2014-05-12_PERMIT FILE - C2010089 ‎(3)‎

• Permit No: C2010089A
• IBM Index Class Name: PERMIT FILE
• Doc Date: 5/12/2014
• Doc Name: Hydrology Description
• Section_Exhibit Name: Section 2.04.7
• Media Type: D
• Archive: Yes

Infiltration and Permeability of the Unsaturated Zone Using the soil hydrologic properties
defined by the Soil Conservation Service of the U.S. Department of Agriculture, it is possible to
estimate the infiltration rates of soils occurring within the vicinity of the New Horizon 1 & 2
mining areas. The New Horizon 1 & 2 soils have been mapped at a scale of 1 inch equals 400
feet. The soils maps are included in Section 2.04.9 of this permit application. At the adjacent
New Horizon 2 Mine the majority of the soils have a moderate (0.6 - 2.0 in/hr) permeability and
infiltration rate. A minor amount of the soils have a moderately rapid (2.0 - 6.0 in/hr)
permeability and infiltration rate. The subsurface strata in these areas consist predominately of
tightly cemented sandstones and shales which act as barriers inhibiting vertical percolation.
However, field observation of exposed outcrops, mine high - walls, and aquifer analysis data
indicate that secondary porosity (weathered and fractured bedrock strata) play a significant role
in allowing vertically infiltrating ground water to infiltrate through the unsaturated to the
saturated zone. The NHN permit area is impacted by irrigation which is a primary source of
infiltrating water. Infiltration as a result of precipitation is only a minor component of recharge in
the NHN area but the majority of infiltration comes from irrigation. The large majority of the
soils in the mining area have a slow to medium runoff potential. The strata at the NHN permit
area and the New Horizon Mine are the same. The lithologic logs indicate that the back fill
material will generally be composed of more than 50 percent fragments of blasted sandstone with
lesser amounts of shale and siltstone and minor amounts of bentonite. Sections 2.05.3 and 2.05.4
describe the details of the mining and reclamation methods. The recharge capacity and
permeability of the back fill material will be increased due to greater porosity and hydrologic
conductivities than the undisturbed strata due to increased void volumes. As an example,
Peabody conducted a constant discharge pumping test in the backfill (spoils) of the old Peabody
Nucla Mine using the formula for the well recovery at GW -N27. The results of the test showed
the backfill material to have a transmissivity of 261 ft2/ day and a hydraulic conductivity of 40
ft/day (about 0.21 gpm /ft2 ) which are many times higher than average values of transmissivity
and hydraulic conductivity from tests of the overburden, coal and underburden zones in the area
(see Tables 7 -5 and 7 -6, pgs. 7 -22 and 7 -24 of the New Horizon 1 Mine Permit copies of which
are contained in the Appendix 2.04.7 -2 to this Section). The resaturation of the back fill material
will be greatly limited by its tendency to drain down dip along the floor of the pit to the existing
outcrop where it will discharge at Spoil Spring # 1 (SS #1) as it currently does (see Map 2.04.7 -1
for the location of SS #1 and SS #2).
Discharge Discharge rates from the coal and the underburden is relatively small compared to
the overburden which is more a function of the thickness of the respective zones than it is the
difference in lateral permeability. Again, seasonal irrigation is the cause of the saturation of the
NHN strata as the monitoring wells show. Without the seasonal irrigation the NHN strata would
be dry. The overburden strata is the primary source of discharge to the drainages of Tuttle Draw
(to the south) and Coal Canyon (to the west) which help maintain the surface water base flow of
the two drainages (see Map 2.04.5 -1 this application showing coal outcrop). The primary factor
of which is the much greater surface area of recharge from the seasonal irrigation for the
overburden than for the other two zones. Fourteen aquifer tests have been conducted on the
overburden, coal and underburden strata in the NHN permit area (see Tables 7 -5 and 7 -6, ppgs.7-
22 and 7 -24 of the New Horizon 1 Mine Permit copies of which are contained in the Appendix
2.04.7 -1 of this Section). These tests show average hydraulic conductivities for: the overburden
of 0.72 ft/day; the coal zone of 0.19 ft /day; and the underburden of 1.61 ft/day. One of these tests
was at GW -N9 which is located within the NHN Permit area (see Map 2.04.7 -1). This was a slug
Section 2.04.7 Page 5 October 2013 (TR -05)
E: \New Horizon \DRMS \NHN Permit \04_Technical Revisions TR \TR -05 \Documents from Jason \2.04.7 Hydrology Description_TR- 05.docx