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unless the conductivity of the ir;^igation :vater :vere to exceed 1 ^~mhos/cm. 4aseC ~~ species mposi ion data submitted, significant proC~ction Cecreases (greater than 3% for a farm unit) would not occur unless irrigation water salinity were to exceed 1,5 mmhos/cm. In summary, projected flood irrigation water quality is .5 mmhos/cm and material damage would not occur unless water quality were to exceed 1,5 mmhos/cm. Given the minor effect of mine discharge on Trout Creek surface water quality, a specific projection of alluvial ground water impact was not made. Since alluvial recharge would occur in late spring and early summer when dilution due to snowmelt runoff is at its peak, it follows that alluvial waters (and thus sub-irrigation) would be less affected by mine discharge than Trout Creek surface water (and flood irrigation). 3. The proposed operation would preserve the essential hydrologic functions of the alluvial valley floor, The essential hydrologic functions of the Trout Creek alluvial valley floor have been identified as the capacity to support sub-irrigated and flood irrigated agricultural activities. The proposed plan would not result in any surface disturbance or undermining of the AVF. Also, as discussed previously, no material damage would result from changes in the quality of surface and around water that supply the alluvial valley floor, Thus, the essential hydrologic functions of the alluvial valley floor would not be affected by the proposed operation. Fish Creek The boundaries of the Fish Creek alluvial valley floor include all alluvial deposits within and downstream from the proposed permit area as delineated on TCC supplemental Map No. 1 and Map 6 from the updated C-S1-071 permit document. Recently submitted information discussed below has reaffirmed the Division's original determination that alluvial deposits on Fish Creek meet alluvial valley floor criteria based on existing flood irrigation, potential for flood irrigation and sub-irrigation. The existence of a currently flood irrigated field on lower Fish Creek and the presence of diversion structures and irrigation ditches on various stream segments as delineated on Map TCC 15 document the potential for flood irrigation. Information provided in TCC Life-of-Mine application Exhibit 16 (Soil Mapping Unit Descriptions) and backhoe pit data provided on Page 206 - 9F show that a number of alluvial soil types exhibit late growing season ground water elevations within 6 feet of the surface. Hay crop species commonly grown in the Yampa 9asin would be expected to derive benefit from ground water when present at such depths. The major vegetation type on the Fish Creek AVF within the proposed permit area is a sagebrush meadow community dominated by silver sagebrush with a number of sedge and rush species contributing significantly to the community. .All of these species are hydrophytes typically associated with sub-irrigated conditions. 22