IAH 21st Congress 'KARST HYDHOGEOLOGY AID KARST ENVIRONMENT PROTECTION October 1988 GUILIN.CHBNA

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1 IAH 21st Congress 'KARST HYDHOGEOLOGY AID KARST ENVIRONMENT PROTECTION October 1988 GUILIN.CHBNA THE REGIME OF THE QUALITY OF KARST GROUND WATERS IN EASTERN SERBIA - YUGOSLAVIA Zoran P.Stevanovic Faculty of Mining and Geology, Department of Hydrogeology University of Beograd,Yugoslavia ABSTRACT Quality tests applied to the karst ground waters in eastern Serbia, being particularly intensive since 1980 as regards the control karst springs, indicate relatively uniform properties throughout the year, with certain season variations. The stated variations depend in the first place on the springflow regime and the discharge peak. Chemical composition of these waters is usually pure in the sanitary aspect, mostly for the catechment areas on mountain massifs being unpopulated. Cavern and channel dimensions, high filtration rapidity, or the like, cause frequent bacteriological pollutions, wherefore the entire catechment area of each source should be proclaimed a wider zone of sanitary protection. INTRODUCTION The karst region in the eastern part of Serbia covers 3000 km (30% of the territory). The karst region is mainly formed by Upper Jurassic and ' Lower Cretaceous massive limestones. and dolomites on' mountain massifs within the regional geostructural form of the Carpatho- Balkanides. Most towns in this region (Nis, Bor, Zajecar, Paracin, Pirot, etc.), are supplied with water from the karst ground waters, usually by direct drawing from karst springs. Significant resources and desired qualitative properties of karst ground waters are characteristic of a, karst aquifer. Butexcept for the regular sanitary controls, insufficient attention is being paid, either to observations of the complete chemical and bacteriological composition, and to the protection efforts against pollution. 1000

2 Since 1980, the quality analyses regarding these waters have been carried out with an enhanced intensity in a number of localities, within studious investigations conducted by the Faculty of Mining and Geology in Belgrade. The investigations cover 105 karst springs. Other than the elementary chemical analyses referring to the control springs, they imply investigations of microelements, gas composition, J radioactivity, bacteriological composition, as well as a continuous observation of changes of basic chemical compositional elements. CHARACTERISTICS AND REGIME OF QUALITY OF KARST GROUND WATERS Water temperatures are dependent upon the microclimatic and geological conditions and the hypsometric position of the catechment area. Somewhat lower temperatures are characteristic of higher peak springs. Thermal and subthermal waters, as well as seepage karst springs with different water temepratures in the branched system of karst channels, occur quite often. The mean annual value of the temperature measurements taken in all spring waters, being 11,2 C, is a little higher than the mean perennial air temperature of the region (9,7 C). Throughout à hydrological year, oscilations are weak, their average amplitude being about 1 C, seldom up to 3 C. Karst ground waters are always colourless, odourless and tasteless. Occasional, short-lasting (rarely lasting longer than 2-3 days) turbidities of gravity springs waters make one of the major problems in regard of their usage. The chemical composition of these waters reflects entirely the conditions of their formation, the intensive water exchange and. the rapid filtration. They are weakly mineralized waters with a'prevailing content of HCO-, in the anionian and of Ca in the cathionian composition. The average content of ion HCO ~ is 87%nval? and of ion Ca + it is 75% mval, wherefore ions Mg +, Na +, K* SO4, GL, NO.-,, etc., usually occur inferiorly. Ions NH^+, Fe^'3 +, Mri 2+, as well as microelements,. are usually absent, and if they do occur, it is always within the limits of the valid. quality standards. The ph values imply a generally alkaline, rarely a neutral character (mean value = 7,6).. With regard of the hardness value, these waters cover all transitions from soft to very hard waters. 1001

3 Fig.l. Piper s s trilinear diagram of chemical composition of karst ground waters The gas composition is dominated by N and CL. Very low values are characteristic of U, Ra and Rd contends. All analyzed waters show a low mineralization rate of 0,2-0,4 g/1 (only 10% samples-below, and 6% above these estimates), the total average value being 0,28 g/1. Chemical composition of these waters usually does not substantial changes throughout the year. The amplitude of changes concerning the mineralization values throughout the year is only rarely higher than 0,1 g/1. The content of elementary components is usually increased during low water periods, which results from longer lasting retentions and a slower filtration within the karst aquifer. Quality tests applied to the "seepage" karst spring waters provided data on certain differences in the quality of waters from different discharge zones. Higher space channels, for example (which may be of an occasional character ). usually show lower mineralization values, higher content of Ca and HCO ~ and the like. Such differences, though often minimal, still indicate certain differences within an "integrated" karst aquifer. 1002

4 Fig.2. Radial diagram of ions changes in waters of the karst spring Krupaja Knowledge of these differences may be of a special significance in the case of an eventual pollution, and it also indicates more favourable conditions for the ground waters taping out of deeper karst aquifer parts. SOME ASPECTS OF PROTECTION OF KARST GROUND WATERS Pollution of karst ground waters (bacteriological one in particular) depends on conditions in the catechment area and on presence of potential'pollutants. If they do exist, the possibilities that the karst aquifer gets polluted are considerable due to the exposure and dimensions of karst channels and caverns, where of a slower ground waters filtration gets hindered and autopurificatory capabilities become consequently reduced, The results obtained by the "tracing" experiment and the correlative analysis of precipitations and springlows, confirm considerable rapidities of ground water flows and a faster propagation of the waters produced from heavy precipitations (5-10 days or average) as far as from the remotest parts of the catechment area. 1003

5 There are possibilities not only of a pollution, but also of its extremely fast transmission which may bring about dangerous consequences even before the causes have been discovered and undesirable effects prevented. This is especially characteristic of the high waters periods, wherefore the maximal yields usually condition the lowest quality of ground waters. The results of "tracing" experiments with ground waters indicate that under convenient conditions the pollution may migrate as far as 10 km of rectilinear distance within as early as 24 hours. Active hydraulic connections between the ground and surface waters, where by the harmful components may be carried from great distances including nonkarst terrains, and infiltrated into the narrowest spring zone, have a particular significance in this regard. A typical example of such bacteriological pollution has been registered in the "seepage" karst source "Nemanja", used for water supply of the town Cuprija. The gravity type springs on higher peaks, with the Uneven yield regime, are characterized by the rapid transport of. pollution of a. higher rate, while the hypsometrically lower rising spirngs have more favourable characteristics and a far too lower rate of bacteriological impurity. Zubrava Fig.3- Scheme of migration of pollutants from river to karst spring "Nemanja" 1. karst aquifer 2, tertiary sediments 3- karst springs 4. groundwater level 5- migration of pollution. 1004

6 If the quality of these waters is not permanently controlled and the continuous chlorization applied, hydric epidemics may occur, which actually happend in several small towns in Serbia (Boljevac, Sjenica, Valjevo) during the last 15 years. The complexity of conditions of protection in karst terrains often requires an introduction of more zones and belts of sanitary protection, with various control restrictions. In my opinion, such hydrogeological conditions require that the entire catechment area of a karst spring should be proclaimed the widest, zone of sanitary protection, implying adequate measures which would be defined after thorough hydrogeological investigations. REFERENCES Fried J.J. 1975: Groundwater pollution. Elsevier S.P. New York Gavitch I.K. and oth.1985: Metodiohrani podzemnih vod ot zagrjazenija i istoscenija. "Nedra",Moscow Stevanovic Z : The quality of the karst Ground waters in dependence on regime and zone of discharge. Simp."Water and karst 86" "Naâ krâ", Sarajevo Stevanovic Z. 1987: Le qualité des eaux souterraines karstiques dans la Serbie orientale. Recueil des rapports du Com.karst et speleol. III, Ed.spec. Academ.Serbe, Beograd 1005