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3.4.1 Introduction

Consideration must be given to the different types of samples and their sampling requirements of the different media present on a site. Radioactive contamination may be restricted to the soil layer. It may also behave differently in the vadose and saturated layers. Rock or clay layers may be impenetrable to radioactivity or may bind radioactivity.

Measurements in “secondary” media, i.e., other than those containing the main contaminant, may give useful information on the distribution or presence of activity. Biota which concentrate activity may help in detecting the presence of radionuclides which are otherwise buried or at low concentrations. Emanation of gases (radon, tritium) from buried sources can help determine the presence of radioactivity. Most of these measurements should be regarded as qualitative rather than quantitative, but they prove valuable in early stages of characterisation to identify areas for further investigation.

Guidance is given on radiological, biological, soil, liquid and gas sample collection, and the growing area of real-time data collection using sensing techniques.
In each case, it has to be considered for each sample or real-time data collection of samples what is its beneficial value/added information for the conceptual model(s), site characterisation and remediation objectives. This can be achieved by considering the conceptual model(s) and asking a question such as:

  • For what principal pathways in the conceptual model(s) is this sample needed?

The analyses results of the sample(s) may also help to give an answer on other questions such as:

  • For the principal mechanisms of contamination at the site, what are the typical sizes and spacing’s of the source areas?
  • How mobile are the contaminants? For example, is it possible that a contaminant in the soil will also contaminate groundwater?
  • How deep are the contaminants likely to penetrate into the sub-surface environment?
  • What are the objectives of the site investigation, and what is the required level of confidence in the results?
  • If remediation was required, what “averaging volume” would be used for waste characterisation? This issue is of greatest importance on sites where contamination is heterogeneously distributed (i.e., “hot spots” and “cold spots” are present).

Therefore, this section deals also with the concept of “radioactively contaminated sites” and give detail information about possible sources of contamination, radionuclides of concern and their behaviour in specific environments.
As investigations will be performed with different scopes (see Figure 3.4), requirements for samples will also differ. Therefore attention is given to key considerations for sampling of:

  • Dose rates.
  • Alpha and beta emitting radionuclides.
  • Photon emitting radionuclides.
  • Neutron emitting radionuclides.
  • Biological samples.
  • Soil and rock samples.
  • Liquid samples.
  • Gas samples.

The last topic to deal with in this section in the design process of a field-based site characterization is the selection of sampling locations, patterns and frequencies. The more general considerations are dealt with in a separated section while if they are only valid for a certain sample, this information is presented together with the other sample key considerations.