“…The specific retention volume, as a first approximation, equals the partition coefficient 14 and is an index of the soil's ability to adsorb gases. The partition coefficient decreases with soil moisture content 15 but, even if the partition coefficient decreased thousandfold from dry to field moisture contents, passage through 10 cm of soil would remove more than 99% of the benzene content of air. The first 20 cm of travel would remove more than 99.9% of the benzene.…”