BUTTE — Fifteen years ago, as state researchers ventured into the Berkeley Pit to collect their annual samples from the contaminated water, a surprise greeted them.
On this particular day in September, the pontoon boat they use to troll across the water wasn’t docked at its usual spot. Instead, they found the craft about 40 feet above the water, parked on a flat area along the pit’s rocky wall.
How did it get there? A landslide created a large wave, carrying the boat up in the water and docking it on the upper wall, according to Ted Duaime of the Montana Bureau of Mines and Geology.
Duaime, a hydrogeologist, said it was one of the largest landslides recorded in the pit, and it forced a significant wave. Similar landslides — although on a smaller scale — continue to occur in the pit, Duaime said.
The U.S. Environmental Protection Agency, or EPA, reported three landslides that have created wave action over the last seven months in the pit, documents show. The most recent occurred on Feb. 8.
Sara Sparks, remedial project manager with the EPA in Butte, acknowledged these incidents have happened, but the community shouldn’t worry.
“There’s been some wave action, but no threat to public health or the environment,” Sparks told The Montana Standard in a recent interview.
Slides were also reported on Aug. 22, 2012, and Nov. 3, 2012. Sparks said these slides occurred on the southeastern wall, which she said is made up of alluvial soil. While the rest of the pit is encased by more solid rock, the sloughing portion is composed of sand, clay and loose material.
The 1998 landslide — the one that left the pontoon boat 40 feet above the water — dropped 1.3 million cubic yards of material into the pit, according to Duaime. This was enough to affect the water level, he said.
Though the three recent slides were much smaller than the 1998 incident, Duaime said the February slide was still pretty large. The pontoon boat sustained minor dents when wave action slammed it into the dock. However, it wasn’t pushed out of the water as in the 1998 slide.
Duaime said his team noted that the last slide caused the water level to rise in the pit by one foot.
“That’s a fairly significant rise,” he said.
Despite the rise due to displacement from the landslide, Duaime said the water level remains below the rim of the pit. Barring a catastrophic event — such as a major earthquake — Duaime doesn’t believe these landslides will cause water to escape the pit.
The water level is about 200 feet below the rim at its lowest elevation, and about 100 feet below the critical level, Duaime said. The critical level, which was set by the EPA and the Montana Department of Environmental Quality, is the point at which the pit water could potentially seep into the groundwater aquifers. The critical level is set at 5,410 feet above sea level.
The pit water rises about a half to three-quarters of a foot each month, Duaime said.
Montana Tech professor John Ray has been outspoken with his concerns about the Berkeley Pit for years. In February, Ray sent an email to the EPA with questions concerning the slides and structural integrity of the Berkeley Pit. He told The Montana Standard he was disappointed with the answers, saying they were perfunctory and lacked detail.
“If there’s some problem with the structural soundness of the pit and a problem with water displacement, the public needs to know,” Ray said.
He added that he would like the Montana EPA and DEQ to address these concerns in some type of public forum, which has been set for March 19. See breakout.
Tom Malloy, county reclamation manager, works on the county’s team for cleaning and restoring land in Butte damaged by past mining. Malloy said he’s interested in the environmental effects of the pit’s landslides.
“I’d like to see better communication with the public from the MR (Montana Resources) and oversight groups,” Malloy said.
The Berkeley Pit is owned by the Montana Resources mining company. Tad Dale, vice president of human resources and spokesman for Montana Resources, could not be reached for comment, after repeated attempts last week by The Standard.
Open pit mining was in operation at the Berkeley Pit from 1955 to 1982. The pit is 1,780 feet deep with a four-mile circumference. The pit began filling with water after it ceased operations in 1982 and Atlantic Richfield shut off the pumps that kept water out of the pit.