Floods at Pigs Eye Island

Date: Thursday, March 21, 2019

From 50 Years: Treating the Mississippi Right, 1988

Black-and-white aerial image of a large area of land underwater next to a river.The topography of the Twin Cities area made Pig’s Eye Island an ideal site for a sewage treatment plant, at least in most respects. Because the cities were spread out atop the bluffs and hills flanking the Mississippi, the treatment system could be built without expensive pumping stations. Gravity supplied the power needed to bring the sewage to the plant.

Pig’s Eye Island, at 698 feet above sea level, had one major drawback. It was only about 12 feet above the normal level of the river and therefore susceptible to flooding. In most years, the annual spring floods interrupted service for a short period when the river rose above the effluent outfall, making sewage treatment impossible. A dike constructed along with the plant protected against the highest water mark on record, the flood of 1881, when the Mississippi crested at about 702 feet above sea level.

Over the years, however, the river has cared little for the old record. In 1952, 1965, and 1969, the river rose above the 702-foot level, flooding the grounds and threatening to destroy or seriously damage millions of dollars’ worth of equipment inside the plant.

The flood of 1965 was the worst of all. On April 8, with the river rising three feet a day, the plant was shut down and workers began preparing for the flood. The office staff moved to temporary quarters at the St. Paul City Hall. Workers sandbagged building entrances, brought in cots and blankets, and set up a commissary in the laboratory on the second floor of the Administration Building.

On April 11, a crew of 41 men assembled at the plant. That night, the river inundated Warner and Childs roads, isolating the plant and crew. Although [they] had borrowed six boats from the Minneapolis Park Board and had rented an Army duck boat, the strong current of the swelling river and the continuous barrage of floating debris and chunks of ice made it too dangerous to transport the workers in and out of the plant. They were stranded for the next 12 days.

Just before midnight on April 12, the flood waters burst through and over the dike, and the crew scrambled to save the plant. On April 13, water forced its way through the screen and grit chambers and seeped into the tunnel system. Workers sealed the breach with plywood and sandbags. Later that day, the water pressure from the flood blew out the urinals in the Administration Building basement. Again, the crew managed to seal the leak.

On the 14th, at three in the morning, water exploded through the air intake duct in a boiler room. Two scuba divers (employed by a contractor working on a construction project at the plant) stemmed the flow — estimated at 1,000 gallons per minute — by sealing it with a large insultation blanket and assorted boards and timbers.

Although the water kept finding new ways into the buildings, the crew was able to protect most of the equipment by plugging leaks as they sprang and by continuously pumping the water back into the river. On April 16, the river crested at 708.5 feet above sea level; on the 18th, the flood waters began to recede. When the flood subsided, workers discovered that, while the plant had suffered little structural damage, silt had filled the settling tanks and rendered them inoperable. On May 9, after three weeks of clean-up, the plant began operating again.

In 1975, the Metropolitan Waste Control Commission completed construction of the final phase of flood protection projects. The plant is now surrounded by an earthen dike and concrete floodwall that rises to 716 feet above sea level — nearly eight feet higher than the high water mark of 1965. An effluent pumping station, finished in 1977, makes it possible for the Metro Plant to treat sewage even during the annual spring flood — unless the mighty Mississippi opts for a new record.

“50 Years: Treating the Mississippi Right” was published in 1988 by the Metropolitan Waste Control
Commission on the 50th anniversary of the opening of the Metropolitan Wastewater Treatment Plant.

Posted In: Wastewater & Water

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