No abstract available

[en] In hydrogeology, tritium and ¹⁴C are the most widely used isotopes for determining ground water age and dynamics. Beside radioactive isotopes, stable isotopes, e.g. ¹⁸O or deuterium, can also be applied in assessing ground water dynamics. In using stable isotopes, conclusions about groundwater dynamics are made on the basis of the degree of amplitude reduction of precipitation isotope signal. This procedure can be carried out either by applying the formula derived from assumed precipitation isotope composition amplitude or by interpreting the precipitation isotope signal by means of different models and comparing it with the isotope signal of water in the output. In principle, information on the dynamics of a ground water reservoir can be obtained from changes of groundwater isotope composition caused by individual precipitation events. Recent investigations indicate that the mechanisms of ground water flow in water-bearing formations can be reconstructed by monitoring the isotope composition in the discharge during a single event. However, under usual hydrogeological conditions single precipitation events account for a rather small amount in the joint base flow reservoir. The consequence is that the changes in base flow isotope composition are very slight and therefore very difficult to measure. Because of the above difficulties, the sampling period in our research was extended to approximately 6 months, a period in which isotope composition of water in the discharge mostly starts showing more distinct changes. Sampling has shown that ground waters in Slovenian climatic conditions reach the most negative d¹⁸O values in spring and the most positive values in fall. Isotope composition of precipitation over a certain period and changes occurring in the isotope composition in the discharge can serve as the basis for determining the proportion of precipitation water which entered the base flow reservoir during this period

[en] A pumping test of the Klarici water supply near Brestovica was performed in August 2008, in order to determine the karst groundwater resource capacity. Groundwater was pumped for a month with a total capacity of 470 L/s. During the experiment, sampling for chemical and isotopic composition of groundwater and surface water was carried out. Intensive pumping in dry meteorological conditions caused a lowering of the water table and changes in the chemical and isotopic composition of pumped water. Local meteoric waters are infiltrated into the aquifer at a lower mean altitude; therefore the δ¹⁸O is enriched with the heavy oxygen isotope. The duration of pumping resulted in changes in the isotopic composition of oxygen due to a greater impact of the intergranular Soca River aquifer on the karst aquifer. On the basis of isotope composition it was possible to quantify the impact of the Soca River on the karst aquifer. (author)

[en] Full text: For almost 15% of Slovenia's inhabitants living in Ljubljana, the capital of Slovenia, two groundwater sources of drinking water are of great importance. An abundance of groundwater is hidden inside the sandy and gravely Sava river aquifer underneath the urban city area, called Ljubljansko polje, which is one of the largest underground reservoirs of drinking water in Slovenia. Ljubljansko polje is a tectonic basin by its origin and is, together with the second important groundwater resource - Ljubljansko Barje - a part of the Ljubljana basin. Ljubljansko Barje is highly complicated from the hydrogeological point of view - the variety of unconfined and unconfined aquifers stretching along the city suburbs in the South give us just a misty figure of the processes taking place in the sandy layers, in places covered by impermeable clayey layers and surrounded by karst mountains. The Ljubljansko polje aquifer is one of the most investigated Slovenian areas, because its groundwater has been used for public drinking water supply since 1890. Together with the increasing number of Ljubljana's inhabitants and consequently rising withdrawal quantities, groundwater quality began to show unacceptable deviations from the quality standards. The question of acceptable exploitation quantities that would not cause further decrease in groundwater quality was opened. The aim of isotope investigations was to determine the origin of the abstracted groundwater in more detail. The results served as helpful tools in determining priority tasks in planning future water exploitation and protection. Isotope investigations had not been applied in groundwater researches of Ljubljansko polje until recently. As an additional tool for understanding the groundwater recharge and flow of Ljubljansko polje groundwater, oxygen isotope composition was being determined during the period from autumn 1997 to autumn 1999. On the basis of results of previous hydrogeological investigations it was concluded that only two important sources of the Ljubljansko polje groundwater exist, local precipitation and the Sava river water. The two sources showed a noticeable difference in oxygen composition, which served as the basis of groundwater origin determination. The pumping wells included into the public water supply system were used as sampling points. Isotope investigations showed that the share of the river water and of local precipitation strongly depend on the sampling point location, namely on its distance from the Sava river recharging area. As a consequence, the values of physical and chemical parameters show annual changes according to the variations in the portion of the two sources. The sampling points with a high proportion of the recharging river water show better groundwater quality. In other words, human impact in the urban city area is the main reason for deterioration of groundwater partly flowing below the urbanised area of the Ljubljana City. Encouraging results of isotope investigations of the Ljubljansko polje led to the decision to start investigations on the second part of the Ljubljana basin - Ljubljansko barje. The exploitation of the aquifers located south of the city started in the mid-eighties of the previous century. It has been expected that this water resource with its mostly not urbanised recharge area could be protected from the anthropogenic influences more easily than the water resource in the close vicinity of the city. The main aim of the research, based on stable isotope (oxygen, deuterium) techniques, was to confirm the existence of different aquifers determined by former geological investigations and hydrogeological observations and to determine the differences in their recharge dynamics. The investigations started immediately after the conclusion of the Ljubljansko polje research in the autumn of 1999 and took place for two years. The results of isotope composition and chemical parameters, observed simultaneously, contribute to the understanding of groundwater origin, mean altitude of the recharge area, aquifer recharge dynamics and the relation between surface waters and groundwater. Two recent investigations, based on the determination of the stable isotope composition, give important results and form the basis for the decision of the future protection and exploitation of the Ljubljansko polje and Ljubljansko barje aquifers. (author)

No abstract available

[en] In the karst area of NW Yugoslavia calcite is precipitated from fresh water in the form of speleothems in karst caves, as lacustrine deposits in river beds (tufa or travertine), and as lake sediments. The isotopic compositions of these forms of calcite were compared to determine conditions for calcite precipitation, i.e. whether precipitation takes place under isotopic equilibrium or not. The content of stable isotopes of carbon (¹³C) and oxygen (¹⁸O), as well as radiocarbon (¹⁴C) activity, were measured in calcite samples. Speleothems formed under various physicochemical conditions were collected in the Slovenian karst area, while most tufa samples and lake sediments were collected in the Plitvice Lakes area, Croatia. The δ¹⁸O of investigated young speleothems varies from -5 per mille to -7 per mille PDB and that of recent tufa and lake sediment from -8.5 to -10 per mille. The observed variations of δ¹³C content are much higher: δ¹³C of speleothems varies between -6.5 and -11 per mille, and that of tufa between -10 and -2 per mille PDB. However, the most frequent δ¹³C values of speleothems and tufa samples are very similar, indicating similar conditions of calcite formation. Higher δ¹³C values can be explained by the escape of isotopically lighter CO₂ from water and by exchange with atmospheric CO₂. It was observed that δ¹⁸O and δ¹³C values were higher for tufa deposits that were precipitated at waterfalls than those of sediments or tufa formed in lakes or under steady water flow conditions. More pronounced differences between tufa and speleothems were found in oxygen isotopic composition. The δ¹⁸O values of tufa are significantly more negative than the δ¹⁸O of speleothems owing to the different isotopic composition of water from which the calcite was precipitated. Tufa is precipitated from water with mean annual δ¹⁸O values of -10.7 per mille SMOW, while speleothems are formed from water with mean annual 6180 of -8.6 per mille (samples from caves Mackovca, Planina Postojna and Predjama) and -7.2 per mille (Divaca cave). These results prove that the oxygen isotopic composition of calcite formed under equilibrium conditions is governed by the oxygen isotopic composition of the water and by the temperature at which calcite formation occurs. The temperature of recent calcite formation was calculated from Ref. [I]: 1000 Ln α = 2.78 x 10⁶ / T² - 3.4, where α is (1000 + δ¹⁸O_calcite) / (1000 + δ¹⁸O_water). The calculated temperatures of speleothem formation are 0.5 to 3.2 deg C lower than the measured temperatures in caves, because speleothems were formed in a colder period of the year (mostly from September to December). Lake sediment calcite was precipitated under isotopic equilibrium from water having a saturation index higher than 3. This was proved by comparing the δ¹⁸C values in sediment with those in dissolved inorganic carbon in water. The temperature of tufa and lake sediment precipitation was also determined. It turned out that the calculated temperature is higher than the average water temperature measured for several past years. Hence, the sediment was precipitated during the warmer period of the year. The δ¹⁸O value is very uniform throughout the investigated sediment depth, indicating that no significant climatic changes occurred during the sedimentation process, which lasted approximately 8000 years in Lake Prosce. Radiocarbon dating of tufa showed two age groups: the Holocene tufa up to 6000 years old and the older tufa with an apparent ¹⁴C age of 20,000 years or more. It was proved by the ²³⁰Th/²³⁴U method that the true age of tufa was about 120 000 years, i.e. the periods of tufa growth coincided with warm and humid interglacials. The δ¹⁸O values of tufa of various ages are very similar showing that both groups of tufa were formed under similar climatic conditions, supposing that the isotopic composition of meteoric water was the same as during t he Holocene

[en] Poster presentation. 6 refs, 2 figs, 1 tab

[en] Full text: two groundwater sources of drinking water are of great importance. An abundance of groundwater is hidden inside the sandy and gravely Sava river aquifer underneath the urban city area, called Ljubljansko polje, which is one of the largest underground reservoirs of drinking water in Slovenia. Ljubljansko polje is a tectonic basin by its origin and is, together with the second important groundwater resource - Ljubljansko Barje - a part of the Ljubljana basin. Ljubljansko Barje is highly complicated from the hydrogeological point of view - the variety of unconfined and unconfined aquifers stretching along the city suburbs in the South give us just a misty figure of the processes taking place in the sandy layers, in places covered by impermeable clayey layers and surrounded by karst mountains. The Ljubljansko polje aquifer is one of the most investigated Slovenian areas, because its groundwater has been used for public drinking water supply since 1890. Together with the increasing number of Ljubljana's inhabitants and consequently rising withdrawal quantities, groundwater quality began to show unacceptable deviations from the quality standards. The question of acceptable exploitation quantities that would not cause further decrease in groundwater quality was opened. The aim of isotope investigations was to determine the origin of the abstracted groundwater in more detail. The results served as helpful tools in determining priority tasks in planning future water exploitation and protection. Isotope investigations had not been applied in groundwater researches of Ljubljansko polje until recently. As an additional tool for understanding the groundwater recharge and flow of Ljubljansko polje groundwater, oxygen isotope composition was being determined during the period from autumn 1997 to autumn 1999. On the basis of results of previous hydrogeological investigations it was concluded that only two important sources of the Ljubljansko polje groundwater exist, local precipitation and the Sava river water. The two sources showed a noticeable difference in oxygen composition, which served as the basis of groundwater origin determination. The pumping wells included into the public water supply system were used as sampling points. Isotope investigations showed that the share of the river water and of local precipitation strongly depend on the sampling point location, namely on its distance from the Sava river recharging area. As a consequence, the values of physical and chemical parameters show annual changes according to the variations in the portion of the two sources. The sampling points with a high proportion of the recharging river water show better groundwater quality. In other words, human impact in the urban city area is the main reason for deterioration of groundwater partly flowing below the urbanised area of the Ljubljana City. Encouraging results of isotope investigations of the Ljubljansko polje led to the decision to start investigations on the second part of the Ljubljana basin - Ljubljansko barje. The exploitation of the aquifers located south of the city started in the mid-eighties of the previous century. It has been expected that this water resource with its mostly not urbanised recharge area could be protected from the anthropogenic influences more easily than the water resource in the close vicinity of the city. The main aim of the research, based on stable isotope (oxygen, devterium) techniques, was to confirm the existence of different aquifers determined by former geological investigations and hydrogeological observations and to determine the differences in their recharge dynamics. The investigations started immediately after the conclusion of the Ljubljansko polje research in the autumn of 1999 and took place for two years. The results of isotope composition and chemical parameters, observed simultaneously, contribute to the understanding of groundwater origin, mean altitude of the recharge area, aquifer recharge dynamics and the relation between surface waters and groundwater. Two recent investigations, based on the determination of the stable isotope composition, give important results and form the basis for the decision of the future protection and exploitation of the Ljubljansko polje and Ljubljansko barje aquifers. (author)

[en] From the hydrogeological point of view, the Sorsko polje area is a sink, filled with porous conglomerate and gravel, where large quantities of groundwater are accumulated. The Sorsko polje aquifer is one of the richest regions of groundwater and represents an important water source reserve for the central part of Slovenia. The determination of the ¹⁸O isotope composition in water (δ¹⁸O) represents an independent completion of previous hydrogeological investigations of Sorsko polje. Research results give more reliable information about water origin, as well as about the influence of local precipitation and the Sava River water on the dynamics of groundwater restoration in the aquifer (author)

[en] The protection of the environment is one of the main concerns in the management of radioactive waste, especially in repository planning. In different stages of repository lifetime the environmental assessment has different functions: it can be used as a decision making process and as a planning, communication and management tool. Safety assessment as a procedure for evaluating the performance of a disposal system, and its potential radiological impact on human health and environment, is also required. Following the international recommendations and Slovene legislation, a presentation is given of the role and importance of the environmental and safety assessment activities in the early stages following concept development and site selection for a low- and intermediate level radioactive waste (LILW) repository in Slovenia. As a case study, a short overview is also given of the preliminary safety assessment that has been carried out in the analysis of possibilities for long-lived LILW disposal in Slovenia. (author)