Groundwater Vulnerability in Western Herzegovina

Transcription

1 1 Paper N 0 : V.11 Groundwater Vulnerability in Western Herzegovina Mladen Zelenika, Ivan Slišković, Božo Soldo Abstract: The full and partial hydrogeological barriers together with terrains of low and high permeability, springs and surface watercourses have been mapped. The Mayor karst aquifers are highly vulnerable but the quality of groundwater is reasonably good due to the low development in the high karst, where the chief recharge is occurring. The adequate protection zones in the basins and around the springs should be determined and legalized as soon as possible in order to frame a sustainable development as the policy for protection of the groundwater recharge area. Keywords: vulnerability, karst spring, aquifer, hydrogeological barriers, ground water protection 1. Introduction Groundwater vulnerability map is one of the applied environmental maps (Vrana, 1984). It is also one of hydrogeological maps having scarce and heterogeneous data from various sources (Struckmeier, 1989). Vulnerability of groundwater is a relative, nonmeasurable, dimensionless property. The accuracy of its assessment depends above all on the amount and quality of representative and reliable data (Vrba and Zaporozec, 1994). When assessing vulnerability, the attributes or their parameters may be assigned different weights and rating according to their considered importance for the vulnerability assessment. Despite the differences in opinion as to the weight and rating of the individual attributes, it is generally recognized that groundwater vulnerability can be assessed only when the principal basic parameters of the attributes are known. The natural (intrinsic) attributes of primary importance include: the amount and quality of recharge, soil properties, and the characteristics of the unsaturated and saturated zone (Vrba, 1991).

2 446 Zelenika, Slišković, Soldo Natural attributes of secondary importance include: topography, contact with surface and/or sea water and the nature of the underlying geological unit of the aquifer. Beside the principal parameters of the natural (intrinsic) attributes, there are the supplemental parameters which, includes: vegetative cover, evapotranspiration, air-temperature, weathering rates etc. The vulnerability of groundwater in karst aquifers in the region has been assessed using HCS (Hydrogeological complex and Setting methods) with estimation values of 4 basic parameters (Vrana, 1984). The vulnerability has been assessed also using PCSM method - Point Count System Model (Aller et al, 1987) in terms of the risk of the system becoming exposed to contaminant loading. The important parameter in the assessment of specific groundwater vulnerability is the attenuation capacity of the soil, of the unsaturated zone, and of the aquifer with respect to the properties of individual contaminants. Specific vulnerability of groundwater is assessed using the estimated data for: characteristic of the unsaturated zones, average depth to water, hydrogeological features, thickness, textures and mineralogy in the region. The exploration area (Fig. 1) predominantly comprises the drainage basin of the Mostarsko Blato and the Trebizat river. It includes the Cvrsnica and Cabulja mountains and the right bank of the Neretva river, from Jablanica to Gabela. Identification of karst aquifers and basins in the region is stated in order to determine the protection zones around the springs and the sustainable development as a measure to protect the groundwater recharge area from contamination. The Perm-Triassic sediments have been tectonically uplifted to the land surface at Sobac and consist of gypsum and anhydrites. The undifferentiated Middle and Lower Triassic is composed mainly of dolomite and dolomitic limestone in the region of Cvrsnica Mountain and along the northern slopes of Cabulja Mt. The Jurassic limestone and dolomite are found in the central region of the river Drezanka. The Cretaceous deposits are complete and cover the largest area (Figure 1). Tertiary sediments cover a considerably smaller area. The Quaternary deposits extend along the rivers and in karst poljes (Sliskovic, 1994). Groundwater potential of this area has been scarcely explored. Although the basic data about major springs and streams were collected during the budgeting of groundwater of the of the river Neretva drainage basin. This includes data on the springs used for water supply of: Mostar, Grude, Studenci Ljubuski etc.. The conclusion is that the considerable amount of unpolluted groundwater could be extracted even during the hydrological minimum in the places where the water supply/demand problem is very acute, eg. the areas of Posusje, Citluk, Grude and the northern and southern edge of Mostarsko Blato (Sliskovic, 1991). Since the river Neretva is a transboundary watercourse, all appropriate measures should be taken to prevent, control and reduce pollution of waters causing or likely to cause transboundary impact. The groundwater in the Major aquifers of the region facilitates the quality and quantity of water in all surface streams including Neretva. They are sources for majority water supply use: Studenac and Radobolja for Mostar, Grudsko Vrelo for Grude, Listica for Široki Brijeg, Klokun for Klobuk, Crnasnica for Knespolje, Tribistovo for Posusje, Studencica for Studenci, Vriostica for Ljubuski etc. (Figure 1). This paper will discuss the issue related to the vulnerability of the Mayor aquifers in order to determine the protection zones around the springs and contribute to a sustainable development as a measure to protect the recharge area of the major aquifers.

3 Groundwater Vulnerability in Western Herzegovina Hydrogeological characteristics of aquifers and basins Western Herzegovina belongs to one of the High Karst zones; the Orogenic Accumulated Karst (Herak, 1977), characterized by the development of specific geomorphologic, geological and hydrogeological features. Hydrogeological functions of rocks in the region related to their permeability, genetic and sedimentation characteristics, as interpreted from previous exploration data. Limestones are predominant rock units in this region. Within them, fissures and other openings are very heterogenous and reflect the tectonic processes that occurred during the Alpine orogeny. Limestones, dolomitic limestones and some dolomites are classified as highpermeable rocks with cavernous and fissured porosity. The permeability of these rocks depends on their karstification, intensity and density of fissures, structural position, stratification, formation thickness and the relative proportions of their calcitic and dolomitic components. Dolomites of different ages occur from the Lower Triassic to Upper Cretaceous, and range from pure dolomites in the central part of the Neretva river banks, trough a gradual transition to pure limestone in the area of Posusje and Siroki Brijeg. The Upper Triassic dolomites are occasionally karstified but, as a formation, they are impermeable and form barriers to groundwater flows. Dolomite plays a significant role in the formation of water divides in the central Neretva river-banks, in the area of Diva Grabovica and Dreznica. The drainage basin of Veliki Praporac and Mali Praporac (Figure 1) is confined toward the north and south by the dolomites of the rivers Doljanka and Drezanka, while the western border is obscure. The drainage basin of Veliki Praporac and Mali Praporac is separated from the basin of Crno Vrelo by the dolomitic anticline of Diva Grabovica (Figure 1, 2) Taking into account the hydrogeological and morphological conditions of the region, the area can be divided into seven drainage basins having their aquifers of the Major importance regards to their use and protection. Boundaries of the drainage basins were determined on the basis of geological structures, hydrological parameters, and water budget, as well as dynamics of permanent and intermittent spring occurrence and their spatial arrangement. Experimental colorings were performed in all major drainage basins. The testing locations include Grudsko vrelo, Studenac, vrelo Radobolje, vrelo Ugrovace, as well as majority of wells used in water supply. Additional hydrogeological, hydrological and geophysical explorations and exploratory drillings have also been completed. Traced paths of groundwater are presented in Figure 1. Full lines mark proven underground connections during measurements and dashed lines mark probable paths of the ground water. The basins could be shown in the following review: 1 The river Trebizat receives the largest part of its water during a hydrological minimum from Pec Mlini spring (Figure 1) of Tihaljina river, Q min = 1,2 m 3 /s and the springs Kordici, Jaksenica and Klokun. Downstream of Klobuk, the appearance of major permanent and intermittent springs is associated with the Ljubuski-Klobuk thrust of upper Cretaceous limestone over Eocene flysh deposits. The largest springs there are (Figure 1): Podgrab, Radišici, Vriostica - Q min = 1,25 m 3 /s, Studen (No. 19) and the three springs which are creating the river Studencica (No. 22 to 24).

4 448 Zelenika, Slišković, Soldo Figure 1 Drainage basins and chief springs in Western Herzegovina (Zelenika, Sliškovic and Muhovec, 1999) Figure 1A Legend for Figure 1

5 Groundwater Vulnerability in Western Herzegovina The drainage basin of the intermittent course of river Ugrovača, belongs to the bigger drainage basin of Mostarsko Blato as well as the river Lištica drainage basin. 3 The drainage basin of the Mostarsko Blato, having combined Q min = 3,04 m 3 /s from springs, Listica, Crnasnica and Zvatic (No. 10 to 12), gives enough water for the regional water supply system in design and partial use. Exploratory drilling along the northern and southern edges of the Mostarsko Blato, proved occurrence of groundwater in limestones at depths of 20 to 70 m. That is a "transit" area for groundwater flow from Kocerin and more distant recharge areas at northwest, toward springs in the Neretva river valley: Jasenica, Crno Oko and Arape Mlin (No. 7 to 9). 4 and 5 The drainage basin of the spring Studenac (No. 5) and the spring of river Radobolja (No. 6), having combined Q min = 1,4 m 3 /s under natural conditions and additional 1,2 m 3 /s after filling the hydro power reservoir Salakovac, offer a safe water supply for Mostar and its surroundings. 6 The spring of Drezanka river (No. 4), Q min = 0,150 m 3 /s, only 0,002 m 3 /s is used for public water supply and 0,1 m 3 /s for irrigation. 7 Veliki Praporac (No.1, Figure 1), Q min = 0,4 m 3 /s, is used for the water supply of Jablanica town. Mali Praporac (No. 2) and Crno Vrelo (No. 3) flow out free into river Neretva. Minimal dynamic reserves of springs which contribute their water to Trebizat river (total Q min = 17,36 m 3 /s) indicate significant residual reserves in the hinterland of the springs. It makes possible the proven underground hydraulic connection of these springs with ponors in Rakitno (Figure 1), Trebistovo and Posusko polje. Groundwater, flowing from the polje Rakitno, encounters hanging hydrogeological barriers in the areas of Posusko and Imotsko Poljes, resulting in decreasing flow and recharging of the aquifer occurring upstream to the barriers. Therefore, the area from Rakitno to springs is mainly a "transit" one through which groundwater flows from the north and northwest toward its erosion base, in the south and southeast, toward Mostarsko Blato and the river Trebizat, i.e. toward the river Neretva (Sliskovic, 1994). Jurassic and Cretaceous dolomites are relatively insignificant contributors to the impermeability of rock complexes but, where they form the core of anticlines, they function as barriers to ground water flow. The Lower Cretaceous dolomites of the river Listica spring are of this important type (Figure 1). Paleogene and Neogene clastic sediments, deposited in basins of different age and origin, are considerably more important factors in the flow of groundwater. During the Illyrian orogeny, the Paleogene sediments were lifted, repeatedly folded and simultaneously overthrusted by Upper Cretaceous deposits, resulting in the inclination of the syncline toward the southwest. The sea bottom subsided during the Lower Miocene, and Neogene sediments were subsequently deposited. Pliocene and Quaternary neotectonic movements produced the current morphology of this area.

6 450 Zelenika, Slišković, Soldo By the end of Pliocene and early Pleistocene, certain poljes and plateaus underwent heavy tectonism during which karst poljes were formed without marine or lacustrine deposition. Examples include the Imotsko and Dugo Polje in the north and northwest and the Mostarsko Blato in the south of the area of the study. The karst poljes are at different altitudes in western Herzegovina. From the Rakitsko Polje (950 m above sea level), Duvanjsko Polje (860 m), Posusko Polje (Figure 1) (600 m), Imotsko Polje (250 m) and Mostarsko Blato (240 m above sea level) toward the river Neretva drainage basin at the southeastern side of this area (less than 50 m above sea level). The drainage area of the lower Neretva river (Figure 1), to the river Trebizat, is very narrow because the drainage basin of the Mostarsko Blato is considered as a separate drainage area. Attempts to define the divide of the Mostarsko Blato (Figure 1) drainage basin have been futile because the underground divide is, most probably mainly zonal. Groundwater flow tracing in this large drainage basin is lacking and more attention should be focused on this problem in the future. In the northern part of the drainage basin, the relationships with neighboring drainage basins are more obvious because the impermeable rocks along the Drezanka river occur in an anticline, thus directing groundwater flow towards the south (Figure 1). The northwestern divide is approximately defined by tracing of the ponor (swallow hole) Miljacka at the Studena Vrela and by the position of hanging deposits north of Poklecani (Figure 1). Tracing in the Rakitsko Polje proved that the divide with the river Trebizat is wide zone. Within this expressly karst area, the Upper Cretaceous dolomites are often permeable because they occur within imbricated structures. The Upper Cretaceous anticline, in the Siroki Brijeg area, is the reason for the appearance of the major karst spring of the Listica river (Figure 1). Water from the aquifer in northwestern area flows out at this spring. Groundwater may flow in the dry season from this aquifer toward the springs of the river Tihaljina, thus explaining the existence of the intermittent river Ugrovaca by which most of surface water flows toward the Mostarsko Blato during the rainy season (Komatina, 1975). Additional tracings are necessary to prove to which drainage basin the groundwater of minor Neogene poljes, Kocerin, Trn and Mokro Polje pertains. At present, it is most logical to consider that this water belongs to drainage basin of the springs: Crno Oko, Arapa Mlin and the Jasenica river spring in Neretva river valley downstream from Mostar (Figure 1) (Sliskovic, 1994). Paleogene and Neogene deposits in the west of the study area form a significant barrier. In addition, narrow Paleogene zones extending from river Neretva towards the northwest act as hanging barriers to groundwater flow. The best known barrier occurs at the front of the Ljubusko-Klobuk overthrust and it extends along the left bank of the Tihaljina river (Figure 1). The area from Mostar to Citluk and Hamzici is composed of hanging barriers, which extend in several zones up to the Duvanjsko Polje. Impermeable rock units occur at high levels and act as hanging barriers to groundwater formed as an aquifer in the deep karst.

7 Groundwater Vulnerability in Western Herzegovina Aquifers in the region and their vulnerability In the circumstances of the most intensive recharge of the karst aquifer by precipitation in the higher areas with very limited sources of pollution, the present quality of groundwater in the region is good. Lower parts of the region are populated and fortunately have more overlying clay to protect the aquifer. The soil and groundwater there, could be contaminated by run-off water percolated from landfill sites for domestic and industrial wastes, roads, urban areas, farms, storage of manure and slurries from waste water, agricultural land treated by fertilizers and pesticides, and by accidental spillage from leaking oil, fuel and from septic tanks. The scheme on Figure 1 shows the mayor aquifers in the areas of the chief catchment basins in the region. The Major aquifers occur there in Cretaceous limestones and dolomite, which extend from Cabulja Mt. (1683 m), Stitar Mt. (1365 m) and Studena vrela (Ostrc 1309 m) to Gabela (15 m above sea level). Saturated parts of this karstified formation in the contact with the impermeable Tertiary or/and Quartenary formations, are the most important perennial springs utilized for urban and rural water supply (Fig. 1): Jelica (Ugrovaca 980 m above sea level), Listica (300 m, Crnasnica (240 m), Zvatic (240 m), Tihaljina (120 m), Klokun (110 m), Vriostica (100 m), Studenci (60 m) and intermittent springs: Grudsko vrelo (260 m), Kocerin (300 m), Mokasnica (255), Lukoc (300 m), Blaz (245 m), Gromolj, (250), Zelenikove Babe (255 m), Zvec (245 m) etc. The Minor aquifers occur in Tertiary limestones (Dobrinj, Zabljak, Orovnik, Soldino vrilo, Konjsko vrilo etc.), and in Quartarnary clastic layers (wells at Mostarsko Blato, Kocerinsko, Mokro, Imotsko-Bekijsko polje etc.). The chemical composition of the karst springs reflects the comparatively high homogeneity of carbonate rocks, mostly limestones, and increased velocity of groundwater flow. The results of water samples taken from different springs show no specific contaminants in drainage basins. The groundwater in the region is still of a satisfactory quality (Zika & Muhovec,1999)). The total dissolved solids content ( mg/l) is lowest in springs with rapid circulation of groundwater. Intermediate contents ( mg/l) total dissolved solids content occurs in the springs of Crnasnica and Trebizat. The springs in Tihaljina drainage area have increased mineralization. It is characteristic for Klokun, Kordici, Jaksenica and Nezdravica springs located in the upper parts of the river Tihaljina. These are in full agreement with the hydrogeological conditions as observed in the filed. It positively established that groundwater during its flow from Trebistovo to the Tihaljina river, in the area northeast of Posusje, come in contact with the Sobac Permian-Triassic structure. The increased contents of dissolved sulphate in water at springs of the rivers Listica and Crnasnica, indicating deeper circulation of groundwater, even up to Lower Triassic clastic sediments, and prolonged storage within the aquifer (Sliskovic, 1994). 4. Discussion and conclusions Drainage basins having Major karst aquifers and springs captured for water supply in the region are shown in Figure 1. The poljes in the region have clay and sand layers of the lower permeability where landfill, waste water treatment plant and some kind of industrial or other

8 452 Zelenika, Slišković, Soldo contaminants could be located. In the marginal parts of poljes are usually available ponors connected with groundwater, and watercourses convenient to carry contaminants to pollute surface waters, including the river Neretva. Therefore adequate protection zones should be defined and legalized as soon as possible. An additional comprehensive hydrogeological investigation should take place in order to define the policy of a sustainable development and use of land in the high karst of the region. There occurs the most intensive recharge of all 7 drainage basins/major aquifers, and special precautions should be taken to avoid pollution of groundwater in the region. Therefore the establishment should set up an Environment Agency to coordinate a working relationship among the governments authorities, scientific and professional institution, and chief business corporations including industry and agriculture. This Agency should identify those activities presenting the greatest risk of pollution to groundwater, but which are currently not well regulated in order to develop appropriate controls, including necessary legislation. The Agency should provide a better focus for the prevention of pollution of natural resources in the upper region and downstream. Karstification is considerably deeper than the altitude of the sites where groundwater discharges into the rivers Neretva, Tihaljina and Listica. This was discovered from the boreholes at the southern edge of Mostarsko Blato, in the Imotsko Polje and at Salakovac and Studenac in the river Neretva valley (Sliskovic, 1994). Protection of groundwater in karst region against pollution is different from that in unconsolidated water bearing formations. In karstified rock rain water in the rule, enters into terrain carrying its suspended part of the contaminating substances, and these rocks usually have no straining or filtrating capacity. Therefore, little filtration occurs during the flow in such kind of aquifer. On the other side, the velocity of the flow is much higher, even several hundreds or thousands of meters per day. Therefore, the protection zones should be determined after an extended investigation. Since groundwater flows trough fissures, cracks and caves mostly along faults which are crossed by other fissures caused also by faults or other tectonic disturbances, there is a net of many fissures, some extending to the surface, through which water may receive fresh pollution from surface. These facts call for a special and strict regime of protection of ground water in karst aquifers. It is recommended to avoid construction of any industrial structure discharging polluted effluents in the recharging area of aquifer. There should be prohibited discharge of any toxic substance in the soils, caves or ponors. Waste water should be treated and controlled before discharge in the stream or at the soil. In the circumstances of the most intensive recharge of the karst aquifer by precipitation in the higher areas with very limited sources of pollution, the groundwater in the region is yet non-contaminated. The lower parts of the region are populated and more developed, fortunately there are more overlying clay to protect the groundwater in aquifer. The quality of groundwater in the chief springs of the region is still satisfactory. Springs 15, 16 and 17 in the upper part of the Tihaljina river are an exception and their water must be treated before the use in water supply. A comprehensive hydrogeological investigation should take place in

9 Groundwater Vulnerability in Western Herzegovina 453 order to define the policy of a sustainable development and use of land in the high karst region. where the most intensive recharge of all 7 drainage basins/major aquifers occurs. Special precautions should be taken to avoid pollution of groundwater in these highly vulnerable aquifers. In the region should be established a reliable laboratory for a regular control of water quality in water sources and in observation wells. Beside standard control bacteriological and aesthetic quality, the laboratory should be equipped for a regular control of radioactive materials, Pesticides, Trihalomethans, Benzene, Chlorophenol, and inorganic constituents of health significance, like: Arsenic, Cadmium, Chromium, Cyanide, Phenols, Fluoride, Lead, Mercury, Nitrate and Selenium. It could be recommended to the establishment to set up an Environment Agency to coordinate a working relationship among the governments authorities, scientific and professional institutions, and chief business corporations. This Agency should identify those activities presenting the greatest risk of pollution to groundwater, but which are currently not well regulated in order to develop appropriate controls, including necessary legislation. The Agency should provide also a better focus for the prevention of pollution of natural resources in region and downstream. References Aller,L., Bennet,T., Lehr, J. H., Petty, R. J., and Hackett, G.(1987): DRASTIC - a standardized system for evaluating groundwater pollution potential using hidrogeologic settings. U.S. Environmental Protection Agency, Ada, OK, EPA/600/ Herak, M. (1977): Tecto-genetic approach to the classification of karst terrains, Krs Jugosl., 9/4, pg , Zagreb. Komatina, M. (1975): Hidrogeoloske odlike slivova centralnodinarskog karsta, Spec. ed., Geozavod Beograd. Sliskovic, I. (1991): Hidrogeoloski odnosi u cvrstim stijenama Bosne i Hercegovine, Unpublished Ph.D. Thesis, University of Zagreb. Sliskovic, I. (1994): On the Hydrogeological Conditions of Western Herzegovina (Bosnia and Herzegovina) and Possibilities for New Groundwater Extractions, Geol. Croat, Zagreb, pg Vrba, J. (1991): Mapping of groundwater vulnerability. International Association of Hydrogeologists, Groundwater Protection Commission, working paper for meeting in Tampa, Fl, USA. Vrba, J. and Zaporozec, A. (1994): Guidebook on Mapping Groundwater Vulnerability, International Association of Hydrogeologists, Volume 16,, Verlag Heinz Heise. Vrana, M. (1984): Methodology for construction of groundwater protection maps. UNESCO/UNEP Project PLCE- 3/29, Moscow. Struckmeier, W.F. (1989): Types and uses of hydrogeological maps. Memoirs of the International Symp. on Hydrogeological Maps as Tools for Economic and Social Development, Hannover, p Zelenika, M., Muhovec, I. et. al, (1999): Studija izbora lokacija odlagalista otpada u zupaniji Zapadnohercegovackoj, Geotehicki fakultet Varazdin. Narodne novine, 4, (1996): Zakon o potvrđivanju Konvencije o zastiti uporabi prekogranicnih vodotoka i međunarodnih jezera, pg Authors Mladen Zelenika: Faculty Civile Enginering Mostar, Bosnia and Herzegovina Ivan Slišković: Institute of Geology, Zagreb, Croatia Božo Soldo: Geotechnical faculty, Varaždin, Croatia

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