Portage provided engineering and construction support services for developing a 50-million gallon process water/backup fly ash pond at the Colstrip Stream Electric Station. Portage was responsible for design and construction oversight related to the earthwork, subsurface drainage, and geosynthetics installation within the double-lined pond. As part of this effort, Portage designed an automated underdrain/sump system for pumping water from the subsurface and between the double liners. Another unique component of the pond is the presence of a concrete bottom protection layer, designed as protection for the liner in the event dredging becomes necessary. During construction, Portage provided field engineering for dewatering, site drainage, final earthwork lines and grades, and other site-specific concerns. Portage provided construction quality assurance (CQA) for the installation of nearly two million square feet of geosynthetic materials, including reinforced polypropylene liner, geocomposite, drainage net, and geotextile.
