Essential to predicting potential contamination of ground water is the determination of the water movement. The most satisfactory method of obtaining the necessary data for this prediction is by drilling operations. Although these are expensive operations they are carried on extensively at the testing sites. Air While the fallout material from atmospheric tests remains in the air some will be inhaled and will irradiate the lungs. This radiation doS€ to the lungs normally is less than external exposure occurring after the fallout has been deposited on the ground. Also in general, inhalation is only a minor contributor to the intake of fallout debris into the body - ingestion is a much more important route. The whole body will also receive some exposure from the penetrating gamma rays while the fallout is in the air, but this dose will _ generally be small compared to the exposure that follows after the debris is deposited on the ground. Measurements of total fallout activity in air (called gross beta counts) provide only a crude alert system - this is not a reliable procedure for predicting the amount of fallout to be deposed nor the amount of iodine-131 in milk!’-. Because of the transitory nature of the fallout debris remaining in the air (and sometimes because of the particular choice of units used) what may sound like an alarmingly high concentration may, in fact, result in only minor radiation doses. 24.