Extraction and purification of soil vapour can be used to remove volatile contaminants from the soil using vaporisation. Another method is to inject oxygen into the soil. The oxygen accelerates the degradation of contaminants in the zone above the groundwater table. This method is called bioventing: aerobic biodegradation in the unsaturated zone. Frequently, use is also made of injection of nutrients to give biological processes a helping hand. Soil vapour extraction is also known as SVE.