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Mike Qoulnv. DMG © Ociober2l, /993 Pnge 3 ranging from almost 70 percent in the Wadge overburden (Sage Creek, years 2004 to 2009) to more than 300 percent in the Wadge Coal (Sage Creek, years 2004 to 2009). The extern of the predicted TDS change is, however, limited to a close downgradient proximity to the resaturated spoil because significant additional mixing, dilution of unaffected recharge, and geochemical changes will occur in the downgradient direction. The significance of the impact to bedrock water quality will he minimal because the groundwater is currently not suitable for domestic drinking water, irrigation, or livestock usage. Impacts to the alluvial groundwater system in Sage Creek will result in a predicted TDS concentration increase of 0.1 percent. The elevated hydraulic conductivity values of [he alluvial materials, combined with the large cross-sectional area of flow in the subchannel, provide a relatively high volume of flux in the Sage Creek alluvium. Contributions from tributary alluvium and shallow bedrock units will also provide dilution of the spoil discharge as it mixes with much larger volumes of groundwater in the Sage Creek alluvium. The predicted 7DS concentration increase measured during the low-flow season Qune through September) in Sage Creek surface water is relatively large. This increase, al[hough large in magnitude, will not significantly impact the potential use of this water for livestock (the water quality will remain appropriate for stock use), domestic drinking water (the water quality in Sage Creek is currently unsuitable for drinking water), or irrigation (water quality in the creek is currently unsuitable for irrigation; refer to Tab 7, Surface Water Suitability). As depicted in the above summary discussions, the current SCC permit for mining activities at the Yoast mine includes predicted impacts within the Sage Creek drainage. Each of the issues addressed above is discussed in de[ail in permit Tab 17 and the other referenced permit tabs. STIPULATION NO. 9 PRIOR TO CONDUCTING ANY MINING OPERATIONS WHICH MIGHT AFFECT ALLUVIAL VALLEY FLOORS IN THE SAGE CREEK WATERSHED, THE APPLICANT SHALL HAVE A REVISION TO THE YOAST PERMIT APPROVED WHICH ADDRESSES THE REQUIREMENTS OF RULE 2.06.8(4) BY DOCUMENTING: ].) THE CHARACTERISTICS OF THE ALLUVIAL VALLEY FLOORS WHICH ARE ESSENTIAL HYDROLOGIC FUNCTIONS (FLOOD AND/OR SUBIRRIGATION); Alluvial Valley Floors (AVFs) in the Sage Creek watershed are characterized in Actachmen[ 16-3 (1990 Alluvial Valley Floor Investigations of Sage Creek and Upper Grassy Creek) of Tab 16 (Protection of the Hydrologic Balance). The Attachment addresses AFV geomorphology and irrigation types and uses within the watersheds. Land use designation, flood-irrigated areas, and subirrigated areas within Sage Creek are shown in map view on Exhibit 6-3, Sheet 2 of 2.