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i <br />42.05 APPLICATION FOR PERMIT FOR SDRFACE OR UNDERGROUND MINING ACTIVITIES -- <br />MINIMUM REQUIREMENTS FOR OPERATION AND RECLAMATION PLANS. <br />2.05.6 Mitigation of Surface Coal Hiving Operation Impacts. (Cont'd.) <br />(3) (b) (iv) (Cont'd.) <br />thickness of solid strata cover above the seam <br />is less [h an 5 times the maximum entry width <br />(SS) or ZO times the maximum entry weight <br />(lOT), whichever is greater. 4fiere at least <br />one competent bed of sandstone or similar ma- <br />terial is present within the solid strata and <br />has a thickness at least 1.75 times the maxi- <br />mum entry width, mining at a lesser cover than <br />Ss or lOt may be considered. <br />• <br /> <br />"2. In the case of drifts or tunnels beneath <br />or in the vicinity of the body of surface wa- <br />ter driven through the strata for the purpose <br />of gaining access to a coal seam, the provi- <br />sion of lOT or SS should also apply unless <br />drifts or tunnels are permanently supported <br />and are so maintained. In the latter event, <br />however, there should be a minimum solid cover <br />of 1.75 times the maximum drift or tunnel <br />width". <br />These guidelines are considered very conserva- <br />tive and were "aimed at maximinn efficient <br />utilization of underground coal resources con- <br />sistent wi[h minimizing inunda[ion hazards,". <br />~~ Theoretical calculations and rules of thumb <br />~I ~ ~~~ ~~1 must be substantiated by site specific data. <br />}ICI ~/ CWI s hydrologic and subsidence monitoring <br />~~/-! programs are designed to substantiate the "no <br />N~~~ ~ impact" predictions. <br />For colluvial springs and ponds located less <br />than 800 ft. of overburden, a deleterious im- <br />pact is possible, based upon site specific ob- <br />servations at the Orchard Valley Mine. Drain- <br />ing of storage ponds and disruption of collu- <br />vial spring discharges may occur as the result <br />of surface subsidence. In consultation with <br />State and Federal agencies, CWT has developed <br />a rating of significant hydrology features to <br />sustain the pre-mining land use of grazing and <br />wildlife habitat within the permit area. P.ny <br />Added 12/26/84 <br />Added 03/07/85 <br />Revised 10/01/87 <br />129 <br />