Physical dispersion of radioactive wastes into regolith at the Radium Hill uranium mine site, South Australia

The Radium Hill uranium deposit was mined for radium\ud between 1906 and 1931 and uranium between 1954 and 1961.\ud Rehabilitation was limited to removal of mine facilities, sealing of underground workings and capping of selected waste repositories. Radium Hill has a semi-arid climate and the area is subject to wind and water erosion. In 2002, gamma-ray data, plus tailings, uncrushed and crushed waste rock, stream sediment, soil and vegetation samples were collected to determine the dispersal of mine wastes by wind and water into the local regolith.\ud \ud The mine and former processing site covers an area of approximately 100 ha. Numerous stable waste dumps of uncrushed rock occur for 800 ill along the line of lode. These consist of broken rock material from underground workings and represent the various rock types (feldspar-quartz-biotite gneiss, amphibolite, pegmatite, retrograde rock types, lode material) encountered during mining. Ore grade material (0.1-0.2% U) has significant davidite, high radiation levels (max. 5000 cps; max. 4.2 mSv/hr) and LREE, Nb, Sc, Th, Ti U, V and Y enrichments. Crushed rock material from the mine is found in several dumps in the mine and mill areas, and has been used widely for road and building construction. It is more radioactive than the uncrushed waste rock. Several former mill tailings dams are covered by soil and rock, with the largest containing approximately 0.5 Mt of tailings averaging 200 ppm U. Tailings have elevated radiation levels (1400-5500 cps; max. 3.5 mSv/hr) and prior to covering in the early 1980s, wind deflation and water erosion had caused widespread dispersal into surrounding regolith, with some soils having >90 % of tailings material. Despite partial coverings, mine wastes at the site remain susceptible to water and wind erosion. Regional airborne radiometric data outline the former town and mine sites and roads as pronounced U-Th anomalies. \ud \ud Capping of tailings storage facilities did not ensure long-term containment of low-level radioactive wastes due to erosion of sides of the impoundments. Continued wind and water erosion of physically unstable waste repositories causes radiochemical and geochemical impacts on local soils and sediments. Additional capping of mine wastes is required in order to minimise impacts on surrounding soils and sediments. However, measured radiation levels are generally below Australian Radiation Protection Standards (20 mSv/year averaged over five consecutive years), except for exposed railings