Vergennes officials seek solutions to wastewater overflow woes

VERGENNES — The long-term solution to the occasional, but persistent, problem of the Vergennes wastewater collection system overflowing into Otter Creek could be a large holding tank — or tanks — to collect stormwater that can overwhelm a key pump station.
That’s what Vergennes wastewater plant supervisor Rick Chaput and public works head Jim Larrow told the city council at its Oct. 23 meeting.
City officials have said for years the Vergennes combined sewer overflow problem centers on the pump station on Macdonough Drive. Across Otter Creek from the treatment plant, that pump station serves all of the city on the river’s east side.
After heavy rains, particularly thunderstorms, stormwater surges lead to overflows from the pump station of a mélange of rainwater and water from toilets and other household and business waste disposal systems. Those overflows have added up to a large discharge into the creek — in 2016, for example, overflows totaled 459,200 gallons and in 2017 it was 661,300 gallons.
Chaput told the council that he expects four engineering firms to respond to requests for proposals to design a tank that would temporarily store overflows from that pump station.
He said the limited area and slope between Otter Creek and Macdonough Drive and just above the road could pose an engineering challenge for tank design, and in response to a question said multiple tanks could be one answer.
Vergennes had since at least the 1990s been operating under a series of Agency of Natural Resources 1272 orders to work on the overflow problem, and several years ago installed a metering pit under Macdonough Drive near the pump station.
Overflows are diverted into that pit, which Chaput described to the Independent last year 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.
 But now the city faces a definite timetable. In 2015 the ANR replaced its 1272 orders with a “Combined Sewer Overflow” directive that stated, “There shall be no overflows within 20 years.”
Former City Manager Mel Hawley in 2015 told the city council a 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,” Hawley said.
Chaput and Larrow outlined the contributing factors to the overflow issue, and explained what it isn’t as well as what it is.
Chaput said overflows do not come from the treatment plant on the west side of Otter Creek.
“That doesn’t overflow,” Chaput said. “Where we overflow is in the Macdonough Drive pump station, on the east side.”
Septic waste and stormwater from downtown, the neighborhoods that immediately surround it, both schools, and the residential areas along New Haven Road and Green, South Maple and South Water streets all funnel through that Macdonough Drive pump station.
Chaput said on a typical day the pump station handles around 280,000 gallons. The station has two pumps, each of which theoretically can each send 1,000 gallons a minute under the river to the treatment plant, so it can easily handle the typical flow.
The problems occur when heavy rains strike and send the station, for example, Chaput said, 180,000 gallons in two hours.
They can’t handle that surge, in part, because items such as allegedly flushable wipes and sanitary napkins (known as “rags” in the wastewater field) get caught up in the suddenly heavier flow and clog the pumps just when they are needed most.
“People are putting things down the drain that they shouldn’t be putting down the drain,” Chaput said, thus the pumps’ capacity is “probably cut in half or worse, and it’s at the worst possible time.”
Aldermen and Chaput said only a small percentage of what hits the creek is raw sewage. Mayor Renny Perry called the amount of raw sewage as a percentage of the whole “a very minute” amount.
Chaput said, “99 percent of wastewater to begin with is water,” and that percentage of water is higher during overflow events triggered by stormwater surges.
“I’m certainly not defending the overflows, but it’s not raw sewage,” Chaput said.
Also, despite the volume of the city problem in the larger scope of Lake Champlain basin pollution it is not large. A two-year-old 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.
The collection system’s aging pipes are compounding the city’s problem.
Larrow described the condition of many of the system’s pipes, 40 percent of which are the original clay pipes dating back more than 50 years. He said the clay pipes are in three-foot sections loosely fitted over one another with no sealant and are particularly vulnerable to damage from plant roots.
Chaput added some of the clay pipes are broken or simply worn away.
The next generation of pipes were made of asbestos pipes and came in 12-foot sections; those, Larrow said, have “failing gaskets” holding them together. The remaining pipes are newer, more modern pipes and generally in better condition, he added.  
Finding and replacing the older, problematic pipes will be an expensive and challenging project, Larrow said, requiring camera equipment to identify them. That equipment rents for $2,700 a day for a project that could last a couple of months.
“It’s going to be a hard, hard thing to do,” he said.
The council could consider buying a $10,000 specialty camera instead, Larrow suggested. 
The problem is further complicated by the many city homes and commercial buildings that use sump pumps and roof drains that empty — technically illegally — into the wastewater collection system.
 Chaput said some homes probably could and should disconnect, but others in some crowded neighborhoods, particularly near downtown lack anywhere to pump water from wet basements.
“They have no place to put their water,” he said.
Chaput said that a typical solution to wet basements, a drainage pit filled with stone in basement floors, doesn’t work in the heavy clay soils under Vergennes.
Larrow said he couldn’t guess how many sump pumps there were in the city, but said in one subdivision of around a dozen homes each home had a sump pump.
Chaput suggested the word be spread that owners of sump pumps would not be penalized for working with the city to find a solution.
“People now don’t want to let you know they have a sump pump,” he said.
Chaput dismissed one possible larger solution — upgrading the pump station to the point that it could immediately handle the storm surges.
Doing so would create a potentially worse situation, he said.
“It would move the problem over to the wastewater plant,” Chaput said.
Chaput and Larrow told the council they would continue to work together on what Chaput called the “infiltration issue” by replacing and fixing old lines and working with property owners.
But Chaput said a holding tank solution would allow the Macdonough Drive pump station to continue to send wastewater to the treatment plant at a rate it could handle.
“The solution seems to be a tank on the east side to absorb some of this flow,” he said.

Share this story:

No items found
Share this story: