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Earlier this month, my colleague Andy Rezendes and I had the opportunity to host a live webinar titled “Clearing the Air: Decoding State Regulations on Vapor Intrusion.” Our goal was to shed light on the complex, and often fragmented, landscape of Vapor Intrusion (VI) guidance across the United States. Vapor intrusion is a critical issue in environmental due diligence, site remediation, and risk assessment, and understanding how it is regulated across different states is essential for environmental professionals.
In this blog, we have recapped some of the key takeaways and themes from the webinar,
Watch: Clearing the Air: Decoding State Regulations on Vapor Intrusion
Federal Frameworks: EPA vs. ITRC—Two Different Lenses on Vapor Intrusion
At the heart of our discussion was the contrast between two major VI guidance documents used nationally: the U.S. Environmental Protection Agency (EPA) guidance and the Interstate Technology & Regulatory Council (ITRC) guideline.
EPA’s Cautious, Step-by-Step Approach
The EPA's vapor intrusion guidance is built around a deliberate, methodical framework, focusing on conservative assumptions and multiple lines of evidence before initiating indoor air sampling. This approach prioritizes:
- Protection of public health, by ensuring that no risks are overlooked
- Efficient allocation of resources, by avoiding premature or unnecessary investigations
- Scientific rigor, through a stepwise methodology and established screening levels
The EPA framework is particularly useful for regulators and practitioners seeking clear, repeatable protocols. However, its conservative nature can sometimes lead to longer timelines and higher costs, especially for sites with complex or ambiguous data sets.
ITRC’s Practical, Flexible Guideline
In contrast, the ITRC’s “Vapor Intrusion Pathway: A Practical Guideline” offers a more generalized and adaptable roadmap. Developed through collaboration between state and federal agencies, industry experts, and consultants, the ITRC guidance: 
- Encourages site-specific professional judgment
- Presents a phased investigation approach (screening → data collection → risk evaluation → mitigation, if necessary)
- Avoids a “one-size-fits-all” methodology
ITRC's strength lies in its practicality and flexibility, making it particularly valuable for states and practitioners who need a baseline guide that can be customized to local conditions and regulatory requirements.
Understanding the State-by-State Patchwork of VI Regulations
One of the most eye-opening segments of the webinar focused on the variability in VI regulations at the state level. While federal guidance provides a foundation, many states have developed their own regulations, policies, and screening levels—some aligned with EPA or ITRC guidance, others diverging significantly.
Key Areas of Variation Include:
- Generic Screening Levels:
These levels, often derived using default attenuation factors, vary in how conservatively states want to be with risk threshold for screening into further investigation.
- Contaminants of Concern (CoCs):
States may differ in their prioritization of certain chemicals, such as chlorinated solvents, petroleum hydrocarbons, or emerging contaminants like 1,4-dioxane and PFAS.
Mapping the Landscape: Our “Snapshot of State Guidance”
We presented a visual slide mapping VI guidance types by state, which proved to be one of the most engaging parts of the session. Here's a quick overview of what that map revealed:
- Green States:
The green states have developed VI guidance addressing both chlorinated and petroleum hydrocarbons. Examples include California, Massachusetts, and New Jersey. These states address the Vapor Intrusion pathway whether it's chlorinated or for both chlorinated and petroleum sites. Examples include California, Massachusetts, and New Jersey.
- Blue States:
A smaller group of states focus specifically on petroleum vapor intrusion, often with unique criteria that reflect the different behavior of petroleum compounds in soil and vapor phases.
- No Guidance States:
Several states have no formal VI guidance and instead defer to federal guidance (typically EPA's or ITRC’s). This can create challenges for project planning, permitting, and stakeholder communication.
The Takeaway?
Environmental professionals must navigate a state-specific regulatory landscape that is anything but uniform. Knowledge of your local state’s VI policies is essential—and it’s not uncommon for regulatory expectations to change even within the same region over time.
Passive Sampling in Vapor Intrusion: From Emerging Technique to Core Tool
One of the most forward-looking topics in our webinar was the evolving role of passive sampling in VI investigations. Over the last decade, passive sampling has gone from being a supplemental, often qualitative tool to a more accepted, sometimes preferred, method for characterizing vapor conditions at contaminated sites.
The Evolution of Passive Sampling
Originally, passive samplers were used to support traditional sampling methods (e.g., SUMMA canisters, active sorbent tubes). Today, due to technological advances, they are increasingly recognized for their ability to deliver quantitative and representative data—particularly when deployed over extended periods.
Most states now acknowledge passive sampling as an available tool in the VI toolbox, though they often recommend prior consultation with regulatory agencies before implementation. Some states have gone even further:
- California: Encourages passive sampling in sewer laterals and building cleanouts, especially where access or intrusiveness is a concern.
- Oregon and Wisconsin: Have released draft guidance documents supporting the routine use of passive samplers in specific scenarios.
Advantages of Passive Sampling
- Extended Deployment Periods
Passive samplers can remain in place for several days to several weeks, offering a time-integrated picture of vapor concentrations—more reflective of real-world exposure scenarios.
- Lower Visibility and Risk of Tampering
Their compact, discreet design makes them ideal for use in residential or commercial spaces, where traditional sampling equipment might raise concerns or be more vulnerable to tampering.
- Cost-Effectiveness
Without the need for active pumping systems or vacuum canisters, passive samplers are often more economical, especially for long-term monitoring projects.
- Better Performance in Adverse Conditions
In high-moisture or low-permeability environments, traditional soil gas sampling can be unreliable. Passive samplers are less sensitive to these challenges, making them a good fit for tough site conditions.
Challenges and Limitations
However, passive sampling is not without its limitations:
- Limited Opportunity for Reanalysis
Many passive samplers use thermal desorption, which destroys the sample during analysis. This means QA/QC is more difficult if data is questioned post-analysis.
- Potential for Background Interference
Long deployment periods can introduce background contamination, especially in occupied buildings. Household products, cleaning agents, and human activity can skew results.
- Environmental Sensitivity
Temperature and humidity can affect sorbent performance. Improper handling during shipment or storage can also lead to pre-deployment contamination.
Despite these challenges, passive sampling continues to gain acceptance as a reliable, non-intrusive, and affordable tool—especially when used in conjunction with traditional methods to form a comprehensive, defensible investigation strategy.
The Bigger Picture: No Universal Blueprint for Vapor Intrusion
One of the most important messages we hoped to convey in the webinar—and reiterate here—is this:
There is no one-size-fits-all solution when it comes to vapor intrusion.
The combination of evolving science, technology, and regulatory diversity means that every VI investigation demands a thoughtful, site-specific strategy. Rigidly applying a checklist without considering local guidance, site geology, and vapor pathways can lead to mischaracterization of risk or delays in project closure.
What This Means for Environmental Professionals
- Stay Informed.
Track updates from your state agency and professional organizations like ITRC, ASTM, and EPA.
- Engage with Regulators.
Early and proactive communication with state and local regulators can smooth project approval and reduce the risk of rework.
- Use a Weight-of-Evidence Approach.
Relying on multiple lines of data—passive, active, sub-slab, indoor air, etc.—builds stronger, more defensible conclusions.
Final Thoughts: Moving the Industry Forward, One Site at a Time
Our recent webinar was a great opportunity to explore these topics with professionals from across the country. Whether you’re an environmental consultant, risk assessor, or regulatory stakeholder, understanding the nuances of vapor intrusion is critical to effective site management and public health protection.
If you missed the webinar, we hope this recap provides you with a deeper understanding of the topics we covered. If you’re navigating complex VI issues at your site—or simply want to learn more about how regulations and technologies are evolving—feel free to reach out. We’re always happy to share insights, collaborate, or answer questions.
Watch: Clearing the Air: Decoding State Regulations on Vapor Intrusion
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