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CIPP Project Requires Complex, Challenging Bypass Pumping Plan
“To provide the full 40 mgd pumping capacity, the six 18-inch pumps were put in place, one being a backup which actually allowed for more than 50 mgd capacity,” Gould said. “All six pumps were set up on transducers to avoid unnecessary fuel burn. In addition to the suction structures, the six pumps were ‘benched down’ by lowering the elevations of the pump pads four feet to reduce the suction lift, thereby increasing bypass efficiency.”
Once the pumps were placed, the discharge was then piped into a 40-foot-long, 42-inch manifold with six 18-inch ports with knife gate valves for the bypass pumps, and five 18-inch ports with valves for the five 7,800-foot lengths of 18-inch HDPE discharge lines.
A month after the project was bid, the status of the project became unclear when Jefferson County filed for Chapter 9 bankruptcy protection.
“After reassurances from the county and project engineers, work proceeded as planned,” said Gould. “However, mobilization of the bypass was delayed due to permitting issues with a railroad. The bypass discharge pipes had to pass through a creek under a railroad bridge, which caused concern for the railroad about the amount of potential water displacement if there was a heavy rain event. To address this concern, we added a 24-inch, Sunbelt 425 horsepower auto-priming diesel pump with auto-start to elevate any excess high water from the creek.”
Sunbelt utilized three setup crews with three McElroy 617 TracStar fusion machines working in different locations to expedite the set up.
“While the 38,500 feet of bypass piping was installed, the pumps and manifold were tied in to the system,” Gould continued. “Once everything was connected, the bypass was then hydrostatically tested and liquid level transducers were programmed to run the pumps at different surcharge levels.”
Construction of the bypass took almost two months to complete.
“This time would have been reduced had there not been a major weather event during the second week of the bypass build,” said Gould. “The town of Bessemer, where the discharge piping was located, experienced heavy rainfall and tornados causing approximately 2,000 feet of discharge piping to be washed down the creek. Our crews spent the next few days retrieving the discharge pipe. Needless to say, the flash flood became a major concern of the project from a liability standpoint, requiring that a new plan be developed.”
Sunbelt worked with Layne to get a new route approved by CH2MHill.