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2.4.9 Develop a conceptual model of the site

Starting with project planning activities, one gathers and analyzes available information to develop a conceptual site model. The model is essentially a site diagram showing locations of known contamination, areas of suspected contamination, types and concentrations of radio-nuclides in impacted areas, potentially contaminated media, and locations of potential reference (background) areas. The diagram should include the general layout of the site including buildings and property boundaries. When possible, produce three dimensional diagrams. The conceptual site model will be upgraded and modified as information becomes available throughout the radiation survey and site investigation process.

The model should be used to assess the nature and the extent of contamination, to identify potential contaminant sources, release mechanisms, exposure pathways, human and/or environmental receptors, and to develop exposure scenarios. Further, this model helps to identify data gaps, determine media to be sampled, and assists staff in developing strategies for data collection. Site history and preliminary survey data generally are extremely useful sources of information for developing this model. The conceptual site model should include known and suspected sources of contamination and the types of contaminants and affected media. Such a model can also illustrate known and potential routes of migration and known or potential human and environmental receptors.

The site should be classified or initially divided into similar areas. Classification may be based on the operational history of the site or observations made during the site reconnaissance. After the site is classified using current and past site characteristics, further divide the site or facility based on anticipated future use. This classification can help:

  • To assign limited resources to areas that are anticipated to be released without restrictions;
  • To identify areas with little or no possibility of unrestricted release.

Figure 2.7 shows an example of how a site might be classified in this manner.

Figure 2.7 Example showing how a site might be classified prior to clean-up based on preliminary investigations, historical site assessment
Figure 2.7 Example showing how a site might be classified prior to clean-up based on preliminary investigations, historical site assessment

Further classification of a site may be possible based on site disposition recommendations (unrestricted vs. release with passive controls).