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• Table 3 Condition Factor of Safety Steady State Seepage Full Height 1.51 Steady State Seepage Half Height 2.6 Steady State Seepage Quarter Height 4.3 i Based on the results of the stability analysis, the embankments ppear to be stable for all the considered cases. The static Factor of safet is above 1.5 and the horizontal yield acceleration is approximately 0.2 G at factor of safety of 1.0. According to standard procedure [2], deformation due to seismic should not be a problem, and a specific deformation anal sis was not made. i II. Evaluation of the 25-year Flood • The flood plain of the Middle Fork South Platte River is char actdrized by a small cobble-bottom/sandy channel with a wide gentle upper bank ominated with willow and other vegetation. It is restricted by a twin 10 foot box culvert, labeled as G-12-G as it crosses under Highway 9. The 25-year flood is estimated at about 600 cfs [4] from the 33. square mile watershed. This flow will cause only minor water pooling immedi tely above the culverts. Since the channel section is generally uniform al ng the embankment area, the flow depth was computed using Manning's equ tion. The flow depth for the 25-year flood will only be about 4 feet, whit is below the toe of the embankment. This flood flow is not considered to imp se any threat to the embankment or adjacent mined areas. III. Evaluation of the 5-rear. 6-hour Storm Runoff The 5-year, 6-hour storm will produce a total precipitation dept of 1.2 inches [5 ]. Hased upon a site investigation, the soil-use class'fication is given as "C" soils (moderate infiltration) with a forest canopy ver of 40 percent. The SCS complex curve number is 74, with a computed ru ff of 0.09 inches [67. The computed volume of runoff over the 150 acre xate shed above the mine area is 49,000 cubic feet (1.13) acre-Feet. ~ The storage capacity of the recirculation ponds is adequate to cotain all the runoff from the mined area, in addition to mine-use water. The 'ne water level will be maintained 3 feet below the embankment crest, and t e 5-year, 6- hour storm volume would raise the level to about 2 feet below the crest for a short period of time. The remaining freeboard is left Far emerge cy surcharge, wave action, and dam stability reasons.