conditions and boundaries determined by the topography and geology of the area. Plant uptake as a basic for transfer to food chains (to be discussed later) is no longer considered significant. For these reasons, it is useful to examine not only certain aspects of the geology of the area but also the topography, hydrology, and soils of the area. Topography, Hydrology, and Soils Among those areas of interest at NTS, because of Pu contamination, are Yucca, Frenchman, and Groom valleys, which are all closed basins as far as surface drainage is concerned. That is, rainfall into any of these basins and its erosive products, insofar as water per se is concerned, remain there and do not flow away from the area into streams which eventually reach the Pacific as generally occurs outside such basins. In addition, because of the low rain- fall in the region, soil surfaces outside the actual drainage patterns do not receive sufficient water to reach the deep subsurface drainage patterns. fers is very slow, Yucea Flat. Moreover, movement in subsurface aqui- 7 to 730 ft per yr (Anonymous, 1973), beneath Although water moves faster in Frenchman's aquifers to reach downward to the Paleozoic aquifer, it apparently must pass through Tertiary tuffs where the rate of movement is 0.2 ft per yr or less. Paleozoic aquifer depths vary from a few hundred feet to a few thousand feet, depending on the depth of the alluvial materials which cover the basins' floors; i.e., both these valleys, and presumably Groom also, are filled from a few hundred feet to a few thousand feet with alluvial material eroded from the surround ing mountains, it is thought, during earlier pluvial periods correlated with times of extensive worldwide glaciers (Fernald et al., 1968). Near the mountains, these pluvial fans are dissected by more recent washes. Soils in these areas are often ill-defined as to horizons and frequently underlain by caliche hardpans. Those soils derived from limestone outcrops on the surrounding mountains are often strongly calcareous as compared to those derived from volcanic materials. ; 169 \ Ss \