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Lake Isabelle <br />1. No Action Alternative <br />One course of action considered was to do no repair or rehabilitation of the dam. The results of <br />this alternative would not necessarily result in zero cost to the Company. The result of not <br />repairing the dam could ultimately result in the loss of use of the outlet due to further deterioration <br />of the outlet conduit, or failure of the gate or gate operator, or due to a temporary loss of access due <br />to failure of the wood ladder and platform system. There is risk of injury to employees accessing <br />the bottom of the shaft due to the poor condition of the wood access ladders. There is also some <br />potential for problems due to air quality in the shaft. <br />While this alternative has no immediate capital expenditures, the risk and potential costs can be <br />very great. A failure of the outlet during or after the irrigation season could result in the loss of <br />the reservoir for multiple seasons due to the difficult access to the dam. Thus the cost of not <br />providing for the dam repair can potentially be very high even without failure of the dam. <br />2. Construction Alternative 1— Upgrade Existing Outlet Works <br />This alternative considered replacing the wood access ladders and platforms in the existing vertical <br />shaft, replacing the control gate and operator, and repairing the outlet pipe downstream of the gate. <br />This work is needed to ensure safe access and increased reliability of the gate and operator. A <br />general summary of the work proposed follows and preliminary details considered are shown on <br />Figure 5. <br />In order to gain proper and safe access to the gate valve and the pipe the existing wooden landings <br />and ladders will need to be removed and replaced with a more direct and safer mode of access. <br />Because of the design of the shaft the process of removing the existing landings-and ladders will be <br />slow and time consuming. Constant monitoring of the air in the shaft has the potential to increase <br />the time needed for the removal of the ladders and may prohibit the use of some types of <br />equipment for long periods of time. <br />Once proper and safe access to the gate valve has been established the removal of the gate valve <br />and pipe can begin. The design of the gate valve and the pipe that pass through the shaft will <br />require that the entire gate valve will need to be hoisted out of the shaft. Rocks and rubble at the <br />bottom of the shaft will also need to be removed to provide clear access to the entire valve and the <br />pipe. The size and weight of the gate valve will require the removal of the roof of the existing <br />control building and the installation of a winch and a lift. <br />After the removal of the gate valve and pipe a new 24 -inch diameter pipe will need to be grouted <br />into the wall cavity left by the removal of the existing 30 -inch diameter pipe. A new 24 -inch gate <br />valve will also need to be installed to control the flows from the lake. A gate stem and operator <br />will be required to operate the gate from the control building. After the installation of the new <br />gate valve the stem and operator will be installed in the control building and the control building <br />roof can be rehabilitated. <br />Allen Lake and Lake Isabelle — 12.012 <br />Left Hand Ditch Company Page 14 <br />