Looduslik radioaktiivsus Kambrium-Vendi põhjavees – mõõtemetoodikad, veetöötlustehnoloogia seire ja veekasutusega kaasnevad muutused põhjavee kvaliteedis

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKambrium-Vendi (Cm-V) põhjaveekiht on üks peamisi joogiveeallikaid Põhja-Eestis. Uraani- ja tooriumirikka kristalse aluskorra peal asuv Cm-V on kurikuulus oma kõrge radionukliidide sisalduse poolest. 2009. a hinnangute põhjal tarbib ligi 18% Eesti elanikkonnast (230 000 inimest) joogivett, mille radioloogilised näitajad ületavad määruses kehtestatud viitetaset. Kui nõuded joogivee radioloogiliste näitajate kohta Eesti seadusandlusesse üle võeti, oli Eestis vähe võimalusi radioloogiliste parameetrite määramiseks veeproovides. Lünga täitmiseks arendati ja valideeriti käesoleva töö raames metoodikaid raadiumi mõõtmiseks. Akrediteeriti gammaspektromeetriline analüüs Ra-226 ja Ra-228 määramiseks, mis võimaldab nüüd pakkuda usaldusväärselt analüüsiteenust. Veebruaris 2012 avati Viimsis esimene veepuhastusjaam Eestis, mis kasutab spetsiaalselt raadiumi eemaldamiseks mõeldud tehnoloogiat. Kolme aasta jooksul kogutud seiretulemused näitavad, et Cm-V põhjavee kasutamise puhul on väga keeruline vältida NORM-jäätmete (Naturally Occurring Radioactive Material) teket. Kuigi põhjavees tekitavad kiirguskaitse seisukohast muret vaid Ra-226 ja Ra-228, tuleb vee töötlemise protsessis tähelepanu pöörata ka radoonile (Rn-222) ja tooriumile (Th-228), mis tekivad filtermaterjalides Ra-226 ja Ra-228 radioaktiivsel lagunemisel. Viimsis kasutatav tehnoloogia on tänaseni suutnud tagada vastavuse joogivee kvaliteedinõuetega, kuid intensiivne põhjavee kasutus võib kutsuda esile muutusi sisendvee kvaliteedis. Võtmenäitajateks Cm-V põhjavee kvaliteedi jälgimisel osutusid kloriidid ja Ra. Intensiivse veevõtu tulemusel võib põhjavee Cl-sisaldus muutuda kas merevee sissetungi tagajärjel või kristalses aluskorras sisalduva kõrge soolsuse vee sissetungi tõttu, millega kaasneb meteoorse vee sissetung läbi uhtorgude. Ra-sisalduse kasvu taga võib olla kas raadiumirikka vee sissetung või muutused põhjaveekihi geokeemilistes tingimustes, mis põhjustavad Ra lahustumist setete pinnalt põhjavette. Doktoritöö tulemused näitavad, et sotsiaalministri määrusega „Joogivee kvaliteedi- ja kontrollinõuded ning analüüsimeetodid“ kehtestatud seiresagedus radioloogilistele näitajatele – kord 10 aasta jooksul – ei Cm-V põhajvee puhul piisav.One of the most important public water supplies in North-Estonia, the Cambrian-Vendian (Cm-V) aquifer system, lays on the uranium and thorium rich crystalline basement rock and is known to be contaminated with naturally occurring radionuclides. It has been estimated that ca. 18 % of Estonian inhabitants (230 000 peoole) consume drinking water where radiological parameters exceed parametric values given by regulations. The capacity to conduct radiological analysis of water in Estonia was very limited when the requirements for radiological parameters in drinking water where adopted into local legislation. To fill the gap, analytical procedures for radium measurements were developed and validated. As a part of this thesis, procedures based on simultaneous determination of Ra-226 and Ra-228 by gamma spectrometry were accredited. This now enable to offer a reliable measurement service. In February 2012, the first Estonian water treatment plant specially designed for radium removal started operation in Viimsi. The facility was monitored for three years. The thesis demonstrated clearly that NORM (naturally occurring radioactive material) generation is difficult to avoid when Cm-V groundwater is used for drinking water production. In addition to Ra isotopes, which are the only radionuclides of concern in groundwater, radon-222) and thorium-228) become of interest in the treatment process because they are generated by the decay of Ra-226 and Ra-228 in the filter material. As for now, the treatment facility has been able to provide water compliant with the drinking water requirements. Yet the intensive use of groundwater brings about changes in its quality. Cl and Ra are critical parameters to monitor for sustainable management of the Cm-V groundwater. Possible explanations for the increase of Cl are intrusion of sea water into the aquifer or inflow of highly saline water from the crystalline basement accompanied by inflow of meteoric water. Ra concentration may rise either because of migration of Ra into the system or by changes in geochemical conditions that may lead to desorption of Ra from sediment surface. The present study proved that the monitoring frequency set for radiological parameters in local regulation is not sufficient for ensuring stable drinking water quality in case of aquifer systems as sensitive as Cm-V.https://www.ester.ee/record=b5252147~S

NORM-related industrial activities in Estonia - establishing national NORM inventory

There is incomplete information available concerning NORM-related (naturally occurring radioactive material) industries in Estonia. In order to fill the gap in this knowledge, a nationwide study was carried out between 2015 and 2017 to determine and radiologically characterize potential NORM-related industries. The study included compiling available literature and studies as well as on-site measurements (external dose rate and radon) and samplings in multiple industries, which had been determined to be potential NORM creators. The results from this study concluded that there are 3 industries in Estonia where the activity concentrations of naturally occurring radionuclides can reach an increased level which may require further regulatory control. Radionuclide exemption values were clearly exceeded in the filter materials of drinking water treatment plants that use water from Cambrian-Vendian aquifer. 226Ra and 228Ra values in filter materials reached over 40 kBq kg−1. Additionally, the gross radionuclide activity concentrations of 238U and 232Th in waste from a rare metal production industry reached up to 191 kBq kg−1. Clinker dust from the cement industry showed elevated concentrations of 210Pb, rising to over 2 kBq kg−1 in fine clinker dust. The creation of a national NORM inventory can be the basis for establishing a national NORM strategy for the management of NORM residues. This work provides a thorough overview of the radiological parameters of the potential NORM-related industries, describes the radionuclides that have elevated concentrations, provides estimations on their yearly creation amounts and produces input for determining possible NORM management options

Intrusion of Saline Water into a Coastal Aquifer Containing Palaeogroundwater in the Viimsi Peninsula in Estonia

The Viimsi peninsula is located north-east of Tallinn, capital of Estonia. The Cambrian-Vendian (Cm-V) aquifer system is a sole source of drinking water in the area. Historically, the groundwater exploitation has led to freshening of groundwater in the peninsula, but in recent years an increase in chloride concentrations and enrichment in δ18O values has been detected, but in recent years hydrochemical parameters indicate an increasing influence of a saline water source. The exact origin of this saline water has remained unclear. The aim of the current study is to elucidate whether the increase in Cl− concentrations is related to seawater intrusion or to the infiltration of saline water from the underlying crystalline basement. To identify the source of salinity, chemical composition of the groundwater and the isotope tracers (e.g., δ18O and radium isotopes) were studied in the Viimsi peninsula in the period from 1987 to 2018. Our results show that chemical composition of Cm-V groundwater in the peninsula is clearly controlled by three-component mixing between glacial palaeogroundwater, saline water from the underling crystalline basement and modern meteoric water. The concentrations of Ra are also significantly affected by the mixing, but the spatial variation of radium isotopes (226Ra and 228Ra) suggests the widespread occurrence of the U in the surrounding sedimentary sequence. Our hypothesis is that, in addition to U originating from the crystalline basement, some U could be associated with secondary U deposits in sedimentary rocks. The formation of these secondary U deposits could be related to glacial meltwater intrusion in the Pleistocene. Although the results suggest that the infiltration of saline groundwater from the underlying crystalline basement as the main source of salinity in the study area, the risk of seawater intrusion in the future cannot be ruled out. It needs to be highlighted that the present groundwater monitoring networks may not be precise enough to detect the potential seawater intrusion and subsequent changes in water quality of the Cm-V aquifer system in the Viimsi peninsula