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<br />-44- <br />The effects of mining upon lower Middle Creek are summarized in Table 1. <br />The modelling indicates that mining will increase discharge, total <br />dissolved solids, and total salt load in the receiving stream. The <br />increase in discharge results from the pump age of ground water from the <br />underyround mine workings. This discharge may be sufficient to sustain <br />perennial flow in Foidel Creek and Middle Creek. (See discussion of <br />probable hydrologic consequences.) The increases in dissolved solids <br />concentrations and total salt load would result from the discharge of <br />water from the underground workings, the discharge of runoff and sediment <br />control systems, and the discharge of affected ground water systems to <br />receiving streams. The projected short-term effects would not be <br />expected to limit the use of this water for flood irrigation. The <br />projected total dissolved solids concentration resulting from the <br />long-term effects of mining would sometimes exceed a total dissolved <br />solids concentration of 1000 mg/l. Water having TDS concentrations <br />greater than 1000 mg/1 may have adverse effects on many crops (EPA, 1975, <br />p. 208). This effect, however, is caused by the other mines in the <br />Foidel Creek and i4iddle Creek drainages. An examination of the long-term <br />scenario used in the model show that most of this increase is the result <br />of the projections used for the Middle Creek underground mine. (The <br />Middle Creek Mine is currently inactive, and its application is under <br />review by the Division. As apart of that review, the long-term <br />hydrologic effects of the Middle Creek Mine can be more closely examined.) <br />Model results for lower Fish Creek are summarized in Table 2. The <br />short-term effects show a slight decrease in stream flow resulting from <br />the Foidel Creek Mine intercepting ground water currently discharging to <br />the stream system. (See discussion of probable hydrologic <br />consequences.) Both total dissolved solids and total salt loading would <br />increase as a result of short-term and long-term effects. Again, the <br />long-term effects of mining have a greater influence on receiving <br />streams. The long-tens effects of mining may limit the use of water <br />during the low flow months of dry years. During these months, total <br />dissolved solids concentrations could limit the use of this water for <br />flood irrigation. During the seventy-two month period projected by the <br />J.S. Geological Survey water quality model, the total dissolved solids <br />concentrations resulting from the long-tens effects of mining fell on or <br />near a total dissolved solids concentration of 1000 mg/1 on six months, <br />and significantly exceed the 1000 mg/1 total dissolved solids <br />concentration on only four months. <br />In the lower Trout Creek drainage (Table 3), mining would again cause <br />increases in flow, total dissolved solids and total monthly loading. <br />However, Trout Creek is a perennial stream whose natural flows greatly <br />dilute the effects of mining. Although long-term effects are more <br />significant than short-term effects, neither the short-term effects, nor <br />the long-term effects would increase total dissolved solids <br />concentrations to the level that would limit water use. Surface waters <br />