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The Mesaverde Formation is unconformably overlain by the Tertiary Age Rudy or Wasatch <br />Formation. This formation consists of red to buff-colored shales, red sandstones, and red to gray <br />conglomerates. The sediments of this formation are weathered volcanic rocks. The Ohio Creek <br />conglomerate is the basal unit within the formation and is 100 to 200 feet thick. <br />Tertiary igneous intrusive rocks exist within the North Fork drainage basin. A diorite plug about <br />1,000 feet in diameter outcrops along Hubbard Creek in the SE 1/4 of Section 7, Township 13 <br />South, Range 91 West of the 6th P.M. This may represent the erosional remnants of a volcanic <br />flow feeder. Sills have injected the Lower Coal Bearing member, particulazly the B and C seams. <br />These sills consist of diorite and appear to have their source to the northwest of Terror Creek. <br />Hydrologic Balance -Rules 2.04.5, 2.04.7, 2.05.3, 2.05.6(31, 4.05 <br />Ground Water - <br />Ground water information can be found on pages 27 to 4I of Section 2.04 and on pages 114 to <br />138 of Section 2.05.6 of Volume 1. Water quality documentation may be found in Volume 4 and <br />is supplemented by annual hydrologic reports prepared since 1982. For a description of the <br />ground water hydrology of the mine azea and permit revision area and a discussion of the impacts <br />of mining on ground water, please refer to the Hydrologic Balance portion and the Probable <br />Hydrologic Consequences portion of Section B of this Document. <br />Three categories of potential aquifers occur in the general area. These are alluvial and terrace <br />deposits associated with the North Fork of the Gunnison River, the localized shallow <br />alluvial/colluvial azeas in the stream drainages, and ground water in the lenticular sandstones and <br />the Rollins Sandstone of the Mesaverde Formation. <br />The most significant occurrence of ground water in the general area is associated with the <br />alluvium of the North Fork of the Gunnison River, located approximately two (2) miles southeast <br />of the mine portals and 1,500 feet lower in elevation. Significant alluvial sand and gravel <br />deposits averaging 34 feet thick exist along the North Fork from the mouth of Terror Creek to the <br />confluence of the Gunnison River. There aze numerous wells in the area which draw water from <br />this alluvium; well yields range from 5 gpm to 120 gpm, with average yields of approximately 17 <br />gpm (page 31 of Section 2.04.7, Volume 1). <br />Steven's Gulch, an ephemeral stream located in the center of the permit area, drains an area of 6.0 <br />square miles and contains several reaches of shallow alluvium/colluvium. Most of these reaches <br />have little ground water except during periods of stream flow. The most significant area of <br />alluvium/ colluvium occurs in the NW 1/4 of Section 13, Township 13 South, Range 92 West <br />(Steven's Gulch wellfield), where a 25-foot-thick sandstone outcrop has created a topographic <br />restriction such that a considerable thickness of alluvial sands and colluvial material have been <br />deposited. Test wells drilled by the applicant indicate that the alluvium in this area can support a <br />pumping rate of approximately 28 gpm (Ground Water Hydrology Appendix, Volume 4). The <br />applicant has installed a production well and currently uses this water for domestic use, dust <br />control, and fire control. <br />14 <br />