In spring 2016, a significant rain event sent the Jonesborough Wastewater Department in Tennessee back to the drawing board. In spite of upgrades to the Jonesborough wastewater treatment plant in 2014, and a reduction in inflow and infiltration (I&I) in 2015, the rain event in 2016 caused overflows at the pump station located in the plant.
Realizing that additional steps were needed to properly address longterm prevention of future sanitary sewer overflows (SSOs), the Town of Jonesborough brought in the local Xylem branch team to design a permanent solution that wouldn’t require revamping the entire pump station. A typical fix for a municipality or utility would be to install a backup power generator, but Xylem engineers saw that this type of solution wouldn’t help Jonesborough if the station’s pumps or generator’s switch-gear failed – and wouldn’t allow for additional flow capacity brought on by severe rains.
Town officials agreed with the assessment. “A mechanical failure of our pumps or a lightning strike that blows out the pump controls would leave the pump station idle, causing a sanitary sewer overflow and another environmental and embarrassing disaster for the town,” says Cobern Rasnick, Environmental Services Director for Jonesborough.
Casting the stock backup-generator solution aside, the Xylem team made a different type of recommendation.
Solution
Instead of a backup generator, the Xylem team recommended a redundant pump system that would provide both mechanical and electrical backup capabilities.
“Having a backup pump designed to turn on whenever there was a major storm event or when our pumps went down would keep the sewage flowing under any circumstances,” says Rasnick. “It was a solution that made sense to us, like having a contingency plan in place and giving us the peace-of-mind we were looking for. The added bonus with the backup pump is that we have it available whenever any of our primary pumps in the well require maintenance. It’s always there and ready to go.”
The pump station at the wastewater treatment plant now has four pumps permanently installed that together are able to handle upwards of 2.2 millions of gallons per day (MGD) of flow. The pumps are set up sequentially, with one as the lead, one as the lag, one to handle additional flow from a storm event, and one pump that serves as a mechanical backup if any of the other three pumps fails.
The redundant backup solution that Xylem engineers designed for the Jonesborough Water Department is centered on a Godwin Dri-Prime Backup System, or DBS, which was permanently installed as a backup pump. Working with Jonesborough staff, the Xylem team installed a Godwin diesel-driven, critically silenced CD225M Dri-Prime pump that can handle 3 MGD of flow. Even in the most extreme peak-flow weather events, the Godwin DBS is more than adequate to provide protection and coverage.
The high-level float in the primary pump station wet well activates the pump at a predetermined level, in case of pump station failure or a significant flow event. Xylem installed a level transducer in the secondary wet well to regulate pump speed based on flow rates. The pump is also equipped with a critically silenced enclosure to enable ultra-quiet operation when it is running.
Another key feature of the Xylem solution is the Godwin PrimeGuard controller, which is designed to tie into the plant’s supervisory control and data acquisition (SCADA) system. This enables plant operators to remotely monitor and control pump activity, and to monitor flow levels coming through the pump station. Given the propensity for chilly winters in the Appalachian hills of Jonesborough, the Godwin DBS system is equipped with two cold weather features – a block heater on the pump engine and heat tape on all of the exposed piping.
Result
The Godwin Dri-Prime Backup System, with its ability to handle whatever flow rates enter the influent pump station, is now on permanent standby and ready to go no matter what environmental or mechanical issue occur.
