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<br />Proposed Decision and Findings of Compliance July 2018 <br />Permit Renewal No. 7 P a g e | 15 <br />to be mined lies within a 392-foot interval in the Fairfield Member of the Williams Fork Formation. <br />The quality of the coal seams is midway between bituminous and sub-bituminous. Underlying <br />these coal beds are 9,000 feet of Mesozoic and 4,500 feet of Paleozoic sediments. The Williams <br />Fork Formation is estimated to be 1,600 feet thick in the permit area and is underlain by the <br />ridge-forming Trout Creek Sandstone member of the Iles Formation. <br /> <br />Overburden material consists of a sequence of sedimentary claystones, siltstones, shales and <br />carbonaceous silty shales. These sediments are typical of the cyclothems deposited along the <br />western interior of North America during the Late Cretaceous time. The site-specific stratigraphy <br />is described in Exhibit 6 and on Map 8 of the PAP. There are four coal seams below the "F" seam <br />which cannot be economically mined by surface mining methods. <br /> <br />Results of test borings are included in Section 2.04.6 of Volume 1 (East and West Pit), Volume 12 <br />(South Taylor Pit and Lower Wilson Area), and Volume15 (Collom Pit) of the PAP. Test borings <br />resulted in information on the presence of subsurface water, characterization of the physical <br />properties of the overburden, and testing and evaluation of the geochemical properties of the <br />overburden. Additional discussion of the results of this testing can be found in Section III E of the <br />Findings section of this document. <br />4.6 Climate <br /> <br />Climatic information is found in Section 2.04.8 of Volume 1 of the PAP. The region is <br />characterized by a semi-arid steppe climate regime. Precipitation averages 18 inches per year with <br />a significant portion of this yearly precipitation occurring as snowfall. Prevailing winds over the <br />permit area are from the southwest and average eight to nine miles per hour. High winds are not <br />common due to the protection afforded by local terrain. <br />4.7 Soils <br /> <br />Soils information is found in Section B, Item IV of this document, as well as i n Section 2.04.9 of <br />Volume 1, Volume 12 and Volume 15 as well as Exhibit 9 of the PAP. The most prevalent soils, <br />including Burnette, Work, Lamphier, Rhone, and Northwater Loams, are mollisols of the suborder <br />boroll, which developed from residuum or colluvium on gently sloping to rolling ridgetops, <br />moderately steep sideslopes, and in gently sloping, concave narrow stream valleys. Shallow, rocky <br />soils of the order entisol occur to a limited extent within the area to be disturbed on steep, <br />south-facing slopes. The very thick Silas loam soil, developed from alluvium, is found within <br />narrow bands along the larger ephemeral drainages. <br /> <br />The predominant hill-slope soils have relatively thick, loamy textured mollic epipedons, well <br />suited for reclamation use. Salvageable thickness of these soils average from 12 inches to 30 <br />inches. Subsoils in these units are somewhat marginal due to heavier texture or excessive cobbles. <br />The Silas loam soil along the drainage valley bottoms is generally suitable for salvage to d epths <br />of five feet or more.