Over the past year, the failure of a critical piece of equipment as well as electricity usage overages resulted in some unanticipated expenses at Derry’s wastewater treatment plant.
Councilors learned of the unplanned costs during a presentation by Deputy Public Works Director Thomas Carrier at their Tuesday, June 20 meeting.
“This particular year, we’ve had a couple of unanticipated expenses in the sewer department budget, and it was a tight budget to start with,” Carrier explained.
Following the presentation and acting as sewer commissioners, councilors approved a supplemental appropriation of $40,000 to the 2017 Fiscal Year Sewer Enterprise Fund to cover the expenses.
In his presentation, Carrier said the piece of equipment, an aeration blower, was critical in the wastewater treatment process and had to be replaced to restore service. Carrier added that because of past odor issues at the plant, administrators felt it was vitally important to replace the part.
“We’ve had odor issues at the lagoons before, so we felt it necessary as an emergency to move forward with that expense,” he said.
Along with the failure of the equipment, there was an overage in flows at the plant that resulted in increased pumping and aeration costs. When flows at the plan increase, electrical costs also go up.
“We do our best to make our estimates,” Carrier said. “The weather can impact the flows to the sewage plant, and the problem comes down to trying to predict flows. Last year, there was a surplus in the water budget because of the drought. We do our best, but it’s very weather-dependent.”
Following the presentation, Carrier explained during questioning by councilors that funds were needed to cover the unanticipated costs.
“We just couldn’t absorb those over-expenses in the budget this year,” he said.
Derry’s treatment facility is somewhat unique to the state as it incorporates a system of two large, open lagoons to break down and treat millions of gallons of untreated sewage. Each lagoon is 20 feet deep and contains 42 million gallons.
The system is aerated by mechanical means, which provides an environment for biological activity to break down and treat the waste.
Over the winter, the biological activity decreases, and a layer of sludge builds up and falls to the bottom of the ponds to lie dormant. In the spring, as it becomes warmer, bacteria become active again and begin breaking down the waste. As this process occurs, gases such as hydrogen sulfide, which has a rotten egg-like smell, are produced.
In 2014, a pungent smell emanated from the town’s wastewater plant that affected even Londonderry residents living in the area near Home Depot and Market Basket, Carrier said at the time.
He added that a string of warmer days in early May that year, with temperatures in the 70’s and 80’s, helped exacerbate the growing stench that came from the treatment facility at 43 Transfer Lane. Humidity only added to the problem.