The Maine Board of Environmental Protection voted unanimously Thursday to provisionally adopt new regulations that could open the door for large-scale metal mining that hasn’t occurred in Maine since 1977.

Environmental groups immediately announced they were mounting a campaign to convince state lawmakers, who must still approve the regulations, to reject them and to replace the 2012 law the regulations were developed under.

The BEP’s decision means the Legislature will vote for the third time on mining regulations developed by the Department of Environmental Protection after lawmakers twice voted down previous versions created under the same law. That law changed Maine’s two-decade-old mining regulations in an attempt to streamline and modernize permitting of metal mines.

Since the latest proposed regulations were introduced publicly in September 2016, environmental groups and 441 citizens have voiced their opposition in public comments to the BEP, according to the Natural Resources Council of Maine, which analyzed and tallied the comments. The DEP and the BEP acknowledged Thursday that the rules received significant criticism from members of the public.

“Many have asserted that no standards could be sufficiently protective,” said Melanie Loyzim, DEP deputy commissioner, referencing the public comments during a discussion with the BEP before the vote Thursday morning.

The latest version incorporates changes aimed at addressing some of the concerns about groundwater pollution and long-term contamination from large open pit mines.

While the proposed regulations allow mining, they “provide a stringent, comprehensive approach” with “performance based standards,” Loyzim said.

The 2012 law was spearheaded by Rep. John Martin of Eagle Lake in part because of an interest by Canadian forest products giant JD Irving Ltd. in potentially developing a mine for copper, zinc and other metals at Bald Mountain in Aroostook County, where the company owns industrial timberland in the North Woods.

The law replaced a 1990 law that was passed in the wake of pollution issues at the Callahan Mine in Hancock County, which closed in 1972 and is now a federal superfund hazardous waste cleanup site. Some legislators and mining advocates said the 1990 law essentially banned mining in Maine, while environmental groups criticize the new law as being too lax for allowing groundwater contamination in mining areas, among other things.

The Legislature had ordered the DEP to draft new rules to implement the 2012 law, but lawmakers have since twice rejected proposed regulations. Environmental groups have said that the law also limits the regulations the DEP can develop, and that it should be repealed and rewritten with stronger protections.

“These rules will not protect Maine’s clean water or its taxpayers,” Nick Bennett, a staff scientist with the Natural Resources Council of Maine, said in a media release issued Thursday.

The Natural Resources Council of Maine and other groups are looking to galvanize mining opponents to voice their concerns about the regulations to the Legislature and to urge their representatives to vote against them. Before a vote by the full Legislature, the Environment and Natural Resources Committee will be holding a public hearing on the regulations in Augusta, likely in February or March.

The BEP also is sending a memo to the Legislature highlighting areas in the 2012 law that should be revisited and possibly changed — a sign that the BEP is listening to concerns of the public, according to Bennett.

Based on criticism and public comments from citizens, the BEP is suggesting to the Legislature that lawmakers “clarify” a number of issues in the mining law, including about locating waste impoundments in floodplains. The board also suggests lawmakers clarify provisions of the law concerning discharges to groundwater — which environmental advocates say amount to allowing groundwater contamination. In addition, the board seeks clarification of the DEP’s regulatory authority over mining on public lands.

In some changes adopted since a public hearing in September 2016, the DEP attempted to address a range of concerns raised by members of the public, according to Jeff Crawford, the DEP’s state implementation plan specialist.

The mining regulations provisionally adopted by the BEP include new language governing mine tailings (collections of mine processing effluent), mine waste, and long-term financial assurances for potential cleanup costs.

The proposed regulations would ban “wet tailings” impoundments with acidic-generating waste, while allowing “wet mine waste,” such as the unprocessed top layers of rocks that could be used to fill in areas of mine, such as mine shafts, during the life of the mine.

The rules would still allow open pit mining and allow mining under wetlands and water bodies.

Crawford said the revised proposal will require an independent third-party monitor to track compliance with environmental standards. The proposal also would require a company to cover all costs of cleaning up contamination from catastrophic mine failure for a minimum of 100 years, as well as remediation and restoration of air and water quality in surrounding areas.

“This addresses virtually every possible situation,” short of an “asteroid strike,” Crawford said.