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RULE 4 PERFORMANCE STANDARDS <br />4.05 HYDROLOGIC BALANCE <br />4.05.1 General Requirements <br />Please see Section 4.05.1 in Volume 1. <br />In addition to the mining, reclamation, and treatment methods referenced in this section, further <br />protection of the hydrologic balance will be established by an on-going plan for monitoring potential <br />changes in surface water quality and quantity and valley fill groundwater quality. This monitoring plan is <br />described under Section 4.05.13 and the monitoring locations are graphically shown on Map 1013. <br />4.05.2 Water Quality Standards and Effluent Limitations <br />Please see Section 4.05.2 in Volume 1. <br />4.05.3 Diversions and Conveyance of a Watershed Less than One Square Mile <br />The drainage and sediment control measures described under Section 2.05.6 and presented in the Erosion <br />and Sedimentation Control Plan will provide for clean water diversion of surface drainages within the <br />Collom Pit area, as needed for mine operations (please see Exhibit 7, Item 23, Part A) . A system of <br />clean water diversion ditches upslope from the mining activities will be constructed to divert surface <br />runoff away from the disturbed areas (Collom Pit). These temporary diversions will be constructed to <br />pass at a minimum the runoff from the precipitation event with a two-year recurrence interval. <br />Any topsoil stockpile areas that may be constructed outside the confines of engineered sediment control <br />structures will be required to have a perimeter ditch and berm constructed around the entire footprint of <br />the stockpile sufficient to capture and retain any rainwater/snowmelt that may be generated from the <br />stockpile area to preclude loss and/or contamination of the topsoil resource. A demonstration of the <br />effectiveness of sediment control structures to be constructed around several topsoil stockpiles planned <br />outside of primary sediment control may be found under Exhibit 7, Item 23, Part D. <br />4.05.4 Stream Channel Diversions (Relocation of Streams) <br />The drainage and sediment control measures described under Section 2.05.6 and presented in the Erosion <br />and Sedimentation Control Plan (Exhibit 7, Item 23) will provide for temporary diversion of surface <br />drainages within the permit area, as needed for mine operations. A system of temporary ditches will be <br />used to divert runoff from disturbed areas to sediment ponds. The natural drainage systems will be <br />restored to historic drainage patterns once diversion ditches are removed; therefore, there will be no <br />permanent diversions of these channels. <br />The only stream channel that will be impacted by the Collom Pit is the main stream of Little Collom <br />Gulch, an ephemeral stream draining less than one square mile at the upstream pit boundary. Clean water <br />diversions will be installed above the Collom Pit (Exhibit 7, Item 23, Part A) and will be removed as <br />mining progresses. It will also be channelized further downstream, alongside the haul road leading from <br />the Collom Pit to the spoil pile, where it drains greater than one square mile (Exhibit 7, Item 2, Part B). <br />4.05.5 Sediment Control Measures <br />Sediment control measures to be implemented are shown in Exhibit 7, Item 23 Erosion and Sedimentation <br />Control Plan, and postmining channels are shown on Map 41 B. These facilities, consisting primarily of <br />Collom — Rule 4, Page 4 Revision Date: 3/3/16 <br />Revision No.: TR -108 <br />