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Remediation: 2014 Natural Gas Odorant Spill Site Work Complete
NorthWestern Energy, working with the Montana Department of Environmental Quality, completed remediation in October 2023 at the site of a 2014 spill of the odorant added to natural gas.
The odorant is not toxic but contains mercaptan, which has a strong, skunk-like odor. It is added to natural gas to make it easy to detect leaks.
The spill was at NorthWestern Energy’s natural gas facility east of Cut Bank, Montana.
When the spill occurred, crushed rock, a specially manufactured liner and other materials were used to construct an engineered cap and vapor extraction system over the spill site.
Vapor mitigation took place for the next nine years, after which it was determined in consultation with Montana Department of Environmental Quality that the cap could be removed, the final step of the site’s remediation.
Monitoring for odors took place at the site during the work, including along the perimeters of NorthWestern Energy’s natural gas facility.
“Proactive measures to handle any detected odor were part of our site remediation plan to prevent a nuisance for the public and calls about suspected natural gas leaks to local officials,” said NorthWestern Energy Project Engineer Ben Sorensen. “Odorant, which contains mercaptan, is added to natural gas to signal a leak in order to reduce the chances that the leak causes safety or health-related issues. It is extremely effective, but that meant our remediation work needed to include processes to mitigate any residual odor remaining from the 2014 spill.”
Common household bleach is used to neutralize mercaptan odor and was on hand and used when the remediation crew encountered residual odors in the soil around the location where the leak began.
“We worked closely with the Montana Department of Environmental Quality for a plan to contain the odors from the spill, utilize methods to mitigate the non-toxic vapors and, after an appropriate amount of time, remediate the site,” Ben said.
