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to the Colorado Permanent Regulatory Program, the alluvial valley floor regulations <br />did not apply to underground coal mines or associated loadouts. For those mining <br />facilities already constructed on alluvial valley floors, the Division is ensuring that <br />those areas will be restored after mining in accordance with Rule 4.24. However, all <br />new mining operations proposed by the operator were reviewed under the full <br />context of alluvial valley floor regulations. For the purposes of this section, the mine <br />and loadout will be discussed separately. <br /> <br />A. Mine Site <br /> <br />The operator conducted a reconnaissance-level study of the mine area to determine <br />those areas that might qualify as alluvial valley floors. The study area is indicated on <br />Map D-5-1 and discussed in Volume I, Section 5.2, of the application. The study <br />area included the potential 20+ year life-of-mine area, in addition to the first <br />permitted five-year mine plan area. Also, areas adjacent to the life-of-mine were <br />considered for distances in excess of three miles. The total area considered for this mine <br />investigation was in excess of 75 square miles. Black and white and color aerial photos <br />were used for the study. In addition, areas were field checked for accuracy. <br /> <br />The study identified areas of unconsolidated streamlaid deposits along the North, <br />Middle, and South Thompson Creeks and their tributaries. Surveys and field checks of <br />these deposits revealed that the alluvium is relatively thin, intermittent, and <br />restricted to the immediate stream channels. No identifiable soils were mapped <br />within alluvial areas; the alluvium is primarily boulders and cobbles with minor <br />stretches of sand, gravel, silt, and clay. <br /> <br />There are two criteria used by the Division to identify alluvial valley floors. They are: <br /> <br />1. Sufficient unconsolidated streamlaid deposits holding streams, and <br /> <br />2. Sufficient water to support agricultural activities. <br /> <br />Hydrologic data available for North Thompson Creek indicates an annual runoff of <br />16.2 cfs or 0.6 cfs per square mile. Eighty percent of this runoff occurs during the <br />snowmelt season of April through June. Low flows during late summer average less <br />than one cubic foot per second. Although water is limited within the Thompson <br />Creek drainage, the Division determined that sufficient water is available to support <br />limited agricultural activity. Therefore, the Thompson Creek drainage satisfies one <br />of the criteria for alluvial valley floors. <br /> <br />The second and final alluvial valley floor criterion that needs to be considered is <br />that of unconsolidated streamlaid deposits. Using current Federal Office of Surface <br />Mining guidelines, the Division identified three areas that are sufficient in size to <br />support agricultural activities. Because there is sufficient water available to support at <br />least a portion of these areas, they all qualify as alluvial valley floors. <br /> <br />The first area identified as an alluvial valley floor is the alluvial fan, 14 acres in size, <br />at the confluence of Yank, Sand, and North Thompson Creeks (see Map D-3-7 of the <br />permit application). Its size barely qualifies it as an alluvial valley floor. In addition, <br /> <br /> <br />23 <br /> <br />