Replacement of Iowa’s largest Sewer Pipeline with HOBAS GRP Pipes

One of the city’s largest sewer outfall lines was at stake, a combination of DN 1200 and DN 1100 concrete pipe that carried approximately two-thirds of the city’s wastewater. The pipes were cracked, had offset joints and were corroding away from the inside. In some places, the 15 cm wall thickness had deteriorated to only a couple of centimeters. “We have some real challenges with regard to sanitary sewer flows,” admitted Gregory Reeder, P.E., City Engineer for Council Bluffs. “We have a high water table and very flat terrain in some areas.” To illustrate the problem, he noted that the new sewers in Council Bluffs often have as little as 2 cm fall every linear 30 m. There are areas where the sewage just sits there in the pipe from time to time. That creates hydrogen sulfide which attacks the concrete pipes. In some places the pipes sit underwater which creates installation issues. In 1998-99, the city began exploring repair and replacement options, but finding the right solution was complicated. The pipe’s size, burial depth and high ground water made the project extremely difficult and potentially very expensive. Engineers also had to consider the fact that the line runs under an interstate highway, a street and a levee.