Removal of petroleum hydrocarbons from the vadose zone during multi-phase extraction at a contaminated industrial site

Field trials of multi-phase extraction techniques evaluated the contribution of volatilization and biodegradation to removing petroleum hydrocarbons from a contaminated industrial site. The techniques combined the extraction of soil vapours with the recovery of mobilized non-aqueous phase liquid (NAPL) from wells. Inducing air-flushing of the vadose zone by applying a vacuum to the recovery well promoted both the recovery of mobile NAPL near the water table as well as the volatilization and biodegradation of petroleum hydrocarbons in the vadose zone. Biodegradation and volatilization in the vadose zone were the major processes of removal under high water table conditions where liquid recovery rates were modest. In this case, biodegradation contributed most to removal. Where liquid recovery rates were increased under lowered water table conditions, volatilization and biodegradation still contributed 46% of the total removal rate.