Laserfiche WebLink
_. <br />• diversion ditch below the fill on the lower area. This diversion ditch <br />will then lead to the natural drainage which leads to the retention pond. <br />t is strongly recommended that a natural channel be left in its present <br />condition (partly grassed and supported with vegetation) to prevent <br />excessive erosion. The sedimentation storage is based on three year <br />sediment storage, as determined by the universal soil loss equation. <br />These calculations are also shown as a part of Appendix I. The result <br />is that approximately 0.32 acre feet of sedimentation must be allowed <br />for in the retention pond. This must be cleaned out cahen 60% of the <br />sediment capacity has been reached. ' <br />It will be necessary to reconstruct and enlarge the existing reten- <br />tion pond, The pond has been breached, and is loaded with sediment at <br />• this time. It is suggested that the present sediment in the pond be <br />removed and the soil in the pond and new pond area be removed and stock- <br />piled for use as future cover during the reclamation process. Although <br />some consideration was given to placing the pond directly below the fill <br />of the lower level of the affected mine area, this option was discarded <br />because of the steep slope in that area. Instead, a pond with the di- U v v <br />mensions of 60 feet wide by 210 feet long parallel_to_contou-r should be ~j~v <br />constructed. This pond will be a maximum of five feet deep from the <br />bottom of the pond to spillway. The embankment will be an additional <br />18 inches high to allow for required freeboard and settlement. The em- <br />bankment should be cleaned, scarified and compacted to at least 12 <br />inches below natural grade and then rebuilt in no more than 6 inch lifts <br />with the material taken from the pond site. This material should be <br />• placed at optimum moisture content (plus or minus 2%) and be compacted <br />3 <br />