Dual Phase Extraction and Free Radical Oxidation of Petroleum Hydrocarbons.

Dual aqueous-vapor phase extractions and oxidative degradation can be effective for rapid in situ remediation of hydrocarbons. However, long term impacts of these applications remain challenging in clayey soils. Repetitive extraction events were conducted at a gasoline contaminated area that is underlain by unconsolidated alluvial deposits comprised of sandy clays up to 5.5 m and fine sand underneath through 9 m and beyond. The shallow water table is typically present at around 5 m. After allowing a time lag for natural attenuation to occur, the residual organics were treated with nascent hydroxyl free radicals. The objectives of this study were to reduce immiscible floating product volume at and above the interface with well water and to remove petroleum hydrocarbons within the vadose zone. The extraction process reduced floating product thickness from 20 to <0.30 cm. The extraction events were characterized by rapid hydrocarbon vaporization kinetics, followed by quick decline in concentrations with time. The system extracted up to 336,000 L of groundwater and 358 kg of hydrocarbons with a radius of influence of 3 m. During the post-extraction lag phase, hydrocarbons were detected in the ground water, albeit at much lower concentrations. Over the entire lag phase, gasoline concentrations in the vadose zone declined significantly suggesting plausible natural attenuation. The nascent free radicals started depleting the residual hydrocarbons by at least 50% within only 90 days of reaction. Combinations of these physical and abiotic treatments have high potentials for complete remediation of contaminated areas.