longer term stability issues. Of course, any nearly vertical wall will exhibit some kind of stability problem, even if it is only the occasional falling rock. Gravity insures that. But what is more important is instability on the larger scale that could produce large landslides. After nearly 15 years, no large scale changes in the benches has occurred that would indicate a developing stability problem that could lead to a large scale collapse. That is not say such a failure could not occur. No one can assure that in a mountainous area such as this where even heavily forested slopes are often difficult to climb due to the steepness massive slope failures will not occur. The main point is that because of the highly randomized structure of the large chunks of granite that compose the formation being mined, there is a high degree of natural stability as a result of these chunks of rock settling into a tight structure that has so little void that even water cannot usually accumulate to any great extent. Without water there is no lubrication and even if there is water the individual chunks of granite are so wedged together that large scale movement would be very difficult. MSHA frequently inspects this quarry and one of the aspects MSHA looks at here is bench stability. MSHA insures that benches are within their standards for wall height and bench width, although the latter is not considered as much as the former. But as the permit states, to properly reclaim a quarry bench it has been found that the minimum width for good vegetation growth is very close to 25 feet. Benches that are narrower than 25 feet simply do not usually have sufficient area to allow for the kind of "cooperative growth" needed to produce good vegetation. Cooperative growth occurs where there is sufficient density over a suitable area, considering the local climate, aspect, and soils, so the individual plants effectively help each other to succeed. Thus, the reclamation requirements themselves largely controls the bench width. With the combination of bench width control from reclamation requirements and bench wall height control by MSHA requirements, benches tend to be very stable here, even when the walls are much higher than is currently considered acceptable. This situation is quite different from the limestone quarries west of Colorado Springs. There the formations are largely in tact. The beds are often laced with clay seams that parallel the formation bedding plane and separate portions of the formation composed of hard limestone and dolomite. If steeply dipping, those limestone beds usually dip to the east, away from the mountain. The Menzer Quarry has none of those structural characteristics often seen in the limestone quarries. This type of structure has been implicated as the cause of significant slides, slope failures, and wholesale collapses at quarries that mine sloping sedimentary rock. The structure at Menzer is not conducive to that kind of failure and the lack of significant failures at Menzer over several decades of operation using a variety of mining approaches seems to support that conclusion. Menzer Quarry Corrective Action Amendment Rule 6.5 October 2011 Page 3