Emergency federal government assessments are being sought for a spill of more than 105,000 gallons of tailings slurry at the Kensington Mine that occurred Jan. 31, although officials with mine owner Coeur Alaska say no damage to nearby salmon habitats occurred and there are “no long-term effects from this spill.”

The spill occurred at a welded joint in a pipeline that likely started as a “pinhole” and increased in size due to pressure from the slurry flow, resulting in a leak that lasted 23 hours, according to a report of the incident published by Coeur on Thursday. About half of the tailings from the gold mine about 45 miles northwest of Juneau reached a creek about 430 meters away that drains into Berners Bay, although according to the company much of the flow was diverted.

“Upon discovery of the leak, mill shutdown was initiated immediately,” an executive summary of the report states. “A response team was quickly assembled to place straw watles in drainages to further prevent tailings from entering Johnson Creek. Heavy equipment was deployed to the scene to remove tailings from Pipeline Road. Within 40 minutes of the spill discovery water samples were taken to characterize any impact to Johnson Creek.”

However, requests for emergency Essential Fish Habitat (EFH) assessments have been issued to the U.S. Forest Service and Environmental Protection Agency by local officials with the National Oceanic and Atmospheric Administration, according to an internal federal agency newsletter distributed Monday.

“The spill released over 105,000 gallons of tailings slurry (a mix of mine tailings and water) along a transport road and Johnson Creek, a salmon spawning and rearing stream,” the newsletter notes. “Johnson Creek drains into Berners Bay, an important subsidence[sic] area that is (essential fish habitat) to several groundfish and salmon species as well as habitat to important prey species like herring, eulachon, capelin, and Tanner crab. In our request, we are asking for information on the spill as well as remediation and future monitoring and mitigation measures that will be put in place by our partner agencies.”

The newsletter also notes NOAA Fisheries “responded to a letter from the Central Council of Tlingit and Haida Indian Tribes of Alaska regarding their concerns associated with the Kensington Gold mine tailings spill. A follow up meeting is being scheduled to hear their concerns.”

Molly Zaleski, a NOAA Fisheries resource management specialist, said Monday her division was contacted about the spill at the end of February. She said her agency’s work with Coeur includes the company raising the mine’s tailings dam to increase its holding capacity a few years ago, which resulted in “conservation recommendations in order to avoid any adverse impacts from that.” The current request for other federal agency assessments will allow further review of the situation and possible recommendations.

Steve Ball, the mine’s general manager for Coeur, said in an interview Monday that assessments done by his company prior to the release of its report show the creek poses no environmental risk to species.

“No toxicity has been found,” he said. “There’s no evidence that any tailings material reached salmon-spawning habitat.”

Of the estimated 105,581 gallons of slurry spilled, about 16,787 gallons were tailings, according to the report. It also states “the tailings are geochemically inert, they are comprised mainly of diorite and quartz. They pose no long-term impacts to Johnson Creek as demonstrated by the sediment sampling data and comparisons with historical data.”

Furthermore, Ball said, a series of corrective steps detailed in the report are either occurring or being implemented. Those include establishing formal procedures and providing training for responding to a tailings line release — which he said has not occurred at Kensington previously — conducting a full internal pipeline inspection scheduled for April, adding a pressure indicator alarm to the pipeline and a flow meter near the end of the tailings line.

The company’s report states a control room operator noticed a pressure drop in the tailings line at about noon on Jan. 31, and he contacted supervisors about a possible leak. A pipeline inspection that started at about 1:20 p.m. resulted in the discovery of a leak at about 3 p.m., with the control room initiating a shutdown of the pipeline about 10 minutes later and a response team with heavy equipment responding to the scene at about 3:20 p.m.

“Our pipe is a dual-line pipe, so it has an interior six-inch pipe that is within a 10-inch pipe,” Ball said. “And what happened is through abrasion over time the tails ate away at a section at a joint that had a defect on the joint and that created a small hole. Now with the volume of tails that goes through our pipe, when that hole opened up it created a bit like a jet and when that jet broke through — it started as a pinhole — it opened up to about the size of, say, a quarter. And then that jet broke through the 10-inch line. It created a hole through the 10-inch line about roughly the same size.”

The Alaska Department of Environmental Conservation’s Spill Prevention and Response Division was notified of the spill at 4:12 p.m., according to the report. The Alaska Department of Fish and Game, EPA, and U.S. Coast Guard were notified at about 7 p.m.

In addition to the initial cleanup actions and diversion of flow away from the creek, a vacuum trailer was used to remove residual tailings from freshwater drainage and employees performed in-stream cleanups of tailings, according to the company’s report.

While the duration of the leak is estimated by Coeur at 23 hours, the company’s report states the period of contamination in the creek was much shorter due to the preventative actions taken there.

“Johnson Creek was running clear approximately 2.5 hours after the discovery of the tailings line rupture,” the report states.

In 2019, the EPA reached three settlements totaling $534,500 with Coeur involving discharge violations from the Kensington mine. In 2022, the U.S. Forest Service approved an expansion of the mine’s operations that is expected to extend operations for at least another 10 years though 2034.

• Contact Mark Sabbatini at mark.sabbatini@juneauempire.com or (907) 957-2306.