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

• Permit No: C1981008A
• IBM Index Class Name: PERMIT FILE
• Doc Date: 4/11/1988
• Doc Name: Hydrologic Description ‎(Part 1 of 2)‎
• Section_Exhibit Name: Tab 7
• Media Type: D
• Archive: Yes

when flood irrigation is in full swing, each of the aquifers monitored exhibits a rise in
static water level . This ground water shallowing creates a uniform rise in the
potentiometric surface. Perusal of the water level data indicates that the rise in the
potentiometric surface during the summer months has a negligible effect on the ground
water gradients.
Recharge. A predominate source of recharge to the shallow bedrock aquifer system at the
Nucla and Nucla East mining areas is leakage from the irrigation ditch system and
infiltration of excess flood irrigation waters. Recharge also results from infiltration
of precipitation and subsurface ground water inflow. The Dakota coal and the underburden
are generally confined but there is enough leakage between the adjacent units to afford
some recharge.
Recharge to the alluvial aquifers is by discharge from the bedrock aquifers and
infiltration of surface waters (return irrigation water and precipitation).
Hydrologic Boundaries. Aquifer testing of the low yield strata at Nucla and Nucla East
did not yield the presence of any major hydrologic boundaries. Bedrock aquifer testing of
any duration would not yield the presence of hydrologic boundaries because the cones of
depression in these aquifers, with low transmissivities, would be very small in areal
extent. There are no faults, angular unconformities, or nonconformities within the permit
area which would act as impermeable boundaries. Some minor lithologic boundaries are
present in the bedrock aquifers as a result of their environment of deposition. There is
a no-flow boundary in the unsaturated units in the eastern portion of the Nucla Mine
permit area (NWk, Section 31, R15W, T41N and NEk Section 36, R16W, T41N). Constant and
semi-constant discharge boundaries occur where the aquifers crop in the bottom of the
draws (see Figure 7-1).
Infiltration and Permeability of the Unsaturated Zone. Using the soil hydrologic
properties defined by the Soil Conservation Service of the U.S. Department of Agriculture,
it is possible to estimate the infiltration rates of soils occurring within the vicinity
of the Nucla and Nucla East mining areas. The Nucla and Nucla East soils have been mapped
at a scale of 1 inch equals 400 feet. The soils maps are included in Tab 9 of this permit
application. The unsaturated zone can be divided into two categories. The first is the
undisturbed areas. Contained in Tab 9 on Table 5 and in Appendix 9-5-2 are the soil
hydrologic properties of the Nucla and Nucla East mining areas. In the vicinity of the
7-12 Revised 04/11/88