Bridge Street Bypass in Virginia Solves Potential Sewage Contamination
A Virginia city found itself with an issue. An old, worn-out bridge was badly in need of replacement, but tearing it down and constructing a new one could create long-lasting sewage problems far more serious than anything caused by a faulty bridge. A contracting firm would need to be hired, tasked with replacing the bridge while still preserving the integrity of the existing sewage system through which seven local pump stations flowed.
The job was made difficult due to the proximity of the sewage system to the area in which new construction would occur. City officials were afraid – and rightly so – that the vibration caused by driving the new bridge pillars into the ground would create fractures in the underground pipes, leading to the spilling of catastrophic amounts of sewage at the jobsite.
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Shaw Construction was subcontracted to install the new utility work for the project which included bypassing the existing gravity sewer during bridge construction and rehabilitation of the two existing gravity siphon chambers. Shaw Construction immediately contacted Thompson Pump, a Florida-based manufacturer of top-quality pumps and related equipment that also provides engineering expertise for construction dewatering, bypass, and emergency operations.
The decision was made to use three Thompson 12-in. oil-less vacuum-assisted pumps and 18-in. HDPE pipe to bypass sewage from a manhole in front of the old bridge to a manhole on the other side of it – a distance of about 550 ft.
Thompson Pump was chosen because of its expertise in bypass work and its long-standing relationship with the contracting firm. The decision was made to use three Thompson 12-in. oil-less vacuum-assisted pumps and 18-in. HDPE pipe to bypass sewage from a manhole in front of the old bridge to a manhole on the other side of it – a distance of about 550 ft. These calculations were based on wastewater flow data provided to Shaw Construction and Thompson Pump during their initial meeting with the city’s sewage authority.
Thompson Pump fused the pipe and strung across the bridge using a crane. Once in place, the bypass was activated, allowing construction of the new bridge to commence last summer after months of planning.
From the very beginning, Thompson Pump sales engineer Steve Lyon’s flow meter gave him real-time water flow readings, and it did not take long to realize that the flow was significantly higher than anticipated.
There were a several reasons why this occurred. The area had received above average amount of rainfall that allowed groundwater and stormwater to enter the collection systems (inflow and infiltration). New buildings had been built in the area, including an addition to the VA Hospital and several residential communities. Tidal fluctuations also added to the ever changing flows. All told, what was expected to be about 14 million gallons per day turned out, in reality, to be 19 million gallons each day.
Lyon and his staff remained undaunted. “We were very confident the pumps could handle the extra flow; we just knew we would have to run them harder,” he said. “Our two pumps ran at all times during the project, which lasted about five months – and there were times when the back-up pump was also in operation because of the increased water flow.”
Ever vigilant throughout the entire process, Lyon and his team were on 24-hour call, quickly responding when needed.
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Thanks in large part to the Thompson Pump bypass system and its flawless performance, the construction proceeded as planned without interruption and was completed in January. Once finished, Thompson’s temporary bypass was removed and it was “business as usual” when the new bridge opened.
Thompson Pump left a lasting impression upon city officials, to the point where they have since hired the company for multiple projects, present and future.
“Overall, I would say we are very happy with what happened during this project,” summed up Lyon. “Had we known water levels were going to be as high as they turned out to be, we would have set things up a little differently. For example, we would have deployed 24-in. pipe rather than the 18-in. pipe we used. But you always have to be prepared for the unexpected, and our products, most notably our oil-less vacuum-assisted pumps performed just as we knew they would – even though we were demanding a lot more from them.”
Thompson Pump offers a revolutionary priming system with its oil-less vacuum technology (OVT). The OVT priming system offers multiple improvements to the traditional vacuum priming system. While both allow for a basic pump to prime automatically, the OVT does this more efficiently with no oil lubrication, lower maintenance and higher air handling for faster priming. In addition, the OVT system’s non-contacting rotors eliminate internal wear which increases longevity and provides the reliability of no decrease in performance over time. For this bypass job, this system was crucial.
“The biggest lesson learned from this project is the need for accurate flow data and flow documentation. It is critical to have this information to prevent sewage spills and making decisions on the right equipment. Thompson pump and Shaw construction have built a superior relationship from working together,” said Shaw Construction project manager Shane Harris.
