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5.2.4 Monitoring

Contents
5.2.4.1 Introduction
5.2.4.2 Objectives
5.2.4.3 The scope of monitoring programmes
5.2.4.4 Long-term stewardship monitoring activities and technical uncertainties
5.2.4.5 Monitoring techniques versus regulatory requirements and social ethical challenges
5.2.4.6 Example: Monitoring at former mining sites
5.2.4.6.1 Issues of concern
5.2.4.6.2 Monitoring at waste rock piles and tailing ponds
5.2.4.6.3 Monitoring at closed mines
5.2.4.6.4 Scope of monitoring versus land use

5.2.4.1 Introduction

Many of the concepts applied to the assessment and remediation of contaminated sites were developed in the past century, and were built on established traditions of applied science and engineering. Implicit and often tacit assumptions prevalent at that time included that:

  • Clean-up can be effectuated to near zero residual concentrations.
  • Clean-up can be performed against a fixed set of standards/parameters.
  • Permanent solutions can be applied, and the change over time of both the site itself and the engineered structures, such as barriers, can be largely ignored.
  • Generic solutions can be site independent, and are also independent of the particular economic and social context.
  • The systems in question can be captured by deterministic parameters.

In recent years the validity of these assumptions and their efficiency is being questioned. Emerging new concepts include acceptance of fundamental uncertainties and the appropriateness of risk based clean-up criteria, comprehensive multi-criteria analyses incorporating social as well as technical performance criteria, and acknowledgement of the fact that any engineered structure has only a finite lifetime (see Sections 5.2.1.1 and 5.2.1.4), that a site interacts with its surrounding environment, and hence insistence on an open ended or evolutionary perspective on stewardship. Advances in knowledge permit more and more sophisticated interventions in the functioning of environmental systems. Going far beyond macroscopic intervention in materials (such as building a dam), it is now possible to intervene on the scales of atoms (nuclear fission and fusion), molecules and cellular structures. However, these forms in which matter is organized are dynamic (e.g., change in ecosystems, hydrological cycles and atmospheric circulation), and some of the components introduced into the environment have long lifetimes (toxic organic compounds and radionuclides).

Science and technology applications can sometimes solve, or at least mitigate, the emerging problems inherited from the (recent or distant) past. However, given that the systems in question are complex and will naturally continue to change, there is always the possibility that undetermined changes (including unintended side effects of engineering interventions) can come to dominate design goals.

Leading available techniques in general and the specific remediation techniques applied to (radioactively) contaminated sites in particular are described in Sections 3 and 4 [IAEA-1999], [IAEA-2006b], [IAEA-1999a], [USNRC-2004b], [IAEA-1992]. While they have been implemented worldwide with varying degrees of success, it will be important to assess and ultimately prove their potential against the specific characteristics of the site or sites considered.

Taking into consideration the discussion above, a number of technological challenges for long term management of sites emerge. These technological challenges are within and complementary to the societal framework highlighted in this and other sections.

5.2.4.2 Objectives

Monitoring is usually performed as part of the institutional control measures [IAEA-2002a]. This is to verify that the site functions as designed, that regulations are complied with, and that certain aspects of institutional control are still in place and functioning. The legal basis for the requirement to monitor, and the extent of the monitoring, arises from regulations on radiation protection, regulations on environmental protection and, in the case of mining involving radioactive materials, mining regulations designed to ensure orderly closure of mines and mining sites. In addition, there may be requirements arising from relevant legislation on public safety. The sustained performance of a monitoring programme may be one of the core tasks of a steward.

For new practices, remediation planning commences with the development of a site and continues through the operations on the site; major parts of the post-closure monitoring systems usually develop from the programme of monitoring during operation. Assuming that a licensed operation would have a well developed monitoring system, the closure of the operation and the transition to long term monitoring may justify a modification and even a reduction of the extensive monitoring system operated during the operational phase. There may also be a greater focus on environmental compartments rather than on monitoring releases and discharges. Long term monitoring is a relatively new discipline, and it can be assumed that future monitoring experiences and monitoring data will show the values and shortcomings of current monitoring systems.

The characteristics and state of a site after closure and/or remediation determine the type and scope of monitoring required. In the case of mining and milling sites, on-site residues typically include covered waste rock heaps and stabilized tailings ponds. In addition there may be slightly contaminated and covered sites. Any surface structures would have been decommissioned and demolished, with contaminated debris and scrap being buried on-site if it could not be recycled or sent for disposal at a licensed facility.

Monitoring is an essential element of the long term management programme for a closed and remediated site and may need to be undertaken for a number of purposes, for instance for environmental or socio-economic reasons. Programmes typically cover all pathways for exposure of the critical group for all identified contaminants of concern. The scope and nature of monitoring programmes will differ between sites, depending on the level of restriction for land use applied by the regulators [IAEA-2002a].

There are three major aspects to monitoring in relation to long term stewardship and management:

  1. Monitoring the implementation of a stewardship programme;
  2. Monitoring the performance of engineered remediation solutions;
  3. Monitoring as an essential instrument of quality assurance and quality control (QA/QC).

For all cases, data quality objectives (DQOs) have to be formulated. These help to identify the questions to be addressed and then ways in which the required information can be obtained. The process is designed to ensure that all parties involved decide during the planning phase what specific decisions will be made using the data collected and what the action levels are for those decisions. In addition, the costs and tolerances of making the wrong decision are quantified so that the statistical design of the monitoring programme can be scaled appropriately. The lower the tolerance for making the wrong decision the more data are needed, and consequently the higher the cost of the programme. Once a monitoring system has been designed, the data quality objectives process has to cycle back through the decisions with all the parties involved, to gain agreement [ERICKSON].

Visible monitoring programmes and their associated QA/QC systems are valuable tools for enhancement of public confidence [ERICKSON]. The data from monitoring programmes can be a significant element in a public information and education programme. The data can be made available in a variety of forums and media. An important consideration is to ensure timely dissemination of the information. This can be achieved, for instance, through use of the Internet, where data may be displayed in real time if necessary. In addition, the provision of interpretive comments and control charts enable stakeholders to become aware of the most recent data and their significance. Data may also be distributed through newsletters, notice boards and public displays (including closed circuit TV images of a site), as well as being presented at regular meetings. All of these mechanisms may be used in combination.

Ownership can be created by involving the stakeholders in the monitoring programme. When drawing up the monitoring programme, the steward may need to ensure that a holistic approach is used that will encompass all the relevant issues. For example, sites may be monitored by regularly collecting certain data as well as through inspections. In addition, it may be necessary to check other sources, such as land title registers, to ensure that land use requirements or other essential conditions have not been altered. Again, the reader is referred to IAEA Safety Report No. 27 [IAEA-2002a], which contains comprehensive examples of the methods and systems that may be used for these tasks.

5.2.4.3 The scope of monitoring programmes

Monitoring requirements are usually science based but also need to take into account stakeholder requirements in respect of the timing or frequency, range of parameters studied and proposed duration of a programme. Programmes are, therefore, risk based and include social and political risks.

There is a need to reassess programmes periodically to ensure that the level of monitoring activity is appropriate and continues to provide sufficient data of the correct quality to enable the programme objectives to be met, i.e., that it meets the data quality objectives. Reviews usually include issues of compliance with regulatory requirements, as well as an assessment of ongoing performance of the remediation work and ongoing assurance to the community.

The media to be monitored need to cover all pathways relevant to identified contaminants of concern. These will be water (possibly both surface water and groundwater), soil and vegetation; atmospheric monitoring is carried out for gases and particulates.

There may be a need to identify specific targets of concern and also to consider the natural environment as well as humans and the human-made environment. For example, one of the primary requirements of a capping design is to limit percolation of water into the impounded materials. Therefore, monitoring will focus on indicators of the performance of those elements of the capping system that are designed to prevent percolation of water, namely the hydraulic head in the drainage layer. It would need to be known whether the elements perform according to design and, if not, an early warning of potential problems would be desirable. As an example of such a targeted programme, the monitoring system parameters chosen for the cover at the Fernald (Ohio, USA) environmental management project are given in Table 5.1.

Parameter Critical elements Technology

Differential settlement Condition of barrier layer, maintenance of drainage Topographic survey with settlement plates, ground penetrating radar targets

Head in drainage layer Stability of cover system Pressure transducers

Drainage layer temperature, barrier temperature Stability of cover system, frost protection of barrier layers

Thermistor embedded in a transducer
Root zone status; vegetative soil layer status Erosion control Water content reflectometers, heat dissipation units

Vegetation health and coverage Erosion control Topographic and vegetation surveys, webcam, remote sensing

Table 5.1 Fernald (Ohio, USA) on-site disposal facility monitoring parameters [PROCHASKA].

5.2.4.4 Long-term stewardship monitoring activities and technical uncertainties

Monitoring should provide the information needed to track conditions at the site, determine whether the selected remedies remain effective over time, provide information to decide whether remedies should be altered, and guide decisions on when to stop individual stewardship activities. Environmental elements that may require monitoring include surface water, groundwater, air, and ecological features.

Surface water may be monitored to ensure that water quality, especially water leaving a site, meets the applicable standards. Surface water monitoring can focus on dam integrity and operations, inflows to ponds, stream flows, water quality leaving the site, off-site water quality, and remedy performance.

The primary objectives of groundwater monitoring systems should be to establish contaminant concentration trends, monitor the effects of remedial actions, and provide groundwater flow data for use in water balance and groundwater modelling.

Air monitoring systems may be needed to measure ambient air quality, effluent air, project performance, and meteorological data.

Facilities and structures may also require monitoring. Though the usual approach to physical structures is one of remediation through deactivation, decommissioning, decontamination and dismantlement, certain structures may present a situation in which the short-term human health or environmental risks of conducting remedial activities outweigh the benefits of remediation. In such cases, long-term stewardship, possibly combined with stabilisation, may be an option, and monitoring or some form of modified surveillance becomes necessary. Table 5.2 highlights some examples of long term stewardship activities and technical uncertainties.

Media potentially subject to stewardship Possible stewardship activities Examples of technical uncertainties

Water
All contaminated groundwater and surface water sediments that cannot or have not been remediated to levels appropriate for unrestricted release.

Verification and/or performance monitoring. Use restriction, access controls (comprehensive site land use plan).
Periodic review requirements. Resources management to minimize potential for exposure.

What is the likelihood that residual contaminants will move towards or reach a current or potential potable water resource?
Are dense non-aqueous phase liquids (DNAPLs), heavy metals or long-lived radionuclides present in concentrations and/or locations different from those identified?
Will treatment, containment and monitoring remain effective and adequate?
Will ambient conditions change significantly enough to diminish the effectiveness of the selected remediation strategy?

Soils
All surface and subsurface soils where residual contamination remains, or where wastes remain under engineered caps.

Institutional controls to limit direct contact or food chain exposure.
Maintenance of engineered controls or markers.
Periodic review requirements.

What is the likelihood of future contaminant migration if ambient conditions change?
How will changes in land use affect the barriers in place to prevent contaminant migration and potential exposure?
What is the likelihood of cap failure occurring sooner than expected?
What is the effect of contaminant caused degradation of remediation strategy components?

Engineered structures
All land based disposal units with engineered controls.

Monitoring and inspections, by agreements, orders or permits.
Institutional controls, including restricted land use.
Maintenance, including repairing caps.
Periodic review requirements.
Land and resources use planning to minimize the potential for exposure.


What is the effect of contaminant caused degradation of remediation strategy components?
At what point in time will the remediation solution require significant repair or reconstruction?
Is the monitoring system robust enough to detect remediation failure?

Table 5.2 Examples of long term stewardship activities and technical uncertainties

5.2.4.5 Monitoring techniques versus regulatory requirements and social ethical challenges

In addition to the monitoring challenges imposed by nature on a given solution, changing circumstances, such as regulatory requirements and standards as well as changing public opinion, may continue to give rise to new questions about the chosen or applied solution.

A long term monitoring and surveillance project has often to identify the following aspects in need of monitoring or surveillance:

  • The ecological system associated with the vegetative cover and the ‘buffer’ area (i.e., the surrounding area);
  • Physical changes in the cover system and the buffer area;
  • The effectiveness of institutional controls.

Various monitoring, technological developments and improved scientific understanding might make a chosen solution appear inadequate in hindsight, potentially in both the short and the long term. For this reason, new technologies, techniques, sensors and data logging are being developed, for example, in-situ sensors, sensors acting as sentinels against event related phenomena. Therefore, it is important that regulatory requirements reflect current scientific understanding in order to arrive at the best leading solution for the short term as the long term.

It is also important that evidence of changing large scale or global scale boundary conditions (e.g., in climatology, weather patterns and sea levels) and design bases (e.g., regional water tables and drainage patterns) be reflected in the licensing and other regulatory requirements.
Monitoring protocols should be specified in documents and the effectiveness of monitoring activities may be a major part of regular remedy reviews.

5.2.4.6 Example: Monitoring at former mining sites

5.2.4.6.1 Issues of concern

Large quantities of residues possibly containing radionuclides remaining at or near the surface and mine workings that may remain open are typical of former mining sites. Potential contaminant sources that require monitoring include areas not remediated to free release, surface and underground workings, tailings ponds and waste rock piles.

Increased surface areas underground, the opening of airflow pathways and the lowering of the groundwater table may allow radon to migrate from radionuclide bearing rocks into buildings above the mine site, thus possibly creating a radiological problem. As long as the mine ventilation is operating, the concentrations are kept below levels of concern and the radon is vented in a way that avoids significant exposures. Without ventilation, the radon concentration in dwellings on the surface may increase significantly. Radon levels may need to be monitored and appropriate management strategies introduced.

5.2.4.6.2 Monitoring at waste rock piles and tailing ponds

After remediation, monitoring of seepage water for aqueous contaminants, air for radon and engineered structures, such as covers, for their stability will be required to prove the long term effectiveness of the remediation measures and to provide the necessary reassurance to the public. The duration of the performance verification monitoring phase is usually determined by the licensing authorities in consultation with the operators, taking into account the overall management plan. Inspections may be timed so as to efficiently capture any potential change and may be as far apart as several decades. The measurements mainly relate to the:

  • Quality of seepage water and groundwater; the monitoring of the chemical composition may extend over considerable periods of time, possibly 20 years or more.
  • Radon exhalation and the radon concentration of the air close to the ground over a sufficiently long time to gain confidence that stable conditions have been achieved; such measurements may need to be continued for a considerable number of years. Owing to changing seasonal exhalation conditions, two measurements per annum, one in winter and one in summer, are typically needed.
  • Soil mechanical parameters of covers and other engineered structures in order to detect unfavourable changes in water content, porosity, density, soil fabric, etc.

Measurements are usually carried out by the operator or the site steward and are periodically reviewed by the regulatory authorities.

5.2.4.6.3 Monitoring at closed mines

Closed mines present a special category of objects requiring monitoring, particularly concerning the chemistry of any discharging mine water. Acid mine drainage is a common problem, which is exacerbated in some (uranium) mines by residual fluids from in-situ leaching operations.

A reliable model based forecast of the mine water development can provide a good reference for the scope, frequency and likely duration of monitoring activities. The contaminants to be monitored depend very much on the specific situation, but commonly involve radioactive components, non-radioactive contaminants, such as arsenic and heavy metals, and major constituents. Comparison of measured concentrations with modelled forecasts gives an indication of how long any water treatment and monitoring may be needed.

In deep mines, depending on the mine geometry, the main processes that maintain concentration gradients are convection and diffusion. The water volumes to be treated under a stewardship programme depend on the respective recharge rates in the area and the ensuing water balance in the mine. Mine water volume streams can be as high as 500 – 1000 m³/h.

Underground mines typically extend below the water table, and restoring the water table to pre-mining levels or another suitably defined operational level is part of a decommissioning and stewardship programme. The objectives of the flooding are to:

  • Stop oxidation processes;
  • Minimize water treatment costs and emissions and maximize the radiation protection of the workers by suitable controls of the flooding.

A stepwise flooding scheme, whereby the monitoring results provide data for corrective actions if the system does not behave as predicted or envisaged, is recommendable.

Safe mine closure requires a thorough understanding of the hydrogeology and hydraulics of the mine and the surrounding environment. Meaningful monitoring points are the basis for a model developed with this understanding, which is by no means trivial. A more detailed discussion of the respective requirements, however, is outside the scope of this report.

5.2.4.6.4 Scope of monitoring versus land use

Revegetation of covered waste rock piles is commonly allowed, or rather cannot easily be prevented in temperate or tropical climates. Other uses usually require a more involved permit procedure and appropriate monitoring. In order to determine the scope – from a radiological point of view – of potentially allowable site uses, expected exposures of critical groups or individuals are calculated for each use. The monitoring programmes are then designed to suit the site use chosen. Recreational uses with short term occupancy such as a golf course or an airfield for model aircraft, on waste rock piles, may be preferable, for instance, to industrial or residential developments.