Rain-on-snow events raise fears about Smurfit Stone berms

On Thursday evening, Elena Evans, Missoula City-County Environmental Health manager, told the Frenchtown Smurfit Stone Advisory Group that  the snow from Missoula’s long winter may increase the risk that the Clark Fork River could damage the earthen berm around the Smurfit-Stone mill site, threatening the contaminants within.

After some drought years, the Clark Fork River above Missoula is running very low, only about 1,300 cubic feet per second compared to the average flow of around 2,700 cfs, according to U.S. Geological Survey data. But that could change quickly by the time the flow peaks, usually around late May.

Even though western Montana’s high-elevation snowpack is close to the 30-year average for this time of year, a cooler than average March and early April has allowed the snow at lower elevations to stick around longer than previous years. Some of the snow data sites - such as the Lubrecht Flume at 4,680 feet in the Blackfoot drainage - are registering snow moisture at more than 300% above normal.

“Look at all this snow that we have at lower elevations. That 's going to drive what our spring flows look like - that’s going to drive the danger more than (the high-elevation snow),” Evans said. “We need to keep that in mind when we’re thinking about risk. We need to think about if we have a rain-on-snow event, if we have an atmospheric river, things can change really quick.”

Those who remember the Yellowstone River flood of last June should be familiar with what can happen when those two conditions occur. The mountains of the Greater Yellowstone region had a record low snowpack on April 1, but cool temperatures kept the snow around through May and early June.

Then in mid-June, an “atmospheric river” - a band of heavy moisture rolling northeast from the Pacific Ocean - brought significant rain to the region. But that alone wouldn’t have caused the flood that took out bridges and inundated the towns of Livingston and Red Lodge, said Smurfit Stone CAG member Bruce Sims.

“It wasn’t really such an extraordinary rain event, but it was enough to bring off a lot of snow. Snow can be up to 50% water when it’s melting down. And every drop of rain also brings out more water from the snowpack,” Sims said. “California had 12 atmospheric rivers hit in five weeks this year. Two years ago, British Columbia had three hit in one (week). Everyone who studies this says that the atmospheric river thing - it may not be that there’s more of them but they’re going to be bigger. That's the issue with a warming atmosphere.”

The last time Missoula had significantly high spring runoff was 2018. The Clark Fork River flowed brown and high through town and pounded into the Smurfit Stone berm. Since the earthen berm wasn’t engineered to be a flood-proof levy, cracks developed in the berm and tea-colored water rose in the wastewater ponds, which prompted a lot of emergency action, Evans said.

“That (runoff) was a less than 1-in-25-years event. If we think about what happened in Yellowstone, that was a 1-in-500-years event,” Evans said. “So we had dramatic movement (of the berm) in a 1-in-25-years event. But we haven’t seen the berm really tested since the mill shut down and it was regularly being fixed.”

Sims showed photos illustrating the way the river moved a lot of earth and cobble around during the 2018 event, changing the river channel. A floodplain analysis shows that the river has meandered throughout the valley over the centuries.

Based on that, if a  rain-on-snow event caused the Clark Fork River to flood even more than in 2018, Sims said he could see the berm being breached at a bend where the river hammered the berm in 2018. The river doesn’t have to overtop the berm, being just compacted earth, to wash it out.

“It’s easy to envision that you could have the full might of the Clark Fork coming right through this site. And that’s why we need to know what’s buried in the site because it’s possible that material could end up in the main stream and be washed downstream,” Sims said. “We need to know what that is so we know what the risks are.”

The Environmental Protection Agency has been reluctant to do much more sampling than is needed to clean up the site to a set level. Only recently has the agency agreed to consider doing additional sampling to look at groundwater and soil contamination in more areas of the site.

But investigating what kind and how much toxins - dioxins, furans and PCB’s produced during pulp mill operation - might be scoured out by a flood would require a lot more work.

“It’s something that’s often been discussed and something that isn’t nicely fitting into the Superfund (process) and the data quality objective conversation,” Evans said.

However, that and removal of the berm will be discussed once again during a Missoula County Board of Commissioner meeting on May 16 when the county will have a better idea of how high the spring runoff might get.

Contact reporter Laura Lundquist at lundquist@missoulacurrent.com.