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

multiple completion (overburden and Dakota coal) monitor wells. It was necessary to
include the two multiple completion monitor wells (GW-N8 and GW-N9) in the Dakota coal
potentiometric contour map because they are the only two wells in the northwest portion of
the permit area open to the Dakota coal . Generally (in the Dakota coal) static water
levels are slightly deeper than the overburden so the potentiometric surface in the
vicinity of the multiple completion wells may have a slightly higher water surface
elevation than the Dakota coal.
Ground water in the Dakota coal is confined in all of the areas monitored. The flow in
the Dakota coal aquifer is generally from the northeast to the southwest. The average
water level gradient is .0297 ft/ft with a range between .0228 ft/ft and .0343 ft/ft.
Recharge to the Dakota coal is generally from the agricultural crop areas situated to the
northeast and from vertical leakage from the irrigation ditches and flood irrigation via
overlying units. Discharge mainly occurs along the draws where the Dakota aquifer
intersects the ground surface and by discharge to contiguous aquifers.
Underburden. The potentiometric surface map of the underburden is presented on Exhibit
7-4. The water level contours were constructed based on September, 1987 water level data
from eight underburden monitoring wells.
Ground water in the underburden is under confined conditions. Flow in the underburden is
from the northeast to the southwest. The average water level gradient is .0301 with a
range between .0237 and .0368. The primary recharge area is located northeast of the mine
via leakage from the overlying units. Discharge occurs in the draws where the underburden
aquifer intersects the ground surface and to contiguous aquifers. The mining operation at
the Nucla Mine appears to have no effect on the underburden ground water potentiometric
surface.
Monitor Well GW-N11 has been omitted from use in the construction of the underburden
potentiometric contour map. This monitor well has enigmatic static water level readings
when compared to the rest of the underburden monitor wells. The completion information on
this monitor well (see Appendix 15-2) is inadequate. Because of the poor completion
record and the anomalous static water level readings, it was decided to exclude this well
from the potentiometric surface map.
Effects of the Irrigation System on Potentiometric Surfaces. During the summer months
7-11 Revised 04/11/88