In March 2016, 16 inches of rain fell on the city of Memphis, TN, half of which fell during a two-day deluge. This unprecedented rainfall eroded the soil supporting a 96-inch sanitary sewer main that carried wastewater to one of the city’s central treatment plants.
The damaged sewer main crossed South Cypress Creek and carried wastewater to the T.E. Maxson Wastewater Treatment Plant in Memphis. With nearly 40 million gallons per day (MGD) of raw sewage escaping into Cypress Creek, an emergency bypass was needed to facilitate the repair work on the existing sewer main.
City officials immediately activated their Emergency Response Plan, gathering the management team from the Public Works Division and bringing in global water technology authority Xylem to help assess the damage and map out an action plan. Xylem mobilized an expert team and cutting-edge pumps and accessories, delivering a comprehensive turnkey solution that was up and running in record time.
The emergency bypass system needed to handle 160 MGD at peak flow. Before pumping could begin, several “critical path” construction projects were required to support the bypass, including a 2,400-foot-long, 40-foot-wide road through swamp land, so the site could be accessed. Over 6,500 yards of recycled material was hauled in to act as a base for the right-of-way. In addition, two 86-inch culverts, side-by-side, each 100 feet long, were installed to contain the bypass piping as it crossed Cypress Creek.
A suction pit, measuring 150 feet wide on each side and 40 feet deep, was created to hold the pumps; the base of the pit was built using 40,000 cubic yards of imported material.
Typically, this magnitude of a bypass pumping solution would take between two and three weeks to be designed and constructed. However, the team of nearly 200 people completed the emergency task in just six days.
Fourteen Godwin Dri-Prime CD400M diesel pumps were installed to handle the 160 MGD peak flow. Each pump would push approximately 11.5 MGD through 24-inch HDPE suction tubes and 18-inch discharge tubes and into an 8-foot square, concrete manhole structure.
To accommodate the 2,400-foot distance from the suction point to the discharge location, the bypass utilized 30,000 feet of piping that Xylem shipped in from its rental locations up and down the East coast. A dozen factory-trained and -certified fusion technicians, some from as far away as California, operated fusion machines in four different staging areas. Working non-stop for a week, the teams fused together 50-foot pieces of pipe into 500-foot sections that were then moved into place along the right-of-way.
As the piping was set, the other nine pumps were installed. An additional CD400M pump was also available onsite as a backup option, offering peace of mind to the Memphis officials and allowing them to focus on replacing the damaged sewer main.
In addition to the primary bypass, Xylem installed a separate 36-inch bypass line to handle 11 MGD of flow and ensure minimal impact on the structure. This bypass utilized two Godwin hydraulically driven CD300M pumps and one backup pump – all run by diesel power packs located 100 feet away, behind a berm, for flood protection and to prevent environmental contamination. The discharge piping consisted of two 18-inch HDPE pipes that ran for 2,400 feet to the same discharge structure as the primary bypass.
Once the pumps were online, Xylem switched over to 24/7 bypass operating mode. Two teams of onsite mechanics worked around the clock, alternating shifts to operate, monitor, service and repair the pumps, and turn them on and off as flow fluctuated. The bypass system worked exactly as planned, pumping approximately 60 to 160 MGD of raw sewage.
“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,” said Paul Patterson, environmental engineering administrator, City of Memphis. “One of the benefits of the turnkey solution is that 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.”
The fact that Memphis had an emergency preparedness contingency plan in place enabled city officials to respond without delay when severe weather hit, minimizing environmental impact and ensuring regulatory compliance from the damaged sewer line.
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