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

ditches are flowing and flood irrigation is occurring. Water level responses to
precipitation events are indistinguishable, as the effects of recharge from the ditch
irrigation system have masked any evidence of recharge that could be attributable to
precipitation. Mining at the Nucla Mine area has had no discernible affects on the water
levels of the overburden monitor wells.
Dakota Coal Water Levels. Eight monitor wells have been installed to monitor water levels
in the Dakota coal aquifer. Two of the monitor wells (GW-N4 and GW-N4R) are located at
the Nucla Mine and the remaining six monitor wells (GW-N14, GW-N17, GW-N17P1, GW-N20,
GW-N29 and GW-N30) are located at Nucla East (Exhibit 7-1). Water level data for Well
GW-N4 has been collected since August, 1979 and collecti"on of water level data for Wells
GW-N14, GW-N17, GW-N17P1, and GW-N20 began in July 1986. The remaining three wells
(GW-N4R, GW-N29 and GW-N30) were recently installed (September, 1987) and collection of
water level information began immediately after they were completed and developed.
Exhibit 7-3 shows the Dakota coal potentiometric surface. Monthly water level data
including hydrographs for all monitor well sites are contained in Appendix 7-1.
Ground water in the Dakota coal is under artesian conditions with a general downward
vertical head, but there are areas with upward vertically recharging head pressures. Mean
artesian heads in the lower Dakota coal range from 18 feet at Monitor Well GW-N14 and 42
feet at Monitor Well GW-N29. The average artesian head for the lower Dakota coal is 34
feet. Water levels in the Dakota coal display seasonal variability that coincides with
the irrigation season and operation of the ditch irrigation system. The maximum seasonal
water level fluctuation observed in Monitor Well GW-N4 is about 3.0 feet due to its
location in the valley bottom. The Nucla East wells display seasonal variability from 2.8
feet at Monitor Well GW-N17P1 to 14.6 feet at Monitor Well GW-N20. Shallowing occurs from
April to September and there appears to be little lag between when the irrigation season
starts and the shallowing of the static water levels occurs. There are no discernible
water level responses to precipitation, nor can any affect from mining be observed at any
of the Dakota coal monitor wells at the Nucla or Nucla East mining area.
Underburden Water Levels. Twelve monitor wells have been installed to monitor water
levels in the underburden aquifer system. Six of those monitor wells (GW-N1, GW-N1P1,
GW-N3, GW-N5, GW-N6 and GW-N11) are located in and proximate to the Nucla Mine site. The
remaining six monitor wells (GW-N13, GW-N16, GW-N16P1, GW-N192 GW-N33 and GW-N34) are
located proximate to the Nucla East mining area. Exhibits 7-1 and 7-4 show the
7-8 Revised 04/11/88