2016-05-04_REVISION - C1982056 (12)

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including irrigated pastures 7, 8N, 9, 10, 11, 12E, 12W, 14, 15S, and 15N, as depicted on Map No. 1 of Exhibit 42 of the permit application. Alluvial deposits on Trout Creek meet alluvial valley floor criteria based on extensive acreage of flood irrigated hayland, potential for flood irrigation and a presumed capability to support subirrigated vegetation. Flood irrigated hayland and vegetation sample locations are depicted on Map No. 1. Irrigated hayland is the predominant land use on the Trout Creek AVF and the dominant species are Kentucky bluegrass, Smooth brome and Timothy. Based on the extent of existing flood irrigated farmland, and lack of specific information regarding extent or use of subirrigated alluvium, the Division finds that the Trout Creek Alluvial Valley Floor is significant to farming. The required findings are set forth below. 1. The proposed mining operations will not interrupt, discontinue or preclude farming on the alluvial valley floor. Mining activity would not directly impact any portion of the Trout Creek AVF. Any impacts would be indirect, as a result of discharge of affected water into Foidel Creek and Fish Creek. Fish Creek is tributary to Trout Creek, and Foidel Creek is tributary to Middle Creek, which is tributary to Trout Creek. Indirect impacts are addressed under No. 2 below. 2. The proposed mining operations will not cause material damage to the quantity or quality of surface and ground water that supply the alluvial valley floor. The only potential for the diminution of the quantity of water supplied to the Trout Creek AVF would be as a result of undermining of Fish Creek and Foidel Creek, which are tributary to Trout Creek. Dewatering of the streams as a result of undermining is not considered to be a possibility for reasons explained in the Fish Creek and Foidel Creek AVF Findings section of this document. Rule 2.06.8(5)(c) of the Colorado Regulations specifically refers to potential increases in electrical conductivity of water supplying AVFs to levels above threshold value at which crop yields decrease as constituting material damage. A reference initially used is a paper by E.V. Maas and G.J. Hoffman of the U.S. Salinity Laboratory published in the Journal of the Irrigation and Drainage Diversion, ASCE, June, 1977. In their paper, Maas and Hoffman list research - derived salinity threshold levels and response rates for selected agricultural species, and group those species as well as a number of additional crops into four categories based on relative tolerance to salinity (sensitive, moderately sensitive, moderately tolerant and tolerant). The Division has taken the approach that a positive (adverse) material damage finding would be made if projected salinity increases resulting from mining would result in significant decreases in production or shifts in species composition based on the Maas and Hoffman paper. Page 47 of 52