AUGUSTA — The Maine Board of Environmental Protection endorsed a major rewrite of mining regulations on Thursday, setting the stage for another legislative debate over the contentious issue.

The board voted unanimously to provisionally adopt rules creating a multi-tiered permitting process for mines and obligating operators to provide “financial assurance” to cover the costs of closing the mine or cleaning up any environmental problems. Yet the board also received more than 400 comments opposing the rules during its review, highlighting ongoing concerns about the environmental implications of reviving Maine’s long-dormant mineral extraction industry.

Opponents said the proposed rules will put at risk the health of lakes, rivers and coastal marshes – and by extension the tourism economy – by allowing mining beneath water bodies as well as on public lands. They also questioned the “financial assurance” aspects of the proposal and suggested the rules could allow long-term pollution.

“We still strongly oppose the rules and don’t believe they will protect Mainers from having to pay to clean up a major disaster or that they will protect water quality,” said Nick Bennett, staff scientist at the Natural Resources Council of Maine.

The rules now to go the Legislature’s Environmental and Natural Resources Committee for review.

Officials with the Maine Department of Environmental Protection have said the changes are needed to address inconsistencies between existing rules and statutes that could prevent the department from ensuring the state’s natural resources are protected by a proposed mining operation. Those inconsistencies arose from the fact that the Legislature directed the DEP to update Maine’s decades-old mining rules – which had largely shut down mineral extraction in Maine – but has subsequently rejected several versions of those rules, creating a sort of regulatory limbo.

DEP Deputy Commissioner Melanie Loyzim described the proposed rules as a “comprehensive, robust set of environmental protection standards.”

“We are hopeful that people will recognize that this version is substantially changed over previous versions and it attempts to address many of the concerns that have been raised,” Loyzim said.

Lawmakers have been debating Maine’s mining regulations for more than four years. The first proposed rewrite was introduced at the behest of New Brunswick-based J.D. Irving Ltd, which was hoping to tap into the sizable deposits of gold, silver and other minerals underneath Bald Mountain in Aroostook County. Irving reportedly stepped away from the debate after the last re write attempt failed in 2015, but DEP officials insist the state needs detailed rules to review future applications.

The Maine Geological Survey lists a total of 10 sites with “significant known metallic mineral deposits” scattered around the state. Dozens of other known deposits have yet to be fully explored in part because the mining laws in place prior to 2012 were so stringent that they discouraged investment by the industry.

The proposal that won unanimous support Thursday from the BEP would create a multi-tiered review process for applications to explore an area for minerals as well as to begin mining operations. Mines would have to be inspected by independent inspectors throughout the construction, operation and closure of the facility.

The rules would also require mining operators to cover the costs of cleaning up contamination from any “worse case scenario” for up to 100 years and would prohibit mine operators from storing waste rock underwater for long periods post-closure. (Water is often used as “cover” to prevent weatherization of newly exposed rock that can cause acidic runoff.)

But opponents questioned the feasibility of allowing mine operators to create temporary mine waste storage units filled with water.

“It is hard to conceive that you would be able to create these (containment) structures, put waste in there for up to 30 years and then think you will be able to de-water them and put the waste elsewhere,” said Lew Kingsbury, a Pittston resident heavily involved the mining issue. “These are designed to be permanent structures.”

Kingsbury also pointed out that the proposed rules would allow operators to fill open pits or shafts with water after closure, potentially creating a “death trap” for migratory waterfowl and other wildlife. As proof, Kingsbury pointed to the thousands of migrating snow geese that died in November after the birds landed in the toxic waters of the Berkeley Pit, a former copper mine in Butte, Montana.

In an attempt to address some concerns, the DEP’s latest proposal prohibits “tailings ponds” of ore waste during mine operations as well as the long-term, underwater storage of waste after closure. In a separate memo sent to lawmakers along with the proposed rules, the department and the BEP recommended the Legislature clarify state laws to exclude mining activities in flood plains or flood hazard areas and to clarify the department’s authority for regulating mining on public lands.

Bennett, the staff scientist with NRCM, called the memo a “positive sign” but reiterated that his organization still opposes the overall rules.

“I think these are signs that the overwhelming opposition from Maine citizens, who want rules that will actually protect our clean water and taxpayers, is starting to have an effect,” Bennett said.