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~~= i' ~ ~ III IIIIIIIIII'll III <br />STATE OF COLO[ZADO <br />Roy Romer, Governor <br />DEPARTMENT OFNATURALRESOURCES <br />MINED LAND RECLAMATION DIVISION <br />FRED R. BANTA, Director <br />DATE: October 26, 1989 <br />TO: Daniel Hernandez <br />FROM: Steve Renner_ <br />RE: Snyder Quarry Corrective Action Plan Adequacy Review <br />I have reviewed the Snyder Quarry Corrective Action Plan, and the <br />August 23, 1989 Board Order. The following adequacy comments detail my <br />concerns regarding slope stability and necessary financial warranty, given <br />the Castle Concrete proposed corrective actions, and the requirements of the <br />Board Order. <br />Slope Stability <br />1. The stability analysis performed by CTL/Thompson indicates <br />that the maximum slope at areas one through four should not <br />exceed 2:1. Slopes which are constructed to 2:1 have a <br />nominal factor of safety of 1.32 to 1.35. For comparison, <br />natural soils in the pre-distrubed configuration have a factor <br />of safety of about 1.4. The factor of safety is reduced as the <br />slope angle is steepened. Conversely, as the slope angle is <br />reduced, the Factor of Safety increases. <br />Area 1 <br />The Corrective Action Plan calls for flattening the slope <br />to the recommended maximum 2:1, and filling the upstream <br />pond. It is recommended that the operator c~mstruct a <br />3:1 or gentler slope from the base of the fill to station <br />3 + 26.6 (Area 1/Area 4 cross section). Are,3s upslope of <br />station 3 + 26.6 can be graded to 2:1. A1th~lugh the <br />cross section indicates that a cut and fill operation <br />would occur, operator should specify how the slope <br />gradients will be achieved. <br />In order to maintain a dry condition in the llrea 1 slide, <br />a designed channel should be constructed across the <br />current inundation area, and across the toe of the <br />slope. This will help to transport water away from the <br />slide area, and help to enhance overall stability. The <br />channel design should be submitted for appro~ral prior to <br />initiating construction. <br />215 Centennial Building, 1313 Sherman Street Denver, Colorado 80203-2273 Tel. (303) 866-3567 <br />