1988-04-11_PERMIT FILE - C1981008A (9)

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