Vapor Intrusion Best Practices for Brownfield Redevelopers


Across the country, former industrial facilities are finding new life as they are repurposed for use as nonindustrial commercial spaces, such as retail, churches and even schools. Often these buildings are brownfield properties, complicating redevelopment because of past industrial use that led to contaminated soil and water at the site.

Historically, lenders and buyers have been comfortable financing and purchasing properties where soil and groundwater contamination existed because these buildings often can be used without disturbing existing contaminants. These types of buys are known as “innocent land owners,” because they didn’t cause the pollution, and if their use of the building wasn’t impeded, they weren’t responsible for cleaning up the site.

However, vapor intrusion has significantly changed the landscape for brownfield redevelopers. Now, just by buying a property and putting occupants or tenants into the building, the once innocent landowner now takes on liability for tenants and the potential exposure to harmful vapors caused by contaminants.

There are two property types that are hit hard with the vapor issue. The first is former industrial manufacturing facilities. The harsh chemicals and processes that were historically used at these sites left residual contamination in soil and groundwater. The second is run-of-the-mill strip malls that have been built across the country since the 1960s. Along with retail spaces, these mixed-use buildings often had dry cleaners, which have contributed substantially to the footprint of trichloroethylene (TCE) and perchloroethylene (PCE) contamination. These solvents are very volatile, and persist for quite a distance in the soil. As these buildings are redeveloped to include not only retail spaces but restaurants, groceries and even daycare spaces, the need to mitigate intruding chemical vapors is obvious.

As redevelopers continue to be innovative with the uses for properties, the size of the vapor intrusion problem will only expand. Vapor mitigation and post-mitigation certification are the only ways to ensure everything is working the way it should be and ensure the new and repurposed building is safe.

The U.S. Department of Health & Human Services and the U.S. Environmental Protection Agency, Washington, D.C., have been studying vapor intrusion for decades, from which they’ve ascertained very conservative health threshold values, called Vapor Intrusion Screening Levels (VISLs), for the intrusion of chemical vapors into breathing spaces. Contamination in the air can quickly become widespread. Because indoor-air contaminants can be prevented, the regulatory agencies often take an aggressive approach to enforcement of efforts to minimize or eliminate the pathway.

The first step of any mitigation effort is building diagnosis. This includes testing to determine how well air pressure and vacuum can be applied to the sub-slab below the building. This is conducted by using blowers to create a uniform vacuum pressure field underneath the entire building, using technology similar to residential radon mitigation. If there are no pressure leaks, vapors are swept away so they don’t make their way into the breathing space in the interior of the building. However, if left unmitigated, small cracks and pressure gradients between the indoor air and the sub-slab can allow these vapors to move indoors.

The type of soil under a structure significantly impacts the distance that a negative pressure-field will extend from the point at which the vacuum is applied. In granular soil, a pressure-field vacuum may extend 50-100 feet from the vacuum point, compared to heavy clays where it may only extend 15-20 feet. Soil conditions often vary from one part of the building to the next, so design work must adapt to the subsurface conditions. Once the entire footprint of the building is mapped out for the points of the vacuum field, full scale construction can begin.

A Phase I Environmental Site Assessment (ESA) is the standard by which property due diligence is completed. In 2013, the EPA changed that standard to require all environmental practitioners to determine whether a project is free of potential vapor risk, based on past building use and official property records. If a risk is determined, the buyers are required to do some sort of testing, potentially leading to mitigation. Some states differ on mitigation requirements but the trend is moving toward mitigation, especially as properties change ownership or intended use.

As the problem of vapor intrusion continues to rise to prominence, technologies and best practices in the industry will continue to evolve. The best way to determine if a building is at risk is to proactively work with an environmental practitioner to conduct a Phase I ESA and learn what the options are for the building.

About the Author
Aaron Benker
, Remediation Resource Manager, is a principal at Wenck, an employee-owned consulting enterprise with a united team of engineers, scientists, hazardous materials specialists, construction, and business professionals.