Monitoring is an important component to any successful remediation project. This point is explained further in Steffen Griepke’s previous blog post, “Why Data Management is the Most Underrated Aspect of Thermal Remediation Operations”. The more information you can collect, the better!
Conventional portable monitoring instruments, such as a photoionization detector (PID) or flame ionization detector (FID) are relatively inexpensive and convenient, but are unable to detect certain constituents or quantify their presence, especially in hot, moist vapor streams. This blog post provides an example of a technique TerraTherm is using for selected sites to overcome these limitations.
TerraTherm’s FTIR system provides real-time, continuous monitoring of vapor at up to 7 locations with the use of a multipoint sampler and vapor conditioning system. The FTIR provides speciated data for individual vapor phase components, not just “total” VOCs. Single digit parts per million by volume (ppmV) detection limits are achievable.
How Does the FTIR Work?
As shown in the photo below, inside the FTIR unit a beam of infrared (IR) light is applied to the sample gas in a multi-pass sample cell (where the sample path length intercepted by light is increased with mirrors). Different compounds in the gas stream will absorb IR light in different spectral regions based on molecular structure and chemical functional groups. Therefore, each component present in the sample will have a unique “spectrum” that is used for identification and quantification.
The FTIR is meant to handle hot, wet vapors—which is a great thing since we are running a thermal remediation site and the vapors we are extracting are both at high temperature and usually high moisture content. Thus, the FTIR is well suited for use at our remediation sites. The unit does not require daily calibration; in fact, the calibration is very stable (i.e. it does not experience drift or have any interference from high humidity or other environmental factors) and the manufacturer recommends a calibration check once every few months or as needed.
Benefits to ISTR Site Operations
The benefit of “real time” information cannot be underestimated. The FTIR system gives TerraTherm site operators and project engineers real time knowledge to aid in optimizing the ISTR system. When a process change is implemented (changing flow rates, dilution air, etc.), the site operator or project engineer can instantly monitor the effect of this change on the vapor concentration, without having to collect a discreet grab sample for analysis with a handheld instrument such as a PID. The FTIR system can also be used to monitor the concentration of contaminants in the work zone to ensure worker safety.
Operator/Engineer Screen Views of FTIR System (Control Software)
Via the ThinkThermal® website, clients can not only view the progression of the in situ thermal remediation (ISTR) project in terms of temperature increase, they can view vapor concentrations over time as well. The figure below shows a display of trichloroethene concentrations in the wellfield vapor over the course of an ISTR project. At the start of the project, low concentrations were observed. Over time, as the subsurface temperature increased, wellfield vapor concentrations increased until a peak was reached, and then slowly decreased again to form a typical bell-shaped curve.
Another application for the FTIR system would be to continuously monitor the vapor effluent stream for regulated organic contaminants. This can represent a significant cost savings when compared with the alternative of collecting daily laboratory samples.
This sophisticated monitoring system allows us at TerraTherm the ability to provide our clients with the best ISTR service available.
If you would like to learn more about this topic and are attending Ninth International Conference on Remediation of Chlorinated and Recalcitrant in Monterey, California, make sure you attend my presentation on Tuesday, May 20th.