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A keyway will be cut below existing ground. Suitable material from the <br />excavation area will be placed in the keyway. The placing and spreading of <br />fill material will proceed from the lowest point on the embankment Ikeywayl in <br />horizontal layers of such thickness as to allow for a minimum compaction of 95 <br />percent of standard proctor. Compaction tests will be run on approximately <br />every 2,500 cubic yards of materl al placed in the embankment. Results of these <br />tests will be kept on file at the mine engineer rq o_'fice and will be ava!lable <br />far inspection rf requested. Both the ups[re am and downstream slopes of the <br />embankment will be 3hsly or flatter. <br />During the L00-year storm, with the emergency spillway functtoning as designed, <br />there will be 2.57 feet of freeboard. Taking into account 1.0 foot settlement, <br />there will still 6e 1.57 feet of freeboard. <br />A geotech ni cal investigation and slope stability analysis was conducted by <br />Northwest Colorado Consultants, Inc. INWCC) in May 1997 and their report is <br />ccntai red in Addendum 13 -4 E. 6'pon revrew of the initial report, the Division <br />• revealed a po rential Ea ilure surface with a factor of safety less than the <br />requited 1.30. NWCC Prepared additional stability analysis and embankment <br />construction recommendations for Pond 11. This additional information is in <br />Addendum 13-4E and is at the end of the original report with a cover Letter date <br />of July 9. Based on their revised results, a minimum static safety factor of <br />1.35 was obtained, exceeding the minimum required. <br />Several recommendations will be fo Llowed once construction is initiated. NWCC <br />will be utilized as the consultant during the construction of Pond 011 to do <br />compaction testing and assist with the proper construction of the embankment. <br />1. A layer of stabilisation fa6ri c, such as Mlraf! 600:! o: an equivalent <br />product, will be placed aver the stabill zed subgrade prior [o placing <br />embankment fili materials. <br />2. A toe drain and drainage Elan ket will be required along the downstream toe. <br />The cequiremer~ts for and the size of the drain/blanket should be determined <br />in the field at the time of construction. The drainage blanket will be <br />constructed as shown on Exhibit 13-5 from the proposed keyway elevation and <br />maintain e consistent positive slope Lo Lhe toe of [he embankment. The <br />drainage blanket should be a minimum of one foot thick. The granular <br />13-4-11 Revised 07/15/97 <br />