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Aquifer System

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Rein Vaikmäe – 1st expert on this subject based on the ideXlab platform

  • Origin and formation of methane in groundwater of glacial origin from the Cambrian-Vendian Aquifer System in Estonia
    Geochimica et Cosmochimica Acta, 2019
    Co-Authors: Valle Raidla, Joonas Pärn, Werner Aeschbach, Jüri Ivask, Andres Marandi, Stefan Schloemer, György Czuppon, Holar Sepp, Rein Vaikmäe, Kalle Kirsimäe


    Abstract Groundwater in the Cambrian-Vendian Aquifer System in Estonia is characterised by the most depleted isotopic composition known in Europe (δ18O down to −23‰). The water most likely originates from glacial meltwater recharge from the Fennoscandian Ice Sheet in the Pleistocene. The Aquifer System is characterised by relative high methane concentrations (up to 50% of dissolved gases, estimated absolute concentration up to 1600 μmol L−1), the origin of which has so far remained unclear. In this paper, we focus on the origin of methane, the factors controlling its spatial distribution and its isotope geochemistry in the Aquifer System. The data reveal a large spatial variability in methane concentration, δ13CCH4 and δ2HCH4 values (from −6 to −105‰ and from −220 to −420‰, respectively). We show that local oxidation processes rather than different pathways of methane formation, have affected the initial isotopic composition of methane. Using the least modified δ13CCH4 values (from −85 to −105‰), we conclude that methane most likely originates from the organic material overridden by the Fennoscandian Ice Shield during the Late Weichselian glaciation, that was carried into the Aquifer System with infiltrating glacial meltwater. The estimated δ18O values of the water, where the methane was formed, are −17 ± 1.5‰ supporting the inference that the methane was formed during the Middle Weichselian interstadial. The study shows that groundwater of glacial origin in the Cambrian-Vendian Aquifer System can serve as an alternative palaeoenvironmental archive to be used for studying the variations in climatic and environmental conditions in Northern Europe during glacial–interglacial cycles of the Pleistocene.

  • the origin of increased salinity in the cambrian vendian Aquifer System on the kopli peninsula northern estonia
    Hydrogeology Journal, 2004
    Co-Authors: Enn Karro, Andres Marandi, Rein Vaikmäe


    Monitoring of the confined Cambrian-Vendian Aquifer System utilised for industrial water supply at Kopli Peninsula in Tallinn over 24 years reveals remarkable changes in chemical composition of groundwater. A relatively fast 1.5 to 3.0-fold increase in TDS and in concentrations of major ions in abstracted groundwater is the consequence of heavy pumping. The main sources of dissolved load in Cambrian-Vendian groundwater are the leaching of host rock and the other geochemical processes that occur in the saturated zone. Underlying crystalline basement, which comprises saline groundwater in its upper weathered and fissured portion, and which is hydraulically connected with the overlying Cambrian-Vendian Aquifer System, is the second important source of ions. The fractured basement and its clayey weathering crust host the Ca-Cl type groundwater, which is characterised by high TDS values (2–20 g/L). Intensive water abstraction accelerates the exchange of groundwaters and increases the area of influence of pumping. Chemical and isotopic studies of groundwater indicate an increasing contribution of old brackish water from the crystalline basement and rule out the potential implication of an intrusion of seawater into Aquifer.

Enn Karro – 2nd expert on this subject based on the ideXlab platform

  • The occurrence and hydrochemistry of fluoride and boron in carbonate Aquifer System, central and western Estonia
    Environmental Monitoring and Assessment, 2012
    Co-Authors: Enn Karro, Marge Uppin


    Silurian–Ordovician (S–O) Aquifer System is an important drinking water source of central and western Estonia. The fluoride and boron contents of groundwater in Aquifer System vary considerably. The fluoride concentration in 60 collected groundwater samples ranged from 0.1 to 6.1 mg/l with a mean of 1.95 mg/l in the study area. Boron content in groundwater varied from 0.05 mg/l to 2.1 mg/l with a mean value of 0.66 mg/l. Considering the requirements of EU Directive 98/83/EC and the Estonian requirements for drinking water quality, the limit value for fluoride (1.5 mg/l) and for boron (1.0 mg/l) is exceeded in 47 and 28 % of wells, respectively. Groundwater with high fluoride and boron concentrations is found mainly in western Estonia and deeper portion of Aquifer System, where groundwater chemical type is HCO3–Cl–Na–Mg–Ca, water is alkaline, and its Ca2+ content is low. Groundwater of the study area is undersaturated with respect to fluorite and near to equilibrium phase with respect to calcite. The comparison of TDS versus Na/(Na + Ca) and Cl/(Cl + HCO3) points to the dominance of rock weathering as the main process, which promotes the availability of fluoride and boron in the groundwater. The geological sources of B in S–O Aquifer System have not been studied so far, but the dissolution of fluorides from carbonate rocks (F = 100–400 mg/kg) and K-bentonites (F = 2,800–4,500 mg/kg) contributes to the formation of F-rich groundwater.

  • The origin of barium in the Cambrian-Vendian Aquifer System, North Estonia
    Estonian Journal of Earth Sciences, 2009
    Co-Authors: Robert Mokrik, Enn Karro, Lehte Savitskaja, Grazina Drevaliene


    Identification of the barium occurrence and its origin is made on the basis of the groundwater chemistry study. High Ba content has been detected in the Cambrian-Vendian Aquifer System in the coastal vicinity of the Gulf of Finland in Estonia and St Petersburg. The dissolution of Ba from witherite as the primary source was derived from the analysis of the aqueous solution equilibrium with Ba-related minerals. It is reflected in the chemical composition of groundwater and influenced by the galenite- calcite-fluorite polymetallic mineralization in Vendian sandstones. The dissolution and re-deposition of carbonates and baryte are confirmed by mineral saturation states for an aqueous solution and distribution of other species in the groundwater of the Cambrian-Vendian Aquifer System in North Estonia.

  • Barium anomaly in the Cambrian-Vendian Aquifer System in North Estonia
    Environmental Earth Sciences, 2004
    Co-Authors: Andres Marandi, Enn Karro, Erik Puura


    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-Jarve 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.

Susan Gaskin – 3rd expert on this subject based on the ideXlab platform

  • the basin of mexico Aquifer System regional groundwater level dynamics and database development
    Hydrogeology Journal, 2007
    Co-Authors: J J Carrerahernandez, Susan Gaskin


    The Aquifer System of the Basin of Mexico is the main source of water supply to the Mexico City Metropolitan Zone. Management of the Basin’s water resources requires improved understanding of regional groundwater flow patterns, for which large amounts of data are required. The current study analyses the regional dynamics of the potentiometric groundwater level using a new database called the Basin of Mexico Hydrogeological Database (BMHDB). To foster the development of a regional view of the Aquifer System, data on climatolog- ical, borehole and runoff variables are part of the BMHDB. The structure and development of the BMHDB are briefly explained and then the database is used to analyze the consequences of groundwater extraction on the Aquifer‘s confinement conditions using lithology data. The regional analysis shows that the largest drawdown rates are located north of Mexico City, in Ecatepec (a region that has not yet received attention in hydrogeo- logical studies), due to wells that were drilled as a temporary solution to Mexico City’s water-supply prob- lem. It is evident that the Aquifer has changed from a confined to an unconfined condition in some areas, a factor that is responsible for the large subsidence rates (40cm/year) in some regions.