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2023-08-07_REVISION - C1982056
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2023-08-07_REVISION - C1982056
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Last modified
8/9/2023 7:50:36 AM
Creation date
8/7/2023 3:15:01 PM
Metadata
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Template:
DRMS Permit Index
Permit No
C1982056
IBM Index Class Name
Revision
Doc Date
8/7/2023
Doc Name
Proposed Decision and Findings of Compliance
From
DRMS
To
Twentymile Coal, LLC
Type & Sequence
RN8
Email Name
HR1
MAC
Media Type
D
Archive
No
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classified as AVF's. Detailed discussion concerning alluvial valley floors can be found in <br /> Section B, part XVIII of this document as well as Exhibit 7j of the permit. <br /> Ground Water Hydrology <br /> The stratigraphy and geologic structure within the Twentymile Park Synclinal Basin control the <br /> groundwater flow within the permit and adjacent areas. There are three regional bedrock <br /> aquifers within the permit and adjacent areas of the Foidel Creek underground mine. These <br /> aquifers are the Trout Creek sandstone, the Twentymile sandstone, and the Wadge <br /> coal-overburden zone. All three aquifers exhibit artesian conditions in central portions of <br /> Twentymile Park Basin. Ground water in the Twentymile Park Basin is not suitable for most <br /> domestic uses. Use of groundwater in the general area is restricted to livestock watering, <br /> irrigation and limited domestic use (PAP, page 2.04-24). <br /> The geologic structure created by folding and faulting within the Twentymile Park Synclinal <br /> Basin affects the direction of flow within the rock aquifers. In the permit and adjacent areas, the <br /> direction of ground water flow in the bedrock aquifers is down dip toward the center of the <br /> Twentymile Park Basin. Faults in the area produce localized fracture zones within the rock <br /> strata. These zones of increased permeability increase the potential for vertical and horizontal <br /> movement of ground water within the rock strata. However, experience to date in the Foidel <br /> Creek Mine shows little to no inflow along the fault zones at the level of the Wadge coal seam. <br /> Some inflows were encountered in 9 Right and 6 Right gateroads as they were developed into the <br /> Eastern Mining District. These inflows appeared to be localized, and tapered off over time. <br /> The Twentymile sandstone is separated from the underlying Wadge coal-overburden aquifer by <br /> up to 700 feet of impermeable shale within the permit and adjacent areas. The underlying <br /> 700-foot shale and the overlying shales and siltstones of the upper Williams Fork Formation and <br /> the Lewis Shale Formations produce the confined artesian conditions within the Twentymile <br /> sandstone aquifer. To the northeast, the Twentymile sandstone recharges the alluvial aquifer and <br /> provides base flow to the tributaries of Trout Creek down gradient of the mine. Salts in the <br /> Twentymile sandstone waters are predominantly sodium bicarbonate and result in TDS levels of <br /> 150 mg/l. This aquifer is occasionally used for domestic needs. <br /> The alluvium of Trout Creek and its tributaries is an important source of ground water. The <br /> alluvial bodies are used as water supplies, provide sub-irrigation to vegetation, and supply base <br /> flow to the streams. The alluvial bodies are recharged by both the streams and the bedrock <br /> aquifers. <br /> Local Climate <br /> The local climate is semi-arid with a mean annual precipitation of 14.6 inches. Approximately <br /> 45 percent of this precipitation occurs during the growing season of April through September. <br /> High temperatures generally range from 70-80°F in the summer months to below freezing in the <br /> winter months. Normally, a significant snowpack resides on the ground for 4-5 months during <br /> the winter. <br /> Foidel Creek Mine 10 August 4,2023 <br />
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