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2.2.4 Practical implementation of the management and selection of remedial actions

Contents
2.2.4.1 Introduction
2.2.4.2 Preliminary of scoping analysis on existing data
2.2.4.3 Early decisions regarding further action
2.2.4.4 Public involvement
2.2.4.5 Establishment of remediation goals
2.2.4.6 Site characterization
2.2.4.7 Development and screening alternatives
2.2.4.8 Institutional controls
2.2.4.9 Analysis and design of preferred alternatives

2.2.4.1 Introduction

A general approach for the management and selection of remedial options for radioactively contaminated sites and/or groundwater should consist of a phased strategy to allow for the most cost effective and environmentally sound remedial approach Principle 1. It should also allow that the decisions and choices made during the management and selection process may be clearly seen and examined. This is an essential part of the process, and it can be particularly important, for example, when communicating with affected parties (e.g., members of the public) and competent authorities [IAEA – 1999a].

The initial discovery of radioactive contamination on a site or in the groundwater system and the decision to begin site investigation can result from various factors. For example, a site operator may become aware that the groundwater is contaminated and then must decide what action should be taken to prevent it from leaving the site boundary. Another possibility is that the problem may be discovered through epidemiological studies identifying health problems arising from the utilization of contaminated groundwater. In the former case, there might be ample time to plan a complex strategy, whereas in the second case immediate action would obviously be required. In situations where immediate action is indicated, e.g., to prevent health risks, it should be stressed that hasty decisions regarding remediation may not always be most appropriate. A more satisfactory approach might be to alleviate the health risk by institutional control, e.g., providing alternative water supplies; this would then allow time for a more structured approach to making decisions regarding the remedial action.

A phased approach can be particularly useful to allow for the most cost effective and environmentally sound disposition of a contaminated site. The phased approach would generally consist of the following elements:

  • Assessment of the existing information and data (scoping analysis);
  • Initial planning and decision making to consider what further action is required;
  • Selection of the site characterization or monitoring requirements;
  • Assessment of remediation technologies for appropriate application to the problems at hand; and
  • Selection of the remediation strategy to be employed.

2.2.4.2 Preliminary of scoping analysis on existing data

The logical approach to assessing a contaminated site is to identify the source, the hydro-geologic setting, and the potential receptors, i.e., the affected population, by:

  • Compiling, reviewing and analysing existing data and information;
  • Identifying the contamination and its source;
  • Describing the hydro-geological system, developing a useful conceptual model; and
  • Identifying the potential affected population and their points of contact with the contaminated site and/or groundwater.

This should be based on site history, background information, previous investigations, known and suspected sources of contamination, processes used which generated the waste, routes of migration, and potential human and environmental receptors.

The history and background of the site should be evaluated to determine if any previous activities took place that could potentially impact decisions to be taken concerning characterization or remediation of the site. Such considerations could include previous industrial, commercial, agricultural or military uses.

A literature search or interviews with persons with historical knowledge should be performed to acquire a knowledge base on how the site became contaminated, the period of time which the contamination was released to the environment, release mechanisms, the types and quantities of contamination, and so on.

The existing geologic and hydrologic data for the site should be evaluated to help determine the fate and transport of the contaminants. Information regarding geologic formations and hydrologic parameters may be obtained through the description of sediment samples collected during drilling of production wells, irrigation wells or any other soil borings that may have taken place at the site. The quality assurance of data collected in this manner may be suspect and therefore conclusions based on the data should be treated with caution.

At this stage, some modelling may take place. The complexity of the modelling should reflect the quality and the quantity of site data available. This modelling may include groundwater. As a first pass, relatively simple calculations of radiation dose and risk to individuals and populations may be made using assumptions that are conservative, resulting in estimates for dose and risk that are maximums.

2.2.4.3 Early decisions regarding further action

After all or most of the existing data and information on the contaminated site have been collected and analysed, further action should be defined. The alternatives to be considered may include:

  • No further action needed: A decision of no further action can be made if it is determined that there is no contamination or that the extent of the contamination is below an acceptable risk level and below the regulatory requirements of concentration or radiological dose.
  • Further monitoring of contaminant plume is required: Although no further action (e.g., remedial action) may be required, it might still be necessary or advisable to continue to monitor the site to ensure that the initial assessment of the situation is correct, for example, when it appears that natural processes such as dispersion and radioactive decay would result in the contamination having no significant impact on the receptors, i.e., the affected population. Continued monitoring would allow the assumptions regarding movement of the groundwater contaminant to be routinely checked. In addition, continued monitoring could provide comforting reassurance to affected parties such as the local population.
  • Insufficient data exist to make a decision: Following the assessment of existing data and information, it could be decided that there are insufficient data to make an informed decision regarding the possibility or advisability of remedial action. Under such circumstances, it is common that a site characterization programme be implemented to fill the identified gaps in information and data. If there is a decision to collect additional data, the data collection objectives should be clearly identified and used in designing the site characterization programme.
  • Remedial action is required: In some cases, there will be sufficient data and information regarding a site and the groundwater contamination problem to conclude that remedial action is required. In such a case, the strategy will advance to the technologies evaluation and remedial design phases.

2.2.4.4 Public involvement

A factor to be considered when evaluating technologies or screening for remedial alternatives is involvement by affected parties and the general public Principle 2. The public’s perception of risk due to radiation exposure may be substantial enough to warrant a more stringent remedial goal for a contaminant in groundwater. It is important to involve the public and all affected parties in the decision making process as indicated in Section 2.3, Stakeholder involvement, of this document.

2.2.4.5 Establishment of remediation goals

Preliminary remediation goals are normally site specific. The initial remediation objectives should be established on the basis of the nature and the extent of the contamination, the water resources that are currently or potentially threatened, and the potential for human and environmental exposure. These quantitative goals should define the extent of clean-up that is required to satisfy the established objectives. They include the required clean-up levels and the restoration time frame. Clean-up levels of contaminants are typically based on either drinking water standards or on excess lifetime cancer risk levels.

Past practices have used extremely conservative scenarios for determining the risks of ionizing radiation to human health. As a result, remedial activities have been extremely costly. Recently, using more realistic risk scenarios appears to becoming acceptable. In some cases, remediation has been avoided, with only the cost of monitoring remaining. This strategy has reduced the cost while continuing to adequately protect human health Principle 1. It is recommended that when selecting and analyzing the risk scenarios, the expected land use, the impacts on affected parties and the environment, and the future groundwater needs should all be evaluated. A realistic scenario can then be developed which would allow for a more cost effective remediation while still ensuring the safety of the public. Obviously, the effectiveness and reliability of institutional controls may affect these decisions.

Risk assessment methods may be used, coupled with regulatory requirements, to determine achievable goals. The beneficial use of an aquifer must also be considered. Water which does not meet the required standards for domestic use may still be useful for agricultural or industrial purposes.

The potential effects on environmental receptors such as plant and animal species at or near the site may also affect the remediation goals.

2.2.4.6 Site characterization

Site characterization activities should take place if more data are needed to evaluate risks associated with the contaminated site or to understand the parameters necessary for selecting an appropriate remedial technology. Data collection objectives should be selected with an understanding of the associated uncertainties.

If necessary, a site specific data collection strategy should be organized to provide sufficient data to formulate a conceptual model of the contaminated site. The data collection activities should focus on understanding of:

  • The source term;
  • The geology (i.e. formations, grain size, plasticity, moisture content, density, mineralogy);
  • The hydrogeology, aquifer properties;
  • The geochemistry;
  • The nature and the extent of the contaminant plume; and
  • The exposure pathways.

In characterizing contaminated sites, inherent uncertainties may be encountered. Many of these uncertainties arise from the necessity of characterising the heterogeneity of the aquifer with a limited number of sample points. Aquifer heterogeneity should be considered when developing a strategy for site characterisation.

Aquifer system uncertainties may be identified and addressed using the preliminary site conceptual model to identify the remedial strategy with the highest probability of success. At this stage of the decision making process, the probability of success is based on the “most probable site conditions.” Acknowledging that site conditions have inherent uncertainties, reasonable variations from the “most probable conditions” are identified early, and contingency remedial action strategy alternatives are not ruled out.

To better plan the site characterisation activities, a sensitivity analysis is often used for defining the importance of the parameter input to predicted costs and remedial action performance. Data worthiness (e.g., adequacy or worth) evaluations are also becoming more popular for decision makers in their understanding of the relationship between uncertainty and sensitively of site conditions, and remedial costs and performance. The observational method is an effective and economical means to manage uncertainties associated with remediating contaminated groundwater.

Using the Data Quality Objectives Process will help to ensure that when data collection has been completed it will have accomplished two goals:

  • Provided sufficient data to make the required decisions within a reasonable uncertainty;
  • Collected only the minimum amount of necessary data.

The Data Quality Objectives Process embodies both of these two main goals and it is difficult to separate which is the more important or which drives the other. For example, the Data Quality Objectives Process will strive to provide the least expensive data collection scheme, but not at the price of providing answers that have too much uncertainty.

Data Quality Objectives are intended to ensure that the data generated during site characterization activities are adequate to support management decisions. A clear definition of the objectives and the method by which decisions will be taken must be established early in the scoping process. Data Quality Objectives are determined based on the end uses of the data to be collected. The level of detail and data quality needed will vary based on the intended use of the data. Data Quality Objectives should be reviewed throughout the characterization activity and adjusted based on new available information as appropriate.

All of the data collected during the scoping and characterization phases of the project should be analyzed with the results formally documented. This activity should be co-ordinated with the risk assessment and modelling personnel to provide for a more efficient use of the data. All decisions should be documented with an explanation of the logic used to arrive at the given conclusion. This includes decisions made as a result of scoping, establishment of preliminary remediation goals, data collection objectives, data quality objectives and screening, and the selection of remediation technologies.

2.2.4.7 Development and screening alternatives

Guiding principles for developing alternatives include, among others, technical practicability, cost/benefit analysis, and schedule for implementing and completing the remedial action.

The nature of the source, the size of the plume, and the transmissivity of the aquifer also will directly affect the effectiveness of the remediation whether it be an in-situ or ex-situ treatment. Most groundwater technologies currently available are expensive to implement and take long periods of time to complete. Continued research is ongoing world wide to develop new techniques for in situ and ex situ remediation. A general list and description of these technologies can be found in Section 4, Environmental remediation of radioactively contaminated sites, of this document. Care should be taken to evaluate the success or failure of the technologies which have been developed and to compare the site specific characteristics against the test site to determine the viability at a particular site. Critical parameters of the technology being evaluated should be identified for comparing the viability of success at the site. For example, a technology may work quite well at a site with alluvial sands, but not at all at a site with fractured rock.

Based on the analysis performed on the site characterisation data, a list of alternatives and technologies may be compiled. A screening process should determine if an active remediation is required or if a passive alternative (institutional controls, no action, monitoring, etc.) is desired. If an active remediation option is chosen, a detailed analysis of the technologies should be performed.

2.2.4.8 Institutional controls

Institutional controls may be implemented to reduce or eliminate potential impact of exposure to human health. The following kinds of institutional controls have been established and may be considered to prevent exposure to contaminated sites and/or groundwater:

  • Regulatory restrictions on construction and use of private water wells, such as well construction permits and water quality certifications;
  • Acquisition of property by the government from private entities;
  • Exercise of regulatory and police powers by governments, such as zoning and issuance of administrative orders;
  • Restrictions on property transactions, including negative covenants and easements;
  • Non-enforceable controls, such as well use advisories and deed notices;
  • Relocation of affected populations (in extreme cases).

The effectiveness and reliability of these controls should be evaluated when determining whether rapid remediation is warranted. If there is adequate certainty that institutional controls will be effective and reliable, there is more flexibility to select a response action that has a longer restoration time frame or a determination that no remedial action is required.

2.2.4.9 Analysis and design of preferred alternatives

During the detailed analysis, remedial alternatives that have been retained from the alternative development phase should be analysed against a number of evaluation criteria. The purpose of the detailed analysis should be to compare alternatives so that the remedy that offers the most favourable balance among a set of criteria can be selected, Principle 1. The analysis of a remedial action for contaminated sites and/or groundwater may be made on the basis of the following evaluation criteria:

  • Overall protection of human health and the environment;
  • Compliance with applicable regulations;
  • Long-term effectiveness and permanence;
  • Reduction of toxicity, mobility, or volume;
  • Short term effectiveness;
  • Implement ability;
  • Cost;
  • Community or government acceptance;
  • Final disposal of residues.

Other criteria may also be established based on site specific conditions. A discussion and summary table should be prepared for each part of the detailed analysis to provide a historical paper documenting the decision process.

2.2.4.10 Implementation action and performance assessment

Based on monitoring data, performance evaluations of the remedial action should be conducted periodically to compare actual performance to expected performance. The performance monitoring should be designed to provide information such as:

  • Horizontal and vertical extent of the plume and contaminant concentration gradients, including a mass balance calculation;
  • Rate and direction of contaminant migration;
  • Changes in contaminant concentrations or distribution over time;
  • Rates of contaminant mass removal and transition from adjective removal to diffusion rate limited removal;
  • Effects of hydrological events, such as above average rainfall, on contaminant mass removal and changes to groundwater flow;
  • Calibration of model based on actual results and effects of changes of operational parameters to model predictions;
  • Effects on regional groundwater levels and the resulting impacts;
  • Effects of reducing or limiting surface recharge (if applicable);
  • Effects of re-injection (if applicable);
  • Effects of any modifications to the original remedial action; and
  • Other environmental effects of remedial action, such as saltwater intrusion, land subsidence, and effects on wetlands or other sensitive habitats.

The frequency and duration of the performance evaluations should be determined by site specific conditions. Conducting performance evaluations and modifying remedial actions is part of a flexible approach to attaining the remedial action goals. Decisions should be verified or modified during remediation to improve a remedy’s performance and ensure protection of human health and the environment.

The performance assessment may provide information that can be used to determine whether the remediation goals are being met, have been achieved or, in some cases, are technically impracticable to achieve in a reasonable time.