Vapor Intrusion Assessment & Mitigation

EES is an expert in the environmental vapor intrusion (VI) consulting practice. We apply decades of experience and utilize leading-edge tools to understand, communicate, and resolve complicated vapor-related issues.

VI often represents the most direct and highest-priority human health risk under consideration at environmental sites, and in many cases becomes the main driver for cleanup or mitigation (control) actions.

EES closely tracks and applies current regulatory and published technical guidance to stay on the leading edge of its VI practice.

Recognized Technical Leadership

EES has presented at local, regional, and national technical VI seminars and conferences. Recently, EES was invited by Oregon DEQ technical policy managers to participate in the development of the most recent state VI guidance document update (DEQ, 2025).

Common Project Types

We have worked on many VI projects to evaluate and mitigate impacts from volatile organic compounds (VOCs), fuel hydrocarbons, and other airborne chemicals at these common types of project sites:

Industrial Facilities
Dry Cleaners
Fueling & Bulk Fuel Terminals
Residential Buildings

Commercial & Retail Buildings
Healthcare Facilities
University & Administrative Buildings

Field-deployed monitoring equipment adapts to almost any site type.

What is Vapor Intrusion and Why Does It Matter?

Some common chemicals used in solvents, fuels, and other commercially available products readily vaporize and can migrate from various sources in soil, groundwater, air, and utility conduits into nearby buildings, exposing occupants to potential health risks. Because these chemicals are so common in commercial settings and consumer products and are regulated at very low risk-based concentrations, understanding and addressing their behavior and the factors that govern or modify their movement is challenging and complicated.

EES meets these challenges with technical and practical problem-solving expertise and clear communication. EES asks good questions, uses cutting-edge diagnostic tools, and implements smart strategies to understand every site’s unique conditions and address client goals.

Vapor Intrusion Commonly Asked Questions

What are the contaminants at my site, and how can I reliably measure them?

One of the first and most fundamental steps during a vapor intrusion assessment is to identify and reliably measure the source contaminants that are known or suspected of putting buildings and occupants at risk. EES uses our extensive experience and state-of-the-art tools and techniques to understand the context and setting of your project, then to identify, measure, and evaluate the significance of the levels of contaminants found in subsurface vapors and/or indoor air.

Where do these vapors originate? Are these Volatile Organic Compounds (VOCs) coming from indoors, outdoors, or underground?

EES understands that each site is unique, and a core focus of any assessment is the identification of VI source area(s). We use multiple lines of evidence to effectively and reliably identify VI sources and the factors that control or influence vapor movement.

What about the role of underground utilities?

Underground utilities and other subsurface features can often modify or facilitate vapor movement and act as “preferential pathways ” for subsurface vapor migration between the source area and building occupants (“receptors”). These are often overlooked or misjudged by less experienced practitioners, but EES carefully considers the role of these types of vapor migration pathways using diagnostic tools, sensors, direct testing of pathways, and diligent problem-solving inquiry.

Are there health risks to people who live or work in the building(s) under study?

Some common VI contaminants of interest, including fuels and chlorinated solvents, may present serious health risks to sensitive human receptors inside a building. EES has decades of experience evaluating human health risks as part of the VI investigation and mitigation process.

Which regulatory standards apply, and am I in compliance?

EES understands and applies VI regulatory standards and technical guidance on a routine basis, and we know this framework intimately. We are engaged with Oregon and Washington VI regulatory managers, and we are familiar with other state and national technical guidance documents and practices. Our own practice is focused on helping clients understand and navigate environmental regulatory frameworks throughout the Pacific Northwest. As an experienced and respected practitioner, EES participated in a small focus group to provide technical review and input regarding Oregon Department of Environmental Quality’s recent (2025) VI guidance update. Our clients benefit from our knowledge and application of rapidly evolving VI regulatory criteria and technical know-how.

Will this impact business operations, and if so, how and for how long?

EES takes the time to understand its clients’ business activities and interests and is able to perform timely VI assessment and mitigation (if necessary), often with little or no disturbance to our clients’ business operations. We are excellent communicators and planners.

How do I communicate with and reassure tenants, employees, and other stakeholders?

Community outreach and stakeholder engagement are an important consideration with many VI assessment and mitigation projects. We have worked with a wide range of clients in different settings and can help you develop an appropriate plan to communicate VI issues effectively to building occupants and other community members.

What are the tools and options available to remedy this situation?

Most VI projects are unique, and the appropriate technical approach will depend on timeline and project objectives, as well as regulatory and (occasionally) other third-party involvement. Site-specific conditions, including building construction and operation, subsurface setting, and contaminant distribution, will also impact VIA methods and mitigation strategies. We excel at this work, use top-notch diagnostic equipment, and diligently stay on the front edge of new and emerging technologies, but we always strive to use the best, and sometimes the simplest, approaches to problem-solving.

How long will this take, and how much will it cost?

Our experience, proficiency, and equipment put EES in good position to understand and solve VI issues quickly and efficiently. Because no two VI sites or situations are the same, cookie-cutter or narrow-minded solutions rarely provide satisfactory outcomes. On the other hand, most VI problems can be addressed in a number of different ways and from different perspectives, meaning that we always seek to identify options and alternatives for client consideration as we move through the VI process. EES evaluates every site based on its own unique conditions and client needs.

How Do We Manage Vapor Intrusion Issues?

Our VI practice consists of the following main elements: assessment/characterization, mitigation, and third-party technical review.

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Assessment / Characterization

Identify sources and evaluate risks using accurate and representative field data.

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Mitigation

Design and install systems that control vapor pathways.

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Third-Party Review

Conduct independent technical review for transactions and disputes.

Assessment & Site Characterization

The physical and chemical mechanisms governing vapor migration are fairly straightforward, but their dynamics are highly variable over time, season, location, and building operating conditions. Every site and building present unique conditions that must be evaluated with those dynamics in mind. Evaluating VI conditions correctly, accurately, and in a representative manner requires skill, experience, and good judgment.

EES experts help you:

Choose the right testing approach to meet project objectives
Collect accurate and representative data
Identify and pinpoint VI sources, including contributions from urban and background sources

Evaluate and prioritize risks
Analyze a range of management/action options

Sub-floor vapor sampling + leak detection

Thermal imaging helps identify vapor points of entry

Real-time continuous air monitoring during building pressure test

Building Pressurization Step-Testing vs. Indoor Air Concentrations

A real EES monitoring dataset showing how controlled building pressurization/depressurization steps correspond with measured PCE and TCE concentrations in indoor air. This is the kind of data-driven diagnostic work that identifies and solves problems, and sets our approach apart.

Vapor Intrusion Management, Mitigation Design, and Installation

When building control or VI mitigation is needed, EES develops practical, defensible, and efficient solutions. We consider how existing building components (HVAC system pressurization, floor sealants, air filtration, slab drainage features) may be modified to contribute to effective mitigation; and we incorporate readily new/emerging technologies, passive systems, and real-time system monitoring as needed. We develop creative strategies, including administrative controls that can reduce or eliminate mitigation needs, and we have an established history of developing engaged, constructive dialogue with regulatory managers and decision-makers.

Sub-Slab Depressurization Monitoring

Differential pressure tracked across active mitigation monitoring points over several months.

Due-Diligence Assessment and Third-Party Technical Review

EES helps clients by implementing a thoughtful and comprehensive approach for small or large property transactions, developing “cost to cure” assessments for environmentally impaired facilities, and providing expert witness and litigation support for cost recovery matters. Our clients include owners, developers, lenders, investors, and insurance companies who rely on our understanding and clear communication of complex VI mitigation and risk management issues.

Vapor intrusion is often a highly variable, multi-factor condition that can be studied for months or years. Property transactions typically cannot wait for iterative seasonal sampling and traditional VI assessment processes to unfold. EES can help develop strategies for decision makers on an expedited basis by understanding key issues and using a wide range of advanced tools and instruments. These strategic approaches help identify building dynamics, contaminant points of entry, risk factors, and mitigation tools.