Press Release

Table of Contents

Acknowledgements

Summary and Recommendations

1. Introduction

2. The concept of the critical group and the maximally exposed individual

3. Description of the subsistence farmer scenario

4. International use of the subsistence farmer approach

5. Reasonableness of the subsistence farmer scenario on occupational grounds

6. Relation of the subsistence farmer scenario to Radionuclide Soil Action Levels (RSALs) at Rocky Flats

7. Erosion of the subsistence farmer scenario

8. The Radioactive Wildlife Refuge

9. Enforcement for the eons

10. Conclusions and Recommendations

11. References

The extension of radiation protection to non-worker offsite populations created the problem of measuring dose because it was generally not practical to extend the same kind of measurement protocols to off-site populations as to workers. As discussed later in this document, this led to the idea of the hypothetical maximally exposed individual. The assumption was that if the dose to such an hypothetical individual were kept below a specified limit, then one would be sure that the rest of the population would have a lower dose and hence be protected relative to whatever standard was established for maximum allowable exposure. Of course, all of this is supposed to occur in the general context that the activity that imposes the risk upon people has some beneficial purpose, in order to guard against gratuitous imposition of risk (see below).

The protection of offsite populations from operations of nuclear facilities is complex enough, but the problem of protecting people far into the future from residual contamination of soil and water is far more complicated and difficult. A number of factors enter into the picture. For instance we know the diets of people who live near the facilities today. What about people far into the future? History is no help, other than to tell us that diets and preferences change.

When considering current operations, we know where the facilities are located and the approximate distribution of the pollutants. Even so, getting data that is precise enough for accurate dose determination for compliance can be a costly and difficult business.

When considering doses to populations far into the future, we do not know how the waste and residual activity will have migrated. We do not know what new activities might take place on the site. We do not know the population levels or distribution. We do not know what resources, other than water and food will be regarded as precious by society. We do not know how weather patterns will change or whether major geophysical disruptions will occur. Conditions that exist today will not endure indefinitely. Long-term waste management and long-term stewardship arising from residual radioactivity levels present some of the most conceptually difficult challenges for health protection. For instance, a few hundred years ago it would have been essentially impossible to predict that Las Vegas, Nevada, would become a bustling metropolitan area. Similarly, a hundred years ago the Midwest was being settled by then Europeans anxious to get a lot of land for farming. It would have been difficult to foresee the depopulation that is occurring in the Dakotas, for instance, outside of American Indian reservations, or that many parts of the Midwest now fit the nineteenth century definition of wilderness areas because their population density is below one person per square mile.

Some basic concepts have been put forth in radiation protection to meet the challenge of protection of populations far into the future. The International Commission on Radiological Protection describes three basic concepts:

1. the justification of a practice,
2. the optimization of a practice so as to minimize exposure, and
3. the development of dose limits.²

The first item, justification, means that no activity, including disposal, involving radioactive materials will be undertaken unless its benefits to society outweigh any potential detriments. Optimization is the process by which exposures to individuals and entire populations should be as low as reasonably achievable. Finally, dose and risk limits should be developed before the activity takes place so that no individual is faced with unacceptable risks resulting from the use of radioactive materials.

Two methods have been suggested to meet the goals of radiation protection implicit in these concepts.³ One is the concept of limiting population dose or risk from any facility or activity and the other is to limit individual dose or risk. For estimating the dose to populations in the vicinity of the contaminated area of a disposal site, this approach requires a large number of assumptions about future population distribution patterns and overall resources use. It is difficult to justify specific assumptions about future lifestyles in general and even more difficult to predict demographics thousands of years into the future. The examples of the difficulty of prediction that we have already cited can be easily multiplied. However, there are some areas where population dose estimates are possible and desirable. For instance, releases of carbon-14 to the atmosphere in the form of carbon dioxide has radiobiological effects in terms of dose that are have been established, since carbon dioxide becomes part of the food chain. While uncertainties will remain as to transport of carbon-14 in the atmosphere, the uptake of carbon-14 by plants, and the exact diets in the future, there is no question that the basic food constituents, such as carbohydrates, proteins, etc. will remain in the diet. All of them are affected by the presence of carbon-14 in the atmosphere.

Such an approach cannot be used with ease or accuracy to estimate future local doses. For instance, in attempting to estimate population doses and cancer fatalities as a result of the operation of a high-level waste repository, the EPA calculated future doses based on world average statistics on food and water consumption, water flow, and a future population of ten billion people that consumes water and food at a rate that is three times greater than that of the present population. Using these averages and assumptions, EPA estimates the fraction of world river flow that is used for drinking and growing food, the retention of radionuclides in soil as a result of irrigation with contaminated water, and the uptake of these radionuclides into plants and animals.⁴

This approach was criticized by the National Academy of Science (NAS) Waste Isolation Systems Panel, in its Study of the Isolation System for the Geologic Disposal of Radioactive Waste (1983). A part of the problem with the EPA approach was that it did not couple protection of local individuals who might be living in the area of the geologic repository with the global aim of keeping cancers to below 1,000 over a period of 10,000 years. Adopting such a global goal without sublimits may have permitted local doses to be huge. This was the central theme of the criticism of the repository standard proposed by the EPA in the early 1980s:

The subsistence farmer scenario evolved over a period of time as a model by which the goals of radiological protection could be met in the context of long term waste management and disposal for local populations without recourse to assumptions about local lifestyles over very long time periods. If a future subsistence farmer, who used the local water supply and ate only locally grown food, were to be protected by radiation regulations, then all other people would have a risk of cancer lower than that of the subsistence farmer- and most people's risks would be much lower. The subsistence farmer concept has historically been coupled with defining a set of individuals called the "critical group" to which we now turn.

Next: 2. The concept of the critical group and the maximally exposed individual

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