A decades-long debate over the prospect of a metal mine in the mountains of Aroostook County will be rekindled Thursday as another proposed overhaul of state mining regulations receives a public hearing.

Opponents again are gearing up to voice their concerns about the potential for mining operations to release waste materials and naturally occurring toxins, such as arsenic and cadmium, from the soil into the surrounding waters and environment.

The Department of Environmental Protection is proposing revised regulations governing large-scale metal mining in Maine under legislation passed in 2012 to replace a 1990 law. Such mining operations haven’t existed in Maine since 1977. The new proposal, which has to be approved by the Legislature, would create permits for different levels of exploration and mining and set up rules for mining, waste disposal and long-term pollution control.

Though the 2012 law was prompted by a proposal to mine gold, copper, zinc and other metals at Bald Mountain in Aroostook County, the rules would apply to the entire state.

In a summary of the regulations, the DEP said they offer “performance-based standards” and “requirements designed to prevent the contamination of surface and groundwater.” The Maine Board of Environmental Protection is holding a public hearing in Augusta over the proposal, beginning at 9 a.m. Sept. 15.

Nick Bennett, a staff scientist with the Natural Resources Council of Maine, said the DEP’s proposed regulations “have not gotten significantly better” than the past two versions that were opposed by his organization and rejected by the Legislature. The process of creating an open-pit mine and extracting metals would create large quantities of wastewater and acidic rock, he said.

One of the main problems, he argues, is a part of the 2012 law that would allow mines to degrade groundwater in the mining area. As the law states, “Discharges to groundwater from activities permitted under this article may occur within a mining area, but such discharges may not result in contamination of groundwater beyond each mining area.”

According to the DEP’s proposed regulations, any water that would be discharged outside of the mining area into other water bodies would have to meet quality standards, though Bennett and others are skeptical about controlling impacted groundwater at a mining site that could be larger than 50 acres.

“The idea that you can allow that and keep it on site is a very dangerous idea,” Bennett argues. “In Maine, groundwater connects to surface water very easily.”

While the DEP has taken into consideration comments from the past two rule proposals, the agency “cannot exceed or act contrary to its rulemaking authority and other state laws,” David Madore, communications director for the DEP, said in an email Monday.

“Although the environmental community expressed significant concerns over some elements of the Department’s previous proposal (especially the definition of “mining area’ and restrictions against mining on state lands) the Department does not have the ability to fully address these concerns without statutory changes” by the Legislature,’ Madore wrote in response to publicized criticisms.

Among other provisions in the DEP’s proposed regulations are requirements for preventing leaching from acidic rocks and metals and long-term financial assurance and contingency plans for mine closure, monitoring and remediation.

Maine’s 1990 law and the regulations adopted the next year prohibited groundwater contamination in a mining area, Bennett said. That law was passed in the wake of concern over the Callahan Mine in Hancock County, which closed in 1972 and is now a federal superfund site that has been linked to elevated levels of copper, lead and zinc in a nearby estuary.

No metals have been mined in Maine since 1977, when an underground copper and zinc mine in Blue Hill closed. The 2012 mining law was prompted in part by J.D. Irving Ltd’s interest in potentially developing a mine at Bald Mountain, about 12 miles west of Portage. The company, which did not respond to recent requests for information about its potential mining project, is a majority owner of the forest land around Bald Mountain and has said the existing law and regulations from 1991 effectively prohibit mining in general.

At 1,526-feet tall, Bald Mountain is home to one of several of Maine’s massive sulfide ore deposits, formed more than 250 million years ago through oceanic volcanoes and holds gold, copper, zinc and other metals.

In 1977, after the area had been logged, Auburn native John Cummings, former chief geologist with the Sewall engineering company, discovered the valuable metals at Bald Mountain and set off a wave of interest in a potential mine. In 1990, the Swedish mining company Boliden Resources proposed harvesting gold, copper and zinc at Bald Mountain but ended up not moving ahead with an application. Another company, Black Hawk, also backed out of a plan in 1997 to mine for copper and gold.

Bald Mountain stands in the working forest of the North Maine Woods, in the headwaters of multiple lake and river systems, among logging operations and leased family camps and campgrounds.

“Many families consider this area to be a sacred place,” said Betsy Terrell, an agricultural sciences teacher in Storrs, Connecticut, whose family has long had a camp on Carr Pond, 2 miles north of Bald Mountain. Terrell’s late father was a railroad executive and worked as a guide from his cabin on Carr Pond, where Terrell and her husband Craig plan to spend much of their retirement.

The Terrells, along with Bennet and local environmental advocates, say they are concerned a mine would threaten the region’s natural asset of water, as well as displace camps in the area.

“This area depends so much on natural resources for sustainable jobs that people have — farmers, hunters, guides,” said Gail Maynard, a retired educator and organic beef farmer from Woodland.

The valuable metals in Bald Mountain are contained in and among rocks with a number of substances, including naturally occurring toxins like arsenic, cadmium and lead that the mining opponents fear could be released by a mining operation. They also expressed concerns about the potential failure of mining infrastructure like wastewater-holding ponds, as happened at the Polley copper, gold and silver mine in British Columbia in August 2014, when a dam breach released more than 2 billion gallons of “tailings” water into nearby waterways.

“The more we learned about it, the more we realized that it couldn’t be done safely,” Craig Terrell, a plant scientist, said.

“I think we throw away enough materials that could be recycled,” he added, referring to modern civilization’s dependence on metals for everything from bridges to smartphones and solar panels.

Supporters of a Bald Mountain mine argue that modern industrial technology and regulations can prevent water contamination in the surrounding area and that the project would bring hundreds of jobs and millions in tax dollars over several decades.

“I do believe it can coexist,” said Bob Dorsey, president of the Aroostook Partnership, a nonprofit business coalition. “It does in New Brunswick and other countries.”

Sharing the same northern Appalachian range as Maine, New Brunswick has a long history of mining in the Bathurst Mining Camp, a region once home to the one of the world’s largest lead and zinc mines before it closed in 2013 after 50 years.

This year, production began at the Caribou Mine and Mill, a complex at another formerly closed mine in the Bathurst mining region, with a mine and processing and waste treatment operations for extracting copper, gold, lead, silver and zinc. In central New Brunswick, about 40 miles east of the border with Bridgewater, there are plans for an open pit mine for tungsten and molybdenum.

Irving, which operates forestry and other businesses in Atlantic Canada, has not been involved in a mine before, though Dorsey said the company has the resources and incentives to invest in a long-term, responsibly run mine. Global metal prices are currently low and there has been no formal application for a mine here in Maine.

Dorsey said a mine operating for 20 or 30 years would fit in well with the local economy’s natural resources and leave much of the surrounding forestland undisturbed. He and others also argue that the region, with its aging workforce and gradually shrinking population, would welcome an industry offering jobs for regional residents and employees from out-of-state companies who hopefully would settle in the area with families.

At the same time that Aroostook County’s economy could benefit from a mine, Dorsey said, the region already has good opportunities for job-seekers.

With some 31,000 jobs in The County, there is about 10 percent annual turnover that Dorsey said is largely because of waves of retirements, which are opening up jobs in agriculture, business management, education, insurance, health care and social services. “I don’t know an employer that isn’t looking for qualified workers,” Dorsey said. “We don’t have as many technical jobs or the variety of jobs in the Boston or Portland areas, but we have a lot.”

Before any mining operations or new jobs in the field can be created, however, the debate over the proposed regulations must first wind its way through the BEP and the Legislature.