Contractors in Indianapolis are more than 60% complete with a three-year and roughly $100-million expansion of the city's Southport Advanced Wastewater Treatment Plant to accommodate effluent coming from the city’s ongoing, 25-mile deep tunnel construction program.

A critical part of the city’s plan to mitigate discharge of combined-sewer overflows, upgrades to the 65-acre plant are expected to nearly double the facility’s operating capacity to 250 million gallons per day. The project includes a new headworks, screening and grit removal structure; refurbished settling tanks; eight new 105-ft-dia clarifiers; a new mixed-liquor channel and an ultraviolet structure.

In all, the project requires the demolition of some 30 structures, excavating 120,000 cu yd of earth, placing 19,000 cu yd of concrete, laying 18,000 ft of underground piping and installing 175 dewatering wells inside the plant while it is operating. A strategy of shifting the plant’s process flow has helped smooth construction, engineers say.

“We’re reversing the entire flow of the plant,” said Alan Dale, project manager for general contractor Bowen Engineering Corp., during a hardhat tour this fall.

The company has installed 1,620 ft of 108-in.-dia, prestressed concrete cylinder pipe to carry effluent entering the existing headworks, at the northern end of the plant, to the southern end, so the new headworks construction could proceed, Dale explained. This strategy also eliminated most bypass pumping on the project.

Plant owner Citizens Energy Group also engaged HNTB for lead design work and CH2M for construction management. CEG plans to finish upgrades to the nearly 50-year-old plant in 2017.