Looking below at overflows; stormwater infiltration plaguing Vergennes sewer system
VERGENNES — Vergennes wastewater treatment plant operator Rick Chaput said what he and his crew found under a Main Street manhole during a recent rainstorm typified how hard it is to solve the city’s problem of untreated human waste overflowing into Otter Creek.
That visit was part of just one Chaput’s department’s ongoing efforts to solve that problem, which centers on the Macdonough Drive wastewater pump station — and which city officials blame on too much water getting into the system during heavy rains or major snow melts.
On that day Chaput and company were inspecting a manhole that collects water just uphill from Otter Creek, and from which stormwater and wastewater flows to the pump station just north on Macdonough Drive.
They found five pipes flooding that single manhole, and three in particular that Chaput said were “really ripping.” Those pipes, he said, had in turn collected both wastewater from both private sewer lines and city mains — some of which are clay and between 60 and 100 years old — and stormwater from those sewer mains and many roof drains, sump pumps and catch basins.
And, Chaput said, it was virtually impossible to tell what part of Vergennes each of those pipes served.
“It’s a puzzle, a big puzzle,” he said.
That one manhole offers a look at how complex solving a problem will be in a system with up to 12 miles of sewer mains, some of them broken clay, and hundreds of private perimeter drains, sump pumps and private lines hooked into to those sewer mains, many of those private lines also made of clay.
And that manhole shows what Chaput and City Manager Mel Hawley say is the biggest problem — stormwater pouring into the system from multiple sources.
“It’s not a single-point problem. It’s a holistic problem,” Chaput said.
Hawley believes when the Vergennes sewer plant was built on the west bank of Otter Creek in 1964 stormwater was not taken into account.
“It was based somewhat on water consumption, on the assumption that only water that was consumed is flushed down the toilet and down the sink drain,” Hawley said. “But the fact of the matter is there are roof drains and old clay tile pipes and all kinds of other conditions beyond that that enter the sewer system. And that’s what we have been battling since 1964.”
One thing Chaput noted is the treatment plant itself is having no trouble.
“The wastewater plant works just fine,” Chaput said. “The problem is where is the water coming from.”
Also, despite the volume of the city problem — seven overflows totaled 459,200 gallons in 2016 and four totaling 661,300 gallons in 2017, the largest being 332,000 gallons over two days in this past February — in the larger scope of Lake Champlain basin pollution it is not huge. For example, a recent EPA study stated that only 2 percent of Lake Champlain’s phosphorus intake from the Otter Creek watershed could be traced to municipal treatment plants.
Still, clean water advocates, environmental agency administrators and city officials are all calling for the raw sewage problem to be solved.
And city officials and the sewer department have taken a number of steps in that direction, including an ongoing mapping project and efforts to improve the performance of the Macdonough Drive pump station and learn how unwanted stormwater is entering the collection system.
SCOPE OF THE PROBLEM
And city sewer plant workers have been able to accurately measure the overflows since the beginning of 2016. Before 2014, when Chaput came aboard, the only way city officials knew if there had been an overflow was if a block of wood in the Macdonough Drive pump station — at the bottom of Comfort Hill, next to Potash Brook — had floated off its perch.
That pump station — one of three along Otter Creek, each with two pumps and a wet well — handles the most populous area in Vergennes, including downtown and the neighborhoods that surround it. The others handle the Panton Road trailer park and nearby homes and businesses, and the state-owned Northlands Job Corps.
That latter station formerly overflowed, but the state several years ago took measures to control stormwater on the roughly 60-acre Northlands campus. Hawley said those steps resolved the issue, offering hope the city can fix its larger-scale stormwater problem.
In 2014 the city responded to one in a series of Agency of Natural Resources 1272 orders to work on the overflow problem — Vergennes has complied with all of them, Hawley said — by installing a metering pit under Macdonough Drive near the pump station.
Overflows are now diverted into that pit, which Chaput described as a square box divided in half by a concrete barrier that does not reach all the way to the top. During overflows wastewater crests the barrier, and its volume is then measured and charted.
Although the metering system was put in place in 2014, Chaput said it did not work properly until 2016. In 2015, he said, for example, he would find the meter spinning when only “a trickle” was entering the box.
Chaput said that the overflows occur only during heavy rains, and they consist mostly of the runoff that infiltrates the collection system, not just untreated sewage.
“It gets portrayed as ‘so many tankers of raw sewage’ were spilled. And that’s not the case,” he said.
Regardless, Hawley said the situation is unacceptable.
“We are all serious about eliminating every overflow,” Hawley said. “I don’t like using the word ‘only’ with the words ‘108,000 gallons.’ One gallon is too many.”
Next week, look for a story on the details of steps Vergennes has taken and what might lie ahead.
Andy Kirkaldy may be reached at email@example.com.
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