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3.3.1 Major factors in site characterizations

Major factors in site characterization, to be taken into account, include:

  • Classification of the site. The classification is crucial to the survey design because the classification determines the level of survey effort based on the potential contamination and should involve reviewing all available information, e.g., a performed historical site assessment.
  • Characterization can be a large consumer of project resources. Mistakenly, its practical importance to solving the problem may not always be understood or appreciated. In some instances, the characterizations may be the “last word” measurements (e.g., for peripheral areas) and, as such, their credibility is vital.
  • The amount of characterization should be proportionate to the extent of the likely remediation effort. Over-characterization can result in a disproportionate fraction of the budget being spent on measurements, leaving insufficient means to carry out acceptable remediation.
  • Characterization should be adequate to allow a properly designed remediation; one that does not involve excessive amounts of unnecessary effort or environmental damage.
  • Characterization efforts should be sufficient to demonstrate the existence of clean areas and to provide credible assurances that un-remediated areas are safe.
  • Characterizations should have a sufficiently broad focus that any other unknown contaminants are detected at a stage when they can be dealt with efficiently.
  • The characterization, in the first instance, and the subsequent remediation should not make things worse by ill-advised first attempts that magnify or spread the problem. A guiding principle can be “first, do no harm”.

The nature and amount of radionuclides present will probably need to address the full three dimensional distribution of radioactive contamination. There are many possible contamination scenarios, including:

  • A superficial distribution of deposited activity.
  • Activity which has been deposited on the ground surface and which has migrated into the ground.
  • Activity which has been buried or covered (e.g., by ploughing or building operations).
  • Activity which is to a greater or lesser extent distributed through a substantial depth of soil (e.g., waste tips).
  • Activity which is deeply buried (e.g., due to leakage from underground storage tanks or drains (pipelines) which have carried active material).
  • Activity distributed as hot particles which are individually hazardous.
  • Activity which is uniform over large areas or volumes; and localized hot-spots.

Sometimes there may be a priori reasons to believe that the distribution is known, or can be established with little effort. In other cases, determination of the distribution will be a major part of the characterization. Gamma emitting nuclides found near to the surface may be amenable to measurement by non-invasive means, whereas deeply buried material will usually require more complex and costly methods.

Figure 3.1 shows an estimated correlation between the various site characterization methods [USNRC-2002]. As can be seen, there is a significant unit cost difference in price between in situ spectrometry and laboratory soil sample analysis. This difference is mainly due to the additional time and effort required for sample processing and measurement. There is some variability in this cost estimate, which is dependent on the radionuclide measured and the local factors such as cost of labour and analysis.

Figure 3.1 General pattern of measurement methods and their costs as a function of level of radiation/radioactivity being measured. Unit cost A is equivalent to US $1
Figure 3.1 General pattern of measurement methods and their costs as a function of level of radiation/radioactivity being measured. Unit cost A is equivalent to US $1