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Investigations and radiological assessments of mining residues in Germany
International Congress Series 1225 (2002) 103 – 110
Investigations and radiological assessments of mining residues in Germany E. Ettenhuber Department for Applied Radiation Protection, Federal Office for Radiation Protection, 10318 Berlin, Germany
Abstract For centuries, exhaust air and sewage were released from mines and processing facilities into the environment, and mining debris and waste from ore processing were dumped there. The concentrations of naturally occurring radionuclides can be considerably increased compared to soil and surface-near rocks and significantly increased radiation exposures can result for members of the public. In addition, measures of radiological protection have to be considered in many cases. Since the situation has arisen due to operation prior to regulations of radiological protection or operations conducted under inadequate radiological protection control, it is categorized as intervention situation. The principles for justifying intervention measures and for establishing action levels to be applied in remediation programmes for mining residues are discussed. Since the contamination of mining sites results from naturally occurring radionuclides, the natural background exposure should be taken into account in establishing appropriate action levels. Following the principle that radiation exposures being in normally occurring natural range do not require protection measures, the National Commission on Radiological Protection recommended criteria for the justification of remediation measures in case of radioactive contaminations of the environment arising from mining activities. The figures and the conditions of their application are discussed, as well as the practical approaches developed for the radiological assessment of mining residues in the Wismut remediation programme and in the programme for the evaluation of residues due to former mining activities. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Sewage; Mines; Ores
1. Mining residues — a source of chronic radiation exposure for members of the public Ores of nonferrous metals and other minerals were brought from deeper geological strata to the surface by mining activities. These materials are often mineralized with uranium or 0531-5131/02 D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 3 1 - 5 1 3 1 ( 0 1 ) 0 0 5 2 7 - 1
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thorium and, therefore, the concentrations of these radionuclides and their decay products in both mining debris and, in particular, processing waste can be relatively high in comparison with the concentrations of these nuclides usually occurring in soils and surface near geological strata. In the past, waste from mining and processing was dumped in the environment without taking into consideration the radioactivity in these materials or aspects of radiological protection and thereby the working and living environment of man has been radioactively contaminated. In addition, during mining and processing of ores and minerals natural radionuclides were released into the environment by waste air and waste water resulting in a radioactive contamination of the environment, too. Because of the physical and chemical properties of the radionuclides, the radioactive contamination is long-standing and small changes can be expected over time only. Therefore, the radiation exposure due to mining residues and other environmental contamination due to mining activities is chronic. The dividing line between a man-made radiation exposure and the natural background exposure often is imperceptible since the radionuclides causing the ‘‘man-made’’ contamination occur also naturally. However, in many cases, radiation exposures are significantly increased compared to the natural background level, e.g. if contaminated grounds are used for agricultural purposes or gardening, abandoned sites were built on or waste from mining and processing is used for building.
2. Radiation exposure due to mining residues in the system of radiological protection control The radiation exposure due to residues of mining, processing and other human activities is classified as intervention situation. It has risen under a wide variety of circumstances, mostly due to operations prior to regulations of radiological protection or operations conducted under regulatory control considered inadequate from a present-day point of view. Intervention measures—in case of chronic exposures the measures are termed remediation—are justified only if the achievable benefit, e.g. the reduction in detriment resulting from the reduction in dose, exceeds the disadvantages, e.g. harm, costs including social costs to be attributable to the proposed measure (cost – benefits analysis). The calculation of both the dose to be averted by the proposed measure and the dose to be attributable to the measure itself are important components of the total assessment procedure. Therefore, the dose calculations must be carried out as realistic as possible otherwise hypothetical doses will be ‘averted’ or regarded as ‘harm’ and false interpretations of benefits and costs are the result. Besides, this approach is very costly because of the numerous aspects that have to be taken into account and we have to recognize that the results can be misunderstood by the public. According to the recommendations of the ICRP and IAEA, it is more appropriate for a complex remediation program to set up criteria (action levels) above which remedial actions normally should be taken and below which they should not. For chronic exposure situations, the action level is defined by the ICRP as a level of dose, dose rate, activity concentration or any other quantity above which remedial actions should be carried out. In establishing an action level, the advantages and disadvantages mentioned above and other pros and cons relevant for the programme proposed (e.g. political, economic and
E. Ettenhuber / International Congress Series 1225 (2002) 103–110
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social questions, acceptance by the public) have to be evaluated properly. A comprehensive survey of the situation (e.g. number of radioactively contaminated sites to be considered, dose levels, people affected) is the precondition for the evaluation that should be carried out in a more or less quantitative way. Remembering that the acceptance of a remediation by the public is an important point an action level can also be specified on the basis of an exposure level commonly evaluated as being acceptable. For a remediation programme of mining sites, this level of acceptance should not be derived from more or less hypothetical risk assumptions, it should rather be established taking into account the variation range of the natural background in the mining region. Such action levels do not contradict theoretical risk considerations. It has to be pointed out that the dose limit of 1 mSv per year in force in the system of radiological protection for practices for members of the public has been derived not only from risk assumptions but also from the comparison with the natural radiation exposure (excluding the exposure to radon). In establishing an action level on the basis of the natural background exposure, two approaches can be discussed: the action level can be set at the average or at the upper end of the naturally occurring range. When the average is used, we will have to accept that naturally occurring situations may be remedied if the background in a situation of concern is higher than the average and that unnecessary expenses result due to the overestimation of the situation. On the other hand, if the upper end of the normal variation range, e.g. the 95% percentile of the frequency distribution is established as an action level, a man-made contamination can be regarded as naturally and it will not be remedied.
3. Radiological assessment of mining residues in Germany 3.1. Situation in Germany Mining and ore processing goes back to the Middle Ages. Particularly in Saxopny and in the region around Mansfeld, uranium-bearing ores were mined and processed since then. Numerous mines, shafts, galleries, smelteries and other processing plants were in operation and countless dumps of mining debris and processing waste to be regarded as ‘radiation sources’ are the result. Immediately after World War II, the Soviet-owned stock company started the uranium production in East Germany. Later, this company was converted into a joint Soviet – German stock company (SDAG Wismut). At the beginning, in the post-war times, there was no consideration of the harm to the employees and of the impact on the environment and the population arising from mining activities. At that time, the well-known deposits in the ore mountains (e.g. near Aue and other places) were exploited. In the 1950s and 1960s, the uranium production was extended to other parts of East Germany. Large dumps of mining debris resulted and tailing ponds of considerable dimensions were used to dispose the milling waste from the production of 220,000 t of uranium. In total, about 8 10 8 t of waste were dumped in the environment. Although the SDAG Wismut was obliged to observe the German regulations of radiological protection in handling and disposing waste, the radiological protection with regard to the environment was observed only
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superficially and large areas were radioactively contaminated. After the unification, the uranium production was ceased for economic and other reasons and a complex programme has been started for decomissioning the mines, mills and other facilities used by the SDAG Wismut and for the remediation of sites. In the period up to the 1960s, many facilities, tailings basins and waste rock piles were abandoned or decommissioned by Wismut and were passed over to other enterprises or to communities. Since at that time, radiation exposure due to the waste of mining and milling was not yet an issue of any concern these residues have to be considered a source of serious radiation exposure, in particular, if waste and sites were used. In summary, one can say that both processes—the ore mining lasting for centuries and the uranium production—resulted in relevant radioactive contaminations of the environment and interventions for reasons of radiological protection have to be considered. 3.2. Principles of the radiological assessment Summarizing the results of a discussion on issues of topical interest in the field of radioecology, the National Commission on Radiological Protection (SSK) pointed out that action levels to be applied for limiting the radiation exposure due to both radon and mining residues should be established by figures at the upper end of the naturally occurring range. Below these levels, any remediation is not to be recommended [1]. Considering the situation in the mining regions, the SSK recommended an annual effective dose level of 1 mSv for the use of areas, buildings and dumps radioactively contaminated by mining in addition to the natural background level [2]. In addition, the SSK recommended measurable quantities to be applied as criteria for the radiological assessment of the terrestrial and aquatic exposure pathways in simple cases. They fulfill the dose criterion and can be applied in deciding on the use of land or groundwater only on the basis of measurements. The criteria of 0.2 and 1 Bq g 1 in soil or mining debris recommended in Ref. [2] are key figures and should be applied for deciding like this: if the specific activity of material does not exceed the level of 0.2 Bq g 1 the residue (e.g. a contaminated ground) can be used without restriction, in the range between 0.2 and 1.0 Bq g 1 additional criteria (e.g. the volume of material dumped, the area covered by contaminated materials) restrictions should be observed (e.g. it can be used only for forestry or as grassland). If the specific activity of the material exceeds the level of 1 Bq g 1 site-specific assessment have to be made in order to decide on the use or on the remediation. These criteria are also intended to enable a distinction to be made between areas which do not, and areas which might potentially require a remediation. Concerning the exposure to radon, the SSK recommends in Ref. [3], a separate criterion for the justification of remediation: if the source-related radon concentration (the outdoor radon concentration due to the exhalation of a waste rock heap or another residue of mining) assessed for the nearest residential areas does not exceed the level of 50 Bq m 3, a remediation because of the exposure to radon is not justified. The reason for establishing this concentration value as an action level is the intention that the indoor level of 250 Bq m 3 accepted by the SSK as the upper end of the normal concentration range occurring naturally [4] should not be significantly increased by ‘‘man-made’’ radon from outdoors.
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Since the source-related radon concentration can only be calculated site-specifically and such assessments have to be made for numerous residues and sites, the Commission recommends to measure the outdoor radon concentration in the residential areas of interest. Only in cases in which the annual average of the outdoor concentration exceeds the level of 80 Bq m 3—it is the upper end of normal geogenic radon concentrations outdoors in the mining areas—site-specific assessments should be made to estimate the contribution to the outdoor level due to the emission of the residue. In Ref. [2], the SSK recommended for the demonstration that if the effective dose level is not exceeded in case of a given contamination, conditions must be assumed as realistic as possible but sufficiently conservative and provided in Ref. [5], an approach to the dose calculation that can be applied practically. Two examples (identification of the realistic pathways and consideration of the natural background) are discussed in order to demonstrate how this requirement is translated into instructions for dose calculation. The exposure pathways are listed which are generally to be considered ‘‘relevant’’ for the exposure of the critical group. The SSK stresses that the actually relevant pathways for the exposure of the critical group in a case of interest should be selected from these. On the other hand, the SSK recommends to include additional pathways in the calculation procedure, if appropriate in exceptional cases. However, extreme habits of individuals possibly in exception cases should not be considered in identifying the relevant pathways since the consideration of these scenarios would be contrary to the principle of the critical group. For a realistic assessment, the dose calculation should be based on measurements of the contamination. Since the effective dose level refers to exposures due to mining activities and the radionuclides to be considered are the same which occur naturally, the natural background level has to be subtracted from the measurement to avoid an overestimation. To minimize the expenditures in estimating the natural background levels, the SSK recommends a threestep procedure: First, the calculation should be made based on the measurements without the subtraction of any background level. If the effective dose calculated exceeds the reference level, a generic level of environmental radioactivity recommended by the SSK should be subtracted and, only if the exposure calculated in this way still exceeds the reference level, site specific levels should be estimated and applied in order to calculate the effective dose realistically. 3.3. Residues and sites in the possession of Wismut The Wismut Act [6] prescribes that Wismut has to decommission the tailings basins, dumps and other facilities and to carry out remediations, if required. The decision can be made on the basis of site-specific assessments, since the database is sufficient for such assessment or it can be completed by specific investigations. The radiological assessment is made for each site of concern in the form of a dose calculation applying the approach recommended by the SSK. The criterion for the justification is the annual effective dose level of 1 mSv. Within the framework of the Wismut remediation programme the exposure to radon is included in the annual effective dose of 1 mSv for the justification of a remediation measure. The entire process is under the supervision of the authorities in the federal states which license individual remediation measure proposed.
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3.4. Residues and sites from past mining activities Unlike the information on the Wismut sites, the information on the residues and sites due to the early uranium production and the ore mining in the past was incomplete since this problem was poorly investigated in the past. A decision to consider remediations for all these sites generally had resulted in site-specific assessments for some thousands of waste heaps, sites, grounds, private properties, roads constructed with waste from mining, etc., possibly contaminated and required a lot of investigations, time and money. Therefore, the Federal Ministry decided to carry out an investigation programme to provide a comprehensive survey on the total radiological situation in the mining regions and to identify these residues and sites for which any remediation is not justified (nonrelevant residues and sites) and those which had to be regarded as sources of increased radiation exposure of the public and for which a remediation should be considered (relevant residues and sites). In view of the large number of residues and sites of concern, a step-wise procedure of investigations described in Refs. [7,8] has been developed with the intention of excluding as quickly as possible the residues for which a remediation is definitely not required. It was an important aspect for the local authorities. As a first step of investigations, 34 areas of former mining activities have been defined as ‘‘suspected areas’’ using information on regions where uranium ores and other ores with above-average concentrations of uranium were mined, as well as regions where the terrestrial gamma radiation is increased in comparison with the average level. For these areas, about 1500 km2, all available documentations, e.g. reports on relevant geological explorations, work reports of mines and processing plants, registers of mining authorities have been evaluated. Data and information that might be helpful for the radiological evaluation have been compiled. In this way, about 8000 mining residues of different kinds have been identified and registered in a data bank, most of them being waste rock piles. The total of areas covered by the residues amounts to about 73 km2, the total of areas with above-average gamma radiation to about 170 km2. Further investigations concentrated on these areas (‘‘investigation areas’’). However the data and information available after the first step of investigation did not yet permit the classification intended. Additional efforts to verify and complete the registered data and information were required. By field inspection the information on the state of objects, sites, etc., was updated and the data and information needed for the assessment were checked, revised and completed, if required to provide a standardized database. Screening measurements of the local gamma dose rate were included in this procedure. After that, a first classification was made evaluating in particular the local gamma dose rate measurements. Even at that stage of investigation about 57% of the residues and sites could be classified as ‘‘nonrelevant’’. Within the scope of the Federal Project only the rest (‘‘possibly relevant relics and sites’’) were investigated in greater detail and were subjected to specifically evolved measurement programmes. These final programmes provided comprehensive information requiring for the final assessment within the scope of the investigation programme. The recommended criteria of 0.2 and 1 Bq g 1 are again key figures and have been applied for the classification: if the specific activity of materials investigated exceeds the level of 1 Bq g 1, the residue or site is classified as relevant. If the specific activity of
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material does not exceed the level of 0.2 Bq g 1, the residue or site is classified as nonrelevant. In the range between 0.2 and 1.0 Bq g 1, the classification was carried out taking into account additional criteria, e.g. the volume of material dumped, the area covered by dumped materials and aspects of use. Criteria required for the evaluation of the local gamma dose rate measurements were derived from the figures of the specific activity taking into account conservative assumptions. These criteria were applied for the radiological assessment in combination with the criteria for the volume of materials, the covered area and, if any covers were existing, taking into account the thickness of the cover. The type of use was also a criterion for the classification. Based on this classification, the number of relevant residues or sites requiring site-specific assessments will be 500, most of them are dumps of mining debris. It is evident that the scope of site specific assessments can be substantially decreased. Since the measurements now available for the relevant sites are mostly sufficient for proper dose calculations, and the site specific assessments can be concentrated on the identification of the really relevant pathways.
4. Conclusions Mining activities can result in environmental contaminations and chronic radiation exposures requiring remediation measures. Principles of radiological protection have to be applied in decision-making for remediation. Because of the acceptance by the public, the action level required for the justification of individual remediation measures in a complex remediation programme should be established taking the natural background exposure into account. Separate action levels should be established for the evaluation of both the terrestrial and aquatic pathways and for the radon inhalation. The action level for the evaluation of the terrestrial and aquatic pathways should be established as annual effective dose because this approach gives more flexibility in the decision process and it can contribute to cost saving in a remediation programme. In addition, criteria, e.g. the specific activity of soil, concentrations of radionuclides in other environmental media can be helpful. They can be applied for quick decisions in clear situations on the basis of simple measurements and, in a complex investigation programme, for the identification of cases for which site specific assessment are indispensable.
References [1] SSK, Aktuelle radioo¨kologische Fragen des Strahlenschutzes, Vero¨ffentlichungen der Strahlenschutzkommission, Bd. 37, Gustav Fischer Verlag, 1995, p. 7. [2] SSK, Radiological protection principles concerning the safeguard, use or release of contaminated materials, buildings, areas or dumps from uranium mining, Recommendations of the Commission on Radiological Protection with Explanations, Vero¨ffentlichungen der Strahlenschutzkommission, Bd. 23, Gustav Fischer Verlag, 1992. [3] SSK, Principles for the assessment of radiation exposure as a result of radon emissions from mining residues in uranium mining areas, in: Vero¨ffentlichungen der Strahlenschutzkommission, Bd. 36, Gustav Fischer Verlag, 1994, p. 153. [4] SSK, Radiation protection principles to limit the radiation exposure from radon and its decay products in buildings, Vero¨ffentlichungen der Strahlenschutzkommission, Bd. 36, Seite 129.
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[5] SSK, Berechnungsgrundlagen zur Ermittlung der Strahlenexposition infolge bergbaubedingter Umweltradioaktivita¨t, in press. [6] Federal Government, Gesetz u¨ber die Beendigung der Ta¨tigkeit der SDAG Wismut vom 12, Dezember 1991, BGBl. II Nr. 31 vom 17, Dezember 1991, pp. 1138 – 1144. [7] BfS, Radiologische Erfassung, Untersuchung und Bewertung bergbaulicher Altlasten-Altlastenkataster-, BfS Schrift 8/92. [8] BfS, Radiologische Erfassung, Untersuchung und Bewertung bergbaulicher Altlasten-Altlastenkataster-Bericht zu zweiten Teilprojekt, BfS-SCHR-17/98.
Investigations and radiological assessments of mining residues in Germany E. Ettenhuber Department for Applied Radiation Protection, Federal Office for Radiation Protection, 10318 Berlin, Germany
Abstract For centuries, exhaust air and sewage were released from mines and processing facilities into the environment, and mining debris and waste from ore processing were dumped there. The concentrations of naturally occurring radionuclides can be considerably increased compared to soil and surface-near rocks and significantly increased radiation exposures can result for members of the public. In addition, measures of radiological protection have to be considered in many cases. Since the situation has arisen due to operation prior to regulations of radiological protection or operations conducted under inadequate radiological protection control, it is categorized as intervention situation. The principles for justifying intervention measures and for establishing action levels to be applied in remediation programmes for mining residues are discussed. Since the contamination of mining sites results from naturally occurring radionuclides, the natural background exposure should be taken into account in establishing appropriate action levels. Following the principle that radiation exposures being in normally occurring natural range do not require protection measures, the National Commission on Radiological Protection recommended criteria for the justification of remediation measures in case of radioactive contaminations of the environment arising from mining activities. The figures and the conditions of their application are discussed, as well as the practical approaches developed for the radiological assessment of mining residues in the Wismut remediation programme and in the programme for the evaluation of residues due to former mining activities. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Sewage; Mines; Ores
1. Mining residues — a source of chronic radiation exposure for members of the public Ores of nonferrous metals and other minerals were brought from deeper geological strata to the surface by mining activities. These materials are often mineralized with uranium or 0531-5131/02 D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 3 1 - 5 1 3 1 ( 0 1 ) 0 0 5 2 7 - 1
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thorium and, therefore, the concentrations of these radionuclides and their decay products in both mining debris and, in particular, processing waste can be relatively high in comparison with the concentrations of these nuclides usually occurring in soils and surface near geological strata. In the past, waste from mining and processing was dumped in the environment without taking into consideration the radioactivity in these materials or aspects of radiological protection and thereby the working and living environment of man has been radioactively contaminated. In addition, during mining and processing of ores and minerals natural radionuclides were released into the environment by waste air and waste water resulting in a radioactive contamination of the environment, too. Because of the physical and chemical properties of the radionuclides, the radioactive contamination is long-standing and small changes can be expected over time only. Therefore, the radiation exposure due to mining residues and other environmental contamination due to mining activities is chronic. The dividing line between a man-made radiation exposure and the natural background exposure often is imperceptible since the radionuclides causing the ‘‘man-made’’ contamination occur also naturally. However, in many cases, radiation exposures are significantly increased compared to the natural background level, e.g. if contaminated grounds are used for agricultural purposes or gardening, abandoned sites were built on or waste from mining and processing is used for building.
2. Radiation exposure due to mining residues in the system of radiological protection control The radiation exposure due to residues of mining, processing and other human activities is classified as intervention situation. It has risen under a wide variety of circumstances, mostly due to operations prior to regulations of radiological protection or operations conducted under regulatory control considered inadequate from a present-day point of view. Intervention measures—in case of chronic exposures the measures are termed remediation—are justified only if the achievable benefit, e.g. the reduction in detriment resulting from the reduction in dose, exceeds the disadvantages, e.g. harm, costs including social costs to be attributable to the proposed measure (cost – benefits analysis). The calculation of both the dose to be averted by the proposed measure and the dose to be attributable to the measure itself are important components of the total assessment procedure. Therefore, the dose calculations must be carried out as realistic as possible otherwise hypothetical doses will be ‘averted’ or regarded as ‘harm’ and false interpretations of benefits and costs are the result. Besides, this approach is very costly because of the numerous aspects that have to be taken into account and we have to recognize that the results can be misunderstood by the public. According to the recommendations of the ICRP and IAEA, it is more appropriate for a complex remediation program to set up criteria (action levels) above which remedial actions normally should be taken and below which they should not. For chronic exposure situations, the action level is defined by the ICRP as a level of dose, dose rate, activity concentration or any other quantity above which remedial actions should be carried out. In establishing an action level, the advantages and disadvantages mentioned above and other pros and cons relevant for the programme proposed (e.g. political, economic and
E. Ettenhuber / International Congress Series 1225 (2002) 103–110
105
social questions, acceptance by the public) have to be evaluated properly. A comprehensive survey of the situation (e.g. number of radioactively contaminated sites to be considered, dose levels, people affected) is the precondition for the evaluation that should be carried out in a more or less quantitative way. Remembering that the acceptance of a remediation by the public is an important point an action level can also be specified on the basis of an exposure level commonly evaluated as being acceptable. For a remediation programme of mining sites, this level of acceptance should not be derived from more or less hypothetical risk assumptions, it should rather be established taking into account the variation range of the natural background in the mining region. Such action levels do not contradict theoretical risk considerations. It has to be pointed out that the dose limit of 1 mSv per year in force in the system of radiological protection for practices for members of the public has been derived not only from risk assumptions but also from the comparison with the natural radiation exposure (excluding the exposure to radon). In establishing an action level on the basis of the natural background exposure, two approaches can be discussed: the action level can be set at the average or at the upper end of the naturally occurring range. When the average is used, we will have to accept that naturally occurring situations may be remedied if the background in a situation of concern is higher than the average and that unnecessary expenses result due to the overestimation of the situation. On the other hand, if the upper end of the normal variation range, e.g. the 95% percentile of the frequency distribution is established as an action level, a man-made contamination can be regarded as naturally and it will not be remedied.
3. Radiological assessment of mining residues in Germany 3.1. Situation in Germany Mining and ore processing goes back to the Middle Ages. Particularly in Saxopny and in the region around Mansfeld, uranium-bearing ores were mined and processed since then. Numerous mines, shafts, galleries, smelteries and other processing plants were in operation and countless dumps of mining debris and processing waste to be regarded as ‘radiation sources’ are the result. Immediately after World War II, the Soviet-owned stock company started the uranium production in East Germany. Later, this company was converted into a joint Soviet – German stock company (SDAG Wismut). At the beginning, in the post-war times, there was no consideration of the harm to the employees and of the impact on the environment and the population arising from mining activities. At that time, the well-known deposits in the ore mountains (e.g. near Aue and other places) were exploited. In the 1950s and 1960s, the uranium production was extended to other parts of East Germany. Large dumps of mining debris resulted and tailing ponds of considerable dimensions were used to dispose the milling waste from the production of 220,000 t of uranium. In total, about 8 10 8 t of waste were dumped in the environment. Although the SDAG Wismut was obliged to observe the German regulations of radiological protection in handling and disposing waste, the radiological protection with regard to the environment was observed only
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superficially and large areas were radioactively contaminated. After the unification, the uranium production was ceased for economic and other reasons and a complex programme has been started for decomissioning the mines, mills and other facilities used by the SDAG Wismut and for the remediation of sites. In the period up to the 1960s, many facilities, tailings basins and waste rock piles were abandoned or decommissioned by Wismut and were passed over to other enterprises or to communities. Since at that time, radiation exposure due to the waste of mining and milling was not yet an issue of any concern these residues have to be considered a source of serious radiation exposure, in particular, if waste and sites were used. In summary, one can say that both processes—the ore mining lasting for centuries and the uranium production—resulted in relevant radioactive contaminations of the environment and interventions for reasons of radiological protection have to be considered. 3.2. Principles of the radiological assessment Summarizing the results of a discussion on issues of topical interest in the field of radioecology, the National Commission on Radiological Protection (SSK) pointed out that action levels to be applied for limiting the radiation exposure due to both radon and mining residues should be established by figures at the upper end of the naturally occurring range. Below these levels, any remediation is not to be recommended [1]. Considering the situation in the mining regions, the SSK recommended an annual effective dose level of 1 mSv for the use of areas, buildings and dumps radioactively contaminated by mining in addition to the natural background level [2]. In addition, the SSK recommended measurable quantities to be applied as criteria for the radiological assessment of the terrestrial and aquatic exposure pathways in simple cases. They fulfill the dose criterion and can be applied in deciding on the use of land or groundwater only on the basis of measurements. The criteria of 0.2 and 1 Bq g 1 in soil or mining debris recommended in Ref. [2] are key figures and should be applied for deciding like this: if the specific activity of material does not exceed the level of 0.2 Bq g 1 the residue (e.g. a contaminated ground) can be used without restriction, in the range between 0.2 and 1.0 Bq g 1 additional criteria (e.g. the volume of material dumped, the area covered by contaminated materials) restrictions should be observed (e.g. it can be used only for forestry or as grassland). If the specific activity of the material exceeds the level of 1 Bq g 1 site-specific assessment have to be made in order to decide on the use or on the remediation. These criteria are also intended to enable a distinction to be made between areas which do not, and areas which might potentially require a remediation. Concerning the exposure to radon, the SSK recommends in Ref. [3], a separate criterion for the justification of remediation: if the source-related radon concentration (the outdoor radon concentration due to the exhalation of a waste rock heap or another residue of mining) assessed for the nearest residential areas does not exceed the level of 50 Bq m 3, a remediation because of the exposure to radon is not justified. The reason for establishing this concentration value as an action level is the intention that the indoor level of 250 Bq m 3 accepted by the SSK as the upper end of the normal concentration range occurring naturally [4] should not be significantly increased by ‘‘man-made’’ radon from outdoors.
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Since the source-related radon concentration can only be calculated site-specifically and such assessments have to be made for numerous residues and sites, the Commission recommends to measure the outdoor radon concentration in the residential areas of interest. Only in cases in which the annual average of the outdoor concentration exceeds the level of 80 Bq m 3—it is the upper end of normal geogenic radon concentrations outdoors in the mining areas—site-specific assessments should be made to estimate the contribution to the outdoor level due to the emission of the residue. In Ref. [2], the SSK recommended for the demonstration that if the effective dose level is not exceeded in case of a given contamination, conditions must be assumed as realistic as possible but sufficiently conservative and provided in Ref. [5], an approach to the dose calculation that can be applied practically. Two examples (identification of the realistic pathways and consideration of the natural background) are discussed in order to demonstrate how this requirement is translated into instructions for dose calculation. The exposure pathways are listed which are generally to be considered ‘‘relevant’’ for the exposure of the critical group. The SSK stresses that the actually relevant pathways for the exposure of the critical group in a case of interest should be selected from these. On the other hand, the SSK recommends to include additional pathways in the calculation procedure, if appropriate in exceptional cases. However, extreme habits of individuals possibly in exception cases should not be considered in identifying the relevant pathways since the consideration of these scenarios would be contrary to the principle of the critical group. For a realistic assessment, the dose calculation should be based on measurements of the contamination. Since the effective dose level refers to exposures due to mining activities and the radionuclides to be considered are the same which occur naturally, the natural background level has to be subtracted from the measurement to avoid an overestimation. To minimize the expenditures in estimating the natural background levels, the SSK recommends a threestep procedure: First, the calculation should be made based on the measurements without the subtraction of any background level. If the effective dose calculated exceeds the reference level, a generic level of environmental radioactivity recommended by the SSK should be subtracted and, only if the exposure calculated in this way still exceeds the reference level, site specific levels should be estimated and applied in order to calculate the effective dose realistically. 3.3. Residues and sites in the possession of Wismut The Wismut Act [6] prescribes that Wismut has to decommission the tailings basins, dumps and other facilities and to carry out remediations, if required. The decision can be made on the basis of site-specific assessments, since the database is sufficient for such assessment or it can be completed by specific investigations. The radiological assessment is made for each site of concern in the form of a dose calculation applying the approach recommended by the SSK. The criterion for the justification is the annual effective dose level of 1 mSv. Within the framework of the Wismut remediation programme the exposure to radon is included in the annual effective dose of 1 mSv for the justification of a remediation measure. The entire process is under the supervision of the authorities in the federal states which license individual remediation measure proposed.
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3.4. Residues and sites from past mining activities Unlike the information on the Wismut sites, the information on the residues and sites due to the early uranium production and the ore mining in the past was incomplete since this problem was poorly investigated in the past. A decision to consider remediations for all these sites generally had resulted in site-specific assessments for some thousands of waste heaps, sites, grounds, private properties, roads constructed with waste from mining, etc., possibly contaminated and required a lot of investigations, time and money. Therefore, the Federal Ministry decided to carry out an investigation programme to provide a comprehensive survey on the total radiological situation in the mining regions and to identify these residues and sites for which any remediation is not justified (nonrelevant residues and sites) and those which had to be regarded as sources of increased radiation exposure of the public and for which a remediation should be considered (relevant residues and sites). In view of the large number of residues and sites of concern, a step-wise procedure of investigations described in Refs. [7,8] has been developed with the intention of excluding as quickly as possible the residues for which a remediation is definitely not required. It was an important aspect for the local authorities. As a first step of investigations, 34 areas of former mining activities have been defined as ‘‘suspected areas’’ using information on regions where uranium ores and other ores with above-average concentrations of uranium were mined, as well as regions where the terrestrial gamma radiation is increased in comparison with the average level. For these areas, about 1500 km2, all available documentations, e.g. reports on relevant geological explorations, work reports of mines and processing plants, registers of mining authorities have been evaluated. Data and information that might be helpful for the radiological evaluation have been compiled. In this way, about 8000 mining residues of different kinds have been identified and registered in a data bank, most of them being waste rock piles. The total of areas covered by the residues amounts to about 73 km2, the total of areas with above-average gamma radiation to about 170 km2. Further investigations concentrated on these areas (‘‘investigation areas’’). However the data and information available after the first step of investigation did not yet permit the classification intended. Additional efforts to verify and complete the registered data and information were required. By field inspection the information on the state of objects, sites, etc., was updated and the data and information needed for the assessment were checked, revised and completed, if required to provide a standardized database. Screening measurements of the local gamma dose rate were included in this procedure. After that, a first classification was made evaluating in particular the local gamma dose rate measurements. Even at that stage of investigation about 57% of the residues and sites could be classified as ‘‘nonrelevant’’. Within the scope of the Federal Project only the rest (‘‘possibly relevant relics and sites’’) were investigated in greater detail and were subjected to specifically evolved measurement programmes. These final programmes provided comprehensive information requiring for the final assessment within the scope of the investigation programme. The recommended criteria of 0.2 and 1 Bq g 1 are again key figures and have been applied for the classification: if the specific activity of materials investigated exceeds the level of 1 Bq g 1, the residue or site is classified as relevant. If the specific activity of
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material does not exceed the level of 0.2 Bq g 1, the residue or site is classified as nonrelevant. In the range between 0.2 and 1.0 Bq g 1, the classification was carried out taking into account additional criteria, e.g. the volume of material dumped, the area covered by dumped materials and aspects of use. Criteria required for the evaluation of the local gamma dose rate measurements were derived from the figures of the specific activity taking into account conservative assumptions. These criteria were applied for the radiological assessment in combination with the criteria for the volume of materials, the covered area and, if any covers were existing, taking into account the thickness of the cover. The type of use was also a criterion for the classification. Based on this classification, the number of relevant residues or sites requiring site-specific assessments will be 500, most of them are dumps of mining debris. It is evident that the scope of site specific assessments can be substantially decreased. Since the measurements now available for the relevant sites are mostly sufficient for proper dose calculations, and the site specific assessments can be concentrated on the identification of the really relevant pathways.
4. Conclusions Mining activities can result in environmental contaminations and chronic radiation exposures requiring remediation measures. Principles of radiological protection have to be applied in decision-making for remediation. Because of the acceptance by the public, the action level required for the justification of individual remediation measures in a complex remediation programme should be established taking the natural background exposure into account. Separate action levels should be established for the evaluation of both the terrestrial and aquatic pathways and for the radon inhalation. The action level for the evaluation of the terrestrial and aquatic pathways should be established as annual effective dose because this approach gives more flexibility in the decision process and it can contribute to cost saving in a remediation programme. In addition, criteria, e.g. the specific activity of soil, concentrations of radionuclides in other environmental media can be helpful. They can be applied for quick decisions in clear situations on the basis of simple measurements and, in a complex investigation programme, for the identification of cases for which site specific assessment are indispensable.
References [1] SSK, Aktuelle radioo¨kologische Fragen des Strahlenschutzes, Vero¨ffentlichungen der Strahlenschutzkommission, Bd. 37, Gustav Fischer Verlag, 1995, p. 7. [2] SSK, Radiological protection principles concerning the safeguard, use or release of contaminated materials, buildings, areas or dumps from uranium mining, Recommendations of the Commission on Radiological Protection with Explanations, Vero¨ffentlichungen der Strahlenschutzkommission, Bd. 23, Gustav Fischer Verlag, 1992. [3] SSK, Principles for the assessment of radiation exposure as a result of radon emissions from mining residues in uranium mining areas, in: Vero¨ffentlichungen der Strahlenschutzkommission, Bd. 36, Gustav Fischer Verlag, 1994, p. 153. [4] SSK, Radiation protection principles to limit the radiation exposure from radon and its decay products in buildings, Vero¨ffentlichungen der Strahlenschutzkommission, Bd. 36, Seite 129.
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[5] SSK, Berechnungsgrundlagen zur Ermittlung der Strahlenexposition infolge bergbaubedingter Umweltradioaktivita¨t, in press. [6] Federal Government, Gesetz u¨ber die Beendigung der Ta¨tigkeit der SDAG Wismut vom 12, Dezember 1991, BGBl. II Nr. 31 vom 17, Dezember 1991, pp. 1138 – 1144. [7] BfS, Radiologische Erfassung, Untersuchung und Bewertung bergbaulicher Altlasten-Altlastenkataster-, BfS Schrift 8/92. [8] BfS, Radiologische Erfassung, Untersuchung und Bewertung bergbaulicher Altlasten-Altlastenkataster-Bericht zu zweiten Teilprojekt, BfS-SCHR-17/98.