2011-09-26_PERMIT FILE - C1981012 ‎(24)‎

• Permit No: C1981012
• IBM Index Class Name: Permit File
• Doc Date: 9/26/2011
• Section_Exhibit Name: EXHIBIT 08 HYDROLOGY AND GEOLOGY INFORMATION
• Media Type: D
• Archive: No

Probable Hydrologic Consequences New Elk Mine 27
• 7. PROBABLE HYDROLOGIC IMPACTS OF MINING IN THE APACHE AND ALLEN
COAL SEAMS.
Groundwater inflow to underground workings at the Golden Eagle and New Elk mines has been studied
and documented in analyses by prepared by WWL (1980) and Greystone (1994). Mine inflows were
mapped on an annual basis prior to 1994 and compared to the locations of stream channels along the
Purgatoire River, Apache Canyon, Ciruela Canyon, Santistevan Canyon, and Zamora Canyon. No
correlation was apparent between underground inflows and surface water locations (Greystone, 1994).
WWL estimated maximum inflows to the Golden Eagle Mine to be 120 and 73 gpm from the roof and floor
of the Maxwell seam respectively (193 gpm total). The estimate was based on a manual calculation of
inflow to a room and pillar mine with an aerial extent of six square miles and a perimeter of 4.6 x 104 feet.
The actual observed inflow to the mine in 1993 at approximately 20 percent of the calculated area (1.2
square miles) and 76 percent of the perimeter (3.5 x 104 feet) was 208 gpm. Sources of inflow to the mine
included 74 gpm from the roof and floor, 34 gpm from drill holes and shafts, and 100 gpm from a fault.
Greystone updated the inflow analysis for the golden Eagle Mine in 1994 based on new information and
observations of inflow from previous mining. Their analysis assumed that the Maxwell, Blue, and Red coal
seams were the dominant sources of inflow to the mine and that contributions from channel sandstones and
other sources were minor and localized. Greystone recognized that heads in the overburden varied
significantly in different strata at different locations and used a range of water levels above the coal (195.4
to 482.2 feet) to bracket calculations of potential inflow. Based on calibration of calculated inflows to
observed inflows, Greystone concluded that the transmissivity of the Maxwell seam at the Golden Eagle
mine is about 1.98 ft/day. Packer test data indicate that the transmissivity (T) of the Maxwell seam at New
Elk Mine is somewhat lower and is calculated to be 0.03 ft2 /day (T = Kb) using an average hydraulic
conductivity (K) of 0.013 ft/day and a seam thickness (b) of 2.5 ft. Calculated transmissivities of the Allen
• (2.8 ftZ /day, b = 5.5 ft), Apache (2.1 ft2 /day, b =4.5 ft), and Blue (1.72 ftZ /day, b = 4 ft) seams at the New
Elk Mine are similar in magnitude to the value estimated for the Maxwell seam at the Golden Eagle Mine.
Observed inflows to the Golden Eagle Mine ranged from 0.09 gpm/acre to 0.125 gpm/acre during
operation. Given the heterogeneous stratigraphy and relatively simple structural setting of the mine,
Greystone concluded that the observed inflows provided a direct relationship that could be used to predict
future mine inflows. Observed inflows to the New Elk Mine during previous operation are reported to be
between 123 and 177 gpm (Greystone 1994). Approximately 109 gpm of the inflow originated from a
mined -out area of totaling 2,800 acres (0.039 gpm/acre).
Packer test data indicate that the Allan, Apache, and Blue coal seams have similar hydraulic properties in
the area of the New Elk Mine (K = 0.43 to 0.51 ft/day and T = 1.72 to 2.8 ft2 /day). The calculated range of
transmissivities is also similar to the Maxwell seam at the Golden Eagle Mine. Base on the previously
observed groundwater inflows to the two mines, inflow to the New Elk Mine during mining of the Allen
and Apache seems is expected to be between 0.04 and 0.1 gpm/acre. Inflow along faults (to the extent that
they are present) could modify the range upward. The maximum observed inflow along a fault is 100 gpm
at the Golden Eagle Mine. Calculations performed by Greystone suggest that mine dewatering could draw
water levels in the coal seams down by one foot at distances of up to 2.1 miles away from the underground
workings. Given the heterogeneity and limited lateral continuity of coal beds in the Raton Formation, this
estimate is considered to represent a maximal distance.
Monitoring of impacts during mining and previous studies of probable hydrologic consequences (WWL,
1980 and Greystone, 1994) indicate that underground inflows and mine dewatering have little or no
communication with surface water. This conclusion is consistent with the subsidence analysis and
conceptual model for the New Elk Mine. The maximum extent of subsidence fracturing with increased
vertical transmissivity is projected to extend 195 feet above the top of the highest mined coal (Plate 2). The
minimum thickness of overburden between the Apache seam and drainage bottoms is 450 feet. A zone of
continuous deformation will be present from about 195 feet above the coal to 50 feet below ground surface.
•
4164A.110130 Whetstone Associates
PR 02 Exhibit 8(4) Page 148 Revised 1/31/11