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<br />> <br /> <br />Alternative 3) Placing a three foot thick clay liner on the upstream face of the dam, a toe drain <br />at the downstream toe, a narrow drainage blanket at the downstream toe, and constructing a <br />spillway that meets the State Engineer's requirements. <br /> <br />, <br /> <br />e <br /> <br />Alternative 1 (drainage blanket) will control the seepage by intercepting it and directing the <br />seepage to a collection drain such that the seepage does not exit the dam face. The blanket will <br />be designed as a filter to ensure the seepage forces do not cause piping to take place. The blanket <br />and toe drain will be placed from approximately station 9+00 to station 25+00, and the blanket <br />will be covered with soil to protect the drain and increase the embankment stability. <br /> <br />Alternative 2 (pVC liner) will require the upstream riprap slope protection be removed from the <br />dam and stockpiled for later use prior to placing a PVC liner over the upstream slope. The liner <br />will be placed from approximately station 9+00 to station 25+00 and will be covered with one <br />to two feet of soil for protection. The liner will bi;: anchored in trenches around its perimeter to <br />keep it in place and to inhibit seepage along the face of the liner. After installation of the liner <br />the riprap will be replaced on the dam face for erosion protection. A toe drain will be installed <br />along the downstream toe of the dam from approximately station 9 +00 to station 25 +00 and a <br />15 foot wide blanket drain installed above the dam toe that ties to the toe drain. <br /> <br />Alternative 3 (clay liner) will require the upstream riprap slope protection be removed and <br />stockpiled for later use prior to placing a three fClOt thick clay liner over the upstream slope. The <br />liner will be placed from approximately station 9+00 to station 25 +00 and wil1 end in trenches <br />around its perimeter to inhibit seepage. A toe drain will be installed along the downstream toe <br />of the darn from approximately station 9+00 to station 25 +00 and a 15 foot wide blanket drain <br />installed above the dam toe that ties to the toe drain. <br /> <br />e <br /> <br />All the alternatives will include the construction of a new spillway and spillway discharge channel <br />along the east side of the dam between darn toe and Boulder County Road '10. The spillway would <br />include a concrete cutoff wall and riprap to COntrol the elevation of the spillway crest and to <br />minimize erosion. A 75 foot wide spillway Channel would be excavated downstream of the <br />control section to route the flow along the downstream toe of the dam to the north of the spillway. <br />This would route the discharge flows into the historic flood plain without crossing property not <br />owned by the Highland Ditch Company. <br /> <br />A slurry trench cutoff wall was investigated in the earlier feasibility study, as presented in <br />Appendix H, but at the direction of the Company was not considered further. The alternatives <br />outlined herein are described in more detail in Appendix H. <br /> <br />Foothills Dam- 96.014 <br /> <br />Page 5 <br /> <br />e <br />