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3.3.10 Radiological and additional surveys or investigations versus timeline

Contents
3.3.10.1 Introduction
3.3.10.2 Minimum information (results) required from an investigation
3.3.10.3 Preliminary investigation or scoping survey
3.3.10.4 Exploratory investigation
3.3.10.5 Main investigation or characterization survey
3.3.10.6 Supplementary investigation or remedial action support survey
3.3.10.7 Final investigation or final status survey
3.3.10.8 Confirmatory or verification survey
3.3.10.9 Decisions based on investigation results

3.3.10.1 Introduction

The level of effort associated with the design of the sampling and analysis plan to apply depends on the aim and scope, the complexity of the investigation and on applicable or selected intrusive and non-intrusive characterization methods. Large, complicated sites generally receive a significant amount of effort during the design phase, while smaller sites may not require as much planning. This graded approach defines data quality requirements according to the type of investigations/survey being designed, the risk of making a decision error based on the data collected, and the consequences of making such an error. This approach provides a more effective survey design combined with a basis for judging the usability of the data collected.

In Figure 3.5 the following types of investigations have been defined:

  • Preliminary investigation.
  • Exploratory investigation.
  • Main investigation.
  • Supplementary investigation.
  • Final investigation.

It is evident that:

  • A developed strategy can be applied during different investigations and
  • Each investigation can have a different strategy.

In general the radiological and non-radiological characterizations can be divided in six stages of the site survey, remediation and restoration process (see Figure 3.5).

Figure 3.5 Site characterization and the land time management process timeline.
Figure 3.5 Site characterization and the land time management process timeline.

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3.3.10.2 Minimum information (results) required from an investigation

The minimum information (results) required from the DQO Process to proceed with the methods described in EURSSEM are:

  • Classify and specify boundaries of survey units: this can be accomplished at any time, but must be finalized during final status survey planning (see Section 3.3.2).
  • State the null hypothesis (H0): the residual radioactivity in the survey unit exceeds the release criterion (see Appendix B).
  • Specify a gray region where the consequences of decision errors are relatively minor: the upper bound of the gray region is defined as the DCGLW, and the lower bound of the gray region (LBGR) is a site-specific variable generally initially selected to equal one half the DCGLW and adjusted to provide an acceptable value for the relative shift (see Section 3.5.1 and Appendix B).
  • Define Type I and Type II decision errors and assign probability limits for the occurrence of these errors: the probability of making a Type I decision error (α) or a Type II decision error (β) are site-specific variables (see Appendix B).
  • Estimate the standard deviation of the measurements in the survey unit: the standard deviation (σ) is a site-specific variable, typically estimated from preliminary survey data (see Section 3.9.2.9 and Appendix B).
  • Specify the relative shift: the shift (Δ) is equal to the width of the gray region (DCGLW – LBGR), and the relative shift is defined as Δ/σ, which is generally designed to have a value between one and three (see Section.3.5.1 and Appendix B).
  • Specify the detection limit for all measurement techniques (scanning, direct measurement, and sample analysis) specified in the Quality Assurance Project Plan (QAPP): the minimum detectable concentration (MDC) is unique for each measurement system.
  • Calculate the estimated number of measurements (N) and specify the measurement locations required to demonstrate compliance: the number of measurements depends on the relative shift (Δ/σ), Type I and Type II decision error rates (α and β), the potential for small areas of elevated activity, and the selection and classification of survey units (see Section 3.3.2.3 and Appendix B).
  • Specify the documentation requirements for the survey, including survey planning documentation: documentation supporting the decision on whether or not the site complies with the release criterion is determined on a site-specific basis.

3.3.10.3 Preliminary investigation or scoping survey

The aim of the preliminary investigation is to compile and evaluate the available information on the potentially contaminated site and a preliminary hazard assessment. Preliminary investigations are conducted nowadays completed before the historical site assessment (HAS) in order to take into account the survey results in the historical site assessment (see Section 2.4).

From these data an initial site conceptual model (or models) may be constructed, which will subsequently be used to design the site investigation phases of work. The model(s) will also be the basis for a hazard assessment and aid development of historical site survey, waste management, quality management plans and communications plans.

A preliminary investigation comprises a desk study and site walk over to establish historical activities, current status, and the environmental setting and may include a limited amount of surface scanning, surface activity measurements, and sample collection (smears, soil, water, vegetation, paint, building materials, subsurface materials). From this information, an initial conceptual model of the site can be formed and potential hazards identified.

For evaluating survey results, the survey data should be converted to the same units as those in which DCGLs are expressed (see Section 3.10.1). Identification of potential radionuclide contaminants at the site is performed using direct measurements or laboratory analysis of samples. The data are compared to the appropriate regulatory DCGLs.

If the results of the survey and of the historical site assessment indicate that an area is Class 3 and no contamination is found, the area may be classified as Class 3 and a Class 3 final status survey is performed. If the scoping survey locates contamination, the area may be considered as Class 1 (or Class 2) for the final status survey and a characterization survey is typically performed. Sufficient information should be collected to identify situations that require immediate radiological attention

For scoping surveys that potentially serve to release the site from further consideration, the survey design should consist of sampling based on the historical site assessment data and professional judgment. If residual radioactivity is not identified during judgment sampling, it may be appropriate to classify the area as Class 3 and perform a final status survey for Class 3 areas. Refer to Section 2.7 and Section 3.3.10.7 for a description of final status surveys. However, collecting additional information during subsequent surveys (e.g., characterization surveys) may be necessary to make a final determination as to area classification.

3.3.10.4 Exploratory investigation

An exploratory investigation may be necessary, particularly where the preliminary investigation has found little or ambiguous information and there is a high degree of uncertainty. Non-intrusive investigation techniques, such as surface radiation surveys, are very useful at this stage. It is used to test areas of greatest uncertainty with respect to the conceptual model of contamination and site characteristics. The additional information provided aids to the design of the main investigation and enables historical site survey requirements to be specified. Sufficient information may be provided to update the risk assessment, for example, by eliminating a particular pollutant linkage because a pathway no longer exists. This phase is optional and is mostly seen as an opportunity to gather a limited amount of additional information in order to plan the main (detailed) investigation.

3.3.10.5 Main investigation or characterization survey

Main investigation or characterization survey provides detailed information on the horizontal and vertical distribution of radioactive contamination, together with geological, geotechnical and hydro-geological information. Surface surveys may also be required to provide, for example, ecological and hydrological data. Supplementary investigations may be necessary to produce specific information on areas of uncertainty not resolved by the main phase, information required to clarify technical matters related to remedial and restoration options, or for validation studies.

For areas classified as Class 1 or Class 2, a characterization survey is warranted. The main investigation or characterization survey should be planned based on the historical site assessment, scoping and exploratory surveys.

The characterization survey is the most comprehensive of all the survey types and generates the most data. These characterization objectives should include:

  • Determining the nature and extent of radiological contamination.
  • Evaluating remediation alternatives, e.g., unrestricted use, restricted use, on-site disposal, off-site disposal, etc.
  • Input to pathway analysis/dose or risk assessment models for determining site-specific DCGLs (Bq/kg, Bq/m2).
  • Estimating the occupational and public health and safety impacts during remediation / decommissioning.
  • Surveys of different media, e.g., surface soils, interior and exterior surfaces of buildings.
  • Preparing a reference grid.
  • Systematic as well as judgment measurements.
  • Evaluating remediation technologies.
  • Input to final status survey design.

The decision as to which media will be surveyed is a site-specific decision addressed throughout the Radiation Survey and Site Investigation Process.

In more detail, results of characterisation surveys should include:

  • The identification and distribution of contaminants in surface and subsurface soils.
  • The distribution and concentration of contaminants in surface water, groundwater, and sediments.
  • The identification and distribution of contamination pavement, buildings, structures, and other site facilities.
  • The distribution and concentration of contaminants in other impacted media such as vegetation or paint.
  • The survey should also identify the portions of the site that have not been affected by these activities and where no remediation is anticipated.
  • Sufficient information on the physical characteristics of the site, including surface features, meteorology and climatology, surface water hydrology, geology, demography and land use, and hydrogeology.
  • When planning for the potential use of characterization survey data as part of the final status survey, the characterization data must be of sufficient quality and quantity for that use (see Section 3.3.9 and Section 3.5).
  • This survey should also address environmental conditions that could affect the rate and direction of contaminant transport in the environment, depending on the extent of contamination identified above.

The design of the site characterization or investigation survey is based on the specific DQOs for the information to be collected, and is planned using the historical site assessment, scoping survey, expletory investigation results. The DQO process ensures that an adequate amount of data with sufficient quality is collected for the purpose of characterization. The site characterization process typically begins with a review of the historical site assessment, which includes available information on site description, operational history, and the type and extent of contamination (from the scoping survey, if performed). The site description, or conceptual site model as first developed in Section 2.4.9, consists of the general area, dimensions, and locations of contaminated areas on the site. A site map should show site boundaries, roads, hydro-geologic features, major structures, and other features that could affect decommissioning activities.

Note: That because of site-specific characteristics of contamination, performing all types of measurements described here may not be relevant at every site. For example, detailed characterization data may not be needed for areas with contamination well above the DCGLs that clearly require remediation. Judgment should be used in determining the types of characterization information needed to provide an appropriate basis for decontamination decisions.

By conducting a survey, the selection of survey instrumentation and analytical techniques are typically based on knowledge of the appropriate DCGLs, because remediation decisions are made based on the level of the residual contamination as compared to the DCGL. Exposure rate measurements may be needed to assess occupational and public health and safety. The location of underground utilities should be considered before conducting a survey to avoid compounding the problems at the site.

The applied measuring and sampling techniques should be commensurate with the intended use of the data, as characterization survey data may be used to supplement final status survey data, provided that the data meet the selected DQOs.

Characterization surveys for surface and subsurface soils and media involve employing techniques to determine the lateral and vertical extent and radionuclide concentrations in the soil. This may be performed using either sampling and laboratory analyses, or in-situ gamma spectrometry analyses, depending on the detection capabilities of each methodology for the expected contaminants and concentrations. Note that in-situ gamma spectrometry analyses or any direct surface measurement cannot easily be used to determine vertical distributions of radio-nuclides. Sample collection followed by laboratory analysis introduces several additional sources of uncertainty that need to be considered during survey design. In many cases, a combination of direct measurements and samples is required to meet the objectives of the survey.

Radio-nuclide concentrations in background soil samples should be determined for a sufficient number of soil samples that are representative of the soil in terms of soil type, soil depth, etc. It is important that the background samples be collected in non-impacted areas. Consideration should be given to spatial variations in the background radionuclide concentrations.

Surface water and sediment sampling may be necessary depending on the potential for these media to be contaminated. The contamination potential depends on several factors, including the proximity of surface water bodies to the site, size of the drainage area, total annual rainfall, and spatial and temporal variability in surface water flow rate and volume. Refer to Section 2.4.8.6 for further consideration of the necessity for surface water and sediment sampling.

For the evaluation of the characterization survey data, these data should be converted to the same units as those in which DCGLs are expressed. Identification of potential radionuclide contaminants at the site is performed through laboratory and in-situ analyses. Appropriate regulatory DCGLs for the site are selected and the data are then compared to the DCGLs. For characterization data that are used to supplement final status survey data, the statistical methodology in Section 3.10 should be followed to determine if a survey unit satisfies the release criteria.

For characterization data that are used to help guide remediation efforts, the characterization survey data are used to identify locations and general extent of residual activity. The survey results are first compared with DCGLs. Surfaces and environmental media are then differentiated as exceeding DCGLs, not exceeding DCGLs, or not contaminated, depending on the measurement results relative to the DCGL value. Direct measurements indicating areas of elevated activity are further evaluated and the need for additional measurements is determined.

The documentation of a site characterization survey should provide a complete and unambiguous record of the radiological status of the site. In addition, sufficient information to characterize the extent of contamination, including all possible affected environmental media, should be provided in the report. This report should also provide sufficient information to support reasonable approaches or alternatives to site decontamination

3.3.10.6 Supplementary investigation or remedial action support survey

Supplementary investigations or remedial action support surveys are optional and can be performed to support comparison of options and implementation of preferred remediation and restoration options.

The remedial action support survey typically relies on a simple radiological parameter, such as direct radiation near the surface, as an indicator of effectiveness. The investigation level (the level below which there is an acceptable level of assurance that the established DCGLs have been attained) is determined and used for immediate, in-field decisions (see Section 3.3.2.8). Such a remedial action survey is intended for expediency and cost effectiveness and does not provide thorough or accurate data describing the radiological status of the site. Note that this survey does not provide information that can be used to demonstrate compliance with the DCGLs and is an interim step in the compliance demonstration process. Areas that are determined to satisfy the DCGLs on the basis of the remedial action support survey will then be surveyed in detail by the final status survey. Alternatively, the remedial action support survey can be designed to meet the objectives of a final status survey as described in Section 2.7 and Section 3.3.10.7. DCGLs may be recalculated based on the results of the remediation process as the regulatory program allows or permits.

A remedial action support survey is performed while remediation is being conducted, and guides the clean-up in a real-time mode.

A remedial action support surveys are conducted:

  • To support remediation activities.
  • To serve to monitor the effectiveness of decontamination efforts that are intended to reduce residual radioactivity at or below the DCGL criteria.
  • To guide the clean-up in a real-time mode.
  • To determine when a site or survey unit is ready for the final status survey.
  • To provide updated estimates of site-specific parameters used for planning the final status survey.

The determination that a survey unit is ready for a final status survey following remediation is an important step in the Radiation Survey and Site Investigation Process. In addition, remedial activities result in changes to the distribution of contamination within the survey unit. For most survey units, the site-specific parameters used during final status survey planning (e.g., variability in the radionuclide concentration, probability of small areas of elevated activity) will need to be re-established following remediation. Obtaining updated values for these critical parameters should be considered when planning a remedial action support survey.

There will be radio-nuclides and media that cannot be evaluated at the DCGLW using field monitoring techniques. For these cases, it may be feasible to collect and analyze samples by methods that are quicker and less costly than radionuclide-specific laboratory procedures. Field laboratories and screening techniques may be acceptable alternatives to more expensive analyses. Reviewing remediation plans may be required to get an indication of the location and amount of remaining contamination following remediation.

Field survey instruments and procedures should be selected based on their detection capabilities for the expected contaminants and their quantities. Survey methods typically include scans of surfaces followed by direct measurements to identify residual radioactivity. The residual surface activity levels can be expected to be comparable to the DCGLs, and a determination should be made on the need for further decontamination efforts.

Survey activities for soil excavations include surface scans using field instrumentation that should be sensitive to beta and gamma activity. Because it is difficult to correlate scanning results to radionuclide concentrations in soil, and especially with a multi radionuclide contamination, judgment should be carefully exercised when using scan results to guide the clean-up efforts.
Field laboratories and screening techniques may provide a better approach for determining whether or not further soil remediation is necessary.

If results of these survey activities indicate that remediation has been successful in meeting the DCGLs, decontamination efforts can be ceased and final status survey activities can be initiated. Further remediation may be needed if results indicate the presence of residual activity in excess of the DCGLs.

The remedial action support survey is intended to guide the clean-up and alert those performing remedial activities that additional remediation is needed or that the site may be ready to initiate a final survey. Data that indicate an area has been successfully remediated could be used to estimate the variance for the survey units in that area. Information identifying areas of elevated activity that existed prior to remediation may be useful for planning final status surveys.

3.3.10.7 Final investigation or final status survey

The final investigation or final status survey is used to demonstrate compliance with release criteria and regulations.

The primary objectives of the final status survey are:

  • To select/verify survey unit classification.
  • To demonstrate that the potential dose or risk from residual contamination is below the release criterion for the site and/or for each survey unit and meets the release criterion.
  • To demonstrate that the potential dose or risk from small areas of elevated activity is below the release criterion for the site and/or for each survey unit and meets the release criterion.
  • The final investigation or final status survey provides data to demonstrate that all radiological parameters satisfy the established guideline values and conditions.

Although the final status survey is discussed as if it were an activity performed at a single stage of the site investigation process, this does not have to be the case. Data from other surveys conducted during the Radiation Survey and Site Investigation Process – such as scoping, characterization, and remedial action support surveys – can provide valuable information for planning a final status survey provided they are of sufficient quality.

Professional judgment and biased sampling are important for locating contamination and characterizing the extent of contamination at a site.

The design process of a final status survey begins with the development of data quality objectives (DQOs) and the null and alternative hypotheses should be clearly stated. On the basis of these objectives, hypotheses and the known or anticipated radiological conditions at the site, the numbers and locations of measurement and sampling points used to demonstrate compliance with the release criterion are then determined. Note: the null hypothesis (H0) tested is that residual contamination exceeds the release criterion; the alternative hypothesis (H0) is that residual contamination meets the release criterion.

It is advised that by planning the final status survey early discussions are organized with the regulatory agency concerning logistics for confirmatory or verification surveys.

The final step of the DQO process includes selecting the optimal design that satisfies the DQOs. For some sites or survey units, the guidance provided in this section may result in a survey design that cannot be accomplished with the available resources. For these situations, the planning team will need to relax one or more of the constraints used to develop the survey design as described in Section 2.7.

At the data evaluation of final status surveys two statistical tests are used. For contaminants that are present in background, the Wilcoxon Rank Sum (WRS) test is advised. When contaminants are not present in background, the Sign test is advised.

To determine data needs for these tests, the acceptable probability of making Type I decision errors (α) and Type II decision errors (β) should be established (see Section 2.7 and Appendix B, Section B.2). The acceptable decision error rates are a function of the amount of residual radioactivity and are determined during survey planning using the DQO Process. The evaluation of survey results may cause that additional data and/or additional remediation and/or resurvey may be necessary. The scope of further actions should be agreed upon and developed as part of the data quality objective process before any action begins.

Documentation of the final status survey should provide a complete and unambiguous record of the radiological status of the survey unit, relative to the established DCGLs. In addition, sufficient data and information should be provided to enable an independent re-creation and evaluation at some future time. Much of the information in the final status report will be available from other decommissioning documents; however, to the extent practicable, this report should be a stand-alone document with minimum information incorporated by reference. The report should be independently reviewed (see Section 3.10.8) and should be approved by a designated person (or persons), who is capable of evaluating all aspects of the report prior to release, publication, or distribution.

3.3.10.8 Confirmatory or verification survey

A confirmatory survey (also known as an independent verification survey), may be performed by the responsible regulatory agency or by an independent third party (e.g., contracted by the regulatory agency) to provide data to substantiate results of the final status survey.

Another purpose of the confirmatory activities may be to identify any deficiencies in the final status survey documentation based on a thorough review of survey procedures and results. Independent confirmatory survey activities are usually limited in scope to spot-checking conditions at selected locations, comparing findings with those of the final status survey, and performing independent statistical evaluations of the data developed from the confirmatory survey and the final status survey.

3.3.10.9 Decisions based on investigation results

Compliance demonstration is simply a decision as to whether or not an investigation/survey unit meets the release criterion. For most sites this decision is based on the results of one or more surveys. When survey results are used to support a decision, the decision maker1 needs to ensure that the data will support that decision with satisfactory confidence.

Usually a decision maker will make a correct decision after evaluating the data. However, since uncertainty in the survey results is unavoidable, the possibility of errors in decisions supported by survey results is unavoidable. For this reason, positive actions must be taken to manage the uncertainty in the survey results so that sound, defensible decisions may be made. These actions include proper survey planning to control known causes of uncertainty, proper application of quality control (QC) procedures during implementation of the survey plan to detect and control significant sources of error, and careful analysis of uncertainty before the data are used to support decision making.

Decisions are made, in coordination with the stakeholders, e.g., responsible regulatory agency, based on the conclusions drawn from the assessment process. The ultimate objective is to make technically defensible decisions with a specified level of confidence.

1 The term decision maker is used throughout this section to describe the person, team, board, or committee responsible for the final decision regarding disposition of the survey unit.

In situ spectrometry can be used to characterize vertical profiles of gamma emitters (see IAEA TECDOC 1363)
– by Rafael Garcia-Bermejo Fernandez about 6 years ago