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,ifike Boalav, DA1G © October?1.1993 Page a 2.) WHETHER MINING OPERATIONS WILL INTERRUPT, DISCONTINUE, OR PRECLUDE FARMING OPERATIONS ON THE ALLUVIAL VALLEY FLOORS; Per page 16-3-6 of Attachment 16-3, the Yoasc mining and reclamation plans, as proposed, will minimize disturbances to the hydrologic balance by preserving essential hydrologic functions of the AVFs adjacen[ to the mining artd reclamation operations, including xhose located in Sage Creek. That is, the mining :md reclamation operations will not interfere with or impede the valley floor area's ability to collect, store, and regulate the natural flow of surface water and groundwater. If anything, the quantities of water available to the alluvial groundwater and surface water systems in the Sage Creek drainage have the potential to increase following mining. Per page 12 of Tab 16 and page 40 of Tab 17 (Probable Hydrologic Consequences), three subirrigated hay fields were identified within the Sage Creek watershed. Two of the subirrigated hay fields are located in Sections 30 and 19 of TSN, R87W, and are upstream of all proposed mining disturbances associated with the Yoast Mine (see Exhibit 6-3, Sheet 2 of 2). The third subirrigated field is located in Section 18, TSN, R87W, approximately 1.5 miles downstream from the mine and immediately above the failed Sage Creek Reservoir dam. The field is used to produce grass hay. The minimal TDS increase predicted for the Sage Creek alluvial flow system as a result of mining activities at the Yoast mine (less than one percent or 1.0 mg/L) will have no appreciable impact on this subirrigated field. Because available groundwater level data suggest that a majority of Sage Creek between the mine permit boundary and the downstream subirrigated field is characterized as a gaining stream reach (refer to Exhibit 7-2), surface water within the creek should have minimal contact with groundwater in the subirrigated field. Therefore, TDS concentrations in the creek should not impact groundwater concentrations in the alluvial groundwater system. Ground water in the Sage Creek :illuviutn is currently unsuitable for domestic drinking water and is marginally suitable for irrigation. Downgradient Sage Creek alluvial groundwater may be chemically suitable for livestock, and the minimal, predicted increase in TDS will not change this potential suitability. 3.) WHETHER MINING OPERATIONS WILL RESULT IN MATERIAL DAMAGE TOTHE QUALITY OF SURFACE WATER SUPPLYING THE ALLUVIAL VALLEY FLOORS; As stated previously when addressing Stipulation No. 7, and as cited on pages 42 and 43 of permit Tab 17, the cumulative predicted TDS concentration increase in Sage Creek surface water from Yoast mining activities is relatively large (230 percent). The predicted postmining TDS value at surface water station WSSF4, located approximately 1.3 miles downstream of the mining boundary in Sage Creek, is 2118 mg/L. This TDS concentration increase, although large in magnitude and long Germ, will resuh in minimal impacts. The TDS increase will not significantly impact the potential use of this water for livestock watering (the livestock TDS standard is 5,000 mg/L), domestic drinking water (the water quality in Sage Creek at WSSF4 is currently unsuitable for drinking water), or irrigation (sulfate and pH values at station WSSF4 are currently unsuitable for irrigation). The TDS increase will also have no significance regarding flood irrigation at the historically flood-