These Vapors Aren’t Water

Mention “vapor barrier” and many people are like to think of “moisture barrier,” something to keep water vapor out of wall cavities and prevent the growth of mold. That’s not what Wes Robb has in mind.

For Robb, director of technical strategies and applications at Vapor Mitigation Strategies, a vapor barrier is something that keeps chemical vapors out of a building. It is very different from a moisture barrier.

Last year, the US Environmental Protection Agency issued guidance on protecting building occupants from the intrusion of chemical vapors.

Previously, “remediation dealt with soil contamination and ground water contamination,” Robb said. Vapor, he said, is a new pathway the EPA is now addressing.

Remediation of soil contamination often consists of digging up the contaminated soil and hauling it away or covering it with a concrete cap. Remediation of contaminated ground water often consists of pumping and treating the water or monitoring it by way of wells and hoping that nature takes care of it.

Where there’s a vapor plume, however, “There are very few ways it can be addressed and a vapor barrier system is needed to close the pathway into the building,” Robb said.

It is important to understand that a moisture barrier is not like a typical vapor barrier system. “Water has chemical properties that are different from those of penetrating solvents, so you need something different,” he said. “Moisture barriers provide no protection against chemical vapors. Solvents go right through them.”

A vapor barrier has two main parts, he explained, a trenched channel to guide vapor to upright flues to take it out of the building and a 3-component, chemical resistant layer that blocks vapors from entering the breathing zone of the building.

“A building, like any box you put on the ground, creates negative pressure, especially when the HVAC system draws air from within the building. When you have negative pressure, vapors get drawn into the building from underground. If you have a vapor barrier system, the vapors bounce into the 3-component layer, migrate to the channel, and go up the pipe out of the building so that they never enter the breathing zone,” he said.

Alternatively, if the vapor concentration is high, “It is also possible to install active venting systems, like radon-style systems, to pull vapors out,” he added.

The EPA installed a vapor barrier system at Meramec Caverns this summer, Robb said, because of TCE (trichloroethylene) fumes entering the show cavern from a nearby vapor plume. The EPA is installing vapor barriers in Washington, MO, to protect homeowners adjacent to a former chemical manufacturing plant. And the State of Missouri and the EPA are installing vapor barriers in the Chicago Heights neighborhood off of Page Avenue, because ground water contamination is producing vapor plumes.

Vapor Mitigation Strategies is a new subsidiary of Wellington Environmental. One of the things that led Wellington to create Vapor Mitigation Strategies, Robb said, is that in performing Phase 1 assessments or AIA due diligence for customers, they were uncovering vapor risk issues. “If it is found, it needs to be addressed. There are liability issues and sampling requirements. It is pretty complex and we realized we were leading clients into a world where they were being told that there is a problem, but there may not be a solution. Now, we can offer them a solution,” Robb said.

“Nationally, there are not a great many folks doing this kind of work. Locally, we think we might be the only ones,” he said.

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