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quality along lower segments of the West Fork will be degraded by discharge of this relatively <br />high salinity spoil water. <br />Based on reconnaissance investigation performed by the operator and described on page R2-126 <br />of Volume 12, and supplemental adequacy response submittal information, and based further on <br />site visits conducted by Division staff, the Division has determined that the West Fork Good <br />Spring Creek valley does not meet the alluvial valley floor criteria. <br />Reconnaissance investigation revealed narrow, intermittent reaches of alluvium, with the valley <br />bottom constricted in various locations by sheet wash and debris flows from the steep south <br />facing slopes. The valley bottom ranges from tens of feet wide to a maximum width of <br />approximately 250 feet in the vicinity of the confluence; the stream channel itself is incised <br />throughout much of the reach. <br />There is no current flood irrigation along the West Fork and no indications of historic flood <br />irrigation. Vegetation on the relatively flat valley bottom benefits from precipitation and snow <br />melt runoff from the steep valley side slopes. As a result, the predominately clayey soils of the <br />terrace support a relatively lush growth of native grasses, dominated in most areas by basin <br />wildrye. Areas of colluvial deposition that are not as flat, and exhibit coarse material at the <br />surface support upland shrub communities. Riparian species are restricted to a very narrow <br />band, immediately adjacent to the channel. Monitoring Well A-7, located in the West Fork <br />alluvium near the mouth of the drainage shows average depth to water table of approximately <br />28.7 feet (28.7 feet in May 2006). Well A-8, located approximately 1 mile upstream from the <br />mouth shows average water table depth of 19.5 feet. These observations and data support the <br />conclusion that the native grasses on the West Fork alluvium are not subirrigated. <br />Although forage production is higher along the valley bottom than on adjacent upland slopes, the <br />increased production appears to be due to "run on" precipitation, and not due to surface or sub- <br />surface irrigation. The valley is contained within a larger rangeland "pasture unit", and is not <br />hayed, fenced, or otherwise developed or managed differently than surrounding uplands. <br />Due to the restricted width of the alluvial deposit along most of the reach, and the absence of <br />sub-irrigated or flood irrigated agricultural activity (current or historic), the Division has <br />determined that the West Fork of Good Spring Creek is not an alluvial valley floor, based on <br />geomorphic and land use criteria. <br />Wilson Creek (Middle Segment) <br />A segment of Wilson Creek approximately four miles in length within the Permit Revision 02 <br />expanded permit area was determined to be an alluvial valley floor during initial permitting of <br />the Colowyo Mine. However, in 1985, this segment of the Wilson Creek valley was altered by <br />severe erosion and mass wasting. The Division's July 1987 Renewal Findings states: <br />Proposed Decision and Findings of Compliance 14 September 2009 <br />Permit Renewal 05 Page 70