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Memo to Gregg Squire 3 March 13 2001 reclaimed pit floor or otherwise destabilize the liner. The Division suggests that the Applicant modify the reclamation plan to include keying the liner into the bedrock or provide a demonstration that the clay liner will not fail under the plan currently proposed. b) The application states that the depth to ground water in the area of the proposed pit is 12 to 1 S feet below ground surface. At these depths, ground water pressure is unlikely to destabilize the reclaimed pit slopes. However, the Division observed during the pre-operational inspection of the proposed Bonser Pit that the existing pond in the southwest comer of the site has a water surface only a few feet below the surrounding ground. The Division requests that the Applicant describe the basis for the determination that the water table is 12 to 1 S feet deep and provide any documentation (borehole logs, piezometer data, etc.) demonstrating the depth to ground water. A high water table at any location around the perimeter of the reclaimed pit could cause increased seepage into the pit, and potentially bulging or failure of the reclaimed pit slope. Mitigation for the effect of a high water table could be to buttress the slopes, install drainage facilities, or construct the slopes at a shallower angle. c) Even though the installation of a liner will limit ground water inflows to the reclaimed pit, the amount of water that will seep through the liner may be sufficient to create swampy ground. Swampy ground would not be suitable for the proposed post mining land use of cropland and may leach salts from the underlying compacted clay creating an alkali condition also unsuitable for cropland. Moreover, if floodwaters from the Big Thompson River were to spill into the pit with no facilities for pumping or otherwise removing the water back to the river, asemi-permanent lake would be created further compromising the lands use for crops. The Applicant must describe how seepage into the pit will be managed to prevent interference with the cropland use, and must describe how floodwater will be returned to the river or otherwise managed following a large flood. Similar to the aforementioned R&O Pit, a pond could be constructed in the pit floor and act as a sump to collect any ongoing seepage. For elimination of floodwaters, pumping would likely be required since drainage to the river by gravity does not appear to be feasible. d) The following list of items must be incorporated by the Applicant into the liner specifications: i) The liner soil will contain a minimum of 50 percent material passing the No. 200 sieve on a dry weight basis. ii) The liner soil will have a plasticity index of from ] 0 to 35 percent. iii) The percentage of gravel, defined as material retained on the No. 4 sieve, will not exceed 10 percent. iv) The liner soil will be compacted to a minimum of 95 percent maximum dry density as determined by the Standard Proctor (ASTM D698). v) No brush, roots, sod, frozen material, or other deleterious or unsuitable materials shall be incorporated into the fill. Fill shall not be placed upon frozen material. vi) If moisture conditioning is required to meet the moisture content specification, the added moisture shall be worked into the fill by harrowing or other means until a uniform distribution of moisture is obtained. vii) Compacted soil liner fill shall be protected from desiccation and from freezing. The finished soil liner will be covered as soon as practicable with the layer of overburden and