GENERAL30783 - Laserfiche WebLink

Home Browse Search

practiced on the flood plain. The potential for hydrologic impacts to the Williams Fork River AVF is negligible and is further discussed later in this document. Description of Applicant's Proposal The applicant does not propose to physically disturb any areas underlain by unconsolidated streamlaid deposits. All areas that meet the geomorphic criteria of an AVF are located either downstream of the mine or on the other side of a drainage divide. There is a slight potential for the quality of water supplied to the AVFs to be degraded as a result of mining. This is discussed in the following section. Discussion of Potential Impacts to AV Fs The only AVFs identified in the vicinity of the Trapper Mine are the Yampa River, the Williams Fork River, and Flume Gulch. The potential for each of these to be impacted by the proposed mining operations will be discussed next. The potential for the Yampa River AVF to be impacted by the proposed mining operations is negligible. The applicant has presented justifications for this conclusion on page 2-533 of the permit application. Generally, the Yampa River AVF receives very little of its water supply (both ground water and surface water) from the proposed mine area. The majority of the flow in the river and the alluvial aquifer comes from the headwater portions of the drainage. The applicant states that the contribution of surface water from the Trapper Mine is insignificant and is estimated at 0.07 cfs/mil. Further, the ground water contribution to the base flow of the Yampa River is undetectable. This is substantiated by seepage, runoff and potentiometric studies (see Appendix Hof the permit application) which basically show the following: (1) The Yampa River loses surface water flow to the alluvial aquifer as it flows past the mine are, and (2) The Yampa alluvial aquifer is hydraulically isolated from the bedrock aquifer of the Williams Fork Formation. In addition, all disturbance related to the mine is located at least one mile from the southern boundary of the Yampa River AYF. Therefore, it is very unlikely that the Yampa P.iver AVF will be impacted by the proposed mining operation. The potential for the Williams Fork River AVF to be impacted by the proposed Trapper mining operation is also negligible. The Williams Fork River is located on the opposite side of a major drainage divide from the Trapper Mine. A11 ground water flow is towards the Yampa River. All surface water flow except for 98 acres is also towards the Yampa River. This 98 acres is in Elk and Ute Gulch drainages of the Williams Fork drainage basin. These drainages are controlled by sediment ponds and will not degrade the Williams Fork River. An additional 25 acres is proposed to drain into the Deer Gulch during this permit term, also tributary to the Williams Fork. This flow is controlled by a sediment pond and will not degrade the Williams Fork. Therefore, the Williams Fork AVF should not be impacted by the proposed mining operation. _1 g_