Relevant radionuclides in Estonian drinking and ground waters - measurement techniques and activity concentrations

First comprehensive studies of the radionuclides' concentration and its composition in Estonian ground water began in 1990s. It was quickly realized that the activity concentration of Ra-226 and Ra-228 in Cambrian-Vendian (Cm-V) aquifer are the highest contributors to the total indicative dose (TID). About 22% of the population in Estonia uses Cm-V ground water for drinking water supply. In recent study [1], it was concluded, that about 91% of Cm-V aquifer consumers (20% of the Estonian population) obtain higher TID doses (TID exceeding 0.1 mSv/y) than set by European Commission and national regulations. Over the years, a good representation level by the number of measured samples for Ra-226 and Ra-228 from Cm-V aquifer has been obtained. However, for other widely used aquifers - Ordovician-Cambrian, Silurian-Ordovician and Devonian - only poor data is available. In several southern counties, only few percent of , the water supplies have been surveyed. Data for other natural radionuclides (U-234,U-238, (210)po and Pb-210) is also poor. Scarce data has been partly due to the lack of analysis techniques available in Estonian nuclear analysis laboratories. This has been the motivation in the development of gamma spectrometric and liquid scintillation (LSC) counting techniques for ground and drinking water applications.