HAMPDEN – Casella Waste Systems Inc. officials have proposed shutting down part of the gas extraction system at the Pine Tree Landfill for two weeks in early July for testing, which intensifies the recurring concern about the facility’s stench.

In a letter drafted by Casella, the company that owns Pine Tree Landfill, officials have suggested the temporary shutdown to the Department of Environmental Protection in order to collect data for their Conventional Landfill Corrective Action Plan.

While the gas extraction system is turned off at the conventional landfill – the oldest portion of the facility that was built in the mid-1970s and falls below the liners that Casella has built on the site – officials can determine gas quantities, identify gases and their sources, and find where and how the gases are traveling.

Only the conventional landfill gas extraction system will be shut down. The remaining systems will be operating fully during this time.

“The most controversial part is shutting the system down to find out what’s going on,” Cyndi Darling, spokeswoman for the DEP, said Tuesday.

“Shutting the system down would give very beneficial information, but Pine Tree has been told by the town and the department that there would need to be provisions. If gas builds up more than expected, there would need to be a way to stop the testing,” she said.

Thirty years of waste now sits on top of the conventional landfill, according to Don Meagher, manager of planning and development at Casella. Gas is extracted from the bottommost part of the landfill using horizontal trenches at its top, which leaves gases buried deep in the landfill to escape only through the soil at the bottom.

The DEP is concerned that the landfill gas is affecting water quality, according to Darling.

The major focus of the study, according to Meagher, is to collect data on the quantity of gas generated, methane in particular, which is an odorless gas that has potential to contaminate groundwater. Once Casella identifies the quantity of gas emitted, the company can then choose the most appropriate technique to capture the gas before it moves offsite, which is the ultimate goal of the corrective action plan.

Approximately a year ago, Casella was given a list of proposed corrective actions by the DEP, which asked the company to create immediate, short-term and long-term plans to address the issue of gas migration. The immediate and short-term plans were met and approved by DEP, but this testing is part of a long-term plan that will help Casella control offsite gas migration.

“We want to stop offsite migration of methane sooner than later,” Meagher said.

The DEP is expected to respond to Casella’s proposal “fairly soon,” according to Darling, at which time the company will submit a work plan to the department and the town for review and approval.

Meagher said preliminary tests show that gas may generate at a much lower rate at the conventional landfill than the rest of Pine Tree, which he attributes to the waste being older and emitting less gas with age. As a result, Meagher said he does not think Hampden residents will notice a difference between the stench during the testing period and any other typical July day.

“We need to be prepared for everything [during the test period]. Our expectation is based on our understanding to date of the site,” Meagher said. “It should be absolutely unnoticeable to anybody in town, but we will monitor odors and respond to them if they do occur.”

The main concern of town officials is the proposed testing date. During the humid days of July, the landfill odor is most recognizable, and residents become more aware of the hydrogen sulfide, or “rotten egg” smell, when they have their windows open or are outside enjoying the summer.

“I understand why they need to find this information and respect it’s not easy to do,” Town Manager Susan Lessard said Tuesday morning. “But my job is to see it’s done in a manner that will have the least impact on residents and visitors in terms of air quality and odor.”