The assessment of potential radiation hazards from gold mines in the Free State Goldfields to members of the public

Abstract

The gold mines In the Free State Goldfields extract and process ore from underground, which contains naturally radioactive uranium and its associated decay products. This assessment aimed to cost effectively determine the major potential radiation hazards to the public from the gold mines in the area. The potential exposure sources from the mines are radon gas, radioactive dust, contaminated water and external gamma radiation. The assessment focussed mainly on the public's potential exposure to radon gas emanating from tailings dams, waste rock dumps and upcast shafts from underground workings. The rate of radon emanation from the dams was measured using several different techniques, and the potential dispersion of the radon was modelled using internationally accepted modelling codes and local weather data for the Free State Goldfields. A maximum potential contribution to the natural background radon levels of 6 Bq m-3 was calculated. This is a small increment to the background levels in the order of 25 to 35 Bq m-3". Environmental measurements of outdoor radon concentrations confirmed the modelling results to the extent that no significantly high radon concentration could be detected in the environment. Background radon levels in towns outside the Free State Goldfields are in the same order as those measured around the mines. Similar environmental measurements of airborne dust and water sources around the mines indicated relatively low levels of radiation. A conservative estimate of the total potential exposure of the public in the Free State Goldfields is in the order of 130 to 250 µSv/a. This can be interpreted as well within the internationally accepted public dose limit of 1000 µSv/a.