HAMPDEN – The volume of waste being trucked into one of the state’s largest landfills has more than tripled over the last three years, and the company that owns it wants to make room for even more trash.

Casella Waste Systems Inc., however, has yet to resolve how it will address groundwater contamination at its Pine Tree Landfill.

Water quality and the booming fill rate at the landfill, situated next to Interstate 95 and Cold Brook Road, are among the issues detailed in Pine Tree Landfill’s recently released annual report. The commercial landfill accepts wastes from Maine and out-of-state.

The company is preparing an application to increase the landfill’s 6 million-cubic-yard capacity by nearly 50 percent, but is waiting for the state Department of Environmental Protection to decide whether the company must first resolve its groundwater contamination issue, according to Donald Meagher, Casella’s manager of planning and development.

“I’m sure we will reach something that’s agreeable to both us and them,” Meagher said Wednesday.

Waiting for word from the state are town officials, who will conduct their own review of the proposed application.

“DEP really is the key for all of us in going forward,” Town Manager Susan Lessard said Tuesday.

Causing concern is the escape of gases from deep within the oldest, or “conventional,” layer of the landfill, according to Cyndi Darling, an environmental specialist with DEP. Some of those gases, including methane, are being picked up by rainwater passing through the landfill, resulting in leachate, which then flows into nearby groundwater, she said Tuesday.

“We need to determine if the impacts are caused solely by the conventional landfill,” she said.

The oldest layer of the landfill, constructed in 1975 under different ownership and less stringent regulation, sits over an unlined gravel pit.

The water quality problem is confined to landfill property and has not led to contamination of the nearby Souadabscook Stream, Darling of the DEP said.

Landfill officials have acted to reduce the leachate issue, including installing a drain 15 years ago around the perimeter of the landfill, Meagher said.

“It isn’t as if the corrective actions and the improvements started today,” he said. “It’s been going on for 15 years.”

From the town’s perspective, the water problem should be resolved before an application to increase capacity is considered, Lessard said.

Pine Tree officials have proposed to reduce the escape of gas from the landfill by opening up the liner that covers the conventional layer and pumping out the leachate, Meagher said.

Though that method would address quickly and effectively the problem, puncturing the liner would be a risky move, Darling said.

“The department has some serious concerns about putting holes in the liner system,” she said.

Meanwhile, Casella continues to prepare its application to add 2.5 million cubic yards of capacity at Pine Tree. Without the extra space, the landfill will run out of room by early 2007, Meagher said.

“In order not to run out of capacity, we essentially have to build next summer,” he said.

Pine Tree took in more than 568,000 tons, or 660,000 cubic yards, of waste in 2004, more than triple the rate in 2001.

When the landfill’s last expansion was approved in 2001, Pine Tree officials estimated the annual fill rate would be 250,000 cubic yards per year, and said the landfill’s life span would increase by 10 to 12 years, Lessard said.

“The election to fill faster is a self-inflicted wound,” she said.

Much of the growth results from an increase in construction and demolition debris coming into the landfill, Meagher said. Last year, it represented more than half of the waste received at Pine Tree, according to the annual report.

The most recent proposal to increase capacity would add six to seven years to the landfill’s life span, Meagher said, revising the prediction he made in April, when the proposal became public, that it would last 10 to 12 years.

His projection is made with the assumption that more than half of Pine Tree’s trash will be diverted to the West Old Town Landfill, Meagher said.

Estimating future fill rates, however, continues to be a guessing game, he said.

“We have no more of a crystal ball than anyone else does,” Meagher said.

Data from Pine Tree Landfill’s annual report for 2004:

Tons of waste received: 568,133 (compared to 566,877 in 2003)

Composition of all 2004 waste accepted at Pine Tree Landfill:

53 percent construction and demolition debris

19.3 percent front-end process residue

11.7 percent ash

6.5 percent water and wastewater treatment sludge

5 percent municipal solid waste

2 percent miscellaneous special and nonspecial wastes

1.7 percent oversized bulky waste

Remainder: nonfriable asbestos, slaker grit, leather scrap and sandblast grit