First observations of tritium in ground water outside chimneys of underground nuclear explosions, Yucca Flat, Nevada Test Site

Abnormal levels of radionuclides had not been detected in ground water at the Nevada Test Site beyond the immediate vicinity of underground nuclear explosions until April 1974, when above-background tritium activity levels were detected in ground-water inflow from the tuff beneath Yucca Flat to an emplacement chamber being mined in hole U2aw in the east-central part of Area 2. No other radionuclides were detected in a sample of water from the chamber. In comparison with the amount of tritium estimated to be present in the ground water in nearby nuclear chimneys, the activity level at U2aw is very low. To put the tritium activity levels at U2aw into proper perspective, the maximum tritium activity level observed was significantly less than the maximum permissible concentration (MPC) for a restricted area, though from mid-April 1974 until the emplacement chamber was expended in September 1974, the tritium activity exceeded the MPC for the general public. Above-background tritium activity was also detected in ground water from the adjacent exploratory hole, Ue2aw. The nearest underground nuclear explosion detonated beneath the water table, believed to be the source of the tritium observed, is Commodore (U2am), located 465 m southeast of the emplacement chamber in U2aw. Commodore was detonated in May 1967. In May 1975, tritium activity May significantly higher than regional background. was detected in ground water from hole Ue2ar, 980 m south of the emplacement chamber in U2aw and 361 m from a second underground nuclear explosion, Agile (U2v), also detonated below the water table, in February 1967. This paper describes these occurrences of tritium in the ground water. A mechanism to account for the movement of tritium is postulated