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• Nucla Mine the soils have a moderately slow Co moderate (0.2 - 2.5 in/hr) permeability and <br />infiltration rate. At the Nucla East mining area the majority of the soils have a <br />moderate (0.6 - 2.0 in/hr) permeability and infiltration rate. A minor amount of the <br />soils have a moderately rapid (2.0 - 6.0 in/hr) permeability and inf i'l tration rate. The <br />subsurface strata in these areas consist predominately of tightly cemented sandstones and <br />shales which act as barriers inhibiting vertical percolation. However, field observation <br />of exposed outcrops and aquifer analysis data indicate that secondary porosity (weathered <br />and fractured bedrock strata) play a significant role in allowing vertically infiltrating <br />ground water to infiltrate through the unsaturated to the saturated zone. Oua ntification <br />of the transmissi vi ty and permeability associated with secondary porosity is difficult <br />because of the lack of reliable aquifer analysis techniques to determine secondary <br />porosity in low yielding aquifers. The entire study area is impacted by irrigation which <br />is the primary source of infiltrating water. Infiltration as a result of precipitation is <br />a relatively minor component of recharge in the Nucla area. The large majority of the <br />soils in the mining area have a slow to medium runoff potential. <br />The second area of concern is the reclaimed areas. The strata at tha Nucla and Nucla East <br />• mining areas are quite similar. Lithologic logs for the areas are contained in Tab 15, <br />Appendix 15-2, and Tab 9, Appendix 9-X. The lithologic logs ind ica~te that the spoils <br />material will generally be composed of more than 50 percent fragments of blasted sandstone <br />with lesser amounts of shale, bentoni to and gypsum. Tabs 20, 21 and 22 describe the <br />details of the mining and reclamation methods. Using the described mining and reclamation <br />techniques the approximate recharge capacity and permeability of the spoils material will <br />be equal or slightly less than the premi ned strata for the respective areas. The <br />resaturation rate of the spoils will be quite rapid because of the irrigation occurring in <br />the area. Resaturati on will occur both horizontally as well as vertically, greatly <br />increasing the rate of resaturation. Infiltration resulting from prec~i pitation is only a <br />very minor component. <br />Discharge. Cround water is discharged through streams, evapotranspiration, wells, springs <br />and seeps, and by subsurface outflow to contiguous aquifers to the southwest. <br />Discharge rates from overburden, Dakota coal and the unde rburden can be calculated using <br />Darcy's lan: <br />• 0=KA1 <br />7-14 Revised 04/11/88 <br />