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The safe disposal of radioactive waste products remains a challenging and controversial issue, yet their burial in a stable geological environment is the option favoured by most countries. Past investigations of the Vaalputs facility in South Africa's semi-arid Bushmanland Plateau demonstrated its suitability for the disposal of low-level, short-lived (<300 years) radioactive waste, but also the need for more data on hazardous seismotectonic and climatic processes for the potential storage of longer-lived spent nuclear fuel. We review and then provide new information on the regional geomorphological and morphotectonic features of the Bushmanland Plateau, focusing on pedogenic features and compressive shear fractures in the trenches excavated over the past two decades. The fractures, provisionally dated between ~75 ka and ~46 ka, resemble east-verging thrust faults of limited horizontal displacement (≤1 m) and die out at depths of 4 m. Having discounted a pedogenic origin, the shear fractures likely represent stress relief structures triggered by the seismogenic reactivation of one of the Quaternary active faults in the area. The most likely candidate is the Santab Fault Zone (SFZ), which has a strike length ≥20 km and a throw of up to ~5 m at its closest point (8 km) to the Vaalputs site. Regional remote sensing and off-site investigations in the Bushmanland Plateau relate the neotectonic episodes at Vaalputs and environs to a late Pleistocene climax of the Namaqualand seismic source zone. This zone is characterised by the Wegener Stress Anomaly, a long-lived ~northwest-southeast oriented compression that, at its apex in the Late Santonian, caused large scale folding and thrusting not only in Bushmanland and parts of central-southern Namibia, but also swept across the entire African plate. [ABSTRACT FROM AUTHOR]

Vaalputs is the only South African nuclear waste disposal facility; it is licensed to dispose of low and intermediate level radioactive waste. Possible disposal of long-lived waste, potentially including spent fuel rods, prompted a study to establish a baseline of naturally-occurring radionuclides from the U and Th decay chains in the groundwater of Vaalputs. This baseline was created by investigating a dataset containing 25 years of analyses of the groundwater at the Vaalputs site. The behaviour over time, of 23 radionuclides in groundwater samples from 13 annually and three quarterly sampled boreholes, was evaluated and integrated in order to establish changing trends in the activities of radionuclides, the relative contributions of individual radionuclides to total radiation levels and how these were influenced by groundwater conditions. 238U levels showed a natural anomaly in the near-field of the disposal site that was attributed to the underlying basement rocks (granites) which are anomalously enriched in U. A set of duplicate samples from 2009 determined that the activity ratio of 234U/238U in the groundwater of Vaalputs is 4.1; this is ascribed to more rapid leaching of 234U relative to 238U, because of increased crystal structural damage around sites surrounding 234U atoms. High levels of 226Ra, unsupported by 238U, were found in groundwater from boreholes on the western side of the property: this groundwater yielded low values for 234U/238U, lower pH and stronger oxidizing conditions than groundwater from the rest of the area. The absence of overlying sedimentary rocks, which tend to ameliorate the effects of high radiation from granites by absorption, is suggested as the reason for the different geochemical conditions of the groundwater from boreholes in the west. This suggestion may apply to those boreholes elsewhere in Namaqualand with low published concentrations of 238U, but exceptionally high levels of α -and β-emitters. 232Th and its daughter radionuclides yielded radiation levels far below the guideline of 1 Bq.L-1 specified by the World Health Organization; this result is in line with the known low mobility of Th in groundwater systems. [ABSTRACT FROM AUTHOR]

Cosmogenic 21Ne and 10Be analyses across a subhorizontal fossil alluvial fan flanking the Cape Mountains near Laingsburg (Western Cape, South Africa) indicate a formation age for this fan of at least 2 Ma. Maximum erosion rates obtained from samples of quartzite ridges protruding through the fan alluvium deposits are very low (<~0.4 m/Ma) and analytically indistinguishable from those derived from pebbles from the fan surface (<~1.5 m/Ma). Our results are consistent with the low denudation rates obtained from other cosmogenic nuclide analyses and predicted by apatite fission-track and offshore sedimentation analyses for southern Africa during the Cenozoic. They integrate already existing substantial evidence to show that relative tectonic stability has prevailed across southern Africa throughout this period, and that the present-day large-scale topography is largely inherited from the Cretaceous and has been only minimally resculptured by denudation during the Cenozoic. [ABSTRACT FROM AUTHOR]

Measurements of cosmogenic He and Ne concentrations in dolerite and quartzite samples from selected sites across the South African coastal escarpment and the interior plateau provide valuable estimates of the short-term (i.e., a few hundred thousand years) denudation rates. Present-day denudation rates at the summit of the escarpment and on the inland plateau are more than an order of magnitude lower than those in the Cretaceous. Values between 1.0 and 2.1 m/Ma obtained from resistant quartzite samples and between 1.5 and 3 m/Ma from dolerite sills suggest a strong lithology control on the erosion. The observed patterns of denudation across different landform sites on the high plateau and along its flanking escarpment suggest that the morphology of the sampling sites together with the local climate conditions have controlled the denudation processes. [ABSTRACT FROM AUTHOR]

Late Mesozoic palaeosoils and Cenozoic deposits in the Northern Province, South Africa, centered on Vaalputs, Namaqualand are exposed in radioactive waste disposal trenches and buried beneath the surficial sands that cover much of the Bushmanland region. The sediments are preserved in a depression, in the "Vaalputs Basin", inland of the Great Escarpment. They overly a kaolinized and silicified basement of Late Mesozoic arenites (Dasdap beds) and by high grade rocks of the Namaqualand Metamorphic Complex. The Vaalputs sediments are interpreted to be fluvial in origin, possible deposited as unchannelized floodouts from a provenance area in the west. Extensive bioturbation and pedogenesis accompanied deposition. The age of the sediments is poorly constrained but post-dates ∼67 Ma volcanic pipes of the region. The Vaalputs sediments are influenced by north-northwesterly trending faults which also displace the underlying kaolinized and silicified basement. To the east of Vaalputs faulting in this orientation has produced a local depression (the Santab-se-Vloer). The distribution and apparent ages of the kaolinized and silicified surface, the Dasdap and Vaalputs sequences, and the position of the Santab-se-Vloer depression suggest to us that the continental margin has been characterized by an easterly migrating arch of uplift since the opening of the Atlantic, accompanied by increasing aridification of the region. [ABSTRACT FROM AUTHOR]