Ugotavljanje izvornih mest večtočkovnih onesnaženj s šestvalentnim kromom v visoko izdatnem medzrnskem vodonosniku : doktorska disertacija

Svetina, Janja (author), Brenčič, Mihael (mentor)

Onesnaženje podzemne vode iz več točkovnih virov se pogosto odraža v razpršenih in neenakomerno porazdeljenih koncentracijah, kar otežuje iskanje izvorov onesnaženja, zlasti kadar rezultati vzorčenja niso popolnoma zanesljivi. Prvi del raziskav je bil osredotočen na izboljšanje znanstvenih spoznanj in razumevanja značilnosti in spremenljivosti tokov v vrtinah. Rezultati karotažnih meritev na območju Ljubljanskega polja so pokazali, da navpični hidravlični gradienti niso omejeni na zapletene vodonosne sisteme, ampak se lahko pojavijo tudi v debelih aluvialnih vodonosnikih brez zveznih neprepustnih plasti. Na smer in hitrost teh tokov močno vplivajo položaj in dolžina filtrskih odsekov ter morfologija kamninske podlage. Rezulati numeričnega modeliranja so pokazali, da so lahko hitrosti toka vode v vrtinah do 4 velikostne razrede višje od navpične komponente hitrosti toka podzemne vode v vodonosniku. Pretoki v vrtinah so lahko tudi znatno višji od običajnih pretokov črpanja pri vzorčenju, kar vpliva na reprezentativnost vzorčenja. S sistemom dvojnega pakerja je bilo na primeru šestvalentnega kroma [Cr(VI)] dokazano, da lahko izmerjene koncentracije odstopajo od realne vrednosti tudi za 10-15 µg/l. Drugi del raziskave je bil osredotočen na prostorsko interpretacijo onesnaženja s Cr(VI) v vodonosniku Ljubljanskega polja. Na podlagi sektorskega vzorčenja in analize sledenja delcev v numeričnem modelu je bilo ugotovljeno, da prihaja do značilnih razlik v porazdelitvi Cr(VI) po globini vodonosnika, kar lahko povezujemo z različnimi izvori. V vodonosniku se prepletajo ostanki starega onesnaženja iz 80. let in vplivi potencialno še aktivnih virov. Na podlagi dolgoročnih trendov je bil s pomočjo analitičnega modela zadrževalni koeficient Cr(VI) v obsežnem in dobro prepustem medzrnskem vodonosniku ocenjen na 9,5 s koeficientom sorpcije med 1,06-1,33 l/kg. Grobe ocene potencialnih lokacij še aktivnih virov so bile izdelane v treh značilnih vzdolžnih prerezih.

• Language: English
• Keywords: podzemna voda, industrijsko onesnaženje, tokovi v vrtinah, reprezentativnost vzorcev, šestvalentni krom, analitično modeliranje, numerično modeliranje
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FGG - Faculty of Civil and Geodetic Engineering; NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: J. Svetina
• Year: 2025
• Number of pages: XXVI, 166 str., A-1-H-2
• PID: 20.500.12556/RUL-170222
• UDC: 55
• COBISS.SI-ID: 241249283
• Publication date in RUL: 02.07.2025

Secondary language

• Language: Slovenian
• Title: Identification of hexavalent chromium multipoint pollution sources in a highly productive intergranular aquifer : doctoral dissertation

Abstract

Groundwater pollution from multiple point sources is often characterised by scattered and unevenly distributed concentrations, which makes source identification more difficult, especially when sampling results are not entirely reliable. The first part of the research focussed on improving scientific knowledge and understanding of characteristics and variability of intraborehole flows (IBFs). The results of borehole logging in the Ljubljansko polje aquifer showed that vertical hydraulic gradients are not limited to complex aquifer systems, but can also occur in thick alluvial aquifers without continuous aquitard layers. Direction and velocity of these flows are strongly influenced by the position and length of the screen sections and the morphology of the bedrock. Numerical modelling has shown that velocities of IBFs can be up to 4 orders of magnitude higher than the vertical component of groundwater flow velocity in the aquifer. Ambient IBFs can also be significantly higher than conventional pumping rates during sampling, which affects the representativeness of sampling. Using a double packer system, the example of hexavalent chromium [Cr(VI)] showed that measured concentrations can deviate by 10-15 µg/l from the actual value. The second part of the research focussed on the spatial interpretation of Cr(VI) contamination in the Ljubljansko polje aquifer. Based on depth-discrete sampling and particle tracking in a numerical model, it was found that there are characteristic differences in the distribution of Cr(VI) along the depth of the aquifer that can be associated with different sources. The aquifer is intertwined with remnants of old contamination from the 1980s and the effects of potentially still active sources. Based on long-term trends, the Cr(VI) retardation factor in the extensive and well-permeable intergranular aquifer was estimated by analytical modelling to be 9.5 with a partition coefficient between 1.06-1.33 l/kg. Rough estimates of the potential locations of still active sources were made in three characteristic longitudinal cross-sections.

• Keywords: groundwater, industrial pollution, intraborehole flows, representativeness of samples, hexavalent chromium, analytical modelling, numerical modelling