Flow Monitoring System Helps Prevent Overflow

By Jeff Huebener

During recent construction in the Knoxville Utilities Board’s (KUB) wastewater collection system, a potentially large storm-induced sewer overflow was avoided in downtown Knoxville thanks to a wireless depth monitoring and alarming system that alerted KUB staff, allowing them to take just-in-time corrective actions.

In May 2008, a project named SmartFix40 began in downtown Knoxville, TN. The project involved a very aggressive schedule for reconstruction of surface and elevated sections of Interstate Highway 40, as well as improvements to utility infrastructure passing under the highway. One of the sub-projects included in the SmartFix40 scope was to replace a section of trunk sewer that ran underneath an elevated section of highway.

This KUB-managed sub-project was referred to as the “SmartFix40 Bypass”. A major part of this sub-project was to ensure that the bypass pumping (provided by outside contractors) never failed and that the trunk sewer level remained at or below normal gravity levels. The trunk sewer runs parallel to a creek with a greenway next to it and was being carefully monitored for flow levels by the ADS Environmental Services® FlowAlert™ system. KUB was determined to avoid overflows onto this greenway.

FlowAlert is a depth-based alarm system offering an economical approach to wastewater collection system monitoring. This new wireless alarming system features a combination float switch and depth sensor device designed for deployment in networks requiring rapid notification and response to abnormal flow conditions. KUB contracted with ADS to deploy a single FlowAlert to monitor trunk sewer levels during this month-long bypass pumping effort. The project included bypass pumping to keep the upstream sewer at the correct level while also being ready to handle wet weather flow events.

The monitor was positioned one manhole upstream of the pump location, and was configured to send time-stamped alarms via text messages and email to the SCADA Operations Center as well as to key KUB engineering personnel. Alarms were configured based on float switch closures and on user-selectable depth level set points. Alarms were simulated by tipping the float switch and confirming alarm and return-to-normal messages were received by the SCADA and engineering staff. Logged data was reviewed by ADS to ensure the simulations were recorded. The installation and wireless testing took just under one hour.

While the project was underway, in a routine data collection and review, ADS staff noticed that the level in the trunk was running consistently near full pipe where earlier observations showed a typical diurnal pattern. ADS staff contacted KUB engineering staff and provided a hydrograph showing the level data. This resulted in a call to KUB Operations personnel, and it was quickly determined that the constant level in the sewer flow was being produced by an upstream overflow into a 4 million gallon tank that was only to be used to store wet weather flows.

When the tank level was read by the KUB SCADA staff, it was found to be almost full. This all occurred at a time when heavy rain was forecasted to arrive overnight for the greater Knoxville area. Steps were quickly taken to discharge the retained tank flows back into the trunk sewer while running the bypass pumps at their maximum rate. A race was on to empty the tank to ensure there would be adequate capacity to store any flows resulting from the impending storm.

During the next heavy rain, flows increased in the collection system upstream of the bypass. This required excess flow in the trunk sewer to be diverted into the retention tank. Because KUB had lowered the level in the storage tank, there was enough tank capacity to handle the load shedding, and no overflow occurred.

KUB engineering and pollution control staff complimented the FlowAlert performance and ADS staff for their oversight and identification of a potentially serious process related condition. Steps were implemented by KUB to have their own operations staff more closely monitor the levels in the retention basin during the SmartFIX 40 Project. From that point forward, pump operation was very closely monitored and flow levels have been kept at levels below half pipe. WW

About the Author:
Jeff Huebener is Hardware Product Manager at ADS Environmental Services. He has over 30 years experience in wastewater process instrumentation, open-channel flow monitoring and custom telemetry applications. Huebener has executed environmental monitoring projects in 35 states in the US, as well as in 30+ cities in Europe and the Pacific Rim.