In addition to the possibility of arsenic getting into the groundwater, the rocks in the ore’s geologic formation are largely sulfides — they have a lot of the element sulfur in them. When sulfide rock interacts with air and water, it produces sulfuric acid — battery acid. That’s another reason the tailings have to be kept from the rest of the environment.
If the acidic water is uncontained, it not only can kill fish and other life directly: When it reacts with rock it causes dangerous chemicals — like arsenic and toxic metals — to leach out of the rock and into the water.
The same process could happen with the “waste rock” that doesn’t go to the mine’s mill. It, too, would produce acid.
“You just dig this stuff up and throw it on the ground,” but water and air “can migrate through the waste-rock piles easily,” says David Chambers, president of the Montana-based Center for Science in Public Participation and a mining expert whom the NRCM brought to Maine in April to talk to the Legislature’s Environment and Natural Resources Committee.
Acid drainage from a sulfide mine can go on for hundreds and thousands of years. There are mines in the United States that have produced acid-making waste that will have to be controlled, for all intents and purposes, forever — “perpetual-storage issues,” Chambers calls these mines.
Of course, it’s impossible to guarantee protection forever.
Despite his criticism of an open-pit mine for Bald Mountain, Cummings is far from opposed to mining. He spent much of his career working for mining companies. He agrees with the critics of the current DEP mining rules that they too-severely restrict mining for metal — a “de facto ban,” he has written.
He believes Bald Mountain could be mined in either of two ways that would minimize environmental risks. One way is underground, in shafts. If the mining is done underground, the rock can be gone after precisely, and the mine would produce far less waste because “you’re dealing with a fraction of the materials” compared to what is produced if you just dig a gigantic hole in the ground to get at the ore.
But underground mining is more expensive than open-pit mining because of the equipment, skills, and care involved. It’s the rifle versus the shotgun approach, craftsmanship versus mass production, many miners employed versus a few.
Cummings also thinks the “gossan,” the 30-to-70-foot-deep near-surface top layer of weathered bedrock, could be mined for gold and some silver. But that would be a small and less financially remunerative operation — comparable, he says, to digging out a gravel pit.
In a letter Cummings wrote earlier this year to Democratic Representative Jeff McCabe, the House assistant majority leader, he estimated that 94 percent of the high-sulfide deposit at Bald Mountain would end up as tailings — more than 30 million tons.
They would be full of arsenic. Cummings added: “No one has informed the public or the Legislature that the arsenic content” is so high.
McCabe was sponsoring a bill in the legislative session that ended in June that would have largely retightened the mining rules. It was supported by the environmentalist community. With the Democrats now controlling the Legislature, McCabe convinced a majority of his fellow House members to vote for it.