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Knight Piesold eora•u~rrro Mr. Steve Onorofskie Centex Eagle Gypsum Company LLC J January 19, 2001 8. Sediment Stornge and Removal: Removal of the deposited sediment from the sediment control ponds is of paramount importance to ensure maximum efficiency of the ponds; since the ponds operate most effectively with little or no deposited sediment, frequent and thorough maintenance beyond the following recommendations may be necessary. Given the high erodibility of the area soils, the deposited sediment should be excavated from the ponds on a regular basis, approximately twice per year. Also, the ponds should be examined and if necessary, maintained and/or excavated following each major storm event. In addition to these maintenance schedules, [he ponds should be regularly examined and maintained to ensure that the deposited sediment does no[ accumulate to within 1.5 feet of the top of the perforated riser. 9. Vnlley Fill Waste Rock Disposed: There are a number of factors that contribute to the inherent stability of the valley fill waste rock disposal facility, especially with respect to drainage; • The waste material itself consists of clastic sediments comprised of shale and sandstone that occur in lenses in the ore body; anhydrite encountered is not wasted and is blended into the wallboard plant feedstock; • The existing mining operation has utilized valley fill construction techniques for long term storage of this material for the last 10 years without a single incident or indication of slope instability; • The haul road surfaces and road fills leading to the existing pit are constructed of this waste material which has shown to be stable; • The waste material is excavated using a ro[o-milling machine and is typically granular in nature and is therefore well-drained; • The valley fill will be constructed at nearly the head of the drainage so the watershed above the site is relatively small, much smaller than the watersheds above current waste disposal areas that have been in place for a decade; • There is no evidence of ground water seepage in the valley fill site; and • The end dumping of mine waste results in some particle size segregation so that coarse-grained materials collect at the toe of the slope, automatically creating a drainage layer at the bottom of the waste mass. In the unlikely event that wet areas are encountered during topsoil salvage efforts in the waste disposal area, or if any signs of instability due to a lack of drainage are observed, \\FS]\GILLIGAN\t6005\1645A\NP\5\ale response Coc