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<br /> <br /> <br />stockpile area and receipt of a determination of revegetation success, <br />Sedimentation Pond No. 4 will be reclaimed and discharge from the <br />permanent collection ditches will be routed to lower Newlin Creek through <br />the reclaimed pond area. <br />Existing permanent diversions are shown on the Mine Area Surface and <br />Groundwater Hydrology Map, (Map 12), Drainage and Sediment Control Map, <br />(Map 20), and are reflected in the post-mining configuration illustrated <br />by the Mine Area Post-Mining Topography Map, (Map 28). Supporting <br />calculations and a discussion of design methodology for permanent <br />diversion structures is presented in Exhibit 19, Drainage and Sediment <br />Control Plan. <br />Both temporary and permanent diversions, as described in this section, <br />have been designed and constructed to minimize potential contributions of <br />suspended solids to surface water flows. These diversion structures have <br />been constructed with the minimum allowable gradient given the topographic <br />configuration, and channel configuration and lining reflect erosion <br />control considerations as dictated by calculated flow velocities. It <br />should be noted that all of the existing diversion ditches, with the <br />exception of the recently reconstructed refuse pile collection and <br />diversion ditches have been in place a minimum of five (5) years. To <br />date, there is no evidence of any significant erosion, and comparison of <br />overland flows and discharge to sedimentation ponds does not indicate any <br />significant increase in suspended solids as a result of flow routing <br />through the diversion ditches. <br />No landslides or other areas of surface instability are known to exist in <br />the mine and loadout disturbance areas. Existing diversions generally <br />conform to natural drainage patterns and none are located where they might <br />increase the potential for landslides or other surface instability. The <br />access road collection ditch is located ad,~acent to the permanent coal <br />refuse stockpile. This ditch drains a very limited area, essentially <br />consisting of the access road and related disturbance. Potential flow <br />4.05-9R Revised -November, 1990 <br />