Washington, DC 20555, USA. 2 Environmental Measurements Laboratory, Department of Homeland Security,

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1 MARSSIM (Multi-Agency Radiation Survey and Site Investigation Manual) PLUS: Measurement Methods for Clean-up, Materials and Equipment, and Subsurface Radioactivity Robert A. Meck 1, George Powers 1, Carl Gogolak 2, Alexander Williams 3, David Alberth 4, Ramachandra Bhat 5, Daniel Caputo 6, Steven Doremus 7, Kathryn Klawiter 8, Colleen Petullo 9 1 Office of Nuclear Regulatory Research, Nuclear Regulatory Commission, Washington, DC 20555, USA. ram2@nrc.gov 2 Environmental Measurements Laboratory, Department of Homeland Security, New York, NY Environmental Management, Department of Energy, Washington, DC US Army, Aberdeen Proving Ground, MD US Air Force, Bolling AFB, DC US Air Force, Brooks City-Base, TX US Navy, Yorktown, VA Environmental Protection Agency, Washington, DC US Public Health Service, (at Environmental Protection Agency), Las Vegas, NV Abstract. The Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) describes technically defensible measurement methods for demonstrating that clean-up criteria have been met for surfaces of land and buildings. The methods usually lead to an optimized number of required measurements. The statistical tests are non-parametric, and thus, are not dependent upon assumptions of the statistical distribution of the measurement data. The latest version of MARSSIM is Revision 1, with June 2001 updates; it is available on the world-wideweb at This website is frequently updated and contains additional useful information such as answers to frequently asked questions. The MARSSIM Workgroup is preparing supplements to provide measurement methods to demonstrate that release criteria have been met for materials and equipment. While the draft Multi-Agency Radiation Survey of Materials and Equipment, (MARSAME) is not expected to be available for technical comment until late 2004 or 2005, progress on the development of this manual can be followed in meeting summaries, which are posted on the MARSSIM website. The Workgroup is also developing a second supplement entitled, Multi-Agency Radiation Survey and Assessment of the Subsurface, (MARSAS). The technical basis for this manual is at an earlier stage of development, and thus, will sequentially follow MARSAME. The approach for MARSAS will incorporate a personal computer-assisted indicator of where, specific to the site, measurements would most likely yield the most information. It is a Bayesian approach, that is, it incorporates actual data, knowledge of the site, and expert judgment. 1. Introduction Key US Federal agencies have collaborated to provide uniform guidance on defensible measurement processes and approaches to support clean-up and release of sites, buildings, materials, and equipment where radioactivity may be found. The Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) Workgroup has already published MARSSIM [1], which primarily addresses final survey measurements of the surfaces of lands and structures, including buildings and rooms. The Workgroup plans to publish two supplements to MARSSIM. The first is entitled, Multi-Agency Radiation Survey of Materials and Equipment (MARSAME); the second is entitled, Multi-Agency Radiation Survey and Assessment of the Subsurface (MARSAS). The main features and status of each of these manuals are described below. 2. Manuals for technically defensible measurement processes and approaches Demonstrations that lands, buildings, rooms, structures, materials and equipment have met radiological clean-up or release criteria of State or Federal regulators often are supported by survey measurements. In turn, technically defensible measurements that demonstrate that clean-up or release criteria have been met require planning and statistical analyses of the data. However, there is always 1

2 statistical uncertainty associated with the measurement data. Thus, in addition to the regulatory criteria in terms of concentration levels, the required level of confidence needed to satisfy the criteria must be known before the measurements are made. Technically defensible guidance on how to efficiently demonstrate compliance with regulatory criteria has been developed for surfaces of lands and structures, and additional guidance is being developed for materials and equipment and for radionuclides in subsurface soil. The manual and its supplements described in the following sections are designed to provide guidance for measurements to support demonstration that regulatory criteria have been met. While preliminary processes and measurements are required for adequate planning, the focus is on whether or not the regulatory criteria have been met and are technically defensible. The manual and supplements separately address different measurement situations, namely, radioactivity: on the surfaces of lands and structures; on or in materials and equipment; and in subsurface soil. The guidance in the manual and supplements is based on the assumption that the concentration of what is to be measured is already given. Thus, modelling of regulatory criteria from risk or dose to a measurable concentration is generally out of the scope of these manuals. However, there is an interface between the planning design for the measurements and the models specifically, the area or volume for the measurements. These interfaces with modelling vary with the situation and are addressed below MARSSIM MARSSIM is already published and applies to measurements of radioactivity on the surfaces of lands and structures, including the interiors and exteriors of buildings General processes and approaches There are four general processes described in MARSSIM. They are planning, implementing, assessing, and deciding. The approach is to demonstrate in parallel that the average concentration and the elevated measurements both meet the concentrations from the regulatory criteria. These concentrations may be fixed by the regulatory authority or derived from a dose or risk based requirement. Statistically, the general approach is hypothesis testing. Generally, the statistical hypothesis to reject is that the concentration exceeds the regulatory criteria. Nonparametric statistics are used to avoid the need to defend the assumption that the measurement data are from some standard distribution, such as a normal or log-normal distribution. The regulatory authority must also set or approve the acceptable error level, the Type I error. That is the acceptable statistical probability of an erroneous decision that the criteria were met Planning Efficiency, coupled with technically defensible decisions are the goals of planning, and they are reached with an integrated survey design. An integrated survey design takes a number of factors into account. Ultimately, the decision on whether an area meets the regulatory criteria is made on an area called the survey unit. The size of the survey unit is directly related to the establishment usually through modelling of the concentrations to be measured. In some cases, the regulatory authority specifies the area over which measurements may be averaged. In many cases, the criteria are in terms of dose or risk, and the corresponding concentrations must be derived. These concentrations could be derived in general by the regulatory authority or could be determined on a case-by-case basis. Typically, the modeller must assume an effective area from which the exposure to an individual occurs. This assumed effective area of exposure from the modelling translates to the maximum size of the survey unit. The depths of surface soil or building surfaces must correspond to those assumed in the modelling. The size of areas to be measured for elevated concentrations of radionuclides is also derived from the modelling assumptions. These dimensions dictate the grid size for sampling. The data required in the planning process most often include an historical site assessment, which incorporates written records, process knowledge, and recall from the memory of workers. The kinds and distribution of radionuclides may be determined from previous surveys, namely scoping, characterization, and remedial action support surveys. This information helps to classify the survey unit with respect to the number of samples and the required coverage of scanning measurements. Determination of the minimum detectable concentration needed indicates the types of instrumentation 2

3 needed. At the end of the planning, the integrated survey design designates the grid size and the number and locations of measurements Implementing Adequate quality control is needed for the collection of measurement data. Appropriate instruments must be selected according to the integrated survey design and calibrated. Records of the calibrations and measurements need to be documented and preserved in a manner that facilitates the assessment Assessing Assessing the measurements includes the quality control for data verification and validation. The overall objectives and the integrated survey design should be reviewed to ensure that the implementation was correctly performed. A graphical analysis of the data should be performed to reveal anomalies in the spatial distribution of the measurements. Finally, the statistical tests need to be performed, and the elevated measurement comparison test is required Deciding The integrated survey plan requires estimates of the variance of the data, usually based on previous surveys. The data require an evaluation to verify that the power of the statistical tests is at least as much as the design objective in the planning. Once the power of the tests is established to be sufficient make the decision, the test is performed. The decision is yes or no as to whether compliance was demonstrated with the given confidence level. Failure to demonstrate compliance requires investigation of the causes of the failure. If the average concentration is greater than the criteria, then usually additional remediation and another complete survey needs to be performed. If the cause of failure is due to a very small number of elevated measurements in small areas, then the regulator may allow remediation of those specific areas and documentation of the results without the requirement for another complete survey Status MARSSIM, Revision 1, was published in August It is available on the MARSSIM website: MARSSIM is endorsed by the author agencies: the Department of Defense, the Department of Energy, the Environmental Protection Agency, and the Nuclear Regulatory Commission. The MARSSIM Workgroup considers MARSSIM to be subject to revisions and clarifications based on implementation experience. Clarifications, updates, answers to frequently asked questions, and additional information are posted on the website as needed MARSAME MARSAME will apply to measurements of radioactivity on the surfaces or in the volume of materials and equipment. Because MARSAME is currently (2003) under development, the descriptions that follow are provisional and working draft concepts. The starting point for MARSAME was based on a draft NRC technical report, NUREG-1761 [2]. For simplicity and clarity these working draft concepts are presented for the endpoint of clearance General processes and approaches The processes for classifying materials and equipment as candidate for clearance measurements can be simple or complex, because of the very large variety of forms and kinds of materials and equipment that could potentially be cleared. The intrinsic value of the materials and equipment and the costs of disposal have roles in these processes. The dimensions of the complexity in addition to those considered in MARSSIM include surfaces that are difficult to access along with the ability to detect radionuclides distributed within the volume of materials or equipment Planning High quality initial assessments are critical for all processes that could result in clearance. For example, efficient and cost effective clearance could include determining whether materials and equipment are non-impacted by radionuclides. Non-impacted means no reasonable possibility (extremely low probability) that there are residual radionuclides. With sufficiently high quality processes that ensure that historical records, process knowledge, and qualified recollections from key 3

4 personnel provide a high-level of confidence that materials and equipment are non-impacted, a survey for clearance may not be required. When materials and equipment cannot be declared as non-impacted, experience has shown that it is possible to establish a highly discriminating selection process for identifying candidate materials and equipment for clearance. This process separates a large majority of the materials and equipment with very low concentrations of radionuclides, if any, from those that clearly require cleaning or disposal. With this classification, a simple scanning or in toto measurement may be adequate to demonstrate that clearance criteria have been met. Levels of radionuclides that are near or below clearance levels, but above background levels, may require more detailed measurements to demonstrate that the clearance criteria are met. The cost of more detailed measurements could be a factor in the decision on whether to implement clearance or disposal. If there is a difficult to access surface, or a radionuclide distributed in the volume, or a significant intrinsic value of the materials and equipment, then cost considerations may play an even more significant role, especially where cleaning maybe required before clearance is an option. In Figure 1., below, likely actions are indicated for four situations. Disposition means either clearance or disposal in a radioactive waste repository, and costs include the value of the material or equipment and the costs of implementing the disposition. If the replacement costs or resale value of materials or equipment are large, and if there is a low potential that there are radionuclides in concentrations that exceed the clearance criteria, then the likely action is to implement the clearance process. Optimization means that a case-specific cost-benefit assessment should be performed. In the cases indicated, the decision to implement clearance would require a net benefit from clearing the case-specific materials or equipment. That is, if the materials or equipment are low in value or their disposal costs are low, and if there is a low potential that the clearance criteria would be exceeded, then that potential would need to be evaluated and compared to the disposition costs for that case. Similarly, the potential for highly valued materials or equipment to exceed clearance criteria would need to be evaluated. In the case where the disposition costs are low, disposal may be preferred from the beginning rather than risk the costs of failing a clearance survey and then disposing the materials or equipment in the end. CLEARANCE High Disposition Costs Low Potential to Exceed Clearance Criteria OPTIMIZATION Low Disposition Costs Low Potential to Exceed Clearance Criteria OPTIMIZATION High Disposition Costs Some Potential to Exceed Clearance Criteria DISPOSAL Low Disposition Costs Some Potential to Exceed Clearance Criteria FIG. 1. Decision dependence on disposition costs and potential to exceed clearance criteria. Cost considerations are not within the scope of MARSAME. Rather, MARSAME is focused on providing defensible measurement processes to demonstrate that concentration criteria have been met with a given level of statistical confidence. Figure 1., illustrates that in some situations, complex measurements may be desirable, for example, when an expensive piece of equipment is involved or disposal is prohibitive. For completeness and since the need for complex measurements is likely to arise, MARSAME also will address these more complex measurement situations. 4

5 The optimum choices of the measurement methods depend upon classification of the potential for associated radionuclides, the kinds of radionuclides, the size of the survey unit, as dictated by modelling or regulatory criteria, the clearance level, and the detection capabilities of instrumentation, at a minimum. The large variety of possible measurement situations requires that MARSAME categorize processes applicable to particular configurations and circumstances. A generic treatment is not practical. For example, depending on the particular situation, difficult to access surfaces may have to be made accessible. Scanning surveys may be adequate in some cases, and sampling may be needed in others. A statistically based sample design may be required for conventional static measurements and samples. Combinations of measurement techniques may be required to meet clearance criteria at the required level of statistical confidence. For large clearance projects, such as during decommissioning, an integrated survey design likely could increase efficiency and decrease costs Implementing Standard quality control is needed for the collecting of measurement data. Appropriate instruments must be selected according to the integrated survey design and calibrated. Records of the calibrations and measurements would need to be documented and preserved in a manner that facilitates the assessment Assessing Assessing the measurements includes quality control for data verification and validation. The objectives of the measurements and the integrated survey design, when there is one, should be reviewed to ensure that the implementation was correctly performed. Where appropriate, a graphical analysis of the data should be performed to reveal anomalies in the distribution of the measurements. Finally, if applicable, the statistical tests need to be performed, and the elevated measurement comparison test is needed. Non-parametric statistical tests are recommended because they are independent of specific, standard statistical distributions Deciding The decision that the measurements indicate that the clearance criteria have been met may vary significantly, depending on the particular circumstance. For example, hand tools with a low probability of associated radionuclides may be scanned or counted in toto and a pre-determined measurement threshold could indicate the immediate decision, on the basis of a high-quality controlled process. In other cases, such as sample measurements from a bulk material, statistical analyses, verification of the data, and validation of the assumptions may be required before a decision could be made Status MARSAME is in an early stage of development. An intra-agency draft for review and comment is expected in the summer of Responses to comments and a revised draft likely will require several months to produce a revised draft. At that time, a peer review by the Environmental Protection Agency s Science Advisory Board will be requested, and the draft will be also available to the public for review and comment. The final report likely will take an additional year for clarifications and resolution of the peer review and public comments MARSAS MARSAS applies to measurements of radioactivity below the surface of lands. Because MARSAS is currently (2003) under development, the descriptions that follow are provisional and working draft concepts General processes and approaches The sampling plan in MARSAS is an iterative approach based on mapping the probability that a predetermined concentration will be exceeded at subsurface locations at the site. The locations are mapped in three dimensions. The iterative approach incorporates soft data as well as measurement data. Soft data may include knowledge of the site physical characteristics, process knowledge, and expert judgment. These data are combined with characterization or initial measurements using Bayesian statistics to aid in the survey design for additional measurement locations. This approach 5

6 requires personal computer-based software to assist in designing the sampling plan. This software also assists in the analysis of the data a postiori. The sampling plan and implementation are closely linked to the model interface, in contrast to the approaches in MARSSIM and MARSAME Planning Planning begins with the knowledge of the regulatory criteria to be met, including the concentrations of radionuclides (or risk) and the acceptable probability that they are at the mapped locations. Based on the data from a historical site assessment, including characterization and any initial measurements, the number and locations of the next iteration of samples are computed with the aid of Spatial Analysis and Decision Assistance (SADA) software. A description of this software and a free download are available at the following URL: Figure 2., below, is an example of a preliminary sample designs overlaid on a site map. Figure 3., illustrates that additional soft data can be used to locate the first iteration of samples. Maximizing Clean Zone Locate those decision points that would result in the largest reduction of volume classified as contaminated under a specified confidence level (e.g. 90%). Johnson s A Bayesian/Geostatistical Approach to the Design of Adaptive Sampling Programs. Geostatistics for Environmental and Geotechnical Applications, FIG. 2. Example two-dimensional site map overlays with preliminary sample design. Geobayesian Initial Designs Prior information can be used to formally drive a initial sample design. FIG. 3. Example use of prior information to locate samples. 6

7 Implementing Implementation is a step-wise series of measurement inputs into the SADA software and continues until a predetermined level of confidence that an accurate map of the locations and concentrations radionuclides is developed. Figures 4. and 5., below are illustrate this iterative process. Geobayesian Update The actual samples can be used to update the initial conceptual model. FIG. 4. Example of probable location of radionuclides after first iteration of sample data. Geobayesian Iterative Approach The process can be repeated by utilizing a secondary design strategy over the new update. FIG. 5. Example of second iteration sample locations. 7

8 In some cases, the predetermined level of confidence may not be reachable, because the iterative measurements converge on a lower level of confidence. An example of such a situation could occur when the radioactivity is in small, discrete and widely scattered volumes. When the radioactivity is distributed in a continuous way throughout a large volume the mapping is more approachable. Figures 6., below illustrates an example of the progressive refinement of the probable location of radionuclides with additional iterations of sampling. Figure 7., illustrates an example of diminishing incremental information with increased sampling. Iterative Sampling -When To Stop Copyright 2003 University of Tennessee. All Rights Reserved. SAD A softw are at For more information contact Robert Stewart, University of Tennessee, 1060 Commerce Park, Oak Ridge, TN stewart@ utk.edu. FIG. 6. Example decrease of probable volume containing radionuclides with successive iterations. Cost Benefit - When To Stop One approach to determining when to stop sampling comes from the concept of value of information and can be supported by a geospatial analysis. When additional rounds of sampling are not producing a sufficient amount of new information, sampling may cease. One can often quantify the change in information to determine when additional samples are yielding too little information. Info Number Of New Samples FIG. 7. Example decrease of information with additional samples Assessing The assessment of the measurement data likely would require an iterative approach coupled with the mapping iterations. The approach is to use the updated mapping data as input to a dose or risk modelling software program Deciding The decision that the measurements demonstrate that regulatory criteria were met may be as simple as comparing the mapping results with regulatory criteria that are in terms of concentrations. If the regulatory criteria are in terms of dose or risk, then the mapping locations may serve as inputs to the 8

9 modelling of the regulatory criteria. In either case, explicit agreement from the regulatory authority on the use of the software in conjunction with the survey plan and measurements appears critical. If compliance with the regulatory criteria cannot be demonstrated with additional sampling, then alternative strategies may be required, such as remediation or restrictions Status Work on MARSAS is in a very early developmental stage. The software and its use are under development in parallel with the development of guidance on the approaches to measurements and the appropriate use of the software. 3. Summary Guidance on demonstrating that radiological criteria have been met has been developed for the surfaces of buildings and lands. Supplemental guidance is being developed for meeting criteria for materials and equipment and for subsurface radioactivity. The manual and its two supplements are to be focused on measurement, technically defensible, and endorsed by key Federal agencies. 4. References 1. Nuclear Regulatory Commission, Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM), Revision 1.NUREG-1575, Rev.1; EPA-402-R97-016, Rev.1; DOE/EH-0624, Rev.1, NRC, Washington, (2000). 2. Nuclear Regulatory Commission, Radiological Surveys for Controlling Release of Solid Materials; Draft Report for Comment. NUREG-1761, NRC, Washington, (2002). 9