2015-08-18_PERMIT FILE - C1982056A (4)

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Wadge Overburden, Wadge Seam, Wadge/Wolf Creek Interburden, and Wolf Creek Seam The Wadge Overburden consists of a sequence of siltstones, shales, coal, and fine- grained sandstones. The sequence varies in thickness from 50 to 100 feet, averaging approximately 75 feet. The Wadge Coal Seam varies in thickness from 8.5 to 11.5 feet, and forms a gradational contact with the underlying carbonaceous mudstone. The Wadge Seam is relatively consistent and uniform, and is laterally continuous throughout the Twentymile Park Basin. The Wadge/Wolf Creek Interburden is composed of a series of thick shales, claystones, siltstones, and intermittent lenticular sandstones, and is similar to the Wadge Overburden, although typically finer - grained and reflecting greater consolidation. The Wolf Creek Seam is limited in lateral continuity and continuous only within discrete mining areas. Within these areas, the Wolf Creek Seam splits into up to four distinct benches separated by rock partings. The combined total seam thickness ranges from 7.5 to 14 feet. As documented by previous studies (Robson and Stewart 1990), this geologic sequence, which forms the lower portion of the Williams Fork Formation, generally functions as a single hydrologic unit. Both the Wadge Overburden and Wadge /Wolf Creek Interburden have been characterized relative to ground water conditions, and have similar characteristics, although the lower portions of the unit (Wadge /Wolf Creek Interburden and Wolf Creek Seam) are characterized by finer -grain structure and greater consolidation, so ground water occurrence and movement within the lower strata may be more limited. Both the Wadge Overburden and Wadge/Wolf Creek Interburden are characterized by low permeability, limited continuity, low yield and relatively poor water quality. These factors preclude utilization of the ground water contained in this sequence for all practical purposes, except small stock watering installations. The Wadge Overburden and Wadge/Wolf Creek Interburden have been or will be directly affected by ongoing and future mining operations. Field data from ground water monitoring wells shown on the Twentymile Park Hydrology Map (Map 13) were used to construct a potentiometric contour map for the Wadge Overburden sequence in this area for August- September 1983, prior to the start of underground mining. The potentiometric map for the Wadge Overburden was constructed using only water level date which were deemed to be reliable. Previous potentiometric maps had used water level data from wells that were not fully completed in the Wadge Overburden sequence. The following criteria were used to select data for construction of the map. 1. Water level data must be from wells that have reliable completion information to confirm that the well is completed in the Wadge Overburden. 2. Overburden wells in the center of the Twentymile Park Basin, where flowing artesian head conditions exist, must be adequately "shut -in" to obtain a reliable pressure reading. 3. Water level data must be taken with the period of August to September, 1982. Water level elevation data from Wadge Overburden wells which met all the above criteria area shown in parentheses below the well on Map 13, Twentymile Park Hydrology. The Wadge Overburden wells that could not be used for construction of the potentiometric map are listed with the criteria that were not met: Well Criteria Not Met Comments 001-SW-7 3 001 -L -1 3 001 -D -5 006 -W -1 006 -W -17 006 -W -18 006 -80 -2 006-82-38 06 -81 -31 2 06 -82 -62 3 21 -81 -16 2 1 No completion data 1 No completion data 1,2 No completion data 1,3 No completion data 1 Suspect completion data TR13 -83 2.04 -21 11/03/14