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The essential hydrologic functions of the Fish Creek alluvial valley Floor have been identified as the capacity to support subirrigated and Flood irrigated agricultural activities. Mining beneath the AVF has been limited to panels 5, 6 and 7 of the Southwest Mining District and did not result in dewatering of the stream/alluvial system. Also, as discussed previously, no material damage would result from changes in the quality of surface and ground water that supply the alluvial valley Floor. The essential hydrologic functions of the alluvial valley floor were not be affected by the proposed operation. Undermining of a small area of Fish Creek (section 25, TSN, R87W) has been completed and no identifiable impacts were observed in the data. Monitoring of Fish Creek above and below this area continues as per the approved plan. ~ ~~ ~ ~.,,,,,/~ ~~ tS f ""~ ac Trout Creek The boundaries of the Trout Creek alluvial valley Floor which would potentially be affected by the proposed operation and to which these findings apply include irrigated pasture 8S, which encompasses the Middle Creek/Trout Creek Confluence, and all alluvial deposits downstream on Trout Creek to its confluence with the Yampa River, including irrigated pastures 7, 8N, 9, 10, 1 I, 12E, 12 W, 14, 15S, and I SN, 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. lrrigated 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. The proposed mining operations would 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 would 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)(b) 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. The rule further cites a specific 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 [hose species as well as a number of 74