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205 Tunnel Drive Canon City, CO 81212 <br />719-269-1173 719-269-1148 (Fax) <br />Equal Opportunity Employer <br />July 11, 2017 <br />Mr. Tim Cazier, P.E. <br />Environmental Protection Specialist <br />Colorado Division of Reclamation, Mining and Safety <br />1313 Sherman Street, RM. 215 <br />Denver, CO 80203 <br />RE: T.H.E. Aggregate Source, Permit M-1977-193 <br />Response to Division Preliminary Adequacy Review, Technical Revision TR -09 <br />Tezak Heavy Equipment has considered the Division's comments in their April 131 <br />letter and has revised the TR plan to address reviewer's concerns regarding ditch <br />parameters and clarifies some of the details of hydraulic consideration. <br />1) Hydrologic Balance and Erosion Control. <br />a., b. The geometry of the fines stockpile structure has been modified from the original <br />design to a broader footprint (app. 100) along an eastward trending line (cross section <br />B -B) and (app. 50) along a northeast trending axis of the structure. The result is less <br />severe turning radii of the lower ditch which will receive the largest potential loading and <br />which was used for ditch capacity calculations included with this mailing. The largest <br />possible drainage area above the lowest ditch was used for Q100 output with no <br />absorption adjustment resulting in 100% of potential storm delivery to the ditch. Depth <br />of ditch will be revised to 1.5'from the originally proposed 1'to insure adequate <br />freeboard at the outside curves. Tezak Heavy Equipment feels that a 1 % gradient on <br />the ditches is sufficient to maintain a reasonable level of self-cleaning while minimizing <br />the potential for higher flow velocities. Tezak Heavy Equipment has seriously <br />considered the Division's comment regarding increasing the ditch gradient but has <br />decided that peak flow containment can best be addressed by keeping flow velocities as <br />low as possible while maintaining open channel flow. Increasing the depth of the ditch <br />as well as increasing the turn radii as much as possible certainly will help to mitigate <br />potential for overtopping the outside freeboard capacity. <br />