engleski

Hydrochemical characteristics of groundwater from the Kostanjek Landslide in Croatia

Field investigation was carried out to collect groundwater samples from the Kostanjek area in order to better understand groundwater behavior in the Kostanjek landslide using hydrochemical data as tracers. Based on the 71 samples’ hydrochemical data of major ions expressed as meq/L, ground waters are classified into four types: (1) Ca-HCO3 type ; (2) SO4-rich Ca-HCO3 type (0.28<SO4/HCO3<0.40) ; (3) Mg-rich HCO3 type (0.19<Mg/Ca<0.55) ; (4) Cl-rich type (>100mg/L). Ca-HCO3 type waters predominate over the research area and are closely related to the bedrock geology in this area composed of calcareous strata such as limestone and several types of marls. SO4-rich Ca-HCO3 type waters of eight samples are scatted in the northern part and southwestern part of the research area, and are formed by the contamination of Ca-SO4 component originated from gypsum included in the calcareous strata. Mg-rich HCO3 type waters of eight samples are limitedly distributed in the northernmost part, behind the head of landslide, eastern part and southeastern part, in front of the landslide, of the research area and are influenced by dolomite or Mg-rich limestone as the source of solute. Cl-rich type waters are scattered in village in the northern part and western part of the research area, and the possible source of Cl is anthropogenic impact. Here we pay attention to the origin of Mg-rich HCO3 type waters, because there is no dolomite or Mg-rich limestone as the source of solute in this area. On the other hand, the massive dolomite is distributed in more than 1000 m north away from the Kostanjek area and also underlies in more than 200 m depth beneath the Kostanjek landslide mass. Actually, Mg-rich HCO3 type waters are found in a stream near the Kostanjek area flowing from the massive dolomite and also discharged from fissures in a tunnel bored through the landslide mass. Considering sample locations of each Mg-rich HCO3 type ground waters, these waters are derived from the deepest aquifer in the landslide mass and are probably one of the key factors on the occurrence of landslide. More detail behaviors of ground waters should be explained by additional geochemical data set such as dissolved minor constituents and environmental isotope ratios of 2H/1H, 18O/16O and 87Sr/86Sr in the near future.

Kostanjek landslide; groundwater; hydrochemistry

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