Excessive flows at the Glen Walter (Ont.) Water Pollution Control Plant were preventing developers from expanding the township of South Glengarry.
Six years after its construction in 1989, the 138,700-gpd treatment plant averaged 124,700 gpd with peak flows of 419,000 gpd, representing 850 residential accounts and one restaurant. The system was built to service 1,080 customers.
Because the treatment plant met its effluent discharge permit of 25 mg/l BOD and TSS, everyone tolerated the excess flows until 1999, when they jeopardized plans for future development. The local government asked Shawn Killoran, operations manager of the South Glengarry Water/ Wastewater Department and Glen Walter Sewage Collection System, to verify the source of the flows. “We knew that much of the water was coming from roof drains and illegally plumbed residential sump pumps,” he says.
After hiring an engineering firm that only reiterated what was obvious, Killoran took matters into his own hands. A sales representative from Greyline Instruments Inc. in Massena, N.Y., had shown him the portable Stingray level-velocity logger. It works in partially filled pipes, and workers can retrieve data without entering confined spaces. The ultrasonic sensor records the date, time, water level, velocity, and temperature.
Armed with two units, Killoran and his three crew members isolated the sewer pipes with the highest flows and then began a customer education program. “Compliance is an ongoing campaign, but we’re making headway,” he says. “The flows have dropped by 19,000 gpd.”
Spy in the pipe
Wastewater, treated at the plant using extended aeration, is discharged into the St. Lawrence River. The collection system has four miles of 4- to 10-inch PVC pipe and three lift stations. To rule out infiltration, the crew televised the lines using a Gatorcam inspection system from Radiodetection. The lines were sound.
When the Stingray units arrived, the workers installed them where mains entered manholes before branching off. They attached a stainless steel bracket in the pipe, then mounted the sealed sensor to it. After connecting the sensor cable to the watertight electronic logging unit, they hung it inside the manhole and set the sensors to take readings every 10 seconds.
“Our blueprints told us how many homes were on the line, and we calculated the average flow using the formula of 264 gpd per household,” says Killoran. “In 2006, we monitored seven manholes for three to five days.”
Before moving a monitor, workers downloaded the information to Greyline Logger software. At the end of the monitoring period, Killoran generated a graph of the results. “All I did was enter the size of the pipe and the software did the rest,” he says. The graph reflected flow rates 15 to 70 percent higher than statistical flows. It also illustrated spikes with corresponding temperature drops that matched sump pump cycles.
Catch me if you can
The area’s ample groundwater makes sump pumps necessary. The pumps should discharge to storm drains — mostly open ditches — but residents don’t like wet ditches on their property. Using a quick disconnect, they illegally hook the sump pumps to the sewer lateral. “One knock on the door and they fly downstairs to disconnect the sump pump,” says Killoran. “By the time we’re allowed into the basement, everything is proper.”
The local government advised Killoran to hire someone from outside the township for a door-to-door information blitz. Mary-Lee Smith from M.L.H. Smith Contracting Inc., a technical services construction management service, knocked on 350 doors. Most homes had no evidence of illegal hookups.
Residents then received a notice in their next water bill stating that they faced fines if illegally connected to the sewer lateral. To catch them red-handed, workers monitored homes after rains to see if the sump pump line discharged at the ditch. Ditches without sufficient water were another red flag. Crews often observed those conditions while driving through neighborhoods.
To catch one offender, Killoran parked the Gatorcam at the lateral and recorded the discharge when the sump pump started and stopped. When allowed inside, he found the sump pump connected to the lateral. “I drove past a month later to make sure their drainage ditch was wet,” he says. “My guys monitor this home quite often, but they are vigilant wherever they go.”
After two years of continuing education and enforcement, flows to the treatment plant average 105,680 gpd, enabling the township to partially lift its ban on development. Killoran put the ultrasonic sensors to use monitoring the discharge from the plant’s 31-million-gallon lagoon. “We had a sonic head recording flows, but were unhappy with the data,” he says. “The Stingrays, however, generate really accurate flows.”
