After attending the AquaConSoil conference in Barcelona, Spain last week, I’m struck by the impact that thermal remediation is having around the globe. Until a few decades ago, In-Situ Thermal Remediation (ISTR) was only confined to R&D projects by a few major oil companies, notably Shell. Today, ISTR has become mainstream remediation technology in the USA and is routinely considered for grossly contaminated properties. Global awareness and implementation are also accelerating, with applications documented on four continents.
At AquaConSoil, an entire session was dedicated to thermal remediation. TerraTherm also participated in two thermal remediation workshops organized by Krüger and TAUW, leading firms in the practice of ISTR in Europe (see this link for more information).
So why has ISTR become a global phenomenon with increased adoption all over the world? In a nutshell, it boils down to the proven results and experience of users compared to other approaches that might be applicable in similar sites. The many conversations I have at conferences such as the one in Barcelona, lead me to believe there are 5 major reasons for global adoption of ISTR
- Ex Situ remediation can be messy, noisy, dusty and intrusive. Neighborhood friendliness and safety factors often make in situ (in place) thermal a better choice. Until recently, the fastest, most reliable way of cleaning up hot spots was to dig them up, and either treat the soil ex situ (aboveground), or truck it off-site for treatment or disposal. Excavation, however, is intrusive and can expose site workers and nearby residents alike to odors, vapors, dust, and traffic.
- Non-thermal In Situ methods have not proven to be effective for recalcitrant organic contaminants in source zones. The development of other in situ technologies, such as soil vapor extraction, surfactant and cosolvent flushing, and in situ oxidation brought the promise of removal of source zones without excavation, but there are no demonstrated instances where they have proven effective with recalcitrant organic contaminants. By contrast, people have discovered that ISTR consistently delivers reliable results for these contaminants.
- The jury is in: Trying to deliver fluids to areas where the contaminants reside by injection, extraction or both is a hit or miss proposition. ISTR is effective throughout the treatment zone. Non thermal in situ methods rely upon trying to deliver a fluid throughout the subsurface locations where contaminants reside, either by injection, extraction, or both. At the vast majority of sites, however, soil conditions are non-uniform, and it is therefore impossible to fully contact all the contaminants with the treatment fluid. Be it air, liquid or reagent, fluid tends to bypass lower-permeability zones and flow preferentially through higher-permeability zones.
- Time is of the essence and/or time is money… take your pick. Movement of contaminants out of bypassed zones is slow, with diffusion time frames on the order of decades, if not centuries. Freeze and McWhorter (1997) underscored the futility of trying to remediate source areas unless a very high percentage of the mass can be removed. Decision makers all over the world have taken notice that, in project after project, TerraTherm ISTR has demonstrated success in removing extremely high percentages of the mass (>99%) while meeting and exceeding project goals. ISTR offers the timely benefits of robust, predictable outcomes, relatively short timeframes, plus the common result of completion without further remediation required. In situ thermal remediation technologies have been proven to reach very low soil and groundwater concentrations by eliminating the dense non-aqueous phase liquid (DNAPL) source and reducing dissolved and adsorbed chlorinated volatile organic compound (CVOC) concentrations to near non-detect levels. For chlorinated solvents, vaporization is the dominant mechanism, as vapor pressure and Henry’s law constants increase most markedly with temperature. For effective treatment, pneumatic and hydraulic control must be achieved during the heating period, and a clear path for the generated vapors to an extraction system must be provided.
- Stringent remedial goals may be difficult to meet with other technologies with high confidence and confirmation when the site is demobilized. If remedial goals are stringent, target temperatures shall be the in-situ boiling point of the soil and groundwater system, such that a phase change to the vapor state is forced by the heating. During operation, detailed temperature monitoring and process sampling is conducted and compared to the performance calculated based on mass and energy balances. Interim and final soil sampling is used to verify remedial progress and performance prior to site demobilization. The quality of the data and consistency of the end results often combine to make ISTR the best choice for sites with stringent goals.
To request a copy of the presentation I gave at AquaConSoil, or if you have any other questions, please email firstname.lastname@example.org