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Tertiary igneous intrusive rocks exist within the North fork drainage basin. <br />A diorite plug about 1,000 feet in diameter outcrops along Hubbard Creek in <br />the SE 1/4 of Section 7, Township 13 South, Range 91 West of the 6th P.M. <br />This may represent the erosional remnants of a volcanic flow feeder. Sills <br />have injected the Lower Coal Bearing member, particularly the B and C seams. <br />These sills consist of diorite and appear to have their source to the <br />northwest of Terror Creek. <br />Hydrologic Balance - Rules 2.04.5. 2.04.7 2.05.3 2.05.6(3), 4.05 <br />Ground Water - <br />Ground water information can be found do pages 27 to 41 of Section 2.04 and on <br />pages 114 to 138 of Section 2.05.6 of Volume 1. Water quality documentation <br />may be found in Volume 4 and is supplemented by annual hydrologic reports <br />prepared since 1982. For a description of the ground water hydrology of the <br />mine area and permit revision area and a discussion of the impacts of mining <br />on ground water, please refer to the Hydrologic Balance portion and the <br />Probable Hydrologic Consequences portion of Section B of this Document. <br />Three categories of potential aquifers occur in the general area. These are <br />alluvial and terrace deposits associated with the North fork of the Gunnison <br />River, the localized shallow alluvial/colluvial areas in the stream drainages, <br />and ground water in the lenticular sandstones and the Rollins Sandstone of the <br />Mesaverde Formation. <br />The most significant occurrence of ground water in the general area is <br />associated with the alluvium of the North Fork of the Gunnison River, located <br />approximately two (2) miles southeast of the mine portals and 1,500 feet lower <br />in elevation. Significant alluvial sand and gravel deposits averaging 34 feet <br />thick exist along the North Fork from the mouth of Terror Creek to the <br />confluence of the Gunnison River. There are numerous wells in the area which <br />draw water from this alluvium; well yields range from 5 gpm to 120 gpm, with <br />average yields of approximately 17 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, <br />drains an area of 6.O square miles and contains several reaches of shallow <br />alluvium/colluvium. Most of these reaches have little ground water except <br />during periods of stream flow. The most significant area.of alluvium/ <br />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 <br />created a topographic restriction such that a considerable thickness of <br />alluvial sands and colluvial material have been deposited. Test wells drilled <br />by the applicant indicate that the alluvium in.this area can support a pumping <br />rate of approximately 26 gpm (Ground Water Hydrology Appendix, Volume 4). The <br />applicant has installed a production well and currently uses this water for <br />domestic use, dust control, and fire control. <br />The recharge to the Steven's Gulch well field area is through flow from the <br />adjacent colluvial deposits and from a leaky pipeline aqueduct. The ground <br />water flows through the colluvium downslope to the alluvium, where it becomes <br />trapped or temporarily stored. This situation is somewhat modified by the <br />presence of landslide complexes which occur throughout the general area in the <br />-13- <br />