Index > 2 Development of a strategy, implementation and execution program to remediate radioactively contaminated sites >

2.1 Context and objectives

As indicated in Section 1, the Environmental Radiation Survey and Site Execution Manual has been developed to provide a consistent consensus approach and guidance to conduct all actions at radioactively contaminated and potentially radioactively contaminated sites and/or groundwater up to their release for restricted use or for unrestricted use.

The term “site” means land together with any buildings or structures being considered for release from regulatory control [IAEA – 2006a]. Buildings or other structures are not subject of this document. However, techniques used for the characterisation, decontamination and remediation and reuse of buildings and structures might also be used for the characterization, remediation and reuse of sites.

Mixed contamination sites generally result from waste disposal practices, unintentional releases from waste or material storage facilities, accidental spills during transportation or operations at facilities that manage hazardous and radioactive materials, and mining [IAEA – 2006b]. They can also derive from smelting operations and incineration of radioactive and hazardous wastes when air emissions are deposited on land. Releases of hazardous and radioactive contamination to the environment can have an impact on surface soil and the vadose zone, groundwater, surface water and sediments.

The word “soil” has a variety of different meanings depending upon its relevance to the society [IAEA – 2004]. Farmers consider it as the part of the earth’s surface containing decayed and organic material in sufficient quantity to grow plants and crops. Geologists take it as the residual (left over) material from underlying parent rock that supports root growth. To the engineer, soils include all earth materials overlying the rock crust and contain particles of minerals, gasses, and liquids.

In general, soil is a living system that represents a finite resource vital to life on earth. It forms the thin skin of unconsolidated mineral and organic matter on the earth’s surface. It develops slowly from various parent materials and is modified by time, climate, macro— and micro-organisms, vegetation, and topography.

Soils are complex mixtures of minerals, organic compounds, and living organisms that interact continuously in response to natural and imposed biological, chemical, and physical forces. Vital functions that soils perform within ecosystems include: sustaining biological activity, diversity, and productivity; regulating and partitioning water and solute flow; filtering, buffering, degrading, immobilizing, and detoxifying organic and inorganic materials, including industrial and municipal by-products and atmospheric depositions; storing and cycling nutrients and other elements within the earth’s biosphere; and providing support for socio-economic structures and protection for archaeological treasures associated with human habitation.

Different views about soil quality exist. For people active in production agriculture, it may mean highly productive land, sustaining or enhancing productivity, maximizing profits, or maintaining the soil resource for future generations. For consumers, it may mean plentiful, healthful, and inexpensive food for present and future generations. For naturalists, it may mean soil in harmony with the landscape and its surroundings, and for the environmentalist, it may mean soil functioning at its potential in an ecosystem with respect to maintenance or enhancement of biodiversity, water quality, nutrient cycling, and biomass production. In general, soil quality may be defined as: the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation.

Soil quality is therefore related to how well the soil does what we want it to do. This means that we need to have the complete information about the specific kind of soil or the soil characteristics which in fact are always subjected to fluctuations due to changes in management, changing rainfall patterns (including acid rain), changing water table levels and vegetation cover and other environmental factors. These changes in turn disturb the chemical equilibrium pattern in soil. In other words, soils are not material specific, many of their properties are not single valued, many are transient, and many are not randomly distributed but rather systematically time and spatially dependent.
Soil quality can be affected or disturbed by any of the factors described above and when a disturbance is due to the presence of substances in such concentrations which affect or tends to affect the role the soil plays in the ecosystem, it is known as contaminated soil, and the substances involved in this process are called soil contaminants. The standards or the thresholds that are fixed for the various soil contaminants through the national/international legislations provide specific definitions of soil contamination, as contamination here refers to the exceeding of the threshold limiting values prescribed in such legislations.

External contaminants entering a soil body through wet or dry precipitation, such as radionuclides, trace elements or organic compounds behave differently with regard to each soil type according to the absorption properties, texture, density, humidity, and other factors. As these properties are not homogeneously developed in a certain soil bed and soil properties change largely with stratigraphy it is extremely difficult to collect soil samples from a sampling area for chemical analysis in such a way that representativity is assured.

Groundwater is considered to be the water in the subsurface, in both the unsaturated and saturated zone, of a region, being an integral part of the larger hydrologic cycle of the region (Figure 2.1) [IAEA – 1999]. Interactions between groundwater and surface water bodies (recharge and discharge zones) provide one of the major pathways through which site and/or groundwater contaminants interact with humans and the wider terrestrial environment. These interactions can be beneficial by diluting the contaminated groundwater which can be a major factor in the reduction of the impact of groundwater contamination.

Figure 2.1
Figure 2.1 Generalized overview of the subsurface environment

Alternatively, contamination may become concentrated in bottom sediments through precipitation and sorption processes, or may be taken up and accumulated in plants and animals. Contaminants may also be transported to become deposited some distance from the point of discharge, usually at some interface, such as when suspended particulates are deposited when a river flows into a lake. Changes in water chemistry can occur downstream in a river system or where two rivers meet, as may the anaerobic conditions when a polluted river flows into a clean river or where effluents such as sewage are discharged into a water course. All of these processes and others can influence the way in which contaminants interact with man and the environment.

As a result, any program intended to assess and remediate contaminated sites and/or groundwater should start with the development of a structured conceptual model that embodies geology, hydrogeology, toxicology, radiology, and affected populations.
Five principles have been identified for the development of a consistent approach and guidance to conduct all actions at radioactively contaminated and potentially radioactively contaminated sites and/or groundwater up to their release for restricted use or for unrestricted use [CIRIA – 2009]. These principles apply at various stages in site and groundwater management.