Laserfiche WebLink
~ SECTIONFOUR <br />Formulation of Aiternatiues <br />respect to the embankment material. The seepage was generaliy located at the historical location <br />of the abandoned outlet pipe. It could be possible that seepage is running along the pipe and <br />surfacing downstream along the dam toe. <br />Several options were considered to reduce the seepage along the embankments which included <br />an upstream clay liner tied into the foundation shale and also an internal slurry wall constructed <br />alang the dam crest keyed into the shale bedrock. The upstream clay liner would extend from <br />the dam crest down the dam face and then keyed into the foundation rock simzlar to what was <br />suggested in the 2003 Study. The extent of the clay liner would be limited to the seepage areas <br />identified during the field investigation program. The clay material within the reservoir basin <br />could be used to construct the liner. The riprap and vegetation on the embankment would be <br />removed prior to placing the cZay liner. <br />A slurry wall was also investigated but not considered viable due to the presences of several <br />outlet pipe penetrations within the embankment. A slurry wall would need to be placed <br />continuously along the dam axis for it to be an effective seepage barrier. The existing outlets <br />would prevent the construction of the continuous slurry wall. Additional measures would be <br />required along these areas in addition to the slurry wall. These measures would include the <br />construction of a clay liner along the npstream dam face. There was a high risk that the outlet <br />pipes could be damaged during construction and could then require their removal and <br />replacement. The cost for replacing the outlet pipes if they were damaged during construction <br />would be very expensive. <br />Based on preliminary flood hydrology developed for the 2003 Study, it appeared that a smaller <br />spillway would be required compared with Alternative 1. The estimated size of the spillway was <br />approximately 70 feet compared with the 200-foot-wide spillway presented under Alternative 1. <br />The spillway would include a concrete grade cutoff wall located along the dam centerline to <br />prevent possible headcut erosion into the reservoir during discharge. The open cut area would <br />also be protected with bedded riprap to prevent the possibility of surface erosion. <br />The irrigation ditch would also be enclosed using a 12-inch welded HDPE pipe. The SEO will <br />require the ditch to be enclosed to prevent seepage along the downstream dam face. <br />A general layout drawing and detailed construction cost estimate is presented in Appendix G. <br />~S 4-3 <br />