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Balaz & Associates Preliminary Slope Stability, Conger Harvesting Area, Marble, CO November 29, 2000 Page 2 No seismic coefficient was assumed in these calculations. Several models were assumed for the existing and proposed slopes. The critical model assumed a long continuous slope, steepening up toward the upper or northern limits of the permit area. The extraction was assumed to progress relatively slow, probably less than 2000 tons per year. It is further anticipated that the actual extraction face may be as high as 16 to 20 feet and have a temporary slope somewhat steeper than 1: I, h:v. As can be seen from the cross sections, the Talus material which is being harvested is between 10 to 20 feet ta thickness, with a lower Talus material which contains more fines. This lower Talus was assumed to be between 15 to 25 feet in thickness throughout the slope. For purposes of computation, an impenetrable bedrock is assumed beneath these Talus materials. In reality it is known that the Mesa Verde Formation is probably the bedrock th this area. The rocks of the Mesa Verde Formation are assumed to be sufficiently `tight' so as to allow a well defined water table to develop in the lower Talus material. The assumed location of this water table is based on our knowledge of some portions of this slope and seepage which has been observed on the perimeter portions by personnel of Lincoln DcVore, in the course of preparations of other geologic and geotechnical studies in this area. Based on slope stability calculations, the maximum cut slope which can be constructed using the angular Talus is 1.8:1(horizontal to vertical). Natural slopes are steeper than this, however, if the assumed water table is in fact correct and a significant amount of material is left up hill, on the north boundan• of the extraction area, these slopes will be sufficient. It is anticipated that actual final cut slopes th the working areas will be 1.9: I at the upper project boundary and somewhat flatter in the main working areas. The analysis indicated the final slopes will have a sufhcien[ factor of safety, equal to or greater than l.i, assuming our general understanding of this project is correct. Some portions of the existing slope appear to have natural steeper slopes than the recommended cut slopes for this extraction process. These steeper slopes are most prominent immediately south of the lower project boundary and are th the toe area of this Talus slope. Our modeling indicates the natural slopes have a safety factor ranging from l .2 to 1.4, based upon our assumptions that the water table may be relatively high, actually seeping from the toe of the slope and the ground surface bedveen the toe of the slope and the Gunnison County Road 3 is completely saturated, possibly with some free w~atcr. This area of reduced natural slope stability is below the project boundary. During this extraction process, we recommend that no cut slopes in excess of 20 feet high, be allow~cd if the face cut is a 45 degree angle (100% slope or I : I, H: V). Steeper slopes may be allowed on the extraction fact but, must be less than 20 feet high. It is strongly recommended that any slopes steeper than the recommended 1:1 be excavated very carefully utilizing mechanical equipment which can reach and grab the equipment for placement in a working/sorting area. This report is issued with the understanding that it is the responsibilit}• of the owner, or his representative to ensure that the information and recommendations contained herein arc brought to the attention of [hc architect and engineer for the project, and are incorporated into the plans. In addition, it is his responsibility that the necessary steps are taken to see that the contractor and his subdivision~ontractors carry out these recommendations during construction. The findings of this report are valid as of [he present date. However, changes th the conditions of a property can occur with the passage of time, whether they be due to natural