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Due to elevated levels of salinity documented in current mine discharge water and <br />predicted in future mine discharge water, and to potential inhibitory effects of <br />increased soil and alluvial ground water salinity on flood irrigated and sub -irrigated <br />crops, the potential for material damage caused by salt loading was a concern which <br />had to be evaluated for each AVF 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 Hydrologic - <br />Boundaries." This and other information was used by the Division to make the <br />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 />species commonly grown in the Yampa Basin would be expected to benefit from <br />such shallow ground water. <br />Foidel Creek Mine 42 February 25, 2016 <br />