Planning is one of the most crucial stages in a project’s life cycle. A bypass pumping project can be as simple as setting up some equipment or as complicated as having to choose the right equipment that meets different regulations and various restrictions. Engineered systems ensure project goals are met in terms of time, cost and regulatory requirements.
Charlotte Mecklenburg Utilities — serving the largest municipality in the state of North Carolina — had aging infrastructure that was scheduled for rehabilitation, including installation of a new liner and junction box. Two major lines coming into the plant needed to be bypassed during the project. The main influent through 72-in. RCP lines had to be cleaned, inspected and lined. Besides the rehabilitation project, a 54-in. diversion line was needed to handle peak flow.
For the project to be completed successfully, both the main 72- and the 54-in. diversion lines needed to be bypassed. A total of 74 million gals flows (mgd) through these lines daily, creating one of the largest bypass projects in NorthCarolina history. This is divided into 57 mgd of main bypass and 17 mgd of secondary bypass.
The 700-ft bypass was installed in 10 days and completed in just 28 days of the estimated 60-day timeline. Rain for Rent began planning for the project approximately two months before the scheduled start to properly prepare for the municipality’s needs. Rain for Rent’s SWAT (Sewer and Water A-Team) team, which specializes in large, high flow bypasses, along with Rain for Rent engineers, sales and operation groups, worked together to choose the right equipment and prepare a backup plan to ensure the project stayed on track in terms of time and cost. This pre-planning is crucial to the success of a bypass pumping project so that cost savings can be identified and potential liability can be avoided. Because of their pre-planning, Rain for Rent’s team of engineers identified that the use of electric pumps could save more than $100,000 in fuel costs alone.
One of the major obstacles in completing the project was the 74-mgd line that had to enter a grit building, which only had two small doors. Each discharge line had to enter the building, turn horizontally 90 degrees and run 50 ft to a discharge point. Once inside the building, the lines had to turn another 90 degrees vertically and go down 10 ft to discharge below the transducers that operate the grit removal system. Rain for Rent used a small skid steer inside the building to maneuver the large pipe into place. A fall protection system ensured the discharge point was safe for city employees to conduct routine maintenance during the project. The second obstacle was the bypass pipelines needed to be buried to allow access for the liner to be installed and the project completed. Rain for Rent’s engineering team determined the right pipe to ensure that the buried pipeline could sustain the weight of the dirt throughout the whole project and the contractor buried the pipeline.
“The teamwork between our team and (general contractor) Sanders Utilities allowed for a smooth operation for the installation of the bypass line and the burying of the line to be completed,” said Jeff Carpenter from Rain for Rent.
Before bidding for the project, Rain for Rent had to make sure that it offered the most efficient solution for the utility company to make good on the promise of delivering an engineered solution. Rain for Rent assigned a dedicated project manager from the SWAT team to make sure the system was installed and run as planned. Rain for Rent also ensured the project met all requirements by having the bypass plan submittals stamped by a North Carolina Licensed Professional Engineer.
The contractor built and installed a 10-ft x 20-ft suction pit to accommodate the four 24- and 30-in. suction stingers. Rain for Rent’s design also ensured that the equipment was elevated above the flood plain as dictated in the project specifications.
By using electric pumps instead of diesel pumps, the contractor saved an estimated $100,000 per month. In addition to cost savings, the electric pumps also reduced emissions from the diesel engines and mitigated the noise pollution issue, which was a major concern for the city and the contractor. The electric pumps also produced a more constant flow, which allowed the plant manager to observe flows on the SCADA unit, reducing potential disruption of plant operation during the bypass.
“Electric pumps have many benefits, but it can be costly to use this type of pump when there are no nearby sources of electrical power,” said Rain for Rent senior engineer Chris Cannella. “This is where the planning stage is crucial. By knowing that a power source is available, an informed decision can be made when selecting the right pump for the project to maximize efficiency.”
Bypass System Redundancy Mitigated Potential Challenges
Although electricity was supplied by a feed from the local power company, Rain for Rent had a generator on site in case of a power loss. A power failure during a sewer bypasses might cause various issues including sanitary sewer overflow, which could result in fines and legal action.
Rain for Rent also provided a 24-in. pump as a backup for the main 57 mgd bypass. The second 17 mgd bypass used three 12-in. diesel pumps with two as primary and one as a backup. It was cost-prohibitive to use an electric pump for the second bypass because an additional electrical line would need to be installed and buried.
The main bypass was conveyed 800 lf through two separate 24-in. HDPE lines, which ran into each doorway of the grit building. The second bypass used an 18-in. HDPE line running alongside the 24-in. lines and also discharged through a door approximately 600 lf from suction point.
With the help of Sanders Utilities, Rain for Rent was able to have the system installed and operational, as scheduled. Collaboration between Sanders and Rain for Rent allowed the project to run so smoothly that it was completed ahead of schedule. The treatment plant operations ran normally throughout the entire bypass.
“The project went well as planned,” said Sanders Utilities vice president Freddie Young. “The Rain for Rent team did an excellent job in planning and execution. The careful planning saved us a total of $200,000.”
Nur Yusoff is segment marketing manager for Rain for Rent.