This $33.4-million project is the current phase of the City of Joliet’s Combined Sewer Overflow Long Term Control Plan to remedy issues within its oldest sanitary system. The construction of a wet weather treatment facility was proposed to address stormwater capacity, which included the construction of an 865-foot-long tunnel under the Des Plaines River requiring shafts, piping, and other ancillary sewer structures to complete. Because the project required a tunnel boring machine through bedrock 30 feet under the riverbed, several plans and precautions were implemented to investigate and plan for under-river conditions. Significant bypass pumping, staging, and sequencing of construction was necessary to complete the work and maintain operation of the existing combined sewer, including sewer flow diversion and bypass pumping.