are so strongly adsorbed by earth materials that they migrate very slowly, even in reasonably rapid water flow (see Appendix III). The radioactivities in favorable areas generally migrate at rates less than 1/100 the rate of flow of the water. For example, for a ground water velocity of 500 feet per year the radioactivity in such an area will move not more than one mile every 90 1,000 years. Essentially all of the Sr from a nuclear explosion will have decayed after 1,000 years. This second kind of hazard can be evaluated in detail only in connection with a particular experiment. If the geology and the properties of ground water flow at the proposed site are well-known and are favorable, we believe, on the basis of present information, that nuclear explosive techniques can be used safely. In some situations, for example, the water must pass through beds containing clay minerals, with their large adsorption factors. Other projects permit the location of the explosion to be such that water going to beneficial use would not come into contact with most of the radioactivity. In this second circumstance, the few percent of the radioactivity which gets into the broken region above the shot at the time of the explosion can be filtered out or made harmless by dilution. Naturally, tests of the effectiveness of these modes of control of radioactivity will be needed, but there is little reason to believe that they will not work. Another study which will lead to improved control of radioactivity is the development of low-fission explosives, in which the major portion of the energy comes from fusion reactions, rather than from fission. The use of these clean explosives may prove advantageous wherever the associated tritium can be properly controlled. The Laboratory has for some time been working on the design of such clean nuclear explosives for Plowshare applications. In summary, we believe that these novel techniques can be used safely if appropriate precautions are taken. The detailed geology and the flow pattern of the ground and surface water must be satisfactory for each proposed site; any location with highly mineralized water or very soluble rock types would introduce additional problems. Comprehensive laboratory studies should be conducted with samples of water, the minerals, and the soils from a proposed site to determine whether the radioactivities characteristic of nuclear explosives would be very strongly adsorbed by the rocks and soils in the vicinity of the detonation. Finally, no withdrawal of water from the area should be permitted unless tests indicate that the water is safe. IV. UNDERGROUND STORAGE AND UNDERGROUND DIVERSIONS In this section we shall examine a number of potential applications of explosive nuclear energy to the problems of underground water movement. While the economic and legal feasibility of any of these suggestions will depend crucially upon the site chosen for the project, the technical aspects can be discussed in a more general framework, without reference to a specific location. It will be convenient to divide the goals into three categories: 1. Transport of fluids from subterranean regions to the surface; 2. Transport of fluids from one underground place to another; and 3. Transport of fluids from the surface downward into an under ground storage area. Nuclear explosives can assist in the transportation of water to the surface by creating pumping basins. In an aquifer of relatively low permeability, the use of a nuclear explosive either in the aquifer layer itself or in a competent layer beneath to create a fairly large volume of high permeability would appear to be feasible. Since the area available for infiltration of water into the pumping basin would be much larger than that normally available in a well, the well yield could be noticeably expanded. Another group of potential applications of nuclear explosives to water resource problems is their use to break underground barriers. For example, in a volcanic region of high but seasonal rainfall, water may be confined by a set of more or less vertical dikes. It travels downward and eventually reaches If we can puncture these barriers, we can tap this water, which would not otherwise be utilized. In addition to this "one-shot" benefit, any recharge of water into the newly accessible region would thereafter contribute to the water supply of the area. the sea. Barriers to horizontal water flow also occur in non-volcanic regions. If it should prove advantageous, these barriers, too, can be pierced permanently in order to capture water which would not normally be used. Finally, let us look at two examples of the third objective. In a region of high water cost and high evaporation rates, a nuclear explosive can be employed to create underground storage space. Such a reservoir would contain about 4,000,000 gallons of water per kiloton of yield, according to our present knowledge of the scaling laws, and would have negligible evaporation losses. In the course of making the volume for storage, the explosion might also provide a conduit through overlying impermeable rock, as the failure of successive layers of weakened rock might create a cylindrical volume of very high permeability. Precisely this example of the use of nuclear explosives has been studied by members of the Laboratory staff in connection with San Clemente Island. While such an experiment may be technically feasible, other considerations suggest that we not propose its execution at this time. Another application of this basic idea would be the creation of storage volume at depth for the disposal of radioactive waste products from nuclear reactors. By deep burial these noxious materials can be kept out of the biosphere permanently. V. SURFACE RESERVOIRS AND DIVERSIONS OF SURFACE WATER Nuclear explosives can also be used profitably in connection with the development of surface water resources. Four possibilities stand out: 1. The diversion of low quality water from a stream channel to an 2. The diversion of desirable waters for gravity recharge; 3. The creation of deep lakes; and 4. The improvement or alteration of stream channels. The first of these is suggested by the fact that the headwater tributaries of many rivers of the Southwest contain undesirable or brackish waters during the low spring flow period. These saline waters are, in many cases, transmitted by the existing stream system to retention reservoirs, where the quality of water is degraded by their addition. The creation (either by the use of nuclear explosives or by conventional means) of off-channel reservoirs for the diversion of these undesirable saline flows would serve two functions: 1. A large evaporation pond would be formed, from the surface of which water would evaporate; and 2. The reservoir could serve as a conduit to transmit water from the artificial channel to an underground aquifer which is already mineralized. With the aid of these two mechanisms the low saline flow of headwater tributaries may well be eliminated from the stream system, permitting greater beneficial use of the remaining fresh water. If the low-quality water is located in an area of extreme water need, it might even be salvaged by a demineralizing process. If, on the other hand, the impounded brackish waters are to be |