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The last dump level to advance across the controlled underdrain was the 7825 dump. <br />• This dump advancement was dumped from a horseshoe configuration at the head of the fill and <br />controlled underdrain system. Photograph 44 shows the head, or West limit, of the controlled <br />underdrain and rock sorting as the toe of the 7825 dump advances toward the controlled drain. <br />Photograph 45 shows the head of the controlled underdrain being covered and natural rock <br />sorting occurring. <br />The rock sorting provided a protective filter blanket at all dump levels. The controlled <br />underdrain was completely covered by natural sorting on December 18. Throughout the entire <br />construction process there were no signs of weakness or instability noted. Although not <br />required, however, Colowyo took additional measures to assure long term stability including <br />additional site preparation and selective mining of weathered overburden material and selective <br />mining of competent overburden materials. <br />The Professional Engineer's Certification for controlled dumping to achieve rock sorting <br />that both results in a filter system over the underdrain built by controlled placement and prevents <br />the formation of voids that could adversely affect mass stability follows. <br />i <br />• <br />Section 3 -page 2 <br />