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Keeping The Sewer Running In Saskatoon
“For bypass pumping, this project had exceptional site access,” Gould said. “The majority of the project was located in a large park adjacent to the South Saskatchewan River, providing full access to the suction location and discharge path. Where the discharge terminated at the treatment plant, the work area could be easily accessed by driving through the treatment plant grounds.”
Fortunately while constructing the bypass, the weather ‘warmed.’ “We never saw temperatures drop below -22,” said Gould.
Still very cold, but all pumps and the manifold were enclosed in a temporary structure made of insulated fabric with heat pumped into the enclosure.
“It worked so well,” Gould said, “technicians performing pump watch were able to work in t-shirts.”
One of the technical challenges of this bypass design was the depth of the 84-inch sewer at the bypass system’s suction point.
Gould said that it was determined that in order for the bypass pumps to achieve the required design flow, the sewer level would be required to surcharge approximately 10-feet above the sewer line because the ground elevation was almost 18-feet above the pipe.
“This was the most efficient static suction lift level corresponding to the required net positive suction head for the selected bypass pumps,” he explained.
Hamm Construction dug the 13-foot-deep, 72- by 49-foot excavation and cut the five suction ports in the top of the 84-inch sewer.
Gould said that before the plug was installed to divert the sewer line’s flow to the bypass, all pumping equipment was checked and rechecked.
“Once the bypass was in operation,” said Gould, “it could not be shut down because of the risk the three discharge lines would freeze. The bypass system was air tested instead of hydraulically tested to avoid freezing the unprotected HDPE discharge lines. After successfully passing the air test, a pneumatic sewer plug was installed after the plant’s influent lift station reduced the 84-inch line surcharge.”
Operating the bypass began with Sunbelt performing round the clock pump watch with one technician onsite in three, 8-hour shifts.
“However,” said Gould, “this was short lived because it was discovered that the pumps were being clogged with an abnormal amount of debris, causing them to be cleaned constantly. In response, Sunbelt sent another technician to assist in the round-the-clock debris removal. The pump watch was then adjusted to two techs onsite in twelve hour shifts.”