Laserfiche WebLink
action during the recent geologic past. Geologic units <br />underlying the permit area include (in ascending order): <br />Cretaceous Age Mancos shale; the Rollins Sandstone member of <br />the Iles Formation of the Mesaverde Group; the Bowie shale <br />(coal bearing unit) of the Williams Fork formation, Mesaverde <br />Group; and Quarternary Age glacial outwash and alluvial <br />deposits. <br />The D and E coal seams occur within the 300 to 350 feet of <br />strata above the Rollins Sandstone. The strata above the <br />Rollins Sandstone are characterized as predominantly non- <br />marine siltstone, claystone, and alluvial channel sandstone <br />deposits. The E seam averages 6 feet thick and the D seam <br />averages 8 feet thick in the permit area. The beds dip 3 to <br />5 degrees to the northeast. Overburden thickness ranges from <br />less than 100 feet near the portals, to approximately 1000 <br />feet at the northern permit boundary. <br />The outcrop of the contact between the Mesaverde Group and <br />the Mancos Shale generally defines the southern flank of the <br />Piceance Creek Basin. This very large northwest-southeast <br />trending structural depression represents the largest <br />structural basin in northwestern Colorado and contains <br />28,000 feet of accumulated sediments within its boundaries. <br />Stratigraphic units within the basin dip towards a center <br />axis, and at this location the dip is approximately 3 to 5 <br />degrees north, slightly northeast. Near the surface, the <br />beds tend to dip more steeply in the same direction due to <br />the erosion and unloading of several thousand feet of <br />sediments. This action tends to allow the sediments near the <br />surface to expand and exaggerate their true dip. Dip <br />measurements on the Rollins Sandstone indicate a dip of 7 to <br />10 degrees. However, calculated dip from drill hole logs in <br />the permit area indicate a dip of 3 to 4 degrees. <br />A prominent surface geological feature in the area is a <br />gravel deposit which covers a urge portion of the permit <br />area. The deposit is topographically above and primarily to <br />the west of the mine entries. The gravels were apparently <br />deposited by mud flow or glaciation, and reach a depth of <br />over 200 feet in the central and northern portions of the <br />permit area. The deposit is a significant aquifer, fully <br />saturated in most areas and recharged by perennial and <br />intermittent streams, including Williams Creek, Cottonwood <br />Creek and Ward Creek. Alluvial deposits are present in the <br />stream valleys. <br />Analyses of roof and floor material associated with the E <br />seam and analyses of underground development waste which has <br />been exposed to the atmosphere indicate suspect SAR values. <br />SAR values above 20 were reported in both cases (see pages <br />67a-69 of Volume 10, and Table 2.04.9(1)(b)-4. The applicant <br />covered all underground development waste material with 9 <br />18 <br />