NASHUA — With prospective buyer Bernie Plante on board to purchase the contaminated Mohawk Tannery site, environmental advocates are urging the Environmental Protection Agency to take no shortcuts during the cleanup.

Carrying signs stating “Do the right thing,” and “You can’t bury problems,” members of the local group North-East-West (N.E.W.) Nashua Civic Association participated in a public hearing on the project Wednesday at Nashua City Hall.

“We want to make sure the site is finally cleaned up,” Gerardo Millan-Ramos, remedial project manager with the EPA, told those in attendance.

The contaminated property at the corner of Fairmount Street and Warsaw Avenue was previously deemed to have hazardous substances traveling into the Nashua River due to past disposal practices at the tannery, also known as Granite State Leathers; the company produced tanned hides for leather between 1924 and 1984.

About six years ago the city demolished several dilapidated buildings located on the 30-acre tannery site in the northern part of the city. Now, Millan-Ramos said, the local developer has entered a purchase-and-sale agreement for the property and is seriously committed to cleaning it up and developing the parcel.

After considering different cleanup alternatives, the EPA is recommending a preferred alternative of encapsulation and impermeable capping instead of excavation and moving the contamination off site.

“Cost, implementability and effectiveness are all things that we considered,” Millan-Ramos said.

He said the capping alternative is the least expensive option at an estimated price-tag of $8 million to $14.2 million. Excavating and moving materials off site would take about $32.6 million to complete, according to Millan-Ramos.

The parcel is currently owned by Chester Realty Trust.

“It doesn’t sound like anything is going to be addressed underneath,” said Elizabeth Caswell of N.E.W. Nashua Civic Association. If nothing is preventing contamination from seeping down, what is stopping it from getting into the water, Caswell questioned.

Several people said they did not feel the cap alternative would be sufficient.

“Toxic waste should be consolidated at facilities designed to handle toxic waste, not left in a community where a containment breach threatens neighbors and the Nashua River,” Woody Little, New Hampshire community organizer with Toxics Action Center, said in a statement. “The site is not secure as is, but that is no reason to charge forward with half measures.”

Joe Masiello, an abutter to the property, expressed concerns about the proposed secant walls that will encapsulate two contaminated lagoons, insisting that they will eventually leak.

“Who will be responsible for monitoring those leaks?” asked Masiello, stressing there will be disruption when the developer begins to lay foundations.

“We don’t have many of those answers right now,” said Millan-Ramos, adding negotiations and discussions are continuing with the proposed buyer.

The remedial design has been carefully vetted and will include thorough oversight, according to Millan-Ramos.

“There should be no releases to you,” he explained. The preferred alternative for cleanup would take up to 18 months.

It is still unclear who is responsible for paying for the cleanup, however Millan-Ramos said if there are any costs to the city, they would be minimal. Still, he said it is expected the developer, city and the state will be partners in the effort.

Kelsey Dumville of the EPA said the ultimate goal of the cleanup is to protect human health.

“We are not going to put a cap on and run away,” she stressed.

“In all honesty, we are not hiding anything here,” Millan-Ramos said.