Sampling and laboratory measurements

During post-restoration monitoring, most samples taken to verify compliance with the cleanup criteria are solids and liquids. Air samples are usually taken to detect hazardous or toxic chemicals. Radiological air samples are taken for worker protection purposes and to evaluate the remaining risk of exposure of the public due to resuspension of contamination. However, air/gas sampling may also be necessary to verify that contaminants in ambient air at the site boundary are consistent with emissions data and compliant with regulations.

Sampling liquids in surface waters, wells, water impoundment's, etc., is generally straightforward because liquids are homogeneous or can be made so by stirring or sparging.

Even when this is not practical, samples can be taken from different areas and depths to assess the variation within the medium. Composite samples can be taken to assess the average

Airborne or Vehicular use

FIG. 5. Environmental gamma-spectrometer.

composition. Liquids can be sampled using various equipment, including weighted bottles, grab samples, syringe samplers, dippers, pumps or remotely operated submersibles (for pond-floor sludges).

Solids sampling is more complex, as the physical form and characteristics of the solids may vary considerably, i.e. the solids may be viscous or sticky, granular or monolithic. In the case of monolithic solids, the sample must be cut out or otherwise removed from its environment.

Sampling techniques need to be selected on a case by case basis, because the needs and techniques are so varied. Some techniques commonly used for sampling solids are:

• auguring with sampling from the flights (for soils);

• hollow-stem auguring and split spooning (for soils);

• core drilling (for concrete and rock);

• core drilling or trepanning (for metals);

• shovelling or scooping (for granular material);

• scraping (for surface layers);

• collecting drilling debris (for concrete or metal); and

• using a trier (for soil and sticky solids).

Other measurements, samples, and/or methodologies may be required to fulfil the design objectives of the radiological monitoring. Some of these will be required for determining long

term health effects to the public from environmental pathways. The measurement or sample type selected is specific for the site, the radionuclide and for the radiation dose of concern.

These activities should be selected during the preparation for the radiological monitoring or as extraordinary conditions arise during the monitoring. Often these samples or measurements are collected to indicate potential migration of contaminated material from a site.

Measurements may include:

• radon flux rates and exhalation monitoring [32];

• alpha or gamma spectrographs of surfaces, air or liquids to identify the type of contamination;

• alpha, beta or gamma activity in drains, pipes or equipment;

• chemical, hydrological or meteorological conditions on or near a site.

• long-lived radionuclide content in the air or airborne particulate samples;

• alpha, beta or gamma activity of particles in water samples;

• alpha, beta or gamma activity of radionuclides present in building equipment, construction materials or process product;

• radionuclide content of off-site water and sediment samples from sources of standing or running surface water; and

• radionuclide content of samples from the food chain, e.g. vegetation, dairy or poultry products, fruits and meats.

The purpose, methods used and results of these samples and measurements should be reported or referenced in the monitoring report.

4.3.2. Sampling frequency and location

If a grid system has been established over an area, discrete radiological measurements or samples may be taken at the grid points. These measurements can provide definitive radiation levels at precisely defined locations. Furthermore, if the distribution is normal they permit the calculation of mean radiation levels within a given area by averaging individual measurements. The variance about the estimated mean will depend on the degree of heterogeneity remaining. These values can then be used for comparison with other areas or to estimate potential doses to people occupying that area. Grid point measurements may include alpha, beta, beta-gamma, low-energy X ray and gamma radiation. Samples taken typically include soil and routine surface smears. The type of measurement, suitable portable instrumentation and specific methodology to perform the measurement should be selected on the basis of the type of radioactive contamination present, the instrumentation available and the objectives of the monitoring plan in relation to the cleanup criteria.

The grid point measurements may be taken by placing the instrument at the appropriate distance above the surface, taking a discrete measurement for some time interval (e.g.

instantaneous, 10 s or 60 s) and recording the measurement. If samples are to be taken, they should be obtained as near to the grid point as is reasonably achievable. They should then be labelled appropriately and removed for the required analyses.

Composite samples may be proposed to characterise the average conditions in a medium at a location rather than the variation within the medium. They may also be taken to enhance the local representativeness of samples or to optimise the number of laboratory analyses made.

Examples of compositing techniques are available. To prepare composite samples:

• the medium should be thoroughly mixed;

• samples taken from different parts of the medium should be appropriately composited; and

• proportionate amounts of solids and liquids should be obtained.

At locations where anomalous radiation levels are observed or suspected, additional radiological measurements and samples may be taken on the basis of professional judgement.

The purposes of these measurements and samples are to further define the areal extent of potential contamination and to determine maximum radiation levels within the area. Those measurements may include alpha, beta, beta-gamma, low-energy X ray and gamma radiation.

However, at these locations these measurements may also be supplemented with other types of measurements, such as radon flux or gamma spectrographic measurements. Air, water, soil and smear samples may be taken at these locations; samples of vegetation and sediments and radon flux measurements. Such measurements and samples are obtained in the manner specific to the monitoring plan. The locations are selected to define best the areal limits of the anomalous radiation levels. All sample and measurement locations and results are recorded.

The type of biased measurements and samples taken and the methodology used to perform those activities should be properly selected within the limitations of instrumentation, site conditions and monitoring objectives.

4.3.3. Laboratory capabilities

In the field, a material can be directly sampled and measured, whereas the analysis in an off-site laboratory utilises sophisticated and often large equipment and/or detailed laboratory procedures. The detection limit for a radionuclide can depend strongly on the activity of other radionuclides present in the sample, the background of the counting installation and the counting times, sample volumes and chemical treatment used. A review of the limits for qualitative detection and quantitative determination can be found in Ref. [33]. Examples of laboratory analyses applicable to a post-restoration project are shown in Table IV. In this table examples of laboratory detection capabilities for individual determinations are summarised as well. These estimated lower limits apply if background, counting time and sample volume have the values as stated in the table. To illustrate the influence of the activity of the sample on the detection limit for gamma spectroscopy: the detection limit for 60Co in a sample (0.25 dm3) with no other activity present is 0.13 Bq, in a sample with a small amount of other activity present it is 3 Bq and if the other activity of the sample is high, the detection limit for

60Co rises to 35 Bq, almost 300 times higher than in the blank sample.

There are possibilities for enhancing the indicated detection limits. However, the consequence is that the number of samples which the laboratory can measure in a given time may decrease.

The corollary is that, if a very low detection limit is not needed, sample throughput may be increased.

In some circumstances a mobile or field laboratory may be used to minimise the need to transport samples or to initially screen the samples.

4.3.4. Subsurface measurements and samples

Subsurface investigations consist of measurements and samples taken beneath the ground or floor surface. The purpose of these investigations is to locate subsurface contamination and define its depth distribution. These investigations can be conducted by excavating the floor or

TABLE IV. EXAMPLES OF LABORATORY RADIATION DETECTION METHODS IN

ground surface by trenching, auguring, coring, shovelling or other means to depths that are either below a contaminated soil layer, i.e. beneath anthropogenic filling activities, or until a natural sealing formation is reached. The subsurface investigations may include logging or scanning of the vertical surfaces with alpha, beta, beta-gamma, low-energy X ray and shielded or unshielded gamma radiation detection instrumentation including spectrometers.

Excavated material or material from the sides of the vertical walls may be sampled for radionuclide analysis. Water or air in the excavation hole may also be sampled for radionuclide content. The number of excavations and the type of measurements or samples to be obtained with appropriate specific methodology will be selected, based on the type of contamination present, limitations in field conditions, type of instrumentation available and objectives of the monitoring plan.