Hazardous Substances in Karst Aquifer Waters - One of the Results of the Operational Monitoring of Groundwater in Serbia

. Hydrogeological survey of wider Majdanpek mining area in the Carpathian mountain arch of eastern Serbia, including open mine pits, tailings sites, and major karstic springs and caves has been undertaken in order to es­ timate environmental conditions in groundwater body (GWB) "Krs-sever", groundwater quality, and to investigate causes of their earlier indicated poor chemical status. Bearing in mind that Majdanpek copper mine field is directly bordering the karst aquifer and delineated GWB "Krs-sever", the two karst springs namely Valja Fundata and Kaludjerica were in situ measured and sam­ pled in high and low water periods (spring 2019, late autumn 2019 and spring 2020). Sampling and analysis of groundwater were carried out under the frame of project "Operational Monitoring of Groundwater of the Republic of Serbia”, established by the Ministry of Environmental Protection of Serbia. The field measurements of unstable chemical components and physical properties as well as laboratory analyses confirmed very poor and even hazardous water quality of both surveyed springs Valja Fundata and Kaludjerica. Registered concentrations of some ions, such as Fe2+, Mn2+, Ca2+, S042_are high above maxi­ mal permitted level for potable water in Serbia. High turbidity rate also con­ firms impact of colloidal suspensions from the tailing which is located in karstic blind valley. Leakage of mine water passes through joints, open cavities and even large cave system Valja Fundata. Results of undertaken survey con­ firm that low-water period results with worse water quality and much higher concentration of hazardous substances than that characterized high-water season when infiltrated rainy water and/or melted snow dilute application of environmental protection measures of the smaller water treatment facility mitigate the impacts of mining activities dependant

water. Strict application of environmental protection measures and de sign/construction of the smaller water treatm ent facility at both surveyed springs should possibly mitigate the impacts of mining activities to karst groundwaterand dependant ecosystem.

Introduction
Mining has a very long history in eastern Serbia.
Traces of extraction of copper minerals, malachite and azurite and early metallurgy at the archaeolog ical site Rudna Glava date back to five millennia B.C.
Although exploitation of copper minerals continued during the Roman and Ottoman Empires, the period that lasted from the middle to the end of the 1 9 th century was m arked by the opening of new and m odern copper mines. One of them, M ajdanpek (meaning: Mine a t R iverPek) is still in active opera tion with two open pit mines and a flotation tailing lake. The main ore resource iscopper, and,to alesser extent, silver and gold.
The geological setting of the Majdanpek ore field ( Fig. 1] is complex. The area belongs to the Carpathian-Balkanides, a geologically heterogeneous and morphologically very dissected orogenic belt of the Alpine system (P e tko vic, 1 9 3 5 ; Grubic, 1 9 7 4 ) . The oldest m etam orphic rocks, gneisses and schists of Pre-Cambrian to Early Paleozoic age are locally in truded by granites (Hercynian orogeny). The big transgression, which started in Middle Jurassic, re sulted in thick carbonate deposits ofmostly Upper Jurassic-Tithonian age ( A n to n ijevic, 1 9 7 9 ). During the period betw een Turonian and Paleogene, a volcanogenic-sedim entary series called Timok Magm atic Complex (TMC) were formed in the eastern part, in a tectonic trough. The TMC is about 85 km long, and up to 25km wide ( B a n jesev ic , 2 0 1 0 ), with the M ajdanpek area in its northernm ost part. A ndesites, pyroclastics and tuffa rocks, followed by rich porphyry-type copper deposits,prevail in this com plex which is more than 2,000 m etres thick (Janko- vic, 1990;Karamata et al., 1994;J elenkovic & Kozelj, 2002).T h ere were several phases (at least two) of volcanism, and the volcanic processes were sub aerial to submarine eruptive, with hypabyssal intru sion and rarely explosive ( B a n jes ev ic , 2 0 1 0 ). The regional tectonic pattern is com posite. Long regi onal faults elongate in the direction of NNW-SSE, in  Z o r a n S t e v a n o v i£, V e ljk o M a r in o v ic & B r a n is l a v P etr o vic; The fissure aquiferof TMC is not rich in ground water. The groundwater flow pattern is linked to joint and fissure systems as well as main faults. Pa leozoic form ations, m agm atic and m etam orphic rocks mostly represent aquitards or aquifuges and in m ost cases act as a barrier to groundwater flow ( F ilipovic et al. 1975].

Methodology
The

Conditions on Site
In the previous period, very thick TMC deposits Initially, some registered larger faults, fissures and ponors in the blind valley w ere also plugged with   May 1996, the flotation dam broke and 1 0 0,000 m3

Earlier Accidents
The first big accident happened in 1 9 7 4 , after  in 2 0 1 9 and 2 0 2 0 , respectively. It is interesting that turbidity is even higher during the low -w ater pe riod, reaching the value of 12 NTU (MPL = 1 NTU), which is very rare for karst springs and their often dynamic regimes.
The low-water period results in worse water qual ity than the high-water period, as evidenced by the concentration of several other chemical constituents.
For instance, the concentration of ammonium ion (NH3_) is above MPL during the periods of low-water (0.71 mg/1), similar as N 02-0.036 mg/1. The content of the S 0 42-ion, which is dominant in anion compo sition, is regularly high above MPL (250 mg/1), reach ing its maximum value of 1152 mg/1 again during the low-water season (Fig. 4a). W ater of the Valja Fun data spring is characterised bya high concentration of Fe2+ and Mn2+ ions throughout theyear, but the highest value is noted once again during the lowwater season, when the concentration of Fe2+ is six times higher than permitted (1870 |ag/l vs. 300 ng/1), while that of Mn2+is even ten times higher than per mitted (504 |ig/l vs. 50 |ig/l) (Fig. 4b).
In high-w ater periods, w ater samples from the Kaludjerica spring had turbidity values of 25.99 and 122.2 NTU in 2 0 1 9 and 2020, respectively. However, as in case of Valja Fundata, the w ater's turbidity is the highest during the low-water season, reaching all of 694.8 NTU (Fig. 5).
During low-water periods, four chemical compo nents of the Kaludjerica water are above MPL. They Z o r a n S t e v a n o v ić , V e l jk o M a r in o v ić & B r a n is l a v P e t r o v ić  concentration of Fe2+ and Mn2+ ions in the Kaludjerica spring water is enormous, especially during the lowwater season: Fe2+is 200 times higher than permitted (5 3462 |Jg/l), while Mn2+ is 80 ten times higher than permitted (4175 (ig/1) (Fig. 4b).
The heavily polluted w ater of these two karst springs pollutes the streams Valja Mastaka and Veliki Pek. The impact of the poor quality of river water can be observed far downstream. For instance, in the al luvial groundwater of the latter river, which is tapped to supply water to the town of Kucevo, the concen tration of S 0 42-during the low-water period is about two tim es higher than perm itted (363 mg/1). This could be the result of old accidental pollution, but it could also mean that new waves are "refreshing" the pollution of this alluvial aquifer.
In contrast, other examined karst springs, which belongs to other karstified blocks such as those is suing from Rajkova and Paskova caves (Fig. 1) (Fig. 4a). The dering the karst aquifer and the delineated GWB of If EU WFD is fully transposed in Serbian legisla tion, with strictly applied one of its main principles -"the polluter pays", many industrial and mining factories will be obliged to pay m ore attention to their technological processes, and to construct their  S tevanović, Z. 1995. Karst ground waters in Serbia -pre sent and potential uses in regional water supply. In: