Remediation methods guide
A site assessment tells you what is in the ground, where it sits and what it must meet. This guide lists the methods Nelson delivers across its thermal, In-Situ and Earthworks divisions, and the assessment findings that point toward each one.
How to read this guide
A Phase II environmental site assessment, or its equivalent, establishes the contaminants, their concentrations, the soil and groundwater conditions, the land use and the criteria that apply. Each of those findings narrows the options. The methods below are grouped by where the contamination is and what has to happen to it.
Most sites use more than one method. A common pattern is excavating the accessible source for on-site treatment, treating what remains under buildings or below the water table in place, and verifying everything against the same criteria.
Thermal treatment
Mobile ex-situ thermal desorption: excavated soil is heated in a rotary dryer to drive off contaminants, which are destroyed in a thermal oxidizer before gas conditioning and baghouse polishing. Nelson's mobile thermal fleet runs direct-fired and indirect configurations. Assessment fit: petroleum hydrocarbons, BTEX, PAHs and other organics in soil that can be dug out, especially where haul distance is long or the treated soil is wanted back as fill.
High-temperature thermal destruction for PFAS: a pilot-validated program, including participation in the NATO STO PFAS test bed. Assessment fit: PFAS-impacted soil where destruction is preferred to containment, considered case by case at pilot and validation stage.
Specialty thermal streams: fly ash processing, biosolids treatment and tire reclamation by pyrolysis. Assessment fit: industrial residues identified in the waste characterization alongside or instead of contaminated soil.
In-situ treatment
In-situ thermal treatment heats soil where it lies and captures the vapours for treatment above ground. Assessment fit: sources under buildings or utilities, at depth, or where excavation is impractical.
Soil vapour extraction (SVE), multi-phase vacuum extraction (MPE) and air sparging with thermal enhancement remove volatile contaminants from the unsaturated zone and groundwater. Assessment fit: volatile hydrocarbons or solvents in permeable soils, and free product on the water table for MPE.
Remedial injection: in-situ chemical oxidation (ISCO), in-situ chemical reduction (ISCR), colloidal carbon permeable reactive barriers and bio-amendments, matched to the contaminant chemistry. Assessment fit: dissolved plumes and source zones of BTEX, PAHs and chlorinated solvents, and downgradient plume control.
Groundwater and water treatment: pump-and-treat systems, dewatering, containerized above-ground treatment and sediment management. Assessment fit: impacted groundwater or process water that has to be captured and treated before discharge.
High resolution site characterization (HRSC) sits upstream of all of these. Assessment fit: when the existing assessment leaves the source geometry uncertain, HRSC refines it before a remedy is designed.
Earthworks
Excavation, certified haulage and disposal at approved facilities, with confirmation sampling support, clean backfill placement and site reclamation. Assessment fit: material outside a treatment envelope, small or scattered volumes, or sites where disposal is the practical route. Treatment and disposal are both legitimate offerings, and the choice follows the site.
Decommissioning, demolition and environmental construction, including landfill construction and decommissioning, pond decommissioning and barrier, seepage and erosion control systems. Assessment fit: structures or containment that must be removed or built before, during or after remediation.
Assessment finding to method
Hydrocarbon soil that can be excavatedMobile ex-situ thermal desorption, with treated soil verified and returned as fill where the criteria allow. Excavation and disposal for volumes or locations where treatment does not fit.
Source under a building, utility or at depthIn-situ thermal treatment, soil vapour extraction or remedial injection, chosen on soil permeability and contaminant type.
Dissolved plume in groundwaterRemedial injection (ISCO, ISCR, permeable reactive barrier), air sparging or pump-and-treat.
Free product on the water tableMulti-phase vacuum extraction, followed by in-situ or ex-situ treatment of the residual source.
PFAS-impacted soilCase-by-case evaluation through the pilot-validated thermal destruction program.
Uncertain source extentHigh resolution site characterization before committing to a remedy.
Structures, ponds or landfills on siteEarthworks decommissioning, demolition and environmental construction.
Project evidence
The Hub
Contaminant-by-contaminant pages set out behaviour, criteria and the treatment routes that apply.
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Thermal desorption soil remediation