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miles. The total azea considered for this mine investigation was in excess of 75 squaze miles. <br />Black and white and color aerial photos were used for the study. In addition, areas were field <br />checked for accuracy. <br />The study identified azeas of unconsolidated streamlaid deposits along the North, Middle, and <br />South Thompson Creeks and their tributaries. Surveys and field checks of these deposits <br />revealed that the alluvium is relatively thin, intermittent, and restricted to the immediate <br />stream channels. No identifiable soils were mapped within alluvial azeas; the alluvium is <br />primarily boulders and cobbles with minor stretches of sand, gravel, silt, and clay. <br />There are two criteria used by the Division to identify alluvial valley floors. They are: <br />1. Sufficient unconsolidated streamlaid deposits holding streams, and <br />2. Sufficient water to support agricultural activities. <br />Hydrologic data available for North Thompson Creek indicates an annual runoff of 16.2 cfs <br />or 0.6 cfs per squaze mile. Eighty percent of this runoff occurs during the snowmelt season of <br />April through June. Low flows during late summer average less than one cubic foot per <br />second. Although water is limited within the Thompson Creek drainage, the Division <br />determined that sufficient water is available to support limited agricultural activity. <br />Therefore, the Thompson Creek drainage satisfies one of the criteria for alluvial valley floors. <br />The second and fmal alluvial valley floor criterion that needs to be considered is that of <br />unconsolidated streamlaid deposits. Using current Federal Office of Surface Mining <br />guidelines, the Division identified three azeas that are sufficient in size to support agricultural <br />activities. Because there is sufficient water available to support at least a portion of these <br />azeas, they all qualify as alluvial valley floors. <br />The first azea identified as an alluvial valley floor is the alluvial fan, 14 acres in size, at the <br />confluence of Yank, Sand, and North Thompson Creeks (see Map D-3-7 of the permit <br />application). Its size bazely qualifies it as an alluvial valley floor. In addition, subirrigation is <br />restricted to the immediate streambanks and water may not' be available to flood irrigate this <br />azea, as it is in the upper reach of the North Thompson Creek drainage. However, without <br />more information on water availability, the Division must assume this area is capable of <br />supporting agriculture. The essentialltydrologic function of this area is flood irrigation <br />potential. The North Thompson Creek Mines did not impact this azea. The site is 2.3 miles <br />upstream from any mine facility and one mile west of the maximum anticipated life-of--mine <br />for the operation. The operator had not identified any actual or potential impact that might <br />have extend to this azea. The mines aze now in permanent cessation and final stages of <br />reclamation. <br />The second alluvial valley floor body identified by the Division is a 15-acre tract located in <br />Willow Park along Middle Thompson Creek. This azea has the potential to be flood irrigated <br />and is of sufficient size to support agricultural activities. With the exception of apre-permit <br />34 <br />