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Alluvial aquifers affected by the re-saturated spoil include the Annand Draw, Upper <br /> Grassy Creek, Lower Grassy Creek, and Sage Creek alluvium. Within the Grassy Creek <br /> basin, above the confluence with Scotchman's Gulch, the magnitude of the TDS increase <br /> will be high immediately below the re-saturated spoil, but will be undetectable a short <br /> distance beyond within the Upper Grassy Creek Alluvium. This diminution of TDS will <br /> result from low hydraulic conductivities in the Grassy Creek Alluvium, additional <br /> downgradient chemical changes, and dilution and mixing from shallow bedrock units <br /> which discharge to the alluvium. <br /> Seneca Property, LLC predicts that the maximum TDS increase in the Annand Draw <br /> Alluvium will be 58% immediately below the re-saturated spoil, attenuating to less than <br /> 5% near the confluence of Lower Grassy Creek and Scotchman's Gulch. The predicted <br /> TDS increases in the Grassy Creek and Annand Draw Alluvium will not preclude use of <br /> the alluvial 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 below the re- <br /> saturated spoil is 99%, but attenuates to 0.1% within 1000 feet. The high hydraulic <br /> conductivities of greater than 1 ft./day measured in the Sage Creek alluvium, in <br /> combination with the large area of alluvial material, provides for a relatively high volume <br /> of flux in the Sage Creek Alluvium. Contributions from tributary alluvium and shallow <br /> bedrock units will provide dilution of the spoil discharge as it mixes with much larger <br /> volumes of 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 above a <br /> potentially sub-irrigated field. Therefore, the impacts to the field are predicted to be <br /> negligible. The minimal increase in downgradient TDS levels will also not affect the <br /> suitability of the groundwater for livestock watering uses. <br /> Hydrologic monitoring will continue to be implemented by Seneca Property in order to <br /> verify the predicted impacts. The hydrologic monitoring program is outlined in Tab 15 <br /> of the PAP. <br /> Surface Water <br /> The probable hydrologic consequences of coal mining at the Yoast Mine in regard to <br /> surface water include contributions of sediment to streams from storm runoff and impacts <br /> to stream water quantity and quality during and after mining. Potentially affected streams <br /> and drainages include Annand Draw, Grassy Creek, and Sage Creek. The most significant <br /> impact of mining on surface water will be the effect of spoil spring discharges from the <br /> reclaimed mine on surface water quality. Seneca Property LLC's predictions of the <br /> magnitude of these impacts is discussed below. <br /> Sediment Loading <br /> All runoff from areas disturbed during the life of mine will passed through one of five <br /> sedimentation ponds prior to leaving the permit area. Discharges from the ponds are <br /> required to meet NPDES effluent limits, and should, therefore, not contribute additional <br /> suspended solids to stream flows near the permit area. As the site is fully reclaimed <br /> sediment loads should be no larger than those coming from the permit area during mining <br /> 13 <br />