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

There is a considerable international consensus about the subsistence farmer approach, which has been used in Britain, Sweden, Finland, and other countries.³⁷ In Switzerland, the critical group is defined as a self-sustaining agricultural community that obtains no food and water from outside sources and is located in the area of highest potential concentration.³⁸ This concept includes estimates of doses from the food chain (i.e. through crops, cow's milk, etc.)³⁹

The British National Radiological Protection Board (NRPB) uses similar language to define the critical group. They state the critical group (they replace the term critical group with "reference community") should be defined as "'typical' subsistence farmers, i.e., perhaps a few families who produce a range of food to feed themselves."⁴⁰

The Finnish government defines their critical group as a:

The International Atomic Energy Agency writes that:

Norway used several different scenarios, all of which have some similarities to the subsistence farmer scenario to estimate dose calculations for areas around their proposed site for low and medium level waste at Himalden. Calculations were done for five scenarios that included the four critical groups of:

1. Smallholder farming community located close to the facility by a stream.
2. Smallholder farming community located by a river downstream of the facility.
3. Hunter-gatherers consuming wild game from the area around a lake near the facility.
4. Fishermen consuming fish caught in that same lake.⁴³

The Finnish example shows clearly that there is some flexibility in determining what specific scenario should be used depending on local custom and diet. But in all cases, the scenarios are constructed with the idea that a plausible maximum dose should be estimated based on a model akin to the subsistence farmer. The fisherman and hunter-gatherer models are really local variants of the subsistence farmer model and the Arctic climate makes such scenarios plausible. Similarly, the Risk Assessment Corporation used a subsistence rancher scenario as a reasonable local variant of the subsistence farmer scenario in assessing Rocky Flats radionuclide soil action levels (RSALs).⁴⁴ These are the residual levels of radionuclides that would remain in the soil after it has been declared cleaned up by the DOE.

One reason for the international acceptance of the subsistence farmer scenario is that it complies with the recommendations made by the International Commission on Radiological Protection for exposure, risk estimation procedure, and definition of the critical group. ICRP 46 and 43 both recommend calculating the average dose from a repository to a homogeneous group that is expected to receive the highest dose equivalent.

ICRP 43 reads:

ICRP 46 reads:

The subsistence farmer scenario used by other countries where a small community is defined as the critical group meets these criteria. However, it is also valid for institutions to use a single subsistence farmer as their critical group because ICRP recommendations state that "it may be convenient to define the critical group in terms of a single hypothetical individual, for example when dealing with conditions well in the future."⁴⁶ The term "well in the future" is especially applicable in cases such as Rocky Flats or waste repositories because of the long time-frame at issue.

The subsistence farmer also meets several other criteria that have been recommended by ICRP. First, the diet, habits, and dose response of the farmer "should be based on present knowledge using cautious, but reasonable, assumptions."⁴⁷ It is both cautious and reasonable to assume that such a subsistence lifestyle could be viable in the future. It is neither cautious nor reasonable to assume that institutional restraints preventing use of the property as farmland will be effective for thousands of years. Historical examples ranging from house construction on dumps containing radioactive materials and chemical munitions within the space of decades provide ample reason to base future long-term health protection on an approach that does not assume prolonged institutional memory or controls. The subsistence farmer scenario provides such an approach and is therefore supported by both scientific and historical considerations.

Finally, the subsistence farmer represents the upper bound of exposure and the extreme of the actual doses in the entire population. ICRP 46 states that "the critical group represents the extreme" and "is intended to ensure that no individual doses are extremely high."⁴⁸ It has already been argued that the subsistence farmer meets the definition of a critical group. But, the language here shows that it is acceptable to protect this hypothetical individual in order to ensure that no other individual doses are unacceptably high.

One argument against this model is that it is too stringent for proposed geologic disposal sites such as Yucca Mountain or nuclear facilities such as Rocky Flats. However, this argument against the subsistence farmer scenario is weak and may be mathematically unsound (see discussion below). Because the behavior of future people is unknown, using a bounding approach, an approach that maximizes the number of people that would be protected, will limit the number of arbitrary assumptions that can be made to change estimated doses and possibly put future generations at risk. Also, in relation to Yucca Mountain, it has been shown that the repository design adopted by the DOE would in future time exceed established performance limits. This does not mean that the subsistence farmer scenario is too stringent but rather that the repository design is weak. Rather than adopting less stringent regulations, the DOE should improve its designs in order to avoid unacceptably high doses.

Next: 5. Reasonableness of the subsistence farmer scenario on occupational grounds

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