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. ... <br />I would also recommend that this issue be revisited at the time of <br />raise 2 lift construction. The raise 2 lift will be founded on a <br />column of tails that will be considerably thicker than the raise 1 <br />foundation, and the potential for development of additional zones <br />of potentially liquefiable tailing exists. <br />Given the analysis presented in BMG's letter dated September 13, <br />1993, the Division need not require additional freeboard beyond <br />that originally required in the permit. <br />Composite Liner Installation <br />BMG's September 13, 1993 letter reports that composite liner is <br />currently being installed to the elevation of the embankment crest <br />at build out. The letter does not indicate to what eldvation the <br />drainage layer immediately above the liner will be condtructed at <br />this time. If the drainage layer is not going to be constructed to <br />the build-out elevation, the VLDPE liner may be exposed to ultra- <br />violet radiation for an inordinate period, if the drainage layer is <br />being constructed to the ultimate elevation, it will }lave to be <br />maintained such that its effectiveness as a drain is not <br />compromised by erosion or other degradation before it is covered by <br />tails. BMG should provide details on how the VLDPE liner and/or <br />the drainage layer will be protected while they are e~gposed, and <br />the protective measures and exposed liner condition should be <br />inspected during Division site visits. Also, BMG should provide <br />documentation of the QA/QC protocol followed during the liner <br />installation once work is completed (I believe that this is a <br />requirement of the approved permit). <br />cc: Jim Pendleton <br />