2018-08-08_PERMIT FILE - C1982056A ‎(4)‎

• Permit No: C1982056A
• IBM Index Class Name: Permit File
• Doc Date: 8/8/2018
• Doc Name: Pages 2.05-65 to 2.05-197.3 part 2
• Section_Exhibit Name: 2.05 Operation and Reclamation Plans Part 2
• Media Type: D
• Archive: Yes

Overburden monitoring wells have varied, depending on location. Hydrographs for Wells 006-82-74C south of
the portal and 009-79-4 south of the SWMD show little change other than small seasonal fluctuations.
However, hydrographs for Wells 006-87-01 and 91M006 near the Northeast Mains and Well 93M001 near the
southwestern corner of the EMD show significant declines since the early- to mid-1990s, presumably in
response to mine dewatering. The water -level in Well 91M006 declined about 600 feet between 1992 and 2005,
and an additional 125 feet between 2005 and 2010, but between 2010 and 2013, the water level recovered about
40 feet. The water level in Well 93M00l declined about 440 feet between 1995 and 2002, but only an
additional 28 feet between 2002 and 2013.
The extent of potentiometric lowering was investigated using the finite -difference simulation model described in
Exhibit 13, Ground Water Model Documentation. The model did not account for mine inflow derived from
dewatering of the overburden directly above active mining areas. This does not, however, invalidate the
prediction of drawdown effects as this is based on the estimates of lateral movement toward mined areas, which
was correctly assessed. The extent of potentiometric lowering is illustrated by predicted drawdown after 5 years
of mining (starting in 1983) as shown on Figure 13, Predictive Analysis After 5 Years of Mining. This figure
indicates that drawdown effects may extend to the outcrop areas of the overburden units at the margin of the
Twentymile Park Basin. The permeability of the Wadge/Wolf Creek Interburden and Wolf Creek Seam, as
measured in recently -installed monitoring wells WC008 and WC013, is 0.0016 ft/d, or about 25 times lower
than that of the Wadge Overburden. Given the extremely low permeability of the Wadge/Wolf Creek
Interburden and Wolf Creek Seam, mining of the Wolf Creek Seam is not anticipated to result in any significant
incremental impacts on ground water levels or occurrence beyond those that have already occurred in
conjunction with the Wadge Seam mining activities.
Recovery of potentiometric levels within the overburden units will occur following mining, through recharge of
the units, primarily at the basin margins. Subsidence effects will cause fracturing and rubblization of the
overburden units, so that postmining permeability will initially be much higher than typical premining values.
Consequently, the rate of potentiometric recovery will primarily be governed by the rate of recharge.
Recharge to the mine workings will primarily be from the up -dip spoils area of the adjacent Eckman Park
surface mine. During mining, and for most of the recovery period following mining, the workings and overlying
overburden adjacent to these spoils areas will not be saturated, i.e. the effective potentiometric head will be at
the elevation of the base of the mined zone. The spoil at the old highwalls is expected to be fully saturated
under reclaimed conditions, as is the case near the Foidel Creek Mine Portal Area. The effective potentiometric
head in the spoils in these areas is therefore near the land surface elevation. The head differential across the
unmined interval during and following mining is considerably higher than under premining conditions due to the
dewatering of the mined zone and overlying overburden unit. This situation induces recharge at a
proportionately higher rate than under baseline conditions. The rate of recharge to the workings from the spoils
in any given area is governed by the distance between the two areas, the transmissivity of the unmined material
in this interval, the head differential across the interval, and the length over which these conditions prevail. The
total recharge rate is given by the standard steady-state flow equation.
D
where: Q = recharge rate (ft3/day)
T = Transmissivity of un -mined interval (W/day)
h, = potentiometric head in spoils (ft)
h2= potentiometric head in workings (ft)
D = distance between spoil and workings (ft)
L = length perpendicular to flow over which above conditions prevail (ft)
The head differential between the spoils and the Wadge Seam underground workings is approximately 300 ft (hl
— h2). The distance between these two areas in the southeastern part of the permit area is about 1,000 feet (D),
and the length over which these conditions prevail is about 5,000 feet (L). Further to the west, the distance
between existing or proposed spoils and the proposed underground workings increases rapidly due to the
PR14-10 2.05-140 12/18/14