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The Glen Walter Sewage Collection System in Ontario, Canada, was built to service 1,080 customers in 1989. At the time the population was 850, but by 1995 the sewage treatment plant had already reached full capacity. Shawn Killoran took over the operations manager position in 1999 and, along with the mayor and council, he immediately had concerns about the excess flow.
The township started by videotaping all of the lines in the collection system. The pipe work was found to be in good condition, so significant infiltration was unlikely. Killoran realized that he had to rethink the approach and find a way to leverage technology. He decided to monitor flow in high-volume areas within the collection system. The township selected Stingray level-velocity loggers from Greyline Instruments because they are portable, work in partially filled pipes and enable technicians to retrieve wastewater flow data without entering manholes.
Capturing Flow Information
The study of the Glen Walter Sewage Collection was conducted from May 16 to June 9, 2006. The instrument’s ultrasonic sensors were installed in seven different manholes for periods of three to five days. To capture detailed flow information, the township set the Stingrays to take readings at 10-second intervals.
To deploy each unit, a township technician selected a manhole location, attached a stainless steel bracket in the influent pipe and mounted the sealed, ultrasonic sensor into it. The technician connected the sensor cable to the watertight electronic logging unit and hung it inside the manhole. The logger recorded the date and time, water level, velocity and temperature.
To conduct the study, the township recorded weather conditions on a daily basis in the Glen Walter Collection log book and noted the number of homes upstream of the flow monitors. When a Stingray was removed from a specific manhole, the information was transferred to Greyline Logger software and a graph was created that displayed the total flow for that specific area. At the end of the survey, Killoran prepared a flow monitoring report for the mayor and council on high-volume areas within the collection system.
Information in Action
An average of 1 cu meter a day per household was used as a guide for the amount of water used in a 24-hour time interval. Locations monitored by Stingray level velocity loggers recorded flow rates 15% to 70% higher than statistical flows. The loggers captured spikes in flow that matched typical run times from domestic sump pumps. Because the Stingray is able to monitor water temperature, Killoran also observed corresponding temperature drops matching the pump cycles. The evidence was clear: Residents were connecting sump pumps to the municipal collection system.
Municipal agents went door to door informing residents that improper sump pump connections had been identified. They requested that any sump or trough discharges be disconnected from the municipal system.
“After the flow survey, we observed a reduction in influent at the sewage treatment plant,” Killoran said. Since the Glen Walter study, the Stingrays continue to be used to measure flow in other applications in the township of South Glengarry.