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Due to elevated levels of salinity documented in current and future mine discharge water, and to potential inhibitory effects of increased soil and alluvial ground water salinity on Hood irrigated and subirtigated crops, the potential for material damage caused by salt loading was a major concern which had to be evaluated for each of the AVF's identified above. fvtaterial damage projections were calculated in both asub-irrigation and a flood irrigation case analysis. using data obtained during low-flow-of-record years. The sub-irrigation scenario assumed that the stream would recharge the alluvial aquifer in the spring during peak flows. The Hood irrigation case utilized the period between June l and August 31. Assumptions and equations used in projecting water quality impacts are discussed in the Yampa River CHIA, which is on file at the Division office. Salt loading projections were arrived at by stream Flow modeling and analysis of past monitoring results and projected dewatering activities. In the supplemental information package dated September 22, 1986, the applicant submitted information on vegetation cover and production by species for Flood irtigated and sub-irrigated croplands on the affected alluvial valley Floors. Alluvial bodies, irrigated fields and vegetation sample locations are depicted on supplemental Map No. l "Twenrymile Park Salt Loading Study Land Use and Hydrologic -Boundaries." This and other information was used by the Division to make the required findings with regazd to material damage. Required findings for identified alluvial valley floors on Fish Creek, Trout Creek, and Foidel Creek/Middle Creek confluence are presented separately below. Fish Creek The boundaries of the Fish Creek alluvial valley floor are as delineated on Map No. l5 of the Foidel Creek Life of Mine application and include all alluvial deposits within and downstream from the permit area as delineated on supplemental Map No. 1. Information discussed below has reat~irmed the Division's original determination that alluvial deposits on Fish Creek meet alluvial valley floor criteria based on existing flood irtigation, potential for flood irrigation and subirtigation. The existence of a curtently flood irtigated field on lower Fish Creek and the presence of diversion structures and irrigation ditches on various stream segments as delineated on Map l5 document the potential for flood irtigation. Information provided in application E.~dtibit 16 (Soil Mapping Unit Descriptions) and backhoe pit data provided on Page 2.06 -9 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 Basin would be expected to derive benefit from ground water when present at such shallow depths. The major vegetation type on the Fish Creek AVF within the 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 subirtigated conditions. The Division received a letter from one of the surface owners, Nir. Edward Camilletti , on January 23. 1998, regarding the significance of the Fish Creek AVF to farming in sections 10 and 1 i, TSN, R86W. The Camelletti's use these lands as undeveloped rangeland. The landowner estimated that l% of the ranch production is attributed to the Fish Creek AVF. C: \J H B\C82056\R N03\R N 03 F I N D. d oc 29