More than 200 aftershocks have rumbled through Caribou County, Idaho, since a 5.3 earthquake jolted the Soda Springs/Afton, Wyo., region on Sept. 2, just south of the Greater Yellowstone Ecosystem. The unusual swarm of quakes – felt as far west as Pocatello and as far south as northern Utah – has rattled local residents and prompted area phosphate companies to take extra precautions.
The J.R. Simplot Co., Agrium Inc., and Monsanto operate open pit mines and processing plants in the phosphate-rich region. Simplot runs the Smoky Canyon Mine near Afton on the Wyoming/Idaho border and pumps its phosphate through a slurry line to its Don fertilizer complex west of Pocatello. Agrium’s Conda phosphate plant and Monsanto’s elemental phosphorus plant are located outside of Soda Springs and are supplied by mines on the Caribou/Targhee National Forest.
“We are pleased that the recent earthquakes in the area have not impacted the Smoky Canyon Mine or any of our other business interests in the area,” Simplot spokesman Josh Jordan told Green Markets. Jordan said Simplot is closely monitoring all systems, “and thankfully have found nothing irregular. We are committed to providing the safest possible environment for our employees and the communities we operate in, and will continue to move forward with these standards as a guide.”
Agrium spokesman Paul Poister said he knows Agrium employees have felt the tremors, but no workers have been injured and no damage done to Agrium’s facilities. “Having been through a few earthquakes, I know that it can be unnerving,” he said. “The effect on Conda Phosphate Operations has been little to none.”
Poister said there have been several minor trips of detectors at Agrium’s sulfuric acid plant due to the tremors, indicating that its equipment and safety systems are working as they should to protect people, the environment, and equipment. Agrium also uses survey prisms at its mine to monitor walls, but no movements resulting from the quakes have been detected. Poister said Conda has a “robust” wall stability monitoring program that requires specific action anytime there is movement, such as adding extra spotters at the mine to visually inspect areas of concern.
At Agrium’s gypsum stacks, operators have been doing visual reviews of the structural integrity of tailing pond dikes several times a day. “As a precaution, we have consulted an engineer for additional guidance,” Poister said. “Agrium is monitoring the situation closely and is prepared to take additional safety measures if or when they are required.”
Monsanto spokesman Trent Clark said his company’s laser reflectors and sensors on mine walls also have shown no impact to slope stability from the recent quakes.
“Our deepest mines go down around 400 feet. The epicenters of these quakes are over a dozen miles down,” Clark told Green Markets. “We’re fairly confident that the relationship, if any, is in the reverse: The quake activity in this area is historically responsible for some of the bending and folding that has exposed phosphate ore, not the other way around.”
Clark said he has received many inquiries as to whether the quakes might be caused or exacerbated by regional phosphate mining, but he noted that Dr. David Pearson, an Idaho State University assistant professor of geosciences, said there is no fracking in the area and phosphate mining is likely not contributing to the tremors.
“All of the earthquakes are between two and 14 kilometers in depth, which is much deeper than mining operations,” Pearson wrote Clark in an e-mail message.