1993-07-07_REVISION - M1977378 - Laserfiche WebLink

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1111111111111111111 999 STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY 01F,Coto Department of Natural Resources He O 1313 Sherman St.,Room 215 Denver,CO 80203 Phone:(303)866-3567 176 FAX:(303)832-8106 Roy Romer Governor � Michael B.Long VJuly 7, 1993 Division Director Mr. Larry Perino / Sunnyside Gold Corporation P.O. Box 177 Silverton, CO 81433 r� v Re: Revision Approval, Sunnyside Mine, Technical Revision TR-15, File No. M-77-378 Dear Mr. Perino: v The Division is in receipt of your responses to adequacy concerns regarding the above referenced revision, and has determined that the revision can be approved. In item 2 of your letter, it is stated that appropriate overflow sites will be provided for any ditches left as permanent structures that are not capable of carrying the flow resulting from the probable maximum precipitation event. Design, and as-built details for any such structures must be supplied with the post-construction information SGC has already agreed to supply. The overflow structures should be located to direct flow into natural channels, if possible, and should be armored, preferably with vegetation. Per your request, I have enclosed two documents which indicate that there is a continuing uncertainty as to the long-term performance of filter fabrics. I believe that filter fabrics provide an economical alternative to graded sand and gravel filters in many instances, but feel that the use of graded filters in critical or permanent structures is preferable. SGC's proposal to completely wrap the drainage aggregate, and to attempt to match on-site materials for filter compatibility with the drainage aggregate, is acceptable to the Division. The degree to which filter compatibility has been attained should be reported on in the as- builts. In addition, the Division recommends that the filter- wrapped drainage aggregate be surrounded be a non-angular bedding material, preferably a sorted sand, in order to protect the fabric from damage during back-filling or settlement. On July 7 , 1993 , the Division of Minerals and Geology conditionally approved technical revision TR-15, submitted on April 5, 1993 , regarding the Lake Emma groundwater interception and diversion. The terms of TR-15 approved by the Division are hereby incorporated into Permit No. M-77-378 .