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4.2.1 Environmental remediation objectives and criteria

An environmental remediation program should have clearly expressed objectives. The initial environmental remediation objectives should be established on the basis of the nature and extent of the contamination, the water resources that are currently or potentially threatened, and the potential for human and environmental exposure. These quantitative goals should define the extent of clean-up that is required to satisfy the established objectives. They include the required clean-up levels and the restoration time frame.

Past practices around the world have used extremely conservative scenarios for determining the risks of ionizing radiation to human health. As a result, environmental remedial activities have become extremely costly. Recently, a philosophy of using more realistic risk scenarios appears to becoming acceptable. In some cases, environmental remediation has been avoided altogether, with only the cost of monitoring remaining. This strategy has reduced the cost while continuing to adequately protect human health. It is recommended that when selecting and analysing the risk scenarios, the expected land use, the impacts on affected parties and environment, and the future groundwater needs should all be evaluated. A realistic scenario can then be developed which would allow for a more cost effective environmental remediation while still ensuring the safety of the public. Obviously, the effectiveness and the reliability of institutional controls may affect these decisions.

Risk assessment methods may be used, coupled with regulatory requirements, to determine achievable remediation goals. The beneficial use of an aquifer should also be considered. Water which does not meet the required standards for domestic use may still be useful for agricultural or industrial purposes. Finally, the potential effects on environmental receptors such as plant and animal species at or near the site may also affect the remediation goals.

If the environmental remediation is justified and any clean-up action optimized, criteria are needed to target environmental remediation activities, to assess performance as the work proceeds, and to verify that the environmental remediation has been achieved at its conclusion. These criteria may be expressed in terms of reference levels of residual dose, i.e., the projected dose from the future use of the remediated site, or in terms of concentration limits from which the residual dose, through a pathway analysis, can be calculated. Where necessary, re-entry criteria may be established by which it can be decided whether to allow the return of the population and/or reuse of the land for agriculture, and so on [IAEA-1999].

The term ‘reference levels’ (see also Section 2) includes reference levels, intervention levels, investigation levels and recording levels as defined in the IAEA Basic Safety Standards [IAEA-2007a]. The reference level (often expressed in terms of annual effective dose) 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 the natural background radiation. This will normally be assessed as the mean dose for an appropriately defined critical group. Remedial measures would often be justified below the generic reference level and national authorities may define a lower reference level for identifying site areas that might need remediation.