2022-09-06_REPORT - C1982056 (3)

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Foidel Creek Mine C-82-056 2021 Annual Hydrology Report Above the Wadge Overburden is the first major regional aquifer, known as the Twentymile Sandstone. The Twentymile Sandstone aquifer is confined above and below by low permeability shale and interbedded siltstone/shale units. The unit varies in thickness from 100 to 200 feet and is hydrologically isolated from the underlying Wadge Overburden sequence by a low permeability marine shale, which has a thickness of up to 700 feet. Approximately 125 feet above the Twentymile Sandstone is the 35-foot-thick Fish Creek Sandstone. The Fish Creek Sandstone is a discontinuous minor unit in the area that was the contact for a small coal seam that had been surface mined. Beneath the Wadge Overburden is a sequence of low permeability siltstones, shales, and coals, approximately 200 feet thick. This is followed by a fine-grained massive sandstone, approximately 250 feet thick, known as the Trout Creek Sandstone. The Trout Creek sandstone is the second major regional aquifer, which exists in the Twentymile Park Basin. There is very little hydrologic connection between the Trout Creek sandstone and the overlying Wadge Overburden. The Wolf Creek Reserve (WCR) underlies the Wadge Seam. The WCR underlies portions of the EMD and NMD and is part of the same water-table groundwater system, so the associated effects of mining on groundwater in this area will be similar to those previously considered and evaluated for the EMD and NMD. In the proposed mine area, the Wolf Creek Seam is present at depths ranging from approximately 1,000 to 1,700 feet below the land surface. Approximately 150 feet of shale, claystone, siltstone and lenticular sandstone known as the Interburden unit separates the Wadge and Wolf Creek seams. Directly below the Wadge Seam in the planned mine area is a persistent and laterally continuous layer of material composed of clay-sized particles called underclay. Beneath this underclay is a zone of alternating thick shales, claystones, siltstones, and intermittent lenticular sandstones. The shales are generally continuous and the sandstones discontinuous. Near the base of this zone of alternating beds is the Wolf Creek Seam. Within the planned mine area, the Wolf Creek Seam splits into four distinct benches separated by rock partings. The combined total seam thickness ranges from 7.5 to 14 feet, and the coal seams are continuous within discrete mining areas. The WC1 Seam is the lowest of the benches, and ranges in thickness from 2 to 4 feet. The interburden between the WC1 and WC2 seams ranges from 0.5 to 1.5 feet. The WC2 Seam ranges from 2 to 5 feet. The WC1 and WC2 benches will be mined over the entire WCR area. The interburden between the WC2 and WC3 ranges from 0.5 to 7