IEER
We received the following e-mail in response to our feature article in the last issue of SDA (Vol. 4 No. 4), "Calculating Doses from Disposal of High-Level Radioactive Waste." As the letter raises issues central to the debate about Yucca Mountain, SDA invited responses form Virginia Sanchez of the Western Shoshone Nation, where Yucca Mountain is located, and Professor Thomas Pigford, dissenting member of the National Academy of Sciences committee, which produced the report on standards for Yucca Mountain.
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Dear Arjun:
Thanks for tackling the NAS [National Academy of Sciences] analysis of Yucca Mountain exposure scenarios. I have the full report but haven't dared to open it. You asked for comment. I think you fail to point out that, in other areas than radioactive waste disposal, the EPA [Environmental Protection Agency] has begun to back away from the concept of the maximally exposed individual. See for instance the NAS report "Science and Judgment in Risk Assessment," (1994), pp. 46-7. In its guidelines for conducting risk assessments, EPA now prefers "high end" exposure scenarios, which are looser approaches, rather than the maximally exposed individual, MEI, which has become a lightning rod for criticism of the regulators' unwarranted conservatism. You point out that the "subsistence farmer" and the "small critical group" populations around Yucca Mountain are extensions of the MEI concept. [NAS committee member Professor Thomas] Pigford wants to keep them around, but the committee majority favors a looser standard for determining an exposed population (subarea averaging). To my mind the committee majority is in step with current approaches to risk assessment, and Pigford is a lonely throwback. Maybe the ICRP [International Commission on Radiation Protection] is too. By clinging to outmoded constructs such as the MEI, risk assessors become all the more vulnerable to attack from their GOP critics. I don't see how a strategic retreat here is going to open the floodgates of environmental pollution. On the other hand, having reported on Yucca Mountain (Smithsonian, 5-95) and having interviewed a Native American opponent of the project, I can appreciate how a 19th-century Shoshone band fits the description of the 24th-century subsistence farmer. If the Shoshones should by some miracle gain control of their ancestral lands, including Yucca Mountain, they may choose to adopt MEI thinking in their regulation of the white man's high-level repository. Otherwise, let's scrap the concept. This whole business is almost ludicrously hypothetical anyway, angels dancing on the head of a radioactive pin.
Regards,
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Response from Virginia Sanchez:
Mr. Wheelwright, in his fervor to support bad science and unethical risk assessment, misses the point made by Dr. Makhijani entirely. The issue of whether we Western Shoshone regain "control" of our homelands was not the point. The point was that the National Academy of Sciences (NAS) committee chose to entirely ignore our land rights issue. The fact is that Yucca Mountain lies in the heart of Western Shoshone homelands, and that was not stated in the [NAS] report. The second part to this is Western Shoshone ideology and the indigenous perception of the environment. A critically important principle for us to be able to continue as a people is [that] we must pay attention to our relationship/kinship to everything around us, animate and inanimate. Our history tells us how we were first created, placed within our particular bioregions, and provided with instructions on how best to live, allowing for those yet unborn. Soon after the Western Shoshone were created, Water, Air, Wind, and many others told us in unequivocal terms: "Take care of us, and we will take care of you." From the perspective of being kin to water, the Western Shoshone believe the abandonment of explicit groundwater protection is completely unconscionable. The potential for dangerous precedent-setting, if EPA were to adopt such deplorable standards, would open floodgates of environmental pollution. Just look around you. There are no existing solutions to the radioactive contamination and radioactive waste problems -- problems created and perpetuated by shortsighted, greedy interests. I also know that a piece of the solution exists within the indigenous view of the world.
"We must all see ourselves as part of the Earth, not as an enemy from the outside who tries to impose his will on it... Respectfully,
Virginia Sanchez
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Response from Professor Thomas Pigford
(Endnotes found below.) Mr. Jeff Wheelwright states that EPA prefers "high end" performance scenarios rather than the maximally exposed individual (MEI) for calculating radiation doses from environmental releases of radioactivity. Indeed, EPA has adopted language that is more clearly defined, whereas the MEI has had many disparate interpretations in the field of health protection. However, Mr. Wheelwright is incorrect in alleging that the MEI exposure calculation as used in the TYMS1,2 report is inconsistent with EPA's current practice. The term "maximally exposed individual" (MEI) alarms some people who mistakenly think that it is the upper value of all possible dose calculations, obtained by assuming the most conservative limits of all variables and parameters used to calculate exposure and dose. The MEI exposures referred to in the National Research Council's TYMS report on the Yucca Mountain Standard, and as addressed by the Yucca Mountain Project,3 are calculated by establishing probability distributions that represent uncertainties in parameters and variables. The exposure of the MEI is calculated as the expected (mean) value of the resulting probabilistic distribution of exposures, not the value that would result from assuming limits of all parameters and variables. The MEI calculated in this way should not be confused with a new term introduced by EPA, the theoretical upper-bound estimate (TUBE), which is an upper bound of all exposure calculations and is far greater that the reasonable maximum exposure. EPA states that the TUBE is inappropriate for determining exposures in an actual exposure assessment for compliance; it is strictly limited to screening out scenarios. I agree. EPA's stated policy is to make "exposure assumptions that result in an overall exposure estimate that is conservative, but within a realistic range of exposure."4 Under this policy, EPA defines "'reasonable maximum' such that only potential exposures that are likely to occur will be included in the assessment of exposures." For a geologic disposal dump, exposure frequency and duration are in large part a result of the calculable space-time-dependent concentrations of contaminants in the biosphere. Various human activities can also enter the calculation of exposures for near-term operations, but there is no scientific basis for predicting human habits for the far future, when the highest contaminant concentrations are predicted for geologic disposal systems. However, we can identify the subsistence farmer as the conservative choice of the individual who will receive the maximum exposure in a given field of contaminant concentration. The choice is not unreasonable; there are subsistence farmers who use ground water in the Amorgosa Valley down gradient from Yucca Mountain. Therefore, the U.S. projects for geologic disposal of radioactive waste have adopted the subsistence farmer as the basis for calculating doses for the reasonable maximum exposure scenario, as have all other countries with similar projects. Thus, the MEI exposure referred to in the TYMS report appears to be synonymous with EPA's reasonable maximum exposure when applied to geologic disposal at Yucca Mountain. The TYMS committee's belief that the subsistence farmer exposure scenario is too extreme is not justified by EPA guidelines, by the current practice of the Nuclear Regulatory Commission, by the International Commission on Radiation Protection, or by practice in the U.S. and in other countries. The probabilistic analysis of future human activities, as proposed by the TYMS committee, is not scientifically based. It would rely on unjustified guesses of probabilities of exposure by future people. It would result in an enormously lenient relaxation of standards for health protection. The traditional, conservative, scientifically-based subsistence farmer approach, based on the reasonable maximum exposure of future farmers, is the only prudent and defendable alternative for long-term waste disposal. It is most likely to lead to early success in geological disposal. If any standard is to be relaxed, then we should require that scientific fact and logic support the change, rather than what Mr. Wheelwright asserts to be political pressure. At the present time, no scientific bases exist to support a policy less stringent than the traditional subsistence farmer approach in effect today. Policy makers must reject pressures for short-term expediency and economy lest, by enacting policy that compromises scientific validity and credibility, they undermine public confidence and put an end to all further nuclear research and application. Other countries, including Sweden, Finland, the United Kingdom, France, Germany, Switzerland, Canada, and Japan, are designing geologic disposal systems using such conservative safety criteria, either as official criteria or as interim goals. It would be folly for us to do otherwise. For further information, I suggest that Mr. Wheelwright actually read the report as well as my Dissent in Appendix E, which he has not done, by his own admission.
Thomas H. Pigford, Professor |
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Last updated: November, 1996