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August 8, 1983 <br /> Project 116-1.4 <br /> - 7 - <br /> C. LEACHATE COLLECTION SYSTEM <br /> Paragraph 1 <br /> We have reviewed the gradation of the FMC waste with technical staff <br /> of FMC Corpation, Modesto. We find a complete range of grain sizes <br /> in the waste ranging from angstrom size units to approximately 1/4 <br /> inch particle diameter. Graded filter material can be expected to <br /> operate efficiently in only a portion of this range regardless of the <br /> gradation selected. For this reason, we have suggested the use of <br /> Caltrans, Class 2 Permeable Material as being the most versatile and <br /> efficient material while maintaining a relatively high degree of <br /> permeability. We can not submit calculations as requested, because <br /> the filter material selected will be effective only over a portion of <br /> the grain size ranges. We are informed however, that Class 2 <br /> Permeable is the most universally accepted material for use to <br /> prevent clogging of pipe perforations up to 3/16" diameter. <br /> Because it has a portion of the mix in the grain size between 3/8" <br /> and 1", we feel the density of this material would be suitable for <br /> the drainage blanket along the floor of the trench. This material <br /> has a greater capability of remaining in place when waste is unloaded <br /> as opposed to the suggested use of medium to coarse grained sand. <br /> Paragraph 2 <br /> Caps will be placed on the leachate collection sump pipe and the <br /> extended clean out pipes in the floor drains. These caps will prevent <br /> clogging during the filling operation and will be placed in a <br /> position where they are accessible for pipe clean out or leachate <br /> removal both during and after filling operations. <br /> Paragraph 4 <br /> We have discussed the comment in this paragraph with Mr. Gary Reents, <br /> California Department of Health Services, Hazardous Material <br /> Management Branch. We have informed Mr. Reentz that in no case has <br /> subsidence has never taken place over Group 1 Disposal Trenches 1, 2 <br /> or 3. In addition, we have submitted in previous paragraphs the <br /> strength characteristics and the resistence to crushing in the pipe <br /> material selected. The assessment of settlement and bearing capacity <br /> of the trench subsurface is not a concern. Settlement of subsurface <br /> soil or foundation failure could only occur if a portion of the <br /> trench were underlain by voids or if the trench floor contained no <br /> lateral support. <br /> GBeta Associates Q <br />