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2019 Plan of Operations Modification American Gypsum Company, LLC <br /> ~.f - <br /> , � •_ � � Eagle-Gypsum Mine <br /> r -�.r,..jr 1`! �`,, �s� ,rk�r,�,`^^'�.r'}r����2d 1`'p���.-1 �"�J��1 i+•.n. �. t�+v1"' <br /> YJ <br /> e <br /> FIGURE 3.1: GEOLOGICAL MAP (AREA TAKEN FROM TWETO ET AL., 1978) <br /> 3.3.2 Soils <br /> There is virtually no topsoil at the Mine; vegetation typically grows in areas consisting of <br /> weathered gypsum (gypsite) and residual volcanic ash. Previous permits and investigations <br /> reported depths of volcanic ash ranging in thickness from 3 inches to 2 feet. The NRCS soil <br /> resource report (NRCS, 2016) shows the proposed Upper Pit expansion and East Pit consist of <br /> Soil Group B (Gypsum land—Gypsiorthids complex, 12% to 65% slopes) and Soil Group D <br /> (Torriorthents-Camborthids-Rock outcrop complex, 6% to 65% slopes). Hydrologic soil groups <br /> are classified by the minimum rate of infiltration achieved for bare soil after prolonged wetting. <br /> Group A soils have the lowest runoff potential and highest infiltration rates, while Group D soils <br /> have the highest runoff potential and lowest infiltration rates. Group A soils have the lowest <br /> erosion potential and Group D soils have the highest erosion potential (United States Department <br /> of Agriculture (USDA), 1986). Erosion control for the proposed disturbance and post-reclamation <br /> activities, including surface soil stabilization of fill slopes, will be discussed in Section 6.0. <br /> Local terminology for the land type is "Gypsum Badlands". Existing sparse "topsoil" in the area <br /> consists solely of weathered gypsum (gypsite) and residual volcanic ash. Historically, there has <br /> been virtually no interest in the area for agricultural uses or from the Soil Conservation District. <br /> Ridge topsoils consist primarily of gypsite mixed with weathered residue of other clastic sediments <br /> inter-bedded with the gypsum. Exploration drilling has shown that the clastic sediments do inter- <br /> bed at depth with the gypsum zones. The steep side hill slopes are essentially gypsum rock <br /> Am Gypsum Poo Mod ISSD 20190909 September 2019 [131 <br />