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<br />There are some conditions which could make this method ineffective. It would have to be <br />done on a very calm day to minimize the effect of wind related surface currents. It is <br />unlikely, but possible that currents from the outlet gate leakage could influence reservoir <br />surface currents. There may also be prevailing reservoir currents based on thermal or other <br />effects that could over-power the seepage related currents. For Western Engineers to <br />perform this test, it is estimated that the cost would be about $3,000. <br /> <br />2. A second method involving the use of dyes would be to tty and identifY from which <br />area of the shoreline the seepage water is originating. This would also require that the <br />outlet be closed at the desired reservoir level sufficiently prior to the test in order to <br />dampen outlet discharge currents. There are three fluorescent dye colors that are EP A <br />approved for such used. Therefore, tlrree stretches of shoreline could be dyed different <br />colors while the outlet tunnel seepage water was monitored for fluorescent dye. There are <br />possible factors that would make the use of this method ineffective. The indications are <br />that the travel time for seepage water from the reservoir to the outlet tunnel would be fairly <br />short. However, if these travel times are too long, it may not be feasible to be monitoring <br />the tunnel discharge for the necessary length of time. Also, if the dyed water mixes with <br />non-dyed water as it travels along the seepage paths, the dye concentration could be too <br />low for detection by the time it reaches the tunnel. The estimated cost for this test is <br />$5,000. If the initial dye test was successful; a second test might be useful to further <br />narrow down the location of the entry areas. The above cost is for a single test. <br /> <br />3. Subsurface flowing water generates small electrical currents that can be detected on <br />the ground surface by special geophysical methods. Doing so involves perfomting "self <br />potential" surveys twice - once with the reservoir at its maximum level and again with the <br />reservoir at its lowest level. These surveys are generally capable of identifYing the <br />horizontal location of seepage paths but not the depths. If we could identifY the horizontal <br />location of these paths, that would greatly help the decision making process. The cost of <br />such a survey would be about $30,000. <br /> <br />The only method that would address both of the issues previously mentioned (existing and <br />progressive voids) would be subsurface grouting. In our January 22 letter, we estimated <br />the cost of such a program at about $185,000. Because of the cost, other methods for <br />addressing the two issues individually are discussed below. Following is a discussion of <br />potential methods for addressing the possibility of progressive void formation: <br /> <br />1. Progressive seepage would be indicated by suspended solids in the seepage water, <br />significant increases in seepage flow quantities or changes in seepage path pressures. If the <br />tunnel seepage points were completely controlled in such a manner that 100 percent of the <br />seepage water could be measured and sampled, the discharge water could be periodically <br />monitored for changes in both quality and quantity. It is anticipated that such a scheme <br />would consist of the following: <br /> <br />a.' Carefully map the locations and patterns of each seepage area with the <br />reservoir full or nearly so. <br />