Site-specific assessments

In all of the workshops, but especially in the FAT and Exposure Assessment workshops, the need for better understanding and model representation of soil systems, including both unsaturated and saturated zones, was evident. This included the entire range of processes shown in Table II, i.e., transport, chemical and biological transformations, and intermedia transfers by sorption/desorption and volatilization. In fact, the Exposure Assessment workshop (Level II) listed biological degradation processes as a major research priority for both soil and water systems, since current understanding in both systems must be improved for site-specific assessments. 

The uncertainty analysis that is a part of formal EcoRA methodology is designed to ensure adequate estimation of ecological effects based on a state-of-the-art scientific basis. Moreover, if applied on a local scale for site-specific assessments, with the use of empirical input data as biogeochemical parameters, the CLL approach is likely to provide results with a higher degree of confidence than the formal EcoRA model. 

NCRP emphasizes, however, that waste classification does not provide a substitute for establishing requirements on treatment and disposal of specific wastes at specific sites, requirements on remediation of contaminated sites, or decisions by regulatory authorities about the acceptability of any such activities. The acceptability of particular waste management or disposal activities must be based on site-specific assessments of risks posed by well characterized wastes. Waste classification, although useful, can only inform the process of... 

Second, generic and site-specific assessments of near-surface disposal facilities for radioactive waste have shown that allowable doses to hypothetical inadvertent intruders usually are more restrictive in determining acceptable disposals than allowable doses to individuals beyond the boundary of the disposal site. This conclusion is based on predictions that concentrations of radionuclides in the environment (e.g., ground-water) at locations beyond the site boundary usually should be far less than the concentrations at the disposal site to which an inadvertent intruder could be exposed, owing to such factors as the limited solubility of some radionuclides, the partitioning of radionuclides between liquid and solid phases, and the dilution in transport of radionuclides in water or air beyond the site boundary. More people are likely to be exposed beyond the site boundary than on the disposal site, but acceptable disposals of radioactive waste in near-surface facilities have been based on assessments of dose to individuals, rather than populations. 

There are various mathematical models that can be used to describe and analyze experimental data (Scholze et al. 2001). In addition to these curve-fitting approaches, response surface models are also available (e.g., Greco et al. 1995), but these are suitable primarily for the analyses of experimental data, rather than for predictive purposes. As an example, Altenburger et al. (2004) applied both concentration addition and response addition and observed that the combined effect of a 3-compound mixture out of 10 identified sediment toxicants was sufficient to explain the observed combined effect of the more complex mixture. For identifying remediation priorities in site-specific assessment of complex contamination, this approach has great potential. 

Nathanail CP. 2005. Generic and site specific assessment criteria in human health risk assessment of contaminated soil. J Soil Use Manage 21 500-507. 

Furthermore, it is important to consider the accuracy and available resources when defining a mixture problem. It can be difficult to determine the accuracy and costs beforehand, because accuracy often trades off with costs, and it is influenced by data availability and the actual risk level. Efficiency considerations imply that an assessment should be as cheap as possible, but sufficiently detailed to make a motivated decision. For site-specific assessments, a detailed and costly assessment is necessary only when the actual risks are close to the level that is considered unacceptable. For other outcomes, for example, when the actual risk is much lower or higher than the unacceptable level, a more crude and cheap assessment may suffice. Similar reasoning applies when deriving safe exposure or concentration levels. If limited data are available, a conservative value may be derived. If implementation of this conservative value turns out to be too costly, it is worthwhile to invest resources in gathering additional data and subsequently deriving a more accurate value. This is reflected in the loops of the risk assessment approach (Figure 5.1), which has resulted in many tiered approaches, such as those discussed in Section 5.4.4. 

In general, calculations of industrial emissions rely on default values according to the industrial sector, emission rates, wind velocity and direction, anticipated substance flows through the environment, abatement technologies and wastewater treatment processes (see [114]). Site-specific assessments and local environmental exposure assessments must also account for geographic variability caused by climate, hydrology, geology, and biotic conditions [115]. 

As discussed above, for risk management purposes, priority should be assigned to specific chemicals on the basis of site-specific assessments. However, it is also important to pay particular attention to chemicals that have been found in many locations worldwide to present serious human health hazards due to exposure through drinking-water. These chemicals are mentioned below and are discussed in greater detail in the WHO Guidelines for Drinking-water Quality (WHO, 2004 WHO, 2006). 

USES is not specifically designed for site-specific assessments, but adjustment of parameters may allow for insight into specific local or regional situations. 

Tier 2 produces site-specific target levels (SSTLs) that are protective of human health and the environment, but utilizes more site-specific data than Tier 1. This level of sophistication should address 70-80% of the sites. This more site-specific assessment involves the assumption of reasonable use exposure assumptions, considers actual beneficial uses of resources, and provides a tool for determining points of compliance. 

Site-specific assessments of the in situ risks of sediment pollution in The Netherlands are carried out mainly in freshwater systems. The in situ BEBA is then part of a broader evaluation of the risks caused by sediment pollution, aimed at the question of whether the risks make sediment remediation necessary. For this evaluation, a tiered approach is followed ... 

Brady et al. (2003) proposed that a site-specific screening approach followed by sequential extraction measurements could be an appropriate method to determine if a contaminated site is suited for MNA. In the first step, the site s chemical and hydrological conditions are assessed from standard site characterization data. The MNAtoolbox (www.sandia.gov/eesector/gs/gc/na/mnahome.html) provides a rapid initial assessment of the chemical and hydrologic conditions for MNA. The site-specific assessment for natural attenuation is then evaluated using sequential extraction experiments that enhance the site s characterization, determine the hioavailability, fate, and transport of the metal(loid)(s) in question, and assess natural attenuation against other remediation options (such as phytoremediation). 

When there are no generic guidelines, or those available are not compatible with the conceptual model, proceed to setting of site specific assessment criteria. 

Environment Agency, Guidance on Site Specific Assessment of Chronic Risks to Human Health from Contamination, Environment Agency, Bristol, 2001. 

For some contaminants exceedance by as much as one or two orders of magnitude can be within the range of probable over-conservatism in the guideline value and the derivation of site-specific assessment criteria should be... 

Will complement and facilitate the development of site-specific assessment criteria... 

The probabilistic CLEA model is being used to develop UK guideline values for human health risk assessment. In the interim the SNIFFER Framework (Land Quality Management26,27) offers a simple method for determining site specific assessment criteria. 

The second tier of assessment involves further site characterisation and the direct toxicity testing of soil samples. In terms of the latter, the following ex situ tests are recommended for consideration, depending on the site-specific assessment needs ... 

Where a study involves certain types of research procedure, the suitability of each site or sites at which the research is to be conducted requires site-specific assessment (SSA). The SSA is not a separate ethical review, but forms part of the single ethical review of the research. Where there is no objection on site-specific gronnds, a site may be approved as part of the favourable ethical opinion given by the main REC. When submitting an application, the chief investigator shonld declare if in his or her opinion the research does not require SSA at any research site. Where such a declaration is made, this should be considered by the main REC at the meeting at which the application is ethically reviewed. 

AR267 Confidence in models of radionuclide transport for site-specific assessment, Radioactive Waste Management, Workshop proceedings, Carlsbad, NM, 14-17 June 1999. 

A site specific assessment for man-induced external events has been carried out at the Kozloduy NPP. The work was mainly done by Energoproekt, and the results are available to western experts. The assessment took the following factors into account ... 

Further consideration of these discretionary criteria will be necessary for any of the sites identified in the Nuclear NPS that are taken forward for new build. The detailed site specific assessments will need to identify whether any revisions to plant design are required to mitigate impact that new build could have on the surrounding area/environment, and to ensure safe operation of the new... 

The probability of an accidental aircraft impact can be said to be acceptably low because of the regulatory and administrative arrangements that prohibit aircraft access close to UK nuclear power station sites. An aircraft crashing into the APIOOO will need a site-specific assessment to determine if this event is beyond design basis. 

---