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Vapor Intrusion Guidance

Vapor Intrusion Guidance Updates

The Oregon Department of Environmental Quality is updating guidance on how vapor intrusion is evaluated at environmental cleanup sites. The vapor intrusion guidance is a tool to help evaluate current or future buildings that are prone to indoor air pollution from underlying or nearby contamination. This is the first update since DEQ's 2010 Vapor Intrusion Guidance and it includes substantial revisions to align with current science, standards of practice, and the U.S. Environmental Protection Agency's current screening levels. This guidance will improve DEQ's ability to protect Oregonians, especially those most at risk, from health risks associated with vapor intrusion. Oregon's draft vapor intrusion guidance is available for public review until May 31, 2024.

Draft guidance

Current actions

DEQ is inviting feedback from the public on the new draft vapor intrusion guidance. While this is not a formal public comment period, your input is important. DEQ is holding virtual listening sessions via Zoom for people to learn about updates. DEQ will also be engaging the nine tribes of Oregon to seek their input and understand their particular interests.
Zoom details to join by video or phone will be posted here at least five days before the listening sessions and included in GovDelivery email notifications. Sign up to receive GovDelivery emails on DEQ's Cleanup Program

Updated screening levels

A key piece of the updated vapor intrusion guidance is updated Risk-Based Concentrations for vapor intrusion. These are the screening levels that will be used to make decisions about what is needed to address vapor intrusion health risks. DEQ updated its vapor intrusion RBCs in June 2023 by incorporating EPA's vapor intrusion attenuation factors, including lowering the soil vapor and groundwater screening levels. Additionally, soil RBCs were removed because the latest scientific evidence shows that soil data is not a reliable way to screen out risk from vapor intrusion. DEQ also no longer considers the urban residential exposure scenario separately from residential exposure and is now using one set of vapor intrusion RBCs to evaluate residential exposures. DEQ will update the vapor intrusion RBCs annually to remain consistent with the latest science from EPA's updates. In March 2024, DEQ made the first annual update to the vapor intrusion RBCs for consistency with U.S. EPA's 2023 regional screening level updates.  

Where can I find the current Risk-Based Concentration screening levels for vapor intrusion?

The updated RBCs are also available on the Risk-Based Decision Making for the Remediation of Contaminated Sites web page.


Vapor intrusion, the movement of contaminant vapors from spills or releases into buildings, is one of the most commonly complete exposure pathways at environmental cleanup, leaking underground storage tank, and heating oil tank sites. Vapor intrusion contaminants present ongoing potential risks to all people who breathe impacted air in their homes or workplaces. Certain members of the population are more susceptible to vapor intrusion risks, such as children, the elderly, unborn infants, people with disabilities, and those who live in areas impacted by multiple sources of pollution.

Frequently Asked Questions

​For completed and approved evaluations, re-evaluation may be performed on a case-by-case basis. Typically, approved closures do not require reassessment unless a new decision is requested or required, and that decision needs the support of a current screening evaluation or risk assessment.​

The new vapor intrusion guidance document builds on and supersedes previous vapor intrusion guidance documents published by DEQ in 2003 and 2010. Significant changes from the previous guidance include:

  • Revised risk-based concentrations for the vapor intrusion pathway, based on updated attenuation factors.
  • Removal of soil risk-based concentrations for the vapor intrusion pathway because the latest science indicates they may not be sufficiently protective of human health risks.
  • Use of residential risk-based concentrations for all residential exposure scenarios for vapor intrusion, including urban residential exposure scenarios.
  • Revised and new decision flow charts for non-petroleum and petroleum sources, and a heating oil tank (HOT)-specific flow chart.
  • De-emphasis of soil data and the emphasis of soil vapor data for risk screening.
  • A revised approach for demonstrating biodegradation at petroleum vapor intrusion sites.
  • Addition of RBCs to assess acute chemical toxicity and short-term exposure (e.g., trichloroethene).
  • Addition of response times for addressing chronic and acute vapor intrusion impacts to indoor air (Appendix A).
  • Expanded discussion of vapor intrusion mitigation technologies and a rebound analysis method.
  • Clarification of the process for identifying hot spots related to vapor intrusion sources of contamination. 
  • Clarification of expectations for public outreach and engagement related to vapor intrusion assessments.​

It is a significant change in these updated RBCs to not have soil screening values for this pathway. However, soil data has been shown to be unreliable for screening out this pathway due to its inherent heterogeneity and a variety of other reasons.

Groundwater, soil vapor and indoor air are the more reliable and protective screening methods for this pathway.
  • Under limited conditions, such as a soil matrix closure for Leaking Underground Storage Tank sites and a generic remedy for Heating Oil Tank sites, soil values may be used to screen out the vapor intrusion exposure pathway and close out a site.
  • These RBCs are default values to use for screening purposes. They are not rules. Project teams, with manager approval, may choose under certain site-specific circumstances to use soil data for screening out the vapor intrusion exposure pathway. An example may be a de minimis volume of soil contamination. Overall, based on the latest scientific evidence, soil data is not recommended as a reliable way to screen out risks from vapor intrusion. ​

DEQ published the updated RBCs in June 2023 and they went into effect immediately. Below is additional guidance about applying the new RBCs:

  • Use updated RBC tables for all new screenings and risk assessments unless an alternative approach is approved by DEQ. 
  • ​For completed and approved evaluations, reassessment may be performed on a case-by-case basis.​

Please contact the vapor intrusion work group at for technical assistance with this guidance. For site-specific questions, please contact your DEQ project manager.

DEQ's Vapor Intrusion Work Group Members:

  • Franziska Landes, Environmental Scientist and Hydrogeologist
  • Mike Poulsen, Toxicologist – RBCs, risk considerations and hot spots
  • Erin McDonnell, Engineer – Vapor intrusion remediation, mitigation systems and rebound analysis
  • Conrad Barry, Heating Oil Tank Project Manager – Heating oil tanks and petroleum biodegradation
  • Blair Paulik Aguilar, Senior Technical Policy Analyst – Guidance implementation, public outreach and engagement​


For more information, contact DEQ’s Vapor Intrusion Work Group.

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