By Bob Uphues
The superintendent of the Brookfield-North Riverside Water Commission said last week that his agency and the Chicago Zoological Society had permanently solved a water-pressure issue that resulted in nearly two dozen water main failures in North Riverside over a two-month period in 2017.
Water commission Superintendent Robert Novotny said the zoo had installed a main service line control valve to eliminate sudden changes in water pressure that occurred during semi-weekly filter cleaning for the tanks at the Great Bear Wilderness exhibit.
During the twice-a-week cleaning of the three large tanks, crews lower the water by one to two feet and, when the filters are clean, fill the tanks back up. The process caused check valves regulating pressure in the system to open and close, causing rapid changes in water velocity and resulting in a phenomenon called "water hammer," Novotny said.
Those rapid changes in pressure, said North Riverside Public Works Director Tim Kutt, caused more than 20 water main breaks scattered around the west and south ends of the village, where some of the oldest, smallest water mains are located.
The failures weren't just minor cracks, said Kutt. The sudden changes in pressure would blow fist-size or larger holes in the ductile iron pipes. North Riverside's water system and Brookfield Zoo share the same feeder mains, said Kutt.
"I haven't seen blowouts like this in my life," said Kutt, who has worked for the village's public works department for three decades.
Some of the main breaks weren't detected immediately, said Kutt, including one that leaked directly into the sewer system at a rate of 1,000 gallons per minute. The zoo-related water main breaks were a major reason that North Riverside's water loss rate skyrocketed in 2017 compared to 2016, said Kutt.
According to the Illinois Department of Natural Resources, which tracks the loss of water sourced from Lake Michigan, North Riverside accounted for more than 90 percent of its water in 2016. But the following year, said Kutt, that number had fallen to about 80 percent.
"It was absolutely because of the water main breaks," Kutt said.
The blowouts started occurring last summer, said Kutt. That timing aligned with the zoo's installation of backflow preventers on the zoo's main water service lines, something the zoo did in response to new Environmental Protection Agency mandates, Novotny said.
"That, along with changes to our metering and connections, opened up an opportunity for the water hammer to happen," Novotny said.
At first, the water main breaks puzzled local and water commission officials, but they were eventually able to determine that the breaks were occurring on certain days of the week, at certain times of the day.
It so happened that the main breaks happened around the times the zoo backwashed the bear tank filters. Complicating the pressure issues, said Kutt, was that the bears seemed to enjoy the prospect of fresh, cool water – diving into the clean tanks and creating waves that also caused pressure fluctuations.
Novotny and the zoo downplayed the contributions of the bear belly-flops to the problem, but Kutt said he believes it was at least a small factor.
"I've seen them do it," Kutt said. "They're definitely moving water around."
Once officials pinpointed the problem, said Novotny, the water commission would temporarily shut off water service to North Riverside when the bear tanks were being cleaned, eliminating the water-pressure hazard during that time.
The new main service line control valve that had been installed as a permanent fix was dialed in last week, said Novotny. The valve is able to slow the changes in water pressure resulting from the bear tank backwashing process, pretty much eliminating the water hammer effect.
"There's still a little bit, but it's very much within a normal range," Novotny said.