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

2.2.2 Initial decision making

Contents Overall approach Historical site assessment Remediation criteria Development of site specific criteria for remediation Site characterization Overall approach

In principle, an overall remediation process for radioactively contaminated and potentially radioactively contaminated sites and/or groundwater may involve five main activities, see Figure 2.2. [IAEA – 2007a]:

  1. Historical site assessment
  2. Initial site characterization and establishing remediation criteria;
  3. Identification of remediation options and their optimization, followed by subsequent development and approval of the remediation plan;
  4. Implementation of the remediation plan; and
  5. Post-remediation management and stewardship

Following completion of each of these main activities, a decision should be taken about whether to release the site or part of the site for either restricted or unrestricted use, or to proceed to the next activity. The differences in implementation for specific sites will be in the degree of detail and complexity of the activities undertaken in each step in the process. An iterative approach based on the potential risks should be used.

Planning for remediation should begin once a radioactively contaminated or potentially radioactively contaminated site and/or groundwater has been identified or following a priority list defined in a larger project. The necessary funds should be made available either from the responsible party or through other mechanisms provided for in the legislation. The responsible party should collect available information about the radioactively contaminated or potentially radioactively contaminated site and/or groundwater and should perform a historical site assessment, Principle 4. Interested parties, including past and present owners, workers, local industry, residents, neighbouring states and/or local governments, should be consulted to obtain information, as appropriate.

General or specific reference levels should be used for an early analysis to determine the type and the extent of contamination that would require remediation. These levels should provide assistance in the early planning and help to establish the end criteria of any possible remediation activities.

A site characterization should then be performed on the basis of the relevant site information to determine whether the remediation end criteria (in terms of individual doses or derived concentration values) have been met. If the criteria have been met and this is confirmed by a survey, the site can be released without restrictions (i.e., no remedial actions are necessary).

If the site does not meet the criteria for unrestricted release, suitable remedial measures should be identified and an options study should be performed to compare the benefits and detriments of these measures. The options should cover a broad range of situations and should be based on a set of credible exposure scenarios.

For all options identified, a study should be performed to determine the option that is best for the site. The study should factor in both justification and optimization Principle 1. This study should include estimates of the costs and other resources associated with the treatment, removal, transport and disposal of contaminated material for each option; estimated doses to workers and the public due to exposure before, during and after the remediation; overall safety issues during remediation; available technologies; considerations for monitoring and sampling; amounts of wastes that will be generated; and the institutional controls required after implementation of the option, if applicable.

Figure 2.2 Overall remediation process
Figure 2.2: Overall remediation process

For the options under consideration, optimization of protection should be performed for the justified options to determine the option that has the highest net benefit. On the basis of this optimization, a preferred option should be selected that also takes into account non-quantitative considerations such as social and political aspects Principle 3.

The most suitable option may be the one that can be implemented with assurance of success and that provides the most benefits or results in the least damage to the environment as a whole, at acceptable cost, in the long term, as well as in the short term [IAEA – 2006b]. The process of making judgments on what might be the most suitable management option in environmental remediation projects has been illustrated in Figure 2.3 as an example.

Figure 2.3 Example of phases of decision making in remediation strategies
Figure 2.3: Example of phases of decision making in remediation strategies and technologies

For the selected option, a detailed remediation plan showing that remediation can be accomplished safely should be prepared for each radioactively contaminated site and/or groundwater, unless otherwise required by a competent authority and the remediation plan should be subject to the approval of the competent authority prior to its implementation.

Plans should be provided for both the remediation work and the necessary measures for post-remediation, such as maintenance, monitoring and institutional controls to enforce restrictions on land use and buildings, if applicable. Although institutional controls may last for a long period of time, they are part of the post-remediation process and should therefore be covered in the remediation plan.

Once the remediation plan has been approved, it should be implemented as soon as possible. If it is decided not to remediate the site, decisions should be taken on imposing restrictions on its use or access prior to release. If remedial actions are required, they should be implemented as soon as possible.

Two types of remedial action are possible: ( 1 ) source removal, or ( 2 ) pathway change. After the approved remedial actions have been completed, the effectiveness of the implementation should be evaluated, for example by a competent authority.

If the established remediation criteria have been met after source removal actions, the site should be released without further restrictions. If the criteria have been met after pathway change actions, the site should be released with appropriate restrictions. These restrictions would be in the form of institutional control on the use of the site, for example to ensure that restrictions on grazing are followed.

If, after remedial actions have been carried out, the criteria have not been met, the responsible party should determine whether further remediation is feasible or whether the site should be released with restrictions, and should submit a proposal accordingly to the competent authority for approval. If conditions have changed or additional information has been collected, and further remediation is justified, the process illustrated in Figure 2.2 should again be followed, starting at the stage at which the options are to be identified. Historical site assessment

A historical site assessment may be performed for a site subject to a remediation project to collect the information about the historical radiological conditions and to identify what additional information may be necessary to enable an evaluation of the site to be performed. This assessment could be made on the basis of operational and available information.

The objectives of a historical site assessment could be:

  1. To identify possible sources of radiological and non-radiological contamination and other hazards;
  2. To identify the characteristics of the contaminants;
  3. To identify related past activities or accidents that occurred on the site;
  4. To determine the impact of the site on human health or the environment;
  5. To provide input into the design of the characterization survey;
  6. To provide an assessment of the likelihood of migration of contaminants;
  7. To determine possible responsible parties.

Existing information providing a physical description of the site should be collected, including aspects such as location, buildings, buried material, physical barriers, geological and hydro-geological characteristics, type of soil and human activities on or near the site that may help to identify parties that may potentially be affected by the remediation. The information may be collected by means of (1) a review of operational records, past radiological and non-radiological surveys and local government records and files, and (2) interviews with present and former employees or residents.

In the assessment of any environmental contamination, all available information should be used to estimate the scope of the problem and to determine the type, quality and quantity of measurements necessary to make a decision on the extent of the remediation required. Remediation criteria

Reference levels have been defined for use within the system of protection [IAEA – 1996]. A reference level (often expressed in terms of annual effective dose1 indicates a level below which remediation is normally unlikely to be justified, and it serves as a criterion for the unrestricted release of a site. A generic reference level for aiding decisions on remediation is an existing annual effective dose of 10 mSv from all sources, including natural background radiation. This will normally be assessed as the mean dose for an appropriately defined critical group. Remedial measures may be justified below the generic reference level and national authorities may define a lower reference level for identifying sites that might need remediation [IAEA – 2003].

Additionally, a reference level specific to a particular component of the dose (such as that due to the inhalation of radon) may be established to limit the contribution of this component to the annual dose. This specific reference level should be expressed in terms of annual dose as an appropriate fraction of the generic reference level, or in terms of a subsidiary quantity such as dose rate or activity concentration.

In addition to a generic reference level for the total effective dose, a generic reference level for organ doses may also be required. An existing annual equivalent dose of 100 mSv (inclusive of all existing contributions, including doses due to natural background radiation) to any organ shall justify intervention under almost any circumstances [CIRIA – 2009].

The reference levels for the annual effective dose and equivalent organ doses, together with the specific reference levels for dominant components (as far as established by the competent authority), establish the remediation end criteria. These levels should refer to the actual exposures as well as to potential future exposures. Potential future exposures should correspond to the scenarios considered in the options study, which is referred to in Figure 2.2

In general, dose criteria cannot be directly measured, and therefore it is necessary to use assessment models to derive operational quantities that can easily be measured. By proper modelling of the exposure pathways, both the generic reference levels and specific reference levels can be converted into operational quantities, such as activity concentrations in Bq/g or Bq/m2, above which remedial actions should be implemented. This will enable the responsible party to implement remedial actions and demonstrate compliance with dose criteria.

On the basis of a generic reference level for the total effective dose of 10 mSv/year (or lower levels if specified by the competent authority), radionuclide specific generic reference levels for remediation, expressed in terms of bulk activity concentration (for soil and other material) as well as surface activity concentration, should be calculated by acceptable methods and in consideration of the components (e.g., material characteristics).

As an example, a specific approach for the implementation of remediation criteria may be summarised as indicated in the form of the reference levels indicated in Table 2.1 [IAEA – 1997].

The reference levels relate to the annual individual doses, to an average member of the critical group, additional to the regional level of background. For Bands 5 and 6 (and possibly 4), however, the additional dose is usually large compared to this background, and so the criteria might reasonably be applied to the total dose including background if this is more convenient.

The reference levels would, in the first instance, be compared to the doses estimated on the basis of the initial level of contamination. This comparison will give an indication of whether remediation is likely to be justified radiologically. The end point for remediation would then, in principle, be determined by optimization, but the reference levels can also be used to give an indication of the likely acceptability of different end points as a new ‘background’ level, i.e. for a return to normality. With the possible exception of situations initially in the upper end of Band 4 (where a justified and optimized remediation might conceivably leave a situation towards the lower end of Band 4), any remediation would normally need to produce an end point at least one band lower, and no higher than Band 4.

Band No. Range of annual doses
(to average member of the critical group)

Is remediation needed?
With constraint – Without constraint
Band 6

> 100 mSv/a Always Always
Band 5

10 – 100 mSv/a Always Almost always
Band 4

1 – 10 mSv/a Almost always Usually
Band 3

0.1 – 1 mSv/a Usually Sometimes
Band 2

10 – 100 µSv/a Sometimes Rarely
Band 1

< 10 µSv/a Almost never Almost never

Table 2.1 Examples of reference levels for remediation criteria.

The annual doses dividing the bands are approximations in view of the uncertainties involved. Nevertheless, it is convenient to have single numbers to represent criteria, and considerable presentational problems may be expected if slightly different numbers are quoted in different situations.

In this case, the most significant criterion that cannot readily be linked to existing criteria is probably that dividing Bands 4 and 5. This represents a point above which remediation would normally be expected to be undertaken in unconstrained situations, and therefore also represents the maximum level of residual dose that (apart from exceptional circumstances) might be considered acceptable as a new ‘background’ level. Therefore, situations with annual individual doses above this level would never be considered as normal whereas situations with annual doses below this level could, depending on the situation, be considered as normal.

The choice of 10 mSv/a for the boundary is necessarily a judgement, but is felt to be robust in the face of a number of considerations, including:

  • Worldwide variation in annual natural background dose;
  • Action levels recommended by ICRP and the Basic Safety Standards for radon in dwellings;
  • Doses implied by interdiction levels of activity in foodstuffs; and
  • IAEA recommendations on criteria for resettlement of populations.

The generic criteria in Table 2.1 may not be appropriate in all situations. However, any perceived inconsistency in criteria may have negative effects in terms of public acceptance that could well outweigh the economic or radiological benefits to be gained by using situation specific rather than generic criteria. Therefore, where local factors do support the use of situation specific criteria that differ significantly from the generic ones, these factors, and the effect they have been considered to have on the criteria (including any judgments or assumptions made), should be clearly stated. Such factors would include the distribution of individual doses and risks within the population. Development of site specific criteria for remediation

If the responsible party introduces site specific reference levels in place of the generic reference levels, these should be derived from a process of justification and optimization of protection, Principle 1 . Within this justification process (ALARA), it should be demonstrated that the resulting avertable 2 doses and other beneficial effects of the remediation are worthwhile in terms of costs, exposures of workers, any harmful environmental impacts and other disadvantages. From this, a site specific reference level should be derived in terms of an acceptable residual dose. A site specific reference level should not be interpreted as a strict limit but as a level against which the residual doses resulting from a justified and optimized remedial measure are to be compared.

While remediation may contribute to social and economic improvements in the area, remedial measures may also involve considerable cost and social inconvenience, and the line between caution and over-reaction may be difficult to distinguish. In applying the site specific reference levels, therefore, the exposures to be compared with these levels should be assessed on the basis of the average dose to the critical group determined by making realistic assumptions about diet and lifestyle, using realistic socio-economic factors and habitability data, and accounting for all possible pathways. The assumption of extreme or unrealistic characteristics in the dose assessment would be inconsistent with the goal of selecting the most appropriate remedial measure.

The outcome of the assessment of individual doses should be compared with the reference levels for remediation. If these reference levels correspond to doses that are lower than the average individual dose to the critical group, remedial measures are justified and should be implemented. The effects of different remediation options on individual doses should be calculated by using models that are consistent with those that are used to assess the individual doses from the contaminated environment.

As with using a generic reference level, the derivation of operational quantities expressed both as bulk activity concentration (for soil and other material) and as surface activity concentration (for surfaces) should also be performed. These calculations should yield remediation end criteria that are radionuclide specific and site specific. The calculations should be based on the same models, or at least models that are consistent with those that were used for calculating the radionuclide specific generic reference levels for remediation.

“The normal exposure of individuals shall be restricted so that neither the total effective dose nor the total equivalent dose to relevant organs or tissues, caused by the possible combination of exposures from authorized practices, exceeds any relevant dose limit” [IAEA – 2006a]. The dose limit of 1 mSv in a year for members of the public represents an upper bound on the sum of effective doses from all possible combinations of exposures arising from practices.

Clean-up and release from regulatory control of a site is one of the sources of exposure for which a dose constraint should be applied as for an authorized practice [IAEA – 1996]. This dose constraint should take into account multiple pathways of exposure and should not exceed 300 µSv in a year above background [IAEA – 2006a].

Before commissioning a new facility, therefore, the operator should ensure that a baseline survey of the site, including obtaining information on radiological conditions, is performed to define the levels of background radiation at the facility site. These levels will be further used at the end of the practice as a basis for comparison with the levels used to release the site. For existing facilities for which no such baseline survey was carried out in the past to determine these background levels, data from analogous, undisturbed areas with similar characteristics should be used for this purpose. These analogous areas should be areas that have similar physical, chemical, radiological and biological characteristics to those of the site considered for release, but they should not have been contaminated with radioactive material as a result of activities at the site. Such areas are not limited to natural areas undisturbed by human activities [IAEA – 2006a].

The applicable dose constraint for the public after the release of a site should be expected to be no higher than that applied for the operational phase of the practice. However, the two phases do not necessarily share a common set of circumstances (in particular, they do not necessarily have the same critical groups) on the basis of which to prescribe equality between the dose constraints applied before the termination of a practice and those applied afterwards [IAEA – 2006a].

In accordance with the Basic Safety Standards [IAEA – 1996] and the recommendations of the International Commission on Radiological Protection (ICRP), dose constraints should be applied prospectively to exposure from radioactive residues expected to remain in human habitats after the termination of a practice [ICRP – 2000]. The site dose release criteria should thus be based on an optimization of protection under this constraint, with account taken of the fact that optimization below the order of 10 µSv in a year might not be warranted on radiological protection grounds [IAEA – 2006a].

For the unrestricted use of a site, it should be ensured by means of the optimization of protection that the effective dose to a member of a critical group is kept below the dose constraint of 300 µSv in a year. For the restricted use of a site it should be ensured that, with restrictions in place, the effective dose should not exceed the dose constraint of 300 µSv in a year and that if the restrictions were to fail in the future the effective dose should not exceed 1 mSv in a year. The application of dose limitation to the unrestricted and restricted use of a site is shown in Figure 2.4 [IAEA – 2006a].

Figure 2.4: Constrained optimization and regions of effective dose for members of the critical group in the release of sites
Figure 2.4:Constrained optimization and regions of effective dose for members of the critical group in the release of sites

It is reasonable and appropriate to have different dose constraints for the release of sites than for the clearance of material from regulatory control [IAEA – 2006a]. Clearance of material may take place frequently over the lifetime of a practice, as well as at the termination stage. The cleared material may enter into trade with a broad range of potential uses and therefore should comply with clearance criteria, which are of the order of 10 µSv in a year. The dose criteria for the release of land from regulatory control should be optimized and can be higher than those for the clearance of material, because land remains in place and hence the degree of certainty about the potential uses of the land is higher than the degree of certainty associated with the uses of material after its release from regulatory control. Thus it is reasonable to allow a larger fraction of the individual dose limit for the release of sites (i.e. the dose constraint (less than 300 µSv in a year)) than for the clearance of material (of the order of 10 µSv or less in a year) [IAEA – 2004a].

As part of the decision making process for the release for unrestricted use of land and associated buildings or structures, consideration should be given to the potential circulation of material arising from any future modification of the buildings, including demolition after release of the site. Material originating from a released site needs to comply with the national requirements for radiation protection for material outside the scope of regulatory control. The assessment of material originating from the site should be an integral part of the optimization analysis for the clean-up process. Scenarios giving rise to exposure from sites released for unrestricted use should be realistic and should consider the potential uses of the material from the released site [IAEA – 2006a].

Uncertainties, such as those relating to the level of contamination and hidden buried structures and waste, should be taken into account in determining the impact of the release of the site. These uncertainties, together with the uncertainties associated with the future use of the remaining buildings on the released site, should be considered in the optimization of protection, with account taken of the level of confidence that is required for release of a site from regulatory control [IAEA – 2006a].

If the site complies with the appropriate release criteria when a reasonable set of potential future uses and their associated uncertainties have been considered, the site should be released by the regulatory body for unrestricted use, which is the preferred option. The decommissioning phase should then be terminated and the regulatory body does not need further involvement beyond keeping records concerning the released site. If after clean-up of the site it is demonstrated that the site meets the release criteria, it may still be released for unrestricted use (see Figure 2.4) [IAEA – 2006a].

If after clean-up the site does not meet the release criteria, the site can be considered for restricted use [IAEA – 2006a]. The restrictions should be designed and implemented to provide a reasonable assurance of compliance with the dose constraints. The restrictions should serve to exclude or prevent exposure pathways leading to effective doses higher than the dose constraint; for example, if effective doses via food chain pathways could give rise to doses above the dose constraint, institutional restrictions should be put in place to prevent future use of the land for agricultural purposes. The release of sites for restricted use generally requires ongoing institutional involvement and control to implement the necessary restrictions. Existing regulatory limits on the time frames for institutional control should therefore be taken into consideration in deciding whether it is appropriate and reasonable to release a site for restricted use [ICRP – 2000, IAEA – 2004a]. Site characterization

In addition to a historical site assessment, a site characterization survey may be performed to collect current information and to validate the information provided in the historical site assessment. The survey may provide information:

  1. To determine the nature and extent of radiological contamination;
  2. To identify receptors and provide input to pathway analysis and dose assessment or risk assessment models;
  3. To identify various options for the remediation;
  4. To evaluate environmental, occupational and public health and safety issues during remediation;
  5. To evaluate and select remediation technologies;
  6. To classify and quantify potential wastes; and
  7. To assist in the final survey design.

The characterization survey requires proper selection and calibration of instruments, proper sampling and measurement techniques and recording of data. The survey should utilize all types of techniques for collecting the necessary data properly. The design of the characterization survey should be determined by the conditions on the site, the type and extent of on-site contaminants and the available resources. The data should then be compiled and assessed to allow decisions to be taken. The data from the characterization survey should be used as input to models for assessing the individual doses expected to arise from the contaminated environment.

The results of the characterization of the site and the evaluation of the possible remediation options should be reported to the competent authority and to the stakeholders, and the review of the evaluation should constitute a key step in the decision making process. Interested parties should be involved in this process at an early stage before decisions are finalized.

A characterization report should be prepared and submitted to the competent authority as part of the remediation plan.

1 The annual effective dose is the sum of all significant components of annual dose incurred by a typical individual in an exposed group of people, from all relevant sources and via all pathways of a human habitat subjected to prolonged exposure. The existing annual dose therefore includes: the annual dose from natural sources of radiation; the annual dose caused by the accumulation of long lived radio-nuclides released from practices under control; and the annual dose caused by long lived radioactive residues from previous human activities and from long standing accidental contamination of the environment.

2 Avertable dose is the dose to be saved by a protective action; that is to say, the difference between the dose to be expected with the protective action and that to be expected without it [IAEA – 1999a].