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1110. IIIICI] 0.1C ]~~V nii vii riuya ~ .. ...... .. .... ... ...- ~_ application. Design information for the channels is included in Exhibit 7 (4.05.4(2)(0.)). D. Sedimentation Ponds 1. Six sediment ponds are in place as approved by the Division antl have been treating disturbed area surface water runoff during the past two permit terms. These are the Streeter Gulch Pond, Work Area Pond, Gulch A Pond, Loadout Pond, Stoker Pond and Railway Loop Pond. Two new ponds are proposed, Prospect and West Pit Ponds, to treat runoff from the proposed new mining areas. Designs for these ponds are included in Exhibit 7, and locations of the ponds are shown on Map 37. During the Division's adequacy review of this permit revision (PR-O1), questions regarding modeling assumptions used to design these two sediment ponds were raised. The applicant has committed to re-evaluating the modeling methodology by August 31, 1992. The only hydrologic structures to be built during that time are the Prospect Pond and a portion of the South Collection Ditch. These structures are adequately sized to treat any additional runoff from disturbance to be created during the next year. Should modifications be -16- I~ ~~ required following re-evaluation of the hydrologic modeling, they can be implemented by modifying structures or building additional structures. E. Acid-forming and Toxic-forming Spoil Overburden sampling and regraded spoil sampling plans were approved for the East Pit and Section 11 Pit during the first two permit terms. These plans are discussed in Exhibit G and Section 2.05 of the permit application. Results from past sampling are included in the mine's Annual Reclamation Reports. These programs were instituted primarily due to concerns about high sodium adsorption ratios (SAR) in some over- and interburden materials. Analogous sampling will be performed in the West Pit and Section 16 Pit. Sampling during the past nine years of the upper and lower Y seam overburden in the East Pit has encountered only one sample with a suspect SAR value. Approximately seven percent of the overburden samples in the Section 11 Pit have had suspect SAR values. Only one of 99 samples of regraded spoils has had a suspect SAR value. One sample of regraded spoil is collected for each five acres of reclaimed area. No evidence of toxic effects to vegetation on reclaimed areas has been reported to date on the mine site (4.05.8). F. Impoundments