Laserfiche WebLink
Strliar ~ 2.05.6 <br />Approximately 1,450 feet of the lower portion of Elk Creek has been culverted to minimi~r tnining- <br />• related hydrologic irnpacu and facilitate development of required mine support facihties for this <br />portion of the Ells Creek channel. OMI will temporarily culvert two segmenu of Elk Geek totaling <br />an additional 1,600 feet of Elk Geek in the middle portion of Elk Creek Stream culverting is <br />designed to minim;~r mining-related impacts and accommodate construction of the required haul <br />road and portal benches for the Elk Creek Mme. The e.+osting and proposed stream culverting <br />activities fall under the jurisdiction of the US. Army Corps of Engineers (COE) and these activities <br />have been permitted under COE Nationwide 26 Permit Nos. 199675449 and 199975232. <br />A separate COE permit application was filed for stream culverting activities to be conducted in <br />conjunction with the Ells Creek Mme. Additional details on the culvert installation are provided in <br />Section 2.05.3, Ponds, Impoundments, and Diversions. Channel culverting may temporarily effett <br />stream flows during construction and construction, and stream restoration activities following culvert <br />removal may result in increases in sediment contributions. <br />Plaru for stream channel reconstruction following culvert removal as described in Section 2.05.3, <br />Ponds, Impoundments, and Diveaions, and Exhibit 2.05-E3, Drainage and Sediment Control Plan, <br />reflect specific design and operational mitigation measures to minimise potential flow and water <br />quality impacts. These mitigation measures include design of the culverted and subsequently <br />reestablished segments to be stable under all anticipated normal flow conditions, scheduling of <br />construction during the seasonal low flow period if feasible, utilization of site-specific altetxtative <br />sediment control measures to m;nimi~e potential sediment contributions both during and following <br />constmction, extensive use of riprap and other erosion control materials in both the channel and <br />adjacent bank areas, and plate for revegetation of all construction disturbance areas using adapted <br />riparian species and woodyplant species for stabiliTation and wildlife habitat enhancement. <br />• Surface placement of coal and mine development waste materials tray effect surface water quantity <br />and quality in several ways. Surface runof f from the related disturbance areas tray increase, resulting <br />in increased erosion and sediment loss, and surface flows may infiltrate through stockpiled materials <br />generating leachate with both sediment laden runoff and leachate potentially discharging to surface <br />drainages. leachate not collected by an underdrain system may impact ground water, which may later <br />discharge to sedimentation ponds or to the alluvial/colluvial aquifer. <br />Coal stockpile areas will be constmcted to provide effective drainage of both runoff from stockpile <br />surfaces and infiltration through the stockpiles. Designed ditches will collect and route nmoff from <br />coal stockpile areas to designed sedimentation ponds. The locations of the designed ditches and <br />sedimentation ponds are shown on the Drainage and Sediment Control Plan Map, (Map 2.05-M4) <br />and detailed design calculations are presented in Exhibit 2.05-E3, Drainage and Sediment Control <br />Plan. <br />Surface runoff from active developtnen[ waste placement areas will be controlled by site grading and <br />localized drainage control measures and by existing peanartent collection ditches in the mine <br />development waste pile areas. Upgradient drainage will be diverted around the waste pile areas and <br />active development waste bench areas will be graded to assure effective drainage off the pile. The <br />development waste pile ditches have been designed to pass the peak runoff resulting from a 100-yEaz, <br />24-hour storm event with a mimmnm freeboard of 1.0 foot. These ditches collect and route surface <br />runoff from the pile areas to sedimentation ponds for settlement of suspended solids and treatment if <br />necessary. The locations of the ditches and sedimentation ponds associated with mine development <br />waste piles are shown on the Drainage and Sediment Control Plan Map, (Map 2.05-M4) and detailed <br />design calculations are presented in Exhibit 2.05-E3, Drainage and Sediment Control Plan. <br />. Potential impacts of ground water leachate from the coal and mine development waste piles on the <br />surface water system are expected to be negligible because the volume of leachate will be effectively <br />minimised by the acid climate of this area, compaction and grading of coal and development waste <br />materiak, diversion of up-gradient drainage from undisturbed areas, and ongoing reclamation of <br />PR04 2.05-80 Revised August 2000 <br />