East Trunk Sewer Project Solves Weather Risk in
Mequon, Wisconsin Underground tunneling reduces disruptions By Kimberly Paggioli, P.E. and Troy Hartjes, P.E.
While rain is often a welcome sight along the western shore of Lake Michigan, some Mequon, Wisconsin, residents and businesses began to eye the prospect of precipitation with dread. Numerous hazardous bypasses and sanitary sewer backups impacted hundreds of homes and left far too many basements backed up. It was clear that a plan of action was needed in this picturesque city just 15 miles north of Milwaukee. A wet-weather sewer relief study, commissioned by the Milwaukee Metropolitan Sewerage District (MMSD) and approved by the Me- quon Common Council in 2016, prompted the design of the East Trunk Sewer project in 2017. Keeping Stakeholders Informed From the very beginning, collaboration between groups was vital. In order to design a relief sewer that reduced negative impact to residents, businesses, utilities, and traffic—while safeguarding the quality of life—the City of Mequon staff and a consultant team coordinated ef- forts with Ozaukee County, Wisconsin Department of Transportation (WisDOT), Wisconsin Department of Natural Resources (WDNR), Union Pacific Railroad (UPRR), City of Bayside and MMSD. It was necessary for the project to meet the compliance maintenance require- ments of the WDNR and the MMSD capacity management, operation and maintenance requirements of the City’s sanitary sewer system. During both the design and construction phases, MMSD reached out to individual residents and property owners by going door to door and hosted public information meetings. Of particular concern to those affected was the potential increased cost of their utility bills. The meet- ings gave MMSD officials a chance to address concerns and explain how this much-needed project would have minimal impacts on the utility rate. The engineering design consideration was to help alleviate sewer bypasses and basement backups within the affected portions of the City of Mequon. This included civil engineering and surveying firm raSmith partnering with the local office of engineering firm AECOM. To improve sanitary system performance of both inline storage and conveyance systems, the design included the upsizing of approxi- mately 3,000 feet of existing 24-inch sanitary sewer and the addition of 48-inch sanitary sewer. These improvements would also service the City of Mequon’s previously identified East Growth Area. Similarly, lift station location siting and sizes of the facilities were considered for
future planning needs. Route evaluations and recommendations were conducted for the roughly 11,000 feet of new underground infrastructure. WisDOT, UPRR, MMSD and Ozaukee County approved permits and 15 private property easements were obtained for the sewer tunneling underneath private property. Construction of the largest public works project in Mequon's history was well under way by 2018, starting at the county line of Ozaukee and Milwaukee. One goal of the East Trunk Sewer project was to keep interruptions to a minimum so that visitors to a park and nearby areas could still participate in their usual activities. It was also important to preserve pavement and move traffic smoothly on Port Washington Road. A key decision involved tunneling and trenchless methods for sewer con- struction—certainly a more expensive alternative to open-cut sewer construction with road restoration—but fortunately not as disruptive. However, open-cut construction was used for 1,370 feet on the very top end run of the relief sewer because, due to the run’s short length, it was considered more efficient and easier to complete. Tunneling Challenges Along the two-mile sewer route were two challenges: jacking at a depth of 30 feet directly under the Union Pacific Railroad track and jacking at a 22-foot depth under U.S. Interstate 43. Tunneling was also necessary beneath the public areas in the eastern segment of Katherine Kearney Carpenter Park, one of more than 20 parks in the City of Mequon, and under mostly paved Port Washington Road. Tunneling under both the UPRR and USH 43, rather than going with open-cut, kept the railroad cars and highway travelers moving about. Clearly, collapsing earth beneath a highway or railroad tracks would be disastrous, as would digging up a machine resting 20-plus feet un- derground. It was therefore critical that the appropriate engineering design (geotechnical included) was applied to the project. Plus, the right products had to be chosen to ensure that tunneling proceeded as smoothly as possible, despite knowing implications if issues arose dur- ing construction. Key to the success of this underground project was the use of tunneling and trenchless construction, assisted by guided boring and microtunneling.
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may 2020
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