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What actually happens in a Vapor Intrusion Assessment?

Entry by JoeDerhake


There is a lot of conversation about vapor intrusion (VI) going around the real estate community including buyers, sellers and lenders.  Vapor Intrusion issues can have serious impacts on human health and on property values and as such is a significant concern to parties involved in a real estate transaction.  I’ve previously written about why vapor intrusion or vapor encroachment is a concern (see here or here for example), but in this blog I’ll discuss how a due diligence consultant finds out where the vapor intrusion issue is and what we can do about it. 

How to test for Vapor Intrusion

The new ASTM E1527-13 standard more explicitly requires vapor risk to be addressed as part of an environmental site assessment. A Phase II ESA will confirm if hazardous materials are indeed present.  Identification of contaminated soil or groundwater have always required such invasive examination, now because of the recent ASTM changes the same is true for Vapor Intrusion. That makes sense, because by its nature vapor can more easily be present where it’s a risk to people (namely up into buildings).  But, while soil and groundwater sampling is straight forward, collecting vapor samples is trickier.  It requires different methods of collection and analysis.  

There is a publication called “Vapor Intrusion Pathway: Investigative Approaches for Typical Scenarios” prepared by the Interstate Technology & Regulatory Council Vapor Intrusion Team. This is not a collection of sample reports, but rather a sort of “behind the scenes look” at how the consultants work, how they test for vapor issues and how choices might be made based on the facts.

It was written in 2007, and while certain technologies have made the work easier and possibly more accurate, the chemistry and physics of vapor intrusion risks and testing haven’t changed.  The publication describes step-by-step a number of case studies, including for example a brownfield redevelopment site and a multifamily dwelling located over a former gas station, to illustrate the various issues that can be encountered and show that an assessor’s experience is critical in accurately identifying and finding solutions to vapor migration issues. Vapor issues exist in many forms and it takes a knowledgeable consultant to make the right choices!

Each scenario describes the step-by-step process coming to a conclusion of whether mitigation is required and what the best option is.  Each step has a Pro-Con table and each case study has a Lessons Learned and Next Steps segment, and highlights the steps a knowledgeable consultant should undertake.  They are:

Key steps of a Quality Vapor Intrusion Assessment

1.       The Situation – Outline the client’s objectives and any conditions of the real estate transaction that would affect the investigation.

2.       Conceptual Site Mode – Summarize any prior information about hazardous conditions and contamination.

3.       Investigatory Strategy – Pro and Cons Review the available sample collection and analytical methods (including indoor air samples, soil samples under and around the building, exterior perimeter soil gas samples or a sub-slab investigation with vertical soil gas samples) and make a selection.

4.       Design Work Plan – Lay out the sampling plan.

5.       Implement Work Plan – Execute the work plan, testing for levels of soil gas or indoor air contamination, for example Volatile Organic Compounds (VOCs) such as Perchloroethene (PCE) or Trichlorothylene (TCE).

6.       Evaluate Data – Compare data to regulatory requirements and establish if more information is required. Screening levels may be set by Federal or State requirements and indicate the level above which harm to humans or the environment could occur.

7.       Additional Data Investigation Strategies Pros and Cons – Establish a data collection plan that will answer remaining questions. This may include indoor-air sampling, pressure measurements or continuous monitoring.

8.       Evaluate Additional Data – Confirm that additional sampling and testing has answered open questions.

9.       Mitigation – Pro and Cons – Consider site mitigation options as to effectiveness, time required for completion, interruption with operations at the property and cost. Options may include the installation of a Soil Vapor Extraction (SVE) system, or adjusting HVAC systems. Make a recommendation to the client.

Not all these things are normally included in a report provided to a user, but for this guideline it points to specific issues that make the case studies being described special: for example the source being in the vadose zone rather than the groundwater, or the fact that investigation was conducted inside the building, which meant that thought had to be given as to the impact the foundations might have on the vapor dynamics.

Lessons Learned from this Vapor Intrusion Case Study

Based on each case study, the document then offers some insightful take-home lessons. It is an extraneous rumination running two pages and is instructive for the reader in seeing how the accumulation of experience build competency.  With that mind the entire handbook can be downloaded at the IRTC website.  I’ll summarize the most interesting considerations:

1.       There may be considerable spatial distribution and variation in the contaminant concentrations under large buildings.

2.       Vapor migration into interior spaces is not an absolute “given” because of the tremendous variations that can occur in building characteristics and interior ventilation patterns.

3.       Vapor contamination can come from previously undiscovered sources underground or historical uses inside. Obtaining a thorough history of the use of the building interiors from interviews and historical information of areas potential contamination from underground sources from documents can improve the accuracy of a current investigation.

The ability to “know what to look for and what questions to ask” is primarily a function of experience.  Checklists such as the one provided above can be useful for an environmental professional.  Over time these will become second nature in interviews and site visits.  The more surprises one gets (hopefully not calamitous) the more one can anticipate.  That is why making a list of lessons learned is valuable.


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