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Appendix K-5 <br />• order to accommodate the current pit ash disposal and backfilling operations. The proposed <br />final elevation contours were sloped to provide maximum air space volumes for the remaining <br />ash disposal operations in each cell, as well as to reduce the potential amounts of surface water <br />runoff infiltration into the subsurface and the potential accumulation of infiltrated water within <br />the pits and/or saturation of the disposed ash. (Ash disposal is now complete in A-Pit and <br />only final reclamation remains at it's location.) The revised designs overall also serve to <br />improve the final reclamation condition of the two disposal sites. CEC feels that this is good <br />business practice now that mining is no longer taking place and since ash disposal will <br />continue through several future years. <br />All standing water accumulation in the former mined A- and B-Pits, except for the surface <br />water runoff which either has evaporated or infiltrated into the subsurface, has been eliminated <br />and the pit sumps have been backfilled. Due to the deep eolian sand deposits over the CEC <br />site and the sand's high infiltration characteristics at this site, there are significant losses to <br />• deep percolation of rainfall during major storm events. <br />Surface Water Runoff Calculations <br />In 1994, Industrial Compliance (now BE&IVTerranext) completed an initial drainage study for <br />the CEC site, in which the site hydrology was updated (refer to "Technical Revision Drainage <br />Control Plan II," dated June, 1994). Later on, a design re-evaluation of the existing Sediment <br />Pond 2 and the subsequent enlargement of that facility to accommodate a 10-year, 24-hour <br />design storm event was made by BE&IUTerranext, as directed by CDMG (refer to Appendix <br />A in "Technical Revision Drainage Control Plan II," dated November, 1994). <br />During a prolonged period of observed significant rainfall runoff accumulations and the overall <br />general heavy precipitation amounts measured on site by CEC personnel during early to mid <br />1995, the Sediment Pond 2 facility did not experience any flows through the spillway section <br />• <br />2 <br />BEAK/TerraNeXt <br />