Frequently Asked Questions about Low Temperature Thermal Remediation

Thermal remediation is a powerful technology, but you might be concerned about the amount of infrastructure and energy required to produce the level of heat that rapidly treats contamination. Low temperature thermal remediation is a more sustainable alternative that can be an effective option for many sites. With low temperature thermal, contaminated soil is gently heated to temperatures between 30 and 90°C, below the boiling point of water, accelerating aerobic degradation, anaerobic degradation, and/or abiotic degradation of a contaminant.

In today’s blog post, we share some of the questions we often hear about low temperature thermal remediation. To learn more about sustainable thermal remediation, sign up for our February 28 webinar, “Improving the Sustainability of Thermal Remediation.”

What makes low temperature thermal different than traditional thermal?

Because low temperature thermal requires less energy, the subsurface infrastructure to deliver that energy can also be reduced. This may include smaller diameter borings which translate to less drill cuttings and often faster drilling production rates, increased spacing between points, and specialized, lower cost heaters designed for lower power outputs. We have also been exploring repurposing existing wells by inserting heaters in injection or monitoring wells.

Are there geological limitations when using low temperature thermal remediation?

If low temperature thermal is the most appropriate and cost-effective solution for treating site contaminants, then treatment can be carried out in most geologic settings and in most soil types. We may use construction or drilling techniques to reduce installation costs for low temperature heaters, such as using a smaller diameter borehole, or by reusing the same direct push technology (DPT) borehole used to deliver amendment.

Can low temperature thermal reduce NAPL?

Low temperature thermal remediation can be effective at reducing NAPL in some situations; whether it’s feasible depends on the remedial goals, the mechanism and rate of attenuation enhanced by temperature, the ability to deliver sufficient quantities of amendments or oxygen driving the degradation, and the range of acceptable remedial timeframes.  

Contaminants in NAPL that are aerobically degradable—such as petroleum hydrocarbons, gasoline, jet fuel, and diesel—can be an excellent fit for low temperature thermal treatment. LNAPL is typically smeared across the vadose zone and capillary fringe and may even be trapped below the water table, but an assessment can help determine if oxygen should be added (e.g., air sparging)  or other amendments. The addition of gentle heat will accelerate the rate of degradation.

For sites where natural source zone depletion is being monitored, microbial degradation of hydrocarbons creates a signal in the form of generation of methane, carbon dioxide and heat (e.g., a few degrees Celsius), similar to a compost pile. Gentle addition of heat combined with oxygen delivery could be used to enhance this naturally occurring process.

For sites with moderate to high amounts of chlorinated ethenes, for example, 20,000 lbs of DNAPL with PCE, the maximum rate of attenuation achieved through delivery of amendments and enhanced with the addition of heat is often still too slow to meaningful reduce mass in a reasonable timeframe. For low temperature thermal to be effective , we’d have to wait for chlorinated compounds in the DNAPL to partition into water where anaerobic and/or abiotic degradation occurs. Temperature may increase this rate by 2-3 times, which still results in a treatment timeframe on the order of decades or longer.

What is the maximum depth at which low temperature thermal remediation is effective?

There’s no real depth limitation – we have used thermal conduction heating to depths of 165 feet below grade; however, there may be practical limitations based on the drilling technologies available.

What is the maximum radius of influence that can be achieved with low temperature thermal?

It depends on the technology and the target temperature. For instance, for a site targeting temperature-enhanced hydrolysis and increasing temperatures to around 70°C, the spacing of our heaters or electrodes may be analogous to traditional thermal or 15 to 16 ft for heaters and 18 to 20 ft for electrodes but with a lower rate of power delivery or smaller borehole. For sites where we’re increasing temperature to enhance microbial mediated reactions and targeting average temperatures of 35°C, we would use a lower-power output, off the shelf heater. Spacing for these heaters may be closer to 12 to 16 feet for optimal efficiency. Spacing at <20 feet is probably the practical limitation; when heaters are spaced at intervals of more than 20 feet, the treatment zone will not be uniformly heated to the desired temperature. This is true of any thermal remediation approach.

Our goal with the heaters is to install them in the subsurface in such a way that we can effectively heat the soil in between the heaters up to the desired temperature in an efficient and timely manner. Keeping the heaters relatively close to one another minimizes heat loss and allows us to achieve our target temperature in a reasonable amount of time.

To learn more about sustainable thermal remediation, sign up for our webinar, “Improving the Sustainability of Thermal Remediation.”