The zone between the soil-moisture zone and the capillary zone, just above the water-table, which acts as a dispenser and buffer in the infiltration of groundwater flow (Diankov and Nitcheva (2005) Bulgarian. Acad. Scis). See also Sobotovich et al. (1991) Atom. Energy 70, 6 on the reduction of groundwater contamination since Chernobyl, 1986.