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• when flood irrigation is in full swing, each of the aquifers monitored exhibits a rise in <br />static water level. This ground water ~shallowi ng creates a uniform rise in the <br />potentiometric surface. Perusal of the water level data indicates that the rise in the <br />potentiometric surface during the summer months has a negligible effect on the ground <br />water gradients. <br />Recharge. A predominate source of recharge to the shallow bedrock aquifer system at the <br />Nucla and Nucla East mining areas is leakage from the irrigation ditch system and <br />infiltration of excess flood irrigation waters. Recharge also results from infiltration <br />of precipitation and subsurface ground water inflow. The Dakota coal and the underbu rden <br />are generally confined but there is enough leakage between the adjacent units to afford <br />some recharge. <br />Recharge to the alluvial aquifers is by discharge from the bedrock aquifers and <br />infiltration of surface waters (return irrigation water and precipitation). <br />Hydrologic Boundaries. Aquifer testing of the low yield strata at NUCIa and Nucla East <br />• did not yield the presence of any major hydrologic boundaries. Bedrock aquifer testing of <br />any duration would not yield the presence of hydrologic boundaries because the cones of <br />depression in these aquifers, with low transmi ssivities, would be very small in areal <br />extent. There are no faults, angular unconformities, or nonconf ormities within the permit <br />area which would act as impermeable boundaries. Some minor lithologic boundaries are <br />present in the bedrock aquifers as a result of their environment of deposition. There is <br />a no-flow boundary in the unsaturated units in the eastern portion of the Nucla Mine <br />permit area (NW1y, Section 31, R15W, T41N and NE>; Section 36, R76W, T41N). Constant and <br />semi-constant discharge boundaries occur where the aquifers crop in the bottom of the <br />draws (see Figure 7-1). <br />Infiltration and Permeability of the Unsaturated Zone. Using the soil hydrologic <br />properties defined by the Soil Conservation Service of the U.S. Department of Agriculture, <br />it is possible to estimate the infiltration rates of soils occurring within the vicinity <br />of the Nucla and Nucla East mining areas. The Nucla and Nucla East soils have been mapped <br />at a scale of 1 inch equals 400 feet. The soils maps are included in Tab 9 of this permit <br />application. The unsaturated zone can be divided into two categories. The first is the <br />undisturbed areas. Contained in Tab 9 on Table 5 and in Appendix 9-5-2 are the soil <br />• hydrologic properties of the Nucla and Nucla East mining areas. In the vicinity of the <br />7-12 Revised 04/11/88 <br />