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Division, the 1.5:] relationship is considered conservative. No decrease in production of <br />any of the species currently grown on the Trout Creek AVF would be expected unless <br />the conductivity of the irrigation water were to exceed 1000 umhos/cm. Based on <br />species composition data submitted, significant production decreases (greater than 3% for <br />a farm unit) would not occur unless irrigation water salinity were to exceed 1500 <br />umhos/cm. In summary, projected flood irrigation water quality is 500 umhos/cm and <br />material damage would not occur unless water quality were to exceed 1500 umhos/cm. <br />Given the minor effect of mine dischazge on Trout Creek surface water quality, a specific <br />projection of alluvial ground water impact was not made. Since alluvial recharge would <br />occur in late spring and early summer when dilution due to snowmelt runoff is at its <br />peak, it follows that alluvial waters (and thus sub-irrigation) would be less affected by <br />mine dischazge than Trout Creek surface water (and flood irrigation). <br />3. The proposed operation would preserve the essential hydrologic functions of the <br />alluvial valley floor. <br />The essential hydrologic functions of the Trout Creek alluvial valley floor have been <br />identified as the capacity to support sub-irrigated and flood irrigated agricultural <br />activities. <br />The proposed plan would not result in any surface disturbance or undermining of the <br />AVF. Also, as discussed previously, no material damage would result from changes in <br />[he quality of surface and ground water that supply the alluvial valley floor. Thus, the <br />essential hydrologic functions of the alluvial valley floor would not be affected by the <br />proposed operation. <br />Fish Creek <br />The boundazies of the Fish Creek alluvial valley floor include all alluvial deposits within <br />and downstream from the proposed permit azea as delineated on TCC supplemental Map <br />No. 1 and Map 6 from the updated C-81-071 permit document. Information submitted <br />by the operator has re-affirmed the Division's original determination that alluvial deposits <br />on Fish Creek meet alluvial valley floor criteria based on existing flood irrigation, <br />potential for flood irrigation and sub-irrigation. <br />The existence of a currently flood irrigated field on lower Fish Creek and the presence of <br />diversion structures and irrigation ditches on vazious stream segments as delineated on <br />Map TCC 15 document the potential for flood irrigation. <br />Information provided in TCC Life-of--Mine application Exhibit 16 (Soil Mapping Unit <br />Descriptions) and backhoe pit data provided on Page 206 - 9F show that a number of <br />alluvial soil types exhibit late growing season ground water elevations within 6 feet of <br />32 <br />