2010-12-17_REVISION - C1981019 ‎(153)‎

• Permit No: C1981019
• IBM Index Class Name: REVISION
• Doc Date: 12/17/2010
• Doc Name: Exhibit 7 Item 21 Collom Project Pre-Feasibility Hdyrology Report
• Type & Sequence: PR3
• Email Name: JRS
• Media Type: D
• Archive: No

Groundwater 71
r,
10 Water levels in the central part of the proposed mine contain heads that rise 23 to 220 ft
above the F/G sequence. Groundwater in PC- 04 -36FG (screened in the G seams)
occurs 90 ft above the top of the screened interval. In PC- 04 -25FG, the water level is
73 ft above the top of the Fab seam. In PC- 04 -22FG, the water level is approximately
23 ft above the top of the Fa coal. In PC- 04 -20FG, the water level is approximately
150 ft above the top of the Fa coal. On the west side of the mine at MWC- 04 -05FG, the
water surface is approximately 300 ft above the top of the screened F and G seams. At
PC- 04 -04FG, the water table resides at 7,042 ft amsl, approximately 220 ft above the
top of the Fab and G coals where the well is screened.
The single H sandstone well in the central part of the proposed mine is MWC- 04 -05H,
which has a groundwater elevation of 7,160 ft. This places the piezometric surface
564 ft above the H sandstone.
Water levels in the I sandstone range from 7,045 to 7,142 ft. At PC- 04 -81, the water
level is 322 ft above the top of the unit. At PC -04 -201, the piezometric surface is
approximately 253 ft above the top of the unit.
In summary, groundwater in the central area transitions from perched conditions to a
more uniform area -wide water table. Dewatering measures will likely be needed in this
area to control pore pressures in slopes.
North area
C
Water levels in all four units (F sandstone, F/G sequence, H sandstone, and
1 sandstone) in the north portion of the mine area range from about elevation 7,120 to
about 6,950 ft. The pattern of increasing pressure heads above the screened intervals
continues with distance downgradient. The relatively high head difference between the
F/G and H sandstone units indicates that there is an effective confining bed between
them.
Water levels in the F sandstone are available from MWC- 04 -13FS, which has a head
184 above the screened interval. This well is screened just above the Fab, in the lower
portion of the F Sands.
Water levels in the F/G sequence show increasing heads with distance to the north.
MWC- 04 -33FG is screened in the sand /coal sequence just below the G7 coal.
Assuming that the head is reflective of conditions in the Fab coal, the piezometric
surface is 184 ft above the top of the Fab. At MWC- 04 -13FG, the water level is 174 ft
above the top of the Fab coal. In MWC- 04 -14FG, the water level is 291 ft above the top
of the Fab, and'at MWC -04 -01 FG, the water level is 184 above the Fab coal.
Water levels in the H sandstone at MWC- 04 -33H, MWC- 04 -13H, and MWC -04 -01 H have
heads that are 331, 400, and 428 ft, respectively, above the top of the H sandstone.
Water levels in the I sandstone in the northern part of the mine are available only from
PC -04 -201, which has a water level elevation of about 7,045 ft. This is about 285 ft
above the I sandstone.
•
2572 -R2 Colowyo Coal Company
Water Management Consultants