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Under these circumstances, a clavstone reaches its lowest strem_th called residual strength. The following strengths are appropriate for modeling: Claystone Strength Condition Effective Cohesion (sn c' Effective Friction Ankle (deg) 0' Residual 0 14 Fullv Softened 0 26 Peak 700 26 _ In general, peak strength bedrock would be stronger than overlying gravel. If fully softened or residual s[rength bedrock were to be present, the gravel would be stronger and a failure may initiate in the bedrock. At the River Resources site, the geotechnical investigations identified a one-half-foot to two-foot thick highly weathered zone of bedrock immediately below the gravel deposit. Highly weathered claystone is likely to exhibit lower shear strength than a sand and gravel deposit, and must not be neglected in stability evaluations. The applicant has stated that regardless of bedrock strength issues, a failure would not occur into bedrock due to lateral confinement. In fact, during a slope failure materials below the ground surface aze often forced upward creating a chazacteristic bulge at the toe. Also, the mine plan for Riverview Resources includes mining into the weathered bedrock to obtain material for liner construction, and Operators may typically excavate dewatering trenches into bedrock with the trenches located near the toe of the slope. Target safety factors would be 1.1 ~ for analyses considering residual strength, 1.25 for analyses considering fully softened strength, and 1.5 for peak strength analyses. The Operator may petition the Division for lesser setbacks once the pi[ is opened up and the weathered bedrock is exposed for observation and testing. The other alternative for decreasing the amount of required setback would be to obtain written waivers from the owners of structures in accordance with 34- 32.5-115(4)(e), C.R.S. 3) Fences qualify as permanent structures that must be included in geotechnical stability analyses if the structure owners perceive them as `valuable', in accordance with Rule 6.4.19 of the Construction Materials Rules and Reeulations. If a letter from the landowner statine that the structure has no significant value can not be obtained, then the Operator is reminded [hat the residential setbacks must apply to all structures which the landowners wish to be left undisturbed. The proposed 4~' setback from residential fencing has not been verified through analysis. Please submit a stability analysis of these structures. d) Despite the decrease on the water table that may occur due to mining, and the assumed effects on the phreatic surfaces, please re-analyze all cases with the appropriate worst case scenario water levels. using the values noted in the geotechnical evaluations. DMG does not agree that any uniform drop in levels across the site can be assumed. Please re-submit analvses with these values. ~) Given the use of a 0.1 H: I.OV mine slope for this stability analysis, DMG would appreciate the re-submittal of all analyses so that we may evaluate them.