GROUNDWATER VULNERABILITy Of THE KARST - f ISSURE Hy DROGEOLOGICAL STRUCTURE Of SOUTH – f ACING SLOPES Of THE NÍZKE TATRy MTS., SLOVAKIA RANLJIVOST PODZEMNE VODE V KRAŠKO-RAZPOKLINSKI STRUKTURI JUŽNIH POBOč IJ NIZKIH TATER, SLOVAŠKA Erika KOV Áč OV Á 1 & Peter MALÍK 2 Izvleček UDK 556.3:551.44 (437.6) Erika Kováčová & Peter Malík: Ranljivost podzemne vode v kraško-razpoklinski strukturi južnih pobočij Nizkih Tater, Slovaška V članku obravnavamo ranljivost vodonosnika (v smislu Zwahlen et al., 2004) na kakršnokoli onesnaženje z uporabo Malikove (2005) razširitve Kullmanove (2000) metode. Slednja temelji na obravnavi vpliva stopnje razpokanosti in zakraselosti kamnine na recesijo pretočnega hidrograma kraških izvirov. Metoda temelji na domnevi, da je naravno dušenje intenzitete onesnaženja odvisno od stopnje zakraselosti oz. razpokanosti kamnine. Metodo smo uporabili na območju sestavljenem iz kamnin mezocojskih starosti v najbolj pomembni hidrogeološki strukturi južnih pobočij Nizkih Tater. Na osnovi analiz recesij- skih krivulj izvirov, ki jih izkoriščajo oz. jim merijo pretok, smo sklepali o stopnji absorbcije in drugih procesov izločitve onesnaževal med podzemnim pretakanjem vode. Recesijske krivulje ne odražajo le območje iztoka, pač pa celoten sistem pretakanja, vključno z infiltracijo in akumulacijo. Skupaj smo analizirali 68 recesijskih krivulj z 9 izvirov. Dobljene stopnje ranljivosti smo ovrednotili po 10 stopenjski lestvici in vrednosti uporabili na obravnavanih območjih glede na litologijo zaledja spremljanih izvirov. V študiji obravnavamo tudi območja lami- narnih in turbulentnih tokov, ki se pojavijo v kraško razpoklin- skem vodonosniku in tipe nezveznosti v kamninah, od mikro do makro razpok in kraških kanalov. Ključne besede: ranljivost podzemne vode, občutljivost na onesnaženje, analiza hidrografa, stopnja zakraselosti, receijska krivulja, Nizke Tatre, Slovaška 1 State Geological Institute of Dionyz Stur, Mlynská dolina 1 Bratislava, Slovakia; e-mail: kovacova@geology.sk 2 State Geological Institute of Dionyz Stur, Mlynská dolina 1, Bratislava, Slovakia; e-mail: malik@geology.sk Received/Prejeto: 18.09.2006 COBISS: 1.01 ACTA CARSOLOGICA 36/2, 261-268, POSTOJNA 2007 Abstract UDC 556.3:551.44 (437.6) Erika Kováčová & Peter Malík: Groundwater vulnerability of the karst - fissure hydrogeological structure of south – facing slopes of the Nízke Tatry mts., Slovakia An “intrinsic vulnerability” (according to Zwahlen et al., 2004) to any contamination in general is considered using Malík´s extension (2005) of the Kullman´s method (2000), based on the assessment of the degree the rock disruption and karstifica- tion, affecting the shape of spring discharge recession curves. It is based on the presumption that the intensity of natural con- tamination attenuation processes depends on rock disruption/ karstification. The method is applied on the Mesozoic rock en- vironment of the most important hydrogeological structure in the southern slopes of the Nízke Tatry Mountains. Hydrograph analyses of groundwater depletion in the gauged or exploited springs were used for assessment of groundwater vulnerability to human and/or natural pollution. Differences in character of individual depletion hydrographs enable assessment an extent of absorption and elimination processes during the groundwa- ter penetration through the rock environment from the infiltra- tion area to the outflow in the spring or exploited source. The depletion hydrographs reflect not only the character (effect) of outflow area but reflect the effects whole infiltration and accu- mulation area. In total, 68 individual recession curves from 9 gauged springs were analysed. Obtained degrees of groundwater vulnerability are evaluated by 10 degree range of the Kullman´s vulnerability scheme, adjusted by Malík. The reached vulner- ability values are consequently applied and assigned to the lith- ological types of discharge area of gauged springs. This study also describes an existence of individual laminar and turbulent sub-regimes that occur in the karts-fissure rock environment, the type of rock disruption from open micro– to macro fissures - to karst channels and subsequent estimation of the karstifica- tion degree. Key words: groundwater vulnerability, sensitivity to pollution, hydrograph analyses, karstification degree, recession curves, Nízke Tatry Mts., Slovakia. ACTA CARSOLOGICA 36/2 – 2007 262 The concept of groundwater vulnerability is based on the assumption that the physical environment may provide some degree of protection to groundwater again anthro- pogenic and/or natural impacts, and that degree of vul- nerability is a function of the hydrogeologic setting and prevailing patterns of pollution (Vrba & Zaporozec, 1994; Ibe et al., 2001). Vulnerability is regarded as an intrinsic property of a groundwater system that depends on the sensitivity of that own system to human and/or natural impacts. Two types of vulnerability of groundwater were recognized by Daly et al. (2002): intrinsic and specific vulnerability. Definitions of these types of groundwater vulnerability were established in the framework of mul- tilateral project of European hydrogeologists – „COST Action 620 - Vulnerability and risk mapping for the pro- tection of carbonate aquifers“. Not only these definitions, but also common understanding of the groundwater vulnerability factors were recognized within this project (Zwahlen et al., 2004), and a set of methodical steps – a „European approach“ of groundwater vulnerability as- sessment. Although primarily addressed to the karst rock media, this approach can be applied to all kinds of rock environments as it only extends assessments of some special features of karst environments (groundwater flow concentration) if exists (Malík & Švasta, 2004). An “intrinsic vulnerability” , evaluating a geologi- cal, hydrological and hydrogeological characteristics of site and does not depend on patterns of pollution. A “specific vulnerability” is defined as a vulner- ability of groundwater against specific contaminant or several contaminants caused by human activity. The output of Kullman´s method (2000) using hydrograph analysis of groundwater depletion of the gauged springs can be marked as an „intrinsic vulner- ability“ as it does not recognize the specific properties of individual types of contaminants (heavy metals, pes- ticides, nitrates …). However, as it does not correspond in all aspects with the “standard European” definitions and approaches (Daly et al., 2002, Zwahlen et al., 2004), some authors (Malík, 2005) prefer to name this output as “groundwater sensitivity to pollution” to make clear difference between both concepts. The target Kullman´s method application in this case was the groundwater in the karst-fissure hydrogeological structure of the Nízke Tatry Mountains, Slovakia, located between the munici- palities of Podbrezová, Krpáčovo, Jasenie and Lopej. INTRODUCTION CHARACTERISTIC Of Hy DROGEOLOGICAL STRUCTURE BETWEEN PODBREZOVÁ, KRPÁč OVO, JASENIE AND LOPEJ The Nízke Tatry Mountains as the western part of the Carpathian arch are located in the north of Slovakia. The highest peak is Ďumbier with an elevation of 2,043 metres a. s. l. By geological structure, the Nízke Tatry Mts. be- long to the “core-type” of mountain ridges, with a crystal- line “core” and “envelope” built by autochthonous Meso- zoic sediments plus several overthrusted units built also by Mesozoic sediments. The Mesozoic carbonate rocks, mostly various types of limestones and dolomites, are of Middle and Upper Triassic age. They represent one of the most important karst water resources areas in Slovakia. Hydrogeological structure of the southern slopes of the Nízke Tatry Mountains between Podbrezová, Krpáčovo, Jasenie and Lopej (37.74 km 2 - f ig.1) is the most important natural groundwater reservoir with high quality drinking water, bound also to Triassic - Mesozoic rock environment. This highly permeable structure is about 1,200 metres thick. Considering the main geologi- cal units, the carbonate rocks in the structure belong to Hronikum unit with middle Choč nappe at the bottom, overlayed by two independent segments of upper Choč nappe. All these partial nappes are from the bottom to top built by the same lithology: Lower Triassic seiss and kampil layers (sandy shales and sandstones), Middle Triassic Gutenstein limestones, “Choč dolomites” , rei- fling limestones, lunz layers (claystones and sandstones), Upper Triassic “main dolomites” - hauptdolomites, and dachstein limestones. All these layers have their equiva- lents in Ober Ost Alpine units in Austrian Alps. Under the Choč nappe, the Veporikum unit is placed as an un- derlying sequence of Mesozoic isolators and aquifers. The hydrogeological structure itself has a very complicated hydraulic and hydrogeochemical system of groundwater flow, due to the several open fault systems. Complex tectonic settings of the area enabled a creation of three main hydraulic systems of groundwater flow (f ig.2), which were defined by Kullman (1983, 1990): 1. dynamic system of groundwater flow connected with the Hronský fault, a boundary fault of uplift of the Nízke Tatry Mts., ERIKA KOVÁč OVÁ & PETER MALÍK ACTA CARSOLOGICA 36/2 – 2007 263 2. dynamic system of groundwater flow connected to transverse open fault zones cutting the structure along the Vajskovská and Suchá valleys – causing the circula- Fig. 1: map of Slovakia with the position of research area. tion of the biggest groundwater amount, with quick and shallow movement, 3. inner system inside the hydrogeological structure itself - slower groundwater movement through the less disrupted parts of the hydrogeological structure. The first hydraulic system – groundwater circulation con- trolled by the Hronský zlom fault is drained by 2 springs, in Krpáčovo and Tále area. In spite of its importance, this open fault hydraulic system could not be evaluated because of missing data of discharge time series. The second hydraulic system – transverse open fault zones passing Vajskovská valley and Suchá valley, is drained by 6 springs: Spring of king Matth- ias (No. 1257) in Lopej, Uhlište (No. 1311), Vrabec (No. 1312), Horný 1, 2, 3 (No. 1313), Horný 4 (No. 1314) a Dolný (No. 1315) in Dolná Lehota. The third hy- draulic system (groundwater movement within hydrogeologi- cal structure) is drained by 6 springs, from which 3 data available (gauged) springs are Hámor (No. 1255), Za Fig. 2: Hydrogeological structure between Podbrezová, Krpáčovo, Jasenie and Lopej and three different hydraulic systems of groundwater flow. Fig. 3: Gauged springs of hydrogeological structure between Podbrezová, Krpáčovo, Jasenie and Lopej. GROUNDWATER VULNERABILITy Of THE KARST - f ISSURE Hy DROGEOLOGICAL STRUCTURE Of SOUTH ... ACTA CARSOLOGICA 36/2 – 2007 264 továrňou (No. 1310) in Dolná Lehota and Starý mlyn (No. 1317) in Horná Lehota (f ig.3). Estimated specific groundwater runoff of whole hy- drogeological structure is ranging from 8.5 to 9.5 l.s -1 .km -2 and the total sum of dynamic natural groundwater re- sources originating in the structure is 320 -359 l.s -1 (Kull- man, 1983, 1990). Prognostic groundwater reserves (co- unting also external groundwater outputs) are estimated as 468 l.s -1 (Hanzel et al., 1990). METHODS The applied Kullman´s method (1997, 2000) adjusted by Malík (2005) is based on the assessment of the degree of groundwater vulnerability resulting from the rock disruption and karstification. Proposed vulnerability classification has 10 degrees of vulnerabilities assigned by differences in character of karstification and rock dis- ruption signalized by individual depletion hydrographs. Differences in character of individual depletion hy- drographs enable assessment of the anticipated possi- bility of reduction, absorption or elimination processes during the groundwater penetration through the rock environment. Degree of vulnerability equal to 1 represent low vulnerability and only one laminar groundwater flow is present here. The risk of groundwater contamination is very low. The highest vulnerability equal to 10 th degree represents groundwater circulation exclusively in open karst channels, where only turbulent sub-regimes are present, without a mark of single laminar one. The risk of extensive groundwater contamination is very high. The highest vulnerability is then connected to developed karstification in large areas, with wide opened channels, swallow holes or sinkholes. Besides vulnerability, several other characteristics of rock environment, mainly the ap- erture of joints present, are influencing the final shape of recession curves: the existence of laminar or turbu- lent sub-regimes points out on the ratio of microfissures, macrofissures and open karst channels. Discharge time series were analyzed for their de- creasing parts, exceeding suggested threshold value of at least 8 weeks of uninterrupted decrease. f rom these, recessions possibly influenced by sudden precipitation events were excluded, as in spite of their decreasing char- acter there is a danger of lowering the “decrease angle” on the hydrograph. f inally, a master recession curve was created by “best fit” simulation of the curve using the dif- ferent starting discharge points of each subregime and 3 possible α depletion coefficients and 3 possible β deple- tion coefficients. The method was applied on the Mesozoic rock en- vironment – Triasic carbonates of Hronicum unit. In total, 68 recession curves from 9 gauged springs were analyzed. f inal groundwater vulnerability degree of in- dividual springs was based on the classification of the mean values of recession curve´s parameters – depletion coefficients α and β (Malík, 2005). Depletion coefficients also suggest on the type of groundwater flow regime. Coefficient α suggest a laminar regime of groundwa- ter flow and coefficient β suggest a turbulent regime of groundwater flow. Each spring was characterised by its individual depletion coefficients and subsequent vulner- ability (sensitivity to pollution) degree (Malík, 2005). The reached median value of the vulnerability degree was consequently applied also to different lithological types present in the discharge area of gauged springs. In this way, groundwater vulnerability of individual lithological types was defined. The outcome is the groundwater vul- nerability map of studied hydrogeological structure. The same was done for individual hydraulic systems present in the Podbrezová – Krpáčovo – Jasenie – Lopej hydro- geological structure. Based on the recession characteris- tics of the springs bound to different hydraulic systems, mean groundwater vulnerability (sensitivity to pollution) degree of each hydraulic system was described. RESULTS GROUNDWATER VULNERABILITy AND REGIME Of GROUNDWATER f LOW Of INDIVIDUAL SPRINGS The lowest vulnerability degree index of 2 was given to the Starý mlyn spring (No.1317) in Dolná Lehota. The analysis of depletion curves from weekly data of 30 years periods suggest an existence only one laminar regime of groundwater flow (f ig. 4). The risk of groundwater contamination is very low, is only general risk of surface entry of contamination into rock environment, with pos- ERIKA KOVÁč OVÁ & PETER MALÍK ACTA CARSOLOGICA 36/2 – 2007 265 sibility of its great retention, fixation and dispersion. We can expect very low probability of significant contamina- tion of groundwater source. Higher vulnerability degree values – 2.5 and 2.7 – are reached by springs Za továrňou (No. 1310) and Há- mor (No. 1255) in Dolná Lehota. Two laminar regimes are present here. Very low risk of groundwater con- tamination is present, but possibility of surface entry of contamination with its probable retention, fixation and dispersion is high. Probability of groundwater source contamination is very small, with exception of possible entry of contamination from closer vicinity (Kullman, 2000, Malík, 2005). Spring Horný 1, 2, 3 (No. 1313) reaches value 4 of vulnerability degree, and two laminar subregimes of groundwater are present here. Spring Vrabec (No. 1312) with value of vulnerability 4.3 has also two laminar sub- regimes. Spring Horný 4 (No. 1314) in Dolná Lehota with vulnerability 5.0 suggest the combination of one laminar and one turbulent subregime of groundwater flow. This still means a low risk of groundwater contamination by surface entry into the rock blocks, but the possibility of significiant contamination point source with direct con- nection of the karst system to the surface exist. There is also still possibility of its retention, fixation and disper- Fig. 4: Characteristic recession curve of spring No.1317 Starý mlyn in Dolná Lehota – lowest vulnerability (sensitivity to pollution) degree. Fig. 5: Characteristic recession curve of spring No.1257 Spring of king matthias in Dolná Lehota – highest vulnerability (sensitivity to pollution) degree. GROUNDWATER VULNERABILITy Of THE KARST - f ISSURE Hy DROGEOLOGICAL STRUCTURE Of SOUTH ... ACTA CARSOLOGICA 36/2 – 2007 266 sion of contamination, but point contamination sources represent a real danger to groundwater (Kullman, 2000). More vulnerable seem to be spring Uhlište (No. 1311) and Dolný (No. 1315) in Dolná Lehota with vul- nerability value 5.5 typical for karstic areas. Regime of groundwater depletion is composed by two subregimes with laminar flow and one subregime with turbulent flow. There is a limited possibility of its retention, fixa - tion, but mainly dilution. Arrival of contamination to groundwater sources will be rather quick, but in lower concentrations, with longer duration period. The higher vulnerability is determined for Spring of king Matthias (No.1257) in Lopej with vulnerability value 9 and existence of one turbulent regime of ground- water flow (f ig. 5). Possibility of groundwater affection by significant contamination point source with fast trans- port, low retention and dispersion is high. There is very high risk of groundwater contamination from far-away contaminant source and also fast increase of contami- nant in groundwater source, with high concentration, but with limited duration period. GROUNDWATER VULNERABILITy Of INDIVIDUAL LITHOLOGICAL Ty PES f rom existing depletion hydrographs of individual gauged springs is possible to define also a mean value of groundwater vulnerability (sensitivity to pollution) de- gree of individual lithological types, based on the mean characteristics of springs connected to these lithological types. There were enough data to evaluate four different lithological types – Choč dolomites, Gutenstein lime- stones, Hauptdolomites and carbonatic conglomerates of Vajsková. These lithological types are present in the discharge areas of gauged springs. Choč dolomites show mostly laminar discharge sub-regimes and only sometimes turbulent sub-regime can by recognised. Substantial role in groundwater discharge has a sub-regime with laminar flow. The re- gime of groundwater discharge is based on differences in discharge curves and different discharge coefficient. The risk of more extensive groundwater contamination is low, with exception of close vicinity of the source. Degree of vulnerability according to Kullman´s classi- fication (2000) adjusted by Malík (2005) reaches value of 3.3. Conglomerates of Vajsková can by characterised by the presence of two laminar sub-regimes in spring hy- drographs, from time to time a turbulent sub-regime can by present. Rock environment is characterised by irregu- larly developed fissure network, with majority of open macro-fissures. The risk of more extensive groundwater contamination is low. Value of groundwater sensitivity to pollution (groundwater vulnerability) of this rock envi- ronment reaches 4.1 degree of Kullman´s classification (2000) adjusted by Malík (2005). Gutenstein limestones reach the vulnerability de- gree of 5. Regime of groundwater discharge is composed from sub-regime of turbulent flow and laminar flow sub- regime. Substantial role in groundwater discharge has a sub-regime with laminar flow. Rock environment is char- acterised by an existence of crushed water-bearing zones or by dense network of open small fissures in combina- tion with simple, partly phreatic conduit system of con- siderable extent. The risk of groundwater contamination by surface entry into the rock is low. There is a possibility of contamination increase by significant point pollution source with direct connection of the karst system to the surface. “Main dolomites” – “hauptdolomites” reached the highest vulnerability 5.5 from 10 degrees range of used classification. This fact is quite interesting from the point of view of rock composition, but it also documents, that – on the contrary to the Mediterranian dolomite sequences – the Trassic dolomites in the Carpathian arc show a karstification potential and on many places are also strongly karstified. Regime of groundwater flow of the spring Dolný in Dolná Lehota is created by a super- position of two sub-regimes with turbulent flow and one sub-regime with laminar flow. We can assume higher risk of contamination by surface entry and also higher risk coming from possible point source of contamination. GROUNDWATER VULNERABILITy Of DIff ERENT Hy DRAULIC Sy STEMS Of THE Hy DROGEOLOGICAL STRUCTURE ON THE SOUTHERN SLOPES Of THE NÍZKE TATRy M TS. BETWEEN PODBREZOVÁ, KRPÁč OVO, JASENIE AND LOPEJ The first hydraulic system – Hronský zlom fault could not by evaluated because of insufficient data. The second hydraulic system - an open fault zones passing the Vajskovská valley and Suchá valley, is in av- erage characterised by one sub-regime with turbulent flow and one sub-regime with laminar flow. Rock envi- ronment should be then characterised by an existence of crushed water-bearing zones – in this case fault zones of Vajskovská and Suchá valley. Mean degree of vulnerabil- ity reaches value of 5.25 (Tab. 1). We can assume higher risk of groundwater contamination by surface entry into the rock block and also by significant point source of contamination with direct connection of the karst sys- tem to the surface. The third hydraulic system – inner groundwater circulation inside the hydrogeological structure itself – reaches lower, 2.5 value of vulnerability degree (Tab. 2). Generally only a laminar groundwater flow is present in ERIKA KOVÁč OVÁ & PETER MALÍK ACTA CARSOLOGICA 36/2 – 2007 267 this hydraulic system, what is typical for rock environ- ment with dense, regular fissure network, with majority of micro-fissures and small fissures. The probability of groundwater contamination is then very small, with the exception of possible entry of contamination from closer vicinity. Number (SHMI) Name of spring Site Rock environment Groundwater vulnerability of gauged springs Vulnerability of litological types Final vulnerability of second hydraulic system 1257 Kings´s Matyas spring Dolná Lehota Gutenstein limestones 9.0 5.0 5.25 1311 Uhlište Dolná Lehota Gutenstein limestones 5.5 1312 Vrabec Dolná Lehota Choč dolomites 4.3 3.3 1313 Horný 1, 2, 3 Dolná Lehota Choč dolomites 4.0 1314 Horný 4 Dolná Lehota Conglomerates of Vajsková 5.0 4.1 1315 Dolný Dolná Lehota “Hauptdolomites” 5.5 5.5 Tab. 1: Groundwater vulnerability of the second hydraulic system of fault zones of Vajskovská valley and Suchá valley. Number (SHMI) Name of spring Site Rock environment Groundwater vulnerability of gauged springs Vulnerability of litological types Final vulnerability of second hydraulic system 1255 Hámor Dolná Lehota Conglomerates of Vajsková 2.7 4.1 2.5 1310 Za továrňou Dolná Lehota Choč dolomites 2.5 3.3 1317 Starý mlyn Dolná Lehota Choč dolomites 2.0 Tab. 2: Groundwater vulnerability of the third hydraulic system – inner groundwater circulation inside the hydrogeological structure. CONCLUSIONS f inal groundwater vulnerability map of research area (f ig. 6), showing a spatial distribution of groundwater sensitivity to pollution – groundwater vulnerability – was based on the reclassification of geological map. Individ- ual lithological types were linked to certain vulnerability degree, depending on the mean value defined from the individual springs recession curves characteristics. The large part of area is highly vulnerable, with vulnerability values of more than 4.9 degree of Kulman´s scale (2000) extended by Malík (2005). This fissure-karst rock environment in the hydro- geological structure on the southern slopes of the Nízke Tatry Mts. between Podbrezová, Krpáčovo, Jasenie and Lopej is widely crushed, with majority of opened, karstic or non karstic fissures and large karst channels. We can assume higher risk of groundwater contamination by surface entry into the rock block here. But in the case of aerial entry of contamination there is still a possibility of its significant retention, absorption and elimination by other processes. Also large part in the centre of struc- ture reaches moderate vulnerability, between 4.0 and 4.9 degree. In this rock environment we can anticipate the existence of open small fissures in combination with simple, partly phreatic conduit system of considerable extent. Contamination by surface entry is lower, but the possibility of contamination by significant point source with direct connection of the karst system to the surface is real. In the case of aerial entry of contamination, there GROUNDWATER VULNERABILITy Of THE KARST - f ISSURE Hy DROGEOLOGICAL STRUCTURE Of SOUTH ... ACTA CARSOLOGICA 36/2 – 2007 268 is a possibility of its significant natural attenuation. Only few small parts of hydrogeological structure represent areas with low risk of groundwater contam- ination, with value of vulnerabil- ity degree smaller than 3.9. Rock environment represent a dense network of micro-fissures and small fissures, with only limited extent of karst channels. The risk of more extensive groundwater contamination is very low, with the exception of close vicinity to the pollution source Fig. 6: The outcome map of groundwater vulnerability of research area – hydrogeological structure betwen Podbrezová, Krpáčovo, Jasenie and Lopej, Slovakia. 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