Steam Injection

Steam injection remediation addresses those compounds that are not readily removed with conventional remedial techniques, such as soil vapour extraction, air sparging and pump & treat. These conventional techniques have not proven effective for the remediation of semi-volatile and non-volatile compounds in the vadose zone or DNAPLs in the saturated zone.

• Enhanced Volatilisation – The increasing vapour pressure obtained by injecting steam results in increased volatilisation to the point that semi-volatile contaminants such as diesel fuel are almost entirely volatilised at soil temperatures that can be attained by the process (> 100ºC).
• Enhanced Mobility - The mobility of semi-volatile and non-volatile hydrocarbons such as heavy fuel and lube do not readily migrate through the soil and are adsorbed to the soil at high residual saturation concentrations. When thermal energy is applied to the soil, the increasing temperatures cause the viscosity and the residual saturation to decrease markedly. Soil temperature achieved using steam allows these viscous contaminants to behave in a similar manner to diesel fuel, meaning they will migrate readily through the soil and can be easily extracted by conventional techniques such as multi phase high vacuum extraction.
• Hydrous Pyrolysis Oxidation - Hydrous pyrolysis/oxidation (HPO) is a hydrothermal oxidation process that destroys organic contaminants in situ. The injection of steam and oxygen into the contaminated subsoil/groundwater creates a heated oxygenated zone that oxidises and degrades the contaminants. When the steam injection is periodically halted, the steam condenses and contaminated groundwater flows toward the heated treatment zone. The groundwater mixes with the steam condensate, heated groundwater and oxygen, and any dissolved contaminants are destroyed by oxidation. The return process of steam condensation avoids many of the mixing problems encountered in other in situ oxidation schemes that result in contaminant displacement without a return process to mix the oxidising reagent and the contaminant. In addition, the oxidation of contaminants at steam temperatures is very rapid (days/weeks) if sufficient oxygen is present.

Contaminants mobilised by the steam injection process can be removed by a traditional SVE/High Vacuum multi phase extraction and treated at the surface using conventional technologies such as thermal oxidation, catalytic oxidation or carbon adsorption.