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III IIIIIIIIIIIII III ~ ~ ~~ CTLITHOMPSON, INC. CONSULTING GEOTECHNICAL AND MATERIALS ENGINEER`.i July 23, 1990 Castle Concrete P.O. Box 2379 7250 Allegheny Drive Colorado Springs, Colorado 80901 Subject: Black Canyon Quarry Access Road Areas 2 and 3 Colorado Springs, Colorado Job No. CS-1944 Gentlemen: As requested on July 5, 1990, we visited the Black Canyon Quarry to ob- serve "slide" Areas 2 and 3 along the access road. This letter summarizes our observations and presents our opinions regarding remedial action. Area 2 The "fill" that covers Area 2 appeared to be less than 2 feet thick. The material was laid across the natural ground surface which had a slope ratio of about 1.6:1 (horizontal to vertical). We understand the proposed remedial action plan is tc spread top- soil across the surface of the fill and to re-vegetate. We have been asked if the proposed action will resu]t in mass failure of the fill. We believe re-vegetation of this "skin-fill" will li4:ely improve stability. The root system of plants will probably help tie the fill together. We believe in a worst case, the fill material will tend to "creep" downslope. Area 3 The fill at Area No. 3 was thicker than that at Area 2. The upper one-half of the fill appeared to follow the natural ground slope to about mid-height. A comparatively level bench or bulge occurred at mid-height. From a practical standpoint, total removal of this fill will probably require some destruction of otherwise unaffected vegeta- tion, Removal of the upper portions of the fill and a portion of the bulge may be accomplished using a "clam shell" stationed at the edge of the road. Flattening the fill slope will improve stability. Topsoiling the remaining fill and re-vegetating will not, in our opinion, sig- nificantly lessen slope stability since the vegetation is not to be ir- rigated using a permanent sprinkler system. 5240 MARK DARLING BLVD COLORADO SPRWGS.COLORAD080918 ~719)!i28~8300