2012-01-06_PERMIT FILE - C1982057A (4)

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• will be certain short-term impacts to the channel reach below the structure. Sediment loads will temporarily increase as the active channel widens in response to increased runoff potential, Revegetation of the removed embankment and pond area will provide stability during the readjustment period of the active channel. The frequency of the larger runoff events will dictate how fast the channels reestablish to quasi equilibrium with the fluvial system in this tributary to Sage Creek. The impacts of the 009 pond following its removal will last a relatively short time until the active channel readjusts, and reclamation efforts within the removed embankment and ponding area will greatly assist in minimizing these impacts. An alluvial valley floor (AVF) analysis of Dry Creek and Sage Creek was performed and the results of the analysis are presented in Tab 76, Protection of the Hydrologic Balance. The analysis determined that only small areas within each drainage that are limited in extent satisfy requirements for designating areas as AVF`s. Significant observations made in the analysis included the determination that increases in receiving stream water quality (Dry and Sage Creeks) resulting from pond discharges greatly influenced by spoil water chemistry will not significantly affect any existing and potential use of these waters for flood irrigation. In fact, the presence of saline seeps in the lower portions of each drainage will mask any increases in TDS resulting from pond discharges from the Seneca II-W Mine. Discharges from the ponds will likely serve to slightly increase basef low magnitudes and durations; however, due to the incised nature of the stream channels downstream along both drainages, slight increases in basef low will not improve any potential for flood irrigation. Finally, most of the small areas which can be characterized as AVF's within both drainages do not presently depend upon direct diversion of water from either Dry or Sage Creeks, with the exception of small areas in lower Dry Creek (Sections 22 and 10, T6N, RBllw). A previous section within this Tab titled "Potential Impact of Replaced Spoil on Surface Yla ter Ouality" discusses the potential impact of spoil water discharge on Dry Creek tributaries, Dry Creek, a tributary to Sage Creek, and Sage Creek. A mass balance approach was used to assess potential increases in chemical loads and TDS concentrations occurring from water that will discharge from replaced spoil material at the Seneca II-W Mine. The analysis assumed that spoil water will mix directly with surface rva ter flows in Dry Creek and Sage Creek. TDS and flow values used in the analyses were obtained from • monitoring records or reasonable estimates of chemical and flow parameters during the irrigation season (June through September). 59