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West Elk Mine <br />surfaces covered with residuum, mud flows or debris flows, as well as highland azeas underlain by <br />bedrock and covered by residual weathered material or material deposited by sheet wash, rillwash, <br />or wind. <br />Public Law 95-87 states, in Section 701.1, that "Alluvial Valley Floors" means the unconsolidated <br />stream-laided deposits holding streams where water availability is sufficient for subirrigation or <br />flood irrigation agricultural activities but does not include upland areas which aze generally overlain <br />by a thin veneer of colluvial deposits composed chiefly of debris from sheet erosion, deposits by <br />unconcentrated runoff or slope wash, together with talus, other mass movement accumulation and <br />wind-blown deposits. <br />30 CFR, Chapter VII, Subchapter A, Part 701.5 states that "Alluvial Valley Floors" means the <br />unconsolidated stream-laid deposits holding streams with water availability sufficient for <br />subimga6on or flood irrigation agricultural activities but does not include upland azeas which are <br />generally overlain by a thin veneer of colluvial deposits composed chiefly of debris from sheet <br />erosion, deposits formed by unconcentrated runoff or slope wash, together with talus, or other mass <br />movement accumulations, and wind-blown deposits; and "Upland Areas" means, with -respect to <br />Alluvial Valley Floors, those geomorphic features located outside the flood plain and the terrace <br />complex, such as isolated higher terraces, alluvial fans, pediment surfaces, landslide deposits, and <br />surfaces covered with residuum, mud flows or debris flows, as well as highland azeas underlain by <br />bedrock and covered by residual weathered material or debris deposited by sheet wash, rillwash, or <br />wind-blown material. <br />• On the basis of the statutes and regulations, the primary consideration in the AVF investigation is <br />the identification of unconsolidated stream-laid deposits (alluvial deposits). Furthermore, these <br />deposits should be located within the valley floor and should not include isolated high terraces, <br />alluvial fans, or landslide deposits. Once alluvial valley floor deposits aze identified, then the <br />capability to support flood irrigated or subirrigated agricultural activities must be assessed. <br />Identification of locations where unconsolidated stream-laid deposits might occur was performed <br />by analyzing aerial photographs of the mine permit azea and adjacent azeas. A break in valley sides <br />slope and an identifiable valley floor served as the primary criteria for selecting possible alluvial <br />deposits. These potential alluvial deposits locations have been mapped and the surface area <br />calculated (Table 65). <br />From a geomorphic standpoint, the rugged mountainous terrain of the mine permit site has resulted <br />in drainages still in a youthful stage of development. The streams aze confined in narrow, steep- <br />sided, V-shaped valleys with generally steep channel gradients. This is in direct contrast to the <br />broader flood plain type valleys found at lower elevations. Meanders, normally associated with <br />AVF development, aze absent. Generally, the streams aze actively downcutting with the exception <br />of the reaches above the Minnesota and Beaver Reservoirs. For these stream reaches, erosional <br />downcutting has been curtailed by the change in base level these reservoirs represent. <br /> <br />2.Ob3 Revised June 2005 PR10; Rev. March 1006 <br />