Thank you to my colleague Jim Ray for his contributions to this post. Jim is a partner in our Environmental & Energy Practice Group.

We have all been involved in investigating and remediating sites with soil and groundwater contamination. But another form of contamination has been recently gaining attention—vapor intrusion.

Vapor intrusion is the migration of volatile chemicals from soil or groundwater into soil gas and, ultimately, indoor air. The presence of these chemicals in indoor air can cause human health concerns. While regulatory guidance regarding acceptable indoor air levels and vapor intrusion mitigation varies across jurisdictions, vapor intrusion considerations are showing up with more frequency in site investigations.

When evaluating the potential for vapor intrusion, it is important to begin by identifying whether a migration pathway exists. Sampling indoor air will not always answer the question of where the vapors may be coming from—and how to stop them. Indoor air can be contaminated by a number of sources, none of which may involve the migration of volatile chemicals from the subsurface. Oftentimes, the investigations begin with soil and/or groundwater sampling to determine if there could be a subsurface source, followed by evaluation of a structure or building to determine if it is susceptible to vapor migration.

If contaminants are detected in indoor air above a certain level, and it is determined or presumed that those vapors are migrating from the subsurface, both short and long term abatement measures may be required. Because of the potential for human health impacts, immediate action to stop the vapor migration may be required. While these actions do not typically eliminate the source, they aim to prevent the migration of vapors into a building or structure. Long term remediation may require source identification and remediation, such as soil removal or groundwater remediation.

The recent focus on vapor intrusion is impacting sites that are currently under investigation as well as sites that may have already been investigated and/or remediated. Because of this, it is important to evaluate both current and legacy sites to determine whether vapor intrusion is or could be a concern.