Groundwater (1979) by R.A. Freeze and J.A. Cherry, Prentice Hall, Englewood Cliffs, NJ. Figure 1.1, page 3. Physical and Chemical Hydrogeology (1990) by P.A. Domenico and F.W. Schwartz, John Wiley, New York, NY, Figures 1.1 and 1.2, pages 9 and 10.