Index > 3 Characterisation of radioactively contaminated sites >

3.3.8 Additional investigations to support a radiological site characterization

Contents
3.3.8.1 Introduction
3.3.8.2 Geomorphology/topography
3.3.8.3 Climatology/meteorology
3.3.8.4 Geology/geophysics
3.3.8.5 Hydrogeology
3.3.8.6 Hydrology
3.3.8.7 Pedology

3.3.8.1 Introduction

For a more detailed understanding of the behaviour of radioactive contamination in the nature, it is necessary to have good knowledge of the various environmental conditions influencing the fate of radionuclides in the biosphere, as well as of processes governing the radionuclide transport in the environment. In addition, information on human population as a potential receptor of radioactive contamination should also be known.

3.3.8.2 Geomorphology/topography

The geomorphologic investigation is conducted to develop an understanding of surficial features which influence the terrain stability and consequentially the integrity of the contaminated site itself. Namely, a series of slope processes like erosion (including land-sliding, colluvial, and proluvial processes) may seriously threaten the contaminated site and promote the spread of contamination from the site into the environment. Most of the data will be included in the site description. Information on the natural topography and man-made changes can be useful in this context.

3.3.8.3 Climatology/meteorology

Both the climate at a site and the particular weather conditions at the time of a release of radioactivity can be important determinants for the movement of radioactivity.

Meteorological parameters may determine air concentrations and deposition of airborne contamination on the ground and influence the soil-water balance. Statistical data on the climate will give information on likelihood of flooding, re-suspension by wind erosion, risk of fire, and probability of relocation of contamination by melting snow.

In the case of airborne contamination, exact information, or even informed estimates about wind directions and speeds, at various heights at the time can assist greatly in finding the resulting contamination plumes. Depending on the settling time of the material released, the weather patterns on a local, regional or global scale may be important. Precipitation can greatly alter the pattern of deposition of airborne contamination. Other meteorological parameters, such as the presence of temperature inversions or turbulence, can affect the vertical mixing of the radioactive dispersion or cloud.

The longer term climate of a contaminated area will influence the movement of radioactivity into and across the ground. Maximum wind speeds will determine re-suspension of dusts and will therefore affect off-site migration and become a factor in dose assessment. The prevailing wind direction will affect which populations are exposed. The rainfall patterns will affect likely future land use and influence off-site migration. Extreme weather conditions may also affect their choice of characterization techniques that can be used.

The climate can influence the choice of measuring instruments (water tightness requirements; exposure to low or high temperatures; etc.), and the humidity and air pressure may influence some measurements. Parameters generally included are: temperature, precipitation, wind speed and direction, atmospheric stability, humidity conditions, and air (atmospheric) pressure.

3.3.8.4 Geology/geophysics

The geologic investigation is conducted to develop an understanding of the subsurface environment in which the radionuclides may be present. The geology may strongly control the behaviour of the radionuclides, and hence risk assessment and remediation design. Information generally to be collected during a geologic investigation is sought from the following areas, such as stratigraphy, lithology, mineralogy, geotechnics and geochemistry, and tectonics and seism city.

Near surface sediments and features can be further characterized through the utilization of intrusive and non-intrusive geophysical techniques. The acquisition of geophysical data can help to build up a stratigraphic and structural picture of the underlying strata, and therefore tie in information between known geological control points.

Because geophysical techniques are often able to access difficult terrain and can produce data values relatively quickly, such techniques provide a relatively inexpensive way of acquiring data.
Geophysical surveys need to be very carefully planned, with the correct technique and associated methodology selected for the very specific problems of a given site. It will often be important to combine a number of techniques in order to build up an accurate picture of the underlying problem or feature. Examples of the effectiveness of multiple approaches are demonstrated [Digby].

A detailed discussion of the various geophysical techniques is beyond the scope of this document, but examples of their application and limitation are highlighted in Table 3.19.

Technique Application Limitations

Seismic Geological structure, lateral and vertical extend of landfills and trenches

Unconsolidated ground
Resistivity Contaminant plumes geological features

Bad contact of electrodes
Ground penetrating rad r (GPR) Buried objects, geological structure

Build up areas, microwaves
Electric logging Sedimentological and stratigraphic boundaries

Cone penetrometer tests (CPT) Sedimentological boundaries and contaminants

Will not penetrate coarse sediments
Magnetics Buried metallic objects, like drums and tanks

Background cutter
Electromagnetics Buried objects, extent of landfills and trenches

Background cutter

Table 3.19 Summary of common geophysical techniques

3.3.8.5 Hydrogeology

Hydrogeological data are important because they describe conditions above (the vadose zone) and below the water table (the saturated zone). They can also be used to predict future concentrations and movement of the contaminants. Long-term monitoring of the contamination profile and groundwater conditions may be needed for a full understanding of the hydrogeological regime and its likely relevance to, and influence on, any remediation strategy. Parameters which may collected during such an investigation encompass: hydraulic head, flow direction and velocity, recharge/discharge points, hydraulic conductivity, hydrostratigraphy (aquifers/aquitards), and aquifer age and water properties (e.g., pH, conductivity, temperature).

Measurements of these parameters could prove to be expensive tasks. This is because there will often be requirements for involving drilling, placement of piezometers, pumping tests, and tracer tests. However, such studies may be necessary to understand local transport pathways. Long-term monitoring of groundwater flow and contaminant transport and model development are useful for providing a sound understanding of the groundwater regimes and in the cases of risk assessment would be necessary.

3.3.8.6 Hydrology

The hydrologic investigation addresses the physical characteristics of surface water bodies that represent potential pathways. Surface water bodies may be natural (i.e., rivers and lakes) or may be man made (i.e., irrigation, dam reservoirs, waste ponds) [Fetter]. Parameters and descriptions which may be collected or developed during such an investigation include water flow rates, water volumes, circulation patterns (in lake), sediment descriptions, artificial sources, variability’s over time, etc. (e.g., seasonal variations), and flooding history.

It could be beneficial to sample water which is upstream of contaminated areas in order to acquire data about background values. Water samples could be sampled at outset or during a monitoring program continuously to create time series data. Fine grained sediments situated at the localities of highest depositional rates are generally preferred for sample collection.

3.3.8.7 Pedology

Pedologic investigation gives information to understand the properties of the soil layer supporting the contaminated site. Any spread of contamination from the site will penetrate it. Pedologic investigation can identify characteristics of soil as natural barrier for radionuclide transport. These include the physical properties (grain size, drainage class, lithological sequence, permeability, porosity, density, water content); and geochemical properties (leachability, leachate quality, elemental composition of the soil, pH, distribution coefficient Kd).