Presented October 30, 2014 - Presentation Slides
Validated Methods to Distinguish Between Vapor Intrusion and Indoor Sources of Volatile Organic Compounds by Dr. Thomas McHugh
Indoor sources of volatile organic compounds (VOCs) are ubiquitous, resulting in detectable concentrations in indoor air, often at concentrations above regulatory screening levels. As a result, distinguishing between vapor intrusion and indoor sources of VOCs is a significant challenge, greatly increasing the cost and complexity of vapor intrusion investigations. The conventional process includes a questionnaire to identify indoor VOC sources, followed by indoor and sub-slab sampling for off-site analysis with a typical turn-around time of two weeks. When results are finally received, investigators must reconstruct field observations to decipher the potential sources of specific VOCs detected in the indoor air samples. Through ESTCP, we have developed tools and decision logic to allow for rapid and accurate discrimination between vapor intrusion and indoor sources of VOCs. These include on-site GC/MS and stable isotope analyses. The investigation approaches have been validated through application at a number of single-family residences and industrial buildings including buildings with difficult-to-locate indoor sources, a building with immovable indoor sources also found to have vapor intrusion, and a building with vapor intrusion through a sewer line.
Multi-Year Monitoring of a House Overlying a Dilute Chlorinated Hydrocarbon Plume: Implications for Vapor Intrusion Pathway Assessment by Dr. Paul Johnson
Vapor intrusion (VI) is often a risk driver at chlorinated hydrocarbon cleanup sites, particularly those with extensive dissolved plumes underlying residences and other buildings. SERDP funded a multi-year study linking laboratory-scale research and modeling studies with field-scale assessment in a real home overlying a dilute TCE plume next to Hill Air Force Base to enable more accurate and cost-effective assessments of VI. Real-time monitoring of indoor air, building properties, subsurface concentrations and environmental factors has been underway since 2010. Phase I focused on monitoring under natural conditions. Phase II involved monitoring under constant forced building under-pressurization. Phase III, currently in progress, involves studying the impact of a foundation land drain under both depressurized and natural conditions. This presentation presented results from this study in the context of vapor intrusion pathway assessment. Topics covered included sampling duration and frequency, decision-making with typical VI data sets, confounding effects of indoor sources, effects of environmental factors on vapor intrusion, and how new short-term TCE exposure guidelines may lead to rethinking of VI pathway assessment approaches. This project was selected as the SERDP Project of the Year in 2011.
Dr. Thomas McHugh is a toxicologist with GSI Environmental in Houston, Texas. He is a Diplomate of the American Board of Toxicology and has over 20 years of experience in the environmental industry. He received a B.A. in Biochemistry and Environmental Science from Rice University (1990), an M.S. in Environmental Engineering from Stanford University (1993), and a Ph.D. in Toxicology from the University of Washington (1997). Dr. McHugh has conducted and managed a variety of projects related to vapor intrusion including large field investigations and model development. He was the principal investigator for three vapor intrusion research projects funded by the Department of Defense through ESTCP leading to the development of improved methods to distinguish between vapor intrusion and indoor sources of VOCs. He is the lead author of several peer-reviewed journal articles, peer-reviewed conference proceedings and technical documents on vapor intrusion. Dr. McHugh has developed and taught training classes on a number of topics including vapor intrusion.
Dr. Paul Johnson is a professor and the Dean of the Ira A. Fulton Schools of Engineering at Arizona State University in Phoenix, Arizona. He has over 25 years of experience in the remediation field, ranging from theoretical analyses to detailed field-scale studies focused on the design, monitoring, and optimization of soil and groundwater remediation systems and modeling and monitoring related to risk assessment. He has co-authored guidance documents for both industry and regulatory agencies, and has served as advisor to DoD, industry, and EPA. Dr. Johnson was the Editor-in-Chief of the National Ground Water Association's journal Ground Water Monitoring and Remediation from 2003 through 2012 and served on the recent National Research Council Committee on Future Options of the Nation's Subsurface Remediation Effort, the results of which were published in 2013. He has received numerous awards, including NGWA’s Keith E. Anderson Award in 2011 and more recently the Brown and Caldwell Lifetime Achievement Award at the 2014 Battelle Conference. Before joining Arizona State, Dr. Johnson was a senior research engineer for Shell Development in Houston from 1987 through 1994.