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The two alluvial aquifer systems present within the Edna permit area aze the Oak Creek and Trout Creek alluvial aquifers. Both of the alluvial aquifers are in direct hydraulic communication with each associated stream. Baseline water quality data from the Trout Creek alluvial aquifer indicates that the quality of this water is suitable for agricultural purposes. The water is moderately low in TDS levels (less than 350 mg/1) and exhibits a low SAR. The water quality of the Oak Creek alluvial aquifer is generally lower than that found in the Trout Creek alluvium (TDS levels ranging from 400 to 1700 mg/1). This may be attributable to the levels of disturbance and activities already present along the Oak Creek valley. These activities include the presence of roads and railroads situated atop the alluvium and disturbance from past mining activities. The Trout Creek alluvial aquifer roughly parallels the western boundary of the permit area. Currently, the Trout Creek alluvial aquifer is monitored by 5 wells which aze used to observe depth-to-water and water quality trends above, adjacent to and below the mine site. A slight degradation of the alluvial water quality has, and will continue to occur in the alluvium adjacent to portions of the Edna site which have been mined. The resaturation of backfilled pits has been expressed as spoil aquifers. When the elevation head of the aquifer which has developed exceeds the topographic low point along the buried highwall, water is discharged at the surface in the form of springs. Numerous springs and seeps have been identified along the areas mined adjacent to Trout Creek. These springs and seeps discharge water which is high in TDS and sulfates to the alluvial aquifers, as well as directly to Trout Creek. Surface Water The permit azea lies in the upper Yampa River basin and is drained by several ephemeral streams which flow into Trout Creek and Oak Creek. These are both perennial streams which flow in a northeasterly direction toward the Yampa River. The ephemeral streams draining the permit area flow predominantly west-northwest into Trout Creek, which follows the western permit boundary. Oak Creek Ylows along the eastern limit of the permit area. The eastern permit boundary is partially defined by the Trout Creek -Oak Creek drainage divide, therefore, Oak Creek receives only a small portion of the runoff from the permit area. Both perennial streams are incised into bedrock, with Trout Creek draining approximately 54 square miles above the northern limit of the mine, while Oak Creek drains approximately 32 square miles. Runoff events in both these streams are dominated by snowmelt. Peak spring runoff occurs slightly later in Trout Creek than in Oak Creek because the headwaters of the former are located at a much higher elevation. Mining operations facilities should not be significantly impacted by lazge flood events from these streams. The Trout Creek floodplain is well below proposed and existing Edna Mine 6 Permit Renewal No. 4