2010-12-17_REVISION - C1981019 ‎(140)‎

• Permit No: C1981019
• IBM Index Class Name: REVISION
• Doc Date: 12/17/2010
• Doc Name: Exhibit 7 Item 22 Collom Pit Regional Hydrogeologic Model
• Type & Sequence: PR3
• Email Name: JRS
• Media Type: D
• Archive: No

Hydrological system and available data DRAFT 4
Table 2.1 Summary of measured hydraulic conductivities
Unit Maximum Minimum Geometric No. of No. of
mean data points wells
(ft/d) (ft/d) (ft/d)
Valley fill 1,96E+02 1.44E-03 3.26E+01 16 9
F sandstone 5.24E-02 7.87E-03 1.76E-02 6 6
F/G sequence 1.98E-01 4.28E-04 3.88E-02 18 18
Fab seam 7.70E-01 6.66E-03 1.84E-01 9 6
G seams 5.72E-01 9.69E-02 1.97E-01 4 4
H sandstone 7.9E-03 1.67E-04 1.44E-03 4 4
1 sandstone 3.20E-02 9.03E-04 8.06E-03 3 3
J seam 4.28E-04 1 1
Trout Creek 8.90E-02 5.80E-03 2.06E-02 6 3
Sandstone
The F/G sequence was a primary focus of the pre-feasibility study because this
sequence is near the bottom of the proposed mine, will exhibit the highest water
pressures and is key from a dewatering perspective. It contains the thickest and most
permeable coal units and will be a major dewatering target. Based on all hydraulic test
results, the geometric mean hydraulic conductivity of the entire F/G sequence (including
the coal seams and interbed units) is about 0.04 ft/d. Values from the G and Fab coal
seams average about 0.2 ft/d. Based on evaluation of data from the pilot dewatering
test alone, the geometric mean hydraulic conductivity of the F/G sequence is about
0.1 ft/d. The geometric mean value for the Fab seam is about 0.3 ft/d.
Storage coefficient estimates are available from several single-well tests, the historical
Utah International pump test, and the pilot dewatering test-as presented in the Pre-
feasibility Hydrology Report. For all data from the F/G sequence, the storage coefficient
estimates range from 0.057 to 3.74 x 10-6, with a geometric mean of 1.34 x 10-4. In the
Trout Creek Sandstone, storage coefficient estimates ranged from 0.023 to 0.008.
Based on evaluation of the pilot dewatering test alone, the geometric mean storage
estimate for the F/G sequence is about 7 x 10-5 and for the Fab seam is about 5 x 10-5.
2.2 Controls on groundwater flow
2.2.1 Geology
The main water-bearing units underlying the proposed Collom Mine are the coal seams.
The sandstone units also transmit groundwater, but have lower hydraulic conductivities
than the coal seams. The mudstone interbeds act as confining units.
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2572-R3 Colowyo Coal Company, L.P.
Water Management Consultants