Long-term monitoring of water treatment technology designed for radium removal-removal efficiencies and NORM formation.

A drinking water treatment plant in Viimsi, Estonia, was monitored over three years for iron, manganese, radium-226, radium-228, as well as their daughter nuclides, in order to determine the efficiency of the treatment process, gain an insight into the removal mechanisms and interactions between radium, iron, and manganese, and assess the overall longevity and performance of the technology along with the possible build-up of NORM in the treatment process. During the study, samples were collected from raw water, first and second stage filtrate, consumer water, backwash water and filter materials. The results show consistent removal efficiency for iron and manganese, as well as an average of over 85% removal for radium with a slight decline over time. The backwash process has been optimised for maximum radium removal from the filters, while keeping concentrations in the backwash water below exemption levels. However, the accumulation of radium and thorium occurs in the filter material, exceeding exemption levels in the top layer of the filter columns in less than a year. By the end of the observation period, activity concentrations in the top layer of the columns were above 30 000 Bq kg-1 for Ra-226 and Ra-228, and around 15 000 Bq kg-1 for Th-228. Radionuclides are not homogenously distributed in the filter columns. In order to estimate the average activity concentrations in the filter media, the height distribution of radionuclides has to be accounted for. Two years and two months after commissioning the treatment plant, the average activity concentrations of Ra isotopes in the filter columns were in the range 10 000 Bq kg-1, while Th-228 activity concentration was roughly 3500 Bq kg-1.

Long-term monitoring of a water treatment technology designed for radium removal - removal efficiencies and NORM formation.

A drinking water treatment plant in Viimsi, Estonia was monitored over three years for iron, manganese, radium-226, radium-228, and their daughter nuclides in order to determine the efficiency of the treatment process, get an insight of the removal mechanisms and interactions between radium, iron, and manganese, and assess the overall longevity and performance of the technology and possible build-up of NORM from the treatment process. During the study, samples were collected from raw water, first and second stage filtrate, consumer water, backwash water, and filter materials. The results show a consistent removal efficiency for iron and manganese, as well as an average of over 85% removal for radium with a slight decline with time. Backwash process has been optimized for maximum radium removal from the filters, while keeping the radium concentrations in the backwash water below exemption levels. However, accumulation of radium and thorium occurs in the filter material, exceeding exemption levels in the top layer of the filter columns in less than a year. By the end of the observation period, activity concentrations in the top layer of the columns were above 30 000 Bq/kg for Ra-226 and Ra-228, and around 15 000 Bq/kg for Th-228. Radionuclides are not homogenously distributed in the filter columns. In order to estimate the average activity concentrations in the filter media, the height distribution of radionuclides has to be accounted for. Two years and two months after commissioning of the treatment plant average activity concentrations of Ra isotopes in the filter columns were in a range of 10 000 Bq/kg while Th-228 activity concentration was roughly 3500 Bq/kg.

Temporal changes in radiological and chemical composition of Cambrian-Vendian groundwater in conditions of intensive water consumption.

Intensive groundwater uptake is a process at the intersection of the anthroposphere, hydrosphere, and lithosphere. In this study, groundwater uptake on a peninsula where only one aquifer system - the Cambrian-Vendian (CmV) - is available for drinking water uptake is observed for a period of four years for relevant radionuclides and chemical parameters (Cl, Mn, Fe, δ18O). Intensive groundwater uptake from the CmV aquifer system may lead to water inflow either from the sea, through ancient buried valleys or from the under-laying crystalline basement rock which is rich in natural radionuclides. Changes in the geochemical conditions in the aquifer may in turn bring about desorption of Ra from sediment surface. Knowing the hydrogeological background of the wells helps to predict possible changes in water quality which in turn are important for sustainable groundwater management and optimization of water treatment processes. Changes in Cl and Ra concentrations are critical parameters to monitor for sustainable management of the CmV groundwater. Radionuclide activity concentrations in groundwater are often considered rather stable, minimum monitoring frequency of the total indicative dose from drinking water is set at once every ten years. The present study demonstrates that this is not sufficient for ensuring stable drinking water quality in case of aquifer systems as sensitive as the CmV aquifer system. Changes in Cl concentrations can be used as a tool to predict Ra activity concentrations and distribute the production between different wells opening to the same aquifer system.

Pb-210 and fly ash particles in ombrotrophic peat bogs as indicators of industrial emissions.

Peat cores were collected from a Sphagnum-dominated Selisoo bog, which is located about 40 km from the large oil shale-fired power plants (PPs) in Estonia. These PPs have been operational from the 1960's and had the largest negative impact on the surrounding environment during the 1970's and 1980's. Nearby ombrotrophic peatlands are good indicators of atmospheric pollution due to their properties of effectively adsorbing mineral matter and pollutants. Collected peat cores (S1 and S2) from Selisoo peat bog were sliced into 1 cm thick layers and measured gamma spectrometrically. In addition, spherical fly ash particles (SFAP) originating from the combustion of the PPs were counted. The maximum concentrations (particles per cm3) of the SFAP remained between 7 and 12 cm for core S1 and between 11 and 17 cm for core S2. The concentration profiles of the SFAP reflect the combustion and emission history of the PPs. Pb-210 activity concentrations have the maximum values up to 500 Bq kg-1 and 413 Bq m-2 for S1 and for the S2 the values are 441 Bq kg-1 and 535 Bq m-2 (dry weight). The unsupported 210Pb inventory is around 4250 Bq m-2. This represents a 210Pb deposition flux of 133 Bq m-2 y-1. The estimated 210Pb deposition via fly ash from the PPs at Selisoo area remains between 0.2 and 2.2 Bq m-2 y-1. Considering the annual 210Pb deposition from the atmosphere (with a precipitation rate of 600 mm y-1) between 92 and 133 Bq m-2, which is regarded as the natural background value, we show that the radiological burden due to the power plants at these distances is negligible. As the peat cores exhibit noticeable differences from each other (in terms of radionuclide concentration distribution), the SFAP can provide a good additional parameter to improve the validity of results obtained only from radiometric methods in the chronological studies. SFAP can also act as a possible tool to estimate the radionuclide deposition rate via fly ash in the vicinity of the PPs.

Radon leakage as a source of additional uncertainty in simultaneous determination of ²²6Ra and ²²8Ra by gamma spectrometry--validation of analysis procedure.

A series of validation experiments was carried out to assess robustness, repeatability, and trueness of an analysis procedure for simultaneous determination of (226)Ra and (228)Ra in water samples. The study revealed instabilities in the radon holding capacity of the sample matrix (epoxy resin). The discovered effect is a new additional component in the uncertainty budget which should be considered when (226)Ra is measured via its progeny in similar sample matrices.