_GENERAL DOCUMENTS - C1981017 (262)

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-16- There are three ponds located on the mine h'tich, 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, ?4-hour peak flow. The north pond is dessiyne o have a 24-inch CMP and the south ponds are designed to hav 2-inch C-V 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 nigh infiltration capacity. These ponds rill 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 tie iinu bench. It is designed to accormnodate 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 t,) 25-year, 24-hour peak flow with two 12-inch CMP discharge pip:as. "tine 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 bencei. The Division 'lareby grants a small area exemption as long as iNine No. 4 is inactive based on i the following reasons: 1 ) the disturbed drainage area is s;nall , 2) the mine bench is largely composed of coarse rock material , and 3) there is ino 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. The following stipulation is necessary to make a finding of compliance: Stipulation PJo. 2 PRIOR TO REACTIVATION OF '°IINEE NU,,;BER 4, THE PER'i1ITTEE :MUST CONSTRUCT THE SEDI-1ENT PONDS, AS DESIGNED, ON THE SOUTHEAST SIDE OF THE MINE NO. 4 BENCH. 'line No. 5 Sedinlenc Control The disturbed area at '1inN ';o. 5 is 3.0 acres. There are two separat` bench areas which contrioute to Che one sediment pond. Approximately 2.3 acres is on ixc avak. 1 )e it)�: (i i'i `a'_ : lal nl nD 5.2 acre's on fill or excavated coboly sails. Runoff from unaisturDed areas Nill be diverted by ditch?s and c'alvPrts ?r-)iand the jisturbed area. The 'Jo. 5 sediment pone is designed to contain three years of sediment us ino the )nl '/Pr,;l ;,)i 1 loss equation and the r'Jnoff froin a 10-year. dour ?reciait:tion event. The sediment pond is ��asiyned with an emergency spillway doable of passin.3 -he 25-year, 7-4-Hour peat flow.