Radionuclides in Nevada test site groundwater: Transport by clay colloids

The Chishire (U20n) event was a nuclear detonation fired February 14, 176, at the Nevada Test Site (NTS). It was detonated in a fractured ryholitic lava formation 1167 m below the surface and 537 m below the water table. Yield was in the 200 to 500 kiloton range. A slant-drilled re-entry hole was cased and perforated within the cavity. Cavity water was intermittently pumped and sampled between September 1983 and May 1985. Because a number of strongly sorbing or insoluble radionuclides were observed in the ''dissolved'' phase (0.45 μm filtered) of early cavity samples, Lawrence Livermore National Laboratory initiated a series of filtration and ultrafiltration experiments using large-volume samples. Filtrates and ultrafiltrates were dried, weighed, gamma counted and further characterized; filters were gamma counted. X-ray diffraction studies of ultrafiltrate and retentate solids showed that the ultrafiltrates were composed of evaporite salts (halite, trona, aragonite), but that the retentates were dominated by quartz and (Ca, K) feldspars