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Seneca Coal Company predicted that the increase in TDS concentrations <br />in the bedrock aquifers will range from 70% in the Wadge Overburden to <br />over 300% in the Wadge Coal. These predictions are for groundwater in <br />close proximity to the resaturated spoil, within the permit area. As <br />groundwater migrates away from the resaturated spoil, mixing, dilution <br />from unaffected recharge, and geochemical changes will decrease the TDS <br />concentrations. Well yields in these bedrock units, the Wadge Coal and <br />Overburden and the Wolf Creek Coal and Overburden, are insufficient for <br />irrigation purposes. <br />The alluvial aquifers that will be affected by the resaturated spoil include <br />the Annand Draw, Upper Grassy Creek, Lower Grassy Creek, and Sage <br />Creek alluvium. Within the Grassy Creek basin, above the confluence <br />with 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 <br />diminution of TDS will result from low hydraulic conductivities in the <br />Grassy Creek Alluvium, additional downgradient chemical changes, and <br />dilution and mixing from shallow bedrock units which discharge to the <br />alluvium. <br />Seneca Coal Company predicts that the maximum TDS increase in the <br />Annand Draw Alluvium will be 58% immediately below the resaturated <br />spoil, attenuating to less than 5% near the confluence of Lower Grassy <br />Creek and Scotchman's Gulch. The predicted TDS increases in the Grassy <br />Creek and Annand Draw Alluvium will not preclude use of the alluvial <br />groundwater for livestock watering, although the low well yields in these <br />areas may already render these aquifers useless for these purposes. <br />In the Sage Creek Alluvium, the predicted TDS increase immediately <br />below the resaturated spoil is 99%, but attenuates to 0.1% within 1000 <br />feet. The high hydraulic conductivities of greater than 1 ft/day measured <br />in the Sage Creek alluvium, in combination with the large area of alluvial <br />material, provides for a relatively high volume of flux in the Sage Creek <br />Alluvium. Contributions from tributary alluvium and shallow bedrock <br />units will provide dilution of the spoil discharge as it mixes with much <br />larger volumes of groundwater in the Sage Creek Alluvium. The point at <br />which the TDS increase in the Sage Creek Alluvium is predicted to <br />attenuate to 0.1 % is just above a potentially subirrigated field. Therefore, <br />the impacts to the field are predicted to be negligible. The minimal <br />increase in downgradient TDS levels will also not affect the suitability of <br />the groundwater for livestock watering uses. <br />Hydrologic monitoring will continue to be implemented by SCC in order <br />to verify the predicted impacts. The hydrologic monitoring program is <br />outlined in Tab 15 of the PAP. <br />Yoast Mine 26 December 15, 2010