2007-12-18_PERMIT FILE - C1981019A

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 12/18/2007
• Section_Exhibit Name: 4.05 Hydrologic Balance
• Media Type: D
• Archive: Yes

• 4.05.12 Protection of Groundwater Rechar¢e Capacity
The reclamation plan as described in 2.05.4 will return the disturbed lands to approximately
the pre-mining condition; therefore, ground water recharge capacity is expected to
approximate the premining condition. Also, because of the minimal existence of ground
water in the mining area, the mining operation and subsequent reclamation should have no
adverse effect on the existing ground water recharge capacities.
The history of the ground water monitoring plan is further documented in 4.05.13. The mine
has not established Point of Compliance locations for ground water monitoring because of a
lack of ground water. The following discussion is provided to document this:
The aspect of monitoring ground water is dependent on whether or not there is a
continuous, non-perched ground water layer/zone to monitor. Since active mining at
Colowyo Mine began 30 years ago, the mining zone in both the East and West Pits
have not encountered any significant ground water, except for perched ground water.
Therefore, the following is presented to clarify the ground water conditions at the
Colowyo Mine.
Geologv/Topo¢rauhv
The Colowyo Mine is located in the Williams Fork Formation of the Cretaceous
Mesaverde Group. The Williams Fork Formation is comprised of discordant
beds/units of sandstone, siltstone and mudstone and coal seams, with an approximate
• thickness of 1,200 to 1,300 feet in the mine area. Deposited in a deltaic environment,
the beds vary in thickness and lateral extent throughout the Colowyo Mine. The
numerous coal seams also vary in thickness and lateral extent. The sandstones tend
to be very fine grained to fine grained and poorly sorted, with various amounts of silt
and clay. For the siltstones and mudstones, theses units contain various amounts of
finer and coarser materials. The total mined sequence in both pits is up to 450 feet
thick and is comprised principally of mudstones, siltstones and coals, with sandstone
layers being least prevalent.
The Williams Fork Formation conformably overlies the Iles Formation. At the top of
the Iles Formation is the Trout Creek Sandstone (TCSS). The TCSS is a massive,
white to light gray, very fine to fine grained, moderately well sorted sandstone with a
thickness of between 50 and 70 feet and is approximately 1,200 to 1,300 feet below
the Colowyo Mine. This is the only mapped continuous unit in the area of the
Colowyo Mine and has been noted as being an excellent marker bed for correlation
work of the coal seams. Beneath the TCSS, the Iles Formation is comprised of
sandstones, siltstones and marine shales.
Two major features, the Collom Syncline and the Danforth Hills Anticline/Wilson
Dome, control the geologic structure in the area of Colowyo Mine. The axis of the
Collom Syncline, located approximately 0.5 miles north of the north edge of the
reclaimed East Pit, trends west-northwest (approximately N60°W) with a slight dip in
the axis to the west-northwest. The Collom Syncline is sub-parallel to the Axia]
• Anticline on the north and the Danforth Hills Anticline on the south. The Collom
Syncline is asymmetrical, with the north flank of the syncline steeply dipping (20°-
40°) to the south-southwest. The south flank dips to the north-northeast at around
4.05-9a Revision Date: 11/17/05
Revision No.: MR-75