In an effort to refine its understanding of mineral copper, zinc, silver, gold and barite deposits at the Palmer Project, mining exploration company Constantine Metals provided an overview Tuesday to the Haines Borough Assembly of their plan to blast a one-mile tunnel into the mountain that will provide more extensive and year-round drilling access.

The meeting came after the assembly introduced an ordinance that would ban the storage of hazardous material in water, a ban that would effectively prohibit a mine from building a tailings dam to store mine waste. Constantine’s vice president of community affairs Liz Cornejo objected to the ordinance last month.

The company had planned to release its preliminary economic assessment (PEA) this winter, but has yet to do so. Cornejo said the report, which will include details such as estimated mine construction costs, estimated lifespan, mineral tonnage and other economic factors, has been designed around a dry stack tailings surface storage, a more expensive method that is considered less risky than storing waste in a tailings dam.

Takshanuk Watershed Council science director Derek Poinsette attended Tuesday’s meeting.

“(Dry stack storage is) an improvement, in general, over a tailings dam,” Poinsette said. “It doesn’t mean some future mining company couldn’t change the plan. I’m curious to see what that looks like in their PEA because of the conditions up there.”

The project requires a waste management permit from the Alaska Department of Environmental Conservation (DEC) and a reclamation plan. The 16-foot diameter tunnel will create 70,000 cubic meters of waste rock, Cornejo said. The groundwater that drains from the tunnel will be diverted into two settling ponds that, combined, are the size of an Olympic swimming pool, Cornejo said. After sediment settles from the water, the wastewater will be released back into the ground through perforated pipes.

Consulting geologist Jack DiMarchi, who is coordinating permitting with Constantine, said when the water is discharged it can’t legally change the chemistry of the groundwater it flows into. The company plans set monitoring wells above and below the discharge point to measure for such changes.

“We’re going to discharge this water, but if we start seeing that we’re actually changing the chemistry of the groundwater beyond the statistically significant levels then we have to work with DEC to stop doing that,” DeMarchi said.

DEC staff won’t inspect the water, but will rely on Constantine to provide water chemistry reports on a quarterly basis.

Some residents have voiced concerns about avalanche danger in the area, along with negative environmental effects from acid-generating rock. Cornejo said, based on the rock composition studies in the area, that they are unlikely to encounter acid-generating rock. As a contingency, the company plans to store such material by covering it, containing runoff and haul it back into the tunnel for final disposal, according to the permit application.

Cornejo said they’ll use waste rock blasted from the tunnel to create avalanche berms and other surface construction work.

The assembly plans to ask more questions at a future meeting.