In-situ thermal remediation that passes electrical current through the subsurface between buried electrodes, heating the soil and pore water to roughly 100 degrees Celsius. Volatilizes VOCs and SVOCs for capture by soil vapour extraction. Effective in saturated and unsaturated zones with adequate moisture.
Electrical Resistance Heating drives alternating current between arrays of vertical electrodes installed across the treatment volume. Resistance in the soil and pore water dissipates the electrical energy as heat (Joule heating), raising bulk temperatures to the boiling point of water at depth, typically 100 to 105 degrees Celsius. The resulting steam strips volatile and semi-volatile contaminants from soil into a vapour stream captured by an SVE network and treated above ground.
ERH is the workhorse in-situ thermal technology for chlorinated solvent source zones, petroleum NAPL, and PAH-impacted soils where excavation is not feasible. It is most effective in fine-grained, saturated soils that hold a steady moisture content for current conduction. Operating periods are typically 60 to 180 days. Energy demand is significant (roughly 200 to 400 kWh per cubic metre treated), and electrical infrastructure plus three-phase power are prerequisite.
Buyers often weigh resistive heating against ex-situ indirect thermal desorption, and the honest answer is that they solve different problems. ERH treats contamination in place: no excavation, no material handling, and it can reach beneath buildings and active infrastructure. Its ceiling is roughly the boiling point of water, so high-boiling compounds such as PCBs, dioxins, and PFAS are outside its range, and it depends on large grid power or generators on site for months. Indirect thermal desorption treats excavated material in a rotary kiln at 320 to 600 degrees Celsius and above, which destroys the full boiling-point range including PFAS and dioxins, and produces a verified, sampled endpoint on every tonne. Where soil can be excavated, ex-situ thermal is usually faster to closure and carries the lower performance risk. Where the source sits under a building or cannot be dug, ERH or TCH is the correct tool.
Nelson's position in this comparison is deliberate: the company operates one of the largest mobile indirect thermal desorption fleets in the world, with plants engineered for arctic, desert, and tropical deployment, and selects in-situ methods when site geometry genuinely requires them. The deciding variables are excavatability, contaminant boiling range, power availability, schedule, and the verification standard the regulator will accept.
Also known as: ERH, electrical resistance heating, resistive heating, Joule heating, electrical resistive heating.
Electrical resistance heating (ERH), also called resistive heating, is an in-situ thermal remediation technology. Electrical current is passed through the ground between buried electrodes, and the soil's resistance converts it to heat, raising the subsurface to about 100 degrees Celsius so contaminants volatilize and are captured by vapour extraction.
ERH is effective on volatile and semi-volatile compounds: chlorinated solvents (TCE, PCE), petroleum hydrocarbons and NAPL, and lighter PAHs. Its temperature ceiling near the boiling point of water means high-boiling compounds such as PCBs, dioxins, and PFAS are generally outside ERH's effective range.
Resistive heating treats soil in place by heating the subsurface between electrodes, typically to about 100 degrees Celsius. Ex-situ indirect thermal desorption excavates the soil and heats it in a rotary kiln to 320 to 600 degrees Celsius or higher. ERH suits sources that cannot be excavated; thermal desorption suits excavatable soil and destroys the full range of contaminants including PCBs, dioxins, and PFAS.
Typical ERH operating periods run 60 to 180 days of active heating, plus design, drilling, and electrode installation. Total project duration depends on treatment volume, target temperature, and confirmation sampling requirements.
ERH is power-intensive, on the order of 200 to 400 kWh per cubic metre of soil treated, and requires substantial three-phase electrical service or large generators for the duration of the project. Power availability and cost are among the first feasibility questions on any ERH site.
When the soil can be excavated, when the contaminants include high-boiling compounds (PCBs, dioxins, PFAS) that exceed ERH's temperature ceiling, when grid power is limited or expensive, or when the regulator requires verified, tonne-by-tonne treatment confirmation that ex-situ processing provides.
In-Situ Chemical Oxidation (ISCO): treatment approach
In-situ chemical oxidation: injection of a chemical oxidant — permanganate, persulfate, or Fenton's reagent — directly into contaminated soil or groundwater to destroy dissolved-phase organic contaminants without excavation.
An ex-situ soil treatment process that heats contaminated soil to volatilize and separate organic contaminants from the soil matrix, after which the liberated vapors are captured and treated, usually in a high-temperature oxidizer.
A thermal desorption configuration where the heat source contacts the soil directly inside the rotary unit, delivering high heat-transfer efficiency and supporting higher treatment temperatures.
A thermal desorption configuration where heat is conducted through the wall of the treatment vessel without combustion gases contacting the soil, producing a concentrated, lower-volume vapor stream suitable for condensation and recovery.
Treatment that heats contaminated soil and groundwater in place, typically with electrical resistance, thermal conduction, or steam injection, to volatilize and recover contaminants without excavation. Used where excavation is impractical or where the contaminant zone sits beneath active infrastructure.