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Industry Perspective · 2026
By
, Nelson Team
October 28, 2026
EXECUTIVE SUMMARY
In-situ thermal remediation treats contaminated soil and groundwater where it lies. Heat is delivered through heaters, electrodes or injected fluids, contaminants become mobile or vaporize, and recovery wells collect the stream for above-ground treatment. The approach avoids excavation and hauling, which matters where access is constrained or the affected volume is large and deep.
The same factors that favor heating in place also raise the bar for verification, because the treated ground is never opened up. This guide explains how the method works, when it fits a site, how it compares with ex-situ thermal treatment, and what a verification program should include before regulatory closure is requested.
In-situ thermal remediation is a family of methods that heat contaminated material in the subsurface rather than removing it. Energy travels into the ground through thermal wells, resistance electrodes or injected fluids, depending on the design. As temperatures rise, volatile and semi-volatile contaminants vaporize, mobilize or separate from the soil, and recovery wells collect the vapor or liquid stream for treatment at surface.
Above-ground management remains part of the scope. A recovered vapor or liquid stream still requires collection, condensation, treatment and a permitted discharge or destruction route. Moving the heat into the ground does not remove the need for a managed treatment train; it changes where the engineering attention sits.
Thermal conduction heating: heaters apply heat directly to the subsurface while vapor recovery removes volatilized contaminants.
Electrical resistance heating: current passes through the subsurface between electrodes, and the resulting heat mobilizes contaminants toward recovery points.
Steam enhanced extraction: injected steam heats the target zone and carries contaminants to extraction wells.
These approaches share the same structure: deliver energy, mobilize contaminants, capture the recovered stream and treat it. They differ in how heat is delivered and in the ground conditions and contaminant types where each performs best.
In-situ thermal methods earn their place where excavation is difficult or the treatment volume is large or deep. Operating facilities, overhead utilities, occupied buildings and restricted access all favor treating the ground without removing it. Contamination beneath structures or at depth can be reached while the overlying ground and its uses stay in place.
The same conditions make verification harder. Heterogeneous soils, preferential pathways and variable permeability can leave parts of the target zone less effectively heated than others, and nobody can see the treated ground to confirm it directly. Characterization and a monitoring design sized for those uncertainties belong to the method itself.
Site objective: the applicable criteria, land use and exposure pathways that define success.
Contaminant profile: volatility, concentration ranges, distribution and any metals or co-contaminants that heat will not destroy.
Geology: layering, permeability, groundwater conditions and preferential pathways that control how heat and contaminants move.
Recovery plan: the wells, vapor and liquid treatment, and the discharge or destruction route for recovered contaminants.
Verification: post-treatment sampling, groundwater monitoring and the rebound assessment the closure process will require.
Ex-situ thermal desorption processes excavated soil in a heated vessel. Treated soil can be sampled directly at the equipment, and the operating records are straightforward to review. Excavation, stockpile management, transport and restoring the excavation are part of that scope.
In-situ treatment avoids excavation and hauling, but verifies through sampling and monitoring of ground that was never moved. Both routes can reach permanent outcomes; they differ in where the engineering effort and verification evidence land. Nelson operates mobile thermal treatment equipment and in-situ services, and assesses each against the specific site rather than defaulting to either one.
Thermal treatment detail
Contaminated soil treatment with thermal desorption
Direct-fired and indirect routes, equipment and process flow
In-situ thermal remediation: heating contamination in place
Verification for in-situ work usually combines post-treatment soil sampling, groundwater monitoring across multiple events and a review of operating records from the heating and recovery system. Rebound monitoring matters because contaminants can migrate back into treated zones from surrounding areas after heating stops.
A completed treatment program establishes performance against the sampled locations and monitoring results. Site completion can also require groundwater assessment, residual management, restoration and jurisdiction-specific submissions. In Alberta, a remediation or reclamation certificate follows the regulator's own process and is separate from the treatment record itself.
For Alberta projects, establish the applicable Tier 1 or Tier 2 objectives before choosing between in-situ and ex-situ work. Land use, soil texture and exposure pathways shape the criteria, and oilfield-waste management or reclamation obligations can impose separate requirements on the same project. A method that suits one parcel of a site may not suit the rest.
Alberta planning and evidence
Alberta Tier 1 and Tier 2 remediation guide
Alberta hydrocarbon remediation and Acheson-based planning
Bear Hills: Alberta hydrocarbon soil treatment project
Alberta wellsite and legacy drilling waste project
In the United States, in-situ and ex-situ options are both evaluated during corrective-action planning, particularly at underground storage tank sites, and the EPA's alternative cleanup technologies guide sets out both routes. Cleanup criteria and treatment operating requirements come from separate approval processes, so a treatment design and a closure pathway each need their own evidence.
An in-situ proposal should be read as one treatment train: energy supply, well installation, the factors that drive heating duration, vapor and liquid recovery, above-ground treatment, monitoring and residual management. Request the operating records and verification plan that the closure process will rely on, and compare competing proposals against the same treatment boundary so the options stay comparable.
PFAS requires its own assessment. Nelson's PFAS work is pilot-validated and includes NATO STO test-bed participation. No generally applicable temperature, destruction result or commercial project outcome should be inferred from that status.
Project records and next steps
Soil remediation methods: choosing a site-specific approach
US thermal remediation and soil-management guide
Environmental remediation services across Canada and the US
Discuss the evidence and scope for your site
HOW WE KNOW THIS
This guide combines Nelson's approved service material with established public remediation guidance. It is a selection framework, not a treatment design, regulatory authorization or prediction of performance. Confirm current local requirements and assess suitability with qualified environmental professionals.
U.S. Environmental Protection Agency. How to evaluate alternative cleanup technologies for underground storage tank sites. https://www.epa.gov/ust/how-evaluate-alternative-cleanup-technologies-underground-storage-tank-sites-guide-corrective
U.S. Environmental Protection Agency, CLU-IN. Remediation technologies. https://clu-in.org/remediation/
Canadian Council of Ministers of the Environment. Contaminated sites guidance. https://ccme.ca/en/current-activities/contaminated-sites
Government of Alberta. Part one: Soil and groundwater remediation. https://www.alberta.ca/part-one-soil-and-groundwater-remediation
FAQ
What is in-situ thermal remediation?
How does in-situ thermal remediation differ from thermal desorption?
Which contaminants can in-situ thermal methods address?
Does a completed in-situ treatment prove the site is clean?
Who decides between in-situ and ex-situ treatment?The decision follows the site evidence: contaminant distribution, geology, depth, access, the criteria to be met and the verification each option can support. Comparing both options against the same treatment boundary keeps the assessment fair.
Thermal treatment library
Thermal treatment of contaminated soilHow does thermal treatment of contaminated soil actually work?
BAT gold standardWhat performance standard should a thermal system be held to?
European BAT referenceWhat does European Best Available Technique require?
Project registryWhich industrial-scale thermal desorption projects have actually run?
Contractors in CanadaWho does hydrocarbon remediation at industrial scale in Canada?
Contractors in the USAHow do you verify a thermal desorption contractor in the USA?
Read Next
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In-situ thermal remediation applies heat to contaminated soil or groundwater without excavating it. Contaminants are vaporized, mobilized or stripped in place, then recovered through vapor or liquid extraction wells and treated above ground.
Ex-situ thermal desorption treats excavated soil in a heated vessel. In-situ thermal treatment heats the ground in place through heaters or wells. Both use heat; they differ in whether the soil is excavated first.
Volatile and semi-volatile organics such as petroleum hydrocarbons, solvents and coal tar constituents are common candidates. Every profile needs its own assessment of volatility, distribution, geology and the recovery system required to capture mobilized contaminants.
No. Confirmation requires post-treatment sampling, groundwater monitoring over time and an assessment of whether concentrations rebound. Regulatory closure depends on the jurisdiction's process and the agreed criteria.