PROJC00141 - Laserfiche WebLink

Home Browse Search

identify the characteristics of the iniluential zones. It is estimated that the cost of doing so would be $15,000 to $20,000. It seems more likely than not that seepage entry areas are located where the bedrock is either exposed to the reservoir water or is very close to the ground swface below the normal water surface level based on the following considerations: i. As Jolm Blair noted; changes in the measured seepage flows follow the pattern of reservoir level fluctuation very closely. For example, significant seepage flows begin to appear almost immediately after the reservoir reaches the apparent critical level of gage height 45 and the amount of seepage flow levels offvery shortly after the reservoir stops filling. This indicates an almost direct connection between the reservoir water and the seepage aquifer as well as a very permeable flow path. Jf the measured seepage water had to flow through overburden or embankment material, it would be expected that a much greater time lag would be observed in the response of seepage quantity relative to reservoir level fluctuations. 11. Typically, if seepage quantities of the magnitude observed at this structure pass through significant embankment or overburden materials, sufficient soil material will be removed to create surface features such as depressions or sink holes. We believe the implication is that placement of a liner over embankment slopes will likely have little beneficial effect on seepage reduction. As previously discussed; further field investigations would be beneficial in identifying permeable paths through which seepage water is flowing. Without the benefit of such investigations, any lining program should target areas of bedrock exposure or shallow soil cover. The potential costs of a lining program must be estimated in more detail to assure that all significant related costs are included in order to provide a sound basis for evaluation of remediation options. b. The Martin and Wood report suggested consideration of a grouting program along, and from the inside of the outlet tunnel. The report also noted that such a grouting program may not be fully effective and has the potential for forcing seepage flows to [md a new path. We have the following comments regarding the potential for remediation from a grouting project: i. While a well conceived grouting program might include some grouting from inside of the outlet tunne~ we do not believe that the goal of such a program should be to seal the area surrounding the outlet tunnel. In fact, seepage discharge into the tunnel provides some beneficial drainage that increases the embankment stability. The concerns raised in the Martin and Wood report regarding forcing 8eepage flows to find an alternate path are well founded. Seepage following a secondary path could result in increased potential for