HAMPDEN – Officials with the state Department of Environmental Protection on Wednesday refused to process an application to increase capacity at one of the state’s largest landfills, citing technical issues and the need for further review as reasons for the delay.

Wednesday marked the last of 15 working days since Casella Waste Systems Inc. submitted an application to boost capacity at its Pine Tree Landfill by nearly 50 percent. The DEP was required to determine within that time whether the application was complete and ready for processing.

“We are rejecting the application,” DEP Commissioner Dawn Gallagher said Wednesday.

Don Meagher, manager of planning and development for Casella, had not yet been notified Wednesday evening of the decision and said he was surprised to learn the application did not meet DEP approval.

“I don’t know how [Gallagher] came to that conclusion,” Meagher said Wednesday.

Technical issues with the application arose during initial review, Gallagher said, though she could not specify further. Officials also need to decide whether Casella’s proposed plan meets state and local waste disposal laws and policies through a process known as a “public benefit determination,” she said.

The project is on hold until the public benefit determination is complete.

Through that process, the department will look at how the added capacity will affect traffic, the area’s aesthetics, local and state waste policies, and other factors, Gallagher said. The DEP will accept public comment regarding those criteria, and no time constraints apply to the proceedings, she said.

“I plan to make this a very open and inclusive process,” the commissioner said.

Casella has proposed a more than $20 million project to add 2.5 million cubic yards of capacity to the 6 million-cubic-yard landfill through a system of “mechanically stabilized earth berms,” nearly vertical structures that are similar to retaining walls.

The berms would retain waste that essentially would be packed onto the landfill’s sides. The elevation of the lowest of the landfill’s two peaks would grow from 280 feet above sea level to 320 feet above sea level, which is the elevation of the higher peak, according to the application.

The application is for an amendment to Casella’s existing license for Pine Tree, a commercial landfill situated next to Interstate 95 and Cold Brook Road that accepts waste from within and outside the state.

Without the addition, the landfill soon will run out of space, even though 350,000 tons – 60 percent of the landfill’s annual tonnage – will be diverted annually to the West Old Town Landfill, Meagher has said.

The increased capacity is estimated to add six to nine years to the life of the landfill.

If the DEP determines that Casella’s plan does not serve a public benefit, the application becomes moot, Gallagher said. Otherwise, a 20-day period begins during which a public hearing on the application can be requested and funneled through one of two bureaucratic routes.

The DEP can hold its own public hearing, provided the person or group making the request presents “credible conflicting technical information” that could affect the department’s decision on the application, DEP environmental specialist Cyndi Darling said Wednesday.

Alternately, the Board of Environmental Protection, a citizens advisory group of the DEP, can assume jurisdiction over the application by DEP recommendation.

“It’s akin to requesting a jury trial,” Darling said.

In that case, the BEP would render a decision on whether to issue the amended license but would not review all of the application data, Darling said. The board has the discretion to schedule its own public hearing but, like the DEP, is not required to hold one.

Simply opposing the license, even through a formal petition, without supporting evidence isn’t enough to warrant a public hearing, Darling said.

“That’s not a technical criterion that we look at,” she said.

Beyond the public hearing option, those who want to weigh in on the application can appeal to the BEP after a decision has been rendered, Darling said.