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<br />The applicant also considered the runoff estimated from the mine area under <br />"fair hydrologic" conditions. This condition may exist in areas that are <br />compacted with no vegetative cover, such a haul roads. The results of the <br />study showed a runoff depth of 0.07 inches or 4.8 acre-feet for the 1,675 acre <br />mine plan area. Since runoff could occur in areas of "poor" or "fair <br />hydrologic" condition the applicant has constructed two sedimentation ponds on <br />the east edge of the permit area. Pond volumes have been designed to contain <br />ttie 10-year event plus three years of sediment storage. Sediment production <br />estimates were made using the Universal Soil Loss Equation considering a <br />worst-case area of disturbance. <br />On June 27 the Division approved a technical revision to abandon Sediment Pond <br />No. 1 and direct all runoff from its drainage area to Sediment Pond No. 2. <br />This revision was requested because both ponds, as built, were oversized and <br />the surface area of Sediment Pond No. 1 was needed for additional coal <br />storage. Sediment Pond No. 2 is sufficiently sized to handle a 10-year, <br />24-hour precipitation event for the combined drainage areas. <br />Concerns for drainage and sediment control in the permit area have been <br />adequately addressed by the applicant. A small corridor, approximately 37 <br />acres exists between the north edge of B-Pit and the north property line <br />(Extension Area). It is expected that all runoff will enter Sediment Pond No. <br />2. The capacity of Sediment Pond No. 2 will still not be exceeded: No <br />additional drainage and sediment controls are needed for the 233 acre permit <br />extension. Sediment Pond No. 2 will provide all the storage capacity for a <br />24-hour, 25-year storm and the blow sand bottom has been approved as the <br />dewatering device for any runoff that is stored temporarily. Any water that <br />collects in B-Pit will be directed to sumps in the pit and either allowed to <br />evaporate or be used for dust suppression on the roads as is presently being <br />done. <br />Should a storm produce overland flow, the runoff will exit the proposed mine <br />area in a distributed manner, and not as concentrated flow in drainage <br />channels. It would be difficult to appropriately arrange site detention ponds <br />unless channels were constructed to collect and direct runoff to Sediment Pond <br />No. 2. Because of the numerous "blowouts" and other small depressions, the <br />lack of well defined drainage channels, and the highly permeable top-sand, it <br />is likely that the estimate of 9.8 acre feet of surface runoff using the SCS <br />method is higher will occur. <br />Several variances for sediment and drainage control were granted during the <br />initial 5-year permit term. A variance from the dewatering device requirement <br />of Rule 4.05.6(3)(c) was granted since the sediment ponds are built on highly <br />permeable blow sands which allow the water to percolate through the bottom and <br />sides of the pond. A variance from sediment control was also granted on <br />certain reclaimed areas south of the initial spoil pile to the active pit <br />area. The variance to Rule 4.05.2(3) was granted based on the finding that <br />runoff will not be generated from the area and therefore, sediment ponds are <br />not needed to meet the effluent limitations of Rule 4.05.2 or applicable State <br />and Federal water quality requirements. Based on site inspections during the <br />past 5-year period by Division inspectors, the Division concurs with these <br />variances and proposes that they be continued during the next 5-year term. <br />-14- <br />