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Cumulative impacts to colluvium in the Dry Creek drainage will be <br />insignificant. Discharge from bedrock aquifers to the colluvium will be <br />minimal and flows from spoils aquifers which develop in backfilled areas will <br />drain to different drainages. There will be some deterioration of surface <br />water quality as a consequence of spoils spring discharges. Flow in both <br />drainages is ephemeral, and spoils discharges will increase flow but not <br />preclude its existing use for stock watering. No alluvial valley floors have <br />been identified immediately downstream of either operation. <br />Ground water utilization is limited due to the poor quality of the water and <br />low flows. Most adjudicated ground water is utilized for stock watering. Any <br />degradation of quality which would occur as a consequence of mining would have <br />insignificant "impacts or existing ground water uses. <br />Surface Water <br />Cumulative surface water impacts within the basin were analyzed using two <br />different techniques. Initially, a surface water salt-loading model, <br />developed by the USGS in 1983 was loaded with data submitted by the operators <br />from 1983-1985. This model utilizes power curve regression analyses of the <br />relationship between discharge and total dissolved solids or electrical <br />conductivity to predict salt-loading throughout the drainage using a simple <br />accounting system (Parker and Norris, 1985). <br />The results of the model were not representative of salt loading which was <br />observed during the period. The correlation coefficients of the regressions <br />derived from the operators' data were unacceptably poor, and consequently the <br />model predicted minimal impact. Two hypotheses were developed to explain the <br />failure of the model, The operators' data could be of questionable quality. <br />There was some evidence that field conductivity values were inconsistent with <br />laboratory results. t4ore likely, however, the regression analyses were unable <br />to reduce the evolving relationship between discharge and salt concentrations <br />modified by developing spoils aquifer springs in a linear manner. The <br />standard, dramatic, inverse relationship between discharge and TDS or EC is <br />not observed in small drainages disturbed by large surface mines. Peak and <br />low flow salt concentrations can be similar; maximum seasonal discharges are <br />modified by large spoils peak flows while minimal seasonal discharges develop <br />high salt concentrations as a consequence of minimal dilution. <br />Therefore, salt loading predictions were calculated using surface water data <br />from low flow years and predictions df mining-related impacts: underground <br />mine inflows, spoils aquifer discharges, and outflows from flooded workings of <br />underground mines. It is difficult to classify the duration of these impacts <br />as many overlap. tAine inflows from Foidel Creek underground mine will <br />continue through 2015. (TABLE 8). Empire Energy's Eagle No. 5 and 6 <br />f4ine will discharge inflows until 2006. Backfilled spoils discharges take <br />three to fifteen years to develop and then are projected to discharge poor <br />quality water for several hundred years. Discharge from the flooded workings <br />from Foidel Creek underground mine is not projected to begin until the year <br />2365. The discharge will continue for several thousand years at elevated <br />-23- <br />