Laserfiche WebLink
<br />A. Runoff from the area above the highwall fill slope and the <br />upper bench consists of 1,02 acres. The settled water is <br />diverted to the site bench pond. <br />B. The site bench sedimentation pond collects runoff from the <br />highwall fill slope, the bulk of the mine site, and the <br />ramp to the north spoil area. This area consists of 4.21 <br />acres. Settled water from the pond is discharged through <br />a 10" pipe into Lewis Gulch. An energy-dissipating struc- <br />ture has been provided at the outlet in Lewis Gulch. <br />C. The lower sediment pond will collect the runoff From the <br />ramp to the upper bench, the southern portion of the site <br />bench, the fill slopes and access road below the site bench, <br />and the truck loading area, consisting of 3.06 acres. Dis- <br />charge from the lower pond will be directly into Lewis <br />Gulch. All of the pond's outlet structures have been de- <br />signed to handle the 25-year, 24-hour type IIA storm. <br />Details and calculations for the ponds are shown on Sketch <br />Nos. TPS-1 S TPS-2. Division of runoff areas, drainage plans, <br />• berms and location on the mine site are shown on Drawing No. TP-3. <br />Included in the mine plan is a permanent fill across Lewis Gulch <br />which will serve as a truck-loading area during the life of the <br />mine. To accommodate flood flows in the dry gulch, a 60" 0 CMP <br />has been chosen which will handle a l0U-year 24-hour flood. In- <br />corporated with the fill is the lower sedimentation pond. This <br />facility will also serve as a flood control structure during <br />severe rain storms. The embankmen[ is classifiud as a roadway <br />fill and therefore does not fall under the jurisdiction of the <br />State engineer. Design calculations of the Culbert are included <br />in Appendix A . <br /> <br />75 <br />