What’s That Smell? Vapor Intrusion is Next BIG Issue

Every few years, different environmental issues emerge and have varying affects on the real estate/due diligence marketplace. In Illinois, the development and utilization of a risk-based approach to corrective action (known as TACO) in 1996 provided the foundation upon which Brownfields redevelopments were and continue to be built. Since that time, there have been various regulatory changes, including the recent adoption of background levels for PNAs in urban areas, concerns regarding mold, and new requirements for Leaking UST sites. However, the current “hot button” topic is called vapor intrusion, and this issue is sure to have an impact on the real estate/due diligence marketplace.

According to an Illinois EPA representative directly involved in the vapor intrusion rulemaking process, as it stands now, the State of Illinois will not be looking to re-open sites that were previously issued NFR letters.

The concern regarding vapor intrusion is not new but has only become more seriously evaluated over the last 10 years. Vapor intrusion is defined by the USEPA as the migration of volatile chemicals from the subsurface into overlying buildings. With developments in technology and an overall better understanding of the physical and chemical mechanisms governing contaminant fate and transport, as well as the primary pathways for exposure to contaminants, regulators have become increasingly aware of the potential affects of vapor intrusion into indoor air. Ironically, the popularity and acceptance of using a risk-based approach such as TACO has contributed to an increased potential for vapor intrusion by allowing contamination to remain in-place; thereby creating a source for vapors from contaminated soil and/or groundwater to enter into structures located above or adjacent to the contamination. This “unintended consequence” is but one factor that has resulted in the need to develop a specific approach for evaluating the vapor intrusion pathway.

The USEPA recently published a guidance document in January 2007 specifically to introduce a general framework for the evaluation and assessment of the vapor intrusion pathway and a means for addressing vapor intrusion concerns once identified. Approximately 24 States have their own state-specific guidance or policy documents regarding vapor intrusion. A new ASTM standard is expected to be finalized in late 2007 which will become a supplemental but separate part of the current Phase I environmental site assessment standard that is routinely performed during due diligence. The Illinois EPA is currently developing proposed regulations and an accompanying guidance document that are anticipated to be published in draft form this summer, although, the actual rulemaking process will likely not begin until this fall or winter and will take about a year to complete.

Vapor intrusion is essentially an indoor air quality issue, and can be handled either through remediation-to remove underlying volatile contamination at the source, or mitigation to prevent vapors from entering structures and becoming an exposure risk. One of the main considerations for determining an appropriate response will be based on whether there is an existing structure that will remain over the contamination or one proposed to be built in the future. Initial remedies for existing structures may be implemented by borrowing a common approach used in the radon mitigation industry where “subslab depressurization” systems are installed at relatively low costs, and with proper planning and evaluation, new structures can be protected from vapor intrusion by sealing subsurface penetrations and installing appropriate vapor barriers at the time of construction.


The inherent uncertainty of an emerging issue, especially in the environmental field, makes it difficult to predict the actual affect it may have on the real estate/due diligence marketplace. Already, vapor intrusion concerns have been used as “re-opener” triggers at some sites in New York where No Further Action (NFA) letters were previously issued. Here, in Illinois, while there are no regulations or guidelines to follow from the State, the Illinois EPA has avoided issuing closure letters in some cases where it is obvious that vapor intrusion is a potential concern even though all other TACO exposure pathways were adequately addressed and related institutional controls/engineered barriers were in place. Despite this uncertain regulatory climate, Pioneer has already started to address the vapor intrusion concern on active sites where it poses a potential risk and will continue to monitor the issue and advise our clients as the situation develops.

Pioneer continually monitors the regulatory climate in order to serve its clients more effectively and has the requisite experience to perform a broad range of environmental and engineering services. If you have questions regarding the vapor intrusion issue, or would like to discuss a potential project, please feel free to call Pioneer Engineering & Environmental Services, Inc. at 773.722.9200.

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