According to Sarah Venator, geologist at the NPS Alaska Regional Office, Glass-Heifner was originally established as a gold mine and remained active until the 1970s. “At this site, miners would excavate the gold ore, which was primarily a mineral called arsenopyrite in quartz veins. Arsenopyrite is very high in arsenic," Venator said. The minerals were processed, or milled, by crushing and gravity separation to get the gold out. The by-product of milling, which is gravel- to silt-sized crushed rock, is called tailings. “The by-product basically concentrated arsenic in the tailings, because the arsenic had been locked up in solid mineral form inside of quartz veins, but now it was finely ground and released on the surface," Venator said.
After the discovery of the dead moose calf, NPS investigated the site to learn about the presence of contaminants like arsenic and determine the best way to clean them up. “NPS determined that the best response action was to consolidate all the mine tailings into one area on site and cap them with a thick cap of cement, Venator said. “This prevented animals and people from direct exposure to the contaminants and prevented rainwater from flowing into them." This area is called the consolidated tailings impoundment.
The Glass-Heifner mine is located in a remote part of Kenai Fjords National Park which makes it a challenging task to address. “It’s pretty costly to simply get to the site," Venator explained. “It’s nearly a full day each way to transit there from the harbor in Seward by park headquarters." While the NPS believes visitation to the site is low, the site presents significant risk to the environment and wildlife. A return-site visit in 2021 revealed erosion cutting into the bank toward the unlined tailings impoundment, which could lead to a release of the tailings into Ferrum Creek. “The concern is that if the erosion continued at the current rate that it would undercut that impoundment, leading to a failure of the impoundment structure, all of the tailings could be released from below into Ferrum Creek."
Bipartisan Infrastructure Law funds are being used to assist in the cost of removing the contaminants from the mine site. “We have fieldwork scheduled for mid-to-late September 2023, and that timeline is largely constrained by the availability of a large landing craft that’s able to transport equipment to the beach and receive over 100 tons of mine tailings on the deck," Venator said.
While the Bipartisan Infrastructure Law funds helps to dispose of the mine tailings, the long-term risk at the site is an ongoing process. NPS is responding to contamination at Glass-Heifner mine pursuant to a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) response action called a Time-Critical Removal Action. Venator said that future efforts may be dedicated to addressing more of the site. “We think that it’s possible that the arsenic that was present in the mine tailings has affected the surface soils," she said. “We are planning further environmental investigations to identify whether or not we need to take further action to address the entire site."
This project was made possible by the Bipartisan Infrastructure Law - Ecosystem Restoration, signed on Nov. 15, 2021. It is a historic investment in the restoration and protection of the environment. Learn more here.
Source: U.S. Department of the Interior, National Park Service