3.1. REGULATORY FRAMEWORK
The objectives and outcomes of remedial actions have a direct and lasting effect on the level of long term stewardship required at a site. The International Commission on Radiological Protection (ICRP) stipulates that:
“remediation measures shall be justified by means of a decision aiding process requiring a positive balance of all relevant attributes relating to the contamination. In addition to the avertable annual doses, both individual and collective, other relevant attributes shall be assessed” (see Ref. [9]).
The prime objectives for remediation actions are the abatement of environmental impacts and the reduction of risks to human and other receptors. According to Ref. [10]:
“remediation shall (a) reduce the doses to individuals or groups of individuals being exposed; (b) avert doses to individuals or groups of individuals that are likely to arise in the future; (c) prevent and reduce environmental impacts from the radionuclides present in the contami-nated area.”
The criteria for the release of sites from regulatory control upon the termination of practices have been formulated recently in an IAEA Safety Guide [11]. Though strictly speaking this Guide applies only to the decommis-sioning of authorized practices, sites where past practices or accidents have led
to contamination in the ground would have to comply with most of the criteria set out there. The preferred option, according to Ref. [11], is unrestricted release, provided the site meets the appropriate release criteria developed for a reasonable set of possible future uses (see also Section 7.6). In the case of restricted use,
“the restrictions should be designed and implemented to provide reasonable assurance of compliance with the dose constraint for as long as they are necessary… Therefore, existing regulatory limits on the insti-tutional control time frames should be taken into consideration in deciding whether to release a site for restricted use.”
The scope of a stewardship programme is outlined implicitly in Ref. [11]:
“The type, extent and duration of the restrictions and controls for site release can range from monitoring and surveillance to restriction of access to the site. They should be proposed by the operator on the basis of a graded approach and in consideration of factors such as the type and level of residual contamination after completion of cleanup; relevant dose constraints and release criteria; and the human and financial resources necessary for the implementation of the restrictions and controls. The restrictions proposed by the operator should be enforceable by the regulatory body and the cleanup plan should specify which entity will ensure that the restrictions are maintained.”
The actual regulatory framework will vary from Member State to Member State. Even after free release, a site may become the source of contamination, hence:
“consideration should be given to the potential circulation of material coming from future modification of the buildings, including demolition after site release. Materials originating from the site, after the site is released from regulatory control, need to comply with the national requirements for radiation protection... This should be an integral part of the optimization analysis of the cleanup process. Scenarios for exposure to sites released for unrestricted use should be realistic and consider the potential uses of the materials from the released site” (see Ref. [11]).
3.2. REMEDIATION OPTIONS
Decision makers are faced with a fundamental choice with respect to the intended remedial action. They must decide whether they will [12]:
(a) Leave the site undisturbed, while establishing a monitoring scheme for determining the evolution of the site. This option relies on natural processes to prevent significant exposure. The entire process needs to be carefully monitored so that an alternative option can be initiated if required.
(b) Contain or restrict the mobility of the radioactive contaminants. Such technologies aim to immobilize the contaminants inside the area where they already exist, reducing the potential for further migration or entry onto active pathways for exposure.
(c) Remove the radioactive contaminants from the site, implementing an appropriate treatment and disposal scheme. Such treatment technologies aim to extract, concentrate and then safely dispose of the contaminants at another location.
While removal is obviously a permanent solution for the site in question itself, the chosen disposal site may have to be subject to a stewardship programme. Any engineered solution to contain contaminants or to reduce exposures, whether on-site or at the chosen disposal facility, will only have a limited period of useful life. Natural forces will gradually degrade structures such as liners, barriers or cappings. Modelling predictions, based on historical experience and observed parameter values, allow an estimate to be made of how long an engineered near surface structure is likely to perform according to intentions. However, experience in recent times with floodwater defences has shown that our events database extending some 100 years into the past may be insufficient to capture the whole parameter range required for, say, a 1000 year lifetime.
This uncertainty over the long term effectiveness of remediation solutions requires provisions for monitoring [13], periodic performance assessment, and, if required, maintenance; hence the establishment of a stewardship programme. It is this uncertainty that creates the need for long term stewardship. While making remediation decisions, it is important to consider long term stewardship issues and obligations explicitly when comparing remedial alternatives and implementing a final remedy [14].
Stewardship, and by inference the steward’s responsibilities, must be defined at a practical implementing level, that is from the bottom up. For
stewardship to be understandable and affordable, a narrow definition of stewardship is recommendable [15].
Stewardship plans cannot be static but have to be adapted to the development of a site, with respect to both its physical state and its use.
Periodic revision of the stewardship plans will be necessary.
3.3. MEASURING SUCCESS
The USDOE’s Long-Term Strategic Plan [5] noted that:
“cleanup at most DOE sites is proceeding in an iterative fashion. End states appear at present to be emerging as the de facto result of multiple interim actions. These interim actions are being applied in a serial fashion via regulatory definition, often at relatively small and relatively dispersed former operational areas within the larger site, of facilities or disposal areas within operational units. Although individual cleanup actions are usually directed at relatively well defined end states (e.g. meeting regulatory standards), the ultimate end state for the site as a whole may be uncertain or unknown.”
This is almost certainly also true for other countries.
The measurement of remediation success is still a developing science [16, 17], and research sponsored jointly by the mining industry and government is currently being undertaken, for instance in Australia, to identify and apply ecosystem indicators for this purpose [18]. In the Northern Territory (NT), a company’s liability for a mine site ends upon issuance of a Revegetation Certificate by the NT Minister for Mines, and objective information is required to advise the minister accordingly. Thus, the goal and objectives for remediation of the site at Nabarlek are, like those for the site at Ranger, conceptual and value driven, recognizing the absence of sufficient information to enable quantitative targets to be set, such as values for biomass, tree canopy cover and successive colonization of flora or fauna.
The determination of estimation of the time when remediation is complete and long term stewardship begins may differ between Member States and may well vary for different types of sites within a Member State. Many times the determination of when remediation is complete is based on when the regulator certifies or by some means designates that the remedial actions taken have met the originally established remedial objectives. Groundwater remediation in some cases tends to have very long remedial durations, which creates a unique timing issue over when remediation is complete and long term
stewardship begins. The duration depends on the time needed for active water treatment. This is a critical issue to consider early in the remediation phase, especially if the parties responsible for remediation and long term stewardship are not the same entity or may change over time.