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S~ics: - 2.05.6 <br />measures and reclamation activities in mitigating potential impacts were considered in the assessment <br />of probable hydrologic impacts. The following sections present summary descriptions of the <br />probable hydrologic consequences of the previous and ongoing Somerset and Sanbom Creek Mme <br />operations and the planned Elk Creek Mute mining and related activities. <br />Potential Adverse Hydrologic Impacts, Control/Mitigation, and Effects -surface and ground <br />water hydrologic systems may potentially be impacted by Honing and related operations. These <br />impacts are not expected to be significant, will not effect either surface or groundwater users, and are <br />expected to be localized and temporary in nature. Operational mitigation measures and reclamation <br />of disturbance areas will result in effective restoration of surface and ground water conditions sirttilar <br />to those existing prior to initiation of OMI's mining and related disturbance. <br />OMI's planned mining and related activities have the potential to generate temporary impacts to <br />surface water resources. These impacts will typically be localized, being confined to those segments <br />of area drainages directly impacted by mining activities, although in some cases impacts tray have the <br />potential to also effect downstream drainage areas. The primary potential mining-related impacts on <br />surface water resources include: <br />• Temporary increases in nmoff from surface distwbance areas <br />• Mmor reductions in surface flows and alteration of surface flow panems due to <br />operation of sedimentation structures and flow reductions due to mine water supply <br />withdrawak <br />• Changes in surface water chemistry <br />• • Increases in the levels of TDS, TSS, and certain individual chemical constituents <br />• Permanent diversion and culverting of portions of the Elk Creek channel <br />• Permanent placement of mine development waste materials in one or more ephemeral <br />drainages <br />In general, probable hydrologic consequences for surface water resources resulting from OMI's <br />muting operations will be limited by the relatively small surface disturbance area, and will be <br />effectively mitigated by operation of the drainage and sediment control system and ultimate <br />reclamation o£ mine disturbance areas. Section 2.DSA, Reclamation Plan, outlines the extent of <br />proposed mining-related surface disturbance. Probable surface water impacu and their significance <br />relative to the hydrologic system are discussed in the following sections. <br />Existing and proposed new muting-related surface disturbance is limited to required mine surface <br />facilities areas and involves removal of vegetation and soil/substitute materials and grading of <br />disturbance areas for specific mining-related uses. These duttubance activities reduce infiltration <br />potential and evapotranspiration due to elimination of vegetation and generally increase surface <br />runoff and erosion potential For existing disturbance areas in Hubbard Creek and Beaz Creek <br />Canyons, the Elk Creek support facilities area, and those areas associated with the Sanbom Greek <br />Mme, these impacts have already occurred and runoff effects are ongoing. <br />OMI's primary drainage control practice is to effectively minimi~r, the area of surface disturbance by <br />keeping all surface facilities within a relatively limited area. Provisions for minimising mine-related <br />• surface disturbance are detailed in Section 2.05.3, Mme Facilities. In order to effectively conuol <br />erosron and increased runoff from those areas which are disturbed, OMI diverts runoff from <br />undisturbed upgradient areas around areas of disturbance; grades disturbance areas to min'mnp <br />runoff and erosion; controls surface flow velocities through temporary revegetation and the use of <br />PR04 2.05-89 Revised August 2000 <br />