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~~ <br />.~ l.~ . <br /> <br /> I II II I II I II I IIII II I <br />STPTE OF COLORADO RiC HnRD D~. Gov orn or <br />DEPARTMENT OF NATURAL RESOURCES <br />D. Monte Pascoe, Executive Director <br />MIl~iED LAND RECLAMATION <br />423 Centennial Building, 1313 Sherman Street <br />Denver, Cotoratlo 60203 Tel. (3D3) 639-3567 <br />David C. Shelton <br />Director <br />April 2, 1981 <br />T0: Brian Munson <br />FROM: Richard Domingue <br />SUBJECT: The Rockcastle Company - Grassy Creek Mine - Sediment/Runoff <br />Control System Concerns <br />While the plan presented may be workable many of the requirements of Rule 4 <br />have not been addressed. Below is a list of concerns and regulation citations <br />which must be addressed by Rockcastle Company (RC) in order to judge the adequacy <br />of the sediment/runoff control plan. <br />1. Collection and Diversions Ditches: In order to fulfill the requirements of <br />4.05.3 RC must provide the following: <br />a) peak flow estimates and design recurrence intervals for all ditches <br />(4.05.3(1) and (2)), <br />b) design dimensions, drawings and estimates of velocity for all <br />ditches (4.05.3(6)) rip rap must be provided where ditch velocities are erosive, <br />and <br />c) sufficient information must be presented in order to check the <br />criteria generated in a and b above. <br />2. Sediment Ponds: In order to fulfill the requirements of 4.05.6 RC must <br />provide the following: <br />a) the method of pond dewatering as per Rule 4.05.6 (3)(c), <br />b) combination of principal and emergency spillways to discharge <br />the peak flow from the 25-year, 24-hour storm event. (4.05.6(3)(d)) In <br />order to present information adequate for a thorough review RC must: <br />I. give sufficient data for verification of peak flows estimate. <br />If Peak Flows in Colorado w/TR 55 methodology is used all parameters must be <br />shown, such as: <br />A. average watershed slope and correction factor, <br />B, basin shape correction, <br />C. hydrologic soil group, <br />D. vegetative/cover type, and <br />E. CN used. <br />II, Use correct method for sizing weir or spillway used. Do not <br />use Manning's equation. <br />