Expert Judgment on Markers to Deter Inadvertent Human Intrusion into the Waste Isolation Pilot Plant

Kathleen M. Trauth, Stephen C. Hora @foot , and Robert V. Guzowski @foot
Sandia National Laboratories
Albuquerque, NM 87185

Abstract

Sandia National Laboratories (SNL) convened an expert panel to develop design characteristics for permanent markers and to judge the efficacy of the markers in deterring inadvertent human intrusion in the Waste Isolation Pilot Plant (WIPP). The WIPP, located in southeastern New Mexico, is de signed to demonstrate the safe disposal of transuranic (TRU) radioactive wastes generated by the United States Department of Energy (DOE) defense programs. The DOE must evaluate WIPP compliance with the Environmental Protection Agency (EPA) regulation Environmental Standards for the Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes (40 CFR Part 191, Subpart B); this EPA regulation requires: “Disposal sites shall be designated by the most permanent markers , records, and other passive institutional controls practicable to indicate the dangers of the wastes and their location” (Federal Register 50; 38086c). The period of regulatory concern is 10,000 years.

The expert panel identified basic principles to guide current and future marker development efforts: (1) the site must be marked, (2) message(s) must be truthful and informative, (3) multiple components within a marker system, (4) multiple means of communication (e.g., language, pictographs, scientific diagrams), (5) multiple levels 0+ complexity within individual messages on individual marker system elements, (6) use of materials with little recycle value, and (7) international effort to maintain knowledge of the locations and contents of nuclear waste repositories. The efficacy of the markers in deterring inadvertent human intrusion was estimated to decrease with time, with the probability function varying with the mode of intrusion (who is intruding and for what purpose) and the level of technological development of the society. The development of a permanent, passive marker system capable of surviving and remaining interpretable for 10,000 years will require further study prior to implementation.

Acknowledgements

The authors wish to thank the individuals who served on the Marker Development Panel.

• Team A. Dieter G. Ast (Cornell University), Michael Brill (Buffalo Organization for Social and Technological Innovation, Inc.), Maureen F. Kaplan (Eastern Research Group, Inc.), Ward H. Goodenough (University of Pennsylvania), Frederick J. Newmeyer (University of Washington), and Woodruff T. Sullivan, III (University of Washington).
• Team B. Victor R. Baker (University of Arizona), Frank D. Drake (University of California at Santa Cruz), Ben R. Finney (University of Hawaii at Manoa), David B. Givens (American Anthropological Association), Jon Lomberg (independent artist, designer, and writer), Louis Narens (University of California at Irvine), and Wendell Williams (Case Western Reserve University).

Thanks go to members of the Futures Panel who discussed their team's efforts and recommendations with the Markers panel- -Michael Baram (Boston Team), Martin Pasqualetti (Southwest Team), Dan Reicher (Washington A Team), and Maris Vinovskis (Washington B Team). Thanks also go to the Sandia Staff who presented material to the experts- -D. Richard Anderson (6342), Marilyn Gruebel (Tech Reps, Inc. ), Peter Swift (6342), and Wendell Weart (6303). Virginia Gilliland and Molly Minahan (Technical Writers), Debbie Marchand and Hawaii Olmstead (Illustrations), Susan Gill (Technical Editor), Steve Tullar (Production), and Debra Rivard and the Word Processing Department of Tech Reps, Inc. provided support in conducting the meetings and documenting the results.

The authors would also like to thank the technical reviewers, Marilyn Gruebel (Tech Reps, Inc.) and Erik Webb (6331) for their useful comments.

Preface

This SAND report was prepared from information presented by a panel of experts expressing judgments about the design and efficacy of markers to deter inadvertent human intrusion into the Waste Isolation Pilot Plant (WIPP). Appendices F and G were written by the panelists. The authors consolidated and utilized these appendices in preparing the body of the report. The individual reports are reprinted as received by the project coordinator except for (1) correcting typographical errors, (2) editing for internal format consistency, (3) renumbering, repositioning, and captioning figures, (4) updating the table of contents to be in line with the previous changes, and (5) changing the text in accordance with answers to a number of questions that were addressed to the individual teams about their reports as written. The members of the expert panel reviewed a draft copy of the report and the updated versions of Appendices F and G, and responded to the questions provided.

The panel of experts made their judgments based on current (as of November 1991) information from disciplines pertinent to markers and about the WIPP Project itself. A final decision on marker system design and placement will be based on all information that is available to the WIPP Project at the time the decision is made.

Introduction

Expert elicitation was used to determine the potential for markers to deter inadvertent human intrusion by future generations into the Waste Isolation Pilot Plant (WIPP). Specific goals were to obtain information about marker designs and message formats that will remain in existence and interpretable for the required time period of regulatory concern, and to estimate the effectiveness of specific marker designs in deterring intrusion and communicating a warning to future generations about the location and nature of the waste buried at the WIPP. The assumption was made that when individuals know what materials are buried in the area and the dangers of intruding into the material, they will not do so. This effort was undertaken by the Performance Assessment Department at Sandia National Laboratories (SNL).

This effort to communicate a warning to deter inadvertent human intrusion into a repository is necessary because of the hazardous materials that are planned for disposal in the WIPP facility. The radioactively contaminated waste should be isolated from the biosphere until the risks posed by possible releases are acceptably small. In order to accomplish this isolation, knowledge of the location and the nature of the wastes must be maintained and passed on to successive future societies. Markers are physical structures (such as earthworks, stone monoliths, and rock cairns) that are capable of carrying the intended message for a long period of time. The message is the means of communicating with whatever future societies may exist.

The WIPP was authorized by Public Law 96-164 (1979) as a research and development facility "to demonstrate the safe disposal of radioactive wastes resulting from the defense activities and programs of the United States exempted from regulation by the Nuclear Regulatory Commission ... " Physically, the WIPP is a facility located approximately 26 miles (42 krn) east of Carlsbad, New Mexico (Figure 1-1). The planned repository is schematically shown in Figure 1-2. Some of the experimental areas have already been mined at 2157 ft (657 m) below the surface, within the bedded salt Salado Formation (Figure 1-3). If the WIPP is approved as a disposal facility, it will accept laboratory and production waste contaminated with transuranic elements produced by the nuclear-weapons program. Transuranic (TRU) waste is defined for regulatory purposes as waste contaminated with radionuclides having an atomic number greater than 92, a half-life greater than 20 years, and a concentration greater than 100 nCi/g. In addition to TRU waste, lead, radium, thorium, uranium, and contaminants with half-lives less than 20 years are expected to be disposed of at the WIPP. While the WIPP's primary mission is for the disposal of radioactive wastes, the nature of the waste is such that some hazardous materials may contaminate the radioactive waste.

Regulatory Requirement for Markers

The disposal of nuclear waste at the WIPP is governed by the Environmental Protection Agency's (EPA's) Environmental Standards for the Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes (40 CFR Part 191; EPA, 1985), referred to herein as the Standard. Subpart A governs the operation of a repository prior to closure and will not be discussed further in this report. Subpart B governs the operation of a repository after closure and for the entire regulatory period of 10,000 years. Subpart B was vacated and remanded to the EPA by the US Court of Appeals for the First Circuit in 1987. Through the Second Modification to the Consultation and Cooperation Agreement (U. S. DOE and State of New Mexico, 1981), studies regarding the performance of the WIPP will continue under the provisions of the remanded Standard until a new Standard is promulgated.

The Containment Requirements (§191.13) of the Standard set limits for the cumulative release of radionuclides to the accessible environment. The cumulative release limits are couched in terms of the magnitude of a potential release and the probability of its occurrence. Such potential releases are to be calculated during the course of a performance assessment. The performance assessments for the WIPP are conducted by the Performance Assessment Department at SNL. A performance assessment is defined in the Standard (§191.12(q)) as a process that:

@format (1) Identifies the processes and events that might affect the disposal system; (2) examines the effects of these processes and events on the performance of the disposal system; and (3) estimates the cumulative releases of radionuclides, considering the associated uncertainties, caused by all significant processes and events. These estimates shall be incorporated into an overall probability distribution of cumulative release to the extent practicable.

Releases are evaluated within boundaries determined by several definitions. Accessible environment is defined in the Standard (§191.12(k)) as: "(1) The atmosphere; (2) land surfaces; (3) surface waters; (4) oceans; and (5) all of the lithosphere that is beyond the controlled area." The controlled area is defined in the Standard (§191.12(g)) as:

@format (1) A surface location, to be identified by passive institutional controls, that encompasses no more than 100 square kilometers and extends horizontally no more than five kilometers in any direction from the outer boundary of the original location of the radioactive wastes in a disposal system; and (2) the subsurface underlying such a surface location.

The accessible environment and controlled area are shown in Figure 1-4.

The Assurance Requirements (§191.14) state, in part, that:

@format Disposal sites shall be designated by the most permanent markers, records, and other passive institutional controls practicable to indicate the dangers of the wastes and their location.

The term "disposal site" @quote (as here quoted from Subpart B of the Standard) is interpreted to mean the controlled area. In the WIPP Land Withdrawal Act (WIPP LWA) (Public Law 102-579, approved October 30, 1992), Congress withdrew 16 square miles of land " ... from all forms of entry, appropriation, and disposal under the public land laws ... "; @quote transferred jurisdiction from the Secretary of the Department of the Interior to the Secretary of the Department of Energy; and stated that "Such lands are reserved for the use of the Secretary [of the Department of Energy] for the construction, experimentation, operation, repair and maintenance, disposal, shutdown, monitoring, decommissioning, and other authorized activities associated with the purposes of WIPP..." @quote The land withdrawal boundary is shown in Figure 1-4. Performance assessment calculations currently use the land withdrawal boundary to assess compliance with the 10,000-year release limits.

The Standard defines passive institutional control in §191.12(e) as:

(1) Permanent markers placed at a disposal site, (2) public records and archives, (3) government ownership and regulations regarding land or resource use, and (4) other methods of preserving knowledge about the location, design, and contents of a disposal system.

As explained in the Supplementary Information to the Standard, the Assurance Requirements are included in order to address the fact that there are many uncertainties in the analysis of releases to the accessible environment over the 10,000 years of regulatory concern. The requirement for additional measures to improve the operation of a repository is a means to address these uncertainties.

The second context for the use of markers follows from the previous requirement (§191.14). Given the fact that markers must be used for a nuclear waste repository, EPA's Guidance to the Standard allows credit to be taken for the impact of markers in reducing the probability of inadvertent human intrusion (although it can never be assumed to be zero):

The Agency assumes that, as long as such passive institutional controls endure and are understood, they: (1) can be effective in deterring systematic or persistent exploitation of these disposal sites; and (2) can reduce the likelihood of inadvertent, intermittent human intrusion to a degree to be determined by the implementing agency. However, the Agency believes that passive institutional controls can never be assumed to eliminate the chance of inadvertent and intermittent human intrusion into these disposal sites (EPA, 1985, p. 38088c).

Wherever human intrusion is mentioned in the Standard and in the Supplementary Information to the Standard, the references are to inadvertent human intrusion. Statements such as the following suggest that the requirement for passive, institutional controls is to protect against inadvertent human intrusion:

@format The most speculative potential disruptions of a mined geologic repository are those associated with inadvertent human intrusion . ... The Agency believes that the most productive consideration of inadvertent human intrusion concerns those realistic possibilities that may be usefully mitigated by repository design, site selection, or use of passive controls (although passive institutional controls should not be assumed to completely rule out the possibility of intrusion). Therefore, inadvertent and intermittent intrusion by exploratory drilling for resources (other than provided by the disposal system itself) can be the most severe intrusion scenario assumed by the implementing agencies (EPA, 1985, p. 38088c-38089a).

The following statement suggests that once the warning message has been correctly communicated, a potential intruder will cease activity in the area:

@format Furthermore, the implementing agencies can assume that passive institutional controls or the intruders' own exploratory procedures are adequate for the intruders to soon detect, or be warned of, the incompatibility of the area with their activities (EPA, 1985, p. 38089a,b).

Background

Future Societies

The effort undertaken by the Performance Assessment (PA) Department at SNL to design markers for the WIPP builds upon the work of an earlier effort that identified the range of possible future societies that may occur in the vicinity of the WIPP during the next 10,000 years (Hora et al., 1991). The possible modes of humans intruding into a repository, specifically, the WIPP, and the probabilities of such intrusions were considered in this earlier study.

Before one can communicate with future societies about the location and dangers of the wastes, it is important to consider with whom one is trying to communicate. The question of future societies was addressed using a multidisciplinary panel of experts in fields deemed pertinent. This group was called the Futures Panel, and included individuals with backgrounds in history, future studies, economics, law, physics, sociology, geography, engineering, political science, risk analysis, agriculture, climatology, history, and demographics.

The panel was organized into four teams, and each team was given the same charge in order to facilitate a focused but diverse set of responses. The teams were named based on the predominant geographical location of the members: Boston Team, Southwest Team, Washington A Team, and Washington B Team. In addition to the panel members being given a specific task, they were trained in providing judgments in a numerical fashion and provided with background information about the WIPP Project (Weart et al., 1991).

Each team of the Futures Panel analyzed the question of future societies differently. The reports describing the analysis of the problem, prepared by each team, were reproduced in Hora et al. (1991). Hora et al. (1991) also provide a full discussion of the possible future societies, modes of intrusions, and probabilities of intrusions elicited from the teams. The material in the individual team reports expanded the view of what future societies might be like. Not all of the modes of intrusion considered by the teams would be inadvertent. The focus of marking the WIPP is to communicate what is buried in the repository and the possible consequences of intruding into the repository. The applicable regulation (discussed in the previous section) states that it is most important to communicate to protect against inadvertent human intrusion and states the assumption that once a potential intruder realizes the location and dangers of the waste buried in the repository, such activity will cease. Some of the modes of intrusion postulated by the Futures Panel are beyond what is currently required by the applicable regulations for analysis of the future performance of the WIPP.

The Boston Team developed several underlying factors that were believed to impact future societal activities and possible modes and frequencies of intrusion. Certain time periods after the end of the expected 100 years of active institutional control after closure (100-300 years, 300-3,000 years, or 3,000-10, 000 years after closure) and possible levels of technology (lower, similar to today, or higher) were considered to impact all of the possible modes of intrusion. Knowledge of the past, the value of the materials, the level of industrial activity, and population density are the other factors that are important in influencing human actions and the extent of human intrusion. The possible modes of intrusion developed by the Boston Team are resource exploration and extraction, reopening the WIPP for additional storage, waste disposal by injection wells, archaeological exploration, explosive testing, and water impoundment. After the first 300 years after closure, the Boston Team did not believe that boreholes would be drilled in the WIPP area for resource exploration and extraction because of total removal and/or the use of nonpetroleum energy sources.

The Southwest Team based its outlook on the possible intrusion into the WIPP by future societies in political control of the area around the WIPP (the United States of America or another political entity) and the technological development pattern (steady increase from today's level, steady decline from today's level, or a fluctuating seesaw pattern). Possible modes of intrusion associated with a steady increase in the level of technology are deep strip mining and exotic mining techniques that could develop in the future. Conventional drilling and excavation activities were associated with a steady decline in the level of technology or a seesaw situation. The Southwest Team did not make a distinction in their analysis for time periods, stating that society could cycle through the three technological development patterns throughout the 10,000 years.

The Washington A Team examined conditions today in terms of technology level and both energy and other natural-resource use and developed possible futures by extrapolating these factors. The possible futures thus developed are continuity (a continuation of current trends), radical increase (large growth in the use of resources), discontinuity (fluctuations in levels of technology and resource use), and steady state (emphasizing renewable resources and compatibility with the earth). Time was ~mother factor with both the period of 0-200 years and 200-10,000 years after closure of the WIPP being considered. Exploration for and development of resources were considered the most likely modes of intrusion. Other modes included construction between cities of a deep tunnel that would intersect the WIPP, water impoundment, development of well fields, and explosions.

The Washington B Team based its examination of possible future societies and modes of intrusion on the underlying factors of the level of wealth and technology, government control (prudent and effective in controlling the area of the WIPP, or not), climate (relating to water supply development), and the price of resources (more than doubling current levels, or not). The Washington B Team considered the two time periods of 0-200 years and 200-10,000 years after closure of the WIPP, as the near and far futures, respectively. The activities future societies might be undertaking that were believed to be able to cause intrusion qf the repository were resource exploration and extraction, development of water wells, scientific investigations, and weather modification. The far future for resource exploration and extraction only extends from 200-500 years after closure. After that time, all the oil and gas would have been removed and/or society would no longer be on a petroleum-based economy.

Marker Development

The Markers Panel was charged with developing design guidelines for markers to be placed at the WIPP and with developing preliminary forms of messages and formats to communicate the location and dangers of the wastes buried there, for the regulatory period of 10,000 years. The charge was to consider both individual components and an entire marker system. After a marker-system design was developed based on the guidelines, the panelists were asked to estimate the probability over time that the marker system would continue to exist and that the messages would be interpretable. The estimation of probabilities (function of time, technology, and mode of intrusion) is discussed in Chapter 5.

The nature of the design-criteria problem imposed a number of constraints on the work of the Markers Panel. The Futures Panel input suggested that societies quite different from our own may be controlling and inhabiting the area of the WIPP. The markers must be developed to communicate with people whose culture may not be directly descended from our own. This possible cultural change is in addition to the changes in language that normally occur over time, even when societies are in continuous contact. Secondly, the period of regulatory concern (10,000 years) requires that the marker materials, construction techniques, and placement be able to withstand the forces of nature and the tendency of human beings to vandalize structures or to remove pieces. Thirdly, the markers must be able to convey complex information, not just about wastes hidden from view, but also about the hazards of radioactivity as a function of time.

The Markers Panel addressed the complexities of the task by relying on the strengths of a multidisciplinary panel. The individuals on the panel represent disciplines pertinent to addressing the materials and communications aspects of the marker issue. Thus, geomorphology, materials science, and engineering were included to address the issues of markers withstanding natural and human-induced degradation and destructive forces. Design and architecture addressed the design and placement of structures. Archaeology provided information about the materials and structural configurations that historically have been successful in remaining intact over long periods of time. Through the study of human social and cultural development, anthropology brought to the marker effort the understanding of how humans process information and communicate. Linguistics was important to the development of the messages in view of how languages and meanings have evolved through time and the necessity of using linguistic messages that can easily be decoded. Semiotics addressed communication not only with languages, but with signs and symbols. Previous efforts to think broadly about communication in terms of using radio signals or sending a satellite into space to communicate over long time periods with unknown beings led to the selection of individuals from the astronomy and communications disciplines for the Panel. The broad educational backgrounds and work experience of the panelists (related to the various technical aspects of this question) meant that there was broad discussion and cooperation (people not limited to their own specific field) in the development of the design criteria.

Purposes of the Study

This study had two purposes, one qualitative and one quantitative. These purposes were instituted in response to the requirements and guidance of the Standard. The qualitative purpose was developing design guidelines for markers and messages to communicate with future societies about the location and danger of the buried wastes at the WIPP. Such information is intended to deter inadvertent human intrusion. The results of the Markers Panel will be considered in developing the final design and in constructing the markers. The quantitative purpose was to estimate the efficacy of the markers in surviving the required time period and in communicating the intended messages. Other passive institutional controls (such as a records system or a protective barrier system) need to be developed and could also be effective in deterring inadvertent human intrusion. Consideration of other passive controls and their effectiveness in deterring intrusion was beyond the scope of this task.

Organization and Methodology

Using Expert Judgment

The methodology employed in this study to obtain quantitative evaluations of the proposed marker systems performance is referred to as expert-judgment analysis (Bonano et al., 1990). For some aspects of performance assessment for radioactive waste repositories, it is not possible to build models, conduct experiments, or make observations to resolve uncertainties. While certain aspects of marker design such as material decay and symbol recognition can be studied for short periods of time, it is not possible to assess the performance of such a system entirely using these traditional data sources. When unresolvable uncertainties do exist, expert judgments are often used to quantify the uncertainties and to express both the known and the unknown.

The formalization of expert-judgment elicitation for nuclear waste repositories is described in Bonano et al. (1990). Expert judgment is pervasive in complex analyses. Judgments about the selection of models, experimental conditions, and data sources must be made. The choice is not whether expert judgment will be used; instead, the choice is whether it will be collected and used in a disciplined, explicit manner or utilized implicitly where its role in the analysis is not obvious.

Precursor studies have provided a structure for the collection of expert judgment. These studies include, among others, the Electric Power Research Institute (EPRI, 1986) study of seismicity in the eastern United States, the NUREG-1150 study (U.S. NRC, 1990), and the recently completed study of futures of society (Hora et al., 1991). These studies provide models for the collection of expert judgments. These models are designed to avoid the pitfalls that interfere with the collection process.

A formal expert-judgment process should consist of several well-defined activities. Such activities include creating issue statements for the experts to respond to, selecting experts and training them in probability assessment, eliciting probabilities and other information, and processing and presenting findings.

While the NUREG-1150 study was most central in the design of this current effort, there are substantial differences between them that are important to note. The goal of the expert-judgment process in NUREG-1150 was to provide uncertainty distributions for parameters and to judge the likelihood of specific phenomena. The uncertain quantities were relatively well defined. In the present study of marker systems, the issues are less well defined, and the experts are required to employ substantial creative effort in devising marker systems and evaluating their potential performance.

Several organizational forms for experts in an elicitation process have been described (Bonano et al., 1990). One form is the organization of experts into teams. A team structure is useful when disparate disciplines need to be used on a given problem. An added benefit of using teams is enhanced communication among the experts. In contrast, when experts from different disciplines work on separate, but connected, parts of the same problem, coordination and communication among the experts must be explicitly provided.

Through the work that was done with the Futures Panel and the Markers Panel, PA has developed its own procedure for the use of expert judgment. This procedure is documented by Rechard et al., 1992.

Expert-Judgement Panel

Decision to Use an Expert-Judgement Panel

The decision to use the expert judgment process to develop information on markers was based both on the importance of the topic and the lack of alternate sources of this information. Human intrusion appears to be the only credible means by which radionuclides may reach the accessible environment (Marietta et al., 1989; Guzowski, 1990). Deterring human intrusion through the use of markers could significantly enhance confidence in compliance with the Standard. The handling of such a sensitive topic must be done in an open and documented format allowing input from individuals outs ide of the WIPP Proj ect. In addition, the design of. markers is interdisciplinary and must utilize input from many disciplines. Further, estimation of the efficacy of markers in deterring human intrusion cannot be done any other way than through expert judgment--experiments cannot provide this type of information.

Development of the Issue Statement

The development of the issue statement is the first step in the process of conducting an expert judgment panel. Development of the issue statement is important not only to clearly define the issue to be addressed by the panel, but also as a means of identifying the disciplines that need to be represented on the panel.

The issue statement for the Markers Panel is found in Appendix A. It requires judgments for both marker and message design characteristics and estimates of performance of the marker system. Performance of the markers was to be estimated for both the "physical" longevity of the markers and the ability of the markers to convey the correct message to deter inadvertent human intrusion. Marker-design characteristics include a general description of the marker system, as well as a physical description of each marker component within the marker system, including size, location, shape, and materials. Also, the teams were asked to describe the messages upon or within the markers and the method(s) of conveying the messages. For performance of the system of markers, the teams were asked to assess the extent to which the marker system they designed would survive, be correctly interpreted, and evoke the correct response over the 10,000 year period of regulatory concern. The estimates of performance were requested for the individual marker components as well as for the entire system.

The issue statement in Appendix A is the version provided to the Markers Panel. This issue statement was changed once the Markers Panel began their work. Such modifications are not inappropriate if the experts believe that certain questions cannot be answered or the problem should be examined another way. As a result of the emphasis on inadvertent human intrusion, as discussed in Chapter 1, the panel members did not provide probabilities that the correctly interpreted messages would be heeded (i.e., probabilities were not provided for question 6). Team A stated that

@blockquote The regulatory requirement is to deter inadvertent human intrusion, and thus we feel that if the message is understood, our job is completed. Any action that takes place after the message is understood is advertent and intentional.

Team B stated that

@blockquote We cannot guarantee that any simple or complex message, even when recognized and correctly interpreted, will deter a human being from inappropriate action.... Nevertheless, carefully designed warnings could be expected to reduce the chances of inadvertent intrusion into the WIPP. Moreover, an intrusion would not be casual, but would be a planned event. As such, there would be a greater likelihood to consider cautionary data.

A further change was made to the issue statement. Both teams stated that they had developed system designs and that it was inappropriate to consider the effectiveness of individual marker components.

Selection of Experts

Marker design depends upon the expertise of many disciplines, so a multidisciplinary team approach was needed. The disciplines expected to be important included anthropology, archaeology, architecture, astronomy, communications, design, engineering, geology/geophysics, modern languages, linguistics, materials science, psychology, semiotics, and sociology. In addition, parallel teams were to be established to elicit diversity in the responses. Because the teams were to be composed of scientists and scholars from many disciplines, the pool of candidates needed to be sufficiently broad. An established nomination process was employed to achieve this.

Nomination Process

The selection of experts begins with the identification of persons believed sufficiently knowledgeable in the disciplines identified by SNL staff as being pertinent to the project to nominate experts. The nominators were identified through contacts with professional organizations, such as the American Institute of Professional Geologists, the Linguistic Society of America, and the American Anthropological Association. Governmental organizations such as the U. S. Soil Conservation Service and the National Climatic Data Center were also contacted, as were public interest organizations such as the League of Women Voters. Simultaneously, literature searches were performed in the publications of the above listed disciplines. From these literature searches, prominent authors were identified and contacted. The editors of professional journals were also contacted concerning nominations.

An initial contact was usually made by telephone to explain the project to the potential nominator. This contact was used to determine whether the potential nominator would be able to provide nominations and to assist in obtaining the cooperation of other people in the project.

The identification of nominators and the initial contacts took place between June 13 and July 13, 1990. By July 24, 1990, a formal request for nominations (Appendix B) had been sent to all nominators who .had agreed to contribute. This letter outlined the tasks to be accomplished by the experts, provided a tentative schedule, and included a description of the criteria to be used for selection of experts. The letter invited self nomination if the nominator deemed this to be appropriate.

During the following week, additional letters were sent to those nominators who had not responded to the request for nominations. Several potential nominators, who were thought to be sufficiently knowledgeable or their responses considered to be highly desirable but could not be contacted verbally, were also sent letters. The parties to whom these letters were addressed are shown in Appendix C.

From this effort, a total of 92 nominations were obtained by August 8, 1990. By August 14, 1990, a letter was sent to each of the nominees (Appendix D). This letter outlined the tasks to be accomplished and firm dates for the two meetings to be held in Albuquerque. The nominees, if interested and able to participate in the project, were asked to send a letter describing their interests and any special qualifications relevant to the WIPP marker-development study. A curriculum vitae was also requested from each nominee. Letters of interest and curriculum vitae were received from 57 nominees by noon of August 20, 1990. After that time, no further responses were considered.

Selection Advisory Committee

The selection advisory committee assisted the PA Department by evaluating the interest letter and the curriculum vitae from all of the nominees in light of the selection criteria and by making recommendations for the membership of the Markers Panel as well as several alternates. The selection adVisory committee was composed of three university professors with some knowledge of the WIPP Project and the expert judgment process: Dr. G. Ross Heath of the University of Washington (oceanography), Dr. Douglas G. Brookins of the University of New Mexico (geology), and Dr. Detlof von Winterfeldt of the University of Southern California (decision analysis). Dr. Heath is also the chair of the WIPP Performance Assessment Peer Review Panel, which gave him special insights into? the project-related goals of the WIPP PA Proj ect and the regulatory framework of the Project.

The members of the selection committee were provided with copies of the above information several days prior to the meeting during which the final recommendations were made. The recommendations of the selection advisory committee were followed in establishing the Markers Panel.

Criteria for the selection of experts were drafted for use by the selection advisory committee. These criteria were similar to the criteria that were distributed to the nominators and nominees but also included criteria related to the balance of disciplines and geographic location of the teams. The criteria are included in this report as Appendix E.

Selection of Panel

The selection advisory committee recommended members for two teams within the Markers Panel, and these recommendations were accepted in establishing the Markers Panel. The Markers Panel consisted of one team of six members and one team of seven members. Two teams with parallel missions provided a focused but diverse set of responses. The size of the teams was dictated, in part, on the necessity of representing the pertinent disciplines. Table 2-1 lists the members of the Markers Panel, their affiliations, and their discipline(s).

Panel Deliberations

The Markers Panel first met as a group November 4-6, 1991, in Albuquerque, New Mexico. The first meeting included presentations regarding the WIPP Project, the Standard, WIPP performance assessment, and the issue statement (the specific questions the teams were asked to address), as well as long-term climate variability at the WIPP, and the geologic and hydrologic characteristics of the WIPP region as they relate to marker development. At this meeting, the panel members also received an introduction to the expert judgment process and training in the process of expert judgment elicitation. On November 5, the Markers Panel toured the WIPP surface facilities, underground facilities, and surrounding area. Originally, the Markers Panel was scheduled ~o convene in October 1990, to coincide with the meeting at which the Futures Panel discussed their results. The convening of the Markers Panel was postponed for one year because of budgetary constraints. In order to make the connection between the work of the Futures and Markers Panels, each member of the Markers Panel was provided with the reports prepared by the four Futures Panel teams and text of the background information provided to the Futures Panel. In addition, one person from each of the four Futures Panel teams attended the November meeting to discuss their team's results and to answer questions.

The Markers Panel was also provided with literature related both to the WIPP Project and human intrusion, as well as other efforts to address deterring human intrusion into nuclear waste repositories.

After the first meeting when the members of the two teams began developing a strategy for addressing the issue statement, each team met separately for working sessions. (Team A met December 5-6, 1991, in Buffalo, New York, and Team B met December 14-16, 1991, in Kona, Hawaii.)

The two Markers Panel teams presented their results and draft reports to SNL staff, federal and state agency representatives, Nuclear Energy Agency (NEA) Human Intrusion Working Group observers, and several members of the press January 13-14, 1992, in Albuquerque, New Mexico.

Recommended Design Characteristics

Team A and Team B of the Markers Panel were both given the same issue statement (the same set of questions) to address during their deliberations. The issue statement contained a number of requirements and constraints within which the Panel needed to work. The time frame for the Panel to consider must be 10,000 years because of the requirement that performance assessments cover a time period of 10,000 years after closure of the disposal facility (Containment Requirements). The second requirement was that the markers must be developed with a goal of being able to convey information to any future society (considering the broad spectrum of possible future societies developed by the Futures Panel [Hora et al., 1991]). The third requirement was to communicate the dangers associated with the waste buried at the WIPP.

A comparison of the two sets of marker design characteristics highlights the aspects of marker design where the two teams are in agreement. A comparison of the approaches also allows one to see the diversity in the responses and highlights those competing approaches to markers that need to be investigated further.

The reader is directed to Appendices F and G for the Team A and Team B reports, respectively. The reports are reproduced as received by the project coordinator except for (1) correcting typographical errors, (2) editing for internal format consistency, (3) renumbering, repositioning, and captioning figures, (4) updating the tables of contents to be in line with the previous changes, and (5) changing the text in accordance with answers to a number of questions that were addressed to the individual teams about their reports as written. The members of the Markers Panel reviewed a draft copy of this report and the updated versions of Appendices F and G, and responded to the questions provided. The Team A report contains a number of marker alternatives that were considered and rejected by the team and are included in order to show the range of the thought process. The Team A final recommendation is for the use of the “Menacing Earthworks” along with the other components discussed below and in their report. The Team B report is a discussion of their recommended marker system.

This report uses a number of terms that need to be clarified. A marker system is the entire set of physical structures (whatever their form or composition) emplaced to communicate to future societies about the wastes buried in the repository. If earthen berms and buried message disks are used to mark a repository, their combination would constitute a system. The earthen berms and the message disks each would be considered components of the marker system. Each individual message disk would be a marker element.

Team A

Basic Premises

Team A listed their goal in communication as the simultaneous fulfillment of three objectives: (1) to provide a gestalt message (the whole message is greater than the sum of the parts/components), (2) to use a systems approach, and (3) to incorporate redundancy in the markers.

For the gestalt message, the purpose is to convey a message not just with words and pictures, but through the very vehicles of conveying the me~sages, and the messages themselves. That is, the marker materials, their construction, and their arrangement are such that future generations coming upon the markers will understand the message that this place is not one where people would want to spend a lot of time. With the gestalt message, the emphasis is on communicating through the entire marker system.

The systems approach to designing and constructing markers is that the various marker components are linked to each other and supplement the information (or fill in any gaps) from other marker components. Messages are provided in different levels of complexity, in different formats, and convey different aspects of the entire message.

The redundancy within the marker components provides enough individual markers of anyone type (material or message or arrangement) so that if some are vandalized or degraded over time, there are sufficient numbers remaining to communicate the required message. The size and construction of the markers can also provide redundancy in that 'the form of the communication is overdone so that it can still communicate after degradation or defacement. With earthen berms (discussed later in this. section), the size called for would allow the marker to withstand considerable erosion and still remain recognizable as a human construction marking an area.

Assumptions/Bases

Team A made the following assumptions that impacted their marker designs and their recommendations for future studies. While various civilizations have developed and declined over time, history has shown that since literacy first developed 6000 years ago, it has not ceased to exist (Appendix F, Section 1.2). Team A assumed that scholarship capable of translating the messages on the markers will continue to exist somewhere in the world during the time period being considered. This resulted in a major emphasis on written language, and the redundancy of the written languages to aid in decipherment.

Team A assumed that, based on past history, political boundaries are impermanent, and so included the importance of an international effort that would maintain knowledge of the location of all nuclear waste disposal sites.

The evolution of existing cultures and the creation of new ones over the next 10,000 years cannot be known. Thus, a marking system and the messages must be cross-cultural to the extent possible. The marking system must be rooted in basic human concepts and understanding.

Message Levels and Media

Team A recommended the use of five levels of messages in the overall marker system. These five levels are a modification of the following four levels defined by Givens (1982; also see Appendix F, p. F-34), who is also a member of Team B:

@format Level I: Rudimentary Information: "Something manmade is here," Level II: Cautionary Information: "Something manmade is here and it is dangerous," Level III: Basic Information: Tells what, why, when, where, who, and how (in terms of information relay, not how the site was constructed), and Level IV: Complex Information: Highly detailed, written records, tables, figures, graphs, maps, and diagrams.

With the gestalt message, the marker system itself would be able to communicate both Level I and Level II information. Team A created a new Level IV with the level of complexity of information to be between those of the Level III and Level IV messages defined by Givens (1982). The most complex information, Level V, would be the "complete rulemaking record" and would be stored in archives.

In an effort to achieve the three objectives in Section 3.1.1, the team set out to be as unambiguous as possible in how the warning messages were conveyed. This led to a greater reliance on communicating through a sense of place, through written languages and scientific symbols for the specific information, and through the use of the human face with expressions.

Communicating through a sense of place is based on the concept of human archetypes- -that all human beings react similarly to particular physical environments. The team believed that creating an environment that communicated to humans today that the area around the markers was not a welcoming one, would also communicate the same message to future human beings, at least within the time frame required in the Standard.

Language was seen as an unambiguous means of communicating specific information about the repository, as were scientific media such as the periodic table of the elements and star charts. The recommended languages are those of the United Nations (Arabic, English, Spanish, French, Russian, and Chinese) and that of the largest group of Native Americans in the area (Navajo). Space should also be left on the markers for a future society to add a language to the markers. The periodic table of the elements is distinctive in shape and should be recognizable. Drawing on humans' traditional observation of the stars, a chart could be developed to show the positions of the stars when the WIPP was closed and after 10,000 years.

Human facial expressions were seen as unambiguous because humans use the same expressions to convey particular feelings, independent of culture. There is less emphasis on what were perceived as potentially ambiguous pictographs. Team members thought that while human figures and animals would be recognized in the future, the intent of the messages might be lost. For example, one can recognize people and animals in ancient cave drawings but not know what the artists were trying to communicate about them.

Marker System Components

The individual components that comprise the marker system developed by Team A vary with regard to size, materials, specific message and audience, and location. The system can best be explained by discussing it in the sequence of marker components that would be encountered as someone approached the outside and moved to the center. Team A has stated that certain specific aspects of the design require testing before being finalized.

The area over the waste panels (and a buffer area to account for migration of the radioactive materials) would be outlined by earthen berms (Appendix F, Figs. 4.3-8 and 4.3-9). These berms would be jagged in shape and would radiate out from, but not cover, a central, generally square area. The number of berms is sufficient to delineate a central area or "keep" even if some are destroyed. The four corner berms would be higher and provide a "vantage point" to see the area as a whole. The jagged nature of the berms is meant to convey a sense of foreboding (not honorific or pleasant). The exact size, shape, and configuration of the berms would be such that they would not quickly be eroded or covered. The earthworks are meant to convey a Level I message.

Within the “keep” would be multiple “message kiosks” (Appendix F, Fig. 4.3 -18) containing Level II messages in approximately seven languages (those of the United Nations plus a local indigenous language), as well as Level III messages in several of the languages plus a local indigenous language. Space will be left on the kiosk for a future generation to inscribe the message in another language. The construction of the kiosk will include a concrete “mother” wall that will be built to curve around and protect an inner granite wall containing the actual messages. Messages will be placed high up on the wall so as not to be buried by blowing sand and to make it more difficult for individuals to deface them.

The Level IV information, the most complex at the site, will be contained in concrete rooms (Appendix F, Fig. 4.3-17). One such room will be buried in each of the four corner berms, allowing them to be exposed as the berms erode. The rooms will be constructed to allow access but to prevent the removal of informational materials. The "sliding stone entry plug" will protect an opening large enough for a human to enter and leave, but too small to allow removal of an intact stone slab containing the information. Level IV information will be located on stone slabs on the interior walls. Two additional layers of stone slabs with the same messages will be located behind the original layer in case the original wall is damaged or destroyed. In addition, each Level IV room will contain other types of information such a periodic table of the elements to indicate what is buried at depth, and an astronomical calendar to indicate at what point in the past the wastes were buried.

From the top of the earthworks, one would be able to see a world map showing other disposal sites (Appendix F, Fig. 4.3-16), as well as part of the original buildings left as a message center ("left to decay"). The location of the WIPP on the world map will be indicated by a marker that will also sit atop a Level IV room beneath the map.

Other Design Requirements

Team A made a number of recommendations about the design and construction of markers to increase the probability that they will remain recognizable far into the future. Irregularly shaped "blocks" to be used for construction (e.g., message rooms) would make recycling of the blocks for the construction of other structures more difficult. The individual marker elements (e.g., message kiosks) should be large enough to make them difficult to carry off to a future museum. Materials for the construction of the marker elements (message kiosks, message chambers, world map) should have the lowest intrinsic value feasible so that their materials are not worth removing and recycling.

Team B

Basic Premises

Team B developed a list of 10 items that guided their work in developing a marker system. These items relate to the rationale and moral aspects, how to mark, and future activities. Their design was guided by the need for durability of markers and clarity of messages. The team report addresses markers by examining possible alternatives in terms of persistence of markers, recognition of markers and messages, interpretation of the messages, and deterrence of human intrusion. A discussion of each of the 10 items follows.

@format (1) Two of the four teams that comprised the Futures Panel (Hora et al., 1991) recommended to the Markers Panel that the site not be marked so as not to draw curious visitors to the WIPP. Team B disagreed and stated that because of current mining and petroleum production in the area, the site must be marked to reduce the probability of inadvertent human intrusion.

@format (2) The marker strategy must not rely on one location for message carriers, but should use both surface and buried markers. Surface markers would be available for interpretation now and in the future. Buried markers could become available to communicate in the future through possible erosion if the surface markers have been removed, destroyed, or degraded through natural processes. Buried markers could also reinforce the message of surface markers during possible intrusion attempts. If humans begin to intrude upon the site, buried markers (safe from vandals and certain natural weathering processes) could communicate the dangers below. The buried markers also reinforce the message if the surface markers are misinterpreted or ignored.

@format (3) The messages must be truthful. All people have the right to know the potential impacts of their actions. In addition, if future people discover that part of a message is untrue, they may not believe any of the message.

@format (4) The outer extent of the marker system should be visible from the center. This allows a visitor (if they are in the center of the marker system) to cognitively assemble all the markers they are seeing as delineating a coherent site or message about this particular location.

@format (5) The area to be marked should be that area above the waste pa~els. Part of the reason for this delineation is found in (3). If a large area is marked to communicate that one should not dig or drill here because of the hazardous material buried below, and if future societies drill within the designated area but outside the area of the panels and find nothing unusual, they may not believe the other messages. The second reason is found in (4). It may be difficult to convey a sense of a coherent marker system that is attempting to communicate over, for example, what is believed will be the controlled area (16 square miles). People may not be able to relate a marker at one point to something that is two miles away, because of the limits of human perception.

@format (6) The highest probability of success in correctly communicating the location and nature of the buried wastes is to repeat the message in a number of ways so that if one message form is not completely understood, the message in another form may fill in the gaps and reinforce it. The linguistic material must use simple sentences so that future scholars will be more readily able to translate it. The different modes of communication must communicate with different societies having knowledge of or access to different levels of technology. This duplication is necessary because we cannot know what cultures will be like or what levels of technology will be in existence at any future time. The team noted that the message from the Futures Panel (Hora et al., 1991) was that the Markers Panel should make recommendations for a wide variety of cultures and technologies.

@format (7) While current plans call for removing the existing buildings, parking lots, roads, etc. and returning the area to its previous condition, Team B recommended that part of the main building containing the "hot cell" should be left in place for the benefit of future archaeologists—to study it and understand what took place at the WIPP.

@format (8) Detailed information about the WIPP should be stored off-site, but the details of what information should be stored and where and how it should be stored, should be developed in the future, closer to the time when such a record system would be implemented.

@format (9) The marking of nuclear-waste repositories should have an international aspect in terms of a map at the site showing other disposal sites around the world to ensure that all knowledge is not lost. This marking may also include either the existing radiation trefoil symbol or a symbol still to be developed.

@format (10) Testing of markers and messages must be undertaken between now and the time of implementation. This will include testing both for durability (materials and inscriptions) and cross-cultural understanding of the messages.

Assumptions/Bases

Team B was directed in their actions by the recommendations of the Futures Panel. In developing markers, Team B believed that a systems approach (many types of markers, messages, and communication modes) would be the most useful in communicating under the unknown and varying circumstances of what the Washington A Team of the Futures Panel called "radical discontinuity." Under radical discontinuity, society would have gone through considerable changes--political, social, and technological—that might impact existing knowledge bases, languages, and institutional controls and memory. Messages would thus need to communicate to everyone regardless of their culture, technology, or political structure, that not intruding upon the repository was in their own best interest. A second assumption made by the team was that political change will take place (i.e., resulting in the United States of America not being in control of the area around the repository). This assumption led Team B to be concerned with making the marking of repositories an international effort. A third assumption made by Team B was that vandalism will continue to be a tendency of some parts of human society. Multiple marker elements of one component (i.e., the placement of many stone monoliths in the marker system) will allow for the marker component to remain and be able to be interpreted even if some of the individual elements are destroyed or removed.

Message Levels and Media

@format Team B recommended the presentation of messages in four levels based on the work of Givens (1982; also see Appendix G, pp. G-17 and G-36): Level I: Rudimentary Information. The site itself and its component parts would announce "Something made by humans is here." The most important property of a Level- I sign is its own existence. "Human made" would be suggested by the patterned shape - - the unnatural syntax and negative entropy- - of the earthwork, rock structures and inscriptions. Level II: Cautionary Information. and pictographic narratives would materials are buried below." Elementary linguistic scripts convey: "Warning, dangerous Level III: Basic Information. Level III messages, including longer linguistic narratives, pictographic sequences, maps and simple diagrams would explain basic what, why, when, where, who and how information about the site. Level IV: Complex Information. Highly detailed written records, scientific data and diagrams would be available at the site in inscriptions and buried "time capsules."

Team B has delineated the ways in which messages about the WIPP should be conveyed to future societies. The first message medium is through written language. The languages used for these messages would be the main written languages in use today (such as English, Spanish, German, Russian, Japanese, and Chinese), liturgical languages (such as Latin, Hebrew, and Arabic), and the languages of the Native Americans in the area (such as Navajo, Hopi, and Mescalero Apache). Language would be expected to communicate both the basic and complex information about the WIPP. Scientific diagrams would be used to communicate some of the more complex information about the elements buried at the WIPP (the periodic table), the elapsed time since the WIPP was closed (a diagram showing the 26,000-year precession of the stars in the sky), or the stratigraphy of the area (a model that uses samples of materials from the formations between the surface and the repository arranged in the proper order and scale to indicate what would be encountered during a potential intrusion). Pictographs would be used to communicate information about how the WIPP was constructed, how far underground the waste is buried, the activities that should not be undertaken in the area, and what might happen if the waste is disturbed. Some sort of radioactive symbol might be used in text and on the marker elements to make the connection between radioactivity and what is buried in the repository.

Marker System Components

The marker-system components recommended by Team B will be discussed in the sequence they would be encountered by a visitor' approaching the area. Team B believed that by the mere existence of a marker system and by observing the effort that went into creating it, a future society would realize that this was something important (markers are there for a purpose) and worth saving. The largest, outermost component, the berms (earthworks), are encountered first (Appendix G, Figs. 1 and 2). The berms define the marked area above the waste panels, but do not completely cover the area above the waste panels. If an international symbol has been developed by the time the marker system is implemented, the berms could be in that shape. To last for the 10, OOO-year period of regulatory concern, the berms must be massive (to withstand human and natural forces), on the order of 30-ft-high, constructed of local earth and caliche. The berms would be spiked with materials with properties anomalous to the naturally occurring ones (e. g., "different dielectric, radar reflective, and magnetic properties") for detection by aircraft or satellite equipment. Because the berms outline the area above the waste panels, the hot cell of the WIPP buildings, which Team B recommended be left in place, is located outside the berms.

Within the outline of the berms, granite monoliths (specific number to be' a power of two for easier reconstruction) would be erected in a circular pattern. They would be large in size to withstand natural erosion and to deter the removal by humans. The monoliths themselves would be of two types: taller, narrower ones (25-ft-high by IO-ft-wide) designed not to be buried by blowing, accumulating sand; and shorter, wider ones (IO-ft-high by 20-ft wide) "difficult to topple or decapitate." Even the accumulation of sand around monoliths will still mark the area. The monoliths would be inscribed on "protected surfaces" (physically protected from erosion by sand and/or water) with warning messages in the languages discussed previously. Inscribed monoliths also would be buried within the earthworks for future discovery, and granite plugs would be placed in one or more of the shafts originally leading to the repository level and in off-site archives. The importance of placing markers in the shafts is based on the belief that future societies would be able to determine where the shafts were located because of anomalies in the materials and/or densities of the shaft materials.

Also salted in the earthworks and in the area within the earthworks would be "time capsules" (6-in. to 2-ft in diameter) buried deep enough not to be discovered initially by souvenir hunters; the capsules would be placed to be found by those beginning to intrude upon the site--e.g., by archaeologists --or as the earthworks erode. These "time capsules" (clay, ceramics, glass, or sintered alumina) would have information inscribed on the outside. Samples of wood might be included to allow a future society to date the marker activities through carbon-14 dating.

In the center of the marker system would be a granite structure (20-ft by 30-ft) containing the most complex information about the time of the placement of the waste, location, and dangers of the waste. This information (conveyed, through the use of language, pictographs [Appendix G, Figs. 5 through 15], and diagrams) would be inscribed on protected, flat exposed surfaces of the structure. Specific examples include a world map of all known nuclear waste sites at the time of marker emplacement, the periodic table of the elements indicating the radioactive elements contained in the repository, and a diagram showing the precessional cycle of the earth in relation to .the time of burial and the time of the reading (Appendix G, Figs. 15 and 16). In addition, models containing samples of the various layers of materials that would be encountered while drilling through the material overlying the waste 'panels, including the relative location of the shafts and waste panels, would be available both at the site and in other locations (Appendix G, Fig. 4).

Principles of Marking

The purposes of marking a nuclear-waste disposal site are to inform future generations of the site's location and to warn of the hazards associated with the nuclear waste buried at the location. To achieve these purposes, certain principles should be followed in the design of the markers and the development of the messages to maximize the time over which the markers will physically survive with the messages intact and to maximize the interpretability of the messages in view of the potential variety of cultural changes that can occur. The subject areas where these principles need to be identified are architecture, linguistics, material properties, and message levels, and were drawn from the design characteristics developed by Team A and Team B. The goals and principles of each subject area are described in this chapter. Table 4-1 is a summary of these design principles.

Architectural-Design Principles

The principles that need to be included in the design of markers depend on the goals of the markers. These goals are the definition of an area that future generations should avoid disturbing and the definition of this area extending for as reasonably far into the future as possible given the resource limitations of any disposal program.

A single monument defines a spot and is therefore not an adequate approach to marking a disposal location. In order to define an area that future generations should avoid, a single, large marker covering the area of concern or a system of individual monuments or elements of a marker in a pattern surrounding the area should be used. Either marker size, monument, or marker-element pattern can convey to future generations that the structure is not a natural feature. When using a system of marker elements, the sense of an area can be conveyed by a design of structural continuity (e.g., other parts of the marker system or component can be seen from any other location or marker element). Continuity of design allows the recognition of patterns in the marker component(s) or element(s) even with part of the component or element removed, destroyed, or damaged.

To assure longevity, several principles should be used to guide the design of the markers and/or monuments. The design should assure structural stability and durability. Structural stability refers to the marker component or element being able to withstand natural processes and events and retain the original orientation and position. Examples of the types of potential disruptions are winds associated with intense storms and seismic ground motion caused by earthquakes. Stability can be enhanced by designing the components and elements to be massive with low centers of gravity or to be physically anchored to the ground. Durability generally is dependent on the material properties of the markers, although durability can be enhanced by design. For example, aerodynamic design can be used to mitigate the effects of wind-blown sand abrasion.

Linguistic Principles

The current structure of society undoubtedly will undergo changes over time, and these changes may be either gradual or abrupt, continuous or discontinuous. Changes in society can include governmental and economic structures, cultural values, religion, language, and level of technology. The linguistic goal of the marker system is to transmit a warning to future societies about the hazards posed by the buried nuclear waste at a particular disposal location regardless of these societal changes. Several principles should be applied to the development of this warning.

Because languages evolve over time and can be replaced by "new" languages, the warning message should be kept simple for each level of societal development being targeted for contact. This simplicity should be applied to the message itself (e. g., be direct and not misleading), the content of the message (e.g., eliminate extraneous information), and the grammatical structure within the message (e.g., avoid complex sentences and colloquialisms).

Another principle to employ is redundancy. Different cultures may have differing capabilities for interpreting messages and the format in which the message is presented. To account for such differences in capability, redundancy should be incorporated into the message through the use of language, symbols, and graphics as deemed appropriate.

Even without major changes in interpretive abilities, cultural and political changes may occur that can be countered through language redundancy. For those portions of the message conveyed by language, the use of more than one language may increase the likelihood that future societies will understand the message.

Material-Properties Principles

The material properties of the markers are of critical importance to the goal of marking a disposal location for an extended period of time. This time period is a significant portion of the time period of regulatory concern limited by the constraint of resource allocation within the overall program relative to the hazard posed by the waste being disposed of. Under ideal conditions, the markers should be designed to survive for the entire time period of regulatory concern. Material properties play a major role in determining the physical survivability of the markers in the natural environment. These properties also can affect the type and longevity of the messages being transmitted over this time period.

Principles that determine the suitability of material properties of the markers focus on the topics of durability, reactivity, and desirability. Durability refers to the ability of a material to withstand both current and projected climatic conditions. Weather-related processes include but are not limited to wetting and drying, freezing and thawing, and thermal expansion and contraction, along with wind-blown sand abrasion. Materials exposed to these processes should not suffer significant degradation during extended periods of exposure. Material properties also are important in resisting the effects of both individual and societal vandalism.

The materials used for the markers should be nonreactive (inert) for the time frame being considered, the environmental conditions expected, and geologic setting at the disposal location. Reactivity refers to the chemical interaction between two or more materials in contact with one another. The reactivity concern is both between materials used to construct marker elements and between the markers and the local geologic material upon which the marker rests or is embedded or buried. With naturally occurring materials, the chemistry may change as climatic conditions change. For example, a wetter climate may result in changes in vegetative population, which in turn affect the chemistry of soils being developed. Interaction between the soils and the marker material could affect the longevity of the marker.

Another factor that will play a major role in the longevity of the markers is the desirability of the marker material(s) for use by future societies. The material properties of the marker material(s) should be selected to minimize the potential resource value for reprocessing or recycling.

Message-Level Principles

As was the case for linguistics, future societal changes also are likely to affect the type of message that can be interpreted. Scientifically and technologically advanced societies may be more inquisitive than substantially less developed societies and require more information to satisfy their curiosity. For one type of society, a simple warning of danger may be sufficient to deter intrusion, whereas another society may require an explanation of why the area is dangerous before intrusion is deterred.

Because of the possible diversity of future societies and their differing abilities to decipher messages and their differing incentives for heeding the messages, more than one message level should be used to convey the warning about a waste-disposal location. The contents of these messages should be based on the principles of redundancy and complexity.

Redundancy assures that each message level conveys a similar warning about the potential hazards of the location. Level of complexity targets variously scientifically and technologically developed societies based on their estimated ability to decipher a message. Whereas linguistic redundancy repeats the same specific message at a particular level of complexity in different languages, message-level redundancy repeats the same basic message at different degrees of complexity. The number of message levels and the degree of message complexity in each level depends on the spectrum of development of future societies that are expected to pose an intrusion threat to the disposal facility.