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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 Groups 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 6e 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 />