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Michael Cunningham <br /> M-1977-300; Preliminary Adequacy Review <br /> Page 2 <br /> 4. Sheet 4. The features labeled as "Sheet Runoff energy Dissipators" must be re- <br /> designed as stormwater diversion channels with the capacity to safely convey <br /> the peak flow from the 100-year, 24-hour design precipitation event, with <br /> adequate freeboard. This channel design should include depth (with freeboard), <br /> side slopes, bottom width, riprap size and gradation. <br /> 5. Sheet 5. The following need clarification: <br /> a. The "Profile" for the Check Structure is too vague on what constitutes the <br /> "Buffer Zones". The 15-foot dimensions do not coincide with any visible <br /> feature in the detail. Please clarify the buffer zones. <br /> BUFFER ZONES <br /> RALSTON CR. <br /> w- <br /> tti <br /> PROF ILE <br /> I" = 20t <br /> b. Note 2 discusses "Riprap Slope Protection". However there is no <br /> gradation, size or even a detail as to how this riprap is to be constructed, <br /> only a vague location. Additional details for construction are necessary. <br /> c. Note 4: States "RIPRAP SHALL BE ANGULAR, DURABLE QUARRY ROCK MEETING THE <br /> FOLLOWING GRADATION:" No gradation is provided on the drawing. Please <br /> provide gradation for the riprap. <br /> d. The Division also has concerns with respect to the survivability of the <br /> check structures as presented. We strongly recommend following the <br /> Urban Drainage and Flood Control District's updated designs for grade <br /> control structures, which have been revised since 1983. <br /> Slope Stability: <br /> 6. The Division views the waste rock piles as critical structures as they are designed <br /> to keep waste rock out of Ralston Creek. Plates 12 and 13 prepared by McDermid <br /> Engr. Assoc. Inc. in February 1983 summarize slope stability analyses results. It <br /> appears only the cover stability and the contact with the native ground were <br /> analyzed as potential failure surfaces. The various strength parameters used for <br /> bedrock, alluvial soils and colluvial soils were obtained from simple soil testing <br /> and/or literature data. It does not appear that slope failure surfaces thought <br /> M•\Min\TC1\_Uranium\M-1977-300 Schwa rtzwalder\MAC-Memorandum-Stab_Wtr M-77-300-2016-07-27.docx <br />