Travel of pollution, and purification en route, in sandy soils.

The travel of pollution in sandy soils, and the extent to which purification takes place en route, are discussed, with special reference to the possible contamination of ground water-a problem which is of particular importance in the Netherlands, where the water-supply for many of the large towns is drawn from the water underneath the dunes.SPECIFICALLY, TWO TYPES OF SOIL POLLUTION ARE CONSIDERED: (a) severe pollution of the surface layers with matter concentrated in a small volume of water (e.g., faecal matter from pit privies at camping-sites); and (b) moderate pollution of the surface layers with matter contained in large quantities of water (e.g., organic matter and bacteria in river water used for the artificial recharge of ground water). It is shown that in both these types of pollution the self-purification is sufficient to prevent contamination of the ground water, provided that the soil is very fine and-in the case of the first type-dry and well aerated, and provided that the ground-water level is not too high or the rate of infiltration too great.