Aud Venke Sundal

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

Doctor sctentiamm thesis Deyartment of Farth Science, 'University of Bergen. SeytemGer 2003 Aud Venke Sundal

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

Doctor scielztiamm thesis Deyartmmt of Tmth Science, University of %ergen SeytemGer zoo3 Contents

Preface and acknowledgements

summary

Introduction Background Presentation of papers . Synthesis Future work References

Paper T Sundal AV, Henriksen H, SoIda10 & Strand T The iyfluence ofgeological factors on indoor radon concentrutions in Nuiwadv. Submitted to The Science of the Total Environment, 2003.

Paper 11 Sundal AV, Henriksen H, Lauritzen SE, Soldal 0, Strand T & Valen V. Geological und geochernicd facturs afecting rodola concentrations in dwellings located on permeable glacial sedimenis - a case study Jbunz Kilasawik, Nunuuy. Submitted to Environmental Geology, 2003.

Paper III Sundal AV & Strand T. Indoor gmnrn~radiation and radon concentrafims in a Nomvgiun carhormtite 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 Os10 and the Norwegian Radiation Protection Authority), Oddmund Soldal (Interconsult ASA) and Vidar Valen (Sarlmdskonsult 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 I have received during the preparation of this thesis. I 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 stsly 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 (Sogii 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 ani especially grateful for all the support I have received from my family.

Bergen, September 2003

Aud Venke Sundal Summary

Indoor radon levels in 16 18 Norwegian dwellings locatcd in different geological settings were comparcd with geological information in order to determine potential correlations between geologicai 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, dctailed geological and geochemical rnvestigations were carried out in order to explain their e bated natural radiation environment.

Significant correlations bctween geology and indoor radon conccntrations in Norway arc found when the propcrties of both thc bedrock and thc overburdm are takcii into account. Areas of high radon risk in Nonvay includc 1) exposed bedrock with elevated lcvcls of radium (mainly alum shale and granitcs) and b) highly permeable LinconsoIidaicd sediments derived froin 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 dwcllings locatcd in the high risk areas can be cxpccted to contain radon levels exceeding 290 Bq/m3.

Thc elevated radon risk rehtcd to permeable building grounds is jllustratcd in Kinsamik where the highly pcrmeable scdiincnts and thc large vadose zone undcrlying the Husc residential area enablc the transport of radon froin large volumes into the dwellings resulting in cnhanced indoor radon conccntrations. Subtcrraiican air-flows caused by teinper~tur~,'prcssurediffcrences bctwcen soil air and atmospheric air and clcvations differences within thc Huse area are shown to strongly affect the annual variations in indoor radon concentrations. The markcd contrasts in radon risk potential between different types of building grounds arc clcarly illustrated in thc Fen area whcre outcrops of the radium rich Fen carbonatites rcprcsent areas of high radon risk whilc only low Icvels of both indoor radon concentrations and indoor gamma dose rates arc measurcd in the arcas covered by nearly impermeabic silt and clay deposits. Indoor garmna dose ralcs as high as 520 nfjylh are obtained in the areas of cxposed carbonatites. primarily due to cnhanced horium conccntrations iii thcse rock typcs.

The observed corrclations bctwcen geological factors and indoor radon concentrations in Norway indicate that gcolog~catinformation is a useful loo1 in radon risk analysis. Resources can be concentrated to rcgions of high geologic radon potential when scrcening programs arc planned, and cfficient follow-up survcys can be established bascd on geological data in combination with radon measurements in a representative samplc of the building stock. The observcd contrasts in radon risk potentia1 betwecn different typcs of building grounds also enable thc prediction of radon risk in arcas which arc not currently inhabited. I

Introduction

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

Background Norwegian housing stock was calculatcd to 88 Bq,‘m3 (Strand et a/., 200 1 ). In accordancc with international recommendations, Natural ionising radiation is the larsest contributor to the radiation dose received Norwegian householders are advised 10 by the world’s population (UPU’SCEAR, undertake siiiiple and inexpensivc remedial 1993). Tlw radiation dose from natural measures in dwellings where the annual mcan sources is generated by radioelements in radon concentration in the living area rangcs diet and inlialcd radon and radon progenics from 200 Bqh3to 400 Bq/m3 (NRPA, 1995). If the radon levels 400 Bq:m’, remedial (internal exposurc) as well as cosmic rays exceed and garmna rays emitted froin potassium40 work is rccornmcnded until the levels have and membcrs of the uranium and tliorium becn brought bctow 200 Bq/rn’. Thc results from the national study showed that 9 decay chains in the crust of the earth and in YO of building materials (extcmal exposure). Norwegian dwclljngs haw annual average radon conccntrations cxceeding 200 Bq/m’, Doses from the inhalation of radon and its decay products in dwellings arc much and 3 04 of thc dwellings have radon levels in excess of Bq/in3. Out of a housing stock greater than those from all other 400 components of natural radiation of 1;8 inillion uniis, thcse figures correspond to (UNSCEAR,1993). t 60 000 and 50 000 dwellings, rcspectively. Based on nuncrow studjcs of lung Somc of the world’s liighcst average indoor radon concentrations have cancer in radon-exposcd underground mincrs bccn registered in Noway and other Nordic in sevcral countrics, radon is classificd as a countries (Swedjcmark er al., 1993; AN& human carcinogen (IARC, 1988). Inhalation ot‘ radon and radon decay products is el a/., 1993; Strand et al., 2001 ). Bascd on the results from the mosl recent national considcrcd to be the leading cause of lung cancer after tobacco smoking. Exposurc to study of indoor radon levels in Noway, including nearly 29 000 dwellings, thc radon and its progenics is estimated to bc annual meail radon conccntration in the responsible for 100-300 lung cancer cases (5- 2

15 ''41 of thc total) annuaIIy in Norway carricd out by the Nonvcgian Radiation (KWA, 1996). Protection Authority (NRPA), and so far Sourccs 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 revcalcd that thc entry of radon from the databasc at NRPA (Strand ET al., 1992: Strand building ground through the building et a/., 2001). A number of publicity construction IS tlic dominant SOUTCC of campaigns have been dcvclaped to improve indoor radon in Norwegian dwellings radon awareness amongst lhe gencral (Stranden. 19x7). Norwegian dwellings are population and professional bodies involved in primarily madc from wooden materials the housing markct, and in 1999. a financial which have low concentrations of support arrangement was establislicd in order radionuclides, md concretc and brick to encourage houscholders to rcmcdiate high manufxtured in Norway have also bccn radon levels. Still, a major proportion of reportcd to contain low lcvels of Norwegan dwellings with unacccptably high radioactivity (Stranden, t 979). Since 87 94 radon levels are yct to be idcntified. and

of thc Norwegian population is supplied by remedial work has so far only bceii undertaken watcr from surfacc water sources with low in a small proportion of the registcred housings levels of radon, the contribution to indoor with enhanccd radon levels. air from housclioId watcr 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, howcvcr, arise from making measurements in indoor air. High-risk domestic water from privatc drilled bedrock areas of indoor radon can, however. be wells (Strand et a/., 1998). identified using different approaches; by National radon programs have been meamring radon concentrations in a impfementcd in most European and North sufficiently Iarge samplc of existing dwellings,

American countries in ordcr IO identify by studying the gcological factors influencing buildings with radon conccntrati ons indoor radon tevcls, or by a coinbination of cxceeding thc adopted action levels, to offer indoor radon measurements and knowledge advice and encouragcment to the about _geology and building characteristics householders to reducc the high radoa (ICRP, 1993). The usc of geological Ievcls and to prwent new buildings to be information is only justifiable if significant constructed in such a way that thc annual correlations between geological factors and averagc radon conccntration cxcceds thc indoor radon levels in a region arc cstablishcd. action liinits. In Norway, several large- In Swedcn and Finland, where bedrock and scale indoor radon surveys havc been overburdcn characteristics are coinparable to 3 those prevailing in Noway, indoor radon scales. In the first part of the work, indoor concentrations and gcoiogy have bcen radon levels in 1618 Norwegian dwellings found to be related, and geological located in different gcdogical scttings wcre information has becn widely used in the compared with geological information. The prediction of radon risk (Aakerblom ~t al., ciassification of the building ground was 1988; Castren ef a!., 1992). Jn Norway, largely based on existing geological data since studies also indicate that correlations largc-scale surveys do iiot allow detailed between indoor radon lcvcls and geological investigations at each building site, In the fcaiures exist (Stranden et al., 1985; second part of ths work detailed gcological Stranden, 1987; Stranden & Strand, 19881, and geochemical investigations wcre carricd but a more extensive study of thc geological out in two geograpliically limited areas in influence on indoor radon in dwellings order to explain the observed cxceptional located in different gcologicaI 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 becn to dctcrmine potential curicetitrations in the Fen area. correlations between geological factors and indoor radon concentrations in Korway and to establish whether the correlations, if any, Presentation of papers arc strong enough to be useful in radon risk analysis. In rcgions whcrc marked Paper I contrasts in gcologic radon potential exists, and arcas of high and low radon risk can be Sundal AV, Hcnriksen H, Soldal 0 SZ Strand dctcnnined in a relatively simple and cost- T. The it$luence of geological ,fi~clorson efficient manner, gcological information is indoor radon concenlrutions in Noi-cva~7. a \*aluabte tool for identifying high radon Submitted to Thc Sciencc of the Total risk building grounds. However, if no Environment, 2003. obvious contrast in geologic radon potcntial is observed, assessments of radon risk Paper T discusses thc rcsults of a comparison based on gcological inforniatioii arc not betwecn geologc data and indoor radon recommended. concentrations in 16 18 Norwcgian dwcllings. The search for correlations between The dwellings were sclected from a wide range geology and indoor radon concentrations in of geologica1 settings in ordcr to invcstigate this study has bcen carried out at differcnt the influcrice of geology on indoor radon levels 4 and to determine whether gcologicat in radon potential between diffcrent types of information is a valuable tool for building grounds observed in this study identifying high radon risk building indicates that geological infortnation is useful grounds. indoor radon data from the 2000- in radon risk analysis. By concentrating 2001 national indoor radon study carried resources to tlic areas of high geologic radon out by the Norwegian Radiation Protection potential when indoor radon screening Authority werc used for thc comparison, programs and follow up surveys arc planned, The building ground classificatjon was thc idcntification of dwellings with clcvated largcly based on existing geological data, indoor radon levels can be speedcd up. The but additional geological infixmation was observed correlations between indoor radon collected by fieldwork. A comparison of and geology also cnable the idcntification of indoor radon conccntrations and areas whcre preventative measures against information on housc construction and radon must be taken in future buildings. vcntilation habits was also includcd in the The results indicate that scveral study in order lo scarch for correlations paramclers related to building con strucrion and between these factors and indoor radon ventilation habits also affect indoor radon coiiccntrations in Norway. conccntratious in Norway. The factors found The datasct revealed that tu havc a statistica11y significant association permeability and radium content of the with indoor radon levels in the prescnt building ground are important indicators of investigation arc vcntilation system. aeration indoor radon concentrations. Based on habits, and floor levct of the morn where thc thcsc factors. an estimate of thc radon measuremcnts were carried out. potcniial of an area can be given. Arcas of high radon risk in Norway are characterised by I) exposed bedrock with elevated Icvcls Paper 11 of radium, 2) highly perrneablc unconsolidated scdiments dcrived from all Sundal AV, Henriksen H. Lauritzen SE. Soldal rock types, or 3) moderately pcrmeable 0, Strand T & Vaien V. Geolngicul u~d sediments containing radium rich rock geochent icul fucmrs affecting radon fragments. Thc primary radon source rocks cwmwtruliuns in dn'ellings located on in Norway are thc Cambrian-Ordovician perme&& glurial sediments - u cust7 study alum shah and uranium rich granites of from Kiwsarvik, Norway Subinittcd to varying ages. Environmental Geology, 2003. Gcological parametcrs can not provide accurate estimates of radon levels Paper I1 focuscs on thc geological processes in existing homes, but the marked contrast causing the very high indoor radon 5

concentrations and thc scasonal and building constructions arc exposed to large geographically changcs in indoor radon volumes of readily movable soil air resulting in observed in thc Kinsarvik area of Western high indoor radon levels. Norway. Indoor radon measurcinents The investigation carried out in performed during 1996-1997 in a Kinsarvik revealed that general correction residcntial area located on an extensive ice factors for estimating the annual avcrage marginal deposit in Kinsarvik rcvealed indoor radon concentration are not applicable iridooi- 1-adon concentrations of more than in areah wherc temperaturdpressure driven air 40 000 Rq/m3, and mual variations in flows are likely to occur. In order to obtain a indoor radon coriccntrations were found to corrcct estimate of the annual average indoor deviate sigmficantly from thc results radon concentration in dmTelliiigs located on obtained from a prcvjous large-scale study this type of building ground, indoor radon of annual indoor radon variations in measwcments must be pcrfomed both it1 Noway. summer and in winter. Assessments of indoor Geochemical analyscs of bedrock, radon conccntrations based on singlc soil gas groundwatcr and sediments and measurements without a general understanding mcasurements of soil radon concentrations of the geology in the area should bc avoided. rcvcaled that the indoor radon The high indoor radon levels in concentrations in the Huse arca arc strongly Kinsarvik received wide media attention and affected by subterranean air-flows caused contribukd to an incrcased awareness of thc by clcvation diffcrciices and differenccs in licalth risk related to indoor radon exposures in temperaturelprcssurc between soil air and Noway. atmosphel-ic air. Thu air-flows conccntrate thc available radon-ladcn soil air towards 111 the upper part of the icc marginal moraine Paper in winter wliilc the lower part is ventilated Suiidal AV & Strand T. Jndoor gunzma by atmosphcric air. h summer, thc rudiaiion and rcrdnn concentrations in a situation is rcvcrsed. The indoor radon gas Xoi-nvgian curboplabite arm. Submitted to is dcrivcd from the glacial sedimcnts Journal of Environmental Radioactivity, 2003. containing normal to high uranium cnnccntrati on s. Thc coarse-grained glacial Papcr 111 discusscs the rcsiilts of a study of sedimcnts are covered by finer sedimcnts in indoor gainma radiation levcls and radon the residential area but cxposed in thc conccntrations in the Fen area of carboitatite topographic uppcr and lower end of the ice and alkaline silicate rocks in the southern part iiiarginal dcposit. Sincc most of' thc of Norway. The Fen arm has becn famous for dwellings in the Huse area havc ccllars, the 6

its rare rock association since the bcginning radiation in the areas whcrc low permeabk silt of the last ccntury, and during the last and clay deposj ts cover the bedrock surface. decades attention lias also been drawn to A major landfill and many piles of the area due to its elevated natural radiation wastc rock from iron mining activities arc environment. In the present study, indoor present in the north castern part of the Fen gamma radiation lcvcls and radon area. Thorium concentrations behvecn 4000 conceiitrations in 95 wooden dwellings and 5000 Bqlkg arc obtained for this material, were mcasured using thermoluminescence and mcasurernents of gamma radiation abovc dosimeters and CR-39 alpha track plastic the waste rock rcvealed ambient dose detectors, respectively, and a thorough equivalent rates of 3-5 pSv/li. So far, tlic analysis of the indoor data with regard to waste inatcrial has not been secured. and geological factors was performed. remedial rneasurcs like covering the waste rock The results revealed a strong with clay laycrs and restricting the building geologic control on indoor gamma radiatioii activity in the affccted area are currently levels and radon concentrations in the Fen considered. area. Enhanced lcvcls of thorium and slightly elevated levels of radium in the carbonatices are responsible for tlic highest Synthesis gamma dose rates CVCT reported from wooden houses in Norway. An avcrage Significant correlations between geology and indoor gamma dose rate of 200 nGy/h and a indoor radon conccntrations in Norway arc inaximum of 620 nGyh wcre reported from found whcn the propcrties of both the bedrock dwellings locatcd on exposed surfaces of and the overburdcn are takcn into account the most thorium-rich carbonatitc. Using (paper I). The indoor radon risk clearly nonnal conversion factors, these values increases in areas where radium rich bcdrock correspond to effective dosc equivalents of outcrops and in areas where rahm rich rock 1.0 and 3.0 mSv/ycar, respcctively. The fragments arc incorporatcd into the group of dwcllings localcd on exposcd overburdcn, but high radon risk is not always surfaces of carbonatites also has enhanced related to high radium content of the building levcls of indoor radon compared to tllc pound. A significant proportion of averagc for thc country. Duc to the high Norwegian dwcllings are located on perincable radiation dose to local residcnts caused by unconsolidated sediments, and high terrestrial gamma radiatioii in this area, pcrmeability of the building ground favours the special cffoi-ts should be rnadc to reduce the transport of radon from its source to tlic indoor radon concentrations. Low rcadings building construction Consequently, werc obtained for radon and gamma 7 substantial layers of highly permeablc 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 conlcnt of the matcrial is deposit in winter and to the topographical low (figure 1). Moderatcly permeablc lower part in summer. The results imply that sediments like basal tills must also bc in areas where air movcment in the ground is regarded as high risk building grounds if likely to occur, estirnatcs of annual averagc they contain radium rich rock fragmcnts. indoor radon conccntratjons and decisions on Unlcss tlie water table is situated close to remcdial measures should bc based on a thc building construction, more than 20 0/6 combination of winter and summer of Noiwegim dwellings located on the rneasurcments. abovc mentioned types of building grounds Thc Cambrian-Ordovician alum shale can bc expected to contain radon and granites of different ages commonly concentrations exceeding 200 ~q:rn~ contain radium concentrations exceeding 100 Moderatcly permeable sediments derived Bq/kg and are thc primary radon source rocks from rock typcs with normal to low- radium in Norway. Examples of otlicr rock types content constitute building grounds of containing elevated concentrations of radium normal radoii risk, while finc-grained arc the Fen carbonatitcs which, in contrast to scdiincnts like marinc silt and clay deposits alum shale and granitcs, only occur in a and silty and claycy till reprcsent areas of geographically very limited area of the low radon risk unless the permeability of country. The markcd contrasts in radon risk thcse sediments has been incrcased through potential between different typcs of building loss of moisture and soil cracking. grounds are clearly illustratcd in the Fen area The elevated radon risk related to whcre enhanced radon concentrations are permeable building grounds is illustratcd in iiieasurcd in dwellings foundcd directly on the the Husc area in Kinsarvik (papcr 2). The carbonatites while only low radon levels are highly pcrmcable sediincnts and thc large obtained in thc adjacent silt and clay areas vadosc zone underlying the residcntial area (paper 3). Thc silt and clay deposits render the enablc the transport of radon from Iargc ground irnpcrmeable to transport of radon gas volumes into thc dwellings rcsulting in and also reduce the cxposure to local residents ciihanced indoor radon concentiations from terrestrial gamma radiation. Indoor (figure 2). Subtcrranean air-flows caused gamma dosc rates as high as 620 nGy/h ax by temperatul-eiprcssurc diffcrences obtained in thc areas of exposcd carbonatites, between soil air and atmospheric air and primarily due tu enhanccd thorium clevatioiis diffcrences within the Husc area, conccntratjons in these rock types. strongly affect thc aimual variations in 8

The ubscrvcd correlations betwecn gcochernical and geophysical information is geological factors and indoor radon incrcasing, and an interesting challenge is to concentrations in Sorway arc in overall determine to what extent existing digital data concordancc with findings fiom other like bedrock and soil maps and airborne studies in former glaciated areas gamma radiometric mcasurements can be uscd (Aakerblom et a]., 19x8; Castrcn et al., to idcntify risk areas with respect to both 1992) and indicate that gcological ground radon and groundwater radon. information is a useful tool in radon risk analysis. Resources can be concciitrated to regions of high geologic radon potcniial References wlicn screening programs arc planned, and efficient be follow-up survcys can Aakcrblom G, Pettersson €3 & Rosen B, 1988: establishcd based on geological data in Marlmadoil. Hmdbok fir undersbhng och combination with radon measurcinents in a redovi sn i n g av inarkra doiiforh811and en . Kad o n reprcsentativc sample of the building stock. i bostader. Byggforskningsr5det R85, 160 pp. Thc observed coutrasls in radon risk Revised cdition 1990 (In Swedish). potential between different types of building goulids also cnabIe the prcdiction Arvela H, Makekinen 1 & Castren 0, 1993: of radon risk in areas which are not Residential radon survey in Finhid. Report currently inhabiicd. The avaihbility of STUK-A108, Finnish Ccntre for Radiation and cxisting gcologicai infonnation in an arca, Nuclear Safety, Helsinki (abstract only in c.g. soil. bedrock and gamna radiation English). maps, will detemiiie how cosl-efficiently thc evaluation of radon risk can bc carried Castren 0, Arvela H, Makelainen I & out. Voutilainen A, 1992. Indoor radon survey in Finland: Methodology and applications.

Radiation Protcction Dosimetry 45 [ 1>+ 4 13- Further work 418.

lnvestigations haw shown that the ICRP, I993 Protcction against radon-222 at occurrencc of radon prone arcas correlatcs home and at work. A report of the well wit11 gcologicat conditions and that lntcrnationd Corimlission on Radiological important connributi ons to radon risk Protection. ICRP Publication 65. Pcrgamon evaluations can be obtained from gcological Press. data. The availability of digital gcological, 9

IARC, 1988: Man-made Minerd Fibrcs Stranden E, 1979: Radioactivity of building and Radon. Intcmational Agency for materials and the gamma radiatioii in Rcsearch on Cancer monographs on the dwellings. Phys Med Bid 24 (5),92 1-930. evaluation of carcinogenic risks to humans. Stranden E, 1987: Radon-222 in Norwegian Volume 43. World Health Organization. dwellings. In: hoc. Symp. on Radon and its dccay products: Occwencc, properties, and NRPA, 1995: Anbefalte tiltaksnivier for health cffccts. New York, US, 13-18 April radon i bo- og arbeidsmiijo. NRPA 1986, American Clicinical Socicty Symposium Radiation Protcction series 1995, no. 5. Series 331. 70-83. fistcram: Nonvcgian Radiation Protection Authority (in Norwegian). Stranden E & Strand T, 1988: Radon in an alum shale rich Nonvegiaii area. Radiation NRPA, 1996: Radon I inneluft. Protection Dosimetry 24 (I), 367-370. Helserisiko, mblinger, mottiltak. NRPA Radiation Protcction serics 1996, no. 9. Strandcn E, Ulbak K, Ehdwall H & Jonasscn Osteraas: Norwegian Radiation Protection h', 1985: Measuremcnts of radon exhalation Authority (in Norwegian). from the pound: A usable tool for classification of thc radoii risk of building Strand T, Grccn BMR & Lomas PK. 1992: ground? Radiation Protcction Dosimetry. 12 Radon in Norwegian dwellings. Radiation (l), 33-38. Protection Dosimetry 45 (1),503-508. Swcdjcmark GA, Mellander H & Mjiines L, Strand T, Lind B & Tommcsen G, 1998: 1493; Radon. In: The indoor climate in Naturlig radioaktivitet i husholdjngsvann Swedish residential buildings. (In Swedish fra borebronncr i Norge. Norsk with English abstract). Norlen U. and Velrinartidskrift 1 10 (lo), 662-665 (in Andcrsson K. (eds.). Swedish Building Norwegian). Rcscarch Institute, Report TK:30.

Strand T, Aanestad K, Ruden L, Ramherg UNSCEAR, 1993 Sourccs and cffccts of GB, Jensen CL, Wiig AH & Thommcsen ionizing radiation. Report to thc General G, 2001 : Indoor radon survcy in I14 Assembly with Scientific Annexes. (United municipalities. Short prcscntations of Nations Scientific Cornmime on thc Effects of rcsults. SirilevernRapport 6. Usteraas: Atomjc Radiation). United Nations, Ncw York

Norwegian Radi 3ti on Protcction Authority. Valcli V7Soidal 0,Gunter B, Henrikscn H, Jenscn CL, Lsturitzen SE, Rydock J, Rye N, Strand T & Sundal AV, 1999: Variations in radon content io soil and dwellings in the Kinsawik area, Norway, arc strongly dcpendent on air temperature. Extended abstracts, A,4RST-2000 Int Radon Symp, 22-25 October, 1999, Milwukee, Wisconsin, USA. (Gwvell Gtaciofluvial deposits Shore deposits

Clean sand

Marine silt

Clayey till

Marine clay

Alum shala - Granlte - -Gneiss - -Shale - -Sandstone - 1 bl lb2 1'03 Radium concentration Wkg)

Fig. I. ClusslJicrrtionqf ndon risk based cin permeubiliiy and radium content c$/l?e building grou~td.HiEh risk area. Area in which more thun 20 % of ihtl homes ure expected IO have radon cuncenirations in exccss oj 200 h'qim3 Moderafe risk weu: Area in which belween 3 % und 20 96 qfthcl dweliings me expected lo exceed 200 Bq/m3 LIIWrisk area: hew in which less than 3 94 ofthe dtl,eElings we likely to have radon levels ahove 200 Bq/m3 and no dwelling huve rudon levels higher thin 400 Bg/na-l 12 Paper I

Sundal AV, Henriksen H, Soldal 0 & Strand T rhe 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, Menriksen H, Soldal 0 & Strand T. The influence of geological factors on indoor radoii concentrations in Norway. Suhmimd to The Science of the Told Emironment.

Indoor radon lcvels in 161 8 Nonvcgian dwellings located in different geoiogical settin,0s are comparcd with geological information. Thc results show a significant correlation bctwccn indoor radon levels and gcological factors. Radium content and permeability of the building ground have bccii found to bc uschl indicators OC indoor radon concentrations. Based on easily accessiblc geological data, aQassessment of the radon potcntial of an area can be given. Areas of high radon risk in Miway include 1) exposcd bedrock with elevated lcvels of radium and b) highly pcrmeable unconsolidated sediments dcrived from all rock typcs and moderately permeable sediments containing radium rich rock fragments. A comparison of indoor radon with house construction characteristics and ventilation habits suggests that radon conccntrations in Norwegian dwcllings also arc influenced by vcntilation system, aeration habits, and floor lcvel of the room whew the measurements U'CE carried out. Thc significant correlation betwcen indoor radon levels and geological factors obscrved in the present investigation indicates that geological data is a useful tool for identifying high radon risk building grounds in Norway.

Introduction around 213 of the total effective dose. Exposure to the naturally occurring radon222 Thc total effectivc dosc from all radiation gas and its short-lived, solid decay products sources suffcred by ihc Norwegian polonium-2 18, lcad-2 14 and bismuth-2 13 population is currentIy estimatcd to 4,2 makes the major contribution to the total inSv per ycar (NRPA, 1999). The radiation exposure d the population and accounts for dose from iiatural sources constitutes approximately half of the averagc Norwegian's 2 total effective dose from all radiation low levels of radioactivity (Strandcn, 1979). sources. Thc radon-222 isotope is a Since 87 % of the Norwcgian population is mcmbcr of the uranium-238 decay-series supplied by water from surfacc watcr sources and has radium-226 as its iimncdiatc with low levels of radon. the contribution to precursor. Thc contribution to indoor radon indoor air from household water is also from the natural occurring radon isotopes in germally low. However, analysis of water the uranium-235 decay-series (radan-2 19) from 3500 howegian drillcd wells revealcd and thorium-232 dccay-series (radon-220) radon concentrations exceeding thc Norwcgian is in general considered negligible duc to action level of 500 Bq/l in 15 % of thc wells their short half lives. In accordance with and 1000 Bqll in 9 % of tllc weIls (Strand ef intcrnational recoimnendations, rcmcdial uI., 1996). Thc contribution to indoor radon mcasureb in Norwegian dwellings arc from household water can thercfore not be recomncnded if thc annual mean radon ncglcctcd, even though it is considcrably less concentration in the living arca cxceeds 200 important as a radon source &an the building Bqlrnj (KRPA, 1995). grour1d. There are several different radon When thc building ground is the sources in domestic dwellings: Building dominant source of indoor radon, the indoor ground, building material and water supply. radon conccntrations dcpcnd on the ability of Investigations have shown that the entry of the building ground to produce and u'ansport radon from the building ground through the radon, thc leakage of radon from the ground building cnnstniction is the main source of through thc house construction and thc indoor radon in Norwcgian dwellings ventilation rdte of lhc building. The (Strandcn, 1987). For an average production and transport of radon in the Norwegian detached or tcrraced house, 80- building ground arc determined by gcological 90 % of the indoor radon concentration factors like radium content of the bcdrock/soil. orjginatcs from [he building ground. In emanation coefficients, moisture content, block of flats, building material can be pcrmcability, ctc. (Tanner, 1980; Aakcrblom et relatively more important as a radon SOUI'CC, al., 1983; Markkanen and Arvela, 1992; Hutri but the contribution to indoor radon from and Makclainen. 1993; Tell ef a!., 1994: Sun this source rarely cxceeds 200 Bq/in-'. and Furbish, 1995; Schurnann and Gundersen. Norwegian dweilings arc priinarily madc 1996) and indicate thc potential for a radon from wood-based bui I ding materials which problem to exist. How the geologic potential have low concentrations of natural will be realiscd in terms of indoor radon radioactive substances. Building materials couccntrations mainly depends on building like concrete and brick rnanufaclurcd in construction characteristics and ventilation Norway have also becn reported to contain habits of the occupants. 3

Tn regions wlicrc 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 inunicipalities (Strand et al., 200 1). information on geology can aid in Betwccn 2 and 10 '?4 of the housing stock in identifying radon-prone areas (Aakcrblom each municipality was jncludcd in the study, et ul., 1988; Castrcn et ul., 1992). Previous depending on the size and population density investigations in Norway indicatc that of thc arca. Seven of the 1 14 municjpdities indoor radon conccnnations and geology participating in the indoor radon study were arc rclated (Stranden et ul., 1985; Stranden, selected for tlie present investigation. The 1987: Stranden and Strand, 1988), but a selection was inadc with crnphasis on the inore extensivc study of the gcological following criteria: ( 1) Thc municipalities influcncc on indoor radon in dwellings should reprcscnt different gcological rcgions in located in different geological settings was order to enablc a comparison between indoor desirable in ordcr tn determine vhcther radon concentrations in dwellings located on geological information is uscful in radon diffcront types of bcdrock and overburden; (2) risk analysis. The present paper discusses Thc average indoor radon values of thc the results of a comparison bctween selected municipalities should reflect thc geologic data and indoor radon whole range of values obtaincd in the study of concentrations in 161 8 Norwegian all 114 municipalitics. dwellings located in various geological Correlalions between high indoor

settings. The objective of the study wab 10 radon concentrations and uranium-rich rock identify potential corrciations between types have been reported from studies in indoor radon lcvels and geological factors scverai countrics (Voutilaincn er ul., 1988; and to establish whether the correlations, if Gundersen et al., 1892, Ball and Miles, 1953:

any, arc strong enough to be useful in radon Tell el ul., 1994). Enhanccd levels of uranium risk analysis. A comparison of indoor axcommonly found in rock typcs likc granites radon data with house construction and black shales (Gascoyne. 1992). Uranium characteristics and vcntilation habits of thc is incorporated inlo the silica rich granitic occupants was also includcd in the study in rocks duc to the concentration of this clement

order to investigate potential correlations in the liquid phase in the CUUTS~oI' partial between these factors and indoor air radon melting and fractional crystallization of levels in Norway. magma, whiie the organic compounds in black shales are natural concentrators of uraninin and Study areas other metals (Durrance, 1986). Typical rangcs Tn 2000-300 I, the Norwegian Radiation of activity concentrations of radium226 and Protection Authority (NRPA) carricd out thorhm-232 in h'ordic rocks are shown in 4 table 1 Norway is dominated by been reworked by fluvial processcs after crystalline bedrock, and pnites and deglaciation, and fluvial deposits tikc dcltas, granitic gneisscs have a fairly wide river beds and alluvial fans cover large parts of distribution (Sigmond EI al., 1984). Alum rhe numerous glacial vallcys in Norway. Thc shale, an uranium-rich Scandinavian black fluvial sedimcnls are sorted and stratified aiid shale of Cambrian-Ordovician agc, is gcncrally consist of sand and gravel. Like tlic present in the area around Oslo in the glac iofluvial depos j ts they arc highty south-castcm part of the country. pcrmeabk. Typical ranges of activity In glacial arcas like Norway, the concentrations of radium-226 and thorium-232 overburden does not necessary reflect the in Nordic soil types arc presented in tablc 2. characteristics of the undcrtying bedrock. The location of the 7 sclccted Scvcral authors dcliiieate that the properties rnunicipalitics in the different geological of tlic overburdcn have a significant regions of Noiway is prescntcd in figurc 1. A influence on indoor radon concentrations suinincry of the geojogical charactcristics and (e.g. Aakcrblorn et a/., 1983; Ciunderscn et averagc indoor radon concentrations of each ul., 1992; Ball and Milcs, 1993; Hutri and niunicipality is given in table 3. Makelainen, 1993). Thc main types of Three of the selected municipalities overhurdcn in Xonvay are glaciofluvial and arc located in the Southern Precambriai region fluvial sediments, basal till and iiiarine (Tim, Ulvik and Nes) (Fig. 1). The Southern siltlclay. Glaciofluvial sedimcnts are Precambrian region is dominated by gncisscs deposited by streams produccd by melting and granitcs of Precambrian age. hvcrage glacier ice e.g. in tunneIs and crevasses in uranium concentrations between 2.2 ppin and or bencath the ice (cskcrs and kaimcs) or 13.3 ppm haw bccn measured in some of thc where meltwater flows into standing watcr largc granite bocks in the region (Killeen and (deltas). These dcposits mainly consist of Hcicr. 1974; Killcen and Heier, 197Sa, Killeen sand and gravcl and are highiy pcrmeabte. arid Hcicr, 1975b). A major part of the Basal till is dcposited at thc base of the bedrock in the three sclccted municipalities is glaciey and is generally unsorted, covered by basal tit1 and glaciofluvial and containing both fines and largc bouIders. It fluvial sediments. Thc iiiunicipality of Ulvik is is the most extensive typc of overburdcn in located at the wcstern border of the Southern Norway and covers bctween 25 D/U and 30 Precambrian rcgion, and fragments of gneisses, 5% of thc total land arca (Thoresen, 1991). mctasediments and inetavoloanics of thc Due to its unsorted and compact character. Caledonides arc present in thc overburden in thc permeability of the basal till is much this arca. The averagc values of indoor radoii lower than that of the sorted and stratified concentrations for Tim, Ulvik and Nes are glaciofluvial dcposits. The glacial drift has 358, 209 and 266 Bq/m3,respectively. 5

The iiiunicipality of Aurum is about 100 krn noi-th of Oslo where one of the localcd in the Oslo region, which splits the largcst occurrcnccs of alum shale is localised Southern Precambrian rcgion into an (Fig. 1). Earlier studies in this region indicate eastern and western part (Fig. 1). In tlie that the alum shale is the source of enhanced Oslo region, sedimentary rocks of Late indoor radon conccntratioiis (Stranden and Precambrian to Silurian age arc overlain by Strand, 1988; NGU, 1994). A major part of Carboniferous-Pemiaii volcanic s and ihc bedrock in the municipality of Stange is sediments and intruded by ipcuus rocks, overlain by unconsolidated scdiments, largely of Pennim age. Raadc (1973) predominantly basal till and glaciofluvial studied thc distribution of radioactive deposits. Due to a substantial cover of basal elcments in the plutonic rocks of the Oslo till, few outcrops of alum shalc 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 conccntration of 350 Rq/m3 is reported for the type in the municipality of Hurum is the municipality of Stange. Permian Drainmen Ciranitc. A incan The Caledonian orogenic belt uranium valuc of 4.7 ppm for the whole extends from thc south-wcstern part of yranitc body and local averages of inore Southern Norway to the northern part of the than 8 pprn are reported. A small part of country and consists of a sequcnce of nappe- Humm is covcrcd by nearly impcrrneable piles of gneisscs, rnetascdiments and marine silt and clay deposits and sand and metavolcanics of Precambrian to Lower gravel dominated mitrinc shore dcposits. Palaeozoic age. Thc municipality of Midtre- Thc latter type of ovcrburden was formed Gauldal is located in tlic central part of thc by reworking of older sediments by currcnt- Caledonides where Cambrim-Si Iurian and wave processes and can locally have inetasediments dorninatc (Fig. 1). Tlic thickncss oC several mctcrs. The averagc Geological Survey of Norway (NGU) has indoor radon concentration in the carried out a limited number of mcasurements municipality of Hurum is 205 Bq/m’. of total gainma radiation at ground level in this In parts of the Oslo region and area which all showcd very low- levcls of thc immediate arca to the north, the radioactivity (Sordal, pers.com. 2003). Total uraniuni rich Cambrian-Ordovician alum gamma radjatiou measurements carried out in shale occurs. General average uranium the arcas of Calcdoiiian mctasediments in levefs of 50-1 SO ppm over thicknesses of 5- Northern Norway revealed low to normal 15 in and local maximum values of 170 lcvels of radioactivity (Hysingord, 1988a, ppm are reported from this rock type Hysinaord, 1988b; Lindahl el nl., 1988, (Skjeseth, 1958). The selected municipality Lindahl et uI., 1993). A major part or the of Stange is situated in the Hehilark county bedrock in Midtrc-Gauldai is covercd by 6 glaciofluvial and fluvial scdiinents, basal characteristics arc thcrcfore used to describe till and rnarinc siit and clay deposits. The the most important paramctcrs assumed to silt and clay dcposits in tlic northern part of affect indoor radon conccntrations. In the the municipality arc partiaily covered by present study, radium content and pcnneability laycrs of sand and gravel. Thc average werc included as iiidicators of thc production indoor radon concentration in the and transport of radon in thc building ground, municipdity of Midtre-Gauidal is 91 and these paramctcrs were detcnnined by using Bqirnj availablc data on type of bedrock and type of

The municipaiity of Rauma is overburden, rcspc c ti vel y , An appxi matc located in North-Westcim Precambrian cquilibrium bctwcen uranium-238 arid radium- region (Fig. I). This region is situated to 226 was assumed for the present study since the west of the Caledonian orogenic belt radioactive cquilibrium normally prcvails and is dominated hy gneisses of between these radionuclides in Nordic bedrock Precambrian age. Total gamma radiation (Nordic. 2000). Classifications of basement, measurements cairicd out at ground Ievel in foundation walls, ventilation system and Rauma and adjaccnt areas revealcd low to aeration habits were used as surrogatcs of the normal levels of radioactivity (Lindahl and air leakage froin the huilding ground through SSrdal, 1988). A major part of the bedrock the building construction and the ventilation in the selectcd municipality is covered by rate of tlie building. Information on main gIaciofluvia1 and fluvial sediments, basal building material and source of household till and marine silt and clay. In the wcstem, water was abincluded in thc study. low-lying parts of the inunicipality, sill and clay dcposits are overlain by sand and Collection of data gravcl (Follestad et a/., 1994). An averagc TTI order to visualise thc geographical indoor radon concentration of 29 Bq/m' is distribution of thc indoor radon data in each reportcd for the municipality of Rauina. municipality, thc cxact position coordinates for tllc participating dwellings were detcrmined from thc central rcgister of Noiwegian Survey met h udology dw cllin gs . ArcVi ew Geogr apb i cal Information System was used to produce thematic imps by Pararnctcrs linlung thc coordinates of the houses with the h large-scalc surveys of fitctors affcctjng corresponding results from the indoor radon indoor radon concentrations, expensivc and rneasuremcnts. Tlic municipal radon maps time consuming investigations at each give a detailed picture of thc geographical building site arc irnpossiblc. Proxies like distribution of indoor radon levels in each geological fcaturcs and building municipality and arc very useful tools for t]lc 7

comparison of indoor radon data and thus the statistical analyses werc carried out on geology. Detailed soil and bedrock maps logarithmically transformcd levels of radon (scalc 1: 50 000 or larger) wcrc not concentrations. Mcaii values of the available for all the selected areas, thus transformed radon conccntrations werc adhtional information was obtaincd from compared usjng thc Student's l-tcst. fieldwork carried out in each of the 7 Gcornetric means, ranges, and perccntages of municipalities. Data were collected from a dwellings contajn i ng radon concentrations totd of 1618 building sitcs. In addition to above 200 and 400 3qim' are prcscntcd. Two the main study conducted in the 7 selected tailed P-values < 0.05 wcrc required for areas, useful information was obtained by "statistical significance" in all tests. comparing available radon maps and geological maps for 79 of the othcr municipalities participating in the 2000- ResuIts 2001 indoor radon study.

Information 011 bui 1ding Gcology characteristics, aeration habits and water Thc main statistics for the indoor radon data supply was ccltlectcd from questionriaires classified according to geoiogy arc presented completed by thc residents. The in table 4. qucstionnaires were issued and rcturned by In the threc selected municipalities mail together with the alpha track detectors. of the Southern Precambrian region, a Thc qucstionnaires provided information stat is tical 1y sign ificank diffcrence was obscrved on: Category of dwelling, floor lcvel of bchveen the incan indoor radon levels in room in which ineasureincnts were taken, hoines built on the different types of building outer wall material, foundation wall grounds (p < 0.0001 for glaciofluvial versus material. typc of basement, ventilation basal (ill and no overburden versus all thc othcr systcin. aeration habits and source of groups. p = 0.001 for fluvial vursus basal till, p household water. = 0.01 I3 for fluvial versus glaciofluvial). The gcometric mean values of indoor radon Statistics concentrations in dwellings located on The influencc of geology, house glaciofluvial and fluvial deposits were 307 charactcristics, ventilation habits of Bq/m3 and 186 Bqlm'. respectively. In homes occupants and watcr supply on indoor built on basal till the mean air radon radon concentratioils was investigated by concentration was 101 Bq/m', while dwellings analysis of variancc (Snedecor and foundcd on bedrock had a mean radon level of Cochran, 1989). The distribution radon of 34 Bq/m' Sixty-eight o/o and 34 % of the gas concentrations was found to be skewed, dwellings locatcd on the highly permeable 8

glaciofluvial sediments had radon 197 3q/m3. This value IS slightly higher than concentrations in excess of 200 Bq/m3 and thc inean air radon concentration of i 85 Bqlm’ 400 Bq/m’, respectivcly . The highcst measured in dwellings located on the fraction of houses with radon levels moderately permeablc basal till, but thc exceeding 200 Sqiid was registcrcd on difference in radon concentrations between the glaciofluvial deposits in thc muiiicipality of two groups of dwellings was not statistically

Tinn (75 YO). In dwellings built 011 fluvial significant (p = 0.8183). The dwellings dcposits. 42 Sb and 25 94 had radon located directly on bedrock had significantly conccntratioiis exceeding 200 Bqh3 and lower radon lcvcts than the other groups of

400 Bqlm’, rcspectively. In comparison, I9 dwcllings (GM = 58 Bq/m’. p 0.OOOl). The % of thc dwellings located on thc hasal till distribution of air radon levels in homes built containing uranium rich granilcs had radon over both highly and moderately perrncablc lcvcls exceeding 200 Bqh’. whiIe just one types of ovcrburdcn showed approximatcly 50 home built on this type of building ground cxcceding 200 Rq/m3 and 25 9‘0 exceeding had radon lcvcls higher than 400 Bqlm’. 400 Bq/m3 The maximum indoor radon valuc KO dwelling fowdcd directIy on measured in dwcllings located directly on uranium rich pnites in the municipalities bedrock was 200 Bq/rn’. The urdnium rich of the Southcin Precambrian region was alum shale in the nlunicipality of Stange is includcd in the study. but in the covered with a substantial thickness of basal municipality of Hururn (Oslo region) a till, and non of the dwcliings in the study was largc number of dwcllings founded on the located dircctly on this rock type. Thc highest Permian Drainmen Granite were surveycd. radon valuc for all the 16 1 8 buildings included The mcan indoor radon level in homes built in the study was measured in a dwclIing directly on bcdrock in this area was 132 locatcd on basal till (5300 Bq/m3). According Bq/n~’. whilc 37 YO and 17 ?’iof. the to Follestdd [1974), thc basal till in this area dwcllings had radon lcvcls exceeding 200 has a considwabIy higher content of alum Rq/m’ and 400 Bq/m3, rcspectively. The shale than thc glaciofluvial deposits. mcan radon lcvcl in dwellings Iocatcd on In the municipality of Midtrc- shore deposit in tlic samc area was found to Gauldal (Caledonides), thc incan radon levels be 76 Bq/ui3. Only 4 Yo of thcsc dwellings in dwellings locatcd on different typcs of had indoor radon concentrations in cxcess ovcrburden were gencrally lower than in of400 Bq:m3 dwellings built on thc samc types of In the alum shale area of Stange overburden in tlic alum shale area and the (Oslo region), tlic geometric mean indoor Somlicrn Precambrian rcgion (table 4). Thc radon concciitration for dwcllings located average radon conccntration in homes built on highly pernleablc building grounds was over glaciofluvial deposits was 69 Bq/m3. 9 while a mcan radon concentration of 50 Building characteristics and aeration habits Bqlm’ was reported for dwellings located No large differences in building construction on fluvial sediments. The mean radon style or aeration habits were observed between valucs in dwellings located on basal till and the 7 municipalities included in the study. siIt/clay were 43 Bq/m3 and 42 Bqlm3, Conscquently, thc data from all the respcctivcly. Tn homcs located directly on municipalities were collapscd into one dataset bedrock, the mean air radon level was 31 to investigate thc effect of building

Bqm7 In this arm, building ground was constructioii and aeration habits 011 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 excludcd as 21 % and 10 ‘!

concciitrations bctween houscs with naturai 57 Bqlm’ was reported for thc goup of and incchanical vcntilation systcrn (p = dwellings with private water supply from 0.013 I ) 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 Thc daily aeration period was for homcs with public water supply vcrsus the found to be a significant factor affecting other groups, p = 0.0254 bctween the two

indoor radon concentrations (p = 0.0378), groups with private watcr supply). Whcn the and lhc geometric inean indoor radon level results from the 7 mwicipaljties wcrc was reportcd to decrease with incrcasing examined separatcly, water supply was only pcriod of acration. The difference in mean recorded as a significant factor affecting indoor indoor radon concentration was found EO be radon lcvcls in 4 ofthc munjcxpalitics (Hururn. significant bctween the p-oups of dwellings Nes. Slange and Tiim). In all the 4 whcrc thc bedroom’iiving room was aerated municipalitics, the highest indoor radon less than 1 hoia pcr day arid morc than 6 concentration was found in the group of’ hours pcr day (p = 0.0287). Thc indoor dwellings with public water supply. radon conccntrations for a11 the diffcrcnt categories of dwellings listed in tablc 4 ranged from a fcw Bq/m3 to several Discussion tlzousand Bq/m?.

The results of the prescnt study The results from the comparison betwecn showed no cvidence of a systematic cfcct indoor radon concentrations and gcologic data attributable to typc of basemcnt or type of indicate that indoor radon concentratioiis and foundation wall matcrial (p = 0.1 136 and p geology are related in Norway. On a broad = 0.1247, respectivcly). scale of investigation, indoor radon levels in Norway are found to bc highest in regions Water supply where rock types with ekvated uranium A total of 1596 liouscholds rcported concentrations occur. The results show that whether they had public water supply or the indoor radon risk iiicrcases in areas where private water supply from drilled wclls or uranium rich bcdrock outcrops and in areas surface watcrs. The gcoinetric mean indoor where uranium rich rock fragincnts are radon concentration in thc I224 homcs with iiicorporated into the overburden. Thus, the public water supply was 117 Bq/rn3. In the occurrencc of uranium rich rock types appears 203 homes with privatc drilled wclls. the to be onc important indicator of radon risk. geomctric inean iiidoor radon Icvel wits 77 The Cambrian-Ordovician alum shalc aiid Bq/m’. A geomctric mean radon level of granites of different agcs commonly contain 11

rahuin concentrations cxcccding 100 Bqkg the building ground and not only to low and are the primary radon source rocks in uraniuin levels of thc sediincnts. Similar Noway. Thcse rock types are mainly geological conditions are registered in the found in thc Southern Precambrian region, municipality of Huruin where the sand and the Oslo region and the Prccambrian of gravel dominated shore deposits are underlain Northern Norway (Sipiond et ad., 1984). by low perrneablc silt and clay sediments. Thc uranium contcnt of the Thc significant correlation between overburden is an impowant factor indoor radon levels and geological factors controlling the production of radon gas in obscrved in the prcsent investigation indicates thc soil, but the transport of radon gas to the that geological data is B usefid tool for building construction is controlled by other identifying high radon risk building grounds in factors. The results froin the prcscnt study Norway. Important information for the show a statisticalfy significant association classification of both regional and local high betwccn thc indoor radon cnncentrations radon risk areas can bc obtaincd froin already and thc permeability of the overburden. mapped geological parameters. The results Sands and gravels (e.g. glaciofluvial and show that both radium content of tlic bedrock fluvial deposits) appear to contributc and the permeability of thc overburdcn 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 prcsuinably because high permeability of of thc overburden in a formcr glaciated arca the building ground favours the transpurl of may not he the undcrlyjng bedrock, a bedrock radon from its source to the building imp can only be used directly to dcfine high construction. These rcsults indicate that thc risk radon areas iT no supeficial deposits arc pcrmcability of thc building ground is prcscnt. Overburdcn classifications, on thc another important predictor of high indoor other hand, do iiot take into account details of radon conccntrations. The thickness of the the sourcc materials of the glacial drift and permeablc layers is. however, of major must be supplied with information on the rock irnponancc. In the selected municipalities fragncnts incorporated into thc sediment of the Caledonian orogenic belt and the deposits. North-Western gciss area, rnarinc silt and Based on the results from the present clay deposits have becn found to underlie study, high radon risk building grounds in parts of the fluvial and glaciofluvial Norway itre found to be 1) exposed bcdrock deposits. Thc low indoor radon levels with elevated levels of radium {mainly alum measurcd in homes located on thcse shalc and granites) and 2) biglily peimcablc deposits are thereforc partly attributcd to uncoiisolidated scdiments (inaiiily gtaciofluvial the small volume of perrneablc sediments in and fluvial deposits) dcrived froin all rock 12 types as wcll as moderatcly permeable componcnts also provide the basis Tor radon sediincnts (mainly basal till) containing risk classification diagrams presentcd by other radium rich rock fragments. The latter type authors (Strandcn et ul., 1985; Peakc and of high radon risk building ground requires, Schumann, 1991). Howcver, in addition to a however, a significant vertical thickness of generai geological classification of radon risk. permeable unconsolidatcd sediments and a thc comparison of geologic data and indoor low water tabic. Fine graincd sediments radon dues performcd in the prcscnt study fike mariiic silt and clay deposits and silty also provides information on the proportion of and clayey till represent building grounds dwclhgs expcctcd to have indoor radon Ievcis of low radon risk unless the permeability of above 200 Bq/m3 in high, moderatc and low these sediments has bcen increased through risk areas. A high risk area is defined as an loss of moisture and soil cracking. arca in which more than 20 YOof the homes arc Thc most radon prone regions in likcly to havc radon concentrations above 200

Norway arc found to be thc Southcrn Bq/m7 In a modcrate radnn riqk area, the Prccambrian region, thc Oslo region radon level in between 3 YO and 20 ‘51 of thc (including the adjacent alum shale area) and dwdlings is cxpccled to exceed 200 Rq/rn7. the Precambrian of Northern Noway. h An area in which tcss than 3 % of the these regions, both radium cnriched dwellings are likely to havc radon bedrock and pcrmeable unconsolidatcd conccmations abovc 200 Bqlm’ and no scdiincnts arc present. Tn the other regions, dwelling have radon levels higher than 400 the high risk radon arcas are mainly Bq/1n3, is classified as 3 low radon risk arca. concentrated to sand and gravel deposits, The expectcd percentagcs of dwellings having exccpl for a fcw granite arcas within the radon lcvels in exccss of200 Bqhn’ in areas of

Calcdonides. In addition to the previously high, moderate and low radon risk arc based 011 rncntioned lypcs of penneablc deposits, knowlcdgu of the typical Norwegian dwelling, sandy and gravelly marginal moraincs have and the classification is not necessarily valid in bcen reported to haw an incrcased other countries where hffcrent construction probability of generating clevated indoor characteristics predominate. radon levcls due to their high penneability In the dassificalion diagain given in (Valcn ef ai., 1999). figurc 2, permeabilities above cm’ arc The rcsults of tkc present study dcfincd as high sincc convectivc radon arc summariscd by the classification of transport may bccome dominant over diffusion radon risk prcscnted in fiprc 2. Areas of transport at this level (Sextro et ai., 1987). high. moderate and low radon risk arc Due to thc wide range of permeabilities within dctined bascd on permcabitity and radium cach rock type, permeability ranges ‘arc not content of the buiiding ground. These two included for the rock types listcd in the 13 diagram. Gencrally shales and unfractured the mechanisms causing high indoor radon igneous and metamorphic rocks are lcvels, assessments of radon risk based on considcrably less permeable than karst geological information can also be extended to liincstone 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 decidc whether bedrock may, however, increase if blast prcventative measures against radon must be firing at thc building sitc is carried out. The takcn in future buildings. ranges of radiuin concentrations of bedrock Based on an evaluation of a given in thc diagram arc based on prcvious geologically based radon risk map of the studies in Scandinavian countries (Nordic, municipality of Uppsala, Swccdcn, Friis ef ai. 2000). (I 999) concluded that gcological information The rcported correlations is unsuitable for idcntifiing radon prone areas. betwccn indoor radon concentrations and The significant diffcrence in indoor radon geology enable the identification of radon concentrations obtained between areas of high, prone areas in Norway based on geological modcratc and low radon risk in the prcsent information. The idcntitkation can be study contradicts this view aid strongly carried out in a rathcr simple and suggests that areas of different radon potential inexpensive manner by using existing can be dctermined based on gcological geological and geochemicai data. information. Thesc conclusions are in overall Evaluations of radon risk based on concordancc with findings from other s tridies geological criteria can not be used to in formcr glaciatcd areas (e.g. other Norhc predict the radon levels accurately in countrics and somc regions of the United individual homes, but it may contribute in States) where permeable glacial drift and mdkirig national and municipal indoor uranium-enriched rock types like black shale radon measuring programs more effectivc and ganite haw bccn reportcd to be important allowing action to be concentrated where it predictors of radon prone areas (Aakcrblom et is most likcly to be effcctive. The regions al., 1983; Peak, 1988, Gates e/ a!., 1990; of high geologic radon potcntial can be Gundersen er ul., 1992; TclI et a/.,1994; Hutrj given priority when national screening and Makelainen, 1993). In Sweden and prograins are planned, and efficient follow- Finland, particular attention has been drawn to up surveys can be established based on the glacioflwial cskcr deposits which have geological data in combination with radon been shown to be one of the most radoii- mcasurements in a represcntative samplc of critical landforms (Aakcrblom et al., 1983; thc building stock. Since geological Caslren er a/., 1985; Hutri arid Makelaincn. information provides an understanding of 1993, Arvda ef al., 1994). In these countries. 14 geolngic information has been uscd to rank tnechanical ventilation system can be a risk geographical arcas in order to be ablc to factor for indoor radon compared to a balanccd make the most effcctive 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 dcvclopment pressurc gradicnt created by the mcclianical (Aakerblorn et ul.. L9XK; Castren ei id., ventilation system. 1992; Aakerblom, 1994). Investigations havc showii that Whcther thc geologic radon houscs with a full basemcnt or a part basement potciitial is rcalised in tcrms of high indoor are more susceptible to radon problcms than radon lcvels dcpcnds on factors relatcd to houses with no basement (Ankerblorn et af., lhc structure of the building and the way it 19x3). In an carlier survey of factors affecting is uscd. The resuits froin the prcscnt study indoor radon concentrations in Norwegian indicate that several different parameters hoincs, significant higher radon levels wcre rctatcd to building characteristics and found in homes with a part bascment compared aeration habits affect the indoor radon to those with a full bascinent or no basement levcls in Norwegian homes. The data (Strand et ul., 1992). Lanctot et ai. (1992) suggest that thc indoor radon concentration found no significant differcncc in indoor radon decrcascs with increasing floor level of the concentrations in dwellings with a basement room wlme thc dctectors were exposcd. compared lo dwellings without baseinciit. In This result is expected since the building thc present study, corrclations between indoor ground is found to be the main SOUTCC of radon levcls and different typcs of basements radon in Norwegian dwellings. The samc wcre searchcd for, but not found. Likewise, no trend is observed by other investigators evidence of a systcniatic effect attributable to (Gunby cr #I., 1993; Albcring et ul. 1996). type of building matcrial OF tlic fouriciahm Severd authors have observed a walls was observcd. significant influence of aeration habits on In 4 of the municipalities included in the indoor radon Ieveis (Buchli and the prcsent study, liighcr indoor radon levels Buchart, 1989; Strand ef d.,1992; Cunby werc found in dwellings supplicd by watcr el ul., 1993). In accordance with the results from public waterworks cornpared to those of the above listed studies, the prcsent with private water supply (Tinn, Stange, matcrial indicates that the radon levcl Hurum and Nes). Thc public waterworks in 3 decreases with incrcasing daily aeration of the municipalitics are based on surface period of the room where the radon water (Tinn, Stange and Hurum), whilc the ineasurenient was carried OUI. A general municipality of Nes cxtract thcil- water from trend is also observed suggesting that a (Suatcrnary superficial sediments. In 1996, thc public water work in Ncs was included in a bedrock and ovcrburden are takcn intu study of radon levels in raw-watcrs of 33 account. Radium contcnt and permeability of major groundwatcr works in Norway (31 the building ground have becn shown to be based on water from superficial deposits usehl indicators of indoor radon and 2 based on watcr from hard rock) concentrations, and an estimatc of both (Morland et al., 1996). An avcragc radon regional and municipal radon potential can be concentration of 23 Bqll and a maximum given based on casily accessiblc geological valuc of 88 Rqil were reportcd for thc 33 data. watcnvorks. The water sample from Nes Gcologic terrains of high radon risk had a radon level of 83 Bqll. The in Noway include a> exposed bcdrock with Norwegian action level for waterworks is elevated levels of radium and b) highly 100 Bqll, and no radon concentration pcrmeable unconsol id3tcd sediments derived exceeding this level has ever becn rcported from all rock types and inoderately pemicable firm Norwegian waterworks. Amounts of sediments containing radium rich rock radon giving causc for concern are fra-ynent s. generally limited to watcr froin private The obscrvcd correlations between drilled bedrock wells (Reimann e6 a/., 1996; indoor radon and geology indicate that Morland et d.,1997; Banks et d.,1995). geological data is a useful tool for identifying Of the 15 dwcIliiigs in the municipality of areas whcrc preventative mcasures against Hurum supplicd with water from drilled radon must be taken in future buildiiigs. wells in the Pcnnian Drartirne~ Granitc, Geological parameters can not provide only one dwelling had indoor radon Ieds accuratc estimates of radon levels in existing exceeding ZOO ~q/rn~ Radon homes, but the identification of dwcllings with conccntrations in dwellings supplicd froin elevated indoor radon lcvcls can be facilitatcd drilled wells in the dhcr selected by coiiceiitrating resourccs to the areas of high municipalities were also generally tow. geologic radon potential. Thus, household watcr is not believed to bc Sevcrai parameters rclated to an important source of indoor radon in thc building characteristics and aeration habits homes included in the prcsent study. appear to affect indoor radon concentrations in Norway. The factors found to have a statistically significant association wi tli indoor Conclusions radon levels in the prescnt study are ventilation system, aeration habits, and floor level of thc Significant corrcl ations between geology room whcrc the measurcmcnts were carricd and indoor radon concentrations in Norway out. are found when tlic properties of both thc Acbrowledgmeprts - This work was funded Devon, UK. Environ Gcochem and Hcalth by thc Research Council of Norway 1993;15(1):27-36. (project 135370/720). Banks D, Royset 0, Strand T, Skarphagcn H. Radioelement (U, Th, Rn) concentrations in Re fe rencts Norwegian bedrock groundwaters. Environ Gcol 1995;25:165-180.

Aakcrblom G. Ground radon - monitoring proccdures in Sweden. Geoscientist 1994; Buchli R, Burkart W. Influcnce of subsoil geology and construction tcchniyue on indoor 4(4) 12 1-27. air radon-222 levels in 80 houses of the ccntral Phys Aakerbloin G, Andersson P7 Clavensjii 3. Swiss alps. Hcalth 1989;56(4):423-429. Soil gas radon - a source for indoor radon daughtcrs. Rad Prot Dosiin 1983;7(1/4):49- Castren 0, Arvela H, Makeliiinen J, A. survey 54. Voutilainen Indoor radon in Finland: Methodology and applications. Rad

Aakerblom G, Pcttersson R, Rosen B. Prot Dosiin 1892;45( t/4):413-4 18. Markradon. Handbok for undersokning och redovisning av rnarkradonGrhillanden. Caslren 0, Vnutilaincn A, Winqvist K, Miikikelliinen Studies of high indoor radon Radon i bostader, Byggforskningsridet 1. areas in Finland. Sci Tola1 Environ R85 1988, 160 pp (In Swedish). 1985$5:3 11-3 I E,

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Ball TK, Miles JCH. Gcologicaf and kvanmgeologisk kart 1916 II - M 150 000. geochemical factors affecting the radon Geological Survey of Noiway 3 13. 1975; I -62. concentration in homes in Cornwall and FoIlestad BA, Larsen E, Blikra H, Lonpa Gundersen LCS, Schurnann RR, Otton JK, 0, Anda E, Sonstegaard E, Rcilc A, Aa AR. Dubiel RF, Owen DE, Dickinson KA. Losmassckart over More og Romsdal fylke Geology of radon in the Unitcd States. med bcshvclse. M 1250 000. GeologcaI Geological Society or America 1992, Special Survey of Norway, shifter 1 994; 1 12: 1-52 Paper 27 I I - 16. (in Norwegian, with English abstsack). Hutri KL, Makelainen I. Indoor radon in Frcczc RA, Cherry JA. Groundwater. houses built on gravcl and sand deposits in Prentice-Hall, Inc., Englcwood Cliffs N.J., southern Fidand. Bid1 GcoI SOC 1993;65:49- 1979,604 pp. 58.

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bedrock groundwater - selected parameters Lindahl 1, Sordal T. Natutlig radioaktivitet (pH, F, Rn, U, Th, B, Na, Ca) in samplcs from fra berggrunncn. More og Romsdat. M Vestfold and Hordaland, Norway. NGU Bull 1 :500 000. Geological Survey of Norway, 1997;432:103-1 17. 1988 (in Norwegian).

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the Nordic counlries - recommendations. The Lindahl I, Sordal 1, Sdli A. Radioaktiv Radiation Protcction Authorities in Dcnmark, striling fra borggrunnen. Nordland fylkc. Fiuiand, iccland, Norway and Sweden 2000, M 1:500 000. Geological Survey of 80 pp. ISBN 9 I-89230-00-0. Norway, 1993 (in Norwegian).

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Wanty RB, editors, FicId studies of radon in Geological Survcy of Korcvay 1958;203:100- rocks, soils, and water, 1991, U.S. Geol 111 Survey Bull No 1971,pp. 163-175. Snedecor GWI Cochran WC. Statistical Raadc G. Disbibution of radioactivc methods. Towa State University Prcss, 8'" ed, elements in thc plutonic rocks of tlic Oslo Ames, Iowa, 1989, 503 pp. Region. Unpublished cand. real. thesis, Uiiivcrsity of Oslo, 1973, 162 pp. Strand T, Green BMR, Lornas PR. Radon in Norwegian dwclhgs. Rad Prot Dosiin Reimann C, Hall GEM, Siewers U, 1992;45( 1/4):503-508. Bjowah K, Mortand C, Skarphagen H, Strand T. Radon, fluoride and 62 elements Strand T, Lind B, Tommcsen G. IUurIig as determined by ICP-MS in 145 radioaktivitct i husholdingsvann fra Norwegian hard rock groundwater samples. borebronner i Norge. Norsk Vetrinlrtidskrift Sci Total Environ 1996; 192:1-1 9. 1998,l IO (10):662-665 (in Norwegian).

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Valen V. Soldal 0. Gunter B, Henriksen H, Jensen CL, Lauritzcn SE, Rydock .I, Rye N, Strand T: Sundal AV. Variations in radon content in soil and dwellings in the Kinsarvik area, Norway, arc strongly dcpcndeiit 011 air temperature. Exrcnded abstracts, AARST-2000 hit Radon Symp, E N c

-100 km

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

Caledonian orogenic belt Basic metavolcanics and igneous rocks Gneisses and metaigneous rocks Caledonian Granites Late Precambrian metasediments Cambrian-Silurianmetasediments (also present in the Oslo rcgion) ian rocks Sandstones and conglomerates

Oslo region Intrusive rocks Volcanic rocks

Fig 1. Bedrock rnup of-Norwayand the location of the 7 municipaiities included in the study (Source: Digital Bedrock Geology map of Noway, 1:3 million, Geological Survey of Norwuyj 22

1 f34 la -5 Glaciofluvial deposits Share deposits lo-6

I

10 -8

10-9

10-10

lo-”

10-‘2

10-l~ d4

1015

Radium concentration (BqW

Fig, 2. Clms@cution of radon risk based on permeability and radium content of the building gruund. High risk arm: Area in which more than 20 96 of the homes are expected to have radon concentrations in excess of 200 Bq/rn3. Maderate risk area: Area in which between 3 94 and 20 96 of the dwellings are expected to exceed 200 Bq/pn3. Low risk area: Area in which less than 3 % of the dwellings have radon levels above 200 B@t3 and RQ dwelling have radon levels higher than 400 Bq/m3. 23

Table 1 Typical ranges of activity concentrations of radiuin-226 and thoiiurn-232 in Nordic rocks (Nordic 2000) Type of rock Ra-226* Th-232 <(Bq/kg) Granite, normal 20- I30 20-80 Granite, uranium- and thorium-rich 100-500 40-350 Gneiss 25-130 20-89 Carbonatites IO-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 Shalc 10-150 10-60 Alum shale 100-4300 10-40 * 12.3 Bq/kg ruu'iurn-22h is q.yuiwlent to I pym umnium-238 24

Table 2. Typical rangcs of activity concentrations of radium- 226 and thorium-232 in Nordic soils (Nordic 2000) Soil Ra-226* Th-232 (Bqlkg) (Wkg) Gravel 10-90 2-80 Sand < 4-60 2-80 Eolian sand-sill 5 -20 10-20 Silt 5-70 5-70 Clay 15-130 10-100 Till 10-170 15-100 Till with alum shalc 180-2500 30-50 * 12.3 B.q/kg mdiium-226 is quivuient bo I ppm iimnium-238 25

Table 3. Avcragc municipal indoor radon conccntrations and gcological characteristics of the 7 selected municipalities Genlogical region Munici- Mean Kn Type of bedrock Type or overburden palit? indoor (Byld) The Southcrn Tinn 358 Prccambrian granite. gnciss and Precambrian region mitarhyolitc UIvik 2011 Precambrian gnciss and Cambrian- GlacioRuvial and fluvial depusits. Ordovician phyllite basal till Nes 266 Prccambrian granite, quartz shale, .. metasandstonc. gneiss and quartzltc The Oslo region Hurm 205 Pennian granite. Precambrian gnciss Marine shorc dcposits, marine silticlg Stangc 350 Precambrian gnciss. Cainbrian- Glaciufliwial and fluvial dqwsits, Silurian alum shalc, limestone and basal till clay shalc The Caledonian Midtrc 91 Cmnbrian-Silurian phyllite, quanzite, Glaciofluvial and fluvial dcposits, orogenic hclt Gauldal quartz shale and amphibolite basal till, inariiie silt!clay The North Wcstcm Rauma 29 Prccaiiihnan Lmeiss Cilaciofluvial and flurial deposits. Prccambrian region bas$ till, inarine siltklay 26

Table 4. Indoor ail- radon by geology. P-values from thc "one-way Anova" analysis N Geometric Range o/u~200 "hZ400 mean (Bq/m3) (Bqld) (Bq/m3) (Bq/m3j Southern Precambrian region TinnlL-h tk NGS Glaciafluvial (El) 77 307 40 4100 OR 34 Normal to high U-lcvels 111 Fluvial (H) I35 1x6 ~:IO-4SOO 42 2s bedrock' Basal till (M) 100 IO1

Stanre Cilacicitluvial (H) High U-lcr~lsin bedrock' Basal till (M) Ucdruck'

Caledunia n orogenic bell Midtre Gauldal Glaciofluvial (H) Low I,~-lcvclsin bedrockD Flinial (H) Basal till (M) Marinc silt/cIay (L) Bedrock'

3.W. Precambrian region Rauma Glacioflutial (a) l,ow to normal Il-lcvcls in Fluvial (H) bedrock'' Basal till (M) Marine siltklay (L) B&WkS 27

Factor Category Number of Geometric mean Range dwellings ( Bq/m3 ) pq/rn3) or 1 iving ruom Ground floor 1018 90 < 10-5300 First floor 36 58 c: 1 0-2500 p < 0.0001 Baseiiiciit type Cellar 99 1 95 -c i0-4500 Partialicrawl space 383 I I5 10-4900 No ccllar 160 Ill -r10-2500 p = 0.1 136 Buiiding materiaf of Concrete S64 138 <10-5300 foundation walls Light weight concrctt: 673 93 c: I 0-35oc) Natural stonc 1os 123 C I 0-4900 p=O.1247 Ventilation system Natural 1 I39 97 1 0-5300 Mechanical 336 119 1 0-4900 Balanced 64 81 .--10-2IO0 p =0.0174 Mcan daily aeration lcss than 1 h I258 104 .--IO-5300 period I-bh 141 86 < 1 0-3400 morc thaii 6 h 83 75 .:IO-3500 p = 0.0378

Paper I1

Sundal AV, Henriksen H, Lauritzen SE, Soldal 0,Strand T & Valen V Geological and geochemicar factors affecting radon concentrations in dwellings located on permeable glacial sediments - a case study from Kinsarvik, Norway. Submitted to Environmental Geology, 2003. I

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, ODDMWND SOLDAL, TERJE STRAND & VIDAR VALEN

Sundat AV, Henriksen H, Lauritzen SE, Soldal 0, 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 Grolog);.

In 1996-1997, indoor radon values of more than 40 000 Bqlm' and Iargc seasonal and geographical variations in indoor air radon were reported from a residential area located on a highly permeable icc-marginal deposit. Gcochcmical analyscs of bedrock, groundwam and scdiments and comparisons between indoor radon values and soil radon values indicate that the indoor radon conccntrations in this area arc strongly affected by subterranean aix-flows causcd by temperature differences between soil air and atmospheric air. The air-flows concentratc thc radon- laden soil air towards the topographic highest part of ihc deposit in winter and towards the topographic lowest part in suinmcr. ln areas where subtcrranean air-flows are likely to occur, radon measurements pcrformcd both in summer and in winter provide the best estimate of annual averagc indoor radon conccntrations. and assessmcnts of jndoor radon concentrations based on single soil gas measurements are not rccomrnended.

Introduction increasingly been drawn to the problcms concerning enhanced radon conccntrations in

A large proportion of Norwegian dwellings buildings located OD this type of building are located on permeable unconsol idatted ground. Studics in othcr countries haw scdirnents of late glacial or post glacial revealed that highly pcrmeabk sediinent origin. Over the last dccade, attention has deposits must be regarded as radon prone arcas 2 in which the concentralions of radon in The sediment accumulation originates from the buildings is likely to bc higher than the end of the last glacial and is mainly a coarse nationa1 avcrage (Aakerbloin and others grained, morainic deposit. The highest shore 1983; Peak 1988, Hutri arid MakcIainen linc during the accumulation stage was around 1 993; Tcil adothers 1994). In 19%- 1997 I10 m above thc prcscnt sea level (Koltedahl anomalously high levels of indoor radon 1975). Thc surface of the moraine is concentrations were reportcd from the charactciised by mounds and depressions and rcsidentiai area of Husc touted on an large angular boulders. At tl~csurface, a extensive ice-marginal deposit in Kinsarvik, sandy, gravelly matrix is present below the Norway (Jenscn 1997). Radon marine limit, while the matrix is nearly absent measuremcnts carried out in 77 of the in thc area ahme approximately 110 m a.s.1. approximately 130 dwellings revcaled At the western side of the vallcy the main river indoor radon concentrations as high as 40 has cut dirough the icemarginal deposit, whilc 000 Bqlm1 In addition to thc high radon along the rivcrbed the moraine 1s overlain at levcls, large scasonal and geograpliical various levels by fluvial and glaciofluviaI clianges in indoor radon concentration were sediment terraces. A spring horizon is found registcred. The results from the indoor in the steep rivurbanks west and northwest of radon study in the Huso a-ca received tlie Huse area. Thc inaximum thichcss of the nationa1 attention, and detailed geoiogical deposit is estimated to be SO rn. invcstiptions were carried out in ordcr to The bedrock in thc Kinsarvik district identify thc radon sourcc and to understand consists of granites and meta-ipcous rocks the extrcme variations in indoor radon mdinly of carry to middle Proterozoic age concentrations. (Sigmond and others 1998). In the stccp hillsides northcast and west of ttic Huse area Thc invcstigated area mcta-daciie. mcta-aidecite atid fine- to Kinsarvik is situated in the mnunicipa1ity of rncdium-gra i ned, foliated meta-granite occur. Ullensvang, Western Norway (Fig. 1). It is In the main vaIlcy to the south of the ice- a small rum1 area located in the bottom of a marginal deposit, mcta-granite with a typical &cia1 vallcy, with steep hillsides pronounced foliation and largc fcldspar grains and several tributary vdleys. Thc dominatcs. The meta-granitcs are intruded by residential area of Husc is located on thc pegmatite and coarse-graincd granite. South distal slope of an icemarginal deposit and cast of the Kinsarvik area the Prccambrisn extending approximately 1 lun up the valIcy rocks are ovcrlain by Ordovician-Silurian from the Hardangei-Fjord (Holtcdahl 19751, phyllites with layers of quartzite and marble Thc Husc area is approximately 0.S km' (Sigimond and others 1 993). and extends from 40 to I15 m ad.(Fig. 1). 3

Kcarty all the dwcllings located air as tlic drilling fluid. Sedjincnt sarnplcs within the residential area of Huse arc werc collected every I m during drilling. Thc detached houscs of wooden construction, boreholes were installcd to just below thc and most of thcm have cellar construction water tablc with a total length of 24 and 30 m. (Jenscn 1947). Thc majority of the Plastic tubes with 0.3 mm filter openings were buildings were constructed aRsr 1960. and installed in the borcholes to enable nearly all the houses are ventilated by groundwater sampling. natural means (Jensen 1997). The ail- To explorc lateral changes in exchange rate has bccn found to be lower stratigraphy, ground-penetrating radar (GPR) than recommended in several of the surveys wcrc carried out in the area. Eighteen dwcllings. All the households in thc area profiles were collected. having a total lcngth of have public surface water supply. In 1996- approximately 3 km. The georadar device 1997, the Norwegian Radiation Protection used in thc survey was a Maha Gcosciencc Authorities (NRPA) carried out indoor RamacFJ using 100 MHz antennas. radon measureincnts in 77 of the dwellings Interpretation of data was bascd on thc in the Hr~searea at three diffcrcnt seasons methods described by Beres and Haeni ( I99 1). (Jensen 1997). The distribution of annual average indoor radon conccntrations Geochcmical analyses of bedrock, sedimcnts calculated on thc basis of tllcse and groundwater incasurements is prcscnted in Fig. 2. Twenty scven samples from thc iocal bedrock and the phyllilc area soutli and east of Kinsarvik were analysed for U and Th (Tablc Methods 1). From each of thc two borcholes, 5 samples representative of the dcposit werc sclecred for analyses of U, Th and Ra. The aid Th Drilling and ground-penetration U analyses were carried out al thc Memorial radar surveys University of New Foundland by inductively Two boreholes were drillcd in order to coupled plasma mass spectrometry (LCP-MS). investigate the stratigraphy, depth of water The Ra levels of tllc boreholc samples wcrc tablc and petrographical composition of the determined by gamma spcctroscopy at the ice-marginal deposit. One borchoic was Norwegian Radiation Protection Authority. drilled in the topographic lowcsl part of the The borchole sampIcs were split in residential area (borchole A) and thc other two, and one half was treatcd with HCI and borchole in the area of highest clevation NalSO3 before the analyses (Table l), This (boreholc B) (Fig. 1). The drilling was procedure was applied in order to bring Fe- carried out using an ODEX harnmer- and Mn-oxide coatings into solution and rotation mobile rig employing coinprcssed 4 estimate thc leachable fraciion of the different seasons during 1997-1998. radionuclides in the sediment samples. Rn- Temperature and pH measurements of the exhalation rates wcrc determined for the groundwater wcrc carried out in tlic field when untreated sainples and used to calculate the water samples for radon analyses wcre radoii emanation cocfficient of thc collcctcd. sedimeiit s. Thc Rn-cxhalation rneasuremcnts were carried out by Soil gas measurements enclosing oven-dried samples in a sealcd To study the mechanisms responsjbk for the recipient for 20 hours. Air samples wcrc significant seasonal changes in indoor radon taken with an evacuated scintjllation ccll Concentrations in thc Huse area, radon gas (Lucas ccll) and counted by an EDA measurements in the soil air wcrc carried out in scintillation flask (RD-ZOO). Tlic analysed different seasons of the year. Tlie radon borehole sampics were choscn from the concentrations were measurcd by etched track dominating gravel fraction. detcctors (C-39) buried in 23 different In May 2001, watcr samples wcrc localitics within the residential arca. The collected from the main river (river I), a detectors were sealcd inside thin pjastic bags in smaller river draining thc area to the north ordcr to prevent immediate ovcrexposure and of the icc-marginal dcposit (river U), to protcct the detcctors from contamination. borcholc A and lour springs locatcd along The detectors were placed at approximately 20 the riverbanks west and north of the glacial cin depth in all mcasuring stations and exposed deposit (Fig. 1, Tablc 2). One set of foi- 2-3 days. samplcs was analysed at tllc Geological Survcy of Norway (NGU) for U and Th by Statistics ICP mass spectromctry. Another sei of hi order to explore the pattern of geographical

smmplcs was analysed at the Enstitutc for and seasonal changes in soil radon Energy Tcchnology (IFE) for Ra by the concentrations in the Husc arca. the averagc scintillation flask mcthod (RD-200). The summer and wintcr radon concentration for last sct of samplcs was analysed for Rn at cnch measuring station was normal ked against the NFPA by liquid scintillation. thc station-avcrage for tkc whole year. A Tlic isotopic composition of U nonnaliscd value of 1 rhus rcprcscnts a and TI1 in water samples from threc springs measuring station with a summcr value or a was detcrmined by alpha spectromctry at wintcr value quat to the yearly mean of that the Univcrsity of Bergcii (Table 2). In station. Thc summer and winter radon order to investigate scasanal radon concentrations in dwellings wcrc nonnaliscd variations, groundwater from five springs against the yearly mean vaIuc by the samc was analysed for Kn concentrations at method as thc radon rneasurcments in thc 5

ground. The Mann-Whitncy test was used surface downwards with 3n interval of 2-5 m. to compare the medians of the samples Thesc reflectors can bc traced in at1 thc profiles from the different groups obtained (Davis froin the area. The interval between tlic 2002). P-values < 0.05 were required for reflectors is generally decreasing towards the “statistical sigmfjcance’’ wcstern part of the area. A comparison between soil gas The stratigraphy of thc icc marginal concentrations and indoor concentrations of dcposit is presented in the borelogs in Figs. 3a radon at different seasons wits rnadc by and 3b. The logs show that the ice marginal locating thc indoor radon mcasmements deposit is dominated by vcry coarse material. within 30 meters of a soil gas mcasuring Layers of sand and gravel alternate with station. If more than one indoor radon distinct horizons of boulders and pcbbles. Thc measurement existed withn thc buffer content of boulders and pebbles is gencrally distance, the soil gas value for that station highest in the upper part of tlic borelogs, was cornparcd to the averagc of the although boulder-rich horizons occur all the different indoor radon concentrations. way down to tlic water table. The coutcnt of siIt and clay is low. In October 1998, the water table in borehole A and boreholc R was encountcred at 19 m and 29.5 m bclow ground Results bel, respectively. Thc samples froin borehole A are Stratigraphy and petrographic dominated by meta-granitelgranitc in the upper composition of thc icc marginal deposit part and meta-dacite in the lowcr part (Fig. 3a). Thc gcoradar profilcs from the ice marginal Meta-granitdgranitc dominates both Ihc upper deposit in Kinsmik are dominated by and lower part of protile B, whilc phyllite and discontinuous reflectors and diffractions of gneiss are major constituents in SO~Cof the varying sizes (Valen and others 1997). In horizons bctween 7 and 21 m below ground many profiles the diffractions are lcvel (Fig. 3b). Very little phyllite occws in particularly frequcnt in the uppcr few thc sediments. Iron oxide stains (incipient iron meters of thc deposit, but diffractions arc “hard pan”) were observed on the metadacite also prescnt down to the maximum grains and in the granitic material froin the penerration depth of approxiinatcly 20 m. war surface horizons. Tlic source rnatcrial for Rarely do continuous reflectors occur in tlic sedirnenis is assumed to be primarily the these profiles. Sotne continuous rcflectors local bedrock in Kinsarvik and thc bedrock rn are prescnt close 10 thc ground surface and thc immediatc area to tlic south. The a few distinct, nearly horizontal rcflectors dorninancc of metadacite in the lowcr part of occur froin around 4 inetcrs below thc protile A is most likely due to mass 6

rnovcnicnts from thc hillside to the north of radon conccntrations in the groundwater Kinsawik where this rock type occurs. sampks range from 240 Bqll to 364 8qA. The 222FW2'hRaactivity ratio is always greater than Gcochcmistry 1O', dcinonstrating a large enrichment of 222Rn U and Th conccntralions in diffcrcnt rock in the liquid phase. Radon gas concentrations typcs froin bedrock and boulders in the in groundwater samples measurcd at different Kinsanik district are prcscnted in Tablc 3. seasons are shown in Table 4c. No sigificmt The results show that tlic highest uranium temporal fluctuations in thc radon gas content and thoijum levcls arc found in the granitic or differenccs in radon concentrations in water rock types. Granite I, occuring as from springs draining diffcrcnt parts of the icc- intrusions in the foliated meta-granite, marginal deposit arc detected. Groundwater contains the higlicsi average uranium tcrnpcratures in the range 5 "C to 7.5 "C and conccntration of 22.9 ppm. Thc lowest pH-values in the rangc 6.2 to 6.8 are measured averagc uranium and thorium in all ihc groundwater samples at all scasons. conccntrations are obtained froin the meta- Uranium senes radionwlide dacite ( l .4 and 4.3 ppm, rcspectively). concentrations of thc borehole samplcs are Radionuclide coiiccntrations in shown in Figs. 3a and 3b. The U groundwater and surface water froin concentrations in thc 10 samples vary between Kinsarvik are listed in Table 4 a-c. The U 24 and 142 Bq/kg. The Th levels vary bctwccii contents obtaincd from groundwater 9 and 60 Bq/kg. and the Ra conccntrations sarnplcs range from 0.19 to 0.63 pgll. A range from 18 to 84 Bq!kg. Most of the state of discquilibrium bctween 238Uand its samplcs have Ra concentrations above 50 daughter nuclidc z34Uis found in all the Bqlkg. A radioactive disequilibrium between analysed groundwater samples; z34U/z38U '"Ra and % is found in all the samples. the activity ratios geater than 1.0 reflects an 126Rai2"U activity ratios ranging frorn 0.5 to excess '% in the water. Thc Th 0.8. The perccntage of thorium Icached by the concentrations presented in Table 4a are all HCL'Na2S07 treatment is rather constant for under or close to detection level. The low most of the sedimcnt samples, whilc it varies levels of dissolved thorium arc illustratcd to a gcater extent regarding uranium and by the low ratio of '.'"Th to *'4U in the radium. Bctween 50 and 60 %I of tlic U groundwater samplcs. concentration in the mcta-dacite samples from A sihmificant dcparture from thc lowcr part of borehole A and the gneiss secular equi Ii hrium is found between samples in borehole B is leached by the radium and radon in the groundwater. All HCIINa&lJ treatment. The lcaching the water sarriples have radium levels bclow expcrirnents thcrcfoore indicatc a non- dcrection linlit (0.1 Bqll), whilc dissolvcd homogeneous uraniumlradi urn distribuiiun in 7

the boreholc santptas with most of the in the topographic lowest part of the residcntial radionuclidcs occurring in easily leachable area (Fig. 4d). The avcrage atmospheric air positions, e.g. adsorbed to mineral surfaces temperature, average precipitation, averagc or co-precipitated with iron oxides. The wind speed and concentrations of soil radon cmanatjon coefficients for all the 10 for each measuring period arc presented in samples are presenkd in Table 5. The Table 6. emanation coefficients for the grad Due to coarsc rnatcrial in the ground, fraction of thc dry borehole samples lie in it was impossible to reach thc recommcndcd thc rangc 0.13 to 0.39, with an avcrage depth for soil air mcasurements at 0.7-1 m emanation cocfficicnt for the dominating without cxpensive drilling. Radon gas meta-granitdgrani te material of conccnlrations at shallower depths have bcen approxi inate1 y 0.25. shown to be affected by inctcorological changes and arc in general lowcr than the Soil air radon concentrations radon levels obtaincd from the depth of 0.7-1 Tlic 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 relativc radon gas concentrations in thc August 1997, significantly highcr radon different localities rather than information of concentrations were measured in thc radon concentrations at the depth whcre topographic lowest (north-western) part of equilibrium exists between radon supplied and thc residential area compared to the rcmuved. topographic highest (south-castcrn) part of the area (Fig. 4a). The average air Statistical evaluation of indoor and soil air tcmpcrature during the measuring period radon concentrations was 21.3 "C. In Novcmbcr the same year, By gridding aiid srnouthiiig thc noniialised when the mean air tcnipcrature was 5.8 "C, suinrncr values of soil radon, a paltcrn is thc highest radon levcls wcrc measured in rcvealed with the highest values (normalised the topographic highcst part of the Husc values > avcrage + 1/2 standard deviation) in area (Fig. 4b). Similar results wcre thc topographic lowest part of the Huse area obtained for the measurements carricd out and the lowest values (normalised values < in March 1998 at a mean air temperaturc of avcrage - li2 standard deviation) in the - 4.0 "C (Fig. 4c). The radon levels wcrc topographic highest part of the area (Fig. 5a). particularly high in thc area of highest A middle zone where the summer values arc elevation in this period. In May 1998, the closc to the yearIy incan is also readily mean air tempcramre was 12.1 T, and the identified. The reversed pattern is obtained for highcst radon levels wcre again measured the avcragc winter station-values normalised 8 against the ycarly mcan (Fig. 5b). Bawd on part) summer radon coilcentrations clearly thc gridded maps in Figs. 5a and 5b, thc exceed the winter concentrations. Summer measuring stations can be catcgorised in values more than 20 times higher than winter tlzrcc groups (Figs. 6a: b): Lower values were recorded in this area. topngruphird group (statjons 4, 5, 6, 7, 8, The results from the comparison 9, 16, 17, 18, 21, 23) with summer radon between the soil radon conccntrations and the values well abovc and winter radon values indoor radon concentrations at diffcrent welt helow thc ycarly average; Upper- seasons arc prcscnted as scatter plots in Figs. dopogtuphicd group (stations 2. 12, 14, 15, 9a and 9b. Corrclalion coefficients of 0.75 and 20, 22) with sunmer radon values wcll 0.76 for the sufnmcr and winter measurcmcnts, below and wintcr radon values well abovc respectively, indicate a significant corrclation the yearly averagc; Middle pty(stations bctwcen soil radon levels and indoor radon 1, 3, 10. 11, 13, 19) with summcl- and levels at hffcrcnt tiines of the year. winter values closc to the yearly avcragc. P-values from the Mann-Whitney test arc shown iii Table 7. There is a statistical Discussion signihant difference in normaliscd median radon gas concentration bctwccii all three Thc formation of the ice-marginal dcposit in geographical groups for both the suimiiier Kinsarvik and wintcr measurements, The georadar profilcs indicate that a large part Thc iiormalised ratios froin the of the sediment deposition in Kinsarvik has indoor measurements show the saine occurred in a glaciomarinc environment geographical grouping as thc nonnaljsed associated with an active glacier front. Thc ground values (Figs. 7a, b). Thus. the same high ratc 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 dcvelopmcnt of a steep, prograding slope measurcmcnts (Figs. Xa. b). The result of where resedimentation by gavitationai the Mann-Whjtney test is significant at the processes occur (Lome 1995). The units 5% levcl (Table 7). The dwcllings located present froin a depth of approxirnatcly 4 m and in the Uppcr group (topographic highest, downwards in thc georadar profiles arc thought south-castern part) have cotisiderably to be scdiment gravity-flow dcposits formed in higher winter radon values thaii sulllfncr front of an active glacier termini situated in the values. Ratios of winter to suimnc'r castcm part of the area. Thc high penetration concentrations as high as 161 are found in depth and discontinuous reflectors in the this area. In the dwcllings withthc Lower georadar profilcs indicate that these scdiincnts group (topographic lowest, north-westcm are doininatcd by coarse grain sizc fractions. This interpretation is confirmcd by the groundwater lic in the lower range of normal examination of the boreholc sainples from uranium concentrations in groundwater. the same depth which revealed a doininance Groundwatcrs typically contain 0.1 to 50 pgl1 of gravel and coarser material. In the upper uranium, but concentratims as high as 2000 mctcrs of the georadar profiles, diffractions pgll haw been reported. cvcn in unrnincralized seem to occur more frequently than at arcas (Betcher and others 1988). The uranium gcater depths indicating particularly contents of the river watcr in Kinsarvik do not boulder-rich sediments in the upper part of depart from typical urmiuin levels in surface the deposit. The surface of the deposit is waters (Rogers and Adams 1969). Due lo characterised by numerous large boulders prcferential mobilization of "'U comparcd to and many mounds and deprcssions. Thew "'u, t~ic'YJPu activity ratio is almost factors indicate that the uppcr part of the always found to be highcr than its equilibrium ice-marginal accumulation consists of value in watcr (Osrnond and Cowart 1976). ablation sediments deposited at a timc when '''U?~'U ratios lcss than 1.u in water arc the glacier in the Husc valley was inactive. considered di stiiictly anomalous but have bcen The continuous, parallel reflectors close lo reported e.g. in waters circulating through the ground surfacc displayed in somc of the shallow uranium ore deposits and phosphorite georadar profilcs and the sandytgravely beds (Cowart and Osinond 1977). The low sediments found between the boulders Icvels of thorium recorded in the groundwater below the mariiie limit, indicate rcworking from Kinsarvik are normal in natural waters of the ablation scdimcnts by current- and due to thc low solubility of thorianite and wavc processes. Thc rcworking process has ability of the thorium ion to adsorb onto produced a capping of fincr sediments mineral surfaces (Langmuir and Herman above thc boulder rich, and extreinely 1980). pcrmcable, zone below. The accuiuulation of unsupported radon in tlic groundwaicr is of interest when it The primary radon source wmcs to identifying a possible deep-lying The maximum thickness of the ice-marginal major radon source in tllc area. A fracture dcposit is estimatcd to be approxirnatcly 50 zone occurs in the bedrock below the ccntre m. Thc geochemical analyses of thc part of thc Huse arm, and the possibility of groundwatcr were carried out in order to high amounts of radon issuing from this fault search for a potential source for indoor zone was considcrcd as a potcntial sourcc for radon gas in thc lower part of the sediment indoor radon gas (Maalo 1996). Enhanced accuinulation or thc underlying bcdrock. concentrations of radon in soil air above The results from the uranium analyscs showm kdctures and fault zoncs havc bcen reported that uranium values in the Kinsarvik (Varlcy and Flowcrs 1993). However, '"Rn 10 has a liinited lifespan and can only diffuse transported into the area, local dcrivation of approximatcly 5 cm in water. 5 m in air and 222Rnfroin ""Ra in tlic surrounding solid phase 2 m in mil with a normal moisture content is thereforc considered to bc the probable beforc it has decaycd lo 10 YO of its initial cause for thc depamire froin secular concentration (UNSCEAR 1982). if radon equilibrium between radium and radon in the transported from thc fracture zone and Kinsarvik groundwater. This is in accordancc exhaling to the soil air was the primary with the conclusions of studies of source for indoor radon conccntratioiis of radionuciidcs in groundwater in scvcral other up to 40 000 Bq/m', non-diffusive and rapid arcas (Tanner 1964; Wanty and othcrs 199 1 ). vertical transport of anomalously largc An estimatc of the maxirnum radon aiiiounts of radon would have to takc place. concentration in the soil air in tlic Huse arca Tlic rccorded radon lcvcls in the when thc source is the surrmiiding sediments groundwater arc not particularly high, but can be obtained from formula 1 (Andersson since thc springs and borcl~olesampled arc and othcrs 1983): located more than 100 111 downstream [rum the fault zone. thc cxact levels of radon in Formila I. C,,, = A e 6 I-J the groundwater above tlic fault zones has P been impossible to detemlinc. Hnwever, due to the large thickness of the partly saturated uwconsolidatcd sediments and il~c vcry limited life of the '"Rn isotope, the likclihood of a primary sourcc for indaor radon situated in the bcdrock or the Iowcr Assuming a radon emanation coefficient of paits of the unconsolidatcd sediments is 0.25, a compact density of 2700 kg/m3, a considcrcd highly improbable. The porosity of 25 9'0 and a radium concentration of uniformity of the radon lcvels in the various 60 Bqikg, thc radon conccntmtion jn the soil groundwatcr samples indicates that tlie air can reach the levcl of 122 000 Bqlid when '"'Ra source of the "'Rn in thc groundwatcr thc surrounding sediments are dry, according is a dispersed one rather than a concentrated to fomiula I. one. Since radon is cxtl-emely soluble in ScveraI studies have shown that up water and not easily adsorbed on mineral to a certain moisture contcnt: the radon surfaces, secular equilibrium bctween radon cmanation increases with incrcasing rnoisturc and its parents in water is generally rarely content (Strong and Levins 1982; Strandcn and realised and not to be expccted (Wanty and others 1984; Markkaiieii and ArveIa 1492; Sun Schoen 1991). Givcn that it appcars and Furbish 1995). Markkdnen and Arvela unlikely for the large Rn levels to be (1992) found that the radon cinanation froin Finnish tills were higher for moist samples 11

than for dry samples and the maximum depth of 70 cm and are considered to bc more emanation from the gravel fraction occur at representative for the actual radon 1-2 '50 water content. Strong and Levins concentrations in the soil air of the ice- ( 1982) studied Australian ores and tailings marginal deposit than the mcs incasured by and found that the emanation coefficients ctched track detectors. By comparing the from water-saturated tailings were about radon values estimated by formula I and the four times thosc from absolutely dry measured radon Concentrations in the soil air. it materials. It is thercforc reasonable tu can be concluded that there is no need for a believe that soil gas conccntrations of radon deepcr-Iying source of radon in ordcr to scvcral times higher than 122 000 Bq/m3 explain the origin of the measured ration cm be caused by radon cmanating from thc concentrations in the soil air. The emanation sediments in thc ice-marginal deposit. of radon from the surrounding scdiments in The results from thc largc parts of the 50 m thick vadosc xonc is measurcrncnts nf soil gas radon by etched assumed to be high enough to yidd the radon track dctcctors at approximatcly 20 cm concentrations measured in thc soil air. dcpth only showed maximum concentralions of around 60 000 Bqd. Tcmperaturelpresstrre driven air-flows However, given the depth of tliese Radon concentrations in the soil air are known measurcments, these levcls are not to vary with time due to changes in soil considered lo be accurate reflections of the moisture, soil permeability, wind, air soil gas radon levels. In Novcrriber 1997 temperature and air pressurc (c.g. Aslier- and March 1998, soil radon conccntrations Bolinder and others 1990; Washington and

in all the 23 measuring locations WCTC also Rose 1990; Schuinanii and otlicrs 1992; Sun recorded with a portable radon dctector and Furbish 1995: Valen and othcrs 1999). It (Markus- IO) which measures inshnkrieous is therefore not unusual that largc variations in values of radon in soil air samples by soil radon conccntrations arc rccorded in thc registering the alpha decay of thc radon same measuring point during onc year. In thc daughtcr "'Po. The radon concentrations Huse arca, however, there are not only large measured by the Markus-10 detector are in seasonal changes in radon levels but also general highcr than the ones measured by variations according to a distinct geographical etched track dctcctors, but the wsulls froin pattern. It has bccn shown statistically that both studies show the same geographical therc is a significant difference in normalised distribution of radon conccntrations. median soil (and indoor) radon concentration Maximum values of around 350 000 Bq/m' betwccn an upper (topographic highest), lower were mcasured by the portable radon (topographic lowest) and middle (central) area detector. Thcse values were recorded at a of the ice-marginal deposit for both surnmcr 12 and winter measurements. This These sediments are partly covcrcd by finer geographical grouping can not bc cxplained sediments in 1hc area below the marine limit, by observed differences in the physical but axe cxposed above the inariiie limit and in properties of thc sediments ia the different the riverbanks at the topographic lower end of areas. Thc only factor found to distinguish thc dcposit. Since inost of the dwellings in the one geographical area from another is Huse area have ccllars, the building clcvation abovc sea level. It is therefore construction penetrates the uppcr capping of believed that subterranean air-flows occur finer scdimeots and is exposed to easily in the formation due to elevation movable soil air. Given the six ofthe vadose differences and differences in zone, large quantities of soil air containing temperaturdpressure between soil air and relatively high concciitrations of radon are atmospheric air (Valen and othcrs 1999). availabk to maintain a continuous flow of The seasonal and geographical radon into the dwellings. The amount of soil changes in radon concentration arc thought air that pcnctrates the conslructions is, to bc caused by tlic air-flows conccntrating however, depcndcnt on the building type and the available radon-ladcn soil air towards cons tructton methods. one part of the sedinicnt accumulation Studies of radon Icvels in dwcllings whilc thc other part 1s ventilatcd by located on Swebsh and Finnish eskcrs have atmospheric air. In wintcr the soil air is revealcd similar problcms (Aakerhlom and flowing towards the topographic highest others 1983; Hutri and Makelahen 1993; part of thc deposit sincc thc soil air Ailrela and othcrs 1994). Arvela and others tanpcrature is higher than thc atmospheric (1 994) found that radon conccnirations were temperaturc (Fig. 10). The topographic amplified in thc upper part of an esker lowest area is then ventilated by formation iii winter and in certain dope zones atmospheric air low in radon gas. lii in sutiitiicr. The amplification was found to be summer thc process is reversed. The duc to air flows inside the esker caused by groui-id air is flowing towards the arca of differences in temperaturc between thc soil air Iowest clcvation because the soil air and the outdoor air. Tempcralurdpressuc tcrnperature is lower than the air driven air-flows are also known from karst tetnpcralure. During this scasm the areas whcrc transpoi? of radon-Iaden air in and

clcvaicd area of the sediment accumulation out of CBVCS and fissurcs with changes of is vcntilated by air low in radon gas (Fig. pressurc and temperaturc has been reportcd IO). (Gammage and others 1992; O’Connor and The air-flow is facilitated by the others 1992; Hughes and othcrs 1999). cxtrernely permzablc sediments that undcrlie the whole residential area of Husc. 13

Consequences of the scasonai variations rneasurcments in this area will clearly be in soil and indoor radon lev& underestimations while aimual average values Thc large seasonal changcs in indoor radon based on summer measuremcnts will be concentrations docuinented in the Huse area ovcrestirnations. The rcsufts from thc heavily affcct the estimation of thc average Kinsmik study indicatc that radon annual radon conccntration in tlic measurements in dwellings located on dwellings. Since an integration period of 2- permeable unconsolidated material, whcrc air 3 months is frcquently used for indoor movcment in the ground can cause anomalous radon measurements, correclion factors seasonal variations of indoor radon Icvcls, must bc 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 estimatc of the annual concentrations. A study of radon mean indoor radon concentration. A precise concentrations in 7500 randomly selected calculation of thc annual avcrage radon valuc Norwegian dwellings at different seasons is important for the determination of dwellings rcvcaled that tlic indoor radon in need of rcinediation. Owners of Norwegian concentrations in Norway arc generally dwellings with an average annual radon twicc as high in winter than in summer concentration cxceeding 200 Bq/m3 can apply (Strand 1995). Thus, m order to estimate for a financial contribution of 75 O/o of the mual indoor radon concentrations in mitjgdtion costs below NOK 40 000 (US S Norway, winter measurements are 4500). rnultiplicd 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 concentraihs measured different countries vary from very weak during spring and autumn arc found to be correlation in some areas (Varley and Flowers close to thc average and so arc not 1998) lo good correlation in other arms corrected. (Rcimer and Gundcrsen 1989). The The study of indoor radon lcvels correlation coefficicnts of 0.75 and 0.76 show in Kinsarvik, however, reveals that for a significant correlation between indoor and some dwellings tllc summer concentrations soil radon conccntrations in the Huse area for exceed the winter concentrations. both summcr and winter measurements. Dwellings located in thc topographic lowest Dcviations froin a perfect conelatioil most part (Lower group) of thc Huse area havc likely occur due to inhomogciiitics in thc up to 20 times highcr radon concentrations gcological environment and variations in in summer than in winter. Coiiscqucntly, housing construction techniques in the area. any calculated annual avcragc radon Significant correlations bctween indoor and concentration based on winter soil radon concentrations indicate that soil 14

radon measurements are a useful tool for changes in radon conccntrations havc been the prediction of indoor radon levels. reported from an extcnsive ice-marginal However, llie Iargc seasonal and moraine deposit. gcographicai variations in soil radon Speciai precautions are requircd conccntrations in the Huse arca clearly when uncasuring indoor radon concentrations show how insufficieut sin& soil gas in dwcllings located on building grounds measurcments are if the general geological where temperaturdpressure driven air flows conditions are not considered. Indeed, are likcly to occur. Gcneral correction factors several authors del ineatc that results from for estimating thc annual average indoor radon soil gas measurcments must bc interpreted conccntration are not applicable in such areas, in conjunction with gcological data in order and a corrcct estimate of tlic annual indoor to be useful for cstiniates of indoor radon radon value can only be dcrived from concentrations (Reimer and Gunderscn measurements carricd out both in summer and 1989; Ball and others 1992; Albcring and in winter. vihers 1996; Varley and Flowers 1998). Even though significant correlations The prescnt study supports this view and can be obtaincd between indoor and soil radon illustrates that it is particularly importaut to conccntrations, asscwnents of indoor radon avoid estiinations of indoor radon levels concentrations should not bc based on singie solely based on single soil radon soil gas measurements without a general measurements in arcas where air inovemeiit understanding of the gcology in the arca. This in the ground can cause anomalous seasonal has been proved to be of particular importance variations of soil and indoor radon levels. in thc areas wherc the above mentioned permeable bui [ding grounds occur.

Con c 1us i o n s Acknowledgments - This work was fiindcd

In highly pcrmeable building grounds: by thc Research Council of h’orway {project tempcraturdpressurc driven air ff ows 13537W720). Valuable comments on the I hetwccn areas of different elevation can manuscript were given by Dr. J. M. James and cause momalously high seasonal changes Dr. G. Barnes (University of Sydney, in soil and indoor radon conccntrations. Australia) and Dr. S. Whitllcstone (University High indoor radon lcvels are cnsily of Wollongong, Australia). obtained when building constructions are cxposed to large volumes of the rcadily movable soil air. In this paper, high indoor radon concentrations and large scasonal 15

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(1983) Soil gas radon - a source for indoor radon daughters. Radiat Prot Dosirn 7 Beres M Jr, Haeni FP (1991) Application of (1/4):49-~ ground-pcnctrating radar mcthods in hydrogeologic studies. Ground Water 29375-

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Andersson P, Clavensjs B, Aakerblom C; dcposits. 3 Gcochem Explor #:365-379 (1983) Thc cffect of the ground on tlic coiiccntration of radon and gamma Davis JC (2002) Statistics and data analysis in radiation indoors. Swedish Council for gcology, 3rd cdn. Wiley, Ncw York Building research, Report R9: 1983, pp 1- 442 (In Swedish) Gammage RB, Dudney CS, Wilson DL, Saultz RJ, Baucr BC ( 1992) Subterrancan transport of Arvcla II, Voutilainen A, Honkamma T, radon aud elevated indoor radon in hilly karst Rosenbcrg A (1994) High indoor radon terrains. Atmosph Environ 26a ( 12):2237- variations and thc tliermal bchaviour of 2246 cskers. Health Phys 67 (3):254-260 Holtedahl H (1975) The gcology of thc

Asher-Bolinder S, Owen DE,, Schumam Hardangerfjord, Wcst Noway. Geol Suwey RR (I 990) Pedologic and climatic coiitrols of Noway 323: 1-87 on Rn-222 concentrations in soil gas, Dcnvcr, Colorado. Geophys Rcs Letters Hughes JR, Turk B, Cardwell R, Brooks P, 17, 825-828. Fjshcr G, Whitc M, Fitzgerald F, Wilson D, Bryant JO Jr (1999) Karst geology. radon fluctuations, and implicatiotis for mcasureincnt 16 and mitigation. Proc Int Conf on Radon in MaaIii S (1996) Gcoiogisk kartcring - thc Living Environment, 19-23 April 1999, radonprosj ckt& University of Rergen, Athens, Grcccc, pp 173-181 Norway (Unpublished report)

Hutri KL, Makebincn I (1993) Indoor Markkanen M, hela H (1992) Radon radon in houses built on gravel and sand emanation from soils. Radiat Prot Dosim 45 deposits in southern Finland. Bull Gcol (1 /4):26?-272 SOU65:49-58 NGU-Lab (1997) NGU-SD 3 11 ICP-MS

Tvanovich M,Hannnn RS (1992) Uranium andyser 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, gruppc 3: Vaimanal y se, Tvanovich M, Harmon RS (eds), Clarcndon Trondheim: Section for laboratories, Prcss, Oxford Norwegian Geological Survcy

Jcnner GA, Longerich HP, Jackson SE, O'Connor Pj, Gsllaghcr V, Van den Boom G, Frycr B.I (1990) ICP-MS - a powerful tool Hagetzdarf J, Muller R, Madden JS, Duffy JT, for high-precision trace clement analysis in McLaughlin JF, Grimley S, McAulay IR, earth scicnces: Evidciicc from analysis of Marsh D (1992) Mapping of Ru-222 and Hc4 selected U.S.G.S. referencc samples. Chein in soil gas over a karstic lirnestonc-granite Geol 83:133- 148 boundary: Correlation uf high indoor Rn-222 with zones of cnhanced permeability. Radiat Jensen CL (1997) Kartlegging og tiltak mot Prot Dosim 45 (1/4):215-218 radon i Ulicnsvang herad 1996-97. Projcct report, Clllcnsvang herad, pp 1-87 Osmond JK. Cowartrt JB ( 1976) Tlic theory and uses of natural uranium isotopic variations in Langmuir D, Herman JS (1980) Thc hydrology. Atomic Energy Revicw I4:62 1- mobility of tlioriuin in natural waters at low 679 termpcralure s. G cochjm Coxnochiin Acta 44: 1 753- 1766 Peake RT (1988) Radon and geology in the Unitcd States. Radiat Pro1 Dosim 24 Lomc 1 (1995) Sedimentary facies and (1 14):173-1 78 depositi mal irchitecturc of i ce-contact glac iornari nc systems. Scdimentary Gcol Rciincr GM, Gundcrsen LCS (1989) A direct 98313-43 comefation among indoor Rn, soil gas Rn and 17

geology in the Rcading Prong near on radon exhalation. Radiat Prot Dosim 7 Boycrtown, Pennsylvania. Health Phys 57 ( 1/41; 5 5-58 ( 1): 155-160 Strong KP, Levins DM (1982) Effcct of Rogcrs JJW, Adams JAS ( 1969) Uranium. moisture content on radon emanation from In: Handbook of Geochemistry. WedepohI uranium ore and tailings. Health Phys 42 KH (ed) Springer- Verlag, Berlin (1):27-32

Rose AW, Hutter AR, Washington JW Sun H, Furbish DJ (1995) Moisture content (I 990) 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 radon222 in ground water near Great Salt concentrations. Special Paper Gcol SOCof Lake, Utah. In. Adams 3AS aid Lowder WM Am 27 1:45-72 (cds) The natural radiation cnvironicnt, Univ of Chicago Prcss, 253-276 Sigmond EM0 (1998) Bcdrock geology map, Odda, M 1:250 000. Geol Survcy of Tell 1, 3ensryd I, Rylandcr t, Jiinsson G, Norway Daniel E (1994) Geochemistry and grouiid permeability as determinants of indoor radon Strand T (1 995) Time variation of indoor concentrations in southernmost Sweden. radon concentration in ~ypicdNorwegian Applied Geochem 9:647-65 5 homes. Proc Int Couf NE-VI 5-9 June 1995, Montreal, Quebcc, Canada WSCEAR (1982) Ionizing radiation: Sources and biological effects. Annex D. United Strand T and Lind 3 (I 992) Radon in tap Nations Scientific Committee on the Effcct of water from drilled wells in Norway. Proc Atomic Radiation, Report to the Gcneral 1992 Tnt Symp on Radon and radon Assembly, with anncxes. United Nations reduction techiology, Sept 22-25 1492, publication, New Y ork Minneapolis, Minnesota, USA Valen V, Soldal 0, Strand T, Hcnriksen H Stranden E, Kolstad AK, Lind B (1984) (1997) Anrikning og transport av radongass i The influcnce of inoisrure and tempcrature losinasser. Project report, InterConsuft Group ASA, Norway, pp 1-45 18

Valcn V, SoldaI 0,Cunter B, Henriksen H, Jenscn CL, tauritzen 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 depcndent on air temperature. Extended abstracts, AARST-2000 ht Radon Syinp. Milwukcc, Wisconsin, USA.

Varley NR, Flowers AC; (1 993) Radon in soil gas and its relationship with major faults of SW England. Environmenl Geochcm and Health 15 {2/3): 145-15 I

Varley NR, Flowers AG (1998) Indoor radon prediction froin soil gas measurcmcnts. Health Phys 74 (6):7 14-7 18

Wanty RB, Johnson SL, Briggs PH (1991) Radon-222 and its parent radonuclidcs in groundwater hni two study arcas in New Jersey and MaiyIand, USA. Applied Geochem 6: 305-3 18

Wanty RB, Schocn R (1991) A review of thc chemical processes affccting the mobility of radionuclides in natural waters, with applications. In. Ciundersen LCS and Wanty RB (eds) Field studies of radon in rocks, soils, and water, US. GcoI Survey BullNo I971 183-193

Washington JW, Rose AW (1 990) Rcgjonal and temporal relations of radon in soil gas to soil tcmpcrature arid soil moistui-c. Geophys Research Lctters 1 7329-832 19

Fig. 1. The Location qf' Kinsurvik in the ttlcsiern purf qf' Nouwuy and a topogwphicul map showing Ehe residential area ?!f Huse and the location springs und korehdes 20

35 - 41 000 Summer 1996 (June-August) n Autumn (Octok) 30 - -0 1996 Winter 1997 (January-February)

25 -

20 -

1s -

10 -

5-

0-199 200-399 400-799 800-1599 1600-3199 >3200 Rrr-concentration Bq/m3 21

Borehole A

0 ++ 00 + c+ a + a* 0 00 n n If a

A

...Y. ... gn 00 0 22 11Itl[I IIIIII

Concentration (Bqlkg) Leachable ?4 wormnstltlPents $t&amofiy El bleta-grande E!Boulder 0 Uranium a Meb-daate a Cobbb Thonum Phyllite Gravel 0 Radium CI] No sample ..Q. Watertable 22

Borehole B

0 0 I 2 .. , ...... - , .. .. , -, ' 4 ... . -. ,-.--. ., h ,I ... .. ,...., 8 ....,. ..-. IO r.i. P-. >. ...I. E I? ... v ... 14 0 , .- e,...... 0 Ih .... '. D ...... - .. 18 ...- .. . ..,...... - 20 ....., .. ...- ...... , ..-, 21 *. 24 m 'ip i-p rg e.. ,-.,., 26 ..... 28 +I 0 +,&. /.i.. ,.j,A ...I ...... H,...... 0 ._...... -:..-, :...... 30 :...... a.0...... Y... 1111111 Illlll 20 40 60 80 100 120140 I 10 20 30 40 SO 60 Concentration (Bqlkg)

Uranium hmum 0 Radtum 23

Fig. 4 a-d. Distribution ofrudon concentrations in the soil air in the Huse urea in a) August 1997, b) November IYY7+ c) Murch 1998, d) Muy 1998 24

(37155,284655) (37830.2648551

Measuring stations for soit gas Rn Boreholes addedvdues d nmalised Summer rneawnmcnts 0-3.0 - -2.5 Std. Dev. 0-2.5 - -2.0 SW. Dw. I -2.0 - -1.5 SW. Dw. -3.5 - -1 .o sw. Dw.

0.0 - 0.5 Std. Dev. 0.5 - 1.Q Std. OW. t.O-1.5Std.Dev. =1.5 - 2.0 ad. Dtv. 1M- 0 100 200 Meters

(37155,268355)

(37155.284855) (37830,263856)

# Measuring swims for 5ou gas Rn

added values of nmdissd winter measurements I-2.0 - -1.5 Sad. Dw. b-1.5 - -1 .O SM. Dw. .. . I Ij1.0 - -0.5 Std. Dev. 0.5-0.0sw.Dev. Wean 1.0 - 0.5 Std. DW . 0.5-1.0Std.D~. 1 .O - 1.5 Std. Dw. 1.5 - 2.0 ad. Dw. I2.0 - 2.5 Std. Dw. L2.5 - 3.0 Sld. Dev.

I

W'155.263856) (37830.263856)

Fig. 5 Gridded data of a) summer soil radon concentrations normalised against yearIy 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. mw 25

0

D Median 25%-75% 1Non-Outlier Range 0 Outliers

LOWER MIDDLE UPPER Location

n Median 25%-75% 1Non-Outtier Range 0 0 Outliers

Fig. 6. Box plots jbr a) the categorised summer soil radon coneenbutions norrnalisecd aguinst the yearly meun and h) the categorised winler soil radon concentrations normalised against the yearly mean 26

mdded values of normakd indoor wmmw meaSUrClRents -2.0 - -1.5 Std. Dw. ,1.5 - -1 .o std. Dw.

1.0 - 1.5 std. DeY. I1.5 - 2.8 SM. Dw. , !.O - 2.5 Std. OW. 2.5 - 3.0 Std. OW.

(%830,284655) lii p-/ Measuring stations for indoor air Rn @ Boreholes Gridded values of normalised lndoor winter measurements -2.0 - -1.5 Std. Dw. -1.5 - -1.0 Std. Dev. II -1.0 -4.5Std. D~v. -0.5 - 0.0 Std. Dw. I Mean I 0.0 - 0.5 Std. DEW. 0.5- 1.0 Std. Dw. 1.0- 1.5 Std. Dw. 1.5 - 2.0 Std. Dw. 20-2.5Std. Dw. 25 - 3.0 Std. Dw. wo 0 mt&srs c100

(37155,263856) (37830.163856)

Fig, 7. Gridded ratios of (a) indoor summer concentrations to yearly averuge indoor concentrations, and @) indoor winfer concentmions to II year& averuge indoor concentrcrtiom. Locutions of dwellings ure marked wiih dots+ Gridding method: ID W II

I 27

0 8 0

I tl Median 025%-75% Non-Outlier Range LOWER MIDDLE UPPER 1 o Outliers Location

+i0Ot Median 025%-75% . .. Non-Outlier Range LOWER MIDDLE UPPER I o Outliers Location

Fig. 8. Boxplots,for u) ihe cafegorid ratios of indoor summer radon concentrations to the yearly mean and b) the ratios qf indoor winter radon concentrations 10 lhe yearly meun 28

a) pq

1 Soilgas Rn (Bqlm3)

10000- ' ' ' , .

b)

8000 - I I

6000 -

0 0 20000 40000 60000 Soil-gas Rn (Bqlm3)

Fig. 9. Plots of soil radon concentrutions ugainsf indoor radon concenirations for summer and winter measurements: a) uverage ojsoil radon Myand August vs. indoor mdon June-August, b) soil radon March vs. indo or r ado it January- Fe b ruury.

I

I 29

Fig IO. Illustration qf the temperature driven seasonal transport ofradon gas in the Huse area. Wurm air is Jighfer than cold air. In the wintertime the temperature of the soil air is higher thun the atmospheric temperuture, and so soil air,fhws toward the elevutedpart qf the deposit, During the warm semon the ground air jlows toward the arm of lowest elevation because the soil air temperuture is lower thun the air temperature (valeen and others 1999). 30

I

Table 1. Description of laboratory analyses of bedrock and sediment samples Material Treatment 1 Analysed for Method I Estimated accuracy Bedrock Untreated U and Th Inductively coupled plasma mass spectrometry 4 3-7 ?k samples (ICP-MS) (Jenner and others 1990)

1. ICP-MS (Jenncr and others 1990) =t3-7 Ya 2. Gamma spectroscopy (Adams and Gaspirini + 5-15 % Borehule 1970) samples 3. Rn exhalation rate 3. Scintillation flask method f 20-25 % (2-3mm) b.HC1md ILUandTh 1 ICP-MS (Jenner and others 1990) + 3-7 Yo Na2S03 2. =“a 2. Gamma spectroscopy (Adams and Gaspirini * 5-15 % 1970) 31

Sample Treatment Analysed fur Method Estimated volume accuraty

100 ml Filtcrcd through 0.45 pm filter and U and Th ICP-MS (NCIJ-Lab 1997) acidified to pH4 with Supripre HK03 25 1 Filtered through 0.45 pin filter and Isotopic composition Alpha rpectromctry acidificd tu pA

10 rnl Water sample injected into 20-ml. vials Kn I.iq uid Scinti llatiun f 20 "/o containing 10 rnl of scintillation liquid (Strand and Liiid 1992) 32

Rock type Number U (ppm) Range 0 Th Range 0 ThlU of mean (pp@ (PPm) (PPm) samples mean Mcta-granite 1 5 5.8 3.3 - 8.8 2 79 16.X 2.9 Mck-granite 2 3 2.0 2.0 - 2.5 0.24 8.6 3.7 Mcta-granite 3 3 4.1 3.7 - 4.6 0.49 9.1 2.3 Granite 1 4 22.9 10.7 - 31.6 10.88 27.6 27.4 - 37.7 1.2 Ciranire 2 3 3.7 3.4- 4.4 0.61 35.9 29.1 - 45.4 9.7 Pcgmarite 3 6.8 4.8 - 7.2 2.73 9.5 1.4 Meta-dacitc 3 1.4 1.1 - 1.7 0.28 4.3 3 .O Phyllitc 3 2.8 2.7 - 4.1 1.15 11.Q 3.9 33

Table 4a. Radio nuclide contents in groundwater and surface water from Kinsarvik

Sample u (Pm Ra (Bq/l) Rn (Bqll)

Spring no 1 0.44 +i- 0.044 .= 0.005 < 0.1 Bqil 276 .-I- s5

Spring no 2 0.5 1 +i- 0.05 1 < 0.005 0.1 Bqil 310 :(- 62 Spring no 4 0.38 :-i- 0.038 0.005 0.1 Bq/l 364 +I- 73 Spring no 5 0.3 I .-i- 0.03 I < 0.005 < 0.1 Hqll 269 +I- 54 Borcholc A 0.63 ii- 0.063 0.005 < 0.1 Bq/l 240 +I- 48 River I 0.57 +i- 0.057 0.016 +i-0.00 1 6 0.1 Bq/l r' 10 River 11 1 .I2 +/- 0.112 0.028 +I- 0.0028 0.1 Bqll < 10

Sample u (PEW Iq4uI 231tl '"Th / "'U

Spring no 1 0.27 +i- 0.007 1.21 +i- 0.038 0.15 -/- 0.015 Spring no 2 0. I9 +i-0.005 1 19 +i- 0.039 0.06 Ti- 0.013 Spring no 4 0.19 +!- 0.006 2.40 +/- 0.090 0.04 +I-0.007

Table 4c. Radon concentrations in woundwater samnled at different seasons Sample Rn (Bq/l) Rn (BqN Rn (Bq/l) Sampled 20.08.97 Sampled 06.1 1.97 Sampled 06.03.98

Spring 110 I 200 +;- 40 258 +!- 52 312+i-62 333 +I- 67 Spring no 2 370 4-74 276 4-S5 365 +i- 73 387 :-I- 71 Spring no 3 235 +/- 47 276 -ti-55 326 +I- 65 Spring no 4 472 +i- 94 467 +:- 93 Spring no 5 - 367 +/- 73 330 +!- 66 34

Table 5. Radium Ra Emanation Borehole B: Depth Ra Emanation below surface (m) (Bq/kg) coefficient below surface (m) (Bq/kg) coefficient

66 Ai- 3.96 0.22 0- I 31 I:- 2.48 0.33 13 - 14 63 +i-3.I5 0.17 14- 15 18 +i- 2.70 0.39 14- 15 67 3';- 4.02 0.17 23 - 24 84 -1i- 3.36 0.24 17- 1X 47 +i- 2.35 0. I4 27 - 28 74 +/- 3.70 0.2 1 20 - 21 59 +!- 2.95 0.22 29 - 30 A5 +/- 3.25 0.13 35

Table 6. Average air temperature, average precipitation, average wind speed and

Period Ayerage air Average Average Average temperature precipitation wind speed soil-gas Rn ("C) mm (mw (Bq/m3) August 1997 2 I .3 0 0.#5 1700 Novcinber 1997 6.8 0 0.60 4200 March 1998 -4.0 1.0 (snow) 0.55 10000 May 1998 12.1 1.o 1.16 14000 36

Normalised summer soil radon measurements Normalised winter soil radon measurements I UPPER Ix 1 UPPER

I Normalised summer indoor radon measurements 1 Norrnaliscd winter indoor radon measurements1 UPPER X UPPER X MIDDLE X

Sundal AV & Strand T Indoor gamma radiation and radon concentrations in a Norwegian carbonatite area.

Submitted to the Journal of Environmental Radioactivity, 2003 I 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 JoumaL qf Emironmen&d Kadioactiviiy.

Results of indoor gamma radiation and radon measurements in 95 wooden dwellings located in a Norwegian thorium-iich 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 Bqkg in the carbonatites were found to cause elevated indoor radon levels and the hghest indoor gamma dose rates ever reported from wooden houses in Norway. An average indoor gamma dose rate of 200 nGyh and a maximum of 620 nGylh were obtained for the group of dwellings located dirdy 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.

Aud Vmh Sr4ndcr1, Drpavbneiit of Earth Science, University qf Rtrgen, AUegatu 41. N-5007 Bergen, Norway Terjr S&md Norwegian Kadicition Profertiori Authorities, P.0. Box 55, N-1332 BstPrd.&.p,1Vrwway

Introduction emitted from potassium-40 and members of the uranium and thorium decay chains in geological strata and building materials. The Natural1 y occurring radi onudides are rcspotisihle for the major contribution to the total effective dose from naturally occurring total effective dose of ionizing radiation radiation received by the Norwegian 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 shorz-lived decay products accounts sources is generated by internal exposure from radioelements in diet and iihaled for around 1.7 rnSv of the total effective dose, radon and its progenies as well as external while the contributions from radioelements in cosmic rays and gamma radiation from exposure from cnsniic rays and gamma rays diet, 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 cxbonatites (carbonate rocks of volcanic mSv per year, respectively. origin) and was first described by Brogger in

In the 1980s. ;I study of 19 1921. Stules of the rare rock association in dwellings located within the Fen complex the area have played an important role in the of carbonatites and alkahe silicate rocks understanding of carbonatite-complex geology revealed high levels of radon and external (Brogger, 1921; Sxther, 1957; Barth and gamma radiation indoors (Stranden, 1985: Ramberg, 1966). The Fen coniplex is the only Stranden and Strand, 3986) Analysis of occurrence of carbonaiites in Norway. but the rarc rock types in Ihe area reveaIed several other cxbonatite areas are known in enhanced concentrations oi thorium-332 Fennoscandia (Eckerrnann, 1948; Paarm, and radium-226. During the last decades. 1970: Puustinen, I 97 I } the number of dwellings in the Fen area has Thc rock types which occupy the nearly been doubled, and attention has largest fraction of the surface area of the Fen iilcreasirigly been drawn to thc levels of central complex are sovite (calcite carbonatice), radiation received hy the local residents due muhaugite (dolomite carbonatite), rodherg to natural sources. The present paper (hematite-calcite-carbonatite) and fenite discusses the result of a recent study uf (alkal i-merasomatised granitic gneiss) (Fig. indoor sarnma 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 aIpha track detectors, respectively. A complex (Fig. I b). The rixlberg was mined for systematic analysis of the indoor data with iron from 1455 until 1927, and the sovite was regard to geological factors is presented. mined for niobium between 1453 and 1965. The many pit heads and piles of tailings found Study area in the rodberg area arc evidences of the The Fen complex is located in the extensive mining activity at Fen. Studies haw Precambrian qneisscs of Telemark, shown that the Fen carbonatites are strongly approximately 120 km southwest of Oslo mriched in rare earth minerals (REE), but no (Fig. la). The centrd circular intrusive has exploilation of these minerals has taken phce a diameter of about 2 km and represents a so far (Mitchell and Brunfelt. 1975; Andersen, cross-section of the feeder pipc of a volcano 1986). Today, approximately 350 dwellings which WLS active nearly 600 million years are locaced within the Fen central complex. azo (Szther, 1957; Barth and Ramberg, In the beginning of the 1980~ 1966). Around the central complex studies of natural radioactivity were carrid out numerous satellite intrusions occur. in the Fen area (Stranden, 1984; Stranden, 3

1985; Stranden and Strand, 19%; Dahlgren, building grounds. The radon measurements 1983). Elevated ievels 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 radium226 than normal small piece of polycarbonate film endosed in a were also measured in some of the rock smil plastic canister. Each householder types (Stranden, 1984). A study of radon- received two radon detectors which were 222 daughters and thoron daughters indoors exposed €or 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 wits

1984). Measurements of natural gamma cciven as the average value of the two radon radiation indoors carried out by a Studsvik measurements. portable plastic scintillator. indicated higher average external dose rates in the Fen Gamma radiation indoors houses cornpitred 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 (Sollj 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 wack detector. The thmno1uminescent dosemeters consist of two Survey methodology CaFZ:Dy ribbons (3.2 x 3.2 x 0.9 mm3) enclosed in a specially designed polyethylene

Indam radon badge (Wohni, 1993). The ribbons were Measurements of indoor radon annealed in an oven (400°C for 1 h and 15 inin concentrations were perfoimed in 92 and 100°C for 2 h and 30 Inin), and the zero detached dweIlings in the Fen area and 3 readings of the iibbons were checked. Thc dweIlings 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 enabble comparisons of results for determined to 2.5 pSv. The individual buildings founded OR various types of sensitivity of each ribbon was taken into 4

account when calculating the doses. A informtion on building characteristics, cosmic background component aeration habits of the occupants and water corresponding to 30 nGyh was subtracted supply. The quesiionnaires were issued and from the original data. returned by mail together with the thermoluminescent doseineters and the dpha Gamma spectrometry track detectors. The questionnaires provided Ganum-ray spectrometric measurements information on: Category of dwelling, age of were pelformed on rock samples from thc dwelling, floor level of room in which Fen area in order to quantify thc activity measurements were taken, outer wall material, concentrations of the natural radionuclides foundation wall material, type of basement, Ra-236. Th-232 and K4O. Thirty five rock ventilation system, aeration habits and source samples of the rijdberg, siivile, imhaugite 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 (redberg). 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 cquilibriuni between Ra-226 and its daughters. Thc mcasurernents were carried Results and discussion out with a 90-cini Ge(Li) deteclor and a

Canberra Model 8 100 multichannel Radionuclide concentrations in rock malyser. The equipment was calihrated material against standard samples with hiown Activity concentrations of thorium-232, concentrations of all the radionuclides of radium-226 and potassium40 in rock material interest. The Ra-226 and Th-232 contents from the Fen central complex and adjaccnt were computed from Bi-214 (609 keV) and area are presented in Table I. The highest Ac-228 (91 1 keV) activities, respectively, thorium-3-32 levels were measured in rodberg assuming secular equdibrium among the and waste rock from the iron mine (average radionuclides the series. of levels of 3100 and 4500 Bqlkg, respectively). Precambrian gneiss had the lowest mean Data on house comtruction, ventilation thorium level of 66 Bqkg. The average habits and geology radium-226 concentrations were found to Questionnaires completed by each of the range from 20 to 120 Bqkg. The highest mean participating households provided radium-226 value and the maximum value of 5

300 Bqkg were measured in rauhaugite. piles of waste rock are found in the riidberg The average potassium-40 levels ranged area. So far, no action has been taken to secure from 30 Bqkg (sovile) to I060 I3qk.g the waste material. A Iirnited 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 scintjlhtor) enhanced concentrations of natural gave ambient dose equivalent rates in the range radioactivity compared to normal rock 3 - 5 PSvlh. types. The thorium levels in Nordic rock types typically range from 0.5 to 350 Bqkg Indoor radon (Nordic, 2000). The Fen carbonatites have The distribution of indoor iadon concentr9t’ions the highest levels of thorium recorded in measured in the 95 dwellings is presented in

Noiwegian bedrock. The carhonatites Fig. 2. The results show it log normal found to confain the highest concentrations distribution with an arithmetic mean of 204

of thorium (rodkrg and rauhaugite) also Bqlrn’ and ;I 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 1350 Bq/rn3 Thirtyseven 5% of 100 Bqkg are, however, not uncommon in the dwellings included in the study were found rock types like granites, pegmattites and to have radon concentrations above 200 Bq/m3, black shales. Only low to normal while 11 % of the selected housings had radon conccntrations of radium-226 were values in excess of 400 Bqh3 The radon measured in the siivite (Table 1). An concentrations presented in Fig. 2 are corrected average radium-226 concentration of 3 10 to average annual radon concentrations by Bqkg was, however, reported from 6 siivite assuming that the concentration in thc heating samples measured in a previous study. season is twice the level in the summer indicadng somewhat higher Ievels 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 potassium40 exposed carbonatites (Table 2). The arithmetic concentrations measured in the rock types mcan values of indoor radon concentdons in of the Fen area Iie within the normal range dwellings built directIy on bedrock ranged of potassium40 concenmations in Nordic from 340 Bq/m3 in the rodberg area to 69 bedrock (Nordic, 2O00). 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 krn? Bq/rn3 and 62 Bqh?, respectively. No is present by the lake Norsjo, and many dwelling located on Precambrian gneiss had 4 indoor radon values excceding 200 Bqlrn’, material on indoor radon levels. A geometric while radon values above 200 Bq/m3 and mean radon level of 183 Bq/m3 was reported 400 3qlrn’ were measured in 64 o/o 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 Iow readings for indoor and the first floor were 115 Bq/m3 and 33 radon concentrations (Table 2). Arithmetic Bq/rn’, respectively. The Student’s t-test and geometric mean values of 63 Bqh’ yielded a significant difference between indoor and 48 Bq/m3, respectively, were reported radon values for all tloor Ievels (p < 0,OOOL for fox this group of dwellings. The difference basement versus ground floor and basement between indoor radon values in dwellings verws first floor. p = 0.02 for ground floor located on exposed bedrock and dwellings versus first floor). A geometric inem radon located on silt and clay deposits is concentration of 69 Bq/m’ was obtained for the ilIustrated 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 concrcte had 3 located on silt/clay covered carbonate rocks mean radon level of 159 By/m’ 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 siltlclay covered rauhaugite and The indoor radon values measured in exposed sfivitc versus siltlclay covered the present investigation are generally higher sbvite, p = 0.0090 for exposed rodberg than the values registered for the country as a versus siltlclay covered rodberg). whole. In 2000-2001, the Norwegian Like most Norwegian dwellings Radiation Protection Authority (NRPA) carried in rural areas, the surveyed dwellings in the out indour radon measurements in nearIy 29 Fen area are detached houses with outer 000 randomly selected dwellings in 114 out of walls made of wooden materials. 411 435 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 Norwcgian housing stock concentrations have not been undertaken in was calculated to 83 Bqlrn’ (Strand et a1., the surveyed dwellings. Comparisons of 2001). It was estimated that 9 9; and 3 % of indoor radon concentrations with building Noiwegian dwellings have annual average

charactcristics and ventilation habits 01-11y radon concentrations exceeding 200 and 400 revealed a statistidly significant effect of Bqlm’, respcctively. The results from thc 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 Bqlm’ in the Fen the carbonatites are found to be normal 10 high area are several times higher than for the compared to typical radium-2% levels in other whole counlry. The maximum levels Nordic rock types (Nordic, 2000). IC 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 fmn the rauhaugite, rriagriitude 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 suiface render the ai,,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 ail- kerma from terrestrial gamma underlying bedrock. Buildmg materials radiation measured in the 95 dwellings is manufactured in Noiway have been presented in Fig. 4. A cosmic ray contribution rcported to contain low levels of of 30 nGylh has been subtracted, so that the radioactivity (Stranden, 1979), and the variation in the terrestrial gamma radiation is observed discrepancy bet ween indoor radon shown. The distribution approximates to log- levels in dwelling with foundation walls norinal and the arithmetic and geometric mean made of light weight concrete and values are 98 nGylh and 82 nGylh, dwellings with normal concrctc in the Fen respectively (Table 3j. The dose rates for the area is more likely attributable to the higher whole group of dwellings mnged from 35 permeability of the former material, nGyh to 420 nGy/h. facilitating transport or radon 10 Ihc The highest exteimal gamma dose dwellings, rather than enhanced levels of rates were measured in dwellings built directly radium226 in this material. Since the on the carbonatites, the levels being concentrations of natural radioactive particularly high in the riidberg and the

SUhStdnCeS always are low in surface rauhaugite areas (Table 3). The average waters, the major source of indoor radon external dose rate measurd in the rodberg area concentrations in the suiiieyed buildings is was 200 nGy/h, while the geometric mean assumed to be thc building ground. obtained Cor the same group of dwellings wa 157 nGy/h. The corresponding figures for the 8

rauhaugite area were 1 IO Bqd and 99 found to have a significant association with the 8q/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 jn 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, wide the geometric means fur directly on fcnite and Precambrian gneiss measurements carried out in the ground floor were close to 55 nGyh The maximum and first floor wcrc 98 nGy/h and 77 nGyAi, value of 620 nGyfh was registered in the respectively. A significant difference between rGdherg area. external dose rates for a11 floor levels was The dose rates measured in found (p < 0.0001 for basement versus ground dwellings locaied on silt and clay deposits floor and basement versus firsst floor, p = 0.02 were in the same rmgc 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 mcan value of 55 parts of the Fell area are considerably higher nGyIh and ;I geometric mean value of 53 thm the values reported for the countiy as a nGyh were reported for external dose rates whole. Storruste et nl. (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 repoized a mean value of 95 nGyh for all dwellings located nn silt and clay deposits houses and 70 nGyh for wooden houses. thc 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 gavc a value of 79 nCy/h the silt/clay covered areas (p < 0.0001 for (Stranden, 1977). The mean gamma dose ratc exposed rauhaugite versus siltlclay covered in the group of dwellings founded on the most rauhaugm, p = 0.0005 for exposed rodberg radioactive carbonate rock in the Fen area is 3- versus siltMay covered rodberg and 0.0226 4 times higher than the nationa1 average, while for exposed siivite versus siltlclay covered the maximum value of 620 nGyh is siivitej. 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 oil Euivpean countries (e.g. Rannou et al., 1985; gamma dosc rates indoors resulting from Mj iines , 1986: Arvela. 1995). building characteristics. The only factor 9

A correlation between indoor conclusion that the main contribution lo indoor gamma dose rates and geology in the Fen gamma radiation in the Fen dwellings arises area is evident. High indoor gamma from the thoiium-senes radionuclides in the radiation environment was registered in the carbonatites. Since the potassium40 content areas of exposed carbonatites containing of both bedrock and building material is low. elevated levels of radionuclides, while the Ihc contribution to the indoor gamma dose other areah 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 inernhers of the thorium- and uranium-series. the group of dwellings founded on thoiium- 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 sheld reducing the exposure to study of gamma radiation performed in 19 local residents from terrestrial gamma wooden dwellings within the Fen central radialion. The areas of high indoor gamma complex (Stmnden and Strand, 1986). The rates accord well with the reponed areas of rriaxiniuiii bels reported for the two studies high outdoor gamnla radiation (DahIgren, are, howevcr, in the same range (620 nGylh for 1983), The lack of' correlation between the present study: 560 nGylh for the previous indoor gamma radiation and building study). The discrepancy in average dose rates characteristics is most likely due to the car1 therefore be attributed to different critcria extensive use of wooden building material adopted for the selection of the surveyed and dominating contribution of indoor buildmgs. The maximum levcl 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 gmma dose rates and radon dwellings in Norway. Tndoor gamma dose concentrations indoors for thc surveyed rales as high as 950 nGyh 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 part of the gamnia dose rates were registered in Fen area (Stranden and Strand, 1986). dwellings containing indoor radon levels no higher than 100 Bq/rn3. supporting the 10

Dosimetry 7le 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/Ciy 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 rae 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, thc average annual effective dose for Iocal rcsidents 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 .O iSv/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 ConcIusions thorium in the iron mine waste rock give rise to ambient dose equivalent rates of 3-5 pSv/h.

The results from a study ol indoor gaimna Remedial actions to reduce the gamma radiation levels and radon concentrations in radiation to normal levels of < 0.2 pSvh in the a carbonatite area usiiig thermoluminescent affected areas are currently dmussed. 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 thc data with regard io geological factors. from the underlying bedrock, and the covering The results show that enhanced levels of or 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, all average indoor gamma dose 1353701730). rate of 200 nGyh was reported. the range being 37 - 620 nGy/h. Using normal conversion faclors these values correspond to a mean effective dose equivalent of 1.0 niSvlyear and a range of 0.2 - 3.0 mSvlyear. 11

References Jensen, C.L. (1997). Kartlegging og tiltak mot radon i Ullensvang herad 1996-97. Report, Ullensvang herad, 87 pp. Anderson, T. ( 1986). Compositional variation of some rare earth minerals from Mitchell, R.H., Brunfelt, A.O. (1975). Rare the Fen complex (Telemrk, SE Norway): implications for the mobility of rare earths Earth Element Geochemistry of the Fen alkaline complex, Norway. Contributions to in a casbonatite system. Mineralogical Magazine, 50,503-509. Mineralogy and Petrology, 52, 247-259.

L. (1986). Gamma radiation in Awela! H., Hyvonen, H.. Lernmelii, H. and Mjones, Swedish dwellings. Radiation Protection Castren, 0. ( 19951. Indoor and outdoor Dosimetry, 15, (2). 131-140. gamma radiation in Finland. Radiation

Protection Dosimetry, 59 (-1 )? 25-32. Nordic (2000). Naluraly occuiTing

Barth, T.F.W., Ramberg. I.B. (1966). The radioactivity in the Nordic countrics - recommendations. The Radiation Protection Fen circular complex. Tn: 0.F.Tuttle. J .Gittins, Carbonatites. fpp. 225-2571, Authorities in Denmark, Finland, Iceland, Norway and Sweden 2000,80 pp. New York: Tnterscience.

Paarma, (1970). A new carbonatite Brogger. W.C. (1921). Die Eruptivgesteine H. find of in North Finland, the Sokli plug in Savukoski. des Kristidagebietes IV. Das Fengebiet In Telemark, Norwegen. Shifter, Det Norske Lithos, 3, 129-133. videnskaps-akademi i Oslo I, Mat.-namrv. Puustinen, K. (1971). Geology of the klasse, 9,408 pp. Siilinjikvi carbonatite complex, Ezqtem Fin 1and . Bulletin de la Commission Dahlgren, S. (1983). Naturlig radioaktivitet i berggumen. Gammastrll ingskart, gCoIogique de Fhlande, 39,43 pp.

Fensfeltet, Telemark. M. 1 :10 000. Prosjekt tenlakart , Telemark. Ramberg, LB., Barth, T.F.W. (1966). Fylkeskartkontoret i Tekmark. Eocambrian volcanism in southern Norway. Norsk Geologisk tidsskrift, 46, 219-236.

Eckeerrnann, H.V (1948). The alkaline Rannou, A., Madelmont, C., Renouard. H. district of Alno island. Sveriges (1985). Survey of natural radiation in France. Geoiogiska Undersokning, Ser. Ca, 34, 9- The Science of the Total Environmcnt, 45, 36. 467474. 12

Solli, H.M., Andersen, Aa., Stranden, E., Siranden, E. ( 1984). Thoron (?Rn) dmghtcr Langaard, S. (1985). Cancer incidence to radon ('"Rn) daughter ratios in thorium rich among workers exposed to radon and areas. Hedth Physics. 47 (5>,784 - 785. thoron daughters at a niobium mine. Scandinavian Journal of Work, Stranden, E. ( 1985). The rdiologcal impact Environment and Health, 11, 7-13. of mining in a Th-rich Norwegian area. Health Physics, 48 (4),4 15-420. Storruste, A., Reistad, A., Rudjord, T., Dahler, A., Liestol I. (1965). Measurement Stranden, E., Wand, T. (1986). Natural of environmental gamma radiation in gamma radiation in a Norwegian area ri,h in

Norwegian houses. Health Physics, 1 I ~ thorium. Radiation Protection Dosimetry, 16 26 1-269. (4). 325-328.

Strand, T. (1995). Time variation of indoor Sxther, E. { 1957). The alknlinc rock province radon concentration in typical Norwegian of ~hcFen area in southe,im Norway. Det homes. Proceeding of the 61h Inteinational Konglige Norske Vidcnskabers Selshbs Symposium on the Natural Radiation Skrit'ter, 1, 148 pp. Environment, 5-9 June 1495, 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. Unitcd Rarnberg, G.B.. Jensen, C.L., Wiig, AH.. Nations Scientific Committee on the Effects of Thornmesen. G. (2001). lndoor radon Atomic Radiation. United Nations, New Yoik survey in 114 municipalities. Short prcsenhtions of results. Straaleveimapport Wtihni, T. (1993). Dosemeter for low level 2001 :4. Osteraas: Norwegian Radiation externa1 radiation. Radiation Protection Protection Authority. Dosimetry, 48 (4), 347-350.

Stranden, E. (19771. Population doses from environmental ganirna 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 Cfrom Rumberg and Barth, 1966) 14

Fig lb. Combined bedrock and quaternary geology map of die Fer? m-m (based on Scether, 1957 and Ram.berg and Barth, I9661 15

Rn (Bq/m3)

Fig. 2. The distribution of indoor mdorz conct'ntrafions in dwellings in the Fen area 16

3.0

2.8

f

r [1: 2-0 T 1.8

I u f I I Rauhaugite Rodberg Sovite Fenite Gneiss Type of building ground

3edrock covered by siWclay

Fig. 3. Indoor mdon concentrotions iri dwellings grouped by underlying rock type and sediment cover. 17

50 45 r 40 235 .-0 4- 30 m 9 25 .+0 0 L $ 20 E 1 Z 15

10

0 50 TOO 150 200 250 300 350 400 450 5W 550 600 650 Dose rate (nGy/h)

Fig. 4. The distributim of extenzal gamm dose rates in dwellings in the Fen area. A cosmic ray contribution of 30 nGyh has beeiz subtracted. I8

z4 Antthm.meai

10th

T

1 I I I I Rauhaugite Rodberg Sovite Fenite Gneiss Type of building ground

Fig. 5. External gamma dose ram in dwellings groLrped by underlying rock type and sedimeizt cover. 19

1000 r = 0,42 a

10 I t 10 100 1000 1mo Rn-concentrations(Bq/m3)

Fig. 6. Scatter plot qf rudon concentration versus external dose rate for 45 wooden dwellings in the Fen nre-ecr with regression line. The radon concentrations presented have not been corrected to unrzwl means 20

Tahle 1 Activity concentrations of rock samples and tailings from the Fen central complex and adjacent areas Rock type

Mean Range Mean Range Mean Range Riidherg 9 3 100 (390-5900) 70 (20-1 10) 310 (hO-430) Rauhaugite 9 600 (290-930) 120 140-300) 60 (40-70) Fenite 8 130 (20-200) 50 (40-80) 1O(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 pneiss’ 3 64 (68-63) 45 (43-46) ---- ’> 4.0 Bq/kg 1horium--?32is rquivaleut to 1 pprrr Th 12.3 Rq/kg radi~im-226is eqirivalent tu I ppm U 310 Bq/kg prjtassium-40is Pquivuleni to I c/b K # outside The Fen central cornp1c.x 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 % 1200 % 2 400 ground of mean deviation mean (Bq/m3) (Eq/rn3) (Bq/rns) dwelhgs @q/m3) (Bq/m3) (Bq/m3) All dwellings $5 204 214 127 10- 1750 37 11 Rauhaugi te 44 258 206 199 35 - 1030 24 6

Rodherg 11 340 362 189 13 ~ 1750 63 27 Sovite 6 24 I 73 233 160- 280 67 --- Fenite 4 125 247 150 72- 590 15 --- Gneiss 3 69 35 62 35- 105 -_- _-- Siltlclav deposits 27 63 33 48 IO- 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 (nCry/h) (&FA) (nGyh) InGylh) All dwellings 95 98 78 82 35 - A20 Rauhaugite 44 110 54 99 42 - 294 Rddbers I1 200 158 157 47 - 620 Ssvite 6 75 21 71 50- 104 Fenite 4 55 5 55 48- 60 Gneiss 3 S5 15 54 39- 69 17 53 35 - 89