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The alluvial aquifers that will be affected by the resaturated spoil include the <br />Armand Draw, Upper Grassy Creek, Lower Grassy Creek, and Sage Creek <br />alluvium. Within the Grassy Creek basin, above the confluence with <br />Scotchman's Gulch, the magnitude of the TDS increase will be high <br />immediately below the resaturated spoil, but will be undetectable a short <br />distance beyond within the Upper Grassy Creek Alluvium. This diminution <br />of TDS will result from low hydraulic conductivities in the Grassy Creek <br />Alluvium, additional downgradient chemical changes, and dilution and <br />mixing from shallow bedrock units which discharge to the alluvium. <br />Seneca Coal Company predicts that the maximum TDS increase in the <br />Armand Draw Alluvium will be 58% immediately below the resaturated <br />spoil, attenuating to less than 5% near the confluence of Lower Grassy Creek <br />and Scotchman's Gulch. The predicted TDS increases in the Grassy Creek <br />and Armand Draw Alluvium will not preclude use ofthe alluvial groundwater <br />for livestock watering, although the low well yields in these areas may <br />already render these aquifers useless for these purposes. <br />In the Sage Creek Alluvium, the predicted TDS increase immediately below <br />the resaturated spoil is 99%, but attenuates to 0.1% within 1000 feet. The <br />high hydraulic conductivities of greater than 1 ft/day measured in the Sage <br />Creek alluvium, in combination with the large area of alluvial material, <br />provides for a relatively high volume of flux in the Sage Creek Alluvium. <br />Contributions from tributary alluvium and shallow bedrock units will provide <br />dilution of the spoil dischazge as it mixes with much larger volumes of <br />groundwater in the Sage Creek Alluvium. The point at which the TDS <br />increase in the Sage Creek Alluvium is predicted to attenuate to 0.1% is just <br />above a potentially subirrigated field. Therefore, the impacts to the field are <br />predicted to be negligible. The minimal increase in downgradient TDS levels <br />will also not affect the suitability of the groundwater for livestock watering <br />uses. <br />Hydrologic monitoring will be implemented by SCC in order to verify the <br />predicted impacts. The proposed hydrologic monitoring program is outlined <br />in Tab 15 of the PAP. <br />Surface Water <br />The probable hydrologic consequences of coal mining at the Yoast mine in <br />regard to surface water include contributions of sediment to streams from <br />storm runoff, and impacts to stream water quantity and quality during and <br />after mining. Potentially affected streams and drainages include Armand <br />Draw, Grassy Creek, and Sage Creek. The most significant impact of mining <br />on surface water will be the effect of spoil spring discharges from the <br />Yoast Mine 2g February 28, 2006 <br />