Groundwater sampling and analysis

Uranium-238 and 234U/238U activity ratios have been measured for groundwater samples collected at both the end of the wet and dry seasons. Measurable concentrations of 230Th were generally found, although in most cases they were within an order of magnitude of the detection limit. A program to determine phosphate in Koongarra groundwaters has also been undertaken on account of the potential importance of uranyl phosphate complexes in uranyl speciation, and the presence of uranyl phosphate minerals in the tail of the dispersion fan at Koongarra. The results indicated that the concentration of phosphate was sufficient to play a major role in uranyl speciation in Koongarra groundwaters. Uranium speciation calculated using the geochemical code MINTEQA2 showed that for many groundwaters compositions representative of Koongarra groundwaters, the uranyl phosphate complex UO2 (HPO4)22- would be the dominant solution phase complex. 3 refs., 3 tabs., 2 figs