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ID: .. ~ ' . Memo to Berhan Raffelev Cresson Miae dSOTBX / LIFT Revisions page 2 RUG 16'95 9:54 No .003 P.02 material be 100 passing the 12" screen and lase than (ii' passing the No. 200 sieve. insufficient information was provided to allow mo to render an opinion concerning this F~roposa].. No gradation was provided £or the underdrain material. Is 7.ISSC-4 being proposed as a spec for a revised 9eomembzane bedding material "mixture"? we will need a spec for this material. How ie it to be prepared to secs*nplish consistent gradation? It will need to be verified and certified during construction. Will invasion occur if these two materials are in contact.? If so, I have never bean a proponent of geotextile ae a surrogate for e Terzaghi graded filter la}•er. Subsequent to our teleconference, CC&VG submitted a supplemental response to my concerns,in which they modified their request. In hie August 12, 1995 "Re-Revision of Underdrain Layer Sequence", John Hardaway rescinds the proposal to place the geot'ext.ile between the underdrain 12- inch mir,ue and the select fill material, Further they propose to place the geotextile immediately beneath the geomembrane, asp originally prropoeed, with L-he following modification. The geotextile will only extend to 20 feet outside the underdrain 12-inch minus material, rather than 40 feet, and the geotextile and geomembrane will be le~.atered to the geomembrane at the boundary of the underdrain, rather than sewed. John Hardaway's justification for both these changes, ' with which I agree, is that "once outside the area of the underdrain rock fill itself, the pOteritial for migration of the select structural fill is eliminated and, therefore, the ~ need for the geometnbrane to flex in rtsponee to such migration `'p is elitninat®d and the need for cushioning is thereby reduced". A~ ~ I continue to be concerned regarding the actual s12e gradation ,~" of the "mixed" select fill material now being planed. Ie cc&vG proposing a gradation change for this select fill `~iia material? Ia II88C-4 being proposed as a spec for a revised ~ select till material "mixture"? How is this hybrid material N~ to be prepared to accomplish eonsiotent gradation? a ;2) "Placement of Carlton Mill Tailing Material in Arequa Gulc ~- Lift Thickness" Briefly summarized, this revision application requests an increase in Carlton Mill 'railings placement lift thickness specification from a maximum of 1e inches to a maximum of 7 feat. Go18er reports conductingt.reneh density determinations in a test 10-thick lift "compacted with one pass of ~3 SSt l Nu