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3.9.1 Selection of analytical method and detection limit

It is not possible to analyse all samples for all possible contaminants, and a strategy is therefore needed to prioritise and sequence the chemical and radiochemical analyses undertaken. The strategy would take into account:

  • The objectives of the site investigation (for example, is it to determine if a site is radioactively or chemically contaminated or to design a remediation strategy).
  • The conceptual model of the site, which would identify the potential contaminants of concern, potential sources and mechanisms of contamination, and the potential pathways and receptors.
  • The available budget and timescale for the site investigation/characterisation.

A phased approach is generally taken to the chemical and radiochemical testing. This is likely to involve:

  • On-site screening of samples, for example:
    • Radioactivity, using hand-held alpha and beta/gamma monitors.
    • Volatile organic compounds (VOCs), using a photo-ionisation detector (PID) or gas-chromatograph (GC).
  • Laboratory screening techniques, for example:
    • Gamma spectrometry (which also provides detailed analysis for specific radionuclides).
    • Gross alpha/beta.
    • Tritium.
    • Hydrocarbon analyses (e.g., diesel range organics (DRO: C11 – ~C35) and petrol range organics (PRO: C4–C10)).
    • Polyaromatic hydrocarbon (PAH) and polychlorinated biphenyl (PCB) screens.
    • Beryllium.
  • Detailed laboratory analysis, for example:
    • Gamma spectrometry (to determine the nuclide specific radioactivity with high accuracy).
    • Alpha spectrometry to determine activities of uranium and plutonium isotopes.
    • Chemical separation followed by specific radionuclide analysis (for example, 90Sr).
    • Trace metal analyses (e.g., Hg, Pb, Zn, hexavalent chromium).
    • Analyses to determine the potential for in-situ degradation of organic contaminants (e.g., presence of electron acceptors (sulphate, ammonium, nitrate and iron) and indicators of microbial degradation (CO2, methane, sulphide).
    • Analysis to determine presence of potential degradation products, particularly if these are more toxic than the parent material.
    • Analysis of colloids.

In general, for all types of analyses, uncertainty in the results increases with decreasing concentration or activity of contaminant.
Note that some laboratory screening can be undertaken on site. This may be required to confirm that samples are correctly packaged and labelled for off-site transport in accordance with the radioactive materials road transport regulations [ADR].