PERMFILE115349 - Laserfiche WebLink

Home Browse Search

a~~~~ 2-16 Runoff data for the area was calculated using the SCS method with the following base parameters: 1) Soil Group B, 2) ante- cedent Moisture Conditions (AMC) II, and 3) an average Curve Number (CN value of 85. Precipitation for a 10-year, 24-hour event (Q10) for the permit area is 1.70 inches. Runoff for Q10 was calculated to be 0.58 inches. Precipitation for a 25- j~.ear, 24-hour event (Q25) is 2.1 inches with a calculated run- off of 0.87 inches. Q10 and Q25 were used for the design of collector ditches and the emergency spillway of the sedimenta- tion reservoir, respectively (see Appendix As). From runoff calculations, the sedimentation reservoir shall require a liquid volume of 1.72 acre/feet. The reservoir shall be dewatered in approximately six hours using a 12" diameter conduit and an 18" diameter riser (see Appendix As for calculations). The riser shall be equipped with an antivortex device and trash rack combination. The con- duit shall be equipped with a valve which shall be opened once • the quality of the surface runoff has met the standards set forth in the mine permit. Water, which is contained in the reservoir below the riser elevation, may be used for dust abatement. Slurry Ponds To dispose of smaller sized refuse generated at the wash plant, waste water from the plant shall be pumped to a series of three slurry ponds located south of the sedimentation reservoir (for location, see Figure 2.2-25). Each pond shall have a capacity of two million gallons with Ponds No. 1 and No. 2 constructed to receive slurry directly from the wash plant. Fines shall be allowed to settle in either Pond No. 1 or Pond No. 2 with de- canted water transferred to Pond No. 3 where the water shall be recirculated to the wash plant for process water. When Pond No. 1 has accumulated sufficient sediment so that retention time and water quality are significantly reduced, • the slurry will be switched to Pond No. 2. While Ponds 2 and 3 `fir, - - - ` ,~~.