“Understanding Transients in Vapor Intrusion” by Dr. Eric Suuberg
This presentation highlighted results from an ESTCP project in which the project team examined which factors are responsible for the many reports of large, several-orders-of-magnitude variations in indoor air contaminant concentrations resulting from vapor intrusion processes. The insights are provided by a combination of 3-dimensional computational fluid dynamic modeling of vapor intrusion as informed by statistical analysis of data sets from sites that have yielded extensive temporal data (the Arizona State University [ASU] site adjacent to Hill Air Force Base, the EPA site in Indianapolis, and the Naval Air Station North Island site). All these sites have shown significant temporal variations in indoor air contaminant concentrations but for different reasons. The ASU site is characterized by a well-known preferential pathway that delivers contaminant to a gravel sub-base. Modeling has showed that this kind of scenario involves the interplay of the preferential pathway with a permeable sub-base to obtain the observed large variations. Existence of only one or the other condition will not lead to large variations. Modeling results also showed that the existence of subslab preferential pathways will not necessarily be apparent during subslab soil gas sampling. On the other hand, the Navy represents an example in which the behavior is dominated by unusually large pressure fluctuations. Statistical analysis of the data sets also suggested that even absent a preferential pathway or high indoor pressure fluctuations, order of magnitude variations in indoor air contaminant concentrations can be driven by the interplay of normal indoor pressure and air exchange rate fluctuations. Finally, we considered the transient impacts of controlled pressure method sampling.
“New Tools for Radon and Volatile Organic Compound Vapor Intrusion Mitigation” by Dr. Todd McAlary
This presentation highlighted an ESTCP project that demonstrated new tools to reduce the cost of mitigating VOC vapor and radon intrusion to buildings. At present, most mitigation systems are designed using standards developed over 30 years ago when there was a robust radon research program, but these methods are arguably outdated. New equipment like digital micromanometers with data-logging capability have changed our ability to monitor pressure in ways that did not exist decades ago. Using an analogy to groundwater pumping tests, we can now calculate the permeability of materials below the floor slab and the bulk average permeability of the floor slab, which are two critical parameters affecting the radius of influence (ROI) of soil gas extraction wells (a.k.a., suction points, vent-pipes). This research demonstrated several new ways to assess the ROI, including vacuum, velocity, travel time, vertical flow across the floor slab and mass removal rates to design, operate and maintain optimal systems. The return on investment is up to 10 times the cost of the incremental effort to implement this technology for large buildings, which is a significant part of the building stock for the Department of Defense. A summary of the testing methods and four case studies was provided.
Dr. Eric Suuberg is a registered professional engineer in Rhode Island. He presently serves as a Project Leader, Research Translation Core (RTC) Leader, and Associate Director of Brown’s NIEHS-supported Superfund Research Program (SRP). Suuberg was a co-founder of Brown’s program in Chemical Engineering, as well as a cofounder of the Masters Program in Innovation Management and Entrepreneurship. He is also an active consultant on problems related to environmental pollution and its causes, with extensive contacts in the environmental consulting, legal and regulatory communities. His research focus has been in the areas of chemical thermodynamics, kinetics and transport. His work in the SRP and ESTCP programs relates to vapor intrusion and combines study of the thermodynamics of interphase partitioning with consideration of the vapor intrusion transport processes that bring the contaminants to receptors. Related projects involve experimental examination of thermodynamic properties of relevance to environmental fate and transport processes for organic contaminant mixtures such as tars, oils and halogenated hydrocarbons. His group is also looking at how VOC partitioning in indoor environments interacts with the dynamics of vapor intrusion, which might contribute in still unknown ways to the wide swings in indoor air concentrations observed in the field.
Dr. Todd McAlary is a Practice Leader for Vapor Intrusion Services at Geosyntec Consultants in Toronto, ON. Todd has over 30 years of international consulting experience, focused mostly on chlorinated solvents and vapor intrusion. He measured vapor diffusion coefficients for his graduate research in 1986 and performed vapor intrusion assessments at hundreds of sites beginning in 1992. Since 2001, Todd served as a member of EPA’s Expert Panel on Vapor Intrusion and authored or co-authored over a dozen guidance documents on the topic. He conducted applied research and developed several new technologies including high volume sampling, passive sampling, building pressure cycling, mass flux monitoring, tracer testing, aerated floors, isotope analysis and several types of mathematical models with funding from ESTCP, the U.S. Air Force and the U.S. Navy. Todd earned a bachelor’s degree in geological engineering, a master’s degree in hydrogeology and a doctoral degree in chemistry, all from the University of Waterloo. He is licensed as a professional geologist in North Carolina and as a professional engineer in Ontario and British Columbia. He is an Adjunct Professor at the University of Toronto.