2008-08-11_REVISION - C1992080 (19)

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known as the Animas River Alluvial Valley Floor located outside the permit area on the Animas River flowing through Durango, Colorado. Upland Terrace Deposits The upland terrace deposits adjacent to and within the permit area of the mine consist of unconsolidated stream laid deposits laid down by the Animas River when it flowed 400 feet higher than its present level. However, there is insufficient surface water to sustain irrigation of the terrace deposits. Regionally, these types of terraces are not irrigated, and are primarily used for the production of dryland wheat. The potential for flood irrigating these upland terraces using Animas River water is not feasible, given the length of the canal needed and the fact that a canal would have to flow through the city of Durango, Colorado. The coarser gravels at the base of these deposits act as an underdrain and prevent subirrigation. Since the terraces are not capable of irrigation or subirrigation, the Division finds that the upland terrace deposits do not constitute an AVE The Stream Valley in Carbon Junction Canyon Much of the stream valley of Carbon Junction Canyon flows over sandstone bedrock. Alluvial deposits in this canyon are less than 50 feet wide and 10 acres in extent. Alluvial deposits of such limited extent are not considered substantial enough to support agricultural activities. Therefore, the stream valley in Carbon Junction Canyon does not contain an AVE The Animas River Valley Within Two Miles of the Mining Operation The Division has determined that the alluvial deposits and terraces directly adjacent to the Animas River constitute an alluvial valley floor. The unconsolidated stream laid deposits have the potential for flood and subirrigation. These alluvial deposits are flood irrigated south and north of the confluence of Carbon Junction Canyon with the Animas River. The applicant has given the Division little information on subirrigation of the alluvium and lower terrace deposits; however, the Division has made a worst-case assumption that the deposits are subirrigated and therefore constitute an AVE Alluvial Valley Floor Findings 1. Rule 2.06.8(S)(a)(i)(A)(D The Carbon Junction Mine will not mine within the Animas River alluvial valley floor or have surface mining facilities located on the alluvial valley floor. Therefore, the mining operation will not interrupt, discontinue, or preclude farming on the alluvial valley floor. 2. Rule 2.06.8(S)(a i)A)(ll) The mining operation will impact the quantity and quality of water tributary to the Animas River alluvial valley floor. However, the impacts to the quality and quantity of water will be insignificant and not cause material damage to the surface and ground water systems supplying the alluvial valley floor. 16