CSO 032 and Third Street Consolidation Sewer - River Crossing: Under the River, and Through the Levee, to the Siphon Headbox We Go

CSO 032 and Third Street Consolidation Sewer -- River Crossing Under the river, and through the levee, to the siphon headbox we go Statement of Purpose: Design evaluated trenchless techonologies, creative construction methods, but ultimately settled on open cut installation with innovative specification language to allow for contractor flexibility in order to construct the 107 MGD siphon under the St. Mary's River due to cost, risk, and schedule. Project Summary: As part of Fort Wayne's CSO Long-Term Control Plan, consolidations sewers are proposed to convey CSOs to the City's new CSO Conveyance Tunnel. Arcadis designed the consolidation sewer to convey flow from CSO 32 and the Third Street Lift Station. The CSO 32 and Third Street Pump Station Consolidation Sewer project entails 1200 LF of 66-inch pipe, 40 LF of 54-inch pipe, 140 LF of 84-inch pipe, a diversion structure that will intercept combined sewage flow from the Third Street Pump Station and convey it to Drop Shaft 09 (DS-09) located in Headwaters Park, modifications to CSO 032 to add a slide gate, and modifications to the Third Street Pump Station to add floatables control to the CSO outfall. Project was designed to convey 107 mgd of combined sewage into Fort Wayne's new CSO tunnel to reduce CSO overflows. Project challenges include open cut installation of the pipe through the St. Marys River and Army Corp of Engineering floodwall, deep installation, adjacent properties and utility conflicts, constructability concerns, and permitting. Status of Completion: Construction was complete in 1st half of 2022. Contractor Feedback Early in the design, Arcadis obtained feedback from contractors to discuss the Project and get their thoughts regarding trenchless and open cut installation methods based on their experience. Installation methods evaluated included open cut, jack and bore, horizontal directional drill, and microtunnel. River Crossing Coordination A challenging part of design was incorporating specification requirements for the river crossing to allow the contractor time and installation freedom for the crossing to ensure a low bid price. Work items were included for River Crossing, River Crossing Delay, River Crossing Event Cleaning, and Local River Measurement Gauge. The intent of the pay items were to share risk with the contractor during typical low river times and provide flexibility to the contractor during construction. Design Lessons Learned - Identification that a 100-foot working area across the St. Mary's River would be pursued to allow for flexibility in open cut construction. Contractor had the freedom to do an earthen cofferdam, portadam, sheet piling, or other method to install the three siphon pipes across the river. - Identification that the St. Marys River levels are different year to year and an extended construction period would allow for construction flexibility. - Need to plan for floatation and protection of pipes under the St. Mary's River. - Coordination with other projects in the area and the Hosey Dam downstream to adjust the river level to aid in construction, but limit impact to community. Construction Lessons Learned - Contractor will use all the allowable time in the Contract. - Contractor willing to work at risk to meet the project schedule. - Define material removed from the river. Material pulled form the river was uncompactable. Contractor brought in clay fill. - Multiple Stakeholders impacted by river lowering (directly after labor day) - Sheeting is not watertight. Up to 4 pumps operating (8 inch + 2/3 inch pumps) Conclusion: Due to thorough design evaluation, working directly with contractors, and creative design thinking, innovative specification language was added to the Contract to allow contractor freedom to factilitate the construction of the siphon under the St. Mary's River. The project was successfully completed on time and on budget. Other utilities will learn how trenchless options are evaluated and why ruling out open cut could be a mistake, the value of engaging contractors early in the design process, how specifications can be used to share risk with the contractor, and the value of understanding your assets.