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Sctlivt - 2.05.6 <br />significant changes in water chemistry for the receiving drainages. In addition, disturbed area runoff <br />and any mine water discharge flows will be buffered by significantly greater volumes of normal runoff <br />from undisttu-bed drainage basin areas. <br />Contact between disturbed area runoff and surficial materials exposed to weathering and oxidation, <br />drainage f tom coal stockpiles and mine development wazte disposal areas, and any discharge of excess <br />mine drainage flows may result in increazes in TDS and individual chemical constituents in surface <br />runoff flows. In addition, one of the natural consequences of surface disturbance and any associated <br />minor erosion will be increases in sediment loading and TSS levels for the disturbed area runoff. <br />Surface water in the mine area is generally neutral to moderately alkaline with elevated levek of TDS, <br />TSS, and iron. Muting and related activities will probably not result in any significant change in <br />surface water pH although TDS and TSS levels may increase slightly in the disturbed area runoff and <br />any mine water discharge. The same considerations and mitigation meazures previouslydiscussed for <br />potential changes in surface water chemistry are ako applicable for potential increazes in TDS and <br />individual chemical constituents. <br />Potential increases in TSS levels will be effectively addressed on a short-term basis by establishment <br />and operation of the drainage and sediment control system, control of any necessary mine water <br />discharge, the rue of large-capacity underground retention sumps, and compliance tinder the required <br />CDPS perrnirs with applicable monitoring requirements and discharge effluent limitations. <br />Reclamation and restoration of effective surface drainage conditions will address all potential mining <br />and related stuface water impacts over the long-term <br />OMI or its predecessors have previously placed approximately 1,450 feet of 9-foot diameter culvert <br />through the Elk Creek Support Facilities area to safely carry Elk Creek through this area and to isolate <br />the creek from potential mitring-related impacu. OMI will culvert two additional segments totaling <br />• an additional 1,600 feet of the creek to safely carry the creek under portions of the Elk Creek Mute <br />portal benches and ~*+~n~**+~~P potential long-term mtnutg-related impacts. Culverting and diversron <br />may temporarily effett stream Rows during construction, and construction activities may result in <br />increases in sediment contributions both during construction and for a short period of time following <br />diversion of flows az the new channel segment stabilizes under varying flow conditions. <br />OMI will effectively min~m~~r the impacts to stream Rows and sedimentation by scheduling culvert <br />placement, removal, and stream channel restoration during seazonal low flow conditions, if feasible; <br />utilizing siltation fences to minimi~p potential sediment contributions both during and following <br />construction; extensive rue of riprap and other erosion control rnateriak in both the channel and <br />adjacent bank areas; and, revegetating all constnrction disturbance areas. <br />OMI u progressively constructing a permanent mine developtnen[ waste pile in the fast ephemeral <br />drainage west of Elk Creek and may, dependent on total development waste disposal requirernenu, <br />develop one or more additional similar waztepile areas in the future. Pile construction blocks normal <br />flow through the existing ephemeral channel, associated disturbance may change surface runoff <br />conditioru and result in additional sediment contributions, and leaching of infiltration through the <br />waztepile may result in changes in water chemistryand specific chemical constituents. <br />Waste pile design and construction incorporates upgradient diversions to intercept and divert normal <br />flows arotmd the pile; grading of pile fotrndation areas, active pile benches, and bench ouulopes to <br />effectively control drainage and rnuutrrize erosion; constnrction of a sedimentation pond <br />downgradient of the pile disturbance; installation of an underdrain to intercept and route any ground <br />water or infiltration to the sedimentation pond; and progressive reclamation of pile benches and <br />outslopes az theyare completed. <br />• Diversion of normal flows will prevent anysignificant reduction in flow contributions to the receiving <br />drainage. For perspective, it should be noted that monitoring of most of the ephemeral drainages in <br />the area over a period of several years haz not resulted in detection of any measurable flows. The <br />PR04 2.05-93 Revised August 2000 <br />