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III IIIIIIIIIIIIIIII ~ ~ ~~ CTL/THOMPSON, INC. CONSULTING GEOTECHNICAL AND MATERIALS ENGINEERS August 29, 1990 Mined Land Reclamation Division Department of Natural Resources 1313 Sherman Street, Room 213 Denver, Colorado 80203 Attention: Mr. Dan Hernandez Subject: Snyder Quarry CAP Remedial Action Changes Area No. 3 Castle Concrete Colorado Springs, Colorado Job No. CS-1944 Dear Dan: RECEIVED AUG 31 1990 Mined Land Reclamation Division As requested, I have reviewed Obering, Wurth & Associates' letter to MLRD dated August 13, 1990. As we discussed on the phone, I believe removing the upper one-half of the fill at Area No. 3 will help to improve ;stability of the area by removing some of the driving forces. The cross-sections prepared by Obering Wurth and Associates indicates the lower portion of the fill is be- tween 4 and 6 feet thick. The original natural ground slope was estimated to be around 1.8:1 (horizontal to vertical). The face of the slope left in place will reportedly be 1.5:1. I believe the factor of safety for a 1.5:1 slope is slightly greater than 1.0. Considering the thickness of the fill, I believe the more likely failure mode would be a slow creep down the side of the hill proviiied the fill does not become wetted. It is my understanding Castle Concrete ha:>, or is, in the process of re-grading the upper access road to direct drainage away from the crest of the slope. With this drainage scheme, I believe subsltantial wet- ting of the "skin" fill is unlikely. The flattening of the overall slope reportedly will result in a ratio of 1.7:1. I estimate the factor of safety for a 1.7:1 slope to be about 1.15 under dry conditions. Enclosed is my July 23, 1990 letter to Castle Concrete addrl~ssing Areas 2 and 3. 5240 MARK DARLING BLVD. COLORADO SPRINGS. COLORAD080918 (719) 523 8300