Field investigations to define the rates and directions of water movement through the deep unsaturated zone beneath an undisturbed, vegetated area began in the early 1980's and continue today. Image size 79K Figure 4. Installation of vertical shaft used for soil-moisture monitoring in upper 45 feet of unsaturated zone beneath undisturbed, vegetated area. Photograph by David S. Morgan, U.S. Geological Survey, August 1983. Water movement in the unsaturated zone is complex.
Water content indicates how much water is held in the soil.
Water potential indicates how tightly the water is held by the soil matrix. Water moves through soil in liquid and vapor form, and the two forms can move simultaneously as a consequence of water-potential, humidity, and temperature gradients in the soil. Between the depths of 40 and 160 feet, water movement, as liquid and as vapor, is consistently upward. Little is known about how, or to what degree, features of the natural system may be altered by installation of a disposal facility. The effects of disturbance are evaluated in terms of observed differences between data collected at the undisturbed, vegetated site and data collected at the disturbed sites.