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