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Middle Creek <br />Prior to PR -03, no previous AVF determination had been made for areas above the <br />Foidel/Middle Creek confluence AVF on Middle Creek as these areas were not <br />proposed to be affected or impacted by the Foidel Creek mine operation. During the <br />PR -03 review process, the applicant submitted information to support its position that <br />areas along the Middle Creek valley floor in sections 12, 23, and 26 T5N R86W are <br />not alluvial valley floors. Twentymile Coal provided information which is contained <br />in the permit application as Exhibit 42a and consists of vegetation sampling data, <br />valley floor cross-sections, and a transect location map. The applicant also refers to <br />the narrow and deeply incised nature of Middle Creek. <br />There is no indication of past or current flood irrigation of these areas along Middle <br />Creek, and the geomorphic characteristics of this area would not lend themselves to <br />the development of an irrigation system. Based on the lack of flood irrigation <br />potential, the narrow and incised nature of the valley bottom, and the lack of <br />meaningful differences between the creekside and upland vegetative communities, the <br />Division has determined that areas upstream of the Connel ditch lateral crossing of <br />Middle Creek, as shown on Map 15, are not alluvial valley floors. In this case, the <br />extent of farmable acreage would be 10 acres or less. The areas are not presently and <br />have not historically been farmed and evidence presented indicates that farming is not <br />typically practiced on similar parcels in the region. A previous negative determination <br />had already been made for those lands along Middle Creek downstream from the <br />County Road No. 33 in section 12 to the first irrigation ditch crossing (Connel ditch <br />lateral). <br />Effects of Mining on Identified Alluvial Valley Floors <br />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 />Page 42 of 52 <br />