An organization of community activists called on state officials Thursday to pick up the pace developing a cleanup plan for vast amounts of contamination still left at the former HoltraChem factory in Orrington.

Members of the Maine People’ s Alliance acknowledged that “significant progress” has been made removing contaminated buildings, leftover mercury and other toxic materials from the old HoltraChem factory.

But alliance members said they are frustrated that the Maine Department of Environmental Protection has not moved more aggressively to complete a cleanup plan for the rest of the factory grounds.

Specifically, the group wants the former owner of HoltraChem, Mallinckrodt Inc., to remove hundreds of thousands of tons of mercury-contaminated soil buried in several large landfills on-site.

Adam Goode, Penobscot Valley organizer for the alliance, said the DEP needs to make Mallinckrodt “sign on the dotted line” to commit to a full cleanup of the site. He also called on the Board of Environmental Protection to hold hearings on a final remediation plan this year.

“We want a hearing by the end of the year,” Goode said. “The longer this gets drawn out, the more concerned we are about loss of interest and loss of resources.”

Maine People’ s Alliance field canvassers plan to go door-to-door in communities from Orrington to Belfast seeking signatures on a petition putting pressure on the DEP and the company, alliance member Sam Rioux of Holden said Thursday.

The Maine People’ s Alliance and a second organization went to court to force Mallinckrodt to clean up mercury contamination from the chlor-alkali factory, which operated from the 1960s through 2000. Since then, the company has spent about $35 million cleaning up the 235-acre site.

But Mallinckrodt and DEP officials have yet to agree about the best way to deal with the enormous piles of contaminated soil.

Missouri-based Mallinckrodt could not be reached Thursday for comment.

The DEP has consistently said the soil should be removed from the site. But company officials have predicted that digging up the dirt would spread contamination and, instead, have advocated encapsulating the toxic dirt on-site.

Scott Cowger, spokesman for DEP, said the department hopes to complete its recommendation on the final cleanup plan later this year. Cowger said it is likely that the DEP still will call for removing all soils in the final plan, but added that staff have not completed the recommendation yet.

The next cleanup stage is the most complex and will be very expensive, so DEP staff members are working hard on the recommendation, he said.

“We’ re anxious to get it resolved as well,” Cowger said.

Another protracted battle also is looming over how to clean up the large amounts of mercury that flowed from the HoltraChem site into the adjacent Penobscot River. A panel of researchers is studying whether it would be better to remove the contamination or allow the river to flush the mercury naturally over time.

Mercury is a powerful toxin that is particularly dangerous to the neurological development of children and fetuses.