Editor’s note: This is the second of a two-part series. Part 1 described how stormwater infiltration from a variety of sources into the city’s wastewater collection system can outstrip the ability of a pump station on Macdonough Drive to handle sudden surges in flow.
By ANDY KIRKALDY
VERGENNES — Vergennes is confronted with a problem facing many Vermont municipalities — how to stop untreated waste from overwhelming city systems during rainstorms.
Although a recent EPA study showed that only 2 percent of Lake Champlain’s phosphorus intake from the Otter Creek watershed can be traced to municipal treatment plants, including Vergennes’, no one wants to see more events like the 332,000 gallons of wastewater that overflowed from the city plant and into Otter Creek over two days in this past February.
A story in the Sept. 28 Independent examined some of the wastewater issues Vergennes is dealing with — including aging infrastructure such as deteriorating clay sewer mains.
City Manager Mel Hawley said identifying the size of the overflows was a major step.
“You can’t solve a problem until you understand the problem,” he said.
Hawley is recommending that Vergennes seek an $8,000 planning grant to pay for an engineer to study how the Macdonough Drive station can operate more efficiently. If the city does not win the grant, he said he would look to another funding source.
“I would like to focus on the Macdonough Drive pump station,” Hawley said. “It’s critical.”
He said if the station’s capacity could be improved it could handle stormwater surges before a bigger fix to the whole system is completed.
“Those 108,000 gallons over a six-hour period probably could have made it over to the plant,” Hawley said.
Another step toward a bigger fix is already under way. The city this year earned a $50,000 grant to pay for an engineering firm to map and evaluate all its sewer mains.
Hawley estimated there are 10 to 12 miles of those mains. No one yet knows for sure, or exactly how many of those mains are clay that date back to between 1900 and 1960.
“I hope it is less than 25 percent,” Hawley said.
Hawley and Vergennes wastewater treatment plant operator Rick Chaput agree the clay mains are almost certainly a major source of infiltration and must be replaced. Chaput described some of their condition.
“I’ve seen camerawork where the pipe wasn’t even broken or damaged, but just simply by age it has worn the bottom of that pipe away,” Chaput said.
The result of the study is due in March, and Hawley and Chaput hope they can base recommendations on that data to the Vergennes City Council for a larger fix.
In the meantime, Chaput’s department has taken other steps:
•  A third employee joined the department in 2016, allowing more manhole inspections to find underground problems and leaky manhole seals.
•  Wastewater station pumps have technology that allows them to react to water flow, and it has been tweaked to react more quickly to flow surges.
•  Some clay lines have already been replaced by the public works department during culvert replacement and other projects.
‘RAG’ CONTROL
And the sewer department workers have also worked hard on the universal wastewater treatment problem of fibrous wipe products that are flushed down toilets — “rags,” in industry lingo.
“I can’t stress enough this rag problem. It’s huge,” Chaput said.
Rags make the overflows worse because they are swept up by stormwater surges and clog pumps when they are most needed.
“Whoosh, it all comes down at the worst possible time,” Chaput said.
The department does what it can to prepare for the surges. If rain is forecast workers check the pumps, and regularly clean them and a protective grate at the Macdonough Drive station.
“Everything that comes into Macdonough Drive goes through that rack. My guys, Monday, Wednesday, Friday, when they physically check pump stations they clean that rack,” Chaput said. “It’s a dirty job, but it’s gone a long way. We’re just not seeing the frequency of problems.”
One of two Macdonough Drive pumps also has a new impeller, the pump blade that pushes wastewater through a pipe under Otter Creek to the treatment station. It better handles rags, and the other pump will soon get one, Hawley said.
FUTURE STEPS
But a global fix still awaits. In 2015 the Agency of Natural Resources 1272 orders were replaced by a “Combined Sewer Overflow” directive. It stated, “There shall be no overflows within 20 years.”
Hawley in 2015 told the city council the fix might not be cheap: “There’s no question we will have a bond issue. I could be $10 million off when I say $3 million.”
It might not be easy, either. For example, Chaput said enforcing existing bans on roof drains and sump pumps emptying into the system is not simple. He explained what might happen if all downtown buildings were disconnected.
“You can’t run the water out back, because now you’re flooding into the neighbor’s yard and into the neighbor’s basement. And now they’re just going to get a sump pump and pump it down to the next guy’s house. You can’t pump it out into the street,” he said.
Chaput also doesn’t believe slow infiltration from private clay lines contributes to the sudden stormwater surges that overwhelm the Macdonough Drive station.
In looking at the big picture, Hawley returned to the ongoing study.
“We’ve got to get the lines mapped. We’ve got to find the silver bullet,” Hawley said.
Chaput said there might be several answers buried under city streets.
“Maybe we’ve got a storm drain somewhere, and we’ve got a pipe that’s routed the wrong way, or … there is a clay line with a massive break in it,” he said, adding, “If you boil it down it’s tightening up the system to deal with stormwater. We’re actually working on it, we keep chipping away, looking at every structure.”
Hawley said that approach might ultimately be the answer.
“It would be great to find the magic bullet,” Hawley said. “But the problem could be the sum of all the small things that we’re missing.”
Andy Kirkaldy may be reached at [email protected].