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Evaluation of Potential Subsidence Impacts of Longwall Mining in the Spruce Stomp Lease Area <br />to Aquatic Life and Water Supply <br />mobilization, transport or deposition of West Fork Terror Creek. While minor steepening or <br />flattening of the channel may occur and these changes will alter sheer stress, the stream is <br />already capable of transporting much of the sediment located between larger boulders. The <br />projected change in transported grain size is minimal. Also, following completion of the <br />Potential Project and establishment of equilibrium, the subsidence will result in a balanced net <br />change (steepened areas will be equal to flattened areas). Accordingly, reaches that may have <br />slightly more suspended sediment as a result of being steepened may be balanced by reaches that <br />would have slightly less suspended sediment as a result of being flattened. <br />The long -term impact to aquatic life resulting from minimal changes in water quality described <br />above would likely be masked by existing variability in TSS and turbidity. The scope of the <br />expected change is negligible compared to what is likely experienced by aquatic life during high <br />spring runoff conditions. Adverse impacts to aquatic life resulting from a deterioration of water <br />quality caused by channel profile changes are not expected. <br />6.1.4 Potential for New Fish Travel Barriers or Conduits <br />When the potential for new fish travel barriers or conduits is considered, it is important to note <br />that West Fork Terror Creek currently has barriers consisting of culverts with plunge pools. <br />These features create larger obstacles to fish travel than the Potential Project is expected to create <br />(e.g., steepened reaches). Further, GB- lineage cutthroat trout are present upstream, downstream <br />and within the Potential Project area. Based on these considerations, it is highly unlikely that the <br />Potential Project would result in a measureable increase in fish travel barriers nor would a new <br />travel conduit be formed that would allow fish to enter the Potential Project area where they had <br />previously been excluded. Adverse impacts to aquatic life resulting from new fish travel barriers <br />or conduits are not expected. <br />6.1.5 Potential for Impacts to Vegetation Community <br />Impacts to the vegetation community resulting from channel profile changes could occur if water <br />availability along the riparian corridor is significantly altered or if slope instability occurs. <br />Based on the magnitude of slope changes, the wetted perimeter of West Fork Terror Creek is not <br />121 - 014.000 Wright Water Engineers, Inc. Page 23 <br />January 2013 <br />