The Winooski Wastewater Treatment Facility stayed mostly high and dry after Tropical Storm Irene visited Vermont in August 2011 and dropped more than a foot of rain in some areas.

Still, the plant team had made preparations for flooding and took note of how the storm affected other communities nearby. So they were ready in July 2023 when eight inches of rain fell in one day and sent the Winooski River over its banks.

The four-member plant team, assisted by seven public works crew members, used earth berms, tarping and wooden planking to keep floodwater out of the chlorine contact chamber, the aeration basin and the control building.

Utilities manager John Choate and his colleagues watched as the water slowly rose to within one foot of overtopping the wall of the final clarifier and within an inch of flowing over the makeshift barrier around the aeration tanks. Lessons learned from the storm are now informing plans to deal with future rain events, which Choate says appear to be more common in a time of climate change. 

WATCHING THE RIVER

The Winooski River has its source in the Green Mountains and flows through a series of communities and four hydroelectric dams on the way to Lake Champlain. The Winooski treatment plant is one of the last along a low-lying area just a few miles upstream from the lake. 

“The river is raging farther upstream where the elevation is steep, and then it gets wider and deeper down here,” Choate observes. “If the lake level is high, that impedes how fast the river water can get into the lake. When you get a high lake level and a heavy rain, it’s almost a perfect storm. That’s what happened in July.” 

The rain began falling on the night of July 9 and continued all the next day. On the morning of July 10, Choate and colleagues visited websites to monitor water levels at the upstream dams. “We saw that the water was rising rapidly in the catchment areas, and then the dam operators were releasing water to keep from flooding their adjacent communities,” he says. “They were sending water down the river faster than we anticipated.”

PROTECTING THE PROCESS

On July 10, Choate and operators Brian Line, Tim Grover and Brian Giroux arrived earlier than the usual 7 a.m. starting time. “The water continued slowly, slowly rising and never stopping,” says Choate. “Some of us took breaks and went home during that time. We kept in touch with each other and waited, hoping it would finally stop and recede. When it didn’t, we had to throw everybody at it.”  

The first line of defense was to cover the ground-level chlorine contact chamber with tarps and erect a 2-foot-high earth berm around it (about 100 linear feet) to create a flood barrier and hold the tarps in place. The earth came from a stockpile on the plant site and from an asphalt plant in town. Truckloads were dumped in the parking lot and then moved with loaders from the public works fleet. 

The crews then surrounded the aeration basin with similar berms, about 300 linear feet in all. “We had pretty good access to the tanks,” says Choate. “We did some hand shoveling, but for the most part we used loaders to place those berms.” As added protection for the aeration tanks the team used tarps and wood planking that had been measured and precut ahead of Tropical Storm Irene. They fastened the planks to the railing system around the basin. 

“They were cut to the right lengths and numbered, so we were able to deploy them pretty rapidly,” Choate says. “Then we strung up tarps and put dirt on to hold them in place. If we hadn’t done all that, the plant would have been lost. We would have been out of compliance and flooded, and with all the silt in the basins we would have been out of service for a week.”

In the end, the water rose up to three feet high on the tarp and planking system: “We were within one inch of water going into that tank.” Around midnight as the water kept rising, the crews surrounded the control building with a berm, also about 300 linear feet. 

Choate was hesitant about building the berms because removing them after the flood would be labor-intensive, but under the circumstances there was no alternative. “I didn’t want to make work for us at the end of the event,” he says. “We waited as long as we could to berm the different tanks. We’d work on one tank, watch the level rise around it, and then determine whether we wanted to do the next one.”

The water stopped rising at about 2 a.m. on July 11. By then significant amounts of the earth berms had been washed away, but the tarping on the tanks held up. 

READYING FOR NEXT TIME

The July flood brought to light the need for more flood preparations. Already the plant team members have raised all controls around the tanks up to 4 feet above the ground. Choate is considering the purchase of prefabricated flood barriers (Dam Easy) that can be placed in the control building doorways during flood events and then removed: “It’s an off-the-shelf product that can be rapidly deployed and then taken down when conditions return to normal.” 

He’s also investigating more effective flood barriers around the tanks. One solution consists of aluminum planks that would be stacked into vertical supports affixed to the railings and locked in place (Flood Control International). They would be deployed during floods and then removed. 

The cost of that is a concern — about $90,000 not including installation for the chlorine contact tank alone, about 100 feet of planking and related components. “I’m balancing that versus the Vermont redneck approach, which would be to buy diamond-plate steel, bolt that to the railing system, and then seal the bottom with high-tensile-strength caulk,” Choate says.

That solution would be permanent and would double as flood prevention and as a safety barrier around the tanks in line with OSHA requirements. Choate plans to apply to Vermont Emergency Management for a flood mitigation grant: “If we can get the funding, we’ll do the aeration basin as well, because that would be the next thing to flood.” 

Also, since the July storm the plant team has worked with a contractor to replace underground 480-volt high-amperage wiring on which the insulation was compromised during the flood. In an $8,000 project they pulled new wire through the conduits and then sealed the conduits with blown-in foam. 

The team also placed removable plastic inserts (Rainstopper) to seal manholes that had to be covered by tarps during the flood. The plant’s emergency generator is positioned above the 100-year flood elevation. “The water never reached that, but it was lapping at the foundation of it,” Choate says. 

All these preparations will make the Winooski Wastewater Treatment Facility less vulnerable against future storms and floods. Says Choate, “This was a 50- to 60-year storm, and now it seems to occur every 10 years. It’s the new normal.”