May 10, 2019

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Todd McAlary, Justin Knight, and Theresa Gabris to Present on Vapor Intrusion at the EMDQ Conference

Todd McAlary, Ph.D., P.Eng., P.G. (Ontario), Justin Knight, P.E. (Georgia), and Theresa Gabris, P.G. (Washington, D.C.) will present at the 2019 Department of Defense Environmental Monitoring & Data Quality (EMDQ)Workshop in Orlando, Florida on May 13-16, 2019.

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

Justin is a Senior Engineer based in Georgia with more than 12 years of experience focused on site assessment, characterization and remedial investigations; remediation design; vapor intrusion assessment; radiological contamination surveys and mitigation; and community/public relations.

Theresa is a Project Geologist based in Washington D.C. focused on contaminant fate and transport, conceptual site modeling and site remediation, and primarily manages vapor intrusion (VI) projects.

With representatives from the United States Army, Navy, Air Force, and Defense Logistics Agency, the EMDQ Workgroup's primary mission is to develop and recommend Department of Defense (DoD) policy pertaining to environmental sampling, laboratory testing operations, and data quality. The primary goals are to: promote the generation of environmental data of known and documented quality; develop and recommend DoD policy affecting environmental sampling and testing operations; facilitate a coordinated response to legislative and regulatory issues; coordinate the exchange of technology and best management practices within DoD; and improve overall performance.

Geosyntec Participation

Title: New Tools for Vapor Intrusion Mitigation Design
Presenter: Todd McAlary
Time: 10:15-10:45 a.m. on May 13, 2019
Abstract: New methods for design and monitoring of vapor intrusion mitigation systems have been developed through a Demonstration/Validation research program funded by the U.S. Department of Defense through ESTCP Project ER201322. The new methods include: 1) measuring ambient cross-slab pressure over time to establish a building-specific target vacuum level; 2) measuring vacuum as a function of both time and radial distance from the suction point, 3) verifying the gas velocities below the floor using helium tracer testing (inter-well tests and flood tests); 4) measuring the mass emission rate of the system and 5) a mathematical model programmed into a spreadsheet. The new test methods are fast, inexpensive, and not excessively complex. The research indicates that indoor air quality can be protected at significantly lower costs using the new methods, especially for large buildings. Case studies will be discussed.

Title: Rapid and Effective Characterization of Building Susceptibility to Vapor Intrusion using Mass
Loading Techniques
Presenter: Theresa Gabris
Time: 11:45-12:15 p.m. on May 13, 2019
Abstract: Vapor intrusion (VI) risks are challenging to assess using conventional discrete indoor air sampling because of spatial and temporal variability in volatile organic compound (VOC) concentrations. Evaluating mass loading through building pressure control (BPC) and subslab venting (SSV) offer a means of quickly characterizing building susceptibility to VI and estimating the potential VI risks. BPC tests can be conducted in one to two days for most buildings, and provide data that characterize the range of potential impacts that may arise from VI and background sources under the typical operating (baseline) conditions of the building. Measuring contaminant concentrations and flow from SSV system effluent helps estimate worst-case VI potential.

BPC tests were conducted over multiple seasons in a small- (~2,000 SF) and medium-sized (~11,000 SF) commercial building through ESTCP Project ER 201503. During the tests, the buildings were depressurized (which promotes VI) and pressurized (which hinders VI) to various levels using a blower door, while concurrently measuring indoor air concentrations and a variety of physical parameters like cross-slab and cross-building pressure differentials. Mass loading was also monitored over multiple seasons at eight residences with existing SSV systems to inform system shutdown decisions. This presentation will focus on the results of these three case studies and ways to use BPC and SSD data to strengthen VI risk management decisions.

Title: Introduction to High Volume Sampling and a Case Study
Presenter: Justin Knight
Time: 11:30-12:00 p.m. on May 15, 2019
Abstract: High Volume Sampling (HVS) is a new method developed by Geosyntec to assess the potential for vapor intrusion in large buildings, rapidly, with greater confidence and at lower cost. HVS requires significantly less time and is less invasive than traditional approaches. This technique allows collection of more meaningful information that can be used to make decisions on risk management regarding vapor intrusion.

Some guidance documents suggest sampling sub-slab soil gas at a frequency of 1 sample per 1,000 to 1,500 square feet. For small buildings, this is achievable, but for large buildings it can become unworkable. The HVS technique can be used to do the same job faster and with fewer slab penetrations. Unlike conventional, discrete sub-slab sampling, HVS provides information over a broader area by purging and screening tens of thousands of liters of soil gas.

Case Study
A case study will be discussed that highlight how HVS was used to perform a VI investigation in a large, active military manufacturing building. The team built a VI conceptual site model (CSM) and applied the HVS technique to test the VI-CSM across a majority of the hangar.

More Information

About the Sponsor:
For consultation regarding vapor intrusion, contact Todd McAlary at This email address is being protected from spambots. You need JavaScript enabled to view it..
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