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III IIIIIIIIIIIIIIII <br />sss <br />STATE OF COLORADO <br />Roy Romer, Gove <br />DEPARTMENT OF NATURAL RESOURCES <br />MINED LAND RECLAMATION DIVISION <br />FRED R. BANTA, Director <br />DATE: December 6, 1989 <br />T0: Dan Hernandez <br />FROM: Steve Renner <br />RE: Castle Concrete Response to Adequacy Review, Snyder Quarr~~ <br />(M-77-210) <br />As requested, I have reviewed responses 17, 18, 19 and 23 of the Ciistle <br />Concrete November 29, 1989 submittal. hty comments are as follows. <br />17 -Castle has proposed that no remedial grading occur at Areas 2 and 3. <br />Their rationale for not cutting or filling these slopes to a 2:1 (H:V) <br />configuration appears sound, and I would concur with it. However, long term <br />stability of these areas is still a concern which must be addressed. <br />The CTL Thompson report indicates that steep fill slopes are potential areas <br />of failure. The assumed factor of safety for fill slopes up to 1.5:1 is in <br />the range of 1,0 to 1.2. The factor of safety for the natural slope condition <br />has been estimated to be 1.4. <br />Based upon these analyses, it would appear that the potential exists for a <br />fill slope failure to occur at either area. In order to maximize the <br />potential fora stable slope configuration, I would suggest that all fill <br />material, as identified in the November 29, 1989 Area 2/Area 3 cross section, <br />be removed. Removal of the fill to natural ground surface would tend to <br />achieve an overall slope factor of safety nearer to 1.4. Fill removal would <br />reduce the risk of a future failure which would result in more valley <br />disturbance, and would tend to reduce the potential for sedimentation to the <br />stream once the area is tops oiled and revegetated. <br />An alternative to the fill removal option is to complete a Geotechnical <br />analysis of the Areas 2 and 3 fill slopes. In order to be acceptable, this <br />analysis must demonstrate that the fill slopes have a factor of safety of at <br />least 1.35. This analysis should include an angle of internal friction of 34 <br />degrees and cohosion varying between 30 and 36 psf. <br />215 Centennial Building, 1313 Sherman Street Denver, Colorado 80203-2273 Tel. (303) 866-3567 <br />