2012-01-05_REVISION - C1980005 (8)

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Creek to its confluence with Trout Creek and along the length of Trout Creek to its confluence with the Yampa River. Effect of Mining on Identified Alluvial Valley Floors Water quality data were supplied in the Permit Renewal No. 5 application from monitoring of surface water stations on Cow Camp and Bond Creeks, tributaries to Fish Creek. Mining in the Fish Creek drainage basin began in 1982. Since that time, increases in both flow and total dissolved solids (TDS) concentrations have been observed. Whereas flow in the drainage immediately below the mine, Cow Camp Creek, was ephemeral prior to mining, perennial flow is now observed at the permit boundary. This effect is attributable to spoil aquifer discharge, as well as an increase in runoff from mined lands, and a decrease in evapotranspiration due to removal of vegetation from mining areas. Recent observations have indicated, however, that stream flow is not maintained in the channels of the two tributaries during the months of August and September near their confluences with Fish Creek. The surface effects of water discharged from the mine on the downstream AVF locations is restricted to the months of June and July. Subsurface effects are expected to predominate in August and September. Water quality constituents of concern to the AVF identified on Fish Creek include trace metals, sulfate, and TDS. An evaluation of concentration levels present in the mine discharge indicate TDS to be the constituent most likely to place a restriction on the quality of irrigation water. Rule 2.06.8(5)(b) identifies material damage as increases in electroconductivity to levels above a threshold value at which crop yields decrease. The relationship between electroconductivity and TDS level has been demonstrated by Seneca Coal Company in the permit application. The operator has submitted an analysis based on a mass - balance loading of TDS in Fish Creek. Concentrations of TDS in mine effluent were the maximum values from Spoils Spring # 1 in the Cow Camp Creek drainage. Mean flow values for June and July were used for Cow Camp Creek, Bond Creek, and an upstream location on Fish Creek in the calculations. Results indicated significant dilution would take place and maximum expected TDS concentrations of 607 mg /1 were expected in Fish Creek below the mine. The maximum TDS level projected would correspond to a conductivity of less than 1 mmho /cm. A conservative estimate of the relationship between irrigation water salinity and root zone soil salinity, as referenced in USDA Handbook 60, is 1 to 1.5, respectively. Thus, irrigation water applied with a specific conductance of 1 mmho /cm would result in root zone soil water with a specific conductance of 1.5 mmho /cm. No decrease in production of any of the species identified in data submitted by the operator would be expected unless the conductivity of the irrigation water was to exceed 1 mmho /cm. No significant decreases in productivity would occur unless root zone soil water salinity was to exceed 1.5 mmho /cm. 29