A year-and-a-half after a mysterious, oily sheen was reported on the north end of Flathead Lake, a state agency is proposing a ban on new groundwater wells near Somers. It’s part of the cleanup plan for a local Superfund Site.
The Montana Department of Natural Resources and Conservation’s proposed ban would expand an existing controlled groundwater area around the former Somers Tie Plant, which treated railway ties with creosote and other chemicals for several decades before being listed as a Superfund site in the mid-1980s.
A contaminated groundwater plume is moving a couple feet each year and recently migrated beyond the existing controlled groundwater area, prompting the proposed restriction of new or altered wells in an almost 90-acre area.
The DNRC will hold a hearing on its proposal next Tuesday at 1:30 p.m. at the DNRC Northwestern Land Office in Kalispell.
Superfund site-owner BNSF Railway and the EPA announced the discovery of the mysterious sheen in Somers Bay in May of 2017, which was later identified as naphthalene and acenaphthene, two of the contaminants of concern at the Superfund site.
Update: The EPA determined the sheen to be biological in nature. Only one of multiple samples collected exceeded standards.
Roger Hoogerheide, a remedial project manager for the EPA, says while the two compounds exceeded cleanup standards, “the areas where they were detected, it was at such small pools that you had to use a syringe to take the water samples. So it wasn't a stream of water that was going into Flathead Lake.”
BNSF removed the sheen in May of 2017. But Hoogerheide says the sheen led to a more concerning discovery. The shoreline of Flathead Lake had been eroding by four to six feet each year. The lake was within 15 feet of the lined swamp pond that contains waste from the former tie plant as part site’s cleanup plan.
“If we didn't do something immediately it had the potential to erode within two to three years,” Hoogerheide says.
Hoogerheide says BNSF and the EPA built a buffer this April that included an offshore gravel beach, emergent wetlands and a berm to sequester to the contamination in the swamp pond.
As for the mysterious sheen?
“We did not see the sheen this year,” Hoogerheide says.
Hoogerheide theorizes that in 2017, snowmelt in the valley coincided with a freeze-thaw cycle that allowed surface water to infiltrate the ground, leading to tiny pockets of sheeny contamination.
BNSF Railway has a site operator tasked with monitoring the shoreline and is on the hook for future monitoring until groundwater at the site is usable. At that time, the controlled groundwater area can be petitioned to be lifted.