points of lower elevation or pressure. The rate of ground water movement is governed by the permeability of the water-bearing formation, which is a measure of the case with which fluid will pass through it, and the hydraulic gradient or slope of the water table. The rate of flow of radio- nuclides in ground water is generally much slower and under no conditions greater than the rate of flow of the water in which that nuclide occurs, Generally, the rate is very much less. This is because many radionuclides become intermittently attached to the minerals that make up the water-bearing formation. \ From the considerations described above, it is clear that predictions as to rate and direction of ground water movement are dependent upon a knowledge of geologic and hydrologic conditions at the site under consideration. Early~in the feasibility determination for a project, a thorough investigation of the hydrology and geology of the proposed site is under taken, At and near the Nevada Test Site, the U. S. Geological Survey has compiled water-level and water-flow records on over 100:wells, test holes, and emplacement holes, as well as numerous springs, for use in defining areas of grou. water recharge, flow paths underground and discharge points. This information is augmented by chemical and radiochemical analysis of water. On the basis of the composite results of these various studies, underground water movement is known to be from 0.02 to 2.0 feet per day, Taking Yucca Flats as an example, the average rates of movement are believed to be significantly less than one hundred feet per year indicating that the