July 23, 2018

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Todd McAlary Authors "Fluid Flow Model for Predicting the Intrusion Rate of Subsurface Contaminant Vapors into Buildings" Article for the Environmental Science and Technology Journal

Todd McAlary, Ph.D., P.Eng., P.G. (Toronto), authored an article entitled "Fluid Flow Model for Predicting the Intrusion Rate of Subsurface Contaminant Vapors into Buildings " published in the Environmental Science & Technology (ES&T) journal on June 25, 2018.

His coauthors were John Gallinatti, P.G., CEG, CHg (California), Gordon Thrupp, Ph.D. (California), William Wertz, Ph.D. (New York), Darius Mali (Ontario), and Helen Dawson, Ph.D. (Washington D.C.).

Todd is a Senior Principal Engineer with more than 30 years of international consulting experience focused on the evaluation of contaminant fate and transport in soil and groundwater.

ES&T is a source of information for professionals in a wide range of environmental disciplines, published by the American Chemical Society.

The American Chemical Society, founded in 1876 and chartered by the U.S. Congress, is the world's largest scientific society. Their mission is to advance the broader chemistry enterprise and its practitioners for the benefit of Earth and its people, and their vision is to improve people's lives through the transforming power of chemistry.


A new method is presented for calculating a building-specific subslab to indoor air attenuation factor for use in assessing subsurface vapor intrusion to indoor air. The technique includes (1) subslab gas extraction with flow and vacuum measurements and mathematical modeling to characterize the bulk average vertical gas conductivity of the floor slab, (2) monitoring of the ambient pressure gradient across the floor slab with a micromanometer, (3) calculating the volumetric flow of soil gas into the building (Qsoil), and (4) dividing Qsoil by the building ventilation rate (Qbuilding) to calculate a building-specific attenuation factor. Sample calculations using order statistics from 121 individual tests are comparable to the U.S. Environmental Protection Agency empirical attenuation factors for residential buildings and the U.S. Navy empirical attenuation factors for commercial/industrial buildings. A case study of a commercial building shows encouraging agreement between the attenuation factors calculated via this method and via conventional subslab and indoor air sampling.

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Learn more about the article: https://pubs.acs.org/doi/10.1021/acs.est.8b01106"
For consultation regarding subsurface contaminant vapors, contact Todd McAlary at This email address is being protected from spambots. You need JavaScript enabled to view it.
Learn more about Todd at: https://www.geosyntec.com/people/todd-mcalary