Initial construction of the engineered cap.
Thermal oxidation unit and vapor extraction pipe connections.
Passive vapor extraction units.
Remediated site returned to original grade.
REMEDIATION: 2014 NATURAL GAS ODORANT SPILL SITE WORK COMPLETE By Jo Dee Black
ing along the perimeters of NorthWestern Energy’s natural gas facility.
NorthWestern Energy, working with the Montana Department of
“Proactive measures to handle any detected odor were part of our
Environmental Quality, completed remediation in October 2023 at the
site remediation plan to prevent a nuisance for the public and calls about
site of a 2014 spill of the odorant added to natural gas.
suspected natural gas leaks to local officials,” said NorthWestern Energy
The odorant is not toxic but contains mercaptan, which has a strong,
Project Engineer Ben Sorensen. “Odorant, which contains mercaptan, is
skunk-like odor. It is added to natural gas to make it easy to detect leaks.
added to natural gas to signal a leak in order to reduce the chances that
The spill was at NorthWestern Energy’s natural gas facility east of
the leak causes safety or health-related issues. It is extremely effective,
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
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.
was determined in consultation with Montana Department of Environ-
“We worked closely with the Montana Department of Environmental
mental Quality that the cap could be removed, the final step of the site’s
Quality for a plan to contain the odors from the spill, utilize methods to
remediation.
mitigate the non-toxic vapors and, after an appropriate amount of time,
Monitoring for odors took place at the site during the work, includ-
remediate the site,” Ben said.
BRIGHT MAGAZINE Environment Edition | 13
