Testing the Chemical Resistance of VI Barriers: A Closer Look at One Method

According to the Interstate Technology and Regulatory Council, vapor intrusion chemicals of concern vary by regulatory agency and may include:

• Volatile organic compounds (VOCs) such as hydrocarbons (for example benzene), chlorinated hydrocarbons (for example trichloroethylene (TCE), tetrachloroethylene (PCE), and vinyl chloride), and methane
• Select semi-volatile organic compounds such as some polycyclic aromatic hydrocarbons (PAHs), naphthalene, and some polychlorinated biphenyls (PCBs)
• Select inorganic compounds, such as mercury (elemental), pesticides, and hydrogen cyanide
• Per- and polyfluoroalkyl substances (PFAS)

For the performance of barriers that are specifically installed for VOC vapor intrusion, chemical resistance is the most critical factor when evaluating a product's ability to be protective against the chemicals of concern. This is due, in part, to the ongoing debate regarding sub-slab attenuation factors, the liability concerns of building owners/lenders/attorneys, and a regulatory environment that is still evolving. These factors combined place great importance on the protection that vapor intrusion barriers provide, so any claims about a system must be proven. This can be achieved through testing – and reputation.

Similar to ASTM methods used to test physical properties, diffusion and permeation testing can yield results that sometimes vary by several orders of magnitude. However, it is essential to note that diffusion differs from permeation rates and testing methods.

Presently, there is no third-party standard such as an ASTM test for diffusion rates across barriers, but a "de facto" standard has been accepted by three of the major composite barrier manufacturers in the United States. Here, we would like to present an example: GeoKenetics Inc from Irvine, CA developed a simple method that measures how vapors will diffuse through a barrier over a minimum of 120 days.

What is the GeoKinetics Method?

With the Geokinetics method, testing involves placing 7-inch diameter membrane samples between two chambers with different solvent vapor levels. The rate of vapor transmission from one chamber to the other through the membrane is then measured over an extended period of time. The membrane samples were next placed between two cylindrical, 6-inch diameter borosilicate glass test chambers. The lower test chambers were partially filled with a solution of distilled water and solvent. The test cells were maintained at a constant temperature of 70° Fahrenheit (+2° F) throughout each test. The solvent solution was prepared to provide a specific vapor level in the lower chamber based upon the test temperature and the Henry's law constants for the solvents.

Evaluation of Results: The effective diffusion coefficients were evaluated for both solvents using Fick's law, as follows:

Mt=Dc × ∆C∆X×A

Where:

M = the quantity of solvent which diffused across the membrane during the test (mg)

t = the test duration (days)

Dc = the membrane diffusion coefficient (m² / day)

∆C = the difference in the solvent vapor concentration between the lower and upper cells = the concentration in the lower cell (mg/m)

∆X = the thickness of the membrane (m)

A = the membrane area (m²)

Test results were as follows:

Optimal Vapor Intrusion Barrier Systems

The most effective vapor intrusion systems must be tailored to site-specific needs, and it is essential the manufacturer fully understands the intricacies and capabilities of each system they sell. This knowledge sets some companies apart from others, for a trusted manufacturer can help identify and specify the ideal system for specific site conditions. Building owners can then feel peace of mind knowing that any residual vapors are properly contained, and the structure is protected.

At EPRO, we test our systems and can help dial in the exact vapor intrusion barrier for your site needs. Share your site conditions and we can get to work – together.