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activities. Reclaimed loading facilities and office areas, and office areas to be retained, <br />that are adjacent to Oak Creek, are above the 100 -year, 24 -hour floodplain. <br />Trout Creek forms a portion of, or is close proximity to, the western boundary of the <br />permit area. West or northwest ephemeral streams drain runoff from 3;117 acres of the <br />permit area into Trout Creek. This includes runoff from 1193.4 acres of permitted <br />disturbed areas (that flows through sedimentation ponds) and 49 acres of pre -law <br />disturbed areas. The total (permitted and pre -law) disturbed areas of:1242.4 acres are <br />approximately 3.6 percent' of the 54 square mile Trout Creek drainage basin, The average <br />annual runoff in Trout Creek is 37,500 acre- feet.,The mine area is estimated to yield <br />approximately 730 acre -feet of runoff annually or about 2 percent of the total annual <br />stream flow of Trout Creek above the mine. Annual mean minimum discharge is <br />estimated at 10 cubic feet per second (cfs). <br />An ephemeral stream parallel to the east boundary collects runoff from the permit area <br />east of the divide, and flows to Oak Creek. Only a small area of mine - related disturbance <br />drains into Oak Creek. Although no mining occurred within this watershed, the former <br />loadout.and conveyor, access road, and office were situated within the Oak Creek Basin. <br />Of the total 140 acres of Oak Creek basin area within the permit boundary, only about•24 <br />acres are disturbed by - the mine. This area is a. small fraction of the total drainage area of <br />27.4 square, miles upstream of the mine on Oak Creek. Average annual yield is. estimated • <br />at 7,900 acre -feet. Runoff from the permit area is estimated at 25 acre -feet, or 0.3 percent, <br />of the total annual stream flow of Oak Creek above the mine. The estimated mean <br />minimum flow,is 5 cfs. The Loadout, conveyor, access road, and conveyor area were <br />approved for final bond release with approval of SL -10 on December 14, 2009. <br />Seasonal runoff hydrographs for both streams show peak discharge occurring in April, <br />May, and June as a result of snowmelt runoff. Low flows in both streams begin in the late <br />summer and extend through the winter months until the onset of spring runoff. <br />Spoil materials replaced consolidated overburden in those portions of the permit area that <br />were mined. Deep percolation of precipitation through the spoils has created a water table <br />aquifer which abuts against the now buried highwall or box cut near the foot of the <br />previously mined slope. Numerous springs have formed as a result: These,springs <br />emanate above the relatively steep slope. which exists above the alluvium on the east side <br />of Trout Creek (these steep :slopes are of a block of undisturbed ground left between the <br />alluvium and the mine pit). <br />Water quality conditions upstream of the mine indicate that dissolved iron, manganese <br />and other -trace metals . all have occasionally exceeded receiving stream standards. <br />Baseline data indicate minor changes in . water quality occur between upstream and . <br />downstream stations on both Trout and Oak Creeks. This is probably due to the impacts <br />of past mining- activities. The baseline quality of the water in Oak Creek is generally -, <br />poorer than that in Trout Creek above the permit area due to more extensive mining that_ <br />has occurred in the Oak Creek drainage during the past century. <br />C1980 -001 Edna Mine Permit Renewal No. 6 10 <br />