[en] This working group was established to improve the modelling of the transfer of radionuclides from residues containing naturally occurring radioactive material (NORM) for the purposes of radiological assessment. Almost all naturally occurring materials contain radionuclides from the primordial decay chains (for example, uranium-238, uranium-235, thorium-232 and their daughter products radium-226 and radium-228), plus some individual long-lived radionuclides such as potassium-40. Extraction and/or processing of minerals containing these materials results waste containing such radionuclides. Often the processing can enhance the concentration of the NORM in the waste as compared with the original material. The extraction and processing of minerals usually involves large volumes of material and the resulting waste is also present in large volumes which are usually left on the earth's surface. Human exposure to radionuclides from such waste piles can occur as a result of gaseous emanation from the waste (radon-222) or as a result of the leaching by rainfall of radionuclides from the waste into water courses and, possibly, food chains. There are a variety of situations involving NORM that require potential radiation doses to be assessed, they include: (1) surface storage of residues from the extraction and processing of minerals; (2) remediation of NORM-containing waste piles; and (3) the use of NORM-containing waste for backfilling, building materials, road construction etc. In all of these situations there is a need to understand the present and future behaviour of the radionuclides which may be released from NORM so that steps can be taken to ensure that humans are adequately protected from exposure to radiation. Because of the long-lived nature of many of the radionuclides, the assessments must be carried out over long times into the future. This is the first time that the modelling of NORM-containing radionuclides has been examined in this IAEA format and the working group spent much of its time exploring the global situation and determining the availability of modelling tools. In contrast with other EMRAS working groups, the participants of the NORM working group generally chose to apply existing models from the literature to the test scenarios. These models had been developed by other organizations and so the participants were usually model users rather than model developers/users, as was the case in most of the other working groups. For these reasons, the issue of 'ease of use' of the models was an important issue for the working group. It was noted that several of the models examined were not very 'user friendly' with insufficient explanation provided for the user. It was concluded that ease of use could be greatly enhanced by the provision of good documentation and 'help screens', databases containing default values of environmental parameters, and facilities for plotting the results of calculations. It is also extremely important to provide the model user with simple procedures for changing the default values and for adding extra data to existing databases. Predictions were made for the three hypothetical scenarios using several models. The results for the point source scenario showed that the simple models (COMPLY, CROM) predicted higher radionuclide concentrations than the more realistic model PC-CREAM. Predictions were made for the area source scenario using two models (RESRAD-OFFSITE and DOSDIM + HYDRUS). In general, the results obtained from the two models (which use different methodologies for groundwater transport) were consistent with each other. RESRAD was 'calibrated' by estimating the natural background radiation level and comparing it to the existing natural background radiation levels. The limited amount of model testing which was conducted within the working group does not allow proper conclusions to be drawn about the state of modelling in this area. It is clear that more model testing, especially using the real scenarios, is needed and that specific model components and techniques may need to be developed to allow some of the more complex features of the real scenarios to be modelled. This is a subject of importance for many countries and for them competence in predicting the behaviour of radionuclides in situations involving NORM needs to be developed.