1986-12-11_PERMIT FILE - C1981017

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-16- There are three ponds located on the mine bench, one on the north side, and two in series on the south side. The ponds are equipped with emergency Spillways which will pass the 25-year, 24-hour peak flow. The north pond is designed to have -e 24-inch CMP and the south ponds are designed to have two 12-inch CMP discharge pipes. The ponds at Mine No. 3 have historically contain very little runoff. The high evaporation rates which characterize the area is given in the application as one possible reason. Another possible reason is the coarse nature of the mine bench material which would lead to a high infiltration capacity. These ponds will be dewatered by pumping whenever necessary to maintain storage for runoff from a 10-year, 24-hour precipitation event. In addition to the mine bench, the Mine No. 3 lower bin pad comprising 0.45 acres is contained by one sediment pond. This pond is equipped with a cmp principle spillway capable of passing the peak flow from a 10-year, 24-hour precipitation event plus a cmp emergency spillway capable of passing the peak flow from a 25-year, 24-hour precipitation event. Mine No. 4 Sediment Control The Mine No. 4 pad includes 2.86 acres of excavated surface with a 1 to 3 percent grade toward the highwall . One sediment pond is present at the pad and four, in series, are planned to be constructed. The sediment pond already constructed drains 1 .99 acres of the mine bench. It is designed to accommodate the runoff from a 10-year, 24-hour event plus three years of sediment accumulation. The sediment pond will be dewatered by pumping. The emergency spillway is designed to pass the 25-year, 24-hour peak flow with two 12-inch CMP discharge pipes. Mine No. 4 has been inactive since the summer of 1980. The applicant has requested a small area exemption from constructing the four sediment ponds on the southeast side of the Mine No. 4 bench. The Division hereby grants a small area exemption as long as Mine No. 4 is inactive based on the following reasons: 1) the disturbed drainage area is small, 2) the mine bench is largely composed of coarse rock material, and 3) there is no mixture of mine discharge with surface drainage. If Mine No. 4 becomes active, coal fines will be generated and traffic will crush rock which will increase the sediment yield from this area, and the ponds will therefore be required. The following stipulation is necessary to make a finding of compliance: Stipulation No. 1_ PRIOR TO REACTIVATION OF MINE NUMBER 4, THE PERMITTEE MUST CONSTRUCT THE SEDIMENT PONDS, AS DESIGNED, ON THE SOUTHEAST SIDE OF THE MINE NO. 4 BENCH.