NASHUA — Unbeknownst to some Gate City residents, the Four Hills Landfill is home to 70 gas wells producing energy, and revenue, for the New York firm Fortistar.

Kerry Converse, an engineer with the city’s solid waste department, said it’s unclear how much the company makes from the energy, but that they are providing a key service to the city.

“It’s not like we’re giving it away,” he said. “If they didn’t do it we’d have to do it ourselves or pay somebody to do it.”

Methane production has been in operation at the Nashua landfill since 1995 — when a 30-year contract took effect — and has been managed by three different companies during that time.

“There’s a network of pipes and wells inside the landfill, connected to a vacuum blower which sucks the gas out of the landfill,” Converse said.

“If you don’t manage the methane then you have odor problems and it’s an explosive gas, so it’s something that has to be managed.”

In many landfills, methane and other gases are vented into the atmosphere. Fortistar, which serves 40 communities across the country, claims from from an environmental stand-point, methane production is a win-win.

According to the company’s website, by using the methane from landfills, energy can be produced from a green/renewable fuel source.

The city pays nothing to Fortistar, which has two workers onsite. The company is paid by the energy it produces in addition to tax credits, Converse said.

Fortistar is responsible for managing the odors emitted by the landfill — a byproduct of anaerobic decomposition and gaseous compounds emitted into the air. Because of this, the company is not always able to operate its two generators at maximum capacity.

But Converse said sometimes the needs of odor control and generating energy don’t always mesh.

“It’s striking a balance between the needs of the plant … and what the vacuum needs to be on the well field to control odor. But if we get the balance right, then everybody is happy.”

The maximum generating capacity is about 3.1 megawatts at any given time.

Nashua’s Mayor Donnalee Lozeau said the cost of odor mitigation is very expensive. If a company is willing to do that, she said city planners are inclined to sign over gas rights without worrying about how much money could have been made.

“It’s one of the reasons that I get concerned about long-term contracts with the city,” Lozeau said. “When you sign a contract, let’s say 20 years ago for a system like this, you feel pretty confident that the goal that you’re after really isn’t to sell electricity or make money that way. The goal that you’re after is making sure that the neighbors aren’t smelling methane gas leaking from the landfill.”

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Simon Rios may be reached at srios@newstote.com.