Laserfiche WebLink
<br />M-2000-158 TR Memo 6 May 17.2001 <br />is installed at I : I, and not immediately covered, floodwaters flowing over and through the riprap on the steep <br />slope could result in failure of the armor and rapid down cutting. Even if soil cover is installed over the riprap, <br />and used to create a 3:1 slope, the soil could be washed away during a flood and the over steepened riprap layer <br />would be exposed. It is the Division's position that the pit banks where riprap will be installed must be graded to <br />2.5:1 prior to placement of the graded filter (if required) and the riprap. A soil cover may then be placed over the <br />riprap to improve the appearance and utility of the lakeshores, and to achieve the final 3:1 slopes. <br />Placement of Lakeshore riprap at a 2.5: l slope rather than the Applicant's proposed I : I slope, will increase the <br />tonnage of riprap required per linear foot to 11.4 tons and the tonnage of bedding to 2.9 tons per lineaz foot. The <br />cost estimate for riprap per linear foot of Lakeshore then bewmes: <br />[$10.5lT x 11.4T/!j]+ [$8/ T x l 1.4T /Ij]+[$1 /T x 11.4T l!j]+ [$3.5 /T x 2.9T l!f ]+ ~$2 /T x 2.9T /!j] <br />_ $238.25 per linear foot <br />Unless the Applicant provides a technical demonstration that riprap installed on the 1: I mined slope will be <br />effective, placement on a 2.5:1 slope should be required and $238.25 per linear Foot installation cost should be <br />used to establish the amount of reclamation bond. <br />ATTACHMENTS: <br />Division of Minerals artd Geology, 1998. In-stream aggregate extraction and reclamation guidance document. <br />Prepared by Greystone Consultants. 46 pages plus appendices. (Selected pages attached). <br />Urban Drainage and Flood Control District, 1987. Technical review guidelines for gravel mining activities within <br />or adjacent to 100-year floodp{ains. Prepazed Wright Water Engineers. 50 pages. <br />United States Department of Agriculture, Soil Conservation Service. Rock Riprap for Streambank Protection on <br />Smaller Streams. Pages 186-189. <br />Please be aware this item has been scheduled for the May 24, 2001 (Thursday) Mined Land Reclamation Board <br />Hearing located at 1313 Sherman Street, Roam 3 t8 beginning at 9:00 a.m. Your response to this letter must be <br />submitted to the Division as soon as possible. If you have eny questions, please do not hesitate to call me at 303- <br />866-4943. <br />Si r ly, <br />J. <br />Erica Crosby <br />Environmental Protec ' pecialist <br />Enclosure <br />cc: Carl Mount; DMG <br />Cheryl Linden; AGO <br />Mark Held; AGO <br />StevarrO'Brian; Environment tnc. <br />Objectors & Interested Parties (via fax, a-mail or overnight mail) <br />