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Otak <br /> Memorandum <br /> To: Rob Zuber, Hunter Ridley, and Russ Means, Colorado Division of Reclamation, Mining <br /> and Safety <br /> From: Chris Romeyn, PE, CFM (Sr. Water Resources Engineer) <br /> David Graff, PE (Sr. Structural Engineer) <br /> Copies: Ryan Duve, PE, Justin Scharton (City of Greeley), Bill Schenderlein, PE (Blue Earth <br /> Solutions, LLC) <br /> Date: April 26, 2024 <br /> Subject: Response to Comments from March 6, 2024, DRMS Memorandum: 25th Avenue Site <br /> (M-2002-020), TR-03, RDZ review of the riverbank stabilization design and applicant's <br /> adequacy responses <br /> Project No.: 020119.1300 <br /> In response to the memorandum dated March 6, 2024 from Colorado Division of Reclamation, Mining and <br /> Safety (DRMS) regarding the Poudre Ponds bank stabilization design, the following summarizes selected <br /> design calculations for the rockery walls. This analysis shows that the upper wall has a factor of safety <br /> against overturing of 15.6 and the lower wall has a factor of safety against overturing of 4.9. Otak <br /> assumes this response satisfies the requirements of the DRMS Adequacy Review, and no additional <br /> information will be required. <br /> It should be noted that modifications were made to the geometric calculations for the upper wall to <br /> estimate overturing forces more conservatively. This results in a slight decrease in the factor of safety <br /> from that reported in the Poudre Ponds Basis of Design Report. <br /> 1) Water pressure is not considered in Coulombs analysis, considering the following: <br /> a) There is a slurry cut-off wall located immediately to the south of the proposed project. This <br /> prevents any groundwater from seeping out of the ponds through the bank. <br /> b) The material along the bank is granular and free draining. When it is saturated, the river is at the <br /> same elevation as the groundwater in the bank. <br /> 2) The wall design spreadsheet was developed by Otak engineers. These calculations are based on <br /> methods outlined in the following sources: <br /> a) Mack, D.A., Sanders, S.H., Millhone, W.L., Fippin, R.L., and Kennedy, D.G. (2006) Rockery <br /> Design And Construction Guidelines. FHWA-CFL/TD-06-006. Lakewood, CO. <br /> b) Das, M.B. (2010) Principles of Geotechnical Engineering. 7th Edition, Cengage Learning, <br /> Stamford. <br /> 371 Centennial Parkway, Suite 210 1 Louisville, CO 80027 1 Phone 303.444.2073 1 otak.com <br /> o:Iproject120100120119b105 documentslworking fileslwnrlwall design120119b poudre ponds wall design memo 2024-04-26.docx <br />