RECONSTRUCTION OF THE POST-GLACIAL ENVIRONMENTAL VARIATIONS BASED ON THE MULTI-PROXY APPROACH: DŪKŠTELIS LAKE, EASTERN LITHUANIA

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Unsaturated zone models and their application for radioactive waste repository safety alalyse

Two nuclear waste disposal sites (Maišiagala radioactive waste storage facility site and Stabatiškė near surface repository site) were compared in terms of the contaminant movement through the unsaturated zone. Extensive data sets of the hydraulic properties, water content and isotope composition have been collected and summarized. Distribution features of globally widespread radionuclide tritium and the water molecule tracer isotopes in precipitation, unsaturated zone soil moisture profiles and groundwater were determined. Stable isotopes seasonal variation occurring in precipitation almost disappears in the unsaturated zone soil moisture and especially in shallow groundwater, but in both sites slight seasonal peak traces remain, which at the Maišiagala site are a bit more contrasting in comparison with the Stabatiškė site. Both sites were modelled by using unsaturated flow and transport models. Six scenarios have been developed to simulate the water and solute movement under low, moderate, and high water input, and instantaneous and continuous solute input conditions. In order to validate the representativeness of the hydraulic parameters, the model has been used to estimate the tritium distribution in the unsaturated zone, which properly represents the dynamics of the unsaturated zone. The uniformity of the daily input in each month should be kept in mind in the evaluation of the smooth changes of the tritium profile and water budget elements

Unsaturated zone models and their application for radioactive waste repository safety analyse

Two nuclear waste disposal sites (Maišiagala radioactive waste storage facility site and Stabatiškė near surface repository site) were compared in terms of the contaminant movement through the unsaturated zone. Extensive data sets of the hydraulic properties, water content and isotope composition have been collected and summarized. Distribution features of globally widespread radionuclide tritium and the water molecule tracer isotopes in precipitation, unsaturated zone soil moisture profiles and groundwater were determined. Stable isotopes seasonal variation occurring in precipitation almost disappears in the unsaturated zone soil moisture and especially in shallow groundwater, but in both sites slight seasonal peak traces remain, which at the Maišiagala site are a bit more contrasting in comparison with the Stabatiškė site. Both sites were modelled by using unsaturated flow and transport models. Six scenarios have been developed to simulate the water and solute movement under low, moderate, and high water input, and instantaneous and continuous solute input conditions. In order to validate the representativeness of the hydraulic parameters, the model has been used to estimate the tritium distribution in the unsaturated zone, which properly represents the dynamics of the unsaturated zone. The uniformity of the daily input in each month should be kept in mind in the evaluation of the smooth changes of the tritium profile and water budget elements

Investigations of the unsaturated zone at two radioactive waste disposal sites in Lithuania†

The unsaturated zone is an important part of the water cycle, governed by many hydrological and hydrogeological factors and processes and provide water and nutrients to the terrestrial ecosystem. Besides, the soils of the unsaturated zone are regarded as the first natural barrier to a large extent and are able to limit the spread of contaminants depending on their properties. The unsaturated zone provides a linkage between atmospheric moisture, groundwater, and seepage of groundwater to streams, lakes, or other surface water bodies. The major difference between water flow in saturated and unsaturated soils is that the hydraulic conductivity, which is conventionally assumed to be a constant in saturated soils, is a function of the degree of saturation or matrix suction in the unsaturated soils. In Lithuania, low and intermediate level radioactive wastes generated from medicine, industry and research were accumulated at the Maisiagala radioactive waste repository. Short-lived low and intermediate levels radioactive waste, generated during the operation of the Ignalina Nuclear Power Plant (INPP) and arising after the INPP decommissioning will be disposed of in the near surface repository close to the INPP (Stabatiske site). Extensive data sets of the hydraulic properties and water content attributed to unsaturated zone soil profiles of the two radioactive waste disposal sites have been collected and summarized. Globally widespread radionuclide tritium (3H) and stable isotope ratio (18O/16O and 2H/1H) distribution features were determined in precipitation, unsaturated zone soil moisture profiles and groundwater

Hydrogeology Model of Ignalina Region for Visaginas Well Field Protection Zone Substantiation

IAEA safety documents (Safety standarts… 1994; 1999a; 1999b) recommend assessing the safety framework of groundwater exploitation in the proximity of nuclear facilities. The main task of this study is to assess the results on the re-calculation of Visaginas town wellfield well protection zones (WPZ), since the Visaginas town wellfield is installed close to Ignalina Nuclear Power Plant (INPP) site and other sites of existing or planed new nuclear facilities. The numerical model used in this study is based on three-dimensional finite-element code FEFLOW 5.0 which allows modeling of groundwater flow and contaminant transport in a layered threedimensional system. The calibrated model of Visaginas wellfield area simulated the groundwater flow in the Quaternary and Upper-Middle Devonian aquifers systems. The evaluation of well protection zones for wellfields exploiting groundwater is currently determined by the Lithuanian legal documents (HN 44:2006). As a result of modeling the groundwater formation sources were specified and dimensions of wells protection zones in sectors 3a and 3b were established. The groundwater modeling results of this study shows that the third sub-zone (3b) of WPZ should be 0.6-1.1 km away from the wellfield fence. The long axis of WPZ extends for 4 250 m from north to south and for approximately 3 250 m from east to west. Visaginas wellfield capture zone during 50 years operation would reach the site for planned near-surface repository for radioactive waste in case of hypothetical very high wellfield capacity more than 70 000 m3/day

Soil water and stable isotopes in the unsaturated zone profile - field observations and analysis

In this review, we provide research data emphasizing the role of groundwater table and hydrom- eteorological parameters variation on soil water fluctuations in the unsaturated soil profile. We focused on soil water content, air temperature, precipitation and groundwater table observations. The ThetaProbe Soil Water Sensors basing on changes in the apparent dielectric constant were used for soil volumetric water con- tent measurements. The sensors were installed at the different depths of the unsaturated zone profile under natural atmospheric conditions. The observations lasted more than five years (14 November 2013 - 31 De- cember 2018). Groundwater table data was obtained using Diver data loggers, which continuously recorded water pressure and temperature. For more detailed investigations of water and mass transport at the Maisiagala radioactive waste repository site water, stable isotopes as environmental tracers were used as well

C-14 and other radionuclides in the environment in the border region of Lithuania before the start of the Belarusian nuclear power plant operation

In this paper, we analyze the background activity of anthropogenic radionuclides (C-14, H-3, Cs-137, and Pu-239,Pu-240), emphasizing C-14 content, in terrestrial and aquatic ecosystems in the Lithuanian border region before the commissioning of a new nuclear power plant in Belarus (BelNPP). In terrestrial samples, the C-14 concentration varied insignificantly-from 98.6 +/- 0.7 to 102.2 +/- 0.8 pMC, which is close to the C-14 level in atmospheric CO2. In aquatic samples, the C-14 concentration varied within wide limits from 76.9 +/- 0.7 to 99.6 +/- 0.6 pMC, depending on the ecological group of macrophytes. Various ecological groups of macrophytes have experienced the influence of a freshwater reservoir effect. This lowest C-14 content in submerged macrophyte species, within the limits of uncertainty, was very close to the specific activity of C-14 in DIC (78.6 +/- 0.6 pMC) in the water of the Neris River. The background C-14 values, together with the data on H-3, Cs-137 and 239,240Pu obtained in this study, can be used in the future to assess the contribution of the BelNPP conventional radioactive effluents to the levels of C-14 and other radionuclides in terrestrial and aquatic ecosystems of the transboundary region of Belarus and Lithuania

New Archaeological, Paleoenvironmental, and 14C Data from the Šventoji Neolithic Sites, NW Lithuania

Archaeological, geological, and paleoecological investigations supported by radiocarbon dating enabled us to present a reconstruction of chronologically based paleoenvironmental and human activity changes in the Šventoji region, NW Lithuania, during the period 4000–800 cal BC. In addition, we describe the main stages of the Late Glacial and Holocene periods in the area. The Baltic Ice Lake regression was succeeded by a terrestrial period until the Littorina Sea maximal transgression at 5700–5400 cal BC. A marine bay with brackish water was transformed into a freshwater lagoon before the oldest archaeological evidence of human presence, i.e. 4000/3700 cal BC. However, the presence of Cerealia type and Plantago lanceolata pollen dating back to about 4400–4300 cal BC suggests earlier farming activities in the area. Pollen analyses show the minor but continuous role of cereal cultivation after 3250 cal BC. Due to the predominance of the boggy landscape in the immediate vicinity of the Šventoji sites, agricultural fields were situated further away from the sites themselves. Exploitation of remote areas of the freshwater basin by diverse fishing gear was proven by the discovery of a new fishing site, Šventoji 41 (2900–2600 cal BC). This finding together with data of previous research suggest a complex and elaborate coastal economy involving seal hunting and year-round freshwater fishing during the 3rd millennium cal BC. A decline in human activity is seen in the pollen diagram after 1800 cal BC, which could be due to significant environmental changes, including overgrowth of the freshwater lagoon basin with vegetation.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

RECONSTRUCTION OF THE POST-GLACIAL ENVIRONMENTAL VARIATIONS BASED ON THE MULTI-PROXY APPROACH: DŪKŠTELIS LAKE, EASTERN LITHUANIA

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Baltic Sea water tritium and stable isotopes in 2016–2017*

Water samples from the different basins of the Baltic Sea and North Sea were collected during four cruises taken place in 2016–2017. Altogether 60 water samples for 3H activity concentration and 120 water samples for stable isotopes ratio (δ18O and δ2H) were analysed. Exceptionally strong inflow activity from North Sea to the Baltic Sea occurred prior our surveys. The data obtained enabled comprehensive evaluation of tritium and stable isotopes distribution in waters of Baltic Sea and contributing inputs, including riverine and atmospheric freshwater flux and saline water inflow through the Danish Straits. By comparing with the previous studies, we noticed a tendency toward an increase in the δ18O and δ2H values of zero-salinity component over time, which may be due to climate change. In the case of tritium, the influence of artificial sources has also been noticed