Natural background levels and threshold values of monitored parameters in the Cambrian-Vendian groundwater body,Estonia

The Cambrian-Vendian groundwater body plays an important role in drinking water supply of capital Tallinn and other settlements in northern Estonia. Water quality in this deep-seated confined groundwater body is influenced by the intrusion of present-day seawater and pumping-induced upward migration of deeper saline groundwater. The aim of this study is to evaluate the threshold values applying the methodology worked out within the EU 6th FP project “Background criteria for the identification of groundwater thresholds (BRIDGE)” and to compare the results with the values proposed by local authorities. A database containing 250 monitoring points was completed and used for the calculation of natural background levels (as the 90 and 97.7 percentile) in groundwater. The calculation of threshold values is based on natural background levels and reference values. In case of Cambrian-Vendian groundwater body the receptor is drinking water, thus limit values set by Estonian drinking water standard were used as reference values. The threshold values proposed by local authorities are more or less the same as calculated by BRIDGE methodology. Exceptionally different values are derived in case of chloride and ammonium.     

Barium anomaly in the Cambrian-Vendian aquifer system in North Estonia

A barium anomaly with a maximum Ba²⁺ concentration of 6.37 mg/l was distinguished in a Cambrian-Vendian (Cm-V) aquifer system that is widely used as a drinking water source in the towns Kunda, Rakvere and Kohtla-Järve of North-Estonia. The modelling results show that at low sulphate concentrations (below 3 mg/l) Ba²⁺ contents can exceed the limit values for drinking water (such as 2 mg/l set by US EPA). Bicarbonate ions in their common concentration range in groundwater cannot limit Ba²⁺ at its content below 10 mg/l. The probable natural sources of the anomaly are the crystalline basement and its weathering zone. Groundwater in the clayey weathering core is hydraulically connected with the overlying Cm-V aquifer system, thus the upconing of deeper-seated groundwater, caused by intensive exploitation of wells, is possible.     

Recovering the real-space correlation function from photometric redshift surveys

Measurements of clustering in large-scale imaging surveys that make use of photometric redshifts depend on the uncertainties in the redshift determination. We have used light-cone simulations to show how the deprojection method successfully recovers the real-space correlation function when applied to mock photometric redshift surveys. We study how the errors in the redshift determination affect the quality of the recovered two-point correlation function. Considering the expected errors associated with the planned photometric redshift surveys, we conclude that this method provides information on the clustering of matter useful for the estimation of cosmological parameters that depend on the large-scale distribution of galaxies.     

Carbon isotope systematics of the Cambrian–Vendian aquifer system in the northern Baltic Basin: Implications to the age and evolution of groundwater

Groundwater in the Cambrian–Vendian aquifer system has a strongly depleted stable isotope composition (δ¹⁸O values of about −22‰) and a low radiocarbon concentration, which suggests that the water is of glacial origin from the last Ice Age. The aim of this paper was to elucidate the timing of infiltration of glacial waters and to understand the geochemical evolution of this groundwater. The composition of the dissolved inorganic C (DIC) in Cambrian–Vendian groundwater is influenced by complex reactions and isotope exchange processes between water, organic materials and rock matrix. The δ¹³C composition of dissolved inorganic C in Cambrian–Vendian water also indicates a bacterial modification of the isotope system. The corrected radiocarbon ages of groundwater are between 14,000 and 27,000 radiocarbon years, which is coeval with the advance of the Weichselian Glacier in the area.     

Fluoride occurrence in publicly supplied drinking water in Estonia

A study was undertaken to examine the content and spatial distribution of fluoride in drinking water. Water samples (735) from public water systems covering all Estonian territory were analysed using SPADNS method. In order to specify the natural source of fluoride, the chemistry data from five aquifer systems utilised for water supply were included into the study. Fluoride concentrations in tap water, to a great extent, ranged from 0.01 to 6.95 mg/l. Drinking water in southern Estonia, where terrigenous Middle-Devonian aquifer system is exploited, has a fluoride concentration lower than recommended level (0.5 mg/l), thus promoting susceptibility to dental caries. The western part of the country is supplied by water with excess fluoride content (1.5–6.9 mg/l). Groundwater abstracted for drinking purposes originates from Ordovician and Silurian carbonate rocks. The content of fluoride in Silurian–Ordovician aquifer system is associated with the groundwater abstraction depth and the main controlling factors of dissolved fluoride are the pH value and the chemical type of water.     

The age of the Ilumetsa meteorite craters in southeast Estonia

Abstract— The Ilumetsa impact craters were discovered in 1938 in the course of geological mapping. In the crater field area, the Middle Devonian bedrock consists of light‐yellow weakly cemented siltstones and sandstones of the Givetian Burtnieki Regional Stage, which are overlain by a 1–2 m thick layer of reddish‐brown loamy till. Põrguhaud, the biggest crater, has a diameter of 75–80 m at the top of the uplifted rim and is 12.5 m deep. The zone of authochtonous breccias below the apparent crater extends to 30 m deep. The crater is partly filled with a thin layer of gyttja and peat up to 2 m thick. Radiocarbon ages of 6030 ± 100 (TA‐310) and 5910 ± 100 (TA‐725) years B.P. from the lowermost organic layer and palynological evidence suggest that the age of the impact was ～6000 ¹⁴C years B.P. The Sügavhaud crater has a diameter of 50 m at the top of the rim and is 4.5 m deep. Organic matter on the bottom of the crater is absent. As precise age determination of the Ilumetsa craters by direct dating methods has proved inconclusive, we proposed a method of geological correlation which is based on the occurrence of impact spherules in lake and bog sediments around the crater field. Radiocarbon dating of samples from a peat layer with glassy spherules of impact origin in the Meenikunno Bog, 6 km southwest of the Ilumetsa crater field, yielded the ages of 6542 ± 50 (Tln‐2214) for the depth interval 5.6–5.7 m and 6697 ± 50 (Tln‐2316) years B.P. for the depth interval 5.7–5.8 m. These dates suggest that the Ilumetsa craters were formed ～6600 years ago.     

Fractional flow dimensions and hydraulic properties of a fracture-zone aquifer, Leppävirta, Finland

 In order to characterize the hydraulic properties of an aquifer in Finland comprising two subvertical fracture zones, observation-well responses were matched with generalized radial flow (GRF) type curves. The responses in six wells out of seven are consistent with the GRF model. The fractional flow dimensions (1–1.2 and 1.5) were determined by regression analysis of straight-line slopes and type-curve matching. In each test, the flow dimensions in the neighboring fracture zone range from 2–2.25. Comparisons of the late-time responses with the asymptotic GRF solution and the flow dimensions obtained by reversing the pumping and observation points suggest homogeneous hydraulic properties. Deviations in responses can be explained by flow-path tortuosity. After assessments of the extent of the flow and radial distances along the fracture system, hydraulic conductivities and storativities were determined from the results of the type-curve matching procedure. The obtained hydraulic conductivities are 1.3×10^–5 to 7.9×10^–5 m/s and 5.0×10^–6 to 2.5×10^–5 m/s for the western and the eastern fracture zones, respectively. The results were verified by applying them to analytical solutions for pumping wells. The calculated pumping-well responses are consistent with the observations. The analysis of flow dimension also enhances qualitative interpretations on the hydrogeology of fracture zones. Received, April 1997 · Revised, September 1997 · Accepted, May 1998     

Geological sources of boron and fluoride anomalies in Silurian–Ordovician aquifer system,Estonia

The objective of this study was to examine the possible natural sources of fluorides and boron in Silurian–Ordovician (S–O) aquifer system, as the anomaly of these elements has been distinguished in groundwater of western Estonia. Water–rock interactions, such as dissolution and leaching of the host rock, are considered to be the main source of high fluoride and boron concentrations in groundwater. Altogether 91 rock samples were analysed to determine if high F⁻ and B levels in groundwater could be attributed to certain aquifer forming rock types. Fluorine and boron contents in limestones and dolomites vary from 100 to 500 mg/kg and 5 to 20 mg/kg, reaching up to 1,000 and 150 mg/kg in marlstones, respectively. K-bentonites, altered volcanic ash beds, are rich in fluorine (400–4,500 mg/kg) and boron (50–1,000 mg/kg). Thus, clay-rich sediments, providing ion-exchange and adsorption sites for F⁻ and B, are the probable sources of both elements in S–O aquifer system in western Estonia.     

Simulation of the hydrogeologic effects of oil-shale mining on the neighbouring wetland water balance: case study in north-eastern Estonia

The water balance of wetlands plays an integral role in their function. Developments adjacent to wetlands can affect their water balance through impacts on groundwater flow and increased discharge in the area, and they can cause lowering of the wetland water table. A 430 km² area was selected for groundwater modelling to asses the effect of underground mining on the water balance of wetlands in north-eastern Estonia. A nature conservation area (encompassing Selisoo bog) is within 3 km of an underground oil-shale mine. Two future mining scenarios with different areal extents of mining were modeled and compared to the present situation. Results show that the vertical hydraulic conductivity of the subsurface is of critical importance to potential wetland dewatering as a result of mining. Significant impact on the Selisoo bog water balance will be caused by the approaching mine but there will be only minor additional impacts from mining directly below the bog. The major impact will arise before that stage, when the underground mine extension reaches the border of the nature conservation area; since the restriction of activities in this area relates to the ground surface, the conservation area’s border is not sufficiently protective in relation to underground development.