Ocena ranljivosti urbanega vodonosnika na osnovi okoljskih sledil

Groundwater from a Pleistocene sandy-gravel aquifer is a drinking water resource for the Union brewery, located near the centre of Ljubljana (Slovenia). A large part of the aquifer recharge area is highly urbanized, which represents a great risk for the groundwater quality assurance. The groundwater dating techniques were used to study the contamination risk of this drinking-water resource. The application of chlorofluorocarbons (CFCs), sulphur hexafluoride (SF6) and tritium-helium-3 (3H-3He) age indicator was tested, as they haven’t been used in Slovene urban areas so far. The results reflect that the 3H-3He dating technique is the most suitable for a groundwater age determination in the study urban aquifer, since SF6 and particularly CFCs concentrations could be affected by the local contaminations. They indicated that average groundwater residence times range from 10 to 30 years. Boreholes that are more distant from the Šišenski hrib hill are more vulnerable to contamination due to flow of young groundwater from a direction of the main aquifer, which is exposed to the urban pollution. The presented results were supplemented with chemical investigations of groundwater organic pollutants. An unknown trace organic pollutant with a base ion mass-to-charge ratio 147 was put into focus. Its identification based on chromatographic separation and a mass spectrometric detection with GC-MS, LC-MS and LC-TOF MS techniques. The newly detected trace organic pollutant in sampled groundwater represents together with the 3H and 3He data a new technique to study the flow paths and contaminant transport in the urban aquifer in both, the lateral and vertical directions.Podzemna voda pleistocenskega peščeno-prodnega vodonosnika je vir pitne vode Pivovarne Union, v neposredni bližini centra Ljubljane. Velik del napajalnega območja vodonosnika je urbaniziran, kar lahko ogroža kvaliteto pitne vode. Tveganje onesnaženja obravnavanega vira pitne vode se je proučevalo s pomočjo tehnik za določanje starosti podzemne vode. V ta namen se je prvič v slovenskih urbanih območjih testirala uporaba sledila 3H-3He, CFCs in SF6. Razultati so pokazali, da je za določanje starosti podzemne vode v proučevanem urbanem vodonosniku najbolj uporabna 3H-3He tehnika, saj na koncentracije SF6 , zlasti pa CFC, vpliva lokalno onesnaženje. S pomočjo omenjene tehnike je ugotovljeno, da je povprečna starost podzemne vode raziskovanega območja med 10 in 30 let. Bolj ko so vrtine oddaljene od Šišenskega hriba, bolj so ranljive na onesnaženje, ker so pod vplivom dotoka mlade vode s centralnega območja vodonosnika, ki je izpostavljeno urbanemu onesnaženju. Kemijske raziskave organskih onesnaževal v podzemni vodi dopolnjujejo predstavljene rezultate. Le te slonijo na nepoznanem slednem organskem onesnaževalu z osnovnim ionom, v katerem je razmerje med maso in električnim nabojem 147. Omenjena spojina se je odkrila s pomočjo kromatografske separacije in različnimi sklopljenimi tehnikami – plinsko kromatografijio z masno spektrometrijo (GC-MS), tekočinsko kromatografijo z masno spektrometrijo (LC-MS) in tekočinsko kromatografijo z masno spektrometrijo na čas preleta ionov (LC-TOF MS). Odkrito sledno organsko onesnaževalo predstavlja, skupaj s 3H in 3He podatki, novo tehniko za proučevanje toka podzemne vode in prenosa onesnaženja v urbanem vodonosniku, tako v lateralni kot v vertikalni smeri