A method for removing volatile and semi-volatile contaminants from groundwater in which the contaminants are stripped from the groundwater by sparging with an inert carrier gas and the stripped contaminants are transported into a bioactive zone into which at least one gaseous oxidant and at least one nutrient are independently injected, thereby stimulating at least one microbial culture associated with the bioactive zone to remove the stripped contaminants from the bioactive zone. By decoupling the sparging of the groundwater from the introduction of oxidants and nutrient feed gases into the bioventing bioactive zone of the subsurface, the oxygen and nutrient inputs to the bioactive zone can be adjusted (or carbureted) and controlled independently from the hydrocarbon input to the bioactive zone to achieve good kinetic performance in the bioactive zone while avoiding the problems of plugging of groundwater sparging due to biofilm and precipitate formation.