TRC Logo

1Source Safety and Health is now part of TRC, a leading national provider of engineering and consulting solutions supporting a clean energy future. Learn more.

Related Links

Read our latest Risk Factor Newsletter:

3/29/2021 - Odor Surveys and Assessments - 2021

If you ever had an odor or indoor air quality issue within your facility you can appreciate the difficultly in identifying the sources or causes and responding to questions from employees.

Vapor Intrusion

Wednesday, June 17, 2009
Vapor Intrusion

What is vapor intrusion? Why is it now a concern? Is occupant health affected? Are there risk-assessment criteria?

Vapor IntrusionAccording to the EPA, “Vapor intrusion is the migration of volatile chemicals from the subsurface into overlying buildings. Volatile chemicals in buried wastes and/or contaminated groundwater can emit vapors that may migrate through subsurface soils and into indoor air spaces of overlying buildings in ways similar to that of radon gas seeping into homes.” As with radon, there may not be an odor, so the problem can go undetected for a long time. Odors will only be present after the odor threshold of a volatile chemical is reached.

The concentration of vapors in a building will also vary, based on factors including: volatile chemical concentrations in the soil and groundwater, groundwater depth, time of year, temperature, ventilation within the building, and activities within the building. In a worst case scenario, it is possible that vapors from volatile chemicals in a building will accumulate to concentrations that could cause or exacerbate health problems among building occupants.

Vapor intrusion is a rapidly developing field of science as is policy making by the EPA and various states that have guidelines. The EPA first issued a guidance document called “Evaluating the Vapor Intrusion into Indoor Air Pathway” in December 2001. Since then, states such as New Jersey (October 2005), Delaware (January 2007) and Pennsylvania (October 2002) have also developed guidelines. The guidelines typically include information and requirements for:

  • Site-specific screening
  • Sampling procedures and investigation
  • Evaluation of analytical results
  • Understanding background contamination
  • Remedial action
  • Community outreach

Each of these six areas requires significant scientific/engineering expertise to meet the requirements of the guidelines. In addition to input from hydrogeologists, environmental engineers, industrial hygienists and others, there must also be collaboration with the state regulatory staff every step of the way to ensure that the guidelines are met.

One very important document that is required to be developed is the Vapor Intrusion Workplan (VIW) which details every step and process used to identify where samples will be collected, how they will be collected, how they will be analyzed, how data will be interpreted and much more. The VIW must be approved by the regulators before preceding, as it is the road map that must be followed.

Air sampling within a building is done using Summa canisters with specific regulators/orifices to collect samples over an eight- to 24-hour period of time.

Vapor IntrusionSlab and room samples are collected simultaneously to allow for a comparison of compounds found in the sub-slab air to those found in the indoor air.

The comparison will then identify what, if any, contaminant contribution is being made by sub-slab gases entering the indoor air via vapor intrusion.

Please contact Chris Schneider, CIH, President at 610.524.5525, ext 14, or email to discuss any questions or to request a proposal.