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-~ <br />PICKETT <br />ENGINEERING, INC. <br />April 20, 2001 <br />RECEBVE® <br />Erica Crosby APR 2 3 2001 <br />Division of Minerals and Geology Division of Minerals and Geology <br />Department of Natural Resources <br />1313 Sherman Street, Room 2l5 <br />Denver, Colorado 80203 <br />RE: TECHNICAL REVISION TO S&H MINE 112 APPLICATION <br />PLATTE SAND AND GRAVEL, LLC <br />FILE NO. M-2000-158 <br />RESPONSE TO HYDROLOGICAL ADEQUACY REVIEW DATED <br />APRIL 18, 2001 FROM TOM SCHREINER TO ERICA CROSBY <br />PEI No. 01-006 <br />Dear Ms. Crosby: <br />Following the review of information provided by Pickett Engineering, Inc., relative to flood <br />events and erosion potential for the proposed S&H mine, the Department of Minerals and <br />Geology has requested additional information. The packet of information contained herein is <br />intended to address the comments posed by the letter referred to above. <br />Enclosed is an 11" x 17" color coded map showing the locations of sensitive areas with <br />potential for excessive erosion during flooding events and these areas aze associated with <br />recommended mitigation measures, which are addressed within this packet. <br />2. We have provided cross-sectional designs for riprap protection, which will be the sole <br />method of mitigation used for this project. Upon further consideration of the proposed <br />mining activities and the mitigation procedures, it is my opinion that the use of equalization <br />pipes and spillways would not be the most effective means of protecting or stabilizing the <br />areas sensitive to excessive erosion during flooding events. Therefore, as the map indicates, <br />[here aze two types of areas of mitigation. The blue line, which follows the length of the <br />eastern bank of the South Platte River, is specified as "Riverbank Armor." The purpose of <br />this blue line is to indicate the full extent of the potential areas that could be armored by the <br />applicant. This armoring should only occur if the applicant is otherwise required to provide <br />this armoring due to any permit requirements or due to the applicants desire to minimize the <br />directional change of the river, which could possibly impact the applicant's ability to mine <br />their property. Therefore, it should be made clear that this armoring is optional unless it is <br />required by other agencies. The second type is indicated in green and for the most part is <br />808 8th Street - Greeley, CO 80631 <br />Phone (970) 356-6362 -- Fax (970) 356-6486 <br />