2022-09-06_REPORT - C1982056 (3)

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Foidel Creek Mine C-82-056 2021 Annual Hydrology Report Hydrogeology: TC's underground Wadge mining operation is located roughly 1600 feet beneath the surface of Twentymile Park Basin. This is an enclosed synclinal groundwater basin, rimmed by outcrops of major lithologic units. Groundwater in the Twentymile Park Basin exists primarily under confined conditions within the bedrock units. Bedrock aquifers in the general area are recharged by infiltration in outcrop areas, located primarily in the southern and western margins of the Twentymile Park Basin. Recharge is limited, due to the low annual precipitation and high moisture losses from evapotranspiration and sublimation in this semi-arid climatic zone. Groundwater occurrence and movement within the bedrock aquifer system is controlled by geologic structure and lithology. Groundwater movement tends to follow the structural dip of the lithologic units toward the basin axis. Within the permit area, bedrock groundwater generally flows to the north and northwest. This results in confined aquifer conditions down gradient from the outcrop area. A detailed discussion of the geology/hydrology for the site is available in the Twentymile Coal Company, Foidel Creek Mine Permit C-82-056, Volume 1, Rules 2.04.6 and 2.04.7. The Twentymile Park Basin is underlain by multiple large, high quality coal reserves. The reserves, mined by underground operations, are known as the Wadge Seam (Pre-2015) and the lower Wolf Creek Seam (Post 2015). The Wadge Seam lies within a sequence of sedimentary rocks characterized by shales, claystones, mudstones, siltstones, sandstones, and minor coal stringers referred to as the Wadge Overburden. The Wadge Overburden is hydrologically isolated from the two major bedrock aquifer units in the Twentymile Park Basin, the Twentymile Sandstone aquifer and the Trout Creek Sandstone aquifer, which lie above and below the Wadge Overburden, respectively. Lying above the Twentymile Sandstone is a minor aquifer unit, known as the Fish Creek Sandstone. All these geologic units are monitored within the Foidel Creek Mine permit area. The Wadge Overburden is directly affected by the mining operation. Dewatering of this zone in the area of mine operations is currently being conducted. The Wadge Overburden sequence varies in thickness from 50 to 100 feet, averaging approximately 75 feet, and is characterized by low permeability (0.01 to 0.1 ft/day), limited continuity, low yield and relatively poor water quality. 6