Safe Distance in the Location of Wells.
—In the location of a well, the distance of safety from sources of pollution will depend, in a considerable measure, on the character of the soil and the quantity and concentration of the pollution material entering the ground water. When coming from the surface, the danger is usually neither great nor difficult to avoid; but when cesspools and privies in the neighborhood are sunk to a considerable depth in porous earth, from which the supply of water is drawn, the polluting material may reach the well undiluted. No absolute radius of safety can be given, but certain generalizations as to conditions may be made as to character of soil and the different topographical conditions which surround a safe location.
In ordinary clay, or in clay mixed with pebbles and in soils of the same general nature, through which the water circulates by seepage, the pollution is not likely to be carried to a distance of 100 feet. Clay offers marked resistance to the passage of water, which in beds of 3 to 5 feet thick will act as protection from pollution from above. In sandy soils the movement of water is faster than in clayey soils, but 150 feet may be taken as a safe distance, unless the downward slope of the land carries the polluting material directly to the well.