Groundwater pumped from the terrigenous Middle Devonian (D2) aquifer system is naturally rich in iron (Fe), making it a challenge to fulfil the requirements for drinking water quality. The total iron (Fetot) concentrations are above the limit value set for drinking water (0.2 mg/L) in 81% of the analysed water samples. The highest Fetot values reach up to 26 mg/L in some locations of southern Estonia. Due to the reducing conditions in the aquifer system, most of the Fetotconcentrations are caused by a high Fe2+ content. Infiltrated aerobic water becomes anaerobic and Fe3+ reducing along a deep flow path, leading to the downgradient increase in dissolved Fe concentrations. In order to study the natural sources of Fe in the Middle Devonian aquifer system, rock samples from the Narva, Aruküla, Burtnieki and Gauja stages were used for chemical analyses and leaching experiments. The whole-rock chemical analyses showed large variation in the Fe2O3 content (1.20–9.91%), whereas the values were higher in aquifer-forming siltstones than in sandstones. The amount of the leached Fe in groundwater is partly controlled by the granulometric composition of terrigenous rocks. The highest leached Fetot (up to 1.7 mg/L) concentrations were detected in the rocks where the share of the sand fraction is over 70%. As a rule, water is abstracted from sandstones having large pores and good groundwater yield, therefore water quality problems could only be solved by installing Fe removal facilities in southern Estonia.
Appelo, C. A. J. & Postma, D. 2005. Geochemistry, Groundwater and Pollution. Balkema, Rotterdam, 649 pp.
https://doi.org/10.1201/9781439833544
Brown, C. J., Schoonen, M. A. A. & Candela, J. L. 2000. Geochemical modeling of iron, sulfur, oxygen and carbon in a coastal plain aquifer. Journal of Hydrology, 237, 147–168.
https://doi.org/10.1016/S0022-1694(00)00296-1
Bun-ei, R., Kawasaki, N., Ogata, F., Nakamura, T., Aochi, K. & Tanada, S. 2006. Removal of lead and iron ions by vegetable biomass in drinking water. Journal of Oleo Science, 55, 423–427.
https://doi.org/10.5650/jos.55.423
Drever, J. I. 1997. The Geochemistry of Natural Waters: Surface and Groundwater Environments. Prentice-Hall, Upper Saddle River, 436 pp.
Edmunds, W. M., Miles, D. L. & Cook, J. M. 1984. A comparative study of sequential redox processes in three British aquifers. In Hydrochemical Balances of Freshwater Systems (Eriksson, E., ed.), IAHS Publication, 150, 55–70.
Elmore, R. D., London, D., Bagley, D. & Fruit, D. 1993. Remagnetization by basinal fluids: testing the hypothesis in the Viola limestone, Southern Oklahoma. Journal of Geophysical Research, 98, 6237–6254.
https://doi.org/10.1029/92JB02577
European Communities. 1998. Council directive 98/83/EC – on the quality of water intended for human consumption. Official Journal of the European Communities, L 330, 05/12/1998, 0032–0054.
Forte, M., Bagnato, L., Caldognetto, E., Risica, S., Trotti, F. & Rusconi, R. 2010. Radium isotopes in Estonian groundwater: measurements, analytical correlations, population dose and a proposal for a monitoring strategy. Journal of Radiological Protection, 30, 761–780.
https://doi.org/10.1088/0952-4746/30/4/009
Funkt, J. A., von Dodeneck, T. & Reitz, A. 2004. Integrated rock magnetic and geochemical quantification of redoxomorphic iron mineral diagenesis in Late Quaternary sediments from equatorial Atlantic. In The South Atlantic in the Late Quaternary: Reconstruction of Material Budgets and Current Systems (Wefer, G., Multitza, S. & Ratmeyer, V., eds), pp. 237–260. Springer-Verlag, Berlin.
https://doi.org/10.1007/978-3-642-18917-3_12
Heiri, O., Lotter, A. F. & Lemcke, G. 2001. Loss on ignition as a method for estimating organic and carbonate content in sediments: reproducibility and comparability of results. Journal of Paleolimnology, 25, 101–110.
https://doi.org/10.1023/A:1008119611481
Hem, J. 1985. Study and Interpretation of the Chemical Characteristics of Natural Waters. U. S. Geological Survey Water-Supply Paper 2254.
Hiiob, M. & Karro, E. 2012. Iron in the Middle Devonian aquifer system and its removal at Võru County water treatment plants, Estonia. Estonian Journal of Earth Sciences, 61, 181–190.
https://doi.org/10.3176/earth.2012.3.04
Kabata-Pendias, A. 2001. Trace Elements in Soils and Plants. CRC Press, Boca Raton, 403 pp.
https://doi.org/10.1201/9781420039900
Karro, E. 2019. The dynamics of groundwater use, water abstraction charges and water tariffs in Estonia. In 19th International Multidisciplinary Scientific GeoConference SGEM 2019, Water Resources. Forest, Marine and Ocean Ecosystems, pp. 561−568. STEF92 Technology Ltd, Albena.
https://doi.org/10.5593/sgem2019/3.1/S12.072
Karro, E. & Uppin, M. 2013. The occurrence and hydrochemistry of fluoride and boron in carbonate aquifer system, central and western Estonia.Environmental Monitoring and Assessment, 185, 3735–3748.
https://doi.org/10.1007/s10661-012-2824-5
KESE. 2020. Environmental monitoring information system. Estonian Environment Agency [https://kese.envir.ee/kese/ welcome.action].
Kleesment, A. 1994. Subdivision of the Aruküla Stage on the basis of the lithological and mineralogical criteria. Proceedings of the Estonian Academy of Sciences, Geology, 43, 57–68.
Kleesment, A. 1995. Lithological characteristics of the uppermost terrigenous Devonian complex in Estonia. Proceedings of the Estonian Academy of Sciences, Geology, 44, 221–233.
Kleesment, A. & Mark-Kurik, E. 1997. Middle Devonian. In Geology and Mineral Resources of Estonia (Raukas, A. & Teedumäe, A., eds), pp. 112–121. Estonian Academy Publishers, Tallinn.
Marandi, A. 2010. Groundwater in Estonia and Tallinn. In Geology of Tallinn (Soesoo, A. & Aaloe, A., eds), pp. 40–55. Tallinna Raamatutrükikoda, Tallinn.
Mark-Kurik, E. & Põldvere, A. 2012. Devonian stratigraphy in Estonia: current state and problems. Estonian Journal of Earth Sciences, 61, 33–47.
https://doi.org/10.3176/earth.2012.1.03
Ministry of Social Affairs. 2001. Joogivee kvaliteedi- ja kontrollinõuded ning analüüsimeetodid [The quality and monitoring requirements for drinking water and methods of analysis]. Riigi Teataja, RTL 2001/100/1369 [in Estonian].
Mokrik, R., Karro, E., Savitskaja, L. & Drevaliene, G. 2009. The origin of barium in the Cambrian–Vendian aquifer system, North Estonia. Estonian Journal of Earth Sciences, 58, 193–208.
https://doi.org/10.3176/earth.2009.3.04
Mücke, A. 1994. Postdiagenetic ferruginization of sedimentary rocks (sandstones, oolitic ironstones, kaolins and bauxites) – including a comparative study of the reddening of red beds. In Diagenesis IV, Developments in Sedimentology (Wolf, K. H. & Chilingarian, G. V., eds), pp. 361−395. Elsevier, Amsterdam.
https://doi.org/10.1016/S0070-4571(08)70444-8
Passier, H. F., de Lange, G. J. & Dekkers, M. J. 2001. Magnetic properties and geochemistry of the active oxidation front and the youngest sapropel in the eastern Mediterranean Sea. Geophysical Journal International, 145, 604–614.
https://doi.org/10.1046/j.0956-540x.2001.01394.x
Perens, R. & Vallner, L. 1997. Water-bearing formation. In Geology and Mineral Resources of Estonia (Raukas, A. & Teedumäe, A., eds), pp. 137–145. Estonian Academy Publishers, Tallinn.
Perens, R., Savva, V., Lelgus, M. & Parm, T. 2001. The Hydrogeochemical Atlas of Estonia (CD version). Geological Survey of Estonia, Tallinn.
Ponka, P., Tenenbein, M. & Eaton, J. 2007. Iron. In Handbook on the Toxicology of Metals (Nordberg, G. F., Fowler, B. A., Nordberg, M. & Friberg, L. T., eds), pp. 577–598. Elsevier, Amsterdam.
https://doi.org/10.1016/B978-012369413-3/50085-9
Raukas, A. & Teedumäe, A. 1997. Geology and Mineral Resources of Estonia. Estonian Academy Publishers, Tallinn, 436 pp.
Rehema, A., Zilmer, M., Zilmer, K., Kullisaar, T. & Vihalemm, T. 1998. Could long-term alimentary iron overload have an impact on the parameters of oxidative stress? A study on the basis of a village in South Estonia. Annals of Nutrition & Metabolism, 42, 40–43.
https://doi.org/10.1159/000012716
SARV. 2020. Geoscience collections and data repository. [http://geokogud.info/].
Savitskaja, L., Viigand, A. & Jaštšuk, S. 1996a. Ülem-Keskdevoni veekompleksi põhjavee kvaliteedi uurimistöö [Groundwater Quality in the Upper-Middle Devonian Aquifer System]. Eesti Geoloogiakeskus, Tallinn, 42 pp. [in Estonian].
Savitskaja, L., Viigand, A. & Jaštšuk, S. 1996b. Keskdevoni-siluri veekompleksi põhjavee kvaliteedi uurimistöö [Groundwater Quality in the Middle Devonian–Silurian Aquifer System]. Eesti Geoloogiakeskus, Tallinn, 47 pp. [in Estonian].
Shogenova, A. 1999. The influence of dolomitization on the magnetic properties of Lower Palaeozoic carbonate rocks in Estonia. In Palaeomagnetism and Diagenesis in Sediments (Tarling, D. H. & Turner, P., eds), pp. 167–180. Geological Society, London.
https://doi.org/10.1144/GSL.SP.1999.151.01.17
Shogenova, A. & Kleesment, A. 2006. Diagenetic influences on iron-bearing minerals in Devonian carbonate and siliciclastic rocks of Estonia. Proceedings of the Estonian Academy of Sciences, Geology, 55, 269–295.
Shogenova, A., Kleesment, A., Hirt, A., Pirrus, E., Kallaste, T., Shogenov, K. & Vaher, R. 2009. Composition and properties of the iron hydroxides – cemented lenses in Estonian sandstone of Middle Devonian age. Studia Geophysica et Geodaetica, 53, 111–131.
https://doi.org/10.1007/s11200-009-0007-9
Xu, L., Luo, K., Feng, F. & Tan, J. 2006. Studies on the chemical mobility of fluorine in rocks. Fluoride, 39, 145–151.
Zwing, A., Matzka, J., Bachtadse, V. & Soffel, H. C. 2005. Rock magnetic properties of the remagnetized Palaeozoic clastic and carbonate rocks from the NE Rhenish massif, Germany. Geophysical Journal International, 160, 477–486.
https://doi.org/10.1111/j.1365-246X.2004.02493.x
