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as will the first two years of mining at the Nucla East mining area. Mining in years 3 <br /> through 5 at Nucla East may be done using dragline placement of the spoil . At both mining <br /> areas the final contouring of the spoil surface will be accomplished with dozers and <br /> scrapers. <br /> Based on the above discussion, the hydraulic conductivities of the replaced spoil should <br /> vary, with that placed using a dragline exhibiting the highest values. Also, regardless <br /> of the method of placement the overall horizontal hydraulic conductivities should be higher <br /> than that in the surrounding undisturbed portions of the shallow aquifers. The "K" value <br /> for the spoil determined at Spoil Well CW-N27 is estimated to be 40 ft/day which is <br /> significantly higher than any of the "K" values determined for the overburden and coal <br /> aquifers. <br /> Data presented in Tab 9, Soils, indicates that the premining soils at both mining areas <br /> had moderate to slow infiltration rates (Hydrologic Soil Croups B and C) with a higher <br /> percentage exhibiting moderate infiltration rates. The bedrock contains extensive <br /> sandstone ledges and vertical permeabilities would be largely limited to the degree of <br /> fracturing (secondary porosity). The replaced spoil material will not have any ledges as <br /> these units will be thoroughly broken up by blasting and vertical permeabilities will be <br /> dependent on the degree of interconnected porosity rather than fractures. The topsoil to <br /> be replaced is projected to have a more even mixture of moderate to slow infiltration <br /> characteristics (owing to some loss of soil structure). The replaced topsoil will be <br /> somewhat compacted during placement, but the chisel plowing and disking operations used to <br /> prepare the soil for seeding should greatly improve the topsoil infiltration rates. <br /> In comparing the Nucla and Nucla East mining areas, the percentage of shale is less and <br /> the percentage of sandstone is greater in the overburden in the Nucla East area. Thus, <br /> Nucla East should exhibit slightly higher recharge rates. In comparison to premining <br /> conditions, the potential infiltration and recharge rates of the replaced topsoil and <br /> spoil should be comparable or greater than premining rates. The premine and postmine <br /> topsoils exhibit comparable infiltration rates and disking and chisel plowing should <br /> further enhance infiltration. The spoil will have greater porosities and no ledges, but <br /> will exhibit poorer sorting of particle sizes. The undisturbed overburden has extensive, <br /> hard sandstone ledges and recharge would largely be controlled by the degree of <br /> interconnected fractures. The poorer sorting of particle sizes in the spoil should not <br /> impede vertical recharge any more than ledges and varying degrees of vertical fracturing <br /> would. <br /> 17-28 Revised 04/11/88 <br />