| An initial study of airborne radon concentrations was performed at the Sanford Underground Laboratory at Homestake in Lead, South Dakota. Long term, stationary monitoring was conducted using AlphaGUARD detectors to record radon levels along ventilation routes underground at the Homestake Mine. The measurements were made primarily with no radon mitigation techniques underground, such as deployment of materials resistant to radon diffusion, or the installation of radon removing air systems. In addition, the current ventilation system at the Homestake Mine is operating at only 30--50% of its historical operating capacity. Radon monitoring since September 2009 reveals characteristics of the ventilation system as the primary driver behind dynamic radon concentrations. Early monthly averages on the 4850L Ross and Yates Stations were initially around 400 Bq/m3, but have more recently reached monthly averages around 285 Bq/m3 and 225 Bq/m3, respectively. Secondary factors that may affect the baseline emanation of radon underground is the presence of moisture and iron oxide on levels below 4,530 feet underground, which were recently underwater. The adsorption and co-precipitation of radium in the iron oxide layer, which is known to enhance the emanation of radon, is demonstrated experimentally through emanation testing of rock and iron oxide samples from the 4850L. |
