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details were used to size the pond 7 <br /> emergency spillway (shown at right). <br /> Limited information taken from the <br /> hydrologic calculations indicates that a <br /> minimum of two feet of channel depth, <br /> including required freeboard, is <br /> necessary to safely pass the 25-year, <br /> 24-hour storm event. Please review <br /> the field condition and maintain the <br /> spillway as necessary. <br /> Pond 001 is the mine water discharge <br /> pond, located immediately north of the <br /> mine office. The pond water level is <br /> 1-2 feet below the discharge point and water was not observed being pumped to the pond. <br /> Backfilling and Grading <br /> The operator is reconstructing the permanent drainage over the excavated area at the West <br /> Mine (below). Saturation of this area may result in settlement into the mine workings. The <br /> operator may want to consider geotextile or other means to prevent water infiltration along <br /> the reconstructed drainageway. Page 2.05-46a requires that 6 inches of stockpiled growth <br /> medium be applied to the area once the final grade is established. Page 2.05-46 identifies <br /> design details for ditch D18, as shown in Exhibit 19, Table 19-2. Riprap is required for this <br /> ditch. Please ensure that the ditch is constructed exactly as designed. Following <br /> reconstruction, it should be certified by a registered professional engineer. <br /> 4 <br />