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• The Southfield drainage and sediment control network is designed to <br />function as the primary mitigation system to prevent significant impacts <br />on surface water quality. However, inherent in operation of the <br />sedimentation ponds is the potential for increases in TDS as runoff flows <br />are retained in the pond, evaporation occurs, and mineral constituents are <br />concentrated in the remaining retention volume. It is not anticipated <br />that operation of the sedimentation structures will generally cause <br />significant increases in TDS levels. This statement is based upon the <br />fact that most runoff occurs in response to snowmelt when ambient <br />temperatures and consequent evaporation are low. In addition, runoff <br />volumes are limited by upstream diversion of runoff from undisturbed <br />areas, the limited disturbance area, and ongoing reclamation of <br />disturbance areas. EFCI will monitor all discharges from sedimentation <br />structures to ensure compliance with NPDES requirements. If problems are <br />noted with TDS or any other discharge constituent, EFCI will initiate <br />measures as appropriate to effectively control and mitigate the problem. <br />• EfCI's existing and future mining, processing, and loadout operations have <br />the potential to effect groundwater quality by modifying groundwater <br />chemistry, altering pH, and increasing concentrations of TDS and specific <br />chemical constituents. Specific activities which may potentially impact <br />groundwater quality include the following: <br />o Exploration Drilling <br />o Underground Coal Removal <br />o Surface Placement of Coal and Coal Refuse <br />o Retention of Drainage in Sedimentation Pond Structures <br />Of these potential impact mechanisms, coal removal is the most significant <br />since it will result in localized changes in the piezometric surface, <br />create a large void space which will gradually fill with water, and expose <br />coal and overburden materials to oxidation and subsequent groundwater <br />leaching. <br />• As previously noted, EFCI has incorporated a number of control and <br />mitigation measures in mining, processing, and reclamation plans to <br />effectively prevent or minimize significant groundwater quality impacts. <br />2.05.6-21 <br />