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

An official recommendation to do away with the subsistence farmer scenario as the basis for public health protection first appeared in the Technical Bases for Yucca Mountain Standards. This report was prepared by an ad hoc committee of the National Research Council, the research arm of the National Academy of Sciences (NAS). That National Research Council (NAS-NRC) committee on Yucca Mountain standards, chaired by Robert Fri of Resources for the Future, recommended that the concept of establishing secondary measurable standards limiting releases of radionuclides from a repository be abandoned. In fact, the NAS-NRC committee is explicit that it does not include the current goal of protecting groundwater as a resource in its recommendations. The report states that the EPA regulation for high-level waste disposal,

The NAS-NRC committee recommended instead that the risk to a critical group be limited. It also recommended that this group would be defined in a new way. Professor Thomas H. Pigford (Emeritus, Nuclear Engineering, University of California, Berkeley), who was a member of that committee, disagreed and wrote a dissent.

If the recommendation of the majority were to be followed, there would be no explicit limits to the contamination of groundwater as such. It would be legally permissible for water to become highly contaminated, depending largely on the way the critical group was selected. The consequent radiation doses to some of the people using contaminated water could be very high.

The possibility of very high radiation doses, far above allowable limits, from consumption and agricultural use of water contaminated by a high-level waste repository at Yucca Mountain is real. Since water is scarce in the area, there is only a relatively small volume available (compared to other repository locations) to dilute leaking radionuclides.⁷⁰ The 1983 NAS study estimated that peak doses could range from a low on the order of one rem (perhaps less) to about 1,000 rem per year depending on the assumptions about the behavior of the waste and water travel time.⁷¹ Subsequent studies by INTERA (1993) and Sandia (1994) lowered estimated peak doses at 30 and 20 rem per year, respectively.⁷²

The controversy surrounding the proposed Yucca Mountain standards is illustrated by the disagreement between the NAS committee and its lone dissenter, Professor Pigford, . The questions that are at the center of this disagreement include the following:

1. Could the NAS committee's recommendation of limiting risk to individuals be compatible with allowing high doses of radiation to maximally exposed individuals, and in particular to subsistence farmers?
2. Are the committee majority's recommendations in conformity with those of the ICRP?

Insight into these questions can be gained through the analysis of Appendix C of the NAS-NRC report. Here, the majority outlines its eight-step process of determining the exposure of the critical group. The fundamental difference between this protocol and those that preceded it is that it defines the exposure limit for the critical group based on calculated risk from exposure rather than calculated dose. That is, it is recommended by the majority of the panel that dose calculations be made on the basis of hypothesized probabilistic distribution of future populations.

1. Identify the population which contains the people at risk of getting the highest doses. The example adopted by the committee is a farming community in the Amorgosa Valley. However, the term "farming community" could include many occupations, not just subsistence farmers. It could be a large, inhomogeneous group, which would be incompatible with ICRP's recommendation for a critical group, or a small, homogeneous group. For instance, it may consist of farmers, casino operators, and defense workers or it may have farmers only. These farmers may or may not be subsistence farmers.⁷³
2. Quantify the demographic and geographical characteristics of the population so as to determine what areas in the region "have the potential for farming and groundwater use." If possible, limit the area for exposure analysis by excluding some areas, such as those not likely to be farmed or where groundwater might be too deep. On this basis, the area and groundwater in the immediate vicinity of the Yucca Mountain repository could be excluded from the calculations.
3. Identify the intersections of those areas that might be farmed and those beneath which radioactively contaminated water would be present at some time.
4. Model the release of radionuclides from the repository and take into account that the plume of contamination passes through various areas at different times, limiting exposure in this way. Model various possible ways in which the contaminated plume of groundwater might travel (these are called "plume realizations"). People living in such areas before the plume is directly under them will be "at no risk" during these periods.
5. Calculate doses for a large variety of possible conditions and times, sampling from among the various plume realizations. This step acknowledges, in contradiction to the one just above, that people "outside the area overlying the plume" could be exposed due to local export of water or food."
6. Calculate the times at which the groundwater under various exposed populations would be most contaminated.
7. Divide the results of each plume realization into geographical subareas in which doses are to be arithmetically averaged. The population of each subarea should be large enough to "allow computation of a meaningful average dose." Then define a "critical subgroup" consisting of all subareas with average risks within a factor of ten of the "maximum average" subarea risk. The term "meaningful average" is not defined. This requirement could, in some cases, conflict with the ICRP recommendation that the critical group be small.
8. Average the average doses for the critical subgroups in Step 7 for each plume realization. This final average of averages is defined by the committee majority to be the "technically appropriate representation for the critical group risk."

The report implies that this new method is consistent with the ICRP's recommendations for the selection of a critical group, except that the committee uses risk in place of dose. The committee's definition of the critical group is very similar to that of the ICRP.

This definition is close to that of the ICRP except that it does not explicitly define the term "small."

Professor Pigford's dissent is given in Appendix E of the 1995 NAS report and his central arguments are that the majority's opinion is not consistent with ICRP recommendations, the majority's methodology for calculating exposure is not valid, and the standards would be too arbitrary and lenient. He argues that the committee majority abandoned the subsistence farmer scenario that is the most sure and most conservative method for protecting all future populations. This scenario is in conformity with the recommendations of the ICRP and is also consistent with the regulatory procedures of other countries and agencies within the United States itself. In addition, the probabilistic critical group approach recommended by the majority is "demonstrably less stringent in protecting public health than the subsistence farmer approach."⁷⁵ The example of the farming community in the Amorgosa Valley would contain part-time farmers, but the "full-time subsistence farmer will not be found on that distribution." (emphasis in original)⁷⁶ Therefore, this recommendation would not be in conformity with ICRP recommendations. Pigford also argues that the method is subject to manipulation because it allows for the arbitrary choices of parameters such as population characteristics and sizes of subareas. Such choices could lower the calculated doses that would provide "an illusion of safety, but with a serious loss of credibility."⁷⁷

A major argument against the probabilistic critical group method as developed in the 1995 NAS report is that it is not mathematically valid. Pigford's claim is that the procedures set forth in Appendix C of the NAS report do not result in a critical group that corresponds to a critical group as defined by the ICRP. This is because step 7 of the calculation process divides the region into subareas where there is no necessity for homogeneity within the subarea. This means that doses to individuals within the subarea can be very different and a few individuals with high doses could be averaged with a large number of individuals with low doses. This would result in a low average dose to the entire area. These same inconsistencies were noted by Professor Peter Bickel in a letter to Dr. Bruce Alberts, President of the National Academy of Sciences. Professor Bickel noted that the procedure recommended by the majority "could be made arbitrarily discrepant - five times could be turned into 5000 times and more."⁷⁸

ICRP recommendations require that the individuals with the highest dose be part of the critical group. In the probabilistic method, the averaging process over a subarea could result in the highest exposed individuals being in a subarea that has a low average dose. This could result in their exclusion from the critical group defined in step 8 of Appendix C because there may be many subareas with a higher average dose but that do not include the individuals with the highest dose.

EPA stated in its Background Information Document for Yucca Mountain that it did not accept the approach outlined in Appendix C of the NAS report.⁷⁹ It instead decided to use a scenario more along the lines of the subsistence farmer scenario outlined in Appendix D of the report. However in the final standards for Yucca Mountain, a vicinity-average dose has been introduced, which has the effect of introducing leniency into the calculation. According to the EPA rule water under Federal lands is exempt from safe drinking water rules, creating an unprecedented loophole for similar future exemptions. This extends to about 18 kilometers from the repository location. Drinking water and other doses are to be calculated outside this perimeter. Considerable dilution can be expected over such a distance and this would reduce the calculated vicinity average dose.

Another reason to adopt the subsistence farmer scenario is that it has been shown that the uncertainties associated with the subsistence farmer dose decrease over time.⁸⁰ This introduced leniency coupled with the decrease in dose uncertainties may lead to doses that are unacceptably high.

A proposal similar to the NAS-NRC majority has been put forth by the Electric Power Research Institute (EPRI). This is the vicinity-average dose model.⁸¹ However, in this case there is no averaging of averages. Rather, the model converts "the results from calculations for a maximally exposed individual into an estimate of risk to an average individual in a local population group."⁸² This method establishes a standard by calculating an average dose to a future population in the general vicinity of a geologic repository and allowing that average dose to be as large or larger than current exposure limits.⁸³ This would undermine the concept of the reasonably maximally exposed individual in much the same way that the NAS-NRC panel's plan does. The average dose may meet standards but there still exists a possibility that a small subset of the population could be exposed to very high doses while the remainder is exposed to very small ones. This would violate some of the basic tenets of radiological protection. The EPRI scenario was incorporated into legislation put before Congress to assess the performance of the Yucca Mountain disposal site.⁸⁴ This legislation did not pass.

The lowering of protection standards has led to degradation in other regulatory fields as well. A perfect example of this is the Department of Energy's (DOE) refusal to adopt clear national cleanup standards. The DOE remediation program has been operating under rules that allow it to impose site specific standards without any national standard upon which to base them. A process by which the EPA was setting cleanup standards for nuclear weapons sites was ended by a brief letter from an Assistant Administrator of the EPA.⁸⁵ The plan, which had consumed a great deal of time and energy, was abandoned without any plans for its resumption. The 1996 EPA draft 40 CFR 196 of 15 and 85 mrem/year dose limit (the variation depends on the chosen use of the site) was used to calculate Rocky Flats RSALs in 1996. A 15 mrem limit was used by the Risk Assessments Corporation in its calculations.⁸⁶

The lack of clear standards is also illustrated by comparing the cleanup levels DOE has used at various sites across the country, summarized in Table 1. For example, at the Livermore site in California, the industrial preliminary remediation goal is 10 pCi/g and the residential goal is 2.5 pCi/g of soil.⁸⁷ Meanwhile, at the Mound site in Ohio, the cleanup guideline value is 55 pCi/g.⁸⁸

Table 2 shows various nuclear sites around the country and the exposure scenarios they have chosen to adopt. These scenarios are generally less stringent than the subsistence farmer model. Table 2 illustrates this variation as it shows the soil action levels of various contaminated sites and the resultant doses that were estimated using a variety of scenarios.⁸⁹ This data was compiled by RAC. While it is up to the community to decide what scenarios and uses for the site to be used in determining cleanup levels, it is important to state that the process should be based on the same target dose/risk. That is, cleanup levels may be different, but the risks to individuals on site should be standardized. The table clearly shows that there is no clear mandate for clean up levels and that ratios given show the relationship between cleanup levels and the annual dose.

Next: 8. The Radioactive Wildlife Refuge

---

Order this report