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<br />. ; <br />mapped within alluvial areas; the alluvium is primarily boulders and cobbles with <br />minor stretches of sand, gravel, silt, and clay. <br />There are two criteria used by the Division to identify alluvial valley floors. They <br />are: <br />Sufficient unconsolidated streamlaid deposits holding <br />streams, and <br />2. Sufficient water to support agricultural activities. <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 <br />the snowmelt season of April through June. Low flows during late summer <br />average less than one cubic foot per second. <br />Although water is limited within the Thompson Creek drainage, the Division feels <br />that sufficient water is available to support limited agricultural activity. Therefore, <br />the Thompson Creek drainage satisfies one of the criteria for alluvial valley floors. <br />The second and final alluvial valley floor criterion that needs to be considered is <br />that of unconsolidated streamlaid deposits. <br />Using current Federal Office of Surface Mining guidelines, the Division identified <br />three areas that are sufficient in size to support agricultural activities. Because <br />there is sufficient water available to support at least a portion of these areas, they <br />all qualify as alluvial valley floors. <br />The first area identified as an alluvia] valley floor is the alluvial fan, 14 acres in <br />size at the confluence of Yank, Sand, and North Thompson Creeks (see Map <br />D-3-7 of the permit application). Its size barely qualifies it as an alluvial valley <br />floor. In addition, subirrigation is restricted to the immediate streambanks and <br />water may not be available to flood irrigate this area, as it is in the upper reach of <br />the North Thompson Creek drainage. However, without more information on <br />water availability, the Division must assume this area is capable of supporting <br />agriculture. <br />The essential hydrologic function of this area is flood irrigation potential. This <br />will not be impacted by the Snowmass Coal Company operation. The site is 2.3 <br />miles upstream from any mine facility and one mile west of the maximum <br />anticipated life-of-mine for the operation. The operator has not identified any <br />actual or potential impact that might extend to this area. <br />The second alluvial valley floor body identified by the Division is a 15-acre tract <br />located in Willow Park along Middle Thompson Creek. This area has the <br />25 <br />