Appendix A—permeability

In the paper entitled “The measurement of the permeability of porous media for homogeneous fluids” by R. D. Wyckoff and others [42] a unit of permeability is proposed which is based on centimeters, seconds, and atmospheres of pressure (76 centimeters of mercury).

In 1923, when the Hydrologic Laboratory of the United States Geological Survey was organized, much study was given to the question of a coefficient of permeability, and a coefficient was adopted which is based on feet and gallons a day (U.S. Geol. Survey Water-Supply Paper 596, p. 148). This coefficient has been extensively used and has proved very satisfactory in ground-water work. It has the merit of being readily applicable to field-conditions. It is, moreover, of convenient size, the coefficients of most water-bearing materials being integers of two or three figures, that is, between 10 and 1000. It was adopted in place of Slichter's “transmission-constant” (U.S. Geol. Survey Water-Supply Paper 67, p. 27, 1902), after much careful consideration, largely because the “transmission-constant” of most water-bearing materials is inconvenient in being only a small decimal.