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J Birds Mine — Comments to Revised Spillway Design <br />Page 2 <br />February 21, 2012 <br />addressing the shear stress on the 1 -Y2 inch D50 riprap. Please provide this <br />demonstration. <br />B. DRMS appreciates the inclusion of the granular filter option. We cannot evaluate the <br />adequacy of the proposed granular filter without grain size distributions for the <br />embankment material and the proposed 6- and 9 -inch riprap gradations. DRMS can <br />provide design guidelines for granular filters if the Applicant requests them. However, <br />we cannot assess the adequacy of the proposed bedding without this information. Please <br />submit gradations for all three materials for filter evaluation. <br />DRMS is considering allowing the use of a geotextile filter with this second stipulation: <br />2. If subsequent inspections reveal any sign of failure (including geotextile degradation <br />and /or riprap displacement on the geotextile), the spillway will have to be replaced with <br />suitably approved materials. This will require a Technical Revision (TR) to show the <br />replacement materials are suitable for permanent placement and no release of the site can <br />be considered until corrected. <br />If either you or the applicants have any questions regarding the comments above, please call me <br />at (303) 866 -3567, extension 8169. <br />m: rnin\tc11m- 2005 -050 jbirds\ stormwateroomments _mem21feb12.docx <br />