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Creek and along the length of Trout Creek to its confluence with the Yampa River. <br />Effect of Mining on Identified Alluvial Vallev Floors <br />Water quality data were supplied in the renewal application from monitoring of surface water <br />stations on Cow Camp and Bond Creeks, tributaries to Fish Creek. Mining in the Fish Creek <br />drainage basin began in 1982. Since that time increases in both flow and total dissolved <br />solids (TDS) concentrations have been observed. Whereas flow in the channel immediately <br />below the mine, Cow Camp Creek, was ephemeral prior to mining, perennial flow is now <br />observed at the permit boundary. This effect is attributable to spoil aquifer dischazge, as well <br />as an increase in runoff from mined lands, and a decrease in evapotranspiration due to <br />removal of vegetation from mining areas. Recent observations have indicated, however, that <br />stream flow is not maintained in the channels of the two tributaries during the months of <br />August and September near their confluences with Fish Creek. The surface effects of water <br />discharged from the mine on the downstream AVF locations is restricted to the months of <br />June and July. Subsurface effects aze expected to predominate in August and September. <br />Water quality constituents of concern to the AVF identified on Fish Creek include trace <br />metals, sulfate, and TDS. An evaluation of concentration levels present in the mine <br />discharge indicate TDS to be the constituent most likely to place a restriction on the quality <br />of imgation water. Rule 2.06.8(5)(b) identifies material damage as increases in <br />electroconductivity to levels above a threshold value at which crop yields decrease. The <br />relationship between electroconductivity and TDS level has been demonstrated by Seneca <br />Coal Company, in the permit application. <br />The operator has submitted an analysis based on amass-balance loading of TDS in Fish <br />Creek. Concentrations of TDS in mine effluent were the maximum values from Spoils <br />Spring Number 1 in the Cow Camp Creek drainage. Mean flow values for June and July <br />were used for Cow Camp Creek, Bond Creek, and an upstream location on Fish Creek in the <br />calculations. Results indicated significant dilution would take place and maximum expected <br />TDS concentrations of 607 mg/1 were expected in Fish Creek below the mine. <br />The maximum TDS level projected would correspond to a conductivity of less than 1 <br />mmho/cm. A conservative estimate of the relationship between imgation water salinity and <br />root zone soil salinity, as referenced in USDA Handbook 60, is 1 to 1.5, respectively. Thus, <br />irrigation water applied with a specific conductance of 1 mmho/cm would result in root zone <br />soil water with a specific conductance of 1.5 mmho/cm. No decrease in production of any of <br />the species identified in data submitted by the operator would be expected unless the <br />conductivity of the irrigation water were to exceed 1 mmho/cm. No significant decreases in <br />productivity would occur unless root zone soil water salinity were [o exceed 1.5 mmho/cm. <br />Given the limited effect of Seneca II Mine discharge on Fish Creek surface water quality, it is <br />deduced that alluvial ground water quality should not be significantly impaired. Rechazge of <br />the Fish Creek alluvium from the Cow Camp and Bond Creek tributaries would be expected <br />to be minimal compared to upstream contributions. Sub-irrigation would be expected to be <br />38 <br />