Index > 3 Characterisation of radioactively contaminated sites >

3.3 Design of field-based site characterisations: data quality objective process

The first step in designing effective field-based site characterisations is planning [USNRC-2002], [CIRIA – 2009], [IAEA-1998a]. The data quality objective (DQO) process is a series of planning steps based on the scientific method for establishing criteria for data quality and developing survey designs.

Characterization surveys may be performed to satisfy a number of specific objectives. Examples of characterisation survey objectives should include actions as:

  • Determining the nature and extent of radiological contamination;
  • Evaluating remediation alternatives (e.g., unrestricted use, restricted use, on-site disposal, off-site disposal, etc.);
  • Input to pathway analysis/dose or risk assessment models for determining site-specific DCGLs (e.g., Bq/kg, Bq/m2);
  • Estimating the occupational and public health and safety impacts during decommissioning;
  • Evaluating remediation technologies;
  • Input to final status survey design.

Planning radiation surveys using the DQO Process improves the survey effectiveness and efficiency, and thereby the defensibility of decisions. This minimizes expenditures related to data collection by eliminating unnecessary, duplicative, or overly precise data. Using the DQO Process ensures that the type, quantity, and quality of environmental data used in decision making will be appropriate for the intended application. EURSSEM supports the use of the DQO Process to design surveys for input to both evaluation techniques (elevated measurement comparison and the statistical test). The DQO Process provides systematic procedures for defining the criteria that the survey design should satisfy, including what type of measurements to perform, when and where to perform measurements, the level of decision errors for the survey, and how many measurements to perform.

The third step of the Data Quality Objectives (DQO) Process involves identifying the data needs for a survey. One decision that can be made at this step is the selection of direct measurements for performing a survey or deciding that sampling methods followed by laboratory analysis are necessary.
This decision is driven by “identifying the data needs” for the survey being performed and this includes:

  • Area of survey coverage for surface scans based on survey unit classification (Section;
    Radionuclide(s) of interest (Section 3.3.3 and Section 3.3.4);
  • Specific background for the radionuclide(s) of interest (Section 3.3.5);
  • Derived concentration guideline level (DCGL) for each radionuclide of interest (Section 3.3.6);
  • Target detection limits for each radionuclide of interest (Section 3.3.7);
  • Type of samples to be collected (Section 3.4);
  • Sampling locations and frequencies (Section 3.5);
  • Type of measurements to be performed (Section 3.6 and Section 3.7);
  • Selection of equipment (Section 3.8);
  • Selection of applicable analyze methods (Section 3.9);
  • Data interpretation (Section 3.10);
  • Type and frequency of field QC measurements to be performed (Section 3.3.9 and Section 3.10.8);
  • Measurement tracking and documentation requirements (Section 2.11 and Section 3.11);
  • Cost of the methods being evaluated (cost per measurement as well as total cost) (Appendix B).

Some of this information will be supplied by subsequent steps in the DQO process, and several iterations of the process and will be further discussed and may be needed to identify all of the data needs. Consulting with a health physicist or radio-chemist may be necessary to properly evaluate the information before deciding between direct measurements or sampling methods to perform the survey. Many surveys will involve a combination of direct measurements and sampling methods, along with scanning techniques, to demonstrate compliance with the release criterion.

The level of effort associated with planning a survey is based on the complexity of the survey and the objective of the survey(s) (see Section 3.3.10). In general a final site survey will be the most extensive survey to be executed at a site and the guidelines given in the next sections are then most appropriate and a careful consideration should be made during the design what to include and what to exclude explicitly.

Large, complicated sites generally receive a significant amount of effort during the planning phase, while smaller sites may not require as much planning. This graded approach defines data quality requirements according to the type of survey being designed, the risk of making a decision error based on the data collected, and the consequences of making such an error. This approach provides a more effective survey design combined with a basis for judging the usability of the data collected.

The survey methods used to evaluate radiological conditions and develop answers to these questions depend on a number of factors including: contaminants, contaminant distribution, acceptable contaminant levels established by the regulatory agency(ies), future site use, and physical characteristics of the site.

The remediation or decommissioning process assures that residual radioactivity will not result in individuals being exposed to unacceptable levels of radiation or radioactive materials. Regulatory agencies establish radiation dose standards based on risk considerations and scientific data relating dose to risk. Residual levels of radioactive material that correspond to allowable radiation dose standards are calculated (derived) by analysis of various pathways and scenarios (direct radiation, inhalation, ingestion, etc.) through which exposures could occur. These derived levels, known as derived concentration guideline levels (DCGLs), are presented in terms of surface or mass activity concentrations. DCGLs usually refer to average levels of radiation or radioactivity above appropriate background levels. DCGLs applicable to miscellaneous surfaces, e.g., pavements, are expressed in units of activity per surface area (typically Bq/m2 or dpm/100 cm2. When applied to soil and induced activity from neutron irradiation, DCGLs are expressed in units of activity per unit of mass (typically Bq/kg).