engleski

Residence-time of groundwater from flysch formation at the Grohovo Landslide in the Rječina valley, Croatia

Chlorofluorocarbons (CFCs) are useful tracers for age dating of young ground water and spring water. However, the dating groundwater using CFCs is a minor approach in the landslide researches. The CFCs concentrations of two ground waters from the observation wells of W-1 and W-3 in the foot part of Grohovo landslide in the Rjecina valley, Croatia were measured in order to better understand the groundwater behavior in the landslide mass. Both ground water samples have detectable concentrations of CFC-12 (186-259pg/kg), CFC-11 (191-384 pg/kg) and CFC-113 (12-20 pg/kg), suggesting that these were mainly recharged after the 1970s. These CFCs concentrations under the oxidative environment usually indicate a simple relationship showing CFC-11>CFC-12>CFC-113, CFC-11 is approximately two times larger than CFC-12, reflected by the concentration of atmospheric CFCs and solubility of CFCs. However, CFC-11 and CFC-12 concentrations in each sample are relatively close to each other’s value. Under the reductive environment, some kind of bacteria can break out CFC-11 and CFC-113 so that both CFC-11 and CFC-113 were reduced during the ground water circulation. Therefore, we accepted the data of CFC-12 concentration for age dating of ground waters. Assuming that the average temperature and altitude of recharge area are 11°C and 400 m a.s.l, the groundwater ages of W-1 and W-3 are calculated in comparison of equivalent air concentrations (EAC) of the groundwaters with the historical atmospheric concentrations. Apparent ages of waters from W-1 and W-3 are respectively 31 and 24 years old based on the piston flow model (PFM). Other ages of W-1 and W- 3 are respectively 38 and 19 years old estimated by the exponential mixed model (EMM). Both ground waters are hydrochemically characterized by Na-SO4 type because ground waters migrate through the Na2SO4-rich flysch formation. Both Na and SO4 in water from W-3 is less concentration than those of the older water from W-1 because of dilution with much younger Ca-HCO3 type water in the overlain limestone formation.

grounwater; concentration; chlorofluorocarbons

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