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4.3 Remediation planning approaches

The objective of any technique used in a remediation project should be either to remove or to reduce the source term or to block the exposure pathways. This can be achieved in a variety of ways and needs to be tailored to the contaminants and pathways of interest. It may be necessary to use a suite of techniques to achieve the remediation objectives, especially for source term isolation or removal.

In the case of dispersed contamination, a rigorous assessment of the actual and potential pathways is required to determine the optimal action. This assessment begins with the identification and consultation of records, if available. The historical assessment needs to be confirmed by a physical site characterization, for example by walk-over gamma ray measurements. Detailed sampling and analysis may be needed to more clearly identify hot spots and to delineate materials that do not require further attention. In recent years, a variety of strategies and techniques for efficient site characterization have been developed [IAEA-2004b].

For sites with mixed contamination of radioactive and other hazardous substances, it is often necessary to use several remediation technologies, sometimes in series, i.e., treatment trains, to effectively address risk from the radioactive, chemical and physical hazards that could be present. In addition, sites may have contamination in different media. It is not uncommon, for example, on sites with extensive soil contamination, to also have groundwater contamination. Different technologies will probably be needed for remediating the different problems.

However, there are three basic planning approaches for any intended remedial actions. These are:

  1. Monitored non-intervention. This approach relies on natural processes to prevent significant exposure, meaning that the site will be undisturbed, while establishing a monitoring scheme for determining the evolution of the exposure of the site in time. The entire process needs to be carefully monitored so that alternative action can be initiated if required. Relating techniques of monitored non-intervention are in detail described in Section 4.3.1.
  2. Containment or blocking pathway(s). This approach restricts the mobility of the radioactive contaminants: this involves immobilizing the contaminants inside the area in which they already exist, reducing the potential for further migration or entry into active pathways of exposure. Relating techniques of containment or a so-called blocking of pathways are in detail described in Section 4.3.2.
  3. Source term removal. This approach relies on the removal of the radioactive contaminants from the site, using an appropriate treatment scheme: this involves extracting, concentrating and then safely disposing of the contaminants at another location. Relating techniques of source term removal including in-situ as well as ex-situ treatments are described in Section 4.3.3.

The three generic planning approaches that represent the fundamental technical choices for remediation can be summarized as monitored non-intervention, removal and containment. Each of these fundamental technical planning approaches will direct decision makers to follow substantially different paths with regard to their subsequent approaches, actions and potential results, making available significantly different technological options for application.

In addition, since a variety of remediation techniques exist for removing, reducing and containing contamination, the technologies illustrated in Figure 4.1 are grouped by the primary emphasis of the technology into separation, extraction or containment. The groupings are not necessarily mutually exclusive; for example, a barrier system may be used to contain and extract a contaminant, and, in some cases, the use of a particular technique may occur on or off the site.

Figure 4.1 Classification of remediation planning approaches
Figure 4.1 Classification of remediation planning approaches

The selection of a planning approach can not be made solely on the basis of scientific or engineering considerations. In addition to technical constraints, there may be a wide range of regulatory and socio-economic constraints on the selection of an appropriate remediation or disposal strategy [IAEA-2004b]. National regulations may favour certain techniques and prohibit or discourage others.

International agreements may also preclude or restrict some strategies. The local population may want to participate in the remediation decision making process; public acceptability can be a major factor in selecting a particular remediation technique. Active inclusion of the public will increase their knowledge and awareness of the problem, increase acceptance of the remediation technique selected for deployment and increase acceptance of restrictions on land use that may result. Participation may also enhance the public’s willingness to support the long term maintenance of remediation measures and related installations.

A wide variety of remediation techniques are now commercially available or at the demonstration stage. Although most of the techniques are of a generic nature, others use proprietary formulations of reactants and other agents, or applications that are protected by patents and similar means. Because the field is continuously developing, formal methods to assess the applicability and effectiveness of technologies have been developed. Approaches to selecting technologies vary from country to country. Some countries regularly undertake technology assessments to help ensure that proposed projects are effective and efficient. The findings are typically made accessible in technology directories or bibliographies. There are also international, semi-governmental, and industrial or research community sponsored initiatives. Technology and technology supplier directories are also available. Other states and organizations rely on informal approaches, for instance on the basis of personal judgement by experts and managers, to select technologies [IAEA-2006b].