HAMPDEN – Methane gas and leachate are escaping from Pine Tree Landfill and affecting the quality of nearby groundwater, according to the town’s technical consultants.

Addressing the Town Council and a group of more than a dozen residents Wednesday, consultants Matthew Reynolds and Steven Rabaska reviewed water quality and geologic issues at the landfill.

Methane gas, which is generated through the decomposition of waste, is escaping from the landfill and being funneled through a layer of relatively dry sand that is covered by clay, Reynolds said.

At least one residential well on the Coldbrook Road has shown elevated levels of the gas, which can dissolve in water, he said.

“It has migrated quite extensively from the landfill,” Reynolds said.

Seven monitoring wells situated close to the landfill exceed safe drinking levels for benzene, a carcinogenic compound, and five wells exceed the drinking level for arsenic, he said.

The compounds do not pose a health risk, however, because they have not been detected at unsafe levels in residential wells, he said.

Also of concern is a testing site on the Souadabscook Stream located downstream from the landfill that indicates slightly elevated levels of chloride, he said.

The compound also has been detected in higher levels after leachate spilled from pumps and pipes broken during construction periods, Reynolds said.

Among the consultants’ challenges is determining where the compounds – many of them naturally occurring – originate and how they could be escaping from the landfill, he said.

Some attendees expressed frustration that some sources of contamination have not yet been pinpointed and corrected.

“If you’re so unsure of everything, then why are they continuing to operate?” resident Carmen Montes said Wednesday of Pine Tree.

Pine Tree officials have instituted a corrective action plan that includes increased monitoring and gas extraction, but additional information must be collected before the plan is complete, Reynolds said.

Other data presented Wednesday supported the landfill, including the fact that no significant leaks have been detected in the newer sections and construction has been well-monitored.

More testing must be performed, however, before the landfill’s effect on groundwater is fully understood, Reynolds said.

“The understanding of that is evolving,” he said.