Distinguishing Vapor Intrusion from Indoor Sources of VOCs

ESTCP 2014 Project-of-the-Year Award for Environmental Restoration

  • Dr. Thomas McHugh, GSI Environmental Inc.
    Use of Compound-Specific Stable Isotope Analysis and On-Site Gas Chromatograph/Mass Spectrometer to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs
ER ESTCP POY Blog

(Initially Released December 8, 2014) A significant challenge posed in DoD site assessments is distinguishing between vapor intrusion (VI) and indoor sources of volatile organic compounds (VOCs). Migration of vapors from chlorinated solvent groundwater plumes into surface and subsurface structures has become an issue, but the detection of VOCs in indoor air samples does not necessarily indicate vapor intrusion, as background sources of VOCs are ubiquitous. Because conventional methods of investigation do not clearly identify the source of VOCs, additional rounds of sampling are often required, greatly increasing the cost and complexity of investigations.

Working concurrently on two ESTCP projects, Dr. Thomas McHugh of GSI Environmental Inc. and his team performed a field investigation to validate the use of compound-specific stable isotope analysis (CSIA) as a method to distinguish between VI and indoor sources of VOCs, and developed a step-by-step protocol that can be used to provide an independent line of evidence to determine whether buildings are impacted by vapor intrusion. The study found that the CSIA protocol is most useful in buildings that have previously been sampled with investigation results showing VOC concentrations near or above regulatory screening levels, where differentiating between indoor and subsurface sources is critical for site and risk management. CSIA is less intrusive and requires less training to implement than some other methods, but was not found to be a standalone investigation approach.

The team also investigated the use of on-site analysis using a portable gas chromatograph/mass spectrometer (GC/MS) to allow users to understand the distribution of VOCs in real-time and support identification of the VOC source while in the field. This study developed and validated an on-site GC/MS analysis protocol that can be used as a standalone investigation method or within a larger investigation program. This investigation method supports on-site sampling and data interpretation in the field, and can reduce the need for further sampling.

These innovative techniques can now be used to significantly reduce vapor intrusion investigation costs by reducing the need for follow up investigations, and in some cases, by supporting identification and removal of indoor sources of VOCs during the investigation. 

For this important work, Dr. McHugh and his project team received the 2014 ESTCP Project-of-the-Year Award for Environmental Restoration. Project Overview - CSIA; GC/MS

Project Team 

  • Dr. Thomas McHugh, GSI Environmental
  • Lila M. Beckley, P.G., GSI Environmental
  • Ignacio Rivera-Duarte, PhD, SPAWAR Systems Center Pacific 
  • Kyle Gorder, P.E., AFCEC Hill AFB IST
  • Erik Dettenmaier, PhD, AFCEC Hill AFB IST
  • Dr. R. Paul Philp, University of Oklahoma, Norman
  • Dr. Tomasz Kuder, University of Oklahoma, Norman

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