AUGUSTA — A bill proposing some of the nation’s strictest environmental regulations for mining operations passed the Maine House on Thursday after a lengthy debate about whether metallic mines are compatible with Maine’s nature-based tourism economy.

With a lopsided 126-14 vote, the House gave initial approval to a bill that would ban most open-pit mines, prohibit mining under waterways or public lands, and require companies to set aside money to cover any environmental problems. The Senate has already given the bill initial approval, although additional votes and debate are expected on an issue that has been bouncing around the Legislature for five years without resolution.

The margin of victory in the House suggests that the bill, L.D. 820, could have enough support to override a potential veto from Gov. Paul LePage.

After several hours of debate, House lawmakers rejected a bill that would have banned metallic mining in Maine and, instead, endorsed a bill that supporters said would allow mining only under strict conditions. Supporters argued the bill will also resolve a potentially exploitable situation, in which mining companies could seek a permit under existing rules that state regulators say are likely inadequate to protect the environment.

“We have a lot at stake; so much of our economy depends on other natural resources,” said Rep. Bob Duchesne, D-Hudson, a veteran member of the Environment and Natural Resources Committee that has spent years working on various mining bills. “This bill might allow mining but we are not going to take the risk for (companies). If you’re going to mine in Maine, you’re going to do it the Maine way or you’re not going to do it.”

But opponents warned that the bill would still allow open-pit mines smaller than three acres and would likely lead to groundwater contamination because pollution plumes are difficult, if not impossible, to control.

“I believe that the best way to stop pollution is to never allow it in the first place,” said Rep. Denise Harlow, D-Portland, another veteran committee member who regards mining as short-term gain for long-term costs. “The risk is too great. Maine relies on clean water, clean air and clean land. We are tourism based, this is what we rely on and we are putting that at risk.”

Mining has become a perennial fight in the Legislature ever since New Brunswick-based J.D. Irving Ltd. sought to re-write decades-old mining environmental regulations that had discouraged mining in Maine. J.D. Irving was hoping to mine for gold, silver and copper under Bald Mountain in Aroostook County, which is believed to hold one of the largest deposits of precious metals in Maine.

The issue became bogged down in policy fights between the LePage administration, environmental groups and lawmakers, however.

The bill likely headed for final passage last week would ban open-pit mines larger than three acres as well as operations on state-owned public lands, in flood plains and under lakes, rivers or ponds. The legislation would prohibit underwater storage of mine waste – a major contamination concern for environmentalists – and instead require companies to store waste in dry piles.

Additionally, the legislation requires mining companies to create a trust fund sufficient to cover the costs of cleaning up or treating any environmental contamination for at least 100 years after closure of the mine.

More than 150 people or organizations had testified or submitted comments on the bill, which was the subject of weeks of work sessions. Many of Maine’s largest environmental organizations endorsed the final product, which was crafted with input from staff at the Natural Resources Council of Maine. Bill sponsor Sen. Brownie Carson, D-Harpswell, is a former longtime head of the NRCM.

Yet the final product also won support from the Maine Department of Environmental Protection, which had opposed an earlier version. Following a late-April committee vote, deputy DEP commissioner Melanie Loyzim said the compromise represented a “reasonable outcome” that was “very protective but not completely prohibitive” of mining in Maine.

Environment and Natural Resources Committee co-chairman Rep. Ralph Tucker, D-Brunswick, noted that he opposed a mining bill two years ago because he believed it was inadequately protective. The current bill resolves many of his concerns from two years ago over open-pit mines, tailing ponds, which are impoundments, and mining on public lands, Tucker said.

“This is real progress,” Tucker said. “It brings the rules and the statutes together. It gives legal clarity to businesses. It is much more protective than what we have now.”

But Rep. Ralph Chapman, D-Brooksville, cited the estimated $45 billion Superfund cleanup project of the former Callahan Mine in his district as a cautionary toll of the dangers of mining. Chapman said the State House grounds would fit within the allowed three-acre open-pit mine and said he found it difficult to understand why lawmakers want to allow groundwater pollution within 100 feet of a mine site.

“You cannot contaminate the groundwater and expect that it will stay in the region only within 100 feet. There’s no way to do that. There is no known technology to do that. It’s not possible,” he said.

The bill would direct the Maine DEP and Board of Environmental Protection to craft rules consistent with the regulatory standards adopted by the Legislature. LePage has vetoed earlier bills directing the board to rewrite mining rules and accused lawmakers – and environmental groups – of killing potential jobs from mining.