Nestled between Lake Shafer and Lake Freeman in north-central Indiana, the city of Monticello is a Midwest summer vacation destination. The city has 5,400 year-round residents and operates a combined sewer collection system and Class II wastewater treatment plant with a design average flow of 1.1 million gal per day (mgd) and peak capacity of 2.4 mgd. This system has six combined sewer overflow (CSO) outfalls that discharge to the Tippecanoe River and the downstream Lake Freeman. To comply with the Clean Water Act, the city’s long-term control plan included the reduction and elimination of CSOs. The Bryan’s Lift Station Improvements project was created to increase the lift station’s pumping capacity to 2.5 mgd and provide 500,000 gal of detention.

Bryan’s Lift Station originally was constructed in the 1950s and served combined sanitary and storm sewers. During peak water events, the lift station was overwhelmed and unable to handle the full-flow resulting CSO events.

With approximately $1 million in grant funding from the Indiana Office of Community and Rural Affairs, the first phase was able to proceed ahead of schedule. The site location presented challenges of limited space, a high water table and tight hydraulic limitations on the existing sewer systems. Further, property owners directly uphill of the site were concerned with maintaining their aesthetic views of the scenic Tippecanoe River.

With the site layout challenges and its visible public location, traditional storage structure options quickly were eliminated. Open-concrete tanks would be difficult and expensive to build on site. Steel tanks would have required an additional pump station to convey the incoming wet weather flows to the storage structures. A large-diameter tunnel did not appear financially or geographically practical.

With sewer pipe technology innovations, creation of a steel-reinforced polyethylene (SRPE) CSO storage system was economical and practical. This optimal solution modeled an underground, high-performance detention system by using a grid of buried pipe to store combined sewage below grade. Contech’s DuroMaxx SRPE technology was engineered into a CSO detention and drainage system that met the challenges of having a small footprint, water-tight joint performance and long-term durability.

“With tight site constraints and poor subsurface conditions, the DuroMaxx pipe was ideal for maximizing capacity while minimizing the overall footprint,” said Project Manager Jonathan Borgers, P.E., of Wessler Engineering. “DuroMaxx, specifically, was selected for the underground CSO storage structure material based on its availability in larger diameters.”

F&K Construction, the selected contractor, installed the grid of 96-, 84- and 72-in.-diameter SRPE pipe. Because DuroMaxx SRPE is lightweight, installation was quick, which meant less expense and fewer dewatering issues.

“One thing we really like about the product is it is fast and easy to install, and doesn’t need a large machine to lift the large-diameter pipe,” said Greg Kuns, owner of F&K Construction. “It goes together quickly, so it helped the progress of the job move along nicely.”

Due to proximity to the Tippecanoe River and Lake Freeman, joints also were a concern. Electrofusion joints were used because each joint can be individually vacuum tested and would provide the water-tight protection needed. Additionally, since the DuroMaxx SRPE pipe has fewer joints to assemble on site, installation schedules were favorable. With its smaller footprint than alternative systems, the SRPE pipe offered easier constructability and room for future expansion. Storage for 395,000 gal was created during the Phase I configuration. In 2014, as part of Phase II of the project, the 96-in. manifold pipe is expected to be extended west approximately 25 ft, and two more leader pipes will be added to expand the system to the full 500,000 gal of storage volume indicated in the city’s plan.