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02 South Taylor and Lower Wilson expansion areas is included in Section 2.04.9 of Volume 12, <br />Exhibit 9 of Volume 13, and Maps 5A, 513, and 5C of Volume 14. The most prevalent soils, <br />including Burnette, Work, Lamphier, Rhone, and Northwater Loams, are mollisols of the <br />suborder boroll, which developed from residuum or colluvium on gently sloping to rolling <br />ridgetops, moderately steep sideslopes, and in gently sloping, concave narrow stream valleys. <br />Shallow, rocky soils of the order entisol occur to a limited extent within the area to be disturbed <br />on steep, south - facing slopes. The very thick Silas loam soil developed from alluvium is found <br />within narrow bands along the larger ephemeral drainages. <br />The predominant hill -slope soils have relatively thick, loamy textured mollic epipedons, well <br />suited for reclamation use. Salvageable thickness of these soils averages from 12 inches to 30 <br />inches. Subsoils in these units are somewhat marginal, due to heavier texture or excessive <br />cobbles. The Silas loam soil along the drainage valley bottoms is generally suitable for salvage <br />to depths of five feet or more. <br />4.8 Ground Water Hydrology <br />Ground water information is found in Sections 2.04.5, 2.04.7 (Volume 1 for the East Pit, West <br />Pit, Section 16 Pit, Facilities Area and Gossard Loadout and Volume 12 for South Taylor) and <br />Exhibit 7 of the PAP, and in Colowyo's Annual Hydrologic Reports. Ground water occurs as <br />isolated, perched aquifers in interbedded and lenticular sandstones and coals and within isolated <br />alluvial aquifers. Base flow in the two perennial streams in the general area (Good Spring Creek <br />and Wilson Creek) comes mainly from ground water discharge from alluvial aquifers in the <br />stream valleys. Stratigraphically, the Trout Creek Sandstone is the major regional aquifer in the <br />area. It is approximately 800 feet beneath the lowest coal seam to be mined. The principal <br />recharge area for the aquifer is to the south of the permit area in the headwaters of Taylor and <br />Good Spring Creeks. There is no continuous, regional ground water system on the permit area <br />above the flood plain of Good Spring Creek. No saturation was encountered in any of the beds to <br />be mined in test holes drilled by W.R. Grace and Company and the USGS (information <br />contained in the PAP and the Northwest Colorado Environmental Impact Statement). <br />The Trout Creek Sandstone outcrops north of the permit area, where ground water is discharged <br />at the surface. The Mancos Shale underlies the Iles Formation and forms the base of the regional <br />ground water system in the area. This shale is exposed at the surface north of the permit area, in <br />the southern limb of the Axial Basin Anticline. Due to the impervious nature of the Mancos <br />Shale, ground water flow in either the deep bedrock units of the Williams Fork and Iles <br />Formations or the alluvial aquifers of Good Spring and Wilson Creeks is discharged to the <br />streams where they flow across the Mancos Shale. <br />Proposed Decision and Findings of Compliance January 2012 <br />Permit Renewal 06 Page 115 <br />