Determine the number of pore volumes of air required for 99% removal of chlorobenzene from the vadose zone of an aquifer. The total volume of the aquifer is 1 m3. It has a porosity of 0.6, an organic carbon fraction of 0.02, and a bulk density of 1.4 g/cm3. The zone is 5% water saturated and 5% saturated with chlorobenzene.