3 Key Things to Know About Vapor Monitoring at a Thermal Remediation Site

Vapor monitoring is a key component to any thermal remediation project, but it is subject to a unique set of challenges. For many contaminants, such as chlorinated solvents, typically more than 95% of the mass removed from the subsurface is found in the vapor phase. Therefore, it is crucial to have accurate measurement of vapor flow and chemical concentrations in order to calculate this mass removal metric.

Not sure why estimating mass removal is important? My colleague Hillary Easter explains in this blog post.

Curious how mass removal is calculated? My colleague Nikole Huard and I explain in this on-demand webinar.

The combination of potential high temperatures (depending on where the monitoring is taking place), high moisture content, variable vapor flow, and constantly changing chemical composition and contaminant concentrations can lead to data quality concerns.

In this blog post, we will take a look at the top three vapor sampling factors that ensure sampling success and quality: moisture management, practicality, and project objectives.

Moisture Management

Moisture management is one of the most crucial factors that affects the quality of vapor sampling at thermal sites. Many vapor sampling and analytical techniques are negatively affected by the presence of excessive moisture, so some amount of conditioning is needed.

Sometimes, this is easily accomplished simply by moving the sample location to a point in the vapor piping manifold which is after a gross vapor conditioning step, such as after the cooling and moisture knockout steps in the treatment system train. Other times, additional water trap filters or smaller vapor knockouts are required specifically at the sampling location. Alternately, in the case where solid adsorbent tubes are used, the sample volume may be reduced and/or the adsorbent material may be optimized to be amenable to moisture in the stream (e.g. XAD resin, which is hydrophobic).


It is important that the sampling procedures are straight forward and easy to consistently repeat. Standard operating procedures (SOPs) should be in place for all project members to follow, and good communication with the analytical laboratory is a key to success. When designing a sampling program, it can be useful to keep in mind the following questions:

  • What is the sampling location and ease of access? Are there any potential safety issues? Sampling locations should have access to safely perform the required actions.
  • What is the required sampling equipment? Is ice needed? How delicate (e.g. glass) or field hearty (e.g. stainless steel) is the equipment? Generally field hearty equipment is preferred, when possible.  
  • How does the sampling media need to be stored? Is ambient temperature acceptable, or does the media require refrigeration/freezing prior to use? Does the media have an expiration date? Sampling equipment and media should have a designated staging/storage area on site that ideally is temperature controlled and is not located near chemical products or solvents.
  • Can the sampling be performed in inclement weather? How long will the sampling take, and how many staff will be needed to accomplish the task? Is any coordination required with system operations, to get representative samples? Ideally, sampling will be able to be performed in varying conditions (keeping in mind safety due to weather) and will be completed by one or two staff members in a few hours—this allows staff to attend to the various other daily maintenance tasks associated with operating a thermal remediation site.


Vapor sampling often has different objectives related to how the data will be used. For instance, a photoionization detector (PID) is commonly used to measure volatile organic compound (VOC) concentrations at different points in the vapor treatment system. PIDs are generally considered field screening instruments, where often a trend (e.g. are concentrations increasing or decreasing? What is the removal efficiency?) and frequency (daily or several times daily) is more important than accuracy. 

Samples collected for emissions compliance purposes often will follow prescribed methods and be analyzed by a certified offsite analytical laboratory.

There also may be times when vapor sampling, either field screening or analytical lab samples, is conducted for troubleshooting or investigatory purposes. For example, we may be interested in identifying what chemical compounds are present, with less emphasis on the exact concentrations. It is important to keep these objectives in mind when interpreting results and making decisions that can impact the overall budget and success of the project.

If you’re interested in learning more about these topics, or hearing more in depth case studies and examples of unique vapor monitoring techniques TerraTherm has developed, please join me for my platform presentation at Battelle, “Non-Routine Volatile and Semi-Volatile Organic Vapor Monitoring at Thermal Remediation Sites: Lessons Learned.” It is part of Session B2, Thermal Conductive Heating: Best Practices and Lessons Learned on May 24 at 8:50 AM.

Add it to your calendar, and be sure to come and say hello to me after—I’d love to connect!


Alyson Fortune

Senior Scientist

Alyson Fortune joined TerraTherm in 2012 as a Senior Scientist with over 15 years of experience in the environmental industry, including experience with source testing, analytical laboratory testing, and environmental consulting. Alyson is acting as the data quality/operations and compliance monitoring discipline lead for the Engineering department. In this role, she is responsible for developing…

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