Record rainfalls in Memphis, Tennessee, eroded the soil supporting a 96-inch sanitary sewer main, causing the line to fail. With nearly 40 mgd of raw sewage escaping into Cypress Creek, less than a mile from McKellar Lake and the Mississippi River, an emergency bypass was needed fast to facilitate the repair work on the 96-inch sewer main. City officials immediately activated their emergency response plan, gathering the management team from the Public Works Division and bringing in the experts at Xylem, to help assess the damage and to map out an action plan.
Solution
Xylem quickly organized and coordinated around-the-clock job teams to implement a turnkey solution that maintained sewer services, minimized the environmental impact and ensured regulatory compliance. More than 30 Xylem staff members managed and worked side-by-side with approximately 100 Memphis Public Works and 60 contractor personnel to complete the necessary tasks. This “all hands on deck” approach accelerated the project timeline. Bypass solutions of this magnitude typically take upwards of two to three weeks to implement. The Xylem-led teams completed the emergency task in just six days.
The bypass needed to handle 160 mgd of flow and traverse approximately 2,400 linear feet from suction point to discharge location. To execute the monumental effort in an extremely compressed timeframe, Xylem had everything on site within 30 hours.
“Xylem was able to marshal the equipment, the pumps and whatever else was needed and get the job done — plus they had people who knew how to utilize those resources,” says Paul Patterson, environmental engineering administrator for the city of Memphis. “Public Works had the manpower and we had equipment as well. All of that put together resulted in a very successful response.”
Before pumping could begin, several “critical path” projects had to be executed, from creating a right-of-way for the bypass to shoring up 250 feet of embankment on one side of the suction pit where the pumps would be positioned.
To handle the 160 mgd of peak flow, Xylem mobilized 14 Godwin diesel-driven Dri-Prime CD400M pumps. Each pump would push approximately 11.5 mgd of flow through 24-inch HDPE suction tubes and 18-inch discharge tubes into an 8-foot-square concrete manhole structure. Six days after the break, five of the 14 Godwin pumps were operational and handling 50 mgd of flow — an average daily flow rate for the system.
To span 2,400 feet of travel distance, the bypass utilized more than 30,000 feet of piping shipped from Xylem’s rental locations along the east coast. A dozen factory-trained and certified Xylem fusion techs from across the country operated fusion machines in four staging areas. Working non-stop for a week, the teams fused 50-foot pieces of pipe into 500-foot sections and moved them into place along the right-of-way.
As the piping was set, the other nine pumps were installed and all 14 pumps put in place just two weeks after the break. One additional CD400M pump stood by as a redundant backup.
In addition to the primary bypass, Xylem installed a 36-inch bypass line to handle 11 mgd of flow and protect the structure. This bypass utilized two Godwin hydraulically driven CD300M pumps and a backup pump, all run by diesel power packs located 100 feet away behind a berm to prevent flooding and environmental contamination.
Results
Once the pumps were online, Xylem switched to 24/7 bypass operating mode. Two teams of Xylem mechanics worked alternating 12-hour shifts to operate, monitor, service and adjust the pumps as flow fluctuated. The bypass system worked as planned, pumping approximately 60 to 160 mgd of raw sewage. Xylem delivered a safe, compliant, cost-effective and comprehensive turnkey bypass solution that maintained service levels for the city of Memphis, while overcoming numerous obstacles to get it done in a very compressed timeframe. Working around the clock and utilizing more than 20 pieces of heavy equipment and machinery, the Xylem-led team mobilized and installed 18 pumps, nearly 6 miles of 18-inch and 24-inch HDPE pipe and all accessories in just two weeks.
“One of the benefits of Xylem’s turnkey solution,” Patterson says, “is it allowed the city to focus our resources and our efforts entirely on design and construction and getting the pipe replaced. And that was key.”
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