2021-09-03_PERMIT FILE - C1981019A ‎(8)‎

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 9/3/2021
• Doc Name: Permits
• Section_Exhibit Name: Volume 15 Rule 2
• Media Type: D
• Archive: Yes

RULE 2 PERMITS
Colowyo has four monitoring wells in the the Trout Creek Sandstone. Of the four ColowyoTrout Creek
monitoring wells, monitoring well C-05-33 (Sec. 11, T.3N., R.94W.) in the southern part of the Collom
permit expansion area (Map 1013), was drilled as part of the Collom project. This Trout Creek Sandstone
in this monitoring well is dry. The surface elevation of the well casing is 8,353 ft. ams], with the top of
the Trout Creek Sandstone at 7,586 ft. amsl. The other three Colowyo wells drilled into the Trout Creek
sandstone were drilled prior to 2000. These wells are located north and east of the Collom project area.
A fifth well drilled into the Trout Creek Sandstone was drilled by Utah International (DH -76-8), shown
on Map 1113, as an exploration hole and was allowed to remain open by Utah International.
These wells all contain water under confined conditions. The locations of these monitoring wells are as
follows:
DH -76-8 about a half -mile northeast of the Collom Pit (Sec. 36, TAN., R.94W.);
W-95-02 about two miles east of the Collom Pit (Sec. 5, T.3N., R.93W.);
W-95-15, approximately two miles northeast of the Collom Pit (Sec. 29, T.4N., R.93W.); and
UL -95-45, approximately 4.5 miles east-northeast of the Collom Pit (Sec. 27, T.4N., R.93W.).
Along the southern reaches of the stream channels, the deeper units of the Williams Fork Formation,
down to the I coal sequence outcrop. The stream channels cut through successively higher stratigraphic
units from south to north on the southern limb of the Collom Syncline. The valleys provide drainage for
the shallower coal and sandstone units. As a result of these conditions, the southern portion of the
groundwater basin consists of a sequence of perched groundwater zones. In general, the groundwater
levels occur within the respective water -bearing units. Conditions in the southern portion of the Collom
permit expansion area are therefore similar to those at the existing Colowyo mine. Groundwater is present
as perched zones in the upper coal seams and sandstone units, and seeps are typically associated with
perched water tables in the uppermost coal seams. At the existing mine, these seeps normally drain within
a few weeks, although sustained seeps recharged by upgradient drainages also occur, with a total
discharge of approximately 15 to 25 gallons per minute (gpm). With increasing depth below the
elevations of the adjacent stream channels, the bedrock units become fully saturated and groundwater is
present under confined conditions.
Hydraulic Characteristics - Previous studies by CDM (1985a), Dennis (2001, 2006) and WMC (2005)
determined the hydraulic characteristics of the bedrock aquifers in the Williams Fork Formation and the
Trout Creek Sandstone. The results of these studies are presented in Table 2.04.7-39, Table 2.04.7-40 and
Figure 2.04.7-33 and are discussed below.
The valley -fill aquifers have moderate to high permeability where encountered and exhibit a wide range
of hydraulic conductivity values. They exhibited the highest geometric mean hydraulic conductivity (3.2
feet per day (friday)) but also showed a very wide range (0.001 to 196 ft/day). Because of their limited
thickness, however, they typically have relatively low transmissivity. Storativity was not determined by
the testing, but values in the range typical for unconfined aquifers can be expected.
The most permeable bedrock units are in the F/G sequence of the Williams Fork Formation (F sandstone
through Gc coal seams) and the Trout Creek Sandstone. The sandstone units of the Williams Fork
Formation typically have lower permeabilities than the coal seams. The coal seams have hydraulic
conductivities ranging from approximately 0.002 to 0.77 ft/day and a geometric mean of 0.14 ft/day. The
highest hydraulic conductivities were observed in the Fab and G seams. The sandstone units have
geometric mean hydraulic conductivity values ranging from approximately 0.002 ft/day (H sandstone) to
0.008 ft/day (F sandstone). The geometric mean hydraulic conductivity for all the sandstones of the
Williams Fork Formation is 0.006 ft/day. The Trout Creek Sandstone exhibited a range of hydraulic
conductivity values between 0.006 and 0.09 ft/day and a geometric mean of 0.02 ft/day, indicating that it
Collom — Rule 2, Page 24 Revision Date: 4/7/17
Revision No.: RN -07