The project objective is to install a vertical filter to a depth sufficient to provide a filtered exit against backward erosion piping of the upper and more easily pipeable foundation valley sands into the tailrace.
Work will consist of designing/implementing a dewatering system (as needed), placing a vertical filter using modern filter design for approximately 650 feet downstream of the eagle tree to protect against fines transport into the tailrace, tie the vertical filter into the existing filter behind the rip rap downstream of A Wall, remove the riprap along the tailrace bank downstream of the eagle tree and replace rip rap with a properly designed filter underneath. Work may require installation of a dewatering system depending on the method of vertical filter installation utilized to ensure safe excavation and aid in construction.
