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R 21NCORPORATED GEORGE M.L. ROBINSON,P.G. <br />ENVIRONMENTAL AND ENGINEERING SERVICES <br />STRATEGICALLY POSITIONED-TECHNICALLY PREPARED ). ERICH RALIBERP.E. <br />April 11, 2011 RECEIVS0 <br />qPR APR 25 2011 <br />Mr. Wallace Erickson 0 d4r <br />p h9o ?0?J Di0sion of t ocla <br />Department of Natural Resources ;?i? of F0/ Mining oration, <br />Division of Reclamation Mining and Safety ?g C? OC,/ p>fi- and Safety <br />1313 Sherman Street, Suite 215 ??61 ey 6 <br />Denver, Colorado 80203 <br />Re: May Day and Idaho Mill Complex ,General Stormwater Comments, Permit No. M- <br />1981-18?"/CN-01 ". <br />Dear Mr. Erickson, <br />The following responds to the March 1, 2011 adequacy memorandum prepared by Mr. Tim <br />Cazier, P.E. R Squared has formatted the letter respond directly to each question raised by Mr. <br />Cazier. <br />Preliminary Adequacy Issues for General Stormwater Comments are summarized below. <br />Issue #1 <br />The Table SWMP 1 and Tables SWMP A through M comprise 97 pages. There is no narrative <br />describing the general approach to storm water control, hydrologic analyses, purpose of design <br />of hydraulic structures or rationale as to why drainage basins are delineated as shown in Figure <br />SWMP - 2. Please provide a narrative (possibly including an additional figure) describing the <br />rationale used for hydrologic parameters (such as curve number selection and precipitation <br />depths) and analysis methods (e.g., nomographs, TR-55, etc.) drainage basin delineation and <br />hydrologic routing method (if used) or combined drainage basins (if hydrologic routing was not <br />used), and a discussion on hydraulic structure design criteria such as Manning's roughness, <br />riprap sizing, and freeboard estimates; debris basin design; culvert design/analyses; energy <br />dissipation; diversion channel placement and design; erosion protection; etc. <br />Response #1 <br />The information requested by Mr. Cazier is included in the revised Stormwater <br />Management Plan See Exhibit T-4. <br />May Day Idaho Mine Complex 112(d) Permit Application <br />Revised: April 14, 2011 <br />"Strategically Positioned - Technically Prepared" <br />5555 DTC Parkway Suite A-4000, Greenwood Village, Colorado 80111 <br />Phone: (303)832-7664 1 Fax: (303)832-7469