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, HCO3 -, Cl- and SO4 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 sulphateenriched waters (suggesting hydrothermalism) or chlorinerich waters. Principal component analysis (PCA) allowed the extraction of seven factors, which describe, respectively: water–rock interaction mainly on dolomitic rocks; redox conditions of water; Cd–Zn enrichment in chlorinerich waters (probably from industrial wastes); hydrothermal 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 CO2 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 (HCO3 -) 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.