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 sound scientific basis to use the subsistence farmer scenario, or its local equivalent such as the subsistence rancher scenario, as the basis for protection of future populations when long-lived contaminants are present on a site. Site use restrictions are, at best, a temporary expedient. If such restraints are assumed in the absence of a more stringent goal for clean up derived from the subsistence farmer scenario, the health and ecological damage that may result would likely be higher as would the cleanup costs if the site must be revisited. There is plenty of evidence that a revision of prior lax decisions is costly from every point of view - health, environment, fiscal, or public trust in the government.

Beyond the subsistence farmer scenario based on present day risk coefficients and understanding, a safety factor is also needed. The many uncertainties in estimating future risk and the many areas of science that have been relatively neglected that may result in increased risk estimates per unit of dose indicate the need for an substantial safety factor to obviate the necessity of revisiting cleanup due to changes in risk coefficients. The complexity of plutonium chemistry in the natural environment, notably in relation to possible water contamination, also points to the need for an adequate safety factor. These two safety factors combined would reduce the maximum RSAL at Rocky Flats that results from scenario calculations considerably. Such an approach can be justified because a new cleanup effort in the future that would be far more difficult and costly, and the temptation of government inaction or worse would be avoided.

The RAC team recommended an RSAL of about 35 picocuries per gram of plutonium, plus the associated TRUs in specified ratios. Though this RSAL is based on a reasonably conservative subsistence rancher scenario, it reduces the estimated dose from a fire probabilistically. The RAC analysis leads to an RSAL of 10 picocuries per gram if the probability of a fire is taken as 1. As we have discussed, this analysis potentially underestimates doses by the groundwater pathway, if site conditions evolve to allow much faster plutonium migration than assumed in the RAC study. The plausibility of such rapid migration has been discussed in this report.

In light of the fact that these factors and others, discussed above, may increase risk from residual soil contamination at Rocky Flats, it would be highly advisable to set an RSAL below 10 picocuries per gram. This implies a safety factor of about 3 or more relative to the RAC recommended RSAL of 35 pictures per gram. How much larger this safety factor should be is a matter for public debate.

IEER's recommendations can be summarized as follows:

• The subsistence farmer or subsistence rancher scenario should be used as the basis for setting a residual soil action level at Rocky Flats.
• The subsistence farmer or rancher approach should be adopted even if the site is designated as a wildlife refuge, since it is not reasonable to assume that such a designation will endure for hundreds of years.
• Careful investigations of the effect of high residual contamination on wildlife should be undertaken, before the site is actually so designated. Investigations of the potential for such a site designation to enhance the mobility of plutonium into the accessible environment, including groundwater, should also be undertaken.
• RSALs between 1 and 10 picocuries per gram should be considered for Rocky Flats. This range is compatible with a subsistence farmer scenario. At the upper end of this range, the groundwater doses would be downplayed, but a safety factor of about 3 relative to the RAC model would be built in. Such a safety factor is desirable for a variety of reasons discussed in this report. If doses from groundwater are factored in, it would be reasonable to set an RSAL at the lower end of this range. Such an RSAL would also be compatible with the dose implications of the current state of Colorado surface water standard of 0.15 pCi/liter of plutonium, should it be extended to groundwater in the future.
• The steps towards the achievement of the ultimate RSAL, and the institutional arrangements in the interim, are beyond the scope of this report. But any cleanup plan should specify how a standard based on the subsistence farmer or rancher scenario would be achieved, and how any interim steps would relate to this goal.
  Next: 11. References

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