Bypass Pumping

In recent years, establishing funding for long-running projects has become more and more difficult. Interim fixes are relied upon far more often than sustainable solutions. With the economy now on the road to recovery, municipalities are once again able to focus attention toward smarter, reliable, environmentally-responsible solutions.

The City of Columbia, S.C., was coordinating such arrangements when an unexpected failure created a much shorter timeline for its updates.

Collapse at Elmwood Cemetery

In February 2010, a 54-in. gravity sewer main that passes through downtown Columbia, collapsed at the historic, 19th century Elmwood Cemetery, near a monument for fallen Civil War soldiers. An open 120-ft trench was left to convey the sewage to the Metro  wastewater treatment plant. The line that remained passed through the heart of the city, close to the State House — a central location for tourism, residential and commercial activity. In addition to serving as a war monument, the cemetery itself is home to gardens and an arboretum and serves as an attraction for photographers and events year-round.

The collapsed area had been repaired previously, but improved infrastructure was clearly a necessity. City officials decide to fast-track the design project that had been in the planning stages and put it out to bid. Although the collapse did not cause a sewer spill, the immediacy that resulted from the collapse allowed the project to be awarded quickly and work to begin. Efficiency of effort and swift but reliable temporary pumping became urgent, in an effort to restore access to the City’s revenue-bearing district.

Planned Updates to Emergency Rehabilitation

The City of Columbia was preparing for a planned infrastructure rehabilitation. There had been previous failures on the gravity main, and officials were reviewing improved bypass design options. In early 2009, Columbia, S.C.-based BP Barber & Associates approached Godwin Pumps senior sales representative Pete Harper to develop a bypass plan to help facilitate the proposed rehabilitation project. The unique bypass arrangement was already in development when the gravity main collapsed. BP Barber advertised the project for bid and the work was officially awarded to McClam & Associates.

Harper passed away in late 2010 and Godwin’s North Charleston, S.C., branch manager Reed Waterbury assumed Godwin’s bypass pumping responsibilities for the job. “Pete [Harper] built a great foundation for this project, and though I hate to see it completed without him, his efforts have paved the way for what looks to be a seamless rehabilitation effort for all involved parties; from the City to design engineer to contractor,” said Waterbury.

The 54-in. gravity sewer line runs primarily through downtown Columbia, so an alternate route for bypass piping had to be arranged. Several ideas were considered, but design engineers and Godwin Pumps’ engineering and sales team decided that the best method would be to arrange a discharge route parallel to (but not in the right of way) the sewer line. This discharge route remains off the streets and away from the bustling downtown district. The bypass line was laid in and along the water canal and the Broad River and covered over three miles to thoroughly bypass the rehabilitation project with one complete setup. “This setup proved to be the best route and avoided railroad crossings, interstate crossings and, of course, busy downtown streets,” said BP Barber lead engineer Ed Hart.

“One of our main considerations was the impact this rehab would have on the surrounding areas,” said Waterbury. “To provide the most cost-effective solution, one bypass was set up with two 24-in. bypass lines running 16,000 ft each. This was an extensive setup and required approximately four months to complete. But the bypass was proactively planned to be in place and not require any relocation throughout the duration of the project.”

Many Options, Right Pumps, Best Techniques

To accomplish the rehabilitation, eight Godwin Dri-Prime pumps were set up to handle the 30-mgd peak flow anticipated, including an electric-driven, 18-in. model CD400M Dri-Prime pump as the primary pump. McClam & Associates opted to rent the electric drive model CD400M although it was not in the bypass specification. “That 18-in.electric pump will pay for itself and then some when compared to fuel consumption by diesel pumps,” said Rusty McClam.

Six secondary pumps were also used for the installation — diesel-driven Godwin model HL250M pumps. These 12-in. by 10-in. pumps offer flow rates up to 5,700 gpm, total dynamic heads up to 390 ft, and solids handling up to 3 in. in diameter. Another diesel-driven HL250M Dri-Prime pump served as a standby pump for the extent of the bypass. Due to the long discharge run, BP Barber specified the six HL250M pumps to handle the expected peak flow of 30 million gpd at 205 ft of discharge head created by the three-mile run of pipe.

The job used 32,000 ft (two parallel lines) of 24-in. HDPE SDR 17 pipe. The SDR 17 pipe provided a sufficient pressure rating for the required 88 psi being generated by the pumps. Working with McClam & Associates, Godwin technicians fused all 32,000 ft of pipe over a three-month period.

The bypass site includes more components than just trenchless work. Each aspect was designed with the most effective methods available. “Moving or relocating a smaller bypass setup would impact the residents and visitors far more than the one time bypass setup,” said Waterbury. “By doing all updates and repairs at once, we can minimize our presence even more.

“The team is performing multiple pipe rehabilitation options,  open-cut — digging and replacing pipe — where it makes the most sense and trenchless methods in the downtown areas. If progress will be impeded for any reason, the contractor has the capability and experience to provide flexible solutions to complete the job in the necessary timeframe within the allotted budget,” said Waterbury.

In most cases downtown, McClam & Associates is implementing a proven trenchless method. This includes cured-in-place pipe (CIPP). This method typically only requires access to the line through the existing manhole covers on the sewer line.

Minimizing the Footprint

“When planning a rehabilitation of this nature, we have to consider what the town will look like when our technicians go home,” said Waterbury. “First and foremost, we strive to minimize the residential and environmental impact a project of this nature has on both the town and its resident and visitors. But, the ultimate goal is to prevent our customer from requiring another rehabilitation project in the same location that could be prevented by careful planning, experienced execution, and reliable, well-thought solutions.”

Work began on the gravity main rehabilitation in July 2010. Startup occurred in December 2010, and the project is expected to run for approximately 10 months. The complete bypass setup allows for 90 percent unrestricted access to the sewer line for open-cut replacement  and CIPP rehabilitation.

Two additional projects are relying on this bypass setup, and a second contractor must complete work within the same time frame. S

“We are confident that our preparation, placement, setup, and the reliability of our equipment and the responsiveness or our technicians will allow this to remain a successful temporary bypass and a dependable permanent solution,” said Waterbury.

Kristen Gurick is a marketing communications specialist for Godwin Pumps.

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