ORIGINAL ARTICLE A case-study of complex gas–water–rock–pollutants interactions in shallow groundwater: S ˇ alek Valley (Slovenia) Salvatore Giammanco Barbara Justin Natalija Speh Marta Veder Received: 8 January 2008 / Accepted: 3 March 2008 / Published online: 4 April 2008 Ó Springer-Verlag 2008 Abstract The complex geochemical interactions in the groundwater of the industrial area of S ˇ alek Valley (Slovenia) between natural and anthropogenic fluids were studied by means of major (Ca, Mg, Na, K, HCO 3 - , Cl - and SO 4 2- ) and trace elements’ (As , Cd, Cu, Pb, Zn, Hg, Se and V) abundances, geochemical classification and statistical analysis of data. Cation abundances indicate mixing between a dolomitic end-member and an evaporitic or geothermal end-member. Anion abundances indicate mixing between bicarbonate waters and either sulphate- enriched waters (suggesting hydrothermalism) or chlorine- rich waters. Principal component analysis (PCA) allowed the extraction of seven factors, which describe, respec- tively: water–rock interaction mainly on dolomitic rocks; redox conditions of water; Cd–Zn enrichment in chlorine- rich waters (probably from industrial wastes); hydrother- mal conditions in waters close to major faults; Pb and Cu pollution; V and K enrichments, indicating their common organic source; the role of partial pressure of CO 2 dissolved in water, which is highest in three wells with bubbling gases. Average underground discharge rates of solutes from the Valley range between 0.09 t/a (V) and 1.8 9 104 t/a (HCO 3 - ) and indicate how natural fluids can significantly contribute to the levels of elements in the environment, in addition to the amount of elements released by human activities. Keywords Groundwater Á Slovenia Á Geothermal systems Á Principal component analysis (PCA) Á Pollution Introduction Geochemical surveys applied to groundwater provide basic information on water quality in areas where little is known of the sources of solutes, and the need for domestic use of groundwater is increasing. Geochemical surveys of groundwater quality are similarly important in areas that suffer strong environmental pollution due to heavy indus- trial development. This is, indeed, the case of the S ˇ alek Valley (S ˇ V), in the northeastern subalpine part of Slovenia (Fig. 1), which is characterized by strong industrial activity spreading large amounts of pollutants. However, S ˇ V is also an area where hot springs are used for health therapy. The major topographical feature of the S ˇ V is its basin form and its forested fringe slopes. The S ˇ V is traversed by a main river, Paka River, which receives water from the many tributaries from both sides of the valley. The shape of the Valley strongly influences air circulation, which is driven mostly by westerly winds. Air motion inside the valley normally impedes local accumulation of pollutants in the atmosphere; most of the industrial emissions, in terms both of gases and of particulates, are carried to nearby areas. Today, the S ˇ V includes three small communities (Fig. 1): Velenje (83 km 2 ), S ˇ osˇtanj (96 km 2 ) and S ˇ martno by Paka (18 km 2 ) (Pavsˇek et al. 2000). Industrialization in the past decades has led to a population increase as well as to a S. Giammanco (&) Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy e-mail: giammanco@ct.ingv.it B. Justin Á N. Speh ERICo Velenje, Environmental Research and Industrial Co-operation Institute, Korosˇka 58, 3320 Velenje, Slovenia M. Veder Kardeljev trg 2, 3320 Velenje, Slovenia 123 Environ Geol (2009) 57:75–89 DOI 10.1007/s00254-008-1283-3