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Due to elevated levels of salinity documented in current and future mine discharge <br /> water, and to potential inhibitory effects of increased soil and alluvial ground water <br /> salinity on flood irrigated and sub-irrigated crops, the potential for material damage <br /> caused by salt loading was a concern which had to be evaluated for each AVF <br /> identified above. <br /> Material damage projections were calculated in both a sub-irrigation and a flood <br /> irrigation case analysis, using data obtained during low-flow-of-record years. The <br /> sub-irrigation scenario assumed that the stream would recharge the alluvial aquifer in <br /> the spring during peak flows. The flood irrigation case utilized the period between <br /> June 1 and August 31. Assumptions and equations used in projecting water quality <br /> impacts are discussed in the Yampa River CHIA, which is on file at the Division <br /> office. Salt loading projections were arrived at by stream flow modeling and analysis <br /> of past monitoring results and projected dewatering activities. <br /> In a supplemental information package dated September 22, 1986, the applicant <br /> submitted information on vegetation cover and production by species for flood <br /> irrigated and sub-irrigated croplands on the affected alluvial valley floors. Alluvial <br /> bodies, irrigated fields and vegetation sample locations are depicted on supplemental <br /> Map No. 1 "Twentymile Park Salt Loading Study Land Use and <br /> Hydrologic - Boundaries." This and other information was used by the Division to <br /> make the required findings with regard to material damage. <br /> Required findings for identified alluvial valley floors on Fish Creek, Trout Creek, and <br /> Foidel Creek/Middle Creek confluence are presented separately below. <br /> Fish Creek <br /> 1. The proposed mining operations will minimally interrupt, discontinue or preclude <br /> farming on a portion of the alluvial valley floor. <br /> The boundaries of the Fish Creek AVF are as delineated on Map No. 15 of the <br /> PAP. The AVF includes all alluvial deposits within and downstream from the <br /> permit area as delineated on supplemental Map No. 1. Information discussed <br /> below has reaffirmed the Division's original determination that alluvial deposits on <br /> Fish Creek meet AVF criteria based on existing flood irrigation, potential for flood <br /> irrigation and sub-irrigation. <br /> Map 15 shows the following features in the Fish Creek AVF: areas having <br /> potential for flood irrigation, currently flood-irrigated fields, diversion structures, <br /> and irrigation ditches. <br /> Several of the soils in the AVF exhibit late growing season ground water <br /> elevations within six feet of the surface (Exhibit 16, Soil Mapping Unit <br /> Descriptions and backhoe pit data provided on Page 2.06-9 of the PAP). Hay crop <br /> Foidel Creek Mine 38 August 4,2023 <br />