Soil vapor extraction (SVE). A vacuum applied to extraction wells in the unsaturated (vadose) zone induces advective airflow through the soil pores, volatilizing sorbed/dissolved VOCs directly into the vapor phase for capture and off-gas treatment (granular activated carbon or thermal/catalytic oxidation).
Air sparging. Air injected below the water table strips dissolved and sorbed VOCs from the saturated zone into the vapor phase, which then migrates upward into the vadose zone where it is captured — almost always paired with an overlying SVE system (AS/SVE).
Bioventing. Low-rate air injection into the vadose zone supplies oxygen to stimulate in-place aerobic biodegradation of the volatile (and semi-volatile) organics by indigenous soil microorganisms, rather than physically extracting them.
Thermal desorption (ex-situ). Excavated soil is heated in a rotary kiln or thermal screw to volatilize the organics from the solid matrix; the resulting off-gas is collected and treated (afterburner or condensation/carbon adsorption).
Excavation and aeration / land treatment. Contaminated soil is excavated, spread in thin lifts, and periodically tilled to promote volatilization to the atmosphere and aerobic biodegradation simultaneously.
Steam-enhanced extraction. Steam injected ahead of an SVE well raises the soil temperature, increasing the volatility (vapor pressure) of the target compounds and accelerating their removal rate relative to ambient-temperature SVE alone.
Selecting among these six in practice comes down to site-specific factors: soil permeability governs whether an in-situ vapor-flow technology (SVE, sparging, bioventing) can move enough air through the formation to be effective at all, while excavation-based options (thermal desorption, land treatment) become the practical fallback in low-permeability clays or where the contamination footprint is shallow and small enough to dig out economically. A real remediation design frequently combines two or more of these — most commonly an initial high-flow SVE phase followed by a lower-flow bioventing phase once the easily-stripped mass has been removed, matching the physical/biological sequencing described in Question 6.
