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What Brownfield Developers Need to Know about Vapor Intrusion – June 2023

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The 10 Things Brownfield Developers Need to Know about Vapor Intrusion

The federal Infrastructure Investment and Jobs Act, enacted by the 117th United States Congress and signed into law by President Joe Biden on November 15, 2021, is providing renewed and increased incentives for the redevelopment of brownfield sites, both urban and rural. Most voluntary cleanup programs for brownfields allow the developer (private or public) to focus remediation on eliminating risks with source treatment and engineered controls. Many brownfield developers will need to address the potential for vapor intrusion (VI) during the due diligence or development stage. Fortunately, the science and engineering associated with assessing and mitigating potential risks associated with VI have improved significantly, to the extent mitigation costs can be reasonably estimated. Montrose Environmental Group (Montrose) is a leading provider of environmental and grant funding services to brownfield developers. We offer the top 10 things a brownfield developer needs to know about VI:

  1. What causes vapor intrusion?

VI into buildings can occur from soil and/or groundwater impacted with volatile chemicals. Sources commonly include former on-site or existing nearby gasoline stations, dry cleaning businesses, repair shops, and industrial facilities.

  1. How does vapor intrusion occur?

Volatile chemicals create vapors that move vertically and horizontally through the subsurface and can enter a building through floor cracks, sumps, elevator pits, and utility trenches.

  1. Are certain buildings more susceptible to vapor intrusion?

Yes. Brownfields oftentimes have older buildings that may be desirous for repurposing. Older buildings with basements, dirt floors, stone foundation walls, tunnels, below grade utility wall penetrations, old and poorly maintained floors, and shallow groundwater conditions tend to be more susceptible to VI. 

  1. When should I be looking for vapor intrusion?

The potential for VI should be assessed during the initial due diligence period of a real estate transaction or redevelopment plan. Standards that can be used are ASTM E1527-21 for performing Phase I Environmental Site Assessment (ESA), and ASTM E2600-08 for the assessment of VI into structures. 

  1. Do I need to be concerned about vapor intrusion if a property does not have a commercial or industrial history?

 Yes. VI has been known to create unsafe indoor air concentrations at properties with no history of releases. The source of VI can originate hundreds of feet from your site via a groundwater plume that has migrated beneath your site.  Brownfields tend to be in developed areas, and it is important to be aware of both current and historical uses of nearby properties.

  1. How do I know if a building or my property has a vapor intrusion problem?

An ASTM Phase II ESA can be performed that includes collecting soil gas samples immediately below the floor slab, or in the location of a planned building, and have the samples tested at a laboratory.  The number of samples needed will depend on the size of the area and where the potential source of the VI is located.

  1. How do I fix a vapor intrusion problem in an existing building?

A VI mitigation plan starts with understanding the planned use (residential, commercial, industrial, mixed) and how the vapors are entering the building. The simplest solutions include crack sealing and the installation of radon-type sub-slab depressurization systems to control the vapors. These approaches typically require annual inspections and long-term maintenance. Long-term solutions may include finding, and treating or removing the source of the vapors.

  1. Can I prevent a vapor intrusion problem in new buildings?

Yes. During the construction of new buildings, the installation of either a passive or active vapor mitigation system can be very cost-effective and has become common in new construction. In addition, or as a substitute, vapor barriers can be installed. There are many types of membrane systems that can be installed immediately prior to a concrete floor being poured.

  1. Will I have to operate the vapor intrusion mitigation system forever?

Not necessarily; however, a vapor mitigation system is a long-term commitment and requires annual maintenance if source treatment is not planned. A vapor mitigation system can be shutdown permanently if the original source has been treated, eliminated, or naturally attenuated. A demonstration with new sub-slab soil gas data once a system has been turned off for a period of time is usually required. Specific criteria will vary from state to state.

  1. Are there funds to help address vapor intrusion at brownfields? 

Yes. US EPA and state brownfield grants can be utilized to help address vapor intrusion, whether the need is assessment or remediation.


Key Take-aways

  • Understanding and addressing VI should be incorporated into the very early stages of a brownfield redevelopment.
  • Engage an experienced consultant.
  • The planned use and layout of occupied structures impacts how to best address a VI issue.
  • Guidance and regulations vary from state to state, so be sure your consultant has the right experience.
  • Grant money or low-interest loans for assessment and remediation may be available.

Montrose’s grant funding experts have helped many communities obtain grants to address brownfields. Contact Montrose to learn more.

Stephen W. Kirschner, PE

Senior Principal, Montrose Environmental