_GENERAL DOCUMENTS - C1981017 (283)

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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 spi, h will pass the 25-year, 24-hour peak flow. The north pond is dessiyne o have a 24-inch CHIP and the south ponds are designed to hav ?-inch CMP discharge pipes. The ponds at Mine No. 3 have historically contained very little runoff. High evaporation rates 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. 'line 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 inin,� bench. It is designed to accolmnodate 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 spill way is ,j a;i y;, I t;) )is; :h:1 25-year, 24-hour peak flow with two 12-inch CMP discharge pip:1s. 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 '12reby grants a small area exemption as long as Mine No. 4 is inactive based on the following reasons: 1) the disturbed drainage area is ;;,call , 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 incraase the sediment yield from this area. The followingstipulation i s necessary to make a finding of compliance: Stipulation No. 2 PRIOR TO REACTIVATION OF MINE NUi-iBER 4, THE PERMITTEE MUST CONSTRUCT THE SEDI;-LENT PONDS, AS DESIGNED, ON THE SOUTHEAST SIDE OF THE MINE NO. 4 BENCH. Mine No. 5 Sediment Control The disturbed area at ,•tine Mo. 5 is 3.0 -acres. There are two separate bench areas which contribute to the one sediment pond. Approximately 2.3 acres is on excavatz-1d 1)edr,)c% •li t'i ta? r-e A-aining 5.2 acres on fill 0r excavated coboly soils. Runoff from undisturbed areas Nill be divertad by ditches and culverts around the disturbed area. The No. 5 sediment pond is designed to contain three years of sediment using the univer;•_1 ;,)il loss equation and the runoff from a 10-year, 24-hour precipitation event. The sediment pond is designed with an 2meryency spillway capable of passing she 25-year, 24-hour peak flow.