Fig 2 - uploaded by Enn Karro
Content may be subject to copyright.
Source publication
The chemical composition of groundwater was studied and plausible reasons for its peculiarities were evaluated on the basis of long-term groundwater monitoring data. Fluoride and boron anomaly was distinguished in the Silurian–Ordovician aquifer system in western Estonia. The chemical type of groundwater controls the dissolution of fluorides and bo...
Context in source publication
Context 1
... drinking water supply wells trapping the Silurian-Ordovician aquifer system in Estonia were sampled for major ions as well as F -and B during the hydrochemical mapping performed in 2005-06. An analysis of the regional distribution of fluoride concentration shows great variation among different parts of the country (Fig. ...
Similar publications
: In order to determine the fluoride (F) content of aquifer-forming rocks, 17 limestone, dolomite, and K-bentonite samples were analysed for F using a sequential leaching method. The total F content of carbonate rocks was found to range mostly from 100 to 400 mg/kg with levels as high as 1100 mg/kg in clayey dolomite. K-bentonite layers are rich in...
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 gro...
Citations
... The Birimian and Tarkwaian aquifer systems are the major sources of public water consumption in the study area. The interactions between these rocks and water often lead to mineral dissolution revealing groundwater properties such as aggressive carbon dioxide, colour, hardness, and total dissolved solids (TDS) (Karro et al. 2009;Adimalla et al. 2020b). With this in mind, the solute concentrations can be inferred to determine the major ions and trace metals contained in groundwater. ...
The Birimian and Tarkwaian aquifer systems are the main sources of water supply for the Bosome Freho District and Bekwai Municipality inhabitants in the Ashanti region of Ghana. A hydrogeochemical assessment was carried out to ascertain the natural baseline chemistry of the groundwaters and the factors influencing groundwater chemistry in these two areas. A multivariate statistical tool consisting of principal component analysis (PCA) and hierarchical cluster analysis (HCA) together with hydrochemical graphical plots was applied on 64 groundwater samples. The Q–mode HCA results were used to explain the changes in groundwater chemistry along the flow paths where three spatial groundwater zones and water types were delineated. The first type consists of Ca–Mg–HCO 3 freshwater (recharge zone), which transitions into Ca–Na–HCO 3 or Na–Ca–HCO 3 mixed waters (intermediate zone) and finally evolves to the third type of Na–Ca–Mg–HCO 3 –Cl water (discharge zone). The study also reveals that the natural process influencing water chemistry is groundwater–rock interaction from carbonate and silicate weathering/dissolution, aided by carbonic acid from precipitation and releases concentration of Na ⁺ , Ca ²⁺ , Mg ²⁺ , and HCO 3 ⁻ into the groundwaters significantly. The chloro-alkaline indices also reveal cation exchange as the principal natural factor that controls groundwater chemistry in the area. Inverse geochemical modelling shows the dissolution of primary minerals such as dolomite, plagioclase, halite, gypsum, and precipitation of calcite and chlorite along the groundwater flow path. Anthropogenic activities have little influence on groundwater chemistry. The quality of groundwater in the Bosome Freho District and Bekwai Municipality is suitable for irrigational use and drinking water consumption. The results obtained so far will contribute to research paucity in the study area and serve as a guide for decision-makers for improved water resources management.
... The Birimian and Tarkwaian aquifer systems are the major sources of public water consumption in the study area. The interaction between these rocks and water often lead to mineral dissolution revealing groundwater properties such as aggressive carbon dioxide, colour, hardness and total dissolved solids (TDS) (Karro et al. 2009). With this in mind, the solute concentrations can be inferred to determine the major ions and trace metals contained in groundwater. ...
The Birimian and Tarkwaian aquifer systems are the main sources of water supply for the Bosome Freho District and Bekwai Municipality inhabitants in the Ashanti region of Ghana. A hydrogeochemical assessment was carried out to ascertain the natural baseline chemistry of the groundwaters and the factors influencing groundwater chemistry in these two areas. A multivariate statistical tool consisting of principal component analysis (PCA) and hierarchical cluster analysis (HCA) together with hydrochemical graphical plots was applied on 64 groundwater samples. The Q–mode HCA results were used to explain the groundwater quality flow paths where three spatial groundwater zones and water types were delineated. The first type consists of Ca–Mg–HCO 3 freshwater (recharge zone), which transitions into Ca–Na–HCO 3 or Na–Ca–HCO 3 mixed waters (intermediate zone) and finally evolve to the third type of Na–Ca–Mg–HCO 3 –Cl water (discharge zone). The study also reveals that the natural process influencing water chemistry is groundwater–rock interaction from carbonate and silicate weathering/dissolution, aided by carbonic acid from precipitation and releases concentration of Na ⁺ , Ca ²⁺ , Mg ²⁺ and HCO 3 ⁻ into the groundwaters significantly. The chloro-alkaline indices also reveal cation exchange as the principal natural factors that control groundwater chemistry in the area. Anthropogenic activities have little influence on groundwater chemistry. The quality of groundwater in the Bosome Freho District and Bekwai Municipality are suitable for irrigational use and drinking water consumption. The results obtained so far will contribute to research paucity in the study area and serve as a guide for decision-makers for improved water resources management.
... In Estonia, this aquifer constitutes an important and often the only source of potable water (i.e. 85 % of the total and 33 % of domestic groundwater consumption) (Perens & Vallner 1997;Karro et al. 2009;Olesk 2016). The 30 m (or in rare occasions up to 75 m) thick top section of the flat-lying carbonate bedrock is usually fractured and karstified (Heinsalu 1977;Perens & Vallner 1997;Karst ja allikad Pandiveres 2002). ...
As karst aquifers are often characterised by non-linear behaviour, ascertaining the turning points in their hydraulic regime may provide essential information on the functioning of the aquifer. These characteristics also apply to the Silurian-Ordovician aquifer system, composed of diverse carbonate rocks, in Estonia. The aquifer system is an important source of drinking water in northern Estonia. It also comprises the Nabala- Rakvere aquifer, a locally important groundwater resource that underlies the Tuhala karst area famous for an intermittently overflowing karst spring known as the Witch's Well. The water rich in humic substances of the Tuhala River recharges the Tuhala karst system, which is drained by two spring groups. In order to develop measures for the sustainable management of the aquifer in the future, the aim of this study was to enhance understanding of the hydraulic behaviour and hydrodynamic properties of the Tuhala karst system. From October 2014 to December 2016 an extensive field campaign was carried out comprising the observation of 22 surface- and groundwater monitoring points for water level and physico-chemical parameters and the performance of four quantitative tracer tests. The data obtained were evaluated in accordance with the input– output water level relation curves and a conceptual model of the system was set up. The results show that a strong hydraulic link exists, primarily through well-developed conduits between the recharge and discharge area of the karst system. Depending on the hydrological conditions, groundwater flow direc tions vary and maximum linear flow velocities range between ~225 and 800 m/h. A threshold-controlled throughput capacity and interaction with the adjacent aquifer cause imbalances between the input and output discharges of the karst system. Tracer tests coupled with surface and groundwater level relation curve analysis allowed the specification of flow threshold conditions for the Witch's Well spring group and the overflow threshold for the Witch's Well, among other key hydrological events. The hydraulic regime of the karst system was divided into three stages, each with differing threshold controls and hydrodynamic characteristics.
Key words: karst system, shallow carbonate aquifer, monitoring, tracer test, water level relation curve, threshold, overflow.
Določanje mejnih vrednosti tristopenjskega hidravljičnega obnašanja pokritega plitvega karbonatnega vodonosnika (Tuhalski kras, severna Estonija)
Kraški vodonosniki se pogosto obnašajo nelinearno, zato lahko z ugotavljanjem mejnih vrednosti v hidravličnem režimu zagotovimo bistvene informacije o delovanju vodonosnika. To velja tudi za silurijsko-ordovicijski vodonosni sistem v Estoniji, ki ga sestavljajo različne karbonatne kamnine in je pomemben vir pitne vode na severu države. Vključuje tudi vodonosnik Nabala- Rakvere, ki je lokalno pomemben vodni vir. Na tem območju se nahaja Tuhalski kras, ki je znan po občasno bruhajočem kraškem izviru Witch's Well (Čarovničin vodnjak). Tuhalski vodonosnik napaja reka Tuhala, bogata z huminskimi snovmi, prazni pa se skozi dve skupini izvirov. Da bi v prihodnje razvili ukrepe za trajnostno upravljanje vodonosnika, je bil namen te raziskave izboljšati razumevanje hidravličnega obnašanja in hidrodinamičnih lastnosti kraškega sistema. Od oktobra 2014 do decembra 2016 smo opravili obsežno terensko delo, ki je obsegalo spremljanje vodostajev in fizikalno-kemijskih parametrov v 23 površinskih in podzemnih točkah ter izvedbo štirih kvantitativnih sledilnih poskusov. Pridobljene podatke smo ovrednotili na podlagi krivulje odvisnosti vhodnih in izhodnih vodnih nivojev. Vzpostavili smo konceptualni model sistema. Rezultati kažejo na obstoj močne hidravlične povezave predvsem z dobro razvitimi kanali med območji napajanja in praznjenja kraškega sistema. Odvisno od hidroloških razmer se spreminjajo smeri in hitrosti toka podzemne vode, ki znašajo od ~225 do 800 m/h. Kapaciteta prepustnosti, ki jo uravnavajo določene mejne vrednosti, in posledične in terakcije s sosednjimi vodonosniki povzročajo neravnovesja med vhodnimi in izhodnimi pretočnimi vrednostmi kraškega sistema. Združevanje rezultatov sledilnih poskusov z analizo krivulje odvisnosti površinskih in podzemnih vodostajev nam je omogočilo, da smo določili mejne pretočne vrednosti izvira Witch's Well in druge ključne hidrološke dogodke. Hidravlični režim kraškega sistema smo razdelili na tri faze, od katerih ima vsaka določene mejne vrednosti in hidrodinamične lastnosti.
Ključne besede: kraški sistem, plitvi karbonatni vodonosnik, monitoring, sledilni poskus, krivulja odvisnosti vodnih nivojev, prag, preliv.
... In Estonia elevated levels of fluoride (up to 7 mg/L) are found in the Silurian-Ordovician aquifer system, which is an important and often the only source of drinking water in central and western Estonia. The dissolution of fluorides from carbonate rocks and clayey K-bentonite beds is the natural source of fluoride [6,7]. ...
... The high levels of fluoride in groundwater originate from geogenic sources [4,5,7]. The hydro-geochemical studies of groundwater make it possible to delimit the fluoride anomaly (up to 7.2 mg/L) in western Estonia. ...
Fluoride is a naturally occurring contaminant in groundwater in Estonia. There are several regions in Estonia with fluoride contents in public water supplies as high as 7 mg/L. Long-term exposure to high-fluoride drinking water may have several adverse health effects, primarily dental fluorosis. The opportunities for exposure reduction rely highly on water treatment technologies. Since 2004 public water suppliers in Estonia have made efforts to diminish fluoride content in drinking water systems. A follow-up study on a country level was carried out in 2004-2012 to analyze the changes in population exposure to excessive (over 1.5 mg/L) fluoride in drinking water and to get information about the reduction methods applied by public water supplies (PWS) to optimize the fluoride levels in public water system. The results showed that bigger PWS have been more effective in fluoride reduction measures than small PWS. The main methods used to lower the fluoride content were reverse osmosis technology and replacement of water sources with new ones (new drilled wells). As a result of all the measures taken the overall high-fluoride exposure has been reduced substantially (82%).
... According to the European Union drinking water directive (Council Directive 98/83/EC, 1998 ), the permissible limits for F – and B are 1.5 mg/l and 1 mg/l, respectively . Excessive concentrations of these elements are frequently encountered in western Estonia, where a carbonate Silurian–Ordovician aquifer system is the most prominent drinking water source (Karro et al., 2006Karro et al., , 2009; Karro and Uppin, 2013). The natural concentrations of B and F – in western Estonian groundwater reach up to 2.1 and 6.1 mg/l, respectively. ...
High natural fluoride (up to 6.1 mg/l) and boron (up to 2.1 mg/l) concentrations in groundwater are recorded in western Estonia, where a carbonaceous Silurian Ordovician aquifer system is the main source of drinking water. The aim of this study is to examine the dissolution of boron and fluoride from different carbonate rocks using batch dissolution tests. The total boron and fluorine concentration within carbonate rocks varies between 100-1000 and 5-150 mg/kg, respectively. Generally, boron and fluoride concentrations increase as the amount of terrigenous material in the rock increases. Laboratory leaching experiments showed that the amount of leached boron and fluoride was proportional to the content of these elements in the rock samples. Further, boron and fluoride concentrations in leachates were positively correlated with the amount of terrigenous material in rocks. Both boron and fluoride concentrations in leachates continually rose over 49 days of leaching. Long-term water-rock interaction is responsible for the high boron and fluoride contents in groundwater of western Estonia.
... In the passive exchange zone HCO 3 -Cl-Na-Mg-Ca water is more widespread, but HCO 3 -Ca-Mg type can also be found (Karise, 1997). The exception to that occurs in the Cambrian-Vendian aquifer system, where the water, which recharged during the Quaternary glaciation, has variations in water type from Cl-Na to Cl-HCO 3 -Ca-Na (Karro et al., 2009). Sulfate type waters can only be found in one aquifer in the passive exchange zone where gypsum is present, forming a SO 4 -Cl-Ca-Na type water. ...
The concentrations of dissolved cations and anions are fundamental to the water quality of groundwaters, particularily pertaining to their use as a drinking water source. Currently, assessment of total dissolved solids requires laboratory-based analysis of each ionic species, and cannot be reliably tested in the field. Here, a new method is developed that distinguishes between changes in ion concentration or water type based upon field measurement of Electric Conductivity (EC) and the concentration of only one anion. The approach operates under the assumption that all cations contribute equally to EC, whereas almost twice as much of the HCO3- ion is needed to produce the same effect on total solute EC as those of Cl- or SO42- ions for waters at neutral pH. Therefore, many groundwater systems can be treated as two anion systems when the groundwater chemical type and solute EC relationship is assessed. Moreover, by assuming neutral charge and that the correlation between anion concentration and EC is adequately described, changes to anion concentrations will produce corresponding change to cation concentrations. A database consisting of 3555 analyses of major chemical composition from Estonian groundwaters was used to develop the correlations described here, and data for 320 samples with measured EC values together with major chemical constituents was used to verify the new method. As a result, a binary plot has been compiled which can be used: (1) for prediction of chemical composition of groundwater if analytical results of Cl-or HCO3-from anions and measured values of EC are available, or (2) for description of temporal changes in groundwater chemistry if the time series of the same measurements are available.
... Thus, the occurrence of fluorides and boron in groundwater is necessary to be studied due to their considerable impact on human physiology. According to previous studies, elevated fluoride concentrations in Estonian groundwater prevail in western part of the country, where carbonate Silurian–Ordovician (S–O) aquifer system is the most important drinking water source (Indermitte et al. 2006; Karro et al. 2006 Karro et al. , 2009). So far, boron content in groundwater has been examined very scantily in Estonia. ...
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 HCO(3)-Cl-Na-Mg-Ca, water is alkaline, and its Ca(2+) 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 + HCO(3)) 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.
... In some areas, due to the geological conditions, groundwater chemistry does not meet the quality standards set for drinking water. Primarily natural radionuclide, fluorine, boron and iron concentrations are high (Saava 1998; Karro et al. 2009; Karro & Uppin 2010; Forte et al. 2010). The quality of drinking water is a powerful environmental determinant of health, thus it should have good chemical properties. ...
Groundwater abstracted from the Middle Devonian aquifer system is the main source of drinking water in South Estonia. High iron and manganese concentrations in groundwater are the greatest problems in this region. The total iron concentrations up to 16 mg L –1 are mainly caused by a high Fe 2+ content in water, pointing to the dominance of reducing conditions in the aquifer system. A pilot study was carried out to estimate the effectiveness of 20 groundwater purification plants with eight different water treatment systems (aeration combined with Manganese Greensand, Birm, Nevtraco, Hydrolit-Mn, Magno-Dol and quartz sand filters) in Võru County. The results demonstrate that in most cases the systems with pre-aeration effectively purify groundwater from iron, but only 13 out of 20 water treatment plants achieved a reduction of iron concentration to the level fixed in drinking water requirements (0.2 mg L –1). Manganese content decreased below the maximum allowed concentration in only 25% of systems and in cases where the filter media was Birm or quartz sand and pre-oxidation was applied. The study showed that the high level of iron purification does not guarantee effective removal of manganese.
... Silurian–Ordovician (S–O) aquifer system provides 30% of Estonian public water supply, being the most important drinking water source in central and western Estonia. Previous hydrochemical studies have shown that high fluoride and boron values in S–O aquifer system are mostly present in western Estonia (Karro et al. 2006Karro et al. , 2009 Karro and Uppin 2010). The natural concentrations on boron and fluorides in groundwater reach up to 2.1 and 7.2 mg/l, respectively. ...
... A positive correlation between dissolved fluoride, boron and pH has been observed in Estonian groundwater (Karro and Rosentau 2005; Karro et al. 2006), thus, it can be assumed that both fluorine and boron have similar origin and undergo similar geochemical reactions in S–O aquifer system of Estonia. Previous groundwater studies have shown that high fluoride (up to 7.2 mg/l) and boron (2.1 mg/l) concentrations are widespread in western Estonia (Karro and Rosentau 2005; Karro et al. 2006 Karro et al. , 2009 Karro and Uppin 2010 ). Groundwater in S–O aquifer system is mainly HCO 3 –Ca–Mg type and owing to the high Ca 2? contents, quite low amounts of F -may be mobilised. ...
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.
... Interestingly, a particularly low Na + concentration is observed in the crystalline basement in north-western Estonia. Here the Ca 2+ concentration measured in eq/l can exceed Na + concentration by up to two times (Karro et al., 2004), while the TDS is only 2-22 g/l (Raukas and Teedumäe, 1997). Such a low Na + content in respect to Clis not observed even in the deepest parts of the basin in Latvia and Lithuania. ...
... Intensive water abstraction in the Kopli Peninsula, Tallinn, has led to up flow of saline water from the crystalline basement (Karro et al., 2004) as well compromising the water quality. ...
The chemical composition of groundwater is the result of long term interaction between rocks and water complicated by the continuous addition of infiltration water and mixing due to dispersion along flow-lines and diffusion. Thus the geological structure determining groundwater flow and rock composition itself controls the trends of groundwater chemical evolution. A list of the factors that directly affect the composition of the groundwater within the Baltic Artesian Basin can be drawn: (1) the composition of precipitation and infiltration water as a starting point for the chemical evolution and the almost immediate weathering of carbonate minerals in reactions with carbon dioxide derived from the atmosphere and soil; (2) oxidation- reduction systems controlled by the presence of dissolved oxygen and organic matter in a dissolved or solid state that affect the mobilisation of the reduced forms of sulphur, iron and manganese in the groundwater; (3) the dissolution of gypsum and halite found in some parts of the basin adds calcium, magnesium, sulphate sodium and chlorine ions to the solution; (4) the presence of formation brines and the evolution of their composition during geological time and (5) anthropogenic influences that can range from changing flow patterns in areas of intensive water abstraction to the changing composition of infiltration water in agricultural and urban territories.
