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Geotechnical Evaluation of Mine-Intluced Selsmlcity on Monument Dam <br />Dorsey 8 Whitney, LLP <br />I~ <br />C~ <br /> <br />D. <br />E. <br />Outlet Works <br />Inlet Type: <br />Inlet Elevation: <br />Conduit Type: <br />Conduit Length: <br />Conduit Dimensions: <br />Outlet Invert Elevation: <br />Reservoir <br />Drop Inlet <br />7289.6 feet <br />Cast Iron Pipe <br />225 feet± <br />12-inch-diameter <br />7272.6 feet <br />Type of Storage Storage Volume <br />(acre-feet) Surface Area <br />(acres) <br />Irrigation (at spillway) 516 20.7 <br />Irrigation 8 Flood Storage (at dam crest) 632 23.3 <br />F. Drainage Area <br />Total Drainage Area: <br />Contributing Drainage Area: <br />G. Other Data <br />5.5 square miles <br />5.54 square miles <br />Maximum Known Flood at Dam Site: Unknown <br />ON or OFF Stream Res.: ON-Dry Fork Minnesota Creek <br />Notes: <br />1. Elevation based on topographic survey performed by M. Shipman, September 1987. <br />2. Pertinent data dimensions and geometry information obtained from SEO inspection reports <br />and Phase I Inspection Report, National Dam Safety Program, by Hydro-Triad, Ltd., 1979. <br />2.2 Dam Components <br />The left side of the earthfill dam is constructed against and on top of an active landslide in <br />the left abutment (looking downstream). The location of this landslide is shown on <br />Figure 2.3, based on mapping performed by George Van Slyke, Chief, Geotechnical Services <br />Branch, SEO (Van Slyke, 1987), site observations, and good correlation with stereo-pair <br />aerial photographs. The integrity of the earthfill dam depends on both abutments to provide <br />unyielding support of the earthfill structure. Several dam safety deficiencies have been <br />reported for the earthfill dam dating back to a 1979 Phase I Dam Inspection (Hydro-Triad, <br />1979) and include seepage exiting at high elevation on the downstream slope, associated <br />GEI <br />060350 06-03-I6 Monummt Dmn Gmtxlu,iul Evd <br />March 2006 <br />