ST. ALBANS CITY — Sunday’s rainfall caused an overflow at the Lower Welden Street combined sewer overflow, releasing just over 100,000 gallons of rainwater mixed with sewage, explained Brian Burns, superintendent of public works for St. Albans City.

The rainfall also caused water reaching the wastewater treatment facility on Rewes Drive to go into bypass mode, explained Brian Willett, who oversees the water and wastewater department for the city.

The city promptly reported the combined sewer overflow (CSO) to the state, listing the overflow as 100,000 to 500,000 gallons. A flow gauge showed the flow at just over 100,000 gallons, but the state places the violation into broader categories for its classification purposes rather than showing the exact amount of the overflow, explained Burns.

In the city approximately 25-30 percent of the public stormwater system is connected to the sewage system, sending stormwater to the wastewater treatment facility. When too much water comes into the system at once, some of it flows out and into Stevens Brook.

“You’ve got so much flow going into it, it’s just overwhelming,” said Willett.

As storms have increased in intensity, with more water in less time, overflows have become more common, explained Burns.

That water is not all sewage. It’s generally a small amount of sewage diluted by large amounts of rainwater, according to Burns. “It might be only five percent of it is actual sewage,” he said. “That doesn’t make it any better.”

The overflow lasted for about an hour on Sunday evening, a period in which the city received an inch of rain, said Burns.

Similarly, the excess stormwater in the system causes the wastewater treatment facility to go into bypass mode. In that mode, the wastewater is treated with chlorine to kill bacteria, including e coli, and then dechlorinated before being discharged. Bypass water is not treated for phosphorous or other contaminants, explained Willett.

Gauges show 310,000 gallons went through the bypass process on Sunday over the course of two hours, said Willett.

Correcting the problem

The city is currently removing 10 catch basins on Fairfield Street from the sewer system and replacing them with new catch basins and stormwater lines.

During city council discussions of the project, Wayne Elliot of Aldrich and Elliott estimated the cost of the new catch basins at $690,000 and the new stormwater lines to serve those basins at $350,000, meaning stormwater is roughly half of the cost of the $2.1 million project, which includes new sidewalks, curbs, water and sewer lines.

Both Burns and Willett said the Fairfield Street separation project will help reduce the risk of combined sewer overflows and the wastewater plant going into bypass mode. “That should make a big difference,” Willett said of the Fairfield project.

But it isn’t just stormwater from public infrastructure going into the sewage system, Willett explained. Many of the sump pumps in older homes in the city pump water from basements directly into the sewer pipes.

Such an arrangement is against the rules now, but it was common when most of the city’s housing stock was built, according to Willett.

Burns added that many perimeter drains on private property also redirect stormwater into the city’s sewer system.

While the cost and complexity of separating the stormwater from the sewage system is large, it’s likely not insurmountable, but there are also questions of whether the stormwater should be separated out.

If stormwater goes through the wastewater treatment facility, absent a severe storm, it is treated and phosphorous and other contaminants – such as bacteria from pet waste placed near catch basins – are removed, noted Willett.

Removing stormwater from the sewage system would also mean sending it somewhere else, most likely Stevens Brook an impaired waterway. Indeed, the pollutant the state regulates in Stevens Brook isn’t phosphorous, it’s stormwater.

Excessive volumes of stormwater in Stevens Brook bring in sediment while also eroding the stream bank, making the stream inhospitable for aquatic life and carrying nutrients into St. Albans Bay where they encourage the growth of blue-green algae.

“They don’t want us putting too much back into the brook,” Burns said of state regulators.

Which leaves the city with a whole series of questions. Should all of the stormwater be separated from the sewage system? Where should it go? Should it be treated separately from sewage and, if so, where and how?

Those are questions currently under discussion, Burns indicated.