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2019 Plan of Operations Modification American Gypsum Company, LLC <br /> the Mine, including disturbance areas described herein, ultimately reports to the Eagle River <br /> located south of 1-70. Stormwater management is discussed further in Section 8.0. <br /> The depth to groundwater at the Mine is not known; however, groundwater has not been <br /> encountered in either the Lower Pit or Upper Pit to date. <br /> Drawing 03 shows dry creek beds, streams, springs, and rivers (mostly un-named) in relation to <br /> the proposed Upper Pit and East Pit. <br /> 3.3 Geology and Soils <br /> 3.3.1 Geology <br /> The site is predominantly the Eagle Valley Evaporite (IPee), with unconsolidated deposits (Qg) in <br /> the river valley to the south and basalt (Tbb) in the mountains to the north according to available <br /> geology mapping (Tweto et al., 1978). Definitions for these geologic units are included below and <br /> are shown in relation to the mine site in Figure 3.1: <br /> ➢ IPee: Eagle Valley Evaporite (Pennsylvanian) — Gypsum, anhydrite, and interbedded <br /> siltstone and minor dolomite; contains thick salt at depth in some places, as shown by <br /> wells drilled for oil and gas. Intertongues with Minturn, Belden, and Maroon Formations <br /> and grades into fine-grained clastic rocks of Eagle Valley Formation. Diapiritic in structural <br /> configuration in many places, especially in large area in central part of quadrangle. <br /> Thickness indeterminate; <br /> ➢ Qg: Unconsolidated deposits (Pleistocene): Young gravels (Bull Lake and younger) — <br /> Stream, terrace, and outwash gravels; and <br /> ➢ Tbb: Basalt of Bimodal Suite (Pliocene and Miocene)— Dense black resistant alkali basalt <br /> in lava-flow layers 5 to 200 feet thick, and interbedded tuffs and volcanic conglomerates. <br /> Greatest preserved thicknesses are 900 feet on White River Plateau and 800 feet on <br /> Grand Mesa. Ages determined from several locality range from 8 to 23 million years. <br /> Am Gypsum Poo Mod ISSD 20190909 September 2019 [121 <br />