K/O oOøoH^te

Aud Venke Sundal

Geologic influence on indoor radon concentrations and gamma radiation levels in Norwegian dwellings

A? 0 1 M STØ©? \

Doctor scientiarum thesis Department of Earth Science, University of' September 2003 Aud Venke Sundal

Geologic influence on indoor radon concentrations and gamma radiation levels in Norwegian dwellings

Doctor scientiarum thesis Department of "Earth Science, University of'Bergen September 2003 Contents

Preface and acknowledgements

Summary

Introduction • Background • Presentation of papers • Synthesis • Future work • References

Paper I Sundal AV, Henriksen H, Soldal O «fe Strand T The influence ofgeological factors on indoor radon concentrations in . Submitted to The Science of the Total Environment, 2003.

Paper II Sundal AV, Henriksen H, Lauritzen SE, Soldal O, Strand T & Valen V. Geological and geochemical factors affecting radon concentrations in dwellings located on permeable glacial sediments - a case study from , Norway. Submitted to Environmental Geology, 2003.

Paper III Sundal AV & Strand T. Indoor gamma radiation and radon concentrations in a Norwegian carbonatite area. Submitted to the Journal of Environmental Radioactivity, 2003. Preface and acknowledgements

The work presented in this thesis was financed by a three years doctoral scholarship from the Research Council of Norway. The project was carried out at the Department of Earth Science, University of Bergen, with Professor Stein-Erik Lauritzen as supervisor and Professor Terje Strand (Department of Physics, University of and the Norwegian Radiation Protection Authority), Oddmund Soldal (Interconsult ASA) and Vidar Valen (Sørlandskonsult A/S) as co-supervisors. The work has benefited from several stays at the Norwegian Radiation Protection Authority, Oslo, and a 3 months visit at the Department of Chemistry, University of Sydney, Australia.

I would like to thank my supervisors for the help and encouragement 1 have received during the preparation of this thesis. 1 am also indebted to the laboratory staff at the Department of Earth Science, University of Bergen and the Norwegian Radiation Protection Authority for their assistance during the laboratory work. Associated professor Julia James organised my stay at the University of Sydney, and the discussions and comments from her and her colleagues are highly appreciated. I would also like to thank Helge Henriksen ( og Fjordane University College) for teaching me about statistics and fellow students and colleagues at the Department of Earth Science for providing a great social environment. Finally, I am especially grateful for all the support I have received from my family.

Bergen, September 2003

Aud Venke Sundal Summary

Indoor radon levels in 1618 Norwegian dwellings located in different geological settings were compared with geological information in order to determine potential correlations between geological factors and indoor radon concentrations in Norway and to establish whether geological information is useful in radon risk analysis. In two geographically limited areas, Kinsarvik and Fen, detailed geological and geochemical investigations were carried out in order to explain their elevated natural radiation environment.

Significant correlations between geology and indoor radon concentrations in Norway are found when the properties of both the bedrock and the overburden are taken into account. Areas of high radon risk in Norway include 1) exposed bedrock with elevated levels of radium (mainly alum shale and granites) and b) highly permeable unconsolidated sediments derived from all rock types (mainly glaciofluvial and fluvial deposits) and moderately permeable sediments containing radium rich rock fragments (mainly basal till). More than 20 % of Norwegian dwellings located in the high risk areas can be expected to contain radon levels exceeding 200 Bq/m3.

The elevated radon risk related to permeable building grounds is illustrated in Kinsarvik where the highly permeable sediments and the large vadose zone underlying the Huse residential area enable the transport of radon from large volumes into the dwellings resulting in enhanced indoor radon concentrations. Subterranean air-flows caused by temperature/pressure differences between soil air and atmospheric air and elevations differences within the Huse area are shown to strongly affect the annual variations in indoor radon concentrations. The marked contrasts in radon risk potential between different types of building grounds are clearly illustrated in the Fen area where outcrops of the radium rich Fen carbonatites represent areas of high radon risk while only low levels of both indoor radon concentrations and indoor gamma dose rates are measured in the areas covered by nearly impermeable silt and clay deposits. Indoor gamma dose rates as high as 620 nGy/h are obtained in the areas of exposed carbonatites, primarily due to enhanced thorium concentrations in these rock types.

The observed correlations between geological factors and indoor radon concentrations in Norway indicate that geological information is a useful tool in radon risk analysis. Resources can be concentrated to regions of high geologic radon potential when screening programs are planned, and efficient follow-up surveys can be established based on geological data in combination with radon measurements in a representative sample of the building stock. The observed contrasts in radon risk potential between different types of building grounds also enable the prediction of radon risk in areas which are not currently inhabited. 1

Introduction

Geologic influence on indoor radon concentrations and gamma radiation levels in Norwegian dwellings

Background Norwegian housing stock was calculated to 88 Bq/m3 (Strand et al., 2001). In accordance with international recommendations, Natural ionising radiation is the largest Norwegian householders are advised to contributor to the radiation dose received undertake simple and inexpensive remedial by the world's population (UNSCEAR, measures in dwellings where the annual mean 1993). The radiation dose from natural radon concentration in the living area ranges sources is generated by radioelements in from 200 Bq/m3 to 400 Bq/m3 (NRPA, 1995). diet and inhaled radon and radon progenies If the radon levels exceed 400 Bq/m3, remedial (internal exposure) as well as cosmic rays work is recommended until the levels have and gamma rays emitted from potassium-40 been brought below 200 Bq/m3. The results and members of the uranium and thorium from the national study showed that 9 % of decay chains in the crust of the earth and in Norwegian dwellings have annual average building materials (external exposure). radon concentrations exceeding 200 Bq/mJ, Doses from the inhalation of radon and its and 3 % of the dwellings have radon levels in decay products in dwellings are much excess of 400 Bq/m3 Out of a housing stock greater than those from all other of 1,8 million units, these figures correspond to components of natural radiation 160 000 and 50 000 dwellings, respectively. (UNSCEAR, 1993). Based on numerous studies of lung Some of the world's highest cancer in radon-exposed underground miners average indoor radon concentrations have in several countries, radon is classified as a been registered in Norway and other Nordic human carcinogen (IARC, 1988). Inhalation countries (Swedjemark et al., 1993; Arvela of radon and radon decay products is et al., 1993; Strand et al., 2001). Based on considered to be the leading cause of lung the results from the most recent national cancer after tobacco smoking. Exposure to study of indoor radon levels in Norway, radon and its progenies is estimated to be including nearly 29 000 dwellings, the responsible for 100-300 lung cancer cases (5- annual mean radon concentration in the 2

15 % of the total) annually in Norway carried out by the Norwegian Radiation (NRPA, 1996). Protection Authority (NRPA), and so far Sources of radon gas in indoor air information on indoor radon levels in are the building ground, building materials approximately 50 000 Norwegian dwellings and household water. Studies have has been compiled in the national radon revealed that the entry of radon from the database at NRPA (Strand et al., 1992; Strand building ground through the building et al., 2001). A number of publicity construction is the dominant source of campaigns have been developed to improve indoor radon in Norwegian dwellings radon awareness amongst the general (Stranden, 1987). Norwegian dwellings are population and professional bodies involved in primarily made from wooden materials the housing market, and in 1999, a financial which have low concentrations of support arrangement was established in order radionuclides, and concrete and brick to encourage householders to remediate high manufactured in Norway have also been radon levels. Still, a major proportion of reported to contain low levels of Norwegian dwellings with unacceptably high radioactivity (Stranden, 1979). Since 87 % radon levels are yet to be identified, and of the Norwegian population is supplied by remedial work has so far only been undertaken water from surface water sources with low in a small proportion of the registered housings levels of radon, the contribution to indoor with enhanced radon levels. air from household water is also generally The only way to determine radon low. Significant amounts of radon to levels accurately in individual homes is by indoor air can, however, arise from making measurements in indoor air. High-risk domestic water from private drilled bedrock areas of indoor radon can, however, be wells (Strand et ah, 1998). identified using different approaches; by National radon programs have been measuring radon concentrations in a implemented in most European and North sufficiently large sample of existing dwellings, American countries in order to identify by studying the geological factors influencing buildings with radon concentrations indoor radon levels, or by a combination of exceeding the adopted action levels, to offer indoor radon measurements and knowledge advice and encouragement to the about geology and building characteristics householders to reduce the high radon (ICRP, 1993). The use of geological levels and to prevent new buildings to be information is only justifiable if significant constructed in such a way that the annual correlations between geological factors and average radon concentration exceeds the indoor radon levels in a region are established. action limits. In Norway, several large- In and Finland, where bedrock and scale indoor radon surveys have been overburden characteristics are comparable to 3

those prevailing in Norway, indoor radon scales. In the first part of the work, indoor concentrations and geology have been radon levels in 1618 Norwegian dwellings found to be related, and geological located in different geological settings were information has been widely used in the compared with geological information. The prediction of radon risk (Aakerblom et al., classification of the building ground was 1988; Castren et al., 1992). In Norway, largely based on existing geological data since studies also indicate that correlations large-scale surveys do not allow detailed between indoor radon levels and geological investigations at each building site. In the features exist (Stranden et al., 1985; second part of this work, detailed geological Stranden, 1987; Stranden & Strand, 1988), and geochemical investigations were carricd but a more extensive study of the geological out in two geographically limited areas in influence on indoor radon in dwellings order to explain the observed exceptional located in different geological settings was conditions of natural radiation; the desirable in order to determine whether anomalously high indoor radon levels and geological information is useful in radon seasonal and geographical variations in indoor risk analysis. radon in the Kinsarvik area and the enhanced The main purpose of the present indoor gamma radiation and radon work has been to determine potential concentrations in the Fen area. correlations between geological factors and indoor radon concentrations in Norway and to establish whether the correlations, if any, Presentation of papers are strong enough to be useful in radon risk analysis. In regions where marked Paper I contrasts in geologic radon potential exists, and areas of high and low radon risk can be Sundal AV, Henriksen H, Soldal O & Strand determined in a relatively simple and cost- T. The influence of geological factors on efficient manner, geological information is indoor radon concentrations in Norway. a valuable tool for identifying high radon Submitted to The Science of the Total risk building grounds. However, if no Environment, 2003. obvious contrast in geologic radon potential is observed, assessments of radon risk Paper I discusses the results of a comparison based on geological information are not between geologic data and indoor radon recommended. concentrations in 1618 Norwegian dwellings. The search for correlations between The dwellings were selected from a wide range geology and indoor radon concentrations in of geological settings in order to investigate this study has been carried out at different the influence of geology on indoor radon levels 4

and to determine whether geological in radon potential between different types of information is a valuable tool for building grounds observed in this study identifying high radon risk building indicates that geological information is useful grounds. Indoor radon data from the 2000- in radon risk analysis. By concentrating 2001 national indoor radon study carried resources to the areas of high geologic radon out by the Norwegian Radiation Protection potential when indoor radon screening Authority were used for the comparison. programs and follow up surveys are planned, The building ground classification was the identification of dwellings with elevated largely based on existing geological data, indoor radon levels can be speeded up. The but additional geological information was observed correlations between indoor radon collected by fieldwork. A comparison of and geology also enable the identification of indoor radon concentrations and areas where preventative measures against information on house construction and radon must be taken in future buildings. ventilation habits was also included in the The results indicate that several study in order to search for correlations parameters related to building construction and between these factors and indoor radon ventilation habits also affect indoor radon concentrations in Norway. concentrations in Norway. The factors found The dataset revealed that to have a statistically significant association permeability and radium content of the with indoor radon levels in the present building ground are important indicators of investigation are ventilation system, aeration indoor radon concentrations. Based on habits, and floor level of the room where the these factors, an estimate of the radon measurements were carried out. potential of an area can be given. Areas of high radon risk in Norway are characterised by 1) exposed bedrock with elevated levels Paper II of radium, 2) highly permeable unconsolidated sediments derived from all Sundal AV, Henriksen H, Lauritzen SE, Soldal rock types, or 3) moderately permeable O, Strand T & Valen V. Geological and sediments containing radium rich rock geochemical factors affecting radon fragments. The primary radon source rocks concentrations in dwellings located on in Norway are the Cambrian-Ordovician permeable glacial sediments - a case study alum shale and uranium rich granites of from Kinsarvik, Norway. Submitted to varying ages. Environmental Geology, 2003. Geological parameters can not provide accurate estimates of radon levels Paper II focuses on the geological processes in existing homes, but the marked contrast causing the very high indoor radon 5

concentrations and the seasonal and building constructions are exposed to large geographically changes in indoor radon volumes of readily movable soil air resulting in observed in the Kinsarvik area of Western high indoor radon levels. Norway. Indoor radon measurements The investigation carried out in performed during 1996-1997 in a Kinsarvik revealed that general correction residential area located on an extensive ice factors for estimating the annual average marginal deposit in Kinsarvik revealed indoor radon concentration are not applicable indoor radon concentrations of more than in areas where temperature/pressure driven air 3 40 000 Bq/m , and annual variations in flows are likely to occur. In order to obtain a indoor radon concentrations were found to correct estimate of the annual average indoor deviate significantly from the results radon concentration in dwellings located on obtained from a previous large-scale study this type of building ground, indoor radon of annual indoor radon variations in measurements must be performed both in Norway. summer and in winter. Assessments of indoor Geochemical analyses of bedrock, radon concentrations based on single soil gas groundwater and sediments and measurements without a general understanding measurements of soil radon concentrations of the geology in the area should be avoided. revealed that the indoor radon The high indoor radon levels in concentrations in the Huse area are strongly Kinsarvik received wide media attention and affected by subterranean air-flows caused contributed to an increased awareness of the by elevation differences and differences in health risk related to indoor radon exposures in temperature/pressure between soil air and Norway. atmospheric air. The air-flows concentrate the available radon-laden soil air towards the upper part of the ice marginal moraine Paper III in winter while the lower part is ventilated Sundal AV & Strand T. Indoor gamma by atmospheric air. In summer, the radiation and radon concentrations in a situation is reversed. The indoor radon gas Norwegian carbonatite area. Submitted to is derived from the glacial sediments Journal of Environmental Radioactivity, 2003. containing normal to high uranium concentrations. The coarse-grained glacial Paper III discusses the results of a study of sediments are covered by finer sediments in indoor gamma radiation levels and radon the residential area but exposed in the concentrations in the Fen area of carbonatite topographic upper and lower end of the ice and alkaline silicate rocks in the southern part marginal deposit. Since most of the of Norway. The Fen area has been famous for dwellings in the Huse area have cellars, the 6

its rare rock association since the beginning radiation in the areas where low permeable silt of the last century, and during the last and clay deposits cover the bedrock surface. decades attention has also been drawn to A major landfill and many piles of the area due to its elevated natural radiation waste rock from iron mining activities are environment. In the present study, indoor present in the north eastern part of the Fen gamma radiation levels and radon area. Thorium concentrations between 4000 concentrations in 95 wooden dwellings and 5000 Bq/kg are obtained for this material, were measured using thermoluminescence and measurements of gamma radiation above dosimeters and CR-39 alpha track plastic the waste rock revealed ambient dose detectors, respectively, and a thorough equivalent rates of 3-5 pSv/h. So far, the analysis of the indoor data with regard to waste material has not been secured, and geological factors was performed. remedial measures like covering the waste rock The results revealed a strong with clay layers and restricting the building geologic control on indoor gamma radiation activity in the affected area are currently levels and radon concentrations in the Fen considered. area. Enhanced levels of thorium and slightly elevated levels of radium in the carbonatites are responsible for the highest Synthesis gamma dose rates ever reported from wooden houses in Norway. An average Significant correlations between geology and indoor gamma dose rate of 200 nGy/h and a indoor radon concentrations in Norway are maximum of 620 nGy/h were reported from found when the properties of both the bedrock dwellings located on exposed surfaces of and the overburden are taken into account the most thorium-rich carbonatite. Using (paper 1). The indoor radon risk clearly normal conversion factors, these values increases in areas where radium rich bedrock correspond to effective dose equivalents of outcrops and in areas where radium rich rock 1.0 and 3.0 mSv/year, respectively. The fragments are incorporated into the group of dwellings located on exposed overburden, but high radon risk is not always surfaces of carbonatites also has enhanced related to high radium content of the building levels of indoor radon compared to the ground. A significant proportion of average for the country. Due to the high Norwegian dwellings are located on permeable radiation dose to local residents caused by unconsolidated sediments, and high terrestrial gamma radiation in this area, permeability of the building ground favours the special efforts should be made to reduce the transport of radon from its source to the indoor radon concentrations. Low readings building construction. Consequently, were obtained for radon and gamma 7

substantial layers of highly permeable indoor radon concentrations by concentrating sediments like fluvial and glaciofluvial the available radon-laden soil air to the deposits represent areas of high radon risk topographical highest part of the ice marginal even if the radium content of the material is deposit in winter and to the topographical low (figure 1). Moderately permeable lower part in summer. The results imply that sediments like basal tills must also be in areas where air movement in the ground is regarded as high risk building grounds if likely to occur, estimates of annual average they contain radium rich rock fragments. indoor radon concentrations and decisions on Unless the water table is situated close to remedial measures should be based on a the building construction, more than 20 % combination of winter and summer of Norwegian dwellings located on the measurements. above mentioned types of building grounds The Cambrian-Ordovician alum shale can be expected to contain radon and granites of different ages commonly concentrations exceeding 200 Bq/m3 contain radium concentrations exceeding 100 Moderately permeable sediments derived Bq/kg and are the primary radon source rocks from rock types with normal to low radium in Norway. Examples of other rock types content constitute building grounds of containing elevated concentrations of radium normal radon risk, while fine-grained are the Fen carbonatites which, in contrast to sediments like marine silt and clay deposits alum shale and granites, only occur in a and silty and clayey till represent areas of geographically very limited area of the low radon risk unless the permeability of country. The marked contrasts in radon risk these sediments has been increased through potential between different types of building loss of moisture and soil cracking. grounds are clearly illustrated in the Fen area The elevated radon risk related to where enhanced radon concentrations are permeable building grounds is illustrated in measured in dwellings founded directly on the the Huse area in Kinsarvik (paper 2). The carbonatites while only low radon levels are highly permeable sediments and the large obtained in the adjacent silt and clay areas vadose zone underlying the residential area (paper 3). The silt and clay deposits render the enable the transport of radon from large ground impermeable to transport of radon gas volumes into the dwellings resulting in and also reduce the exposure to local residents enhanced indoor radon concentrations from terrestrial gamma radiation. Indoor (figure 2). Subterranean air-flows caused gamma dose rates as high as 620 nGy/h are by temperature/pressure differences obtained in the areas of exposed carbonatites, between soil air and atmospheric air and primarily due to enhanced thorium elevations differences within the Huse area, concentrations in these rock types. strongly affect the annual variations in 8

The observed correlations between geochemical and geophysical information is geological factors and indoor radon increasing, and an interesting challenge is to concentrations in Norway are in overall determine to what extent existing digital data concordance with findings from other like bedrock and soil maps and airborne studies in former glaciated areas gamma radiometric measurements can be used (Aakerblom et al., 1988; Castren et al., to identify risk areas with respect to both 1992) and indicate that geological ground radon and groundwater radon. information is a useful tool in radon risk analysis. Resources can be concentrated to regions of high geologic radon potential References when screening programs are planned, and efficient follow-up surveys can be Aakerblom G, Pettersson B & Rosen B, 1988: established based on geological data in Markradon. Handbok for undersokning och combination with radon measurements in a redovisning av markradonforhållanden. Radon representative sample of the building stock. i boståder, Byggforskningsrådet R85, 160 pp. The observed contrasts in radon risk Revised edition 1990 (In Swedish). potential between different types of building grounds also enable the prediction Arvela H, Måkelåinen I & Castren O, 1993: of radon risk in areas which are not Residential radon survey in Finland. Report currently inhabited. The availability of STUK-A108, Finnish Centre for Radiation and existing geological information in an area, Nuclear Safety, Helsinki (abstract only in e.g. soil, bedrock and gamma radiation English). maps, will determine how cost-efficiently the evaluation of radon risk can be carried Castren O, Arvela H, Måkelåinen I & out. Voutilainen A, 1992. Indoor radon survey in Finland: Methodology and applications. Radiation Protection Dosimetry 45 (1), 413- Further work 418.

Investigations have shown that the ICRP, 1993 Protection against radon-222 at occurrence of radon prone areas correlates home and at work. A report of the well with geological conditions and that International Commission on Radiological important contributions to radon risk Protection. ICRP Publication 65. Pergamon evaluations can be obtained from geological Press. data. The availability of digital geological, 9

IARC, 1988: Man-made Mineral Fibres Stranden E, 1979: Radioactivity of building and Radon. International Agency for materials and the gamma radiation in Research on Cancer monographs on the dwellings. Phys Med Biol 24 (5), 921-930. evaluation of carcinogenic risks to humans. Stranden E, 1987: Radon-222 in Norwegian Volume 43. World Health Organization. dwellings. In: Proc. Symp. on Radon and its decay products: Occurrence, properties, and NRPA, 1995: Anbefalte tiltaksnivåer for health effects. New York, US, 13-18 April radon i bo- og arbeidsmiljø. NRPA 1986, American Chemical Society Symposium Radiation Protection series 1995, no. 5. Series 331,70-83. Osteraas: Norwegian Radiation Protection Authority (in Norwegian). Stranden E & Strand T, 1988: Radon in an alum shale rich Norwegian area. Radiation NRPA, 1996: Radon I inneluft. Protection Dosimetry 24 (1), 367-370. Helserisiko, målinger, mottiltak. NRPA Radiation Protection series 1996, no. 9. Stranden E, Ulbak K, Ehdwall H & Jonassen Osteraas: Norwegian Radiation Protection N, 1985: Measurements of radon exhalation Authority (in Norwegian). from the ground: A usable tool for classification of the radon risk of building Strand T, Green BMR & Lomas PR, 1992: ground? Radiation Protection Dosimetry, 12 Radon in Norwegian dwellings. Radiation (1), 33-38. Protection Dosimetry 45 (1), 503-508. Swedjemark GA, Mellander H & Mjones L, Strand T, Lind B & Tommesen G, 1998: 1993. Radon. In: The indoor climate in Naturlig radioaktivitet i husholdingsvann Swedish residential buildings. (In Swedish fra borebronner i Norge. Norsk with English abstract). Norlen U. and Vetrinartidskrift 110 (10), 662-665 (in Andersson K.. (eds.). Swedish Building Norwegian). Research Institute, Report TN:30.

Strand T, Aanestad K, Ruden L, Ramberg UNSCEAR, 1993 Sources and effects of GB, Jensen CL, Wiig AH & Thommesen ionizing radiation. Report to the General G, 2001. Indoor radon survey in 114 Assembly with Scientific Annexes. (United municipalities. Short presentations of Nations Scientific Committee on the Effects of results. StrålevernRapport 6. Osteraas: Atomic Radiation). United Nations, New York Norwegian Radiation Protection Authority. 10

Valen V, Soldal O, Gunter B, Henriksen H, Jensen CL, Lauritzen SE, Rydock J, Rye N, Strand T & Sundal AV, 1999: Variations in radon content in soil and dwellings in the Kinsarvik area, Norway, are strongly dependent on air temperature. Extended abstracts, AARST-2000 Int Radon Symp, 22-25 October, 1999, Milwukee, Wisconsin, USA. 11

10"3 - High risk 10-4 - | Gravel 10-5 _ Glaciofluvial deposits Shore deposits 10"6 - Fluvial deposits Clean - sand IO"7 - £E 10"8 - Silty i sand 03 10-9 - 0 b 10 ! io- - a) 1 Slit | CL 11 10- - Marine silt

1012- Clayey till

10-13- | Clay | Marine clay 10-,4_ Low risk

Iff15 - • Alum shale - Granite - -Gneiss - - Shale - - Sandstone -

c 10' 10

Radium concentration (Bq/kg)

Fig. 1. Classification of radon risk based on permeability and radium content of the building ground. High risk area. Area in which more than 20 % of the homes are expected to have radon concentrations in excess of 200 Bq/m3 Moderate risk area: Area in which between 3 % and 20 % of the dwellings are expected to exceed 200 Bq/m3. Low risk area: Area in which less than 3 % of the dwellings are likely to have radon levels above 200 Bq/m3 and no dwelling have radon levels higher than 400 Bq/m3 12

Outflow of wcmedair ^ Winter Mann limit Terminal 100- moraine

120—i Summer Marin limit

Outflow of cooled air

Legend

Morain rich in boulders r^Z-^ Marine sandy sediments : AyrijH Boulder rich gravel and A Prevailing direction JE3 sand jgf/ of soil air flow

500 Distance (m)

Fig. 2. Illustration of the temperature driven seasonal transport of radon gas in the Huse area. Warm air is lighter than cold air. In the wintertime the temperature of the soil air is higher than the atmospheric temperature, and so soil air flows toward the elevated part of the deposit. During the warm season the ground air flows toward the area of lowest elevation because the soil air temperature is lower than the air temperature (Valen et al., 1999). Paper I

Sundal AV, Henriksen H, Soldal O & Strand T The influence of geological factors on indoor radon concentrations in Norway. Submitted to The Science of the Total Environment, 2003 1

The influence of geological factors on indoor radon concentrations in Norway

AUD VENKE SUNDAL, HELGE HENRIKSEN, ODDMUND SOLDAL & TERJE STRAND

Sundal AV, Henriksen H, Soldal O & Strand T. The influence of geological factors on indoor radon concentrations in Norway. Submitted to The Science of the Total Environment.

Indoor radon levels in 1618 Norwegian dwellings located in different geological settings are compared with geological information. The results show a significant correlation between indoor radon levels and geological factors. Radium content and permeability of the building ground have been found to be useful indicators of indoor radon concentrations. Based on easily accessible geological data, an assessment of the radon potential of an area can be given. Areas of high radon risk in Norway include 1) exposed bedrock with elevated levels of radium and b) highly permeable unconsolidated sediments derived from all rock types and moderately permeable sediments containing radium rich rock fragments. A comparison of indoor radon with house construction characteristics and ventilation habits suggests that radon concentrations in Norwegian dwellings also are influenced by ventilation system, aeration habits, and floor level of the room where the measurements were carried out. The significant con-elation between indoor radon levels and geological factors observed in the present investigation indicates that geological data is a useful tool for identifying high radon risk building grounds in Norway.

And Venke Simdai, Department of Earth Science, University of Bergen, Allegata 41, N-5007 Bergen, Norway Helge Henriksen, Sogn og Fjordane University College. P.O. Box 133, N-6856 , Norway Oddmund Soldat, Interconsult ASA, P.O. Box. 6051, N-5892 Bergen, Norway Terje Strand, Norwegian Radiation Protection Authorities, P.O. Box 55, N-1332 Osterås, Norway

Introduction around 2/3 of the total effective dose. Exposure to the naturally occurring radon-222 The total effective dose from all radiation gas and its short-lived, solid decay products sources suffered by the Norwegian polonium-218, lead-214 and bismuth-214 population is currently estimated to 4,2 makes the major contribution to the total mSv per year (NRPA, 1999). The radiation exposure of the population and accounts for dose from natural sources constitutes approximately half of the average Norwegian's 2

total effective dose from all radiation low levels of radioactivity (Stranden, 1979). sources. The radon-222 isotope is a Since 87 % of the Norwegian population is member of the uranium-238 decay-series supplied by water from surface water sources and has radium-226 as its immediate with low levels of radon, the contribution to precursor. The contribution to indoor radon indoor air from household water is also from the natural occurring radon isotopes in generally low. However, analysis of water the uranium-235 decay-series (radon-219) from 3500 Norwegian drilled wells revealed and thorium-232 decay-series (radon-220) radon concentrations exceeding the Norwegian is in general considered negligible due to action level of 500 Bq/1 in 15 % of the wells their short half lives. In accordance with and 1000 Bq/1 in 9 % of the wells (Strand et international recommendations, remedial ah, 1998). The contribution to indoor radon measures in Norwegian dwellings are from household water can therefore not be recommended if the annual mean radon neglected, even though it is considerably less concentration in the living area exceeds 200 important as a radon source than the building Bq/m3 (NRPA, 1995). ground. There are several different radon When the building ground is the sources in domestic dwellings: Building dominant source of indoor radon, the indoor ground, building material and water supply. radon concentrations depend on the ability of Investigations have shown that the entry of the building ground to produce and transport radon from the building ground through the radon, the leakage of radon from the ground building construction is the main source of through the house construction and the indoor radon in Norwegian dwellings ventilation rate of the building. The (Stranden, 1987). For an average production and transport of radon in the Norwegian detached or terraced house, 80- building ground are determined by geological 90 % of the indoor radon concentration factors like radium content of the bedrock/soil, originates from the building ground. In emanation coefficients, moisture content, block of flats, building material can be permeability, etc. (Tanner, 1980; Aakerblom et relatively more important as a radon source, al., 1983; Markkanen and Arvela, 1992; Hutri but the contribution to indoor radon from and Makelainen, 1993; Tell et al., 1994; Sun this source rarely exceeds 200 Bq/m3. and Furbish, 1995; Schumann and Gundersen, Norwegian dwellings are primarily made 1996) and indicate the potential for a radon from wood-based building materials which problem to exist. How the geologic potential have low concentrations of natural will be realised in terms of indoor radon radioactive substances. Building materials concentrations mainly depends on building like concrete and brick manufactured in construction characteristics and ventilation Norway have also been reported to contain habits of the occupants. 3

In regions where significant indoor radon measurements in nearly 29 000 correlations between geological factors and randomly selected dwellings in 114 out of 435 indoor radon concentrations exist, Norwegian municipalities (Strand et al., 2001). information on geology can aid in Between 2 and 10 % of the housing stock in identifying radon-prone areas (Aakerblom each municipality was included in the study, et al., 1988; Castren et al., 1992). Previous depending on the size and population density investigations in Norway indicate that of the area. Seven of the 114 municipalities indoor radon concentrations and geology participating in the indoor radon study were are related (Stranden et al., 1985; Stranden, selected for the present investigation. The 1987; Stranden and Strand, 1988), but a selection was made with emphasis on the more extensive study of the geological following criteria: (1) The municipalities influence on indoor radon in dwellings should represent different geological regions in located in different geological settings was order to enable a comparison between indoor desirable in order to determine whether radon concentrations in dwellings located on geological information is useful in radon different types of bedrock and overburden; (2) risk analysis. The present paper discusses The average indoor radon values of the the results of a comparison between selected municipalities should reflect the geologic data and indoor radon whole range of values obtained in the study of concentrations in 1618 Norwegian all 114 municipalities. dwellings located in various geological Correlations between high indoor settings. The objective of the study was to radon concentrations and uranium-rich rock identify potential correlations between types have been reported from studies in indoor radon levels and geological factors several countries (Voutilainen et al., 1988; and to establish whether the correlations, if Gundersen et al., 1992, Ball and Miles, 1993; any, are strong enough to be useful in radon Tell et al., 1994). Enhanced levels of uranium risk analysis. A comparison of indoor are commonly found in rock types like granites radon data with house construction and black shales (Gascoyne, 1992). Uranium characteristics and ventilation habits of the is incorporated into the silica rich granitic occupants was also included in the study in rocks due to the concentration of this element order to investigate potential correlations in the liquid phase in the course of partial between these factors and indoor air radon melting and fractional crystallization of levels in Norway. magma, while the organic compounds in black shales are natural concentrators of uranium and Study areas other metals (Durrance, 1986). Typical ranges In 2000-2001, the Norwegian Radiation of activity concentrations of radium-226 and Protection Authority (NRPA) carried out thorium-232 in Nordic rocks are shown in 4

table 1 Norway is dominated by been reworked by fluvial processes after crystalline bedrock, and granites and deglaciation, and fluvial deposits like deltas, granitic gneisses have a fairly wide river beds and al luvial fans cover large parts of distribution (Sigmond et al., 1984). Alum the numerous glacial valleys in Norway. The shale, an uranium-rich Scandinavian black fluvial sediments are sorted and stratified and shale of Cambrian-Ordovician age, is generally consist of sand and gravel. Like the present in the area around Oslo in the glaciofluvial deposits they are highly south-eastern part of the country. permeable. Typical ranges of activity In glacial areas like Norway, the concentrations of radium-226 and thorium-232 overburden does not necessary reflect the in Nordic soil types are presented in table 2. characteristics of the underlying bedrock. The location of the 7 selected Several authors delineate that the properties municipalities in the different geological of the overburden have a significant is presented in figure 1. A influence on indoor radon concentrations summery of the geological characteristics and (e.g. Aakerblom et al., 1983; Gundersen et average indoor radon concentrations of each al., 1992; Ball and Miles, 1993; Hutri and municipality is given in table 3. Makelainen, 1993). The main types of Three of the selected municipalities overburden in Norway are glaciofluvial and are located in the Southern Precambrian region fluvial sediments, basal till and marine (Tinn, and Nes) (Fig. 1). The Southern silt/clay. Glaciofluvial sediments are Precambrian region is dominated by gneisses deposited by streams produced by melting and granites of Precambrian age. Average glacier ice e.g. in tunnels and crevasses in uranium concentrations between 2.2 ppm and or beneath the ice (eskers and kames) or 13.3 ppm have been measured in some of the where meltwater flows into standing water large granite bodies in the region (Killeen and (deltas). These deposits mainly consist of Heier, 1974; Killeen and Heier, 1975a, Killeen sand and gravel and are highly permeable. and Heier, 1975b). A major part of the Basal till is deposited at the base of the bedrock in the three selected municipalities is glacier and is generally unsorted, covered by basal till and glaciofluvial and containing both fines and large boulders. It fluvial sediments. The municipality of Ulvik is is the most extensive type of overburden in located at the western border of the Southern Norway and covers between 25 % and 30 Precambrian region, and fragments of gneisses, % of the total land area (Thoresen, 1991). metasediments and metavolcanics of the Due to its unsorted and compact character, Caledonides are present in the overburden in the permeability of the basal till is much this area. The average values of indoor radon lower than that of the sorted and stratified concentrations for Tinn, Ulvik and Nes are glaciofluvial deposits. The glacial drift has 358, 209 and 266 Bq/m3, respectively. 5

The municipality of Hurum is about 100 km north of Oslo where one of the located in the Oslo region, which splits the largest occurrences of alum shale is localised Southern Precambrian region into an (Fig. 1). Earlier studies in this region indicate eastern and western part (Fig. 1). In the that the alum shale is the source of enhanced Oslo region, sedimentary rocks of Late indoor radon concentrations (Stranden and Precambrian to Silurian age are overlain by Strand, 1988; NGU, 1994). A major part of Carboniferous-Permian volcanics and the bedrock in the municipality of Stange is sediments and intruded by igneous rocks, overlain by unconsolidated sediments, largely of Permian age. Raade (1973) predominantly basal till and glaciofluvial studied the distribution of radioactive deposits. Due to a substantial cover of basal elements in the plutonic rocks of the Oslo till, few outcrops of alum shale are found region and reported average uranium values within this municipality. A mean indoor radon of 2.0 to 9.1 ppm. The dominating rock concentration of 350 Bq/m3 is reported for the type in the municipality of Hurum is the municipality of Stange. Permian Granite. A mean The Caledonian orogenic belt uranium value of 4.7 ppm for the whole extends from the south-western part of granite body and local averages of more Southern Norway to the northern part of the than 8 ppm are reported. A small part of country and consists of a sequence of nappe- Hurum is covered by nearly impermeable piles of gneisses, metasediments and marine silt and clay deposits and sand and metavolcanics of Precambrian to Lower gravel dominated marine shore deposits. Palaeozoic age. The municipality of Midtre- The latter type of overburden was formed Gauldal is located in the central part of the by reworking of older sediments by current- Caledonides where Cambrian-Silurian and wave processes and can locally have a metasediments dominate (Fig. 1). The thickness of several meters. The average Geological Survey of Norway (NGU) has indoor radon concentration in the carried out a limited number of measurements municipality of Hurum is 205 Bq/m3. of total gamma radiation at ground level in this In parts of the Oslo region and area which all showed very low levels of the immediate area to the north, the radioactivity (Sordal, pers.com. 2003). Total uranium rich Cambrian-Ordovician alum gamma radiation measurements carried out in shale occurs. General average uranium the areas of Caledonian metasediments in levels of 50-150 ppm over thicknesses of 5- Northern Norway revealed low to normal 15 m and local maximum values of 170 levels of radioactivity (Hysingjord, 1988a, ppm are reported from this rock type Hysingjord, 1988b; Lindahl et al., 1988, (Skjeseth, 1958). The selected municipality Lindahl et al., 1993). A major part of the of Stange is situated in the Hedmark county bedrock in Midtre-Gauldal is covered by 6

glaciofluvial and fluvial sediments, basal characteristics are therefore used to describe till and marine silt and clay deposits. The the most important parameters assumed to silt and clay deposits in the northern part of affect indoor radon concentrations. In the the municipality are partially covered by present study, radium content and permeability layers of sand and gravel. The average were included as indicators of the production indoor radon concentration in the and transport of radon in the building ground, municipality of Midtre-Gauldal is 91 and these parameters were determined by using Bq/m3 available data on type of bedrock and type of The municipality of Rauma is overburden, respectively. An approximate located in North-Western Precambrian equilibrium between uranium-238 and radium- region (Fig. 1). This region is situated to 226 was assumed for the present study since the west of the Caledonian orogenic belt radioactive equilibrium normally prevails and is dominated by gneisses of between these radionuclides in Nordic bedrock Precambrian age. Total gamma radiation (Nordic, 2000). Classifications of basement, measurements carried out at ground level in foundation walls, ventilation system and Rauma and adjacent areas revealed low to aeration habits were used as surrogates of the normal levels of radioactivity (Lindahl and air leakage from the building ground through Sordal, 1988). A major part of the bedrock the building construction and the ventilation in the selected municipality is covered by rate of the building. Information on main glaciofluvial and fluvial sediments, basal building material and source of household till and marine silt and clay. In the western, water was also included in the study. low-lying parts of the municipality, silt and clay deposits are overlain by sand and Collection of data gravel (Follestad et al., 1994). An average In order to visualise the geographical indoor radon concentration of 29 Bq/m3 is distribution of the indoor radon data in each reported for the municipality of Rauma. municipality, the exact position coordinates for the participating dwellings were determined from the central register of Norwegian Survey methodology dwellings. ArcView Geographical Information System was used to produce thematic maps by Parameters linking the coordinates of the houses with the corresponding results from the indoor radon In large-scale surveys of factors affecting measurements. The municipal radon maps indoor radon concentrations, expensive and give a detailed picture of the geographical time consuming investigations at each distribution of indoor radon levels in each building site are impossible. Proxies like municipality and are very useful tools for the geological features and building 7

comparison of indoor radon data and thus the statistical analyses were carried out on geology. Detailed soil and bedrock maps logarithmically transformed levels of radon (scale 1: 50 000 or larger) were not concentrations. Mean values of the available for all the selected areas, thus transformed radon concentrations were additional information was obtained from compared using the Student's t-test. fieldwork carried out in each of the 7 Geometric means, ranges, and percentages of municipalities. Data were collected from a dwellings containing radon concentrations total of 1618 building sites. In addition to above 200 and 400 Bq/m3 are presented. Two the main study conducted in the 7 selected tailed P-values < 0.05 were required for areas, useful information was obtained by "statistical significance" in all tests. comparing available radon maps and geological maps for 79 of the other municipalities participating in the 2000- Results 2001 indoor radon study.

Information on building Geology characteristics, aeration habits and water The main statistics for the indoor radon data supply was collected from questionnaires classified according to geology are presented completed by the residents. The in table 4. questionnaires were issued and returned by In the three selected municipalities mail together with the alpha track detectors. of the Southern Precambrian region, a The questionnaires provided information statistically significant difference was observed on: Category of dwelling, floor level of between the mean indoor radon levels in room in which measurements were taken, homes built on the different types of building outer wall material, foundation wall grounds (p < 0.0001 for glaciofluvial versus material, type of basement, ventilation basal till and no overburden versus all the other system, aeration habits and source of groups, p = 0.001 for fluvial versus basal till, p household water. = 0.0113 for fluvial versus glaciofluvial). The geometric mean values of indoor radon Statistics concentrations in dwellings located on The influence of geology, house glaciofluvial and fluvial deposits were 307 characteristics, ventilation habits of Bq/m3 and 186 Bq/m3, respectively. In homes occupants and water supply on indoor built on basal till the mean air radon radon concentrations was investigated by concentration was 101 Bq/m3, while dwellings analysis of variance (Snedecor and founded on bedrock had a mean radon level of Cochran, 1989). The distribution of radon 34 Bq/m3 Sixty-eight % and 34 % of the gas concentrations was found to be skewed, dwellings located on the highly permeable 8

glaciofluvial sediments had radon 197 Bq/m3. This value is slightly higher than concentrations in excess of 200 Bq/m3 and the mean air radon concentration of 185 Bq/m3 400 Bq/m3, respectively. The highest measured in dwellings located on the fraction of houses with radon levels moderately permeable basal till, but the exceeding 200 Bq/m3 was registered on difference in radon concentrations between the glaciofluvial deposits in the municipality of two groups of dwellings was not statistically Tinn (75 %). In dwellings built on fluvial significant (p = 0.8183). The dwellings deposits, 42 % and 25 % had radon located directly on bedrock had significantly concentrations exceeding 200 Bq/m3 and lower radon levels than the other groups of 400 Bq/m3, respectively. In comparison, 19 dwellings (GM = 58 Bq/m3, p < 0.0001). The % of the dwellings located on the basal till distribution of air radon levels in homes built containing uranium rich granites had radon over both highly and moderately permeable levels exceeding 200 Bq/m3, while just one types of overburden showed approximately 50 home built on this type of building ground % exceeding 200 Bq/m3 and 25 % exceeding had radon levels higher than 400 Bq/m3. 400 Bq/m3 The maximum indoor radon value No dwelling founded directly on measured in dwellings located directly on uranium rich granites in the municipalities bedrock was 200 Bq/m3. The uranium rich of the Southern Precambrian region was alum shale in the municipality of Stange is included in the study, but in the covered with a substantial thickness of basal municipality of Hurum (Oslo region) a till, and non of the dwellings in the study was large number of dwellings founded on the located directly on this rock type. The highest Permian Drammen Granite were surveyed. radon value for all the 1618 buildings included The mean indoor radon level in homes built in the study was measured in a dwelling directly on bedrock in this area was 132 located on basal till (5300 Bq/m3). According Bq/m3, while 37 % and 17 % of the to Follestad (1974), the basal till in this area dwellings had radon levels exceeding 200 has a considerably higher content of alum Bq/m3 and 400 Bq/m \ respectively. The shale than the glaciofluvial deposits. mean radon level in dwellings located on In the municipality of Midtre- shore deposit in the same area was found to Gauldal (Caledonides), the mean radon levels be 76 Bq/m3. Only 4 % of these dwellings in dwellings located on different types of had indoor radon concentrations in excess overburden were generally lower than in of 400 Bq/m3 dwellings built on the same types of In the alum shale area of Stange overburden in the alum shale area and the (Oslo region), the geometric mean indoor Southern Precambrian region (table 4). The radon concentration for dwellings located average radon concentration in homes built on highly permeable building grounds was over glaciofluvial deposits was 69 Bq/m3, 9

while a mean radon concentration of 50 Building characteristics and aeration habits Bq/m5 was reported for dwellings located No large differences in building construction on fluvial sediments. The mean radon style or aeration habits were observed between values in dwellings located on basal till and the 7 municipalities included in the study. silt/clay were 43 Bq/m3 and 42 Bq/m3, Consequently, the data from all the respectively. In homes located directly on municipalities were collapsed into one dataset bedrock, the mean air radon level was 31 to investigate the effect of building Bq/m In this area, building ground was construction and aeration habits on indoor not recorded as a significant factor in the radon concentrations. Category of dwelling ANOVA analysis (p = 0.0878). However, and main building material were excluded as 21 % and 10 % of the dwellings located on factors since all the buildings were classified glaciofluvial sediments and 9 % and 3 % of as detached dwellings and 96 % of the the dwellings built over fluvial sediments dwellings were primarily made from wood. A had radon levels above 200 Bq/m3 and 400 summary of the relationship between indoor Bq/m3, respectively. In comparison, 4 % of radon concentrations and building the dwellings located on moderately characteristics/aeration habits for all the permeable building ground had radon levels dwellings included in the study is presented in exceeding 200 Bq/m3, while all the other table 5. dwellings had radon concentrations below A statistically significant association this level. between the floor level of the room where the In the municipality of Rauma in measurements were carried out and indoor the North Western Precambrian region, radon levels was reported (p < 0.0001 for radon concentrations exceeding 200 Bq/m3 basement versus ground floor and basement were only measured in homes located on versus first floor, p = 0.0436 for ground floor sand and gravel. Four % and 2 % of the versus first floor). The geometric mean indoor dwellings located on glaciofluvial and radon level was found to be 154 Bq/m3 in the fluvial sediments, respectively, had radon basement, 90 Bq/m1 on the ground floor and levels in excess of 200 Bq/m3 All the other 58 Bq/m3 on the first floor. dwellings had radon concentrations below The results also indicate a systematic 3 100 Bq/m . The geometric mean indoor effect attributable to type of ventilation system radon level for all the groups ranged from (p = 0.0174). The geometric mean values of 3 19 to 26 Bq/m Building ground was not indoor radon concentrations in dwellings with found to be a statistically significant factor natural, mechanical and balanced ventilation in this area (p = 0.4750). system were found to be 97 Bq/m3, 119 Bq/m3 and 81 Bq/m3, respectively. The t-test yielded a significant difference in mean radon LO

concentrations between houses with natural 57 Bq/m3 was reported for the group of and mechanical ventilation system (p = dwellings with private water supply from 0.0131) and between houses with balanced surface waters. The difference in indoor radon and mechanical ventilation system (p = concentration among the three groups of 0.0230). homes was statistically significant (p < 0.0001 The daily aeration period was for homes with public water supply versus the found to be a significant factor affecting other groups, p = 0.0254 between the two indoor radon concentrations (p = 0.0378), groups with private water supply). When the and the geometric mean indoor radon level results from the 7 municipalities were was reported to decrease with increasing examined separately, water supply was only period of aeration. The difference in mean recorded as a significant factor affecting indoor indoor radon concentration was found to be radon levels in 4 of the municipalities (Hurum, significant between the groups of dwellings Nes, Stange and Tinn). In all the 4 where the bedroom/living room was aerated municipalities, the highest indoor radon less than 1 hour per day and more than 6 concentration was found in the group of hours per day (p = 0.0287). The indoor dwellings with public water supply. radon concentrations for all the different categories of dwellings listed in table 4 ranged from a few Bq/m3 to several Discussion thousand Bq/m3.

The results of the present study The results from the comparison between showed no evidence of a systematic effect indoor radon concentrations and geologic data attributable to type of basement or type of indicate that indoor radon concentrations and foundation wall material (p = 0.1136 and p geology are related in Norway. On a broad = 0.1247, respectively). scale of investigation, indoor radon levels in Norway are found to be highest in regions Water supply where rock types with elevated uranium A total of 1596 households reported concentrations occur. The results show that whether they had public water supply or the indoor radon risk increases in areas where private water supply from drilled wells or uranium rich bedrock outcrops and in areas surface waters. The geometric mean indoor where uranium rich rock fragments are radon concentration in the 1224 homes with incorporated into the overburden. Thus, the public water supply was 117 Bq/m3. In the occurrence of uranium rich rock types appears 203 homes with private drilled wells, the to be one important indicator of radon risk. geometric mean indoor radon level was 77 The Cambrian-Ordovician alum shale and Bq/m'. A geometric mean radon level of granites of different ages commonly contain 11

radium concentrations exceeding 100 Bq/kg the building ground and not only to low and are the primary radon source rocks in uranium levels of the sediments. Similar Norway. These rock types are mainly geological conditions are registered in the found in the Southern Precambrian region, municipality of Hurum where the sand and the Oslo region and the Precambrian of gravel dominated shore deposits are underlain Northern Norway (Sigmond et al., 1984). by low permeable silt and clay sediments. The uranium content of the The significant correlation between overburden is an important factor indoor radon levels and geological factors controlling the production of radon gas in observed in the present investigation indicates the soil, but the transport of radon gas to the that geological data is a useful tool for building construction is controlled by other identifying high radon risk building grounds in factors. The results from the present study Norway. Important information for the show a statistically significant association classification of both regional and local high between the indoor radon concentrations radon risk areas can be obtained from already and the permeability of the overburden. mapped geological parameters. The results Sands and gravels (e.g. glaciofluvial and show that both radium content of the bedrock fluvial deposits) appear to contribute and the permeability of the overburden must be significantly larger amounts of radon to included when assessing the geologic radon indoor air than do less permeable soil, potential of a given area. Since the source rock presumably because high permeability of of the overburden in a former glaciated area the building ground favours the transport of may not be the underlying bedrock, a bedrock radon from its source to the building map can only be used directly to define high construction. These results indicate that the risk radon areas if no superficial deposits are permeability of the building ground is present. Overburden classifications, on the another important predictor of high indoor other hand, do not take into account details of radon concentrations. The thickness of the the source materials of the glacial drift and permeable layers is, however, of major must be supplied with information on the rock importance. In the selected municipalities fragments incorporated into the sediment of the Caledonian orogenic belt and the deposits. North-Western gneiss area, marine silt and Based on the results from the present clay deposits have been found to underlie study, high radon risk building grounds in parts of the fluvial and glaciofluvial Norway are found to be 1) exposed bedrock deposits. The low indoor radon levels with elevated levels of radium (mainly alum measured in homes located on these shale and granites) and 2) highly permeable deposits are therefore partly attributed to unconsolidated sediments (mainly glaciofluvial the small volume of permeable sediments in and fluvial deposits) derived from all rock 12

types as well as moderately permeable components also provide the basis for radon sediments (mainly basal till) containing risk classification diagrams presented by other radium rich rock fragments. The latter type authors (Stranden et al., 1985; Peake and of high radon risk building ground requires, Schumann, 1991). However, in addition to a however, a significant vertical thickness of general geological classification of radon risk, permeable unconsolidated sediments and a the comparison of geologic data and indoor low water table. Fine grained sediments radon values performed in the present study like marine silt and clay deposits and silty also provides information on the proportion of and clayey till represent building grounds dwellings expected to have indoor radon levels of low radon risk unless the permeability of above 200 Bq/m3 in high, moderate and low these sediments has been increased through risk areas. A high risk area is defined as an loss of moisture and soil cracking. area in which more than 20 % of the homes are The most radon prone regions in likely to have radon concentrations above 200 Norway are found to be the Southern Bq/m3 In a moderate radon risk area, the Precambrian region, the Oslo region radon level in between 3 % and 20 % of the (including the adjacent alum shale area) and dwellings is expected to exceed 200 Bq/m3. the Precambrian of Northern Norway. In An area in which less than 3 % of the these regions, both radium enriched dwellings are likely to have radon bedrock and permeable unconsolidated concentrations above 200 Bq/m3 and no sediments are present. In the other regions, dwelling have radon levels higher than 400 the high risk radon areas are mainly Bq/m3, is classified as a low radon risk area. concentrated to sand and gravel deposits, The expected percentages of dwellings having except for a few granite areas within the radon levels in excess of 200 Bq/m3 in areas of Caledonides. In addition to the previously high, moderate and low radon risk are based on mentioned types of permeable deposits, knowledge of the typical Norwegian dwelling, sandy and gravelly marginal moraines have and the classification is not necessarily valid in been reported to have an increased other countries where different construction probability of generating elevated indoor characteristics predominate. radon levels due to their high permeability In the classification diagram given in (Valen et al., 1999). figure 2, permeabilities above 107 cm2 are The results of the present study defined as high since convective radon are summarised by the classification of transport may become dominant over diffusion radon risk presented in figure 2. Areas of transport at this level (Sextro et al., 1987). high, moderate and low radon risk are Due to the wide range of permeabilities within defined based on permeability and radium each rock type, permeability ranges are not content of the building ground. These two included for the rock types listed in the 13

diagram. Generally shales and unfractured the mechanisms causing high indoor radon igneous and metamorphic rocks are levels, assessments of radon risk based on considerably less permeable than karst geological information can also be extended to limestone and highly fractured areas that are not currently inhabited. This metamorphic and igneous rocks (Freeze and enables the prediction of radon risk in areas of Cherry, 1979). The permeability of the development in order to decide whether bedrock may, however, increase if blast preventative measures against radon must be firing at the building site is carried out. The taken in future buildings. ranges of radium concentrations of bedrock Based on an evaluation of a given in the diagram are based on previous geologically based radon risk map of the studies in Scandinavian countries (Nordic, municipality of Uppsala, Sweeden, Friis et al. 2000). (1999) concluded that geological information The reported correlations is unsuitable for identifying radon prone areas. between indoor radon concentrations and The significant difference in indoor radon geology enable the identification of radon concentrations obtained between areas of high, prone areas in Norway based on geological moderate and low radon risk in the present information. The identification can be study contradicts this view and strongly carried out in a rather simple and suggests that areas of different radon potential inexpensive manner by using existing can be determined based on geological geological and geochemical data. information. These conclusions are in overall Evaluations of radon risk based on concordance with findings from other studies geological criteria can not be used to in former glaciated areas (e.g. other Nordic predict the radon levels accurately in countries and some regions of the United individual homes, but it may contribute in States) where permeable glacial drift and making national and municipal indoor uranium-enriched rock types like black shale radon measuring programs more effective and granite have been reported to be important allowing action to be concentrated where it predictors of radon prone areas (Aakerblom et is most likely to be effective. The regions al., 1983; Peak, 1988. Gates et al., 1990; of high geologic radon potential can be Gundersen et al., 1992; Tell et al., 1994; Hutri given priority when national screening and Makelainen, 1993). In Sweden and programs are planned, and efficient follow- Finland, particular attention has been drawn to up surveys can be established based on the glaciofluvial esker deposits which have geological data in combination with radon been shown to be one of the most radon- measurements in a representative sample of critical landforms (Aakerblom et al., 1983; the building stock. Since geological Castren et al., 1985; Hutri and Makelainen, information provides an understanding of 1993, Arvela et al., 1994). In these countries, 14

geologic information has been used to rank mechanical ventilation system can be a risk geographical areas in order to be able to factor for indoor radon compared to a balanced make the most effective use of resources in ventilation system. This result can partly be locating buildings with elevated indoor explained by an increase in radon suction from radon and to anticipate future indoor radon the building ground due to the indoor air problems in areas of development pressure gradient created by the mechanical (Aakerblom et al., 1988; Castren et al., ventilation system. 1992; Aakerblom, 1994). Investigations have shown that Whether the geologic radon houses with a full basement or a part basement potential is realised in terms of high indoor are more susceptible to radon problems than radon levels depends on factors related to houses with no basement (Aakerblom et al., the structure of the building and the way it 1983). In an earlier survey of factors affecting is used. The results from the present study indoor radon concentrations in Norwegian indicate that several different parameters homes, significant higher radon levels were related to building characteristics and found in homes with a part basement compared aeration habits affect the indoor radon to those with a full basement or no basement levels in Norwegian homes. The data (Strand et al., 1992). Lanctot et al. (1992) suggest that the indoor radon concentration found no significant difference in indoor radon decreases with increasing floor level of the concentrations in dwellings with a basement room where the detectors were exposed. compared to dwellings without basement. In This result is expected since the building the present study, correlations between indoor ground is found to be the main source of radon levels and different types of basements radon in Norwegian dwellings. The same were searched for, but not found. Likewise, no trend is observed by other investigators evidence of a systematic effect attributable to (Gunby et al., 1993; Albering et al, 1996). type of building material of the foundation Several authors have observed a walls was observed. significant influence of aeration habits on In 4 of the municipalities included in the indoor radon levels (Buchli and the present study, higher indoor radon levels Buchart, 1989; Strand et al., 1992; Gunby were found in dwellings supplied by water et al., 1993). In accordance with the results from public waterworks compared to those of the above listed studies, the present with private water supply (Tinn, Stange, material indicates that the radon level Hurum and Nes). The public waterworks in 3 decreases with increasing daily aeration of the municipalities are based on surface period of the room where the radon water (Tinn, Stange and Hurum), while the measurement was carried out. A general municipality of Nes extract their water from trend is also observed suggesting that a Quaternary superficial sediments, hi 1996, the 15

public water work in Nes was included in a bedrock and overburden are taken into study of radon levels in raw-waters of 33 account. Radium content and permeability of major groundwater works in Norway (31 the building ground have been shown to be based on water from superficial deposits useful indicators of indoor radon and 2 based on water from hard rock) concentrations, and an estimate of both (Morland et al., 1996). An average radon regional and municipal radon potential can be concentration of 23 Bq/1 and a maximum given based on easily accessible geological value of 88 Bq/1 were reported for the 33 data. waterworks. The water sample from Nes Geologic terrains of high radon risk had a radon level of 83 Bq/1. The in Norway include a) exposed bedrock with Norwegian action level for waterworks is elevated levels of radium and b) highly 100 Bq/1, and no radon concentration permeable unconsolidated sediments derived exceeding this level has ever been reported from all rock types and moderately permeable from Norwegian waterworks. Amounts of sediments containing radium rich rock radon giving cause for concern are fragments. generally limited to water from private The observed correlations between drilled bedrock wells (Reimann et al., 1996; indoor radon and geology indicate that Morland et al., 1997; Banks et al., 1995). geological data is a useful tool for identifying Of the 15 dwellings in the municipality of areas where preventative measures against Hurum supplied with water from drilled radon must be taken in future buildings. wells in the Permian Drammen Granite, Geological parameters can not provide only one dwelling had indoor radon levels accurate estimates of radon levels in existing exceeding 200 Bq/m3 Radon homes, but the identification of dwellings with concentrations in dwellings supplied from elevated indoor radon levels can be facilitated drilled wells in the other selected by concentrating resources to the areas of high municipalities were also generally low. geologic radon potential. Thus, household water is not believed to be Several parameters related to an important source of indoor radon in the building characteristics and aeration habits homes included in the present study. appear to affect indoor radon concentrations in Norway. The factors found to have a statistically significant association with indoor Conclusions radon levels in the present study are ventilation system, aeration habits, and floor level of the Significant correlations between geology room where the measurements were carried and indoor radon concentrations in Norway out. are found when the properties of both the 16

Acknowledgements - This work was funded Devon, UK. Environ Geochem and Health by the Research Council of Norway 1993; 15( 1 ):27-36. (project 135370/720). Banks D, Royset O, Strand T, Skarphagen H. Radioelement (U, Th, Rn) concentrations in References Norwegian bedrock groundwaters. Environ Geol 1995;25:165-180.

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Valen V, Soldal O, Gunter B, Henriksen H, Jensen CL, Lauritzen SE, Rydock J, Rye N, Strand T, Sundal AV. Variations in radon content in soil and dwellings in the Kinsarvik area, Norway, are strongly dependent on air temperature. Extended abstracts, AARST-2000 Int Radon Symp, » 100 km '

Selected municipalities 1 Tinn 2 Ulvik 3 Nes 4 Hurum 5 Stange 6 Midtre Gauldal 7 Rauma Precambrian rocks

1 Gneisses Granites

Caledonian orogenic belt

[ | Basic metavolcanics and igneous rocks Gneisses and metaigneous rocks Caledonian Granites Late Precambrian metasediments I 1 Cambrian-Silurian metasediments (also present in the Oslo region)

Devonian rocks 1 Sandstones and conglomerates

Oslo region I Intrusive rocks Volcanic rocks

Fig. 1. Bedrock map of Norway and the location of the 7 municipalities included in the study (Source: Digital Bedrock Geology map of Norway, 1:3 million, Geological Survey of Norway) 22

E o

JQ ra

10' 10' Radium concentration (Bq/kg)

Fig. 2. Classification of radon risk based on permeability and radium content of the building ground. High risk area: Area in which more than 20 % of the homes are expected to have radon concentrations in excess of 200 Bq/m3. Moderate risk area: Area in which between 3 % and 20 % of the dwellings are expected to exceed 200 Bq/m3. Low risk area: Area in which less than 3 % of the dwellings have radon levels above 200 Bq/m3 and no dwelling have radon levels higher than 400 Bq/m3. 23

Table 1 Typical ranges of activity concentrations of radium-226 and thorium-232 in Nordic rocks (Nordic 2000) Type of rock Ra-226* Th-232 (Bq/kg) (Bq/kg) Granite, normal 20-130 20-80 Granite, uranium- and thorium-rich 100-500 40-350 Gneiss 25-130 20-80 Carbonatites 10-650 40-10 000 Diorite, gabbro and basic volcanic rocks 1-30 2-40 Sandstone and quartzite 5-60 5-40 Limestone and dolomite 2-30 0.5-10 Shale 10-150 10-60 Alum shale 100-4300 10-40 * 12.3 Bq/kg radium-226 is equivalent to 1 ppm uranium-238 24

Table 2. Typical ranges of activity concentrations of radium- 226 and thorium-232 in Nordic soils (Nordic 2000) Soil Ra-226* Th-232 (Bq/kg) (Bq/kg) Gravel 10-90 2-80 Sand <4-60 2-80 Eolian sand-silt 5-20 10-20 Silt 5-70 5-70 Clay 15-130 10-100 Till 10-170 15-100 Till with alum shale 180-2500 30-50 * 12.3 Bq/kg radium-226 is equivalent to 1 ppm uranium-238 25

Table 3. Average municipal indoor radon concentrations and geological characteristics of the 7 selected municipalities Geological region Munici- Mean Rn Type of bedrock Type of overburden pality indoor (Bq/m3) The Southern Tinn 358 Precambrian granite, gneiss and Precambrian region metarhyolite Ulvik 209 Precambrian gneiss and Cambrian- Glaciofluvial and fluvial deposits, Ordovician phyllite basal till Nes 266 Precambrian granite, quartz shale, metasandstone, gneiss and quartzite The Oslo region Hurum 205 Permian granite, Precambrian gneiss Marine shore deposits, marine silt/clay Stange 350 Precambrian gneiss, Cambrian- Glaciofluvial and fluvial deposits, Silurian alum shale, limestone and basal till clay shale The Caledonian Midtre 91 Cambrian-Silurian phyllite, quartzite. Glaciofluvial and fluvial deposits, orogenic belt Gauldal quartz shale and amphibolite basal till, marine silt/clay The North Western Rauma 29 Precambrian gneiss Glaeiofluvial and fluvial deposits, Precambrian region basal till, marine silt/clay 26

Table 4. Indoor air radon by geology. P-values from the "one-way A nova" analysis Geology Geometric Range % £ 200 % > 400 mean (Bq/m3) (Bq/m3) (Bq/m3) (Bq/m') Southern Precambrian region Tinn/Ulvik/Nes Glaciofluvial (H) 77 307 <10 4100 68 34 Normal to high U-levels in Fluvial (H) 145 186 <10-4500 42 25 bedrockA Basal till (M) 100 101 <10- 820 19 1 Bedrock1 18 34 <10- 170 p< 0.0001 Oslo region Hurum Shore deposits (H) 51 76 <10- 520 4 4 2 Normal to (locally) high U- Bedrock 271 132 <10 - 3500 37 17 levels in bedrock8 p = 0.0012

Stange Glaciofluvial (H) 54 197 <10-3500 46 24 c Basal till (M) 437 185 <10-5300 51 25 High U-levels in bedrock 3 Bedrock 59 58 <10- 200 2 p< 0.0001 Caledonian orogenic belt Midtre Gauldal Glaciofluvial (H) 37 69 <10- 1100 21 10 Low U-levels in bedrock0 Fluvial (H) 69 50 <10- 940 9 3 Basal till (M) 50 43 <10- 230 4 Marine silt/clay (L) 9 42 <10- 90 Bedrock4 13 31 <10- 130 p = 0.0878 N.W. Precambrian region Rauma Glaciofluvial (H) 44 26 <10- 310 Low to normal U-levels in Fluvial (H) 57 22 <10- 360 bedrock^ Basal till (M) 54 19 <10- 80 Marine silt/clay (L) 53 23 <10- 90 Bedrock5 20 26 <10- 100 p = 0.4750 N = number of dwellings H = highly permeable M = moderately permeable L = low permeable AKilleen and Heier 1974, Killeen and Heier 1975a, Killeen and Heier 1975b; BRaade 1975; cSkjeseth 1968, Stranden and Strand 1988, NGU 1994, DSordal pers. com. 2003; hLindahl and Sordal 1988 1Precambrian gneiss, dacite, quartz shale and Cambrian-Silurian phyllite; 'Permian granite and Precambrian gneiss; 3 Precambrian gneiss, Cambrian-Silurian limestone and clay shale; 4Cambrian- Silurian phyllite; 5Precambrian gneiss 27

Table 5. Indoor air radon by building characteristics and aeration habits. P-values from the "one-way Anova" analysis Factor Category Number of Geometric mean Range dwellings (Bq/m1) (Bq/m3) Floor level of bedroom Basement 382 154 <10-4700 or living room Ground floor 1018 90 <10-5300 First floor 36 58 <10-2500 p< 0.0001 Basement type Cellar 991 95 <10-4500 Partial/crawl space 383 115 <10-4900 No cellar 160 111 <10-2500 p = 0.1136 Building material of Concrete 564 138 <10-5300 foundation walls Light weight concrete 673 93 <10-3500 Natural stone 105 123 <10-4900 p = 0.1247 Ventilation system Natural 1139 97 <10-5300 Mechanical 336 119 <10-4900 Balanced 64 81 <10-2100 p = 0.0174 Mean daily aeration less than 1 h 1258 104 <10-5300 period 1-6 h 141 86 <10-3400 more than 6 h 83 75 <10-3500 p = 0.0378

Paper II

Sundal AV, Henriksen H, Lauritzen SE, Soldal O, Strand T & Valen V Geological and geochemical factors affecting radon concentrations in dwellings located on permeable glacial sediments - a case study from Kinsarvik, Norway. Submitted to Environmental Geology, 2003. 1

Geological and geochemical factors affecting radon concentrations in dwellings located on permeable glacial sediments - a case study from Kinsarvik, Norway

AUD VENKE SUNDAL, HELGE HENRIKSEN, STEIN ERIK LAURITZEN, ODDMUND SOLD AL, TERJE STRAND & VIDAR VALEN

Sundal AV, Henriksen H, Lauritzen SE, Soldal O, Strand T & Valen V. Geological and geochemical factors affecting radon concentrations in dwellings located on permeable glacial sediments - a case study from Kinsarvik, Norway. Submitted to Environmental Geology.

In 1996-1997, indoor radon values of more than 40 000 Bq/m3 and large seasonal and geographical variations in indoor air radon were reported from a residential area located on a highly permeable ice-marginal deposit. Geochemical analyses of bedrock, groundwater and sediments and comparisons between indoor radon values and soil radon values indicate that the indoor radon concentrations in this area are strongly affected by subterranean air-flows caused by temperature differences between soil air and atmospheric air. The air-flows concentrate the radon- laden soil air towards the topographic highest part of the deposit in winter and towards the topographic lowest part in summer. In areas where subterranean air-flows are likely to occur, radon measurements performed both in summer and in winter provide the best estimate of annual average indoor radon concentrations, and assessments of indoor radon concentrations based on single soil gas measurements are not recommended.

And Venke Sundal, Stein Erik Lauritzen, Department of Earth Science, University' of Bergen, Allegata 41, N- 5007 Bergen, Noway Helge Henriksen. Sogn og Fjordane University College, P.O. Box 133. N-6856 Sogndal, Norway Oddmund Soldal, Interconsult ASA, P.O. Box. 6051, N-5892 Bergen, Norway Terje Strand, Norwegian Radiation Protection Authorities, P.O. Box 55, N-1332 Osterås, Norway Vidar Valen, Sorlandskonsult A/S, Vesten>eien 6, N-4613 Kristiansand, Norway

Introduction increasingly been drawn to the problems concerning enhanced radon concentrations in buildings located on this type of building A large proportion of Norwegian dwellings ground. Studies in other countries have are located on permeable unconsolidated revealed that highly permeable sediment sediments of late glacial or post glacial deposits must be regarded as radon prone areas origin. Over the last decade, attention has 2

in which the concentrations of radon in The sediment accumulation originates from the buildings is likely to be higher than the end of the last glacial and is mainly a coarse national average (Aakerblom and others grained, moraimc deposit. The highest shore 1983; Peak 1988, Hutri and Makclainen line during the accumulation stage was around 1993; Tell and others 1994). In 1996-1997 110 m above the present sea level (Holtedahl anomalously high levels of indoor radon 1975). The surface of the moraine is concentrations were reported from the characterised by mounds and depressions and residential area of Huse located on an large angular boulders. At the surface, a extensive ice-marginal deposit in Kinsarvik, sandy, gravelly matrix is present below the Norway (Jensen 1997). Radon marine limit, while the matrix is nearly absent measurements carried out in 77 of the in the area above approximately 110 m a.s.l. approximately 130 dwellings revealed At the western side of the valley the main river indoor radon concentrations as high as 40 has cut through the ice-marginal deposit, while 000 Bq/m3 In addition to the high radon along the riverbed the moraine is overlain at levels, large seasonal and geographical various levels by fluvial and glaciofluvial changes in indoor radon concentration were sediment terraces. A spring horizon is found registered. The results from the indoor in the steep riverbanks west and northwest of radon study in the Huse area received the Huse area. The maximum thickness of the national attention, and detailed geological deposit is estimated to be 50 m. investigations were earned out in order to The bedrock in the Kinsarvik district identify the radon source and to understand consists of granites and meta-igneous rocks the extreme variations in indoor radon mainly of early to middle Proterozoic age concentrations. (Sigmond and others 1998). In the steep hillsides northeast and west of the Huse area The investigated area meta-dacite, meta-andecite and fine- to Kinsarvik is situated in the municipality of medium-grained, foliated meta-granite occur. , (Fig. 1). It is In the main valley to the south of the ice- a small rural area located in the bottom of a marginal deposit, meta-granite with a typical glacial valley, with steep hillsides pronounced foliation and large feldspar grains and several tributary valleys. The dominates. The meta-granites are intruded by residential area of Huse is located on the pegmatite and coarse-grained granite. South distal slope of an ice-marginal deposit and east of the Kinsarvik area the Precambrian extending approximately 1 km up the valley rocks are overlain by Ordovician-Silurian from the (Holtedahl 1975). phyllites with layers of quartzite and marble The Huse area is approximately 0.5 km2 (Sigmond and others 1998). and extends from 40 to 115 m a.s.l. (Fig. 1). 3

Nearly all the dwellings located air as the drilling fluid. Sediment samples within the residential area of Huse are were collected every 1 m during drilling. The detached houses of wooden construction, boreholes were installed to just below the and most of them have cellar construction water table with a total length of 24 and 30 m. (Jensen 1997). The majority of the Plastic tubes with 0.3 mm filter openings were buildings were constructed after 1960, and installed in the boreholes to enable nearly all the houses are ventilated by groundwater sampling. natural means (Jensen 1997). The air To explore lateral changes in exchange rate has been found to be lower stratigraphy, ground-penetrating radar (GPR) than recommended in several of the surveys were carried out in the area. Eighteen dwellings. All the households in the area profiles were collected, having a total length of have public surface water supply. In 1996- approximately 3 km. The georadar device 1997, the Norwegian Radiation Protection used in the survey was a Malaa Geoscience Authorities (NRPA) carried out indoor Ramac® using 100 MHz antennas. radon measurements in 77 of the dwellings Interpretation of data was based on the in the Huse area at three different seasons methods described by Beres and Haeni (1991). (Jensen 1997). The distribution of annual average indoor radon concentrations Geochemical analyses of bedrock, sediments calculated on the basis of these and groundwater measurements is presented in Fig. 2. Twenty seven samples from the local bedrock and the phyllite area south and east of Kinsarvik were analysed for U and Th (Table Methods 1). From each of the two boreholes, 5 samples representative of the deposit were selected for analyses of U, Th and Ra. The U and Th Drilling and ground-penetration analyses were carried out at the Memorial radar surveys University of New Foundland by inductively Two boreholes were drilled in order to coupled plasma mass spectrometry (ICP-MS). investigate the stratigraphy, depth of water The Ra levels of the borehole samples were table and petrographical composition of the determined by gamma spectroscopy at the ice-marginal deposit. One borehole was Norwegian Radiation Protection Authority. drilled in the topographic lowest part of the The borehole samples were split in residential area (borehole A) and the other two, and one half was treated with HC1 and borehole in the area of highest elevation Na2S03 before the analyses (Table 1). This (borehole B) (Fig. 1). The drilling was procedure was applied in order to bring Fe- carried out using an ODEX hammer- and Mn-oxide coatings into solution and rotation mobile rig employing compressed 4

estimate the leachable fraction of the different seasons during 1997-1998. radionuclides in the sediment samples. Rn- Temperature and pH measurements of the exhalation rates were determined for the groundwater were carried out in the field when untreated samples and used to calculate the water samples for radon analyses were radon emanation coefficient of the collected. sediments. The Rn-exhalation measurements were carried out by Soil gas measurements enclosing oven-dried samples in a sealed To study the mechanisms responsible for the recipient for 20 hours. Air samples were significant seasonal changes in indoor radon taken with an evacuated scintillation cell concentrations in the Huse area, radon gas (Lucas cell) and counted by an EDA measurements in the soil air were carried out in scintillation flask (RD-200). The analysed different seasons of the year. The radon borehole samples were chosen from the concentrations were measured by etched track dominating gravel fraction. detectors (C-39) buried in 23 different In May 2001, water samples were localities within the residential area. The collected from the main river (river I), a detectors were sealed inside thin plastic bags in smaller river draining the area to the north order to prevent immediate overexposure and of the ice-marginal deposit (river II), to protect the detectors from contamination. borehole A and four springs located along The detectors were placed at approximately 20 the riverbanks west and north of the glacial cm depth in all measuring stations and exposed deposit (Fig. 1, Table 2). One set of for 2-3 days. samples was analysed at the Geological Survey of Norway (NGU) for U and Th by Statistics ICP mass spectrometry. Another set of In order to explore the pattern of geographical samples was analysed at the Institute for and seasonal changes in soil radon Energy Technology (IFE) for Ra by the concentrations in the Huse area, the average scintillation flask method (RD-200). The summer and winter radon concentration for last set of samples was analysed for Rn at each measuring station was normalised against the NRPA by liquid scintillation. the station-average for the whole year. A The isotopic composition of U normalised value of 1 thus represents a and Th in water samples from three springs measuring station with a summer value or a was determined by alpha spectrometry at winter value equal to the yearly mean of that the University of Bergen (Table 2). In station. The summer and winter radon order to investigate seasonal radon concentrations in dwellings were normalised variations, groundwater from five springs against the yearly mean value by the same was analysed for Rn concentrations at method as the radon measurements in the 5

ground. The Mann-Whitney test was used surface downwards with an interval of 2-5 m. to compare the medians of the samples These reflectors can be traced in all the profiles from the different groups obtained (Davis from the area. The interval between the 2002). P-values < 0.05 were required for reflectors is generally decreasing towards the "statistical significance" western part of the area. A comparison between soil gas The stratigraphy of the ice marginal concentrations and indoor concentrations of deposit is presented in the borelogs in Figs. 3a radon at different seasons was made by and 3b. The logs show that the ice marginal locating the indoor radon measurements deposit is dominated by very coarse material. within 30 meters of a soil gas measuring Layers of sand and gravel alternate with station. If more than one indoor radon distinct horizons of boulders and pebbles. The measurement existed within the buffer content of boulders and pebbles is generally distance, the soil gas value for that station highest in the upper part of the borelogs, was compared to the average of the although boulder-rich horizons occur all the different indoor radon concentrations. way down to the water table. The content of silt and clay is low. In October 1998, the water table in borehole A and borehole B was encountered at 19 m and 29.5 m below ground Results level, respectively.

The samples from borehole A are Stratigraphy and petrographic dominated by meta-granite/granite in the upper composition of the ice marginal deposit part and meta-dacite in the lower part (Fig. 3a). The georadar profiles from the ice marginal Meta-granite/granite dominates both the upper deposit in Kinsarvik are dominated by and lower part of profile B, while phyllite and discontinuous reflectors and diffractions of gneiss are major constituents in some of the varying sizes (Valen and others 1997). In horizons between 7 and 21 m below ground many profiles the diffractions are level (Fig. 3 b). Very little phyllite occurs in particularly frequent in the upper few the sediments. Iron oxide stains (incipient iron meters of the deposit, but diffractions are "hard pan") were observed on the metadacite also present down to the maximum grains and in the granitic material from the penetration depth of approximately 20 m. near surface horizons. The source material for Rarely do continuous reflectors occur in the sediments is assumed to be primarily the these profiles. Some continuous reflectors local bedrock in Kinsarvik and the bedrock in are present close to the ground surface and the immediate area to the south. The a few distinct, nearly horizontal reflectors dominance of metadacite in the lower part of occur from around 4 meters below the profile A is most likely due to mass 6

movements from the hillside to the north of radon concentrations in the groundwater Kinsarvik where this rock type occurs. samples range from 240 Bq/1 to 364 Bq/1. The 222Rn/226Ra activity ratio is always greater than Geochemistry 103, demonstrating a large enrichment of 222Rn U and Th concentrations in different rock in the liquid phase. Radon gas concentrations types from bedrock and boulders in the in groundwater samples measured at different Kinsarvik district are presented in Table 3. seasons are shown in Table 4c. No significant The results show that the highest uranium temporal fluctuations in the radon gas content and thorium levels are found in the granitic or differences in radon concentrations in water rock types. Granite 1, occuring as from springs draining different parts of the ice- intrusions in the foliated meta-granite, marginal deposit are detected. Groundwater contains the highest average uranium temperatures in the range 5 °C to 7.5 °C and concentration of 22.9 ppm. The lowest pH-values in the range 6.2 to 6.8 are measured average uranium and thorium in all the groundwater samples at all seasons. concentrations are obtained from the meta- Uranium series radionuclide dacite (1,4 and 4.3 ppm, respectively). concentrations of the borehole samples are Radionuclide concentrations in shown in Figs. 3a and 3b. The U groundwater and surface water from concentrations in the 10 samples vary between Kinsarvik are listed in Table 4 a-c. The U 24 and 142 Bq/kg. The Th levels vary between contents obtained from groundwater 9 and 60 Bq/kg, and the Ra concentrations samples range from 0.19 to 0.63 |ng/l. A range from 18 to 84 Bq/kg. Most of the state of disequilibrium between 238U and its samples have Ra concentrations above 50 daughter nuclide 234U is found in all the Bq/kg. A radioactive disequilibrium between analysed groundwater samples; 234U/238U 226Ra and 2,8U is found in all the samples, the activity ratios greater than 1.0 reflects an 226Ra/23xU activity ratios ranging from 0.5 to excess 234U in the water. The Th 0.8. The percentage of thorium leached by the concentrations presented in Table 4a are all HCl/'NaiSO:, treatment is rather constant for under or close to detection level. The low most of the sediment samples, while it varies levels of dissolved thorium are illustrated to a greater extent regarding uranium and by the low ratio of 230Th to 234U in the radium. Between 50 and 60 % of the U groundwater samples. concentration in the meta-dacite samples from A significant departure from the lower part of borehole A and the gneiss secular equilibrium is found between samples in borehole B is leached by the radium and radon in the groundwater. All HCl/Na2S03 treatment. The leaching the water samples have radium levels below experiments therefore indicate a non- detection limit (0.1 Bq/1), while dissolved homogeneous uranium/radium distribution in 7

the borehole samples with most of the in the topographic lowest part of the residential radionuclides occurring in easily leachable area (Fig. 4d). The average atmospheric air positions, e.g. adsorbed to mineral surfaces temperature, average precipitation, average or co-precipitated with iron oxides. The wind speed and concentrations of soil radon emanation coefficients for all the 10 for each measuring period are presented in samples are presented in Table 5. The Table 6. emanation coefficients for the gravel Due to coarse material in the ground, fraction of the dry borehole samples lie in it was impossible to reach the recommended the range 0.13 to 0.39, with an average depth for soil air measurements at 0.7-1 m emanation coefficient for the dominating without expensive drilling. Radon gas meta-granite/granite material of concentrations at shallower depths have been approximately 0.25. shown to be affected by meteorological changes and are in general lower than the Soil air radon concentrations radon levels obtained from the depth of 0.7-1 The measurements of soil gas reveal m (Rose and others 1990). Thus, the results distinct seasonal and lateral changes in from this study mainly provide information of radon concentrations (Figs. 4 a-d). In the relative radon gas concentrations in the August 1997, significantly higher radon different localities rather than information of concentrations were measured in the radon concentrations at the depth where topographic lowest (north-western) part of equilibrium exists between radon supplied and the residential area compared to the removed. topographic highest (south-eastern) part of the area (Fig. 4a). The average air Statistical evaluation of indoor and soil air temperature during the measuring period radon concentrations was 21.3 °C. In November the same year, By gridding and smoothing the normalised when the mean air temperature was 5.8 °C, summer values of soil radon, a pattern is the highest radon levels were measured in revealed with the highest values (normalised the topographic highest part of the Huse values > average + 1/2 standard deviation) in area (Fig. 4b). Similar results were the topographic lowest part of the Huse area obtained for the measurements carried out and the lowest values (normalised values < in March 1998 at a mean air temperature of average - 1/2 standard deviation) in the - 4.0 °C (Fig. 4c). The radon levels were topographic highest part of the area (Fig. 5a). particularly high in the area of highest A middle zone where the summer values are elevation in this period. In May 1998, the close to the yearly mean is also readily mean air temperature was 12.1 °C, and the identified. The reversed pattern is obtained for highest radon levels were again measured the average winter station-values normalised 8

against the yearly mean (Fig. 5b). Based on part) summer radon concentrations clearly the gridded maps in Figs. 5a and 5b, the exceed the winter concentrations. Summer measuring stations can be categorised in values more than 20 times higher than winter three groups (Figs. 6a, b): Lower values were recorded in this area. topographical group (stations 4, 5, 6, 7, 8, The results from the comparison 9, 16, 17, 18, 21, 23) with summer radon between the soil radon concentrations and the values well above and winter radon values indoor radon concentrations at different well below the yearly average; Upper seasons are presented as scatter plots in Figs. topographical group (stations 2, 12, 14, 15, 9a and 9b. Correlation coefficients of 0.75 and 20, 22) with summer radon values well 0.76 for the summer and winter measurements, below and winter radon values well above respectively, indicate a significant correlation the yearly average; Middle group (stations between soil radon levels and indoor radon 1, 3, 10, 11, 13, 19) with summer and levels at different times of the year. winter values close to the yearly average. P-values from the Mann-Whitney test are shown in Table 7. There is a statistical Discussion significant difference in normalised median radon gas concentration between all three The formation of the ice-marginal deposit in geographical groups for both the summer Kinsarvik and winter measurements. The georadar profiles indicate that a large part The normalised ratios from the of the sediment deposition in Kinsarvik has indoor measurements show the same occurred in a glaciomarine environment geographical grouping as the normalised associated with an active glacier front. The ground values (Figs. 7a, b). Thus, the same high rate and localised character of the division into Lower, Upper and Middle sedimentation in such a system lead to the group can be adopted for the indoor radon development of a steep, prograding slope measurements (Figs. 8a, b). The result of where resedimentation by gravitational the Mann-Whitney test is significant at the processes occur (Lonne 1995). The units 5% level (Table 7). The dwellings located present from a depth of approximately 4 m and in the Upper group (topographic highest, downwards in the georadar profiles are thought south-eastern part) have considerably to be sediment gravity-flow deposits formed in higher winter radon values than summer front of an active glacier termini situated in the values. Ratios of winter to summer eastern part of the area. The high penetration concentrations as high as 161 are found in depth and discontinuous reflectors in the this area. In the dwellings within the Lower georadar profiles indicate that these sediments group (topographic lowest, north-western are dominated by coarse grain size fractions. 9

This interpretation is confirmed by the groundwater lie in the lower range of normal examination of the borehole samples from uranium concentrations in groundwater. the same depth which revealed a dominance Groundwaters typically contain 0.1 to 50 pg/1 of gravel and coarser material. In the upper uranium, but concentrations as high as 2000 meters of the georadar profiles, diffractions pg/1 have been reported, even in unmineralized seem to occur more frequently than at areas (Betcher and others 1988). The uranium greater depths indicating particularly contents of the river water in Kinsarvik do not boulder-rich sediments in the upper part of depart from typical uranium levels in surface the deposit. The surface of the deposit is waters (Rogers and Adams 1969). Due to characterised by numerous large boulders preferential mobilization of 234U compared to and many mounds and depressions. These 238U, the 234U/23SU activity ratio is almost factors indicate that the upper part of the always found to be higher than its equilibrium ice-marginal accumulation consists of value in water (Osmond and Cowart 1976). ablation sediments deposited at a time when 234U/238U ratios less than 1.0 in water are the glacier in the Huse valley was inactive. considered distinctly anomalous but have been The continuous, parallel reflectors close to reported e.g. in waters circulating through the ground surface displayed in some of the shallow uranium ore deposits and phosphorite georadar profiles and the sandy/gravely beds (Cowart and Osmond 1977). The low sediments found between the boulders levels of thorium recorded in the groundwater below the marine limit, indicate reworking from Kinsarvik are normal in natural waters of the ablation sediments by current- and due to the low solubility of thorianite and wave processes. The reworking process has ability of the thorium ion to adsorb onto produced a capping of finer sediments mineral surfaces (Langmuir and Herman above the boulder rich, and extremely 1980). permeable, zone below. The accumulation of unsupported radon in the groundwater is of interest when it The primary radon source comes to identifying a possible deep-lying The maximum thickness of the ice-marginal major radon source in the area. A fracture deposit is estimated to be approximately 50 zone occurs in the bedrock below the centre m. The geochemical analyses of the part of the Huse area, and the possibility of groundwater were carried out in order to high amounts of radon issuing from this fault search for a potential source for indoor zone was considered as a potential source for radon gas in the lower part of the sediment indoor radon gas (Maalo 1996). Enhanced accumulation or the underlying bedrock. concentrations of radon in soil air above The results from the uranium analyses show fractures and fault zones have been reported that uranium values in the Kinsarvik (Varley and Flowers 1993). However, 2 :Rn 10

has a limited lifespan and can only diffuse transported into the area, local derivation of approximately 5 cm in water, 5 m in air and Rn from """Ra 2 m in soil with a normal moisture content in the surrounding solid phase before it has decayed to 10 % of its initial is therefore considered to be the probable concentration (UNSCEAR 1982). If radon cause for the departure from secular transported from the fracture zone and equilibrium between radium and radon in the exhaling to the soil air was the primary Kinsarvik groundwater. This is in accordance source for indoor radon concentrations of with the conclusions of studies of up to 40 000 Bq/m3, non-diffusive and rapid radionuclides in groundwater in several other vertical transport of anomalously large areas (Tanner 1964; Wanty and others 1991). amounts of radon would have to take place. An estimate of the maximum radon The recorded radon levels in the concentration in the soil air in the Huse area groundwater are not particularly high, but when the source is the surrounding sediments since the springs and borehole sampled are can be obtained from formula 1 (Andersson located more than 100 m downstream from and others 1983): the fault zone, the exact levels of radon in Formula I. Cmax = A e 5 the groundwater above the fault zones has P been impossible to determine. However, where Cmax = Rn activity concentration due to the large thickness of the partly (Bq/m ) in the pore space with no ventilation saturated unconsolidated sediments and the (0 ach), A = activity of 226Ra (Bq/kg); e = very limited life of the 222Rn isotope, the emanation (%); S = compact density (kg m 3), likelihood of a primary source for indoor p = porosity (%) radon situated in the bedrock or the lower Assuming a radon emanation coefficient of 3 parts of the unconsolidated sediments is 0.25, a compact density of 2700 kg/m , a considered highly improbable. The porosity of 25 % and a radium concentration of uniformity of the radon levels in the various 60 Bq/kg, the radon concentration in the soil 3 groundwater samples indicates that the air can reach the level of 122 000 Bq/m when " Ra source of the "-Rn in the groundwater the surrounding sediments are dry, according is a dispersed one rather than a concentrated to formula 1. one. Since radon is extremely soluble in Several studies have shown that up water and not easily adsorbed on mineral to a certain moisture content, the radon surfaces, secular equilibrium between radon emanation increases with increasing moisture and its parents in water is generally rarely content (Strong and Levins 1982; Stranden and realised and not to be expected (Wanty and others 1984; Markkanen and Arvela 1992; Sun Schoen 1991). Given that it appears and Furbish 1995). Markkanen and Arvela unlikely for the large Rn levels to be (1992) found that the radon emanation from Finnish tills were higher for moist samples 11

than for dry samples and the maximum depth of 70 cm and are considered to be more emanation from the gravel fraction occur at representative for the actual radon 1-2 % water content. Strong and Levins concentrations in the soil air of the ice- (1982) studied Australian ores and tailings marginal deposit than the ones measured by and found that the emanation coefficients etched track detectors. By comparing the from water-saturated tailings were about radon values estimated by formula 1 and the four times those from absolutely dry measured radon concentrations in the soil air, it materials. It is therefore reasonable to can be concluded that there is no need for a believe that soil gas concentrations of radon deeper-lying source of radon in order to 3 several times higher than 122 000 Bq/m explain the origin of the measured radon can be caused by radon emanating from the concentrations in the soil air. The emanation sediments in the ice-marginal deposit. of radon from the surrounding sediments in The results from the large parts of the 50 m thick vadose zone is measurements of soil gas radon by etched assumed to be high enough to yield the radon track detectors at approximately 20 cm concentrations measured in the soil air. depth only showed maximum concentrations of around 60 000 Bq/m3. Temperature/pressure driven air-flows However, given the depth of these Radon concentrations in the soil air are known measurements, these levels are not to vary with time due to changes in soil considered to be accurate reflections of the moisture, soil permeability, wind, air soil gas radon levels. In November 1997 temperature and air pressure (e.g. Asher- and March 1998, soil radon concentrations Bolinder and others 1990; Washington and in all the 23 measuring locations were also Rose 1990; Schumann and others 1992; Sun recorded with a portable radon detector and Furbish 1995; Valen and others 1999). It (Markus-10) which measures instantaneous is therefore not unusual that large variations in values of radon in soil air samples by soil radon concentrations are recorded in the registering the alpha decay of the radon same measuring point during one year. In the daughter 2,8Po. The radon concentrations Huse area, however, there are not only large measured by the Markus-10 detector are in seasonal changes in radon levels but also general higher than the ones measured by variations according to a distinct geographical etched track detectors, but the results from pattern. It has been shown statistically that both studies show the same geographical there is a significant difference in normalised distribution of radon concentrations. median soil (and indoor) radon concentration Maximum values of around 350 000 Bq/m1 between an upper (topographic highest), lower were measured by the portable radon (topographic lowest) and middle (central) area detector. These values were recorded at a of the ice-marginal deposit for both summer 12

and winter measurements. This These sediments are partly covered by finer geographical grouping can not be explained sediments in the area below the marine limit, by observed differences in the physical but are exposed above the marine limit and in properties of the sediments in the different the riverbanks at the topographic lower end of areas. The only factor found to distinguish the deposit. Since most of the dwellings in the one geographical area from another is Huse area have cellars, the building elevation above sea level. It is therefore construction penetrates the upper capping of believed that subterranean air-flows occur finer sediments and is exposed to easily in the formation due to elevation movable soil air. Given the size of the vadose differences and differences in zone, large quantities of soil air containing temperature/pressure between soil air and relatively high concentrations of radon are atmospheric air (Valen and others 1999). available to maintain a continuous flow of The seasonal and geographical radon into the dwellings. The amount of soil changes in radon concentration are thought air that penetrates the constructions is, to be caused by the air-flows concentrating however, dependent on the building type and the available radon-laden soil air towards construction methods. one part of the sediment accumulation Studies of radon levels in dwellings while the other part is ventilated by located on Swedish and Finnish eskers have atmospheric air. In winter the soil air is revealed similar problems (Aakerblom and flowing towards the topographic highest others 1983; Hutri and Makelainen 1993; part of the deposit since the soil air Arvela and others 1994). Arvela and others temperature is higher than the atmospheric (1994) found that radon concentrations were temperature (Fig. 10). The topographic amplified in the upper part of an esker lowest area is then ventilated by formation in winter and in certain slope zones atmospheric air low in radon gas. In in summer. The amplification was found to be summer the process is reversed. The due to air flows inside the esker caused by ground air is flowing towards the area of differences in temperature between the soil air lowest elevation because the soil air and the outdoor air. Temperature/pressure temperature is lower than the air driven air-flows are also known from karst temperature. During this season the areas where transport of radon-laden air in and elevated area of the sediment accumulation out of caves and fissures with changes of is ventilated by air low in radon gas (Fig. pressure and temperature has been reported

10). (Gammage and others 1992; O'Connor and The air-flow is facilitated by the others 1992; Hughes and others 1999). extremely permeable sediments that underlie the whole residential area of Huse. 13

Consequences of the seasonal variations measurements in this area will clearly be in soil and indoor radon levels underestimations while annual average values The large seasonal changes in indoor radon based on summer measurements will be concentrations documented in the Huse area overestimations. The results from the heavily affect the estimation of the average Kinsarvik study indicate that radon annual radon concentration in the measurements in dwellings located on dwellings. Since an integration period of 2- permeable unconsolidated material, where air 3 months is frequently used for indoor movement in the ground can cause anomalous radon measurements, correction factors seasonal variations of indoor radon levels, must be applied in order to seasonally must be carried out both in summer and winter adjust the measurements to average annual in order to give a correct estimate of the annual concentrations. A study of radon mean indoor radon concentration. A precise concentrations in 7500 randomly selected calculation of the annual average radon value Norwegian dwellings at different seasons is important for the determination of dwellings revealed that the indoor radon in need of remediation. Owners of Norwegian concentrations in Norway are generally dwellings with an average annual radon twice as high in winter than in summer concentration exceeding 200 Bq/m3 can apply (Strand 1995). Thus, in order to estimate for a financial contribution of 75 % of the annual indoor radon concentrations in mitigation costs below NOK 40 000 (US $ Norway, winter measurements are 4500). multiplied by a factor of 0.75 and summer The results from correlation studies measurements by a factor of 1.5. The of indoor and soil radon concentrations in indoor radon concentrations measured different countries vary from very weak during spring and autumn are found to be correlation in some areas (Varley and Flowers close to the average and so are not 1998) to good correlation in other areas corrected. (Reimer and Gundersen 1989). The The study of indoor radon levels correlation coefficients of 0.75 and 0.76 show in Kinsarvik, however, reveals that for a significant correlation between indoor and some dwellings the summer concentrations soil radon concentrations in the Huse area for exceed the winter concentrations. both summer and winter measurements. Dwellings located in the topographic lowest Deviations from a perfect correlation most part (Lower group) of the Huse area have likely occur due to inhomogenities in the up to 20 times higher radon concentrations geological environment and variations in in summer than in winter. Consequently, housing construction techniques in the area. any calculated annual average radon Significant correlations between indoor and concentration based on winter soil radon concentrations indicate that soil 14

radon measurements are a useful tool for changes in radon concentrations have been the prediction of indoor radon levels. reported from an extensive ice-marginal However, the large seasonal and moraine deposit. geographical variations in soil radon Special precautions are required concentrations in the Huse area clearly when measuring indoor radon concentrations show how insufficient single soil gas in dwellings located on building grounds measurements are if the general geological where temperature/pressure driven air flows conditions are not considered. Indeed, are likely to occur. General correction factors several authors delineate that results from for estimating the annual average indoor radon soil gas measurements must be interpreted concentration are not applicable in such areas, in conjunction with geological data in order and a correct estimate of the annual indoor to be useful for estimates of indoor radon radon value can only be derived from concentrations (Reimer and Gundersen measurements carried out both in summer and 1989; Ball and others 1992; Albering and in winter. others 1996; Varley and Flowers 1998). Even though significant correlations The present study supports this view and can be obtained between indoor and soil radon illustrates that it is particularly important to concentrations, assessments of indoor radon avoid estimations of indoor radon levels concentrations should not be based on single solely based on single soil radon soil gas measurements without a general measurements in areas where air movement understanding of the geology in the area. This in the ground can cause anomalous seasonal has been proved to be of particular importance variations of soil and indoor radon levels. in the areas where the above mentioned permeable building grounds occur.

Conclusions Acknowledgements - This work was funded

In highly permeable building grounds, by the Research Council of Norway (project temperature/pressure driven air flows 135370/720). Valuable comments on the between areas of different elevation can manuscript were given by Dr. J. M. James and cause anomalously high seasonal changes Dr. G. Barnes (University of Sydney, in soil and indoor radon concentrations. Australia) and Dr. S. Whittlestone (University High indoor radon levels are easily of Wollongong, Australia). obtained when building constructions are exposed to large volumes of the readily movable soil air. In this paper, high indoor radon concentrations and large seasonal 15

References Ball TK, Cameron DG, Colman TB (1992) Aspects of radon potential mapping in Britain.

Aakerblom G, Andersson P, Clavensjo B Radiat Prot Dosim 45 (1/4):211-214 (1983) Soil gas radon - a source for indoor radon daughters. Radiat Prot Dosim 7 Beres M Jr, Haeni FP (1991) Application of (l/4):49-54 ground-penetrating radar methods in hydrogeologic studies. Ground Water 29:375- 386 Adams JAS, Gasparini P (1970) Gamma- ray spectrometry of rocks. Elsevier, Amsterdam Betcher RN, Gascoyne M, Brown D (1988) Uranium in groundwaters of southeastern Manitoba, Canada. Can J Earth Sci 25:2089- Albering HJ, Hoogewerff JA, Kleinjans 2103 JCS (1996) Survey of Rn-222 concentrations in dwellings and soils in the Dutch Belgian border region. Health Phys Cowart JB, Osmond JK (1977) Uranium 70 (l):64-69 isotopes in groundwater: Their use in prospecting for sandstone-type uranium deposits. J Geochem Explor 8:365-379 Andersson P, Clavensjø B, Aakerblom G (1983) The effect of the ground on the concentration of radon and gamma Davis JC (2002) Statistics and data analysis in radiation indoors. Swedish Council for geology, 3rd edn. Wiley, New York Building research, Report R9:1983, pp 1- 442 (In Swedish) Gammage RB, Dudney CS, Wilson DL, Saultz RJ, Bauer BC (1992) Subterranean transport of radon and elevated indoor radon in hilly karst Arvela H, Voutilainen A, Honkamma T, terrains. Atmosph Environ 26a (12):2237- Rosenberg A (1994) High indoor radon 2246 variations and the thermal behaviour of eskers. Health Phys 67 (3):254-260 Holtedahl H (1975) The geology of the Hardangerfjord, West Norway. Geol Survey Asher-Bolinder S, Owen DE, Schumann RR (1990) Pedologic and climatic controls of Norway 323:1-87 on Rn-222 concentrations in soil gas, Hughes JR, Turk B, Cardwell R, Brooks P, Denver, Colorado. Geophys Res Letters Fisher G, White M, Fitzgerald F, Wilson D, 17, 825-828. Bryant JO Jr (1999) Karst geology, radon fluctuations, and implications for measurement 16

and mitigation. Proe Int Conf on Radon in Maalo S (1996) Geologisk kartering - the Living Environment, 19-23 April 1999, radonprosjektet. University of Bergen, Athens, Greece, pp 173-181 Norway (Unpublished report)

Hutri KL, Makelainen I (1993) Indoor Markkanen M, Arvela H (1992) Radon radon in houses built on gravel and sand emanation from soils. Radiat Prot Dosim 45 deposits in southern Finland. Bull Geol (l/4):269-272 Soc 65:49-58 NGU-Lab (1997) NGU-SD 3 11 ICP-MS Ivanovich M, Harmon RS (1992) Uranium analyser av vann; NGU-SD 7.41 • Instrument series disequilibrium: Applications to Earth, og utstyr for ICP-MS, In: Ngu-Labs Marine and Environmental Sciences, kvalitetssystem, gruppe 3: Vannanalyse, Ivanovich M, Hannon RS (eds), Clarendon Trondheim: Section for laboratories, Press, Oxford Norwegian Geological Survey

Jenner GA, Longerich HP, Jackson SE, O'Connor PJ, Gallagher V, Van den Boom G, Fryer BJ (1990) ICP-MS - a powerful tool Hagendorf J, Muller R, Madden JS, Duffy JT, for high-precision trace element analysis in McLaughlin JP, Grimley S, McAulay IR, earth sciences: Evidence from analysis of Marsh D (1992) Mapping of Rn-222 and He-4 selected U.S.G.S. reference samples. Chem in soil gas over a karstic limestone-granite Geol 83:133-148 boundary: Correlation of high indoor Rn-222 with zones of enhanced permeability. Radiat Jensen CL (1997) Kartlegging og tiltak mot Prot Dosim 45 (1/4):215-218 radon i Ullensvang herad 1996-97. Project report, Ullensvang herad, pp 1-87 Osmond JK, Cowart JB (1976) The theory and uses of natural uranium isotopic variations in Langmuir D, Herman JS (1980) The hydrology. Atomic Energy Review 14:621- mobility of thorium in natural waters at low 679 termperatures. Geochim Cosmochim Acta 44:1753-1766 Peake RT (1988) Radon and geology in the United States. Radiat Prot Dosim 24 Lonne I (1995) Sedimentary facies and (1/4): 173-178 depositional architecture of ice-contact glaciomarine systems. Sedimentary Geol Reimer GM, Gundersen LCS (1989) A direct 98:13-43 correlation among indoor Rn, soil gas Rn and 17

geology in the Reading Prong near on radon exhalation. Radiat Prot Dosim 7 Boyertown, Pennsylvania. Health Phys 57 (l/4):55-58 (1): 155-160 Strong KP, Levins DM (1982) Effect of Rogers JJW, Adams JAS (1969) Uranium. moisture content on radon emanation from In: Handbook of Geochemistry. Wedepohl uranium ore and tailings. Health Phys 42 KH (ed) Springer- Verlag, Berlin (l):27-32

Rose AW, Hutter AR, Washington JW Sun H, Furbish DJ (1995) Moisture content (1990) Sampling variability of radon in soil effect on radon emanation in porous media. J gas. J. Geochem Explor 38:173-191 Contaminant Hydrology 18:239-255

Schumann RR, Owen DE, Asher BS (1992) Tanner AB (1964) Physical and chemical Effects of weather and soil characteristics controls on distribution of radium-226 and on temporal variations in soil-gas radon radon-222 in ground water near Great Salt concentrations. Special Paper Geol Soc of Lake, Utah. In. Adams JAS and Lowder WM Am 271:65-72 (eds) The natural radiation environment, Univ of Chicago Press, 253-276 Sigmond EMO (1998) Bedrock geology map, , M 1:250 000. Geol Survey of Tell I, Bensryd I, Rylander L, Jonsson G, Norway Daniel E (1994) Geochemistry and ground permeability as determinants of indoor radon Strand T (1995) Time variation of indoor concentrations in southernmost Sweden. radon concentration in typical Norwegian Applied Geochem 9:647-655 homes. Proe Int Conf NRE-VI 5-9 June 1995, Montreal, Quebec, Canada UNSCEAR (1982) Ionizing radiation: Sources and biological effects. Annex D. United Strand T and Lind B (1992) Radon in tap Nations Scientific Committee on the Effect of water from drilled wells in Norway. Proc Atomic Radiation, Report to the General 1992 Int Symp on Radon and radon Assembly, with annexes. United Nations reduction technology, Sept 22-25 1992, publication, New York Minneapolis, Minnesota, USA Valen V, Soldal O, Strand T, Henriksen H Stranden E, Kolstad AK, Lind B (1984) (1997) Anrikning og transport av radongass i The influence of moisture and temperature losmasser. Project report, InterConsult Group ASA, Norway, pp 1-45 18

Valen V, Soldal 0, Gunter B, Henriksen H, Jensen CL, Lauritzen SE, Rydock J, Rye N, Strand T, Sundal AV (1999) Variations in radon content in soil and dwellings in the Kinsarvik area, Norway, are strongly dependent on air temperature. Extended abstracts, AARST-2000 Int Radon Symp, Milwukee, Wisconsin, USA.

Varley NR, Flowers AG (1993) Radon in soil gas and its relationship with major faults of SW England. Environment Geochem and Health 15 (2/3): 145-151

Varley NR, Flowers AG (1998) Indoor radon prediction from soil gas measurements. Health Phys 74 (6): 714-718

Wanty RB, Johnson SL, Briggs PH (1991) Radon-222 and its parent radonuclides in groundwater from two study areas in New Jersey and Maryland, USA. Applied Geochem 6: 305-318

Wanty RB, Schoen R (1991) A review of the chemical processes affecting the mobility of radionuclides in natural waters, with applications. In. Gundersen LCS and Wanty RB (eds) Field studies of radon in rocks, soils, and water, U.S. Geol Survey Bull No 1971 183-193

Washington JW, Rose AW (1990) Regional and temporal relations of radon in soil gas to soil temperature and soil moisture. Geophys Research Letters 17:829-832 Fig. 1. The location of Kinsarvik in the western part of Norway and a topographical map showing the residential area of Huse and the location oj springs and boreholes 41 ooo m Summer 1996 (June-August) I | Autumn 1996 (October) |//l Winter 1997 (January-February)

41 ooo Maximum indoor radon value (Bq/m3)

11 500 \h 0-199 200-399 400-799 800-159JLll9 1600-3199j >320 0 Rn-concentration Bq/m

Fig. 2 Distribution of annual average values of indoor radon calculated on the basis of measurements during different seasons (from Jensen 1997) 21

Borehole A

o KH 1QI fOO + + o o 2 + +- + A 4 + AA 6 o o o _ 8 E. + + A £ 10 - A Q. A o o hit 101 hCH ( 1 D. 14 Kpi KDH ». 0 ''••• -—' —J 0 o 16 - % A tot H» O O / o A 20 / tCn hCH • O 0 o o o 22 1 1 1 1 1 1 1 1 1 1 1 1 1 0 20 40 60 80 100 120 140 0 10 20 30 40 50 60

Concentration (Bq/kg) Leachable % Major constituents Stratigraphy ED Meta-granite [ZD Boulder • Uranium ED Meta-daate O Cobble • Thorium E3 Phyllite Eel Gravel O Radium I I No sample S. Water table

Fig. 3a. The results of the U, Th, and Ra analyses of sediment samples from borehole A in the topographical lowest part of the ice marginal deposit along with stratigraphy and petrographic composition of the borehole samples Borehole B

K3*W O 5 + 4- +

+ +

4

•«x» O • I S I + +

HOI KH

t p 1BH •* .d .6 -Dl- -f-CM" ••••D—O" i 1 1 1 r- 0 20 40 60 80 100 120140 0 10 20 30 40 50 60 Concentration (Bq/kg) Leachable % Major constituents Stratigraphy E3 Meta-granite ED Boulder • Uranium EZD Gneiss GUI Cobble • Thorium EE3 Phyllite E3 Gravel O Radium SL Water table E3 Sand

Fig. 3 b. The results of the U, Th, and Ra analyses of sediment samples from borehole B in the topographical highest part of the deposit along with stratigraphy and petrographic composition of the borehole samples 23

Fig. 4 a-d. Distribution of radon concentrations in the soil air in the Huse area in a) August 1997, b) November 1997, c) March 1998, d) May 1998 24

(37155,264655) (37830.264655)

• Measuring stations for soil gas Rn

© Boreholes

Gridded values of normalised summer measurements

-3.0 - -2.5 Std. Dev. -2.5 - -2.0 Std. Dev. -2.0--1.5 Std. Dev. -1.5--1.0 Std. Dev. -1.0 - -0.5 Std. Dev. -0.5-0.0 Std. Dev. Mean 0.0-0.5 Std. Dev. 0.5-1.0 Std. Dev. 1.0-1.5 Std. Dev. 1.5 -2.0 Std. Dev. I 100 0 100 200 Meters (37155,268356) (37830.268356)

(37155,264655) (37830,263856) «W

• Measuring stations for soil gas Rn

® Boreholes

Gridded values of normalised venter measurements

-2.0--1.5 Std. Dev. ma5--1. 0 Std. Dev. -1.0 - -0.5 Std. Dev. -0.5-0.0 Std. Dev. Mean 0.0 -0.5 Std. Dev. 0.5-1.0 Std. Dev. 1.0-1.5 Std. Dev. 1.5-2.0 Std. Dev. 2.0-2.5 Std. Dev. 2.5-3.0 Std. Dev.

200 Meters

(37155.263856) (37830,263856)

Fig. 5 Gridded data of a) summer soil radon concentrations normalised against yearly average soil radon concentrations and b) winter soil radon concentrations normalised against yearly average soil radon concentrations. Location of measuring stations are marked with numbers. Gridding method. IDW 25

2,5 «4—in» C 0) E 2,0 2? to <1) E i— 1,5 (D E E to 1,0 TJ p Median Q) W I I 25%-75% To 0,5 I Non-Outlier Range i o o Outliers 2 0,0 LOWER MIDDLE UPPER Location

p Median I I 25%-75% I Non-Outlier Range o Outliers

LOWER MIDDLE UPPER Location

Fig. 6. Box plots for a) the categorised summer soil radon concentrations normalised against the yearly mean and b) the categorised winter soil radon concentrations normalised against the yearly mean 26

(37155.264655) (37830,264655)

IM A • Measuring stations for indoor air Rn

© Boreholes

Gridded values of normalised indoor summer measurements • I-2.0--1.5 Std. Dev. nn-1.5--1.0Std. Dev. I 1 -1.0 - -0.5 Std. Dev. | -0.5 - 0.0 Std. Dev. nMean 0.0-0.5 Std. Dev. _J 0.5 -1.0 Std. Dev. 1.0-1.5 Std. Dev. • 1.5-2.0 Std. Dev. 1 2.0-2.5 Std. Dev. • 2.5-3.0 Std. Dev. 100 100 200 Meters

(37155,263856) (37830,263856)

(37155.264655) (37830.264655)

IN A • Measuring stations for indoor air Rn © Boreholes

Gridded values of normalised indoor winter measurements -2.0--1.5 Std. Dev. -1.5--1.0 Std. Dev. -1.0 - -0.5 Std. Dev. -0.5 - 0.0 Std. Dev. Mean 0.0 - 0.5 Std. Dev. 0.5-1.0 Std. Dev. | 1.0-1.5 Std. Dev. 1.5-2.0 Std. Dev. | 2.0-2.5 Std. Dev. 2.5-3.0 Std. Dev.

100 100 200 Meters

(37155,263856) (37830,263856)

Fig. 7. Gridded ratios of (a) indoor summer concentrations to yearly average indoor concentrations, and (b) indoor winter concentrations to yearly average indoor concentrations. Locations of dwellings are marked with dots. Gridding method: ID W 344

• Median I I 25%-75% I Non-Outlier Range LOWER MIDDLE UPPER o Outliers Location

SS c O) E

=3 nj a> E ®i— c 5 T3

0 Median I I 25%-75% 1 Non-Outlier Range LOWER MIDDLE UPPER o Outliers Location

F/g. Å Boxplots for a) the categorised ratios of indoor summer radon concentrations to the yearly mean and b) the ratios of indoor winter radon concentrations to the yearly mean 28

Soil-gas Rn (Bq/m3)

Soil-gas Rn (Bq/m3)

Fig. 9. Plots of soil radon concentrations against indoor radon concentrations for summer and winter measurements: a) average of soil radon May and August vs. indoor radon June-August, b) soil radon March vs. indoor radon January-February. 29

Outflow of wtmudtir

' Morain rich in boulders Marine sandy sediments I Boulder rich gravel and ^ Prevailing direction sand of soil air flow

T I 0 500 1000 Distance (m)

Fig. 10. Illustration of the temperature driven seasonal transport of radon gas in the Huse area. Warm air is lighter than cold air. In the wintertime the temperature of the soil air is higher than the atmospheric temperature, and so soil airflows toward the elevated part of the deposit. During the warm season the ground air flows toward the area of lowest elevation because the soil air temperature is lower than the air temperature (Valen and others 1999). 30

Table 1. Description of laboratory analyses of bedrock and sediment samples Material Treatment Analysed for Method Estimated accuracy Bedrock Untreated U and Th Inductively coupled plasma mass spectrometry ± 3-7 % samples (ICP-MS) (Jenner and others 1990)

1. Uand Th 1. ICP-MS (Jenner and others 1990) ± 3-7 % a. Untreated 2 . 226 Ra 2. Gamma spectroscopy (Adams and Gaspirini ±5-15% Borehole 1970) samples 3. Rn exhalation rate 3. Scintillation flask method ± 20-25 %

(2-4 mm) b. HC1 and 1. U and Th 1 ICP-MS (Jenner and others 1990) ± 3-7 % 226 Na,S03 2. Ra 2. Gamma spectroscopy (Adams and Gaspirini ± 5-15 % 1970) 31

Table 2. Description of laboratory analyses of water samples Sample Treatment Analysed for Method Estimated volume accuracy

100 ml Filtered through 0.45 |im filter and U and Th ICP-MS (NGU-Lab 1997) ± 10% acidified to pH

25 1 Filtered through 0.45 pin filter and Isotopic composition Alpha spectrometry ±5-10% acidified to pH

500 ml Filtered through 0.45 jam filter and Ra Scintillation flask method ± 20-25 %

acidified to pH

Table 3. U and Th concentrations in different rock types from the Kinsarvik area Rock type Number U (ppm) Range a Th Range CT Th/U of mean (ppm) (ppm) (ppm) samples mean M eta-granite 1 5 5.8 3.3 - 8.8 2 79 16.8 10.8-23.1 6.15 2.9 M eta-granite 2 3 2.0 2.0- 2.5 0.24 8.6 6.3 - 10.1 2.04 3.7 M eta-granite 3 3 4.1 3.7- 4.6 0.49 9.1 8.2- 9.8 0.82 2.2 Granite 1 4 22.9 10.7-31.6 10.88 27.6 27.4- 37.7 5.92 1.2 Granite 2 3 3.7 3.4 - 4.4 0.61 35.9 29.1 -45.4 8.47 9.7 Pegmatite 3 6.8 4.8- 7.2 2.73 9.5 7.7- 12.9 2.96 1.4 Meta-dacite 3 1.4 1.1 - 1.7 0.28 4.3 3.8- 5.1 0.68 3.0 Phyllite 3 2.8 2.7 - 4.1 1.15 11.0 8.8 - 12.9 2.05 3.9 33

Table 4a. Radio nuclide contents in groundwater and surface water from Kinsarvik sampled 10.06.00 Sample U (fig/1) Th (Mg/I) Ra (Bq/I) Rn (Bq/I)

Spring no 1 0.44 +/- 0.044 < 0.005 <0.1 Bq/1 276 +/- 55 Spring no 2 0.51 +/-0.051 < 0.005 <0.1 Bq/1 310+/-62 Spring no 4 0.38 +/- 0.038 < 0.005 <0.1 Bq/1 364 +/- 73 Spring no 5 0.31 +/- 0.031 < 0.005 <0.1 Bq/1 269 +/- 54 Borehole A 0.63 +/- 0.063 < 0.005 <0.1 Bq/1 240 +/- 48 River I 0.57 +/- 0.057 0.016+/- 0.0016 < 0.1 Bq/1 < 10 River II 1.12+/-0.112 0.028 +/- 0.0028 <0.1 Bq/1 < 10

Table 4b. Uranium concentrations in groundwater sampled 06.03.98 234 238 23U 234 Sample u (Hg/1) u/ u Th/ U

Spring no 1 0.27 +/- 0.007 1.21 +/-0.038 0.15 +/-0.015 Spring no 2 0.19+/-0.005 1 19+/-0.039 0.06 +/-0.013 Spring no 4 0.19+/- 0.006 2.40 +/- 0.090 0.04 +/- 0.007

Table 4c. Radon concentrations in groundwater sampled at different seasons Sample Rn (Bq/1) Rn (Bq/1) Rn (Bq/1) Rn (Bq/I) Sampled 20.08.97 Sampled 06.11.97 Sampled 06.03.98 Sampled 27.05.98

Spring no 1 200 +/- 40 258 +/- 52 312+/- 62 333 +/- 67 Spring no 2 370 +/- 74 276 +/- 55 365 +/- 73 387 +/- 77 Spring no 3 235 +/- 47 276 +/- 55 326 +/- 65 Spring no 4 472 +/- 94 467 +/- 93 Spring no 5 367 +/- 73 330 +/- 66 34

Table 5. Radium concentrations and emanation coefficient for the 10 bore tole samples Borehole A: Depth Ra Emanation Borehole B: Depth Ra Emanation below surface (m) (Bq/kg) coefficient below surface (m) (Bq/kg) coefficient

1 -2 66 +/- 3.96 0.22 0-1 31 +/- 2.48 0.33 13-14 63 +/-3.15 0.17 14- 15 18+/-2.70 0.39 14-15 67 +/- 4.02 0.17 23-24 84 +/- 3.36 0.24 17-18 47 +/- 2.35 0.14 27-28 74 +/- 3.70 0.21 20-21 59 +/- 2.95 0.22 29-30 65 +/- 3.25 0.13 35

Table 6. Average air temperature, average precipitation, average wind speed and concentrations of soil radon at different seasons Period Average air Average Average Average Range Median temperature precipitation wind speed soil-gas Rn (Bq/m3) (Bq/m3) (°C) (mm) (m/s) (Bq/m3)

August 1997 21.3 0 0.85 1700 900 - 48000 9300 November 1997 6.8 0 0.60 4200 800-21000 3000 March 1998 -4.0 1.0 (snow) 0.55 10000 200 - 59000 2500 May 1998 12.1 1.0 1.16 14000 1300-42000 6800 36

Table 7. P-values from the Mann-Whitney test. P-values < 0.05 are denoted "significant" Normalised summer soil radon measurements Normalised winter soil radon measurements

UPPER X UPPER X MIDDLE X 0.004 MIDDLE X 0.004 LOWER X 0.001 0.001 LOWER X 0.001 0.001 LOWER MIDDLE UPPER LOWER MIDDLE UPPER Normalised summer indoor radon measurements Normalised winter indoor radon measurements

UPPER X UPPER X MIDDLE X <0.000001 MIDDLE X 0.000001 LOWER X 0.01443 <0.000001 LOWER X <0.000001 <0.000001 LOWER MIDDLE UPPER LOWER MIDDLE UPPER Paper III

Sundal AV & Strand T Indoor gamma radiation and radon concentrations in a Norwegian carbonatite area. Submitted to the Journal of Environmental Radioactivity, 2003. 1

Indoor gamma radiation and radon concentrations in a Norwegian carbonatite area

AUD VENKE SUNDAL & TERJE STRAND

Sundal AV & Strand T. Indoor gamma radiation and radon concentrations in a Norwegian carbonatite area. Submitted to the Journal of Environmental Radioactivity.

Results of indoor gamma radiation and radon measurements in 95 wooden dwellings located in a Norwegian thorium-rich carbonatite area using thermoluminescent dosimeters and CR-39 alpha track detectors, respectively, are reported together with a thorough analysis of the indoor data with regard to geological factors. Slightly enhanced radium levels and thorium concentrations of several thousands Bq/kg in the carbonatites were found to cause elevated indoor radon levels and the highest indoor gamma dose rates ever reported from wooden houses in Norway. An average indoor gamma dose rate of 200 nGy/h and a maximum of 620 nGy/h were obtained for the group of dwellings located directly on the most thorium-rich bedrock. Remedial actions to secure the thorium-rich waste rock from the former iron mining activity in the area are currently considered.

And Venke Sundal, Department of Earth Science, University of Bergen, Allegata 41, N-5007 Bergen, Norway Terje Strand, Norwegian Radiation Protection Authorities, P.O. Box 55, N-1332 Osterås, Norway

Introduction emitted from potassium-40 and members of the uranium and thorium decay chains in geological strata and building materials. The Naturally occurring radionuclides are total effective dose from naturally occurring responsible for the major contribution to the radiation received by the Norwegian total effective dose of ionizing radiation population is currently estimated to 2.9 mSv received by the population (UNSCEAR, per year (Nordic, 2000). Exposure to radon- 1993). The radiation dose from natural 222 and its short-lived decay products accounts sources is generated by internal exposure for around 1.7 mSv of the total effective dose, from radioelements in diet and inhaled while the contributions from radioelements in radon and its progenies as well as external diet, cosmic rays and gamma radiation from exposure from cosmic rays and gamma rays 2

the ground and building materials are The Fen complex is the type area for estimated to 0.35 mSv, 0.3 mSv and 0.5 carbonatites (carbonate rocks of volcanic mSv per year, respectively. origin) and was first described by Brogger in In the 1980s, a study of 19 1921. Studies of the rare rock association in dwellings located within the Fen complex the area have played an important role in the of carbonatites and alkaline silicate rocks understanding of carbonatite-complex geology revealed high levels of radon and external (Brogger, 1921; Sæther, 1957; Barth and gamma radiation indoors (Stranden, 1985; Ramberg, 1966). The Fen complex is the only Stranden and Strand, 1986) Analysis of occurrence of carbonatites in Norway, but the rare rock types in the area revealed several other carbonatite areas are known in enhanced concentrations of thorium-232 Fennoscandia (Eckermann, 1948; Paarma, and radium-226. During the last decades, 1970: Puustinen, 1971) the number of dwellings in the Fen area has The rock types which occupy the nearly been doubled, and attention has largest fraction of the surface area of the Fen increasingly been drawn to the levels of central complex are sdvite (calcite carbonatite), radiation received by the local residents due rauhaugite (dolomite carbonatite), rodberg to natural sources. The present paper (hematite-calcite-carbonatite) and fenite discusses the result of a recent study of (alkali-metasomatised granitic gneiss) (Fig. indoor gamma radiation levels and radon la). Only limited outcrops of the other rock concentrations in 95 dwellings in the Fen types are found due to the thick Quaternary silt area using thermoluminescent dosimeters and clay deposits covering a major part of the and alpha track detectors, respectively. A complex (Fig. lb). The rodberg was mined for systematic analysis of the indoor data with iron from 1655 until 1927, and the sovite was regard to geological factors is presented. mined for niobium between 1953 and 1965. The many pit heads and piles of tailings found Study area in the rodberg area are evidences of the The Fen complex is located in the extensive mining activity at Fen. Studies have Precambrian gneisses of Telemark, shown that the Fen carbonatites are strongly approximately 120 km southwest of Oslo enriched in rare earth minerals (REE), but no (Fig. la). The central circular intrusive has exploitation of these minerals has taken place a diameter of about 2 km and represents a so far (Mitchell and Brunfelt, 1975; Andersen, cross-section of the feeder pipe of a volcano 1986). Today, approximately 350 dwellings which was active nearly 600 million years are located within the Fen central complex. ago (Sæther, 1957; Barth and Ramberg, In the beginning of the 1980s, 1966). Around the central complex studies of natural radioactivity were carried out numerous satellite intrusions occur. in the Fen area (Stranden, 1984; Stranden, 3

1985; Stranden and Strand, 1986; Dahlgren, building grounds. The radon measurements 1983). Elevated levels of thorium-232 in were carried out using NRPA alpha track the carbonatites were reported, and higher detectors (C-39). The detectors consist of a concentrations of radium-226 than normal small piece of polycarbonate film enclosed in a were also measured in some of the rock small plastic canister. Each householder types (Stranden, 1984). A study of radon- received two radon detectors which were 222 daughters and thoron daughters indoors exposed for approximately 3 months revealed that thoron daughter exposure may (February-May). One detector was located in give the dominating contribution to the the living room, and the other detector was effective dose equivalent in dwellings placed in the principal bedroom. The indoor located on thorium-rich ground (Stranden, radon concentration for each dwelling was 1984). Measurements of natural gamma given as the average value of the two radon radiation indoors carried out by a Studs measurements. portable plastic scintillator, indicated higher average external dose rates in the Fen Gamma radiation indoors houses compared to the average for the Measurements of gamma radiation were whole country (Stranden and Strand, 1986). carried out in the selected 95 dwellings An epidemiological study on former simultaneously with the radon measurements. workers in the niobium mine revealed a To get a 2-3 months average, significant increment in lung cancer among thermoluminescent dosemeters (TLD) were the miners (Solli et al., 1985). The outdoor used. One dosemeter was issued to each gamma radiation levels in the Fen central household, and the participants were instructed complex were mapped by Dahlgren (1983). to place the dosemeter in the living room close to the alpha track detector. The thermoluminescent dosemeters consist of two 3 Survey methodology CaF2:Dy ribbons (3.2 x 3.2 x 0.9 mm ) enclosed in a specially designed polyethylene

Indoor radon badge (Wohni, 1993). The ribbons were Measurements of indoor radon annealed in an oven (400°C for 1 h and 15 min concentrations were performed in 92 and 100°C for 2 h and 30 min), and the zero detached dwellings in the Fen area and 3 readings of the ribbons were checked. The dwellings just outside the central complex. readings were done in an automatic TLD The dwellings were selected based on reader with a nitrogen heating system. The underlying geological characteristics in lower limit of detection of the dosemeters was order to enable comparisons of results for determined to 2.5 jiSv. The individual buildings founded on various types of sensitivity of each ribbon was taken into 4

account when calculating the doses. A information on building characteristics, cosmic background component aeration habits of the occupants and water corresponding to 30 nGy/h was subtracted supply. The questionnaires were issued and from the original data. returned by mail together with the thermoluminescent dosemeters and the alpha Gamma spectrometry track detectors. The questionnaires provided Gamma-ray spectrometric measurements information on: Category of dwelling, age of were performed on rock samples from the dwelling, floor level of room in which Fen area in order to quantify the activity measurements were taken, outer wall material, concentrations of the natural radionuclides foundation wall material, type of basement, Ra-226, Th-232 and K-40. Thirty five rock ventilation system, aeration habits and source samples of the rodberg, sovite, rauhaugite of household water. and fenite were collected along with 4 The characteristics of the building samples from the iron mine waste rock ground underlying each of the participating (rodberg). The rock samples were collected dwellings were determined by fieldwork and as close to the selected dwellings as use of existing geological maps. The building possible. All samples were powdered, ground was classified according to type of dried and sealed in 400-ml cylindrical bedrock and type of overburden. plastic beakers for about 3 weeks to ensure secular equilibrium between Ra-226 and its daughters. The measurements were carried Results and discussion out with a 90-cnr Ge(Li) detector and a Canberra Model 8100 multichannel Radionuclide concentrations in rock analyser. The equipment was calibrated material against standard samples with known Activity concentrations of thorium-232, concentrations of all the radionuclides of radium-226 and potassium-40 in rock material interest. The Ra-226 and Th-232 contents from the Fen central complex and adjacent were computed from Bi-214 (609 keV) and areas are presented in Table 1. The highest Ac-228 (911 keV) activities, respectively, thorium-232 levels were measured in rodberg assuming secular equilibrium among the and waste rock from the iron mine (average radionuclides of the series. levels of 3100 and 4500 Bq/kg, respectively). Precambrian gneiss had the lowest mean Data on house construction, ventilation thorium level of 66 Bq/kg. The average habits and geology radium-226 concentrations were found to Questionnaires completed by each of the range from 20 to 120 Bq/kg. The highest mean participating households provided radium-226 value and the maximum value of 5

300 Bq/kg were measured in rauhaugite. piles of waste rock are found in the rodberg The average potassium-40 levels ranged area. So far, no action has been taken to secure from 30 Bq/kg (sovite) to 1060 Bq/kg the waste material. A limited number of (fenite). measurements of total gamma radiation at 1 The results show that the meters height above the waste rock using a carbonatites in the Fen area contain Studsvik Gamma Meter (organic scintillator) enhanced concentrations of natural gave ambient dose equivalent rates in the range radioactivity compared to normal rock 3 - 5 pSv/h. types. The thorium levels in Nordic rock types typically range from 0.5 to 350 Bq/kg Indoor radon (Nordic, 2000). The Fen carbonatites have The distribution of indoor radon concentrations the highest levels of thorium recorded in measured in the 95 dwellings is presented in Norwegian bedrock. The carbonatites Fig. 2. The results show a log normal found to contain the highest concentrations distribution with an arithmetic mean of 204 of thorium (rodberg and rauhaugite) also Bq/nf and a geometric mean of 127 Bq/m3 have higher radium-226 contents than most (Table 2). The radon concentrations ranged rock types. Radium concentrations above from 10 to 1250 Bq/m3 Thirty-seven % of 100 Bq/kg are, however, not uncommon in the dwellings included in the study were found rock types like granites, pegmatites and to have radon concentrations above 200 Bq/m3, black shales. Only low to normal while 11 % of the selected housings had radon concentrations of radium-226 were values in excess of 400 Bq/m3 The radon measured in the sovite (Table 1). An concentrations presented in Fig. 2 are corrected average radium-226 concentration of 310 to average annual radon concentrations by Bq/kg was, however, reported from 6 sovite assuming that the concentration in the heating samples measured in a previous study, season is twice the level in the summer indicating somewhat higher levels of (Strand, 1995). radium-226 in this carbonatite than The highest indoor radon registered in the present investigation concentrations were measured in the areas of (Stranden. 1984). The potassium-40 exposed carbonatites (Table 2). The arithmetic concentrations measured in the rock types mean values of indoor radon concentrations in of the Fen area lie within the normal range dwellings built directly on bedrock ranged of potassium-40 concentrations in Nordic from 340 Bq/m in the rodberg area to 69 bedrock (Nordic, 2000). Bq/m3 in the gneiss area. The corresponding A major landfill of waste rock figures for the geometric mean were 189 covering an area of approximately 0.25 km2 Bq/m3 and 62 Bq/m3. respectively. No is present by the lake Norsjo, and many dwelling located on Precambrian gneiss had 6

indoor radon values exceeding 200 Bq/m3, material on indoor radon levels. A geometric while radon values above 200 Bq/m3 and mean radon level of 182 Bq/m3 was reported 400 Bq/m3 were measured in 64 % and 27 for the measurements carried out in the cellar, % of the dwellings in the rodberg area. while the geometric means for the The areas covered by silt and clay measurements performed on the ground floor deposits gave fairly low readings for indoor and the first floor were 115 Bq/m' and 33 radon concentrations (Table 2). Arithmetic Bq/m3, respectively. The Student's t-test and geometric mean values of 63 Bq/m3 yielded a significant difference between indoor and 48 Bq/m3, respectively, were reported radon values for all floor levels (p < 0.0001 for for this group of dwellings. The difference basement versus ground floor and basement between indoor radon values in dwellings versus first floor, p = 0.02 for ground floor located on exposed bedrock and dwellings versus first floor). A geometric mean radon located on silt and clay deposits is concentration of 69 Bq/m3 was obtained for the illustrated in Fig. 3. The Student's t-test group of dwellings with foundation walls made yielded a significant difference between of concrete, while dwellings with foundation indoor radon concentrations in dwellings walls made of light weight concrete had a located on silt/clay covered carbonate rocks mean radon level of 159 Bq/m1 The and dwellings located directly on these rock difference was found to be statistically types (p < 0.0001 for exposed rauhaugite significant (p < 0.0003) versus silt/clay covered rauhaugite and The indoor radon values measured in exposed sovite versus silt/clay covered the present investigation are generally higher sovite, p = 0.0090 for exposed rodberg than the values registered for the country as a versus silt/clay covered rodberg). whole. In 2000-2001, the Norwegian Like most Norwegian dwellings Radiation Protection Authority (NRPA) earned in rural areas, the surveyed dwellings in the out indoor radon measurements in nearly 29 Fen area are detached houses with outer 000 randomly selected dwellings in 114 out of walls made of wooden materials. All 435 Norwegian municipalities (Strand et al., households have water supply from 2001). Based on the results from the indoor waterworks based on surface water. radon study, the annual mean radon Remedial measures to reduce indoor radon concentration in the Norwegian housing stock concentrations have not been undertaken in was calculated to 88 Bq/m3 (Strand et al., the surveyed dwellings. Comparisons of 2001). It was estimated that 9 % and 3 % of indoor radon concentrations with building Norwegian dwellings have annual average characteristics and ventilation habits only radon concentrations exceeding 200 and 400 revealed a statistically significant effect of Bq/m3, respectively. The results from the floor level and type of foundation wall present study show that the average radon 7

value and the percentages of dwellings The reported levels of radium-226 in exceeding 200 and 400 Bq/nr in the Fen the carbonatites are found to be normal to high area are several times higher than for the compared to typical radium-226 levels in other whole country. The maximum levels Nordic rock types (Nordic, 2000). It is measured in the Fen area are, however, not therefore reasonable to suppose that the indoor among the highest registered in Norway. radon problems in the Fen area are caused by Radon concentrations of an order of radon gas emanating from the rauhaugite, magnitude higher than the values obtained rodberg and the sovite in the building ground. in this study have been reported from other The fine grained sediments covering a large parts of the country (Jensen, 1997; Strand et part of the carbonatite surface render the al., 2001). ground impermeable to transport of soil gas A strong association between and are responsible for the low indoor radon indoor radon concentrations and the levels in these areas. underlying geological structure is observed in the Fen area. The results show that the Gamma radiation indoors risk for high indoor radon levels increases The distribution of external dose rates in terms with increasing radium-226 content of the of free air kerma from terrestrial gamma underlying bedrock. Building materials radiation measured in the 95 dwellings is manufactured in Norway have been presented in Fig. 4. A cosmic ray contribution reported to contain low levels of of 30 nGy/h has been subtracted, so that the radioactivity (Stranden, 1979), and the variation in the terrestrial gamma radiation is observed discrepancy between indoor radon shown. The distribution approximates to log- levels in dwelling with foundation walls normal and the arithmetic and geometric mean made of light weight concrete and values are 98 nGy/h and 82 nGy/h, dwellings with normal concrete in the Fen respectively (Table 3). The dose rates for the area is more likely attributable to the higher whole group of dwellings ranged from 35 permeability of the former material, nGy/h to 620 nGy/h. facilitating transport of radon to the The highest external gamma dose dwellings, rather than enhanced levels of rates were measured in dwellings built directly radium-226 in this material. Since the on the carbonatites, the levels being concentrations of natural radioactive particularly high in the rodberg and the substances always are low in surface rauhaugite areas (Table 3). The average waters, the major source of indoor radon external dose rate measured in the rodberg area concentrations in the surveyed buildings is was 200 nGy/h, while the geometric mean assumed to be the building ground. obtained for the same group of dwellings was 157 nGy/h. The corresponding figures for the 8

rauhaugite area were 110 Bq/m3 and 99 found to have a significant association with the Bq/m3, respectively. The observed levels of external dose rates indoors was the floor level external dose rates in the other areas of of the rooms in which measurements were exposed bedrock were considerably lower. taken. The geometric mean dose rate for The arithmetic mean and median values of measurements performed in the cellar was 114 gamma dose rates in dwellings built nGy/h, while the geometric means for directly on fenite and Precambrian gneiss measurements earned out in the ground floor were close to 55 nGy/h. The maximum and first floor were 98 nGy/h and 77 nGy/h, value of 620 nGy/h was registered in the respectively. A significant difference between rodberg area. external dose rates for all floor levels was The dose rates measured in found (p < 0.0001 for basement versus ground dwellings located on silt and clay deposits floor and basement versus first floor, p = 0.02 were in the same range as the dose rates for ground floor versus first floor). measured in dwellings located on fenite and The gamma dose rates obtained in gneiss. An arithmetic mean value of 55 parts of the Fen area are considerably higher nGy/h and a geometric mean value of 53 than the values reported for the country as a nGy/h were reported for external dose rates whole. Storruste et al. (1965) carried out in this group of dwellings. The difference measurements of indoor gamma dose rates in between the gamma dose rates in dwellings 2026 dwellings in various Norwegian districts located on exposed carbonatites and and reported a mean value of 95 nGy/h for all dwellings located on silt and clay deposits houses and 70 nGy/h for wooden houses, the is illustrated in Fig. 5. The Student's t-test contribution from cosmic radiation being yielded a significant difference between the subtracted. Calculations of the population external dose rates in the areas of exposed weighted average indoor dose rate based on rauhaugite, rodberg and sovite compared to these measurements gave a value of 79 nGy/h the silt/clay covered areas (p < 0.0001 for (Stranden, 1977). The mean gamma dose rate exposed rauhaugite versus silt/clay covered in the group of dwellings founded on the most rauhaugite, p = 0.0005 for exposed rodberg radioactive carbonate rock in the Fen area is 3- versus silt/clay covered rodberg and 0.0226 4 times higher than the national average, while for exposed sovite versus silt/clay covered the maximum value of 620 nGy/h is sovite). approximately 10 times the national average. From the questionnaire These values are comparable to the maximum information there was no statistical indoor gamma dose rates registered in other evidence to confirm any general effect on European countries (e.g. Rannou et al., 1985; gamma dose rates indoors resulting from Mjones, 1986; Arvela, 1995). building characteristics. The only factor 9

A correlation between indoor conclusion that the main contribution to indoor gamma dose rates and geology in the Fen gamma radiation in the Fen dwellings arises area is evident. High indoor gamma from the thorium-series radionuclides in the radiation environment was registered in the carbonatites. Since the potassium-40 content areas of exposed carbonatites containing of both bedrock and building material is low, elevated levels of radionuclides, while the the contribution to the indoor gamma dose other areas were found to give fairly low rates from this radionuclide is assumed to be readings for penetrating radiation. The considerably lower than the contribution from gamma dose rates are particularly high in members of the thorium- and uranium-series. the group of dwellings founded on thorium- The combination of high indoor gamma dose rich bedrock suggesting that the enhanced rates and low radon concentrations can be used indoor gamma dose rates are predominately as a criteria for determining which houses have caused by an elevated gamma radiation an elevated risk of containing high indoor contribution from the thorium-series in the thoron levels. underlying bedrock. In the areas where low The average gamma dose rate permeable silt and clay deposits cover the obtained in the present study is lower than the carbonatite surface, the overburden act as average value that emerged from the previous an efficient shield reducing the exposure to study of gamma radiation performed in 19 local residents from terrestrial gamma wooden dwellings within the Fen central radiation. The areas of high indoor gamma complex (Stranden and Strand, 1986). The rates accord well with the reported areas of maximum levels reported for the two studies high outdoor gamma radiation (Dahlgren, are, however, in the same range (620 nGy/h for 1983). The lack of correlation between the present study; 560 nGy/h for the previous indoor gamma radiation and building study). The discrepancy in average dose rates characteristics is most likely due to the can therefore be attributed to different criteria extensive use of wooden building material adopted for the selection of the surveyed and dominating contribution of indoor buildings. The maximum level of indoor gamma radiation from the building ground. gamma radiation registered in this study is the

A weak positive correlation highest level ever measured in wooden between gamma dose rates and radon dwellings in Norway. Indoor gamma dose concentrations indoors for the surveyed rates as high as 950 nGy/h have, however, dwellings was observed (Fig. 6). The been reported from three dwellings made of results show that some of the highest indoor carbonatite rock located in the outer pail of the gamma dose rates were registered in Fen area (Stranden and Strand, 1986). dwellings containing indoor radon levels no higher than 100 Bq/m3, supporting the 10

Dosimetry The group of dwellings located on The annual effective dose due to indoor exposed surfaces of carbonatites also has gamma radiation was estimated adopting enhanced levels of indoor radon compared to the coefficient 0.7 Sv/Gy recommended by the average for the country. Special attention UNSCEAR (1993) to convert the gamma should be paid to reducing the radon levels and absorbed dose rate in air into effective dose to radon-safe construction of new houses in equivalent. Assuming an occupation factor these areas due to the extra radiation dose to of 0.8, the average annual effective dose for local residents caused by terrestrial gamma wooden dwellings founded directly on the radiation. The combination of high indoor high-radioactive rodberg was calculated to gamma dose rates and moderate indoor radon 1.0 mSv/y, the range being 0.2 - 3.0 mSv/y. concentrations can be used as a criteria for prediction of elevated indoor thoron levels. The enhanced concentrations of Conclusions thorium in the iron mine waste rock give rise to ambient dose equivalent rates of 3-5 jiSv/h.

The results from a study of indoor gamma Remedial actions to reduce the gamma radiation levels and radon concentrations in radiation to normal levels of < 0.2 jiSv/h in the a carbonatite area using thermoluminescent affected areas are currently discussed. Silt and dosemeters and alpha track detectors have clay deposits have been shown to effectively been presented together with an analysis of reduce the radon flux and gamma radiation the data with regard to geological factors. from the underlying bedrock, and the covering The results show that enhanced levels of of the waste material with clay layers as well thorium and slightly elevated levels of as restricting the building activity in the area radium in the carbonatites are responsible are remediation measures to be considered. for the highest gamma dose rates ever reported from wooden houses in Norway. In the areas where housings are founded on Acknowledgement - This work was founded by exposed surfaces of the most thorium-rich the Norwegian Research Council (project carbonatite, an average indoor gamma dose 135370/720). rate of 200 nGy/h was reported, the range being 47 - 620 nGy/h. Using normal conversion factors these values correspond to a mean effective dose equivalent of 1.0 mSv/y ear and a range of 0.2 - 3.0 mSv/year. 11

References Jensen, C.L. (1997). Kartlegging og tiltak mot radon i Ullensvang herad 1996-97. Report,

Anderson, T. (1986). Compositional Ullensvang herad, 87 pp. variation of some rare earth minerals from the Fen complex (Telemark. SE Norway): Mitchell, R.H., Brunfelt, A.O. (1975). Rare Earth Element Geochemistry of the Fen implications for the mobility of rare earths alkaline complex, Norway. Contributions to in a carbonatite system. Mineralogical Mineralogy and Petrology, 52, 247-259. Magazine, 50, 503-509.

Mjones, L. (1986). Gamma radiation in Arvela, H., Hyvonen, H., Lemmela, H. and Swedish dwellings. Radiation Protection Castren, O. (1995). Indoor and outdoor Dosimetry, 15,(2), 131-140. gamma radiation in Finland. Radiation Protection Dosimetry, 59 (1), 25-32. Nordic (2000). Naturally occurring radioactivity in the Nordic countries - Barth, T.F.W., Ramberg, I.B. (1966). The recommendations. The Radiation Protection Fen circular complex. In: O.F.Tuttle, J.Gittins, Carbonatites. (pp. 225-257). Authorities in Denmark, Finland, Iceland, New York: Interscience. Norway and Sweden 2000, 80 pp.

Paarma, H. (1970). A new find of carbonatite Brøgger, W.C. (1921). Die Eruptivgesteine in North Finland, the Sokli plug in Savukoski. des Kristianiagebietes IV. Das Fengebiet in Lithos, 3, 129-133. Telemark, Norwegen. Skrifter, Det Norske videnskaps-akademi i Oslo I, Mat.-naturv. klasse, 9, 408 pp. Puustinen, K. (1971). Geology of the Siilinjårvi carbonatite complex, Eastern Finland. Bulletin de la Commission Dahlgren, S. (1983). Naturlig radioaktivitet géologique de Finlande, 249, 43 pp. i berggrunnen. Gammastrålingskart, Fensfeltet, Telemark. M. 1:10 000. Prosjekt temakart, Telemark. Ramberg, I.B., Barth, T.F.W. (1966). Eocambrian volcanism in southern Norway. Fylkeskartkontoret i Telemark. Norsk Geologisk tidsskrift, 46, 219-236.

Eckermann, H.V (1948). The alkaline Rannou, A., Madelmont, C., Renouard, H. district of Alno island. Sveriges (1985). Survey of natural radiation in France. Geologiska Undersokning, Ser. Ca, 36, 9- The Science of the Total Environment, 45, 36. 467-474. 12

Solli, H.M., Andersen, Aa., Stranden, E„ Stranden, E. (1984). Thoron (220Rn) daughter Langaard, S. (1985). Cancer incidence to radon (222Rn) daughter ratios in thorium rich among workers exposed to radon and areas. Health Physics, 47 (5), 784 - 785. thoron daughters at a niobium mine. Scandinavian Journal of Work, Stranden, E. (1985). The radiological impact Environment and Health, 11, 7-13. of mining in a Th-rich Norwegian area. Health Physics, 48 (4), 415-420. Storruste, A., Reistad, A., Rudjord, T., Dahler, A., Liestol I. (1965). Measurement Stranden, E., Strand, T. (1986). Natural of environmental gamma radiation in gamma radiation in a Norwegian area rich in Norwegian houses. Health Physics, 11, thorium. Radiation Protection Dosimetry, 16 261-269. (4), 325-328.

Strand. T. (1995). Time variation of indoor Sæther, E. (1957). The alkaline rock province radon concentration in typical Norwegian of the Fen area in southern Norway. Det homes. Proceeding of the 6th International Konglige Norske Videnskabers Selskabs Symposium on the Natural Radiation Skrifter, 1, 148 pp. Environment, 5-9 June 1995, Montreal, Quebec, Canada. UNSCEAR (1993). Sources and effects of ionizing radiation. Report to the General Strand, T„ Aanestad, K., Ruden, L., Assembly with Scientific Annexes. United Ramberg, G.B., Jensen, C.L., Wiig, A.H., Nations Scientific Committee on the Effects of Thommesen, G. (2001). Indoor radon Atomic Radiation. United Nations, New York. survey in 114 municipalities. Short presentations of results. Straalevernrapport Wohni, T. (1993). Dosemeter for low level 2001:6. Osteraas: Norwegian Radiation external radiation. Radiation Protection Protection Authority. Dosimetry, 48 (4), 347-350.

Stranden, E. (1977). Population doses from environmental gamma radiation in Norway. Health Physics, 33, 319-323.

Stranden, E. (1979). Radioactivity of building materials and the gamma radiation in dwellings. Physics in Medicine and Biology, 24 (5), 921-930. 13

Fig. la. Bedrock geology of the Fen central complex (from Ramberg and Barth, 1966) 14

Lake Norsjd

Faults (Interred)

K^yTl Granitic brecclo

Damkjernite

ROdberg

Rauhaugite

S6vite Hollaite and other mixed rocks. Vibetoite pr-j urtite. Melteigite IJolite. Fenite

fsj^ Archean gneiss Superficial deposits Mainly silt/clay

Fig. lb. Combined bedrock and quaternary geology map of the Fen area (based on Sæther, 1957 and Ramberg and Barth, 1966) 15

45

40

0 200 400 600 800 1000 1200 Rn (Bq/m3)

Fig. 2. The distribution of indoor radon concentrations in dwellings in the Fen area 16

Rauhaugite Rodberg Sovite Fenite Gneiss Type of building ground

HM Exposed bedrock Bedrock covered by silt/clay

Fig. 3. Indoor radon concentrations in dwellings grouped by underlying rock type and sediment cover. 50

0 50 100 150 200 250 300 350 400 450 500 550 600 650 Dose rate (nGy/h)

Fig. 4. The distribution of external gamma dose rates in dwellings in the Fen area. A cosmic ray contribution of 30 nGy/h has been subtracted. 18

2,6

2,4

03 2,2 •4—» 2 CD C/3 •Oo 2,0 X

1,8

1,6 X

Rauhaugite Rodberg Sovite Fenite Gneiss Type of building ground

mUffl Exposed bedrock fs/vi Bedrock covered by silt/clay

Fig. 5. External gamma dose rates in dwellings grouped by underlying rock type and sediment cover. Rn-concentrations (Bq/m3)

Fig. 6. Scatter plot of radon concentration versus external dose rate for 95 wooden dwellings in the Fen area with regression line. The radon concentrations presented have not been corrected to annual means 20

Table 1 Activity concentrations of rock samples and tailings from the Fen central complex and adjacent areas Rock type Number of Th-232 Ra-226 K-40 samples (Bq/kg)* (Bq/kg) (Bq/kg)

Mean Range Mean Range Mean Range Rodberg 9 3100 (390-5900) 70 (20-110) 310 (60-430) Rauhaugite 9 600 (290-930) 120 (40-300) 60 (40-70) Fenite 8 130 (20-200) 50 (40-80) 1060 (750-1500) Sovite 9 80 (20-190) 20 (10-60) 30 (20-40) Waste rock (iron mine) 4 4600 (4300-4900) 70 (40-100) 320 (280-360) Precambrian gneiss* 3 66 (68-63) 45 (43-46) * 4.0 Bq/kg thorium-232 is equivalent to 1 ppm Th 12.3 Bq/kg radium-226 is equivalent to 1 ppm U 310 Bq/kg potassium-40 is equivalent to 1 % K # outside the Fen central complex 21

Table 2. Indoor radon concentrations in dwellings located on different types of building ground in the Fen area Type of building Number Arithmetic Standard Geometric Range % > 200 % > 400 ground of mean deviation mean (Bq/m3) (Bq/m3) (Bq/m3) dwellings (Bq/m3) (Bq/m3) (Bq/m3) All dwellings 95 204 214 127 10- 1250 37 11 Rauhaugite 44 258 206 199 35 - 1030 24 6 Rodberg 11 340 362 189 13 - 1250 64 27 Sovite 6 241 73 233 160- 280 67 — Fenite 4 225 247 150 72- 590 25 — Gneiss 3 69 35 62 35- 105 — —

Silt/clay deposits 27 63 42 48 10- 175 — — 22

Table 3. External dose rates in dwellings located on different types of building ground in the Fen area. The estimated contribution from cosmic radiation has been subtracted Type of building Number of Arithmetic Standard Geometric Range ground dwellings mean deviation mean (nGy/h) (nGy/h) (nGy/h) (nGy/h) All dwellings 95 98 78 82 35 - 620 Rauhaugite 44 110 54 99 42 - 294 Rodberg 11 200 158 157 47 - 620 Sovite 6 75 21 72 50-104 Fenite 4 55 5 55 48- 60 Gneiss 3 55 15 54 39- 69 Silt/clay deposits 27 55 17 53 35- 89