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Streamflow - Ground Water Relationships <br />Underground mining operations may also affect streamflow conditions by affecting ground water discharge or <br />by induced recharge. The two streams that could be affected are Foidel Creek and Fish Creek. Although <br />underground mining activities are below or downgradient from Foidel Creek, it is conceivable that underground <br />mining and reclamation activities could influence ground water discharge from surface mine spoils upgradient <br />(south) of Foidel Creek. Underground mining, by increasing the effective permeability and storativity of the <br />Wadge and Wolf Creek overburden units, could increase the rate of recharge and thereby reduce ground water <br />discharge to Foidel Creek from upgradient mine spoils. This does not appear to have occurred to date. Springs <br />from backfilled spoils have appeared since the onset of underground mining. The clay barrier constructed to cut <br />off spoil water inflows in the vicinity of the portal may have reduced the effective permeability of the Wadge <br />overburden unit to levels comparable or lower than premining. Still, some spoil water has by- passed the barrier <br />as indicated in the discussion on this issue in the ground water baseline section. <br />Drawdown in the Wadge and Wolf Creek overburdenfinterburden units during mining could also result in <br />induced recharge directly from Foidel Creek. Induced recharge would be expected to show up with the onset of <br />mining beneath the Foidel Creek Valley. Stream depletions would be more than offset by mine discharge. After <br />completion of mining, induced recharge would decline back to premining conditions as potentiometric <br />conditions equilibrate. If induced recharge from Foidel Creek or its alluvium were to occur, a response should <br />have been observed with the onset of mining under the Foidel Creek Valley in 1984. Alluvial Wells S -5 and S- <br />f, completed near the mining operations beneath the Foidel Creek Valley, have shown no response because of <br />initiation of mining beneath the valley. Average inflow during the first year of mining beneath Foidel Creek <br />was 83.2 gpm. Induced recharge from Foidel Creek is a relatively small fraction of this total. <br />Underground mining could also affect streamflow conditions in Fish Creek by changing ground water discharge <br />to the stream or by .induced recharge directly from the stream. The baseline hydrologic analysis indicates that <br />very little groundwater discharges to Fish Creek from the deeper unit units along the reach where the Wadge and <br />Wolf Creek overburden/interburden units would be affected by underground mining. Thus, it does not appear <br />that groundwater discharge from these units to Fish Creek will be affected. Mining- related subsidence may <br />result in minor shifts in recharge /storage /discharge relationships between Fish Creek and the associated <br />alluvium. Relative elevations between alluvial deposits and base or high flow levels may change, and location <br />and extent of streamside alluvial deposits may be altered as minor changes in stream alignment along with <br />accompanying erosion and deposition occur. These changes will occur along a very short segment of Fish <br />Creek. This is located in the area above and immediately downstream of the I-Left pond. Both magnitude and <br />significance of change will be limited by the small area extent of alluvial deposits and the natural response of <br />the dynamic stream system over time. Induced recharge is not likely to occur because of the aquitards located <br />between the Wadge and Wolf Creek seams and Fish Creek. <br />The placement of underground mine waste in the adjacent surface mine pit is an activity that has the potential to <br />affect surface water flows or water quality characteristics. The placement of wastes in the pit decreases the <br />storage capacity. While this may result in less attenuation of pit overflows, the overall water yield due to <br />displacement of fluids by solids is a temporary phenomenon and relatively small when compared to surface <br />runoff contributions to the pit. About 5 of of water will be produced for every yard of waste placed in the pit, <br />provided the pit is at the overflow level. The estimated volume of waste rock disposed in the pit for the 32 -year <br />mine life is 231,000 CY. This would equate to a displacement of discharge of about 0.001 efs. It is possible <br />that, as the pit is partially filled, pit water evaporation could decrease and, therefore, discharge may increase <br />slightly. Total salt load would remain unchanged, and any increase in flow would be associated with a <br />proportional decrease in dissolved solids. <br />The leaching characteristics of the waste rock indicate that it will produce lower concentrations of soluble salts <br />and trace metals than the backfill in which it is being placed. Therefore, we do not anticipate any incremental <br />adverse water quality deterioration due to this activity, other than perhaps a slight shift in ionic composition of <br />water discharged. The ionic composition of leach water from waste rock differs slightly from the ionic <br />composition of backfill spoil water. The leach tests suggest higher levels of sodium and lower levels of calcium <br />in waste rock leachates than in backfill spoils. Thus, we could expect a slight shift in the chemical composition <br />TR13 -83 2.05 -154 11103/14 <br />