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Deep Tunnel Force Main Replaces Aging Infrastructure
Pipe installation seen from above.
PHOTO COURTESY OF HOBAS.
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project undertaken by the Middlesex County Utilities Authority (MCUA), the Edison force mains/Edison Pump Station upgrade aimed to provide a redundant means for sewage conveyance from MCUA’s 85‑million-gallon-per-day (MGD) Edison Pump Station to its 400 MGD Central Wastewater Treatment Plant. The project consisted of two parallel 3,940‑footlong pipelines constructed in a tunnel 70–90 feet beneath the 3,000‑foot-wide Raritan River and some shorter connections constructed in open-trench excavations on the pump-station and treatment-plant grounds. The 15-foot primary tunnel contains two parallel 60‑inch-diameter force mains. The lines will replace MCUA’s existing 60‑inch diameter Arsenal force main, which was installed in 1969. The existing line made of prestressed concrete cylinder pipe, is supported on piles, and is located several feet below the riverbed. It accepts continuous flow of wastewater from the northern part of the county and serves over 200,000 people. Since the pipeline has been in continuous service for 40 years, making it impossible to inspect it internally or externally, there was
concern that the prestressing wire could fail, causing a catastrophic pipe failure and the uncontrolled discharge of raw sewage into the river. Hatch Mott MacDonald of Freehold, New Jersey, was hired to design the new system. Angelo Bufaino, PE, a senior project engineer at the firm, explained that its concerns included both installation and longterm performance criteria. “MCUA wanted a pipe that was corrosion resistant, both inside and out. Since the line was carrying raw sewage, the authority wanted a pipeline that would be resistant to sulfuric acid, a byproduct of hydrogen sulfide gas. Additionally, the pipe was to be installed within a damp tunnel and partially encased in concrete, and there would be no means to perform external repairs if external corrosion occurred. Fiberglass pipe was the only material specified for the force main.” Kenny Construction Company, headquartered in Northbrook, Illinois, was awarded the tunnel portion of the project and purchased the 7,785 linear feet of 60‑inch, 100‑pounds-per-square-inch pressure class, 46‑stiffness pipe from Hobas Pipe USA.
