ECOLOGICAL PROBLEMS OF KARST WATERS CAUSED BY ...

ECOLOGICAL PROBLEMS OF KARST WATERS CAUSED BY OVEREXPLOITATION AND CONTAMINATION On the example of North-East Bulgaria

ERB-CIPA-CT93-0139 Project, coordinated by A. Pulido-Bosch, Professor of Hydrogeology University of Granada (Spain)

This book is co-authored by A. Pulido-Bosch1, M. López-Chicano1, M. Machkova2, B. Velikov3, D. Dimitrov2, P. Pentchev4 and J.M. Calaforra5 1. University of Granada, Spain; 2. National Institute of Meteorology and Hydrology, Bulgaria; 3. University of Mining and Geology, Sofia; 4. Hydrocomp Ltd., Bulgaria; 5. University of Almeria, Spain.

November 1997

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ACKNOWLEDGEMENTS The present study has been carried out within the framework of the program COPERNICUS, project ERB-CIPA-0139, financed by the European Community. In addition, part of the work falls within projects AMB92-0211 and AMB95-0493, financed by the CICYT (A. Pulido-Bosch, J.M. Calaforra, M.L. Calvache and M. López-Chicano).

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PREFACE This book describes the studies carried out by four research teams over a period of three years within the framework of the COPERNICUS Programme, contract CIPA-CT93-0139. It is intended to cover the many and varied field and laboratory activities undertaken and their subsequent analysis, including an initial in-depth interpretation of the great quantity of data obtained from the numerous field trips. In addition to the intensive contributions of each and every one of the team members, active collaboration was also provided for the duration of the project by a series of persons and/or consulting companies to resolve particular problems or assist in the acquisition of certain data. The study area, the Dobrich region, comprising some 4600 km2, presents a wide range of hydrogeological problems of both scientific and immediately practical interest. During the first year of activity, it was found necessary to establish the project goals focussing our attention on two pilot areas, one inland and the other on the coast. This enabled resources to be concentrated in a more rational and realistic way. At all times we enjoyed the active collaboration both of the local authorities - town mayors and staff of the water-supply services - and of numerous resorts and organisations of groundwater consumers within the study area. The local press was always present at acts held to present our project and provided objective and thorough reporting of our activities. This was a factor favouring the subsequent field trips made during the first and second years. On this first page, we wish to express our gratitude to all the above, individuals, organisations and the press, for their great assistance, without which the project would have had serious difficulties in reaching a satisfactory conclusion. Finally, we should make it clear that some aspects and partial results have been published in Journals and/or at Congresses; many more are currently under preparation for submission to various specialized Journals. Among these latter are Hydrogeology Journal, Revista de la Sociedad Geológica de España, Geology and Mineral Resources, 5th International Symposium on Karst Waters and Environmental Impacts (Antalya), 5th International Conference on Developments in Hydrogeology of Mountain Areas (Stara Lesna), TAHICU’96 (Cuba), XXVII IAH Congress on Groundwater in the Urban Environment (Nottingham). Other, already completed, studies have been submitted to Journals such as Journal of Hydrology, Comptes Rendus de l’Académie des Sciences de Paris, Hydrogéologie, Hydrological Sciences Journal. Almeria, Spain, November 1997 Antonio Pulido-Bosch Professor of Hydrogeology

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RESEARCH TEAMS Four teams were responsible for carrying out this research project, assisted by certain collaborators, details of whose contributions are given below. Spanish team (University of Granada) * Prof. Dr. Antonio Pulido-Bosch, team leader, currently at the University of Almeria * Dr. Manuel López-Chicano, senior researcher * Dr. Jose Maria Calaforra, senior researcher (University of Almeria) * Dr. Maria Luisa Calvache, senior researcher We were assisted by Dr. Ignacio Morell (University of Castellon, Spain), who participated in two field campaigns (summers of 1995 and 1996). Bulgarian teams: + National Institute of Meteorology and Hydrology - Forecasting Department * Dr. Marta Machkova, senior researcher. Team leader * Dr. Dobri Dimitrov, senior researcher * Miroslava Ilieva, technical assistant * Yordanka Berova, technical assistant * Valentin Mironov, technical assistant, NIMH branch Varna. The following also made valuable contributions to the project: * Makroukhi Gyulian, chemist. Water Supply Service of Dobrich. * Ivan Stoikov, hydrogeological engineer. Water Supply Service of Dobrich. * Assen Lichev, hydrogeological engineer, from the Ministry of Environment. * Dr. Tsvetan Tsenov, senior researcher, leader of the tracer group, Georedmet Ltd. + University of Mining and Geology * Dr. Borislav Velikov, senior researcher. Team leader * Dimitrinka Dimitrova, technical assistant * Radka Takeva, technical assistant + Hydrocomp Ltd. * Dr. Pavel Pentchev, senior researcher. Team leader * Raina Angelova, researcher * Angelina Petrova, researcher * Georgi Mihov, technical assistant * Mariana Tchvetkova, technical assistant The following also made valuable contributions to the project: * Stanislav Kovatchev, researcher UMG, Department of Hydrogeology * Bojan Tonev, researcher, Geozashtita Ltd. Varna * Petar Stephanov, researcher UMG, Department of Geophysics * Dimo Trifonov, researcher. Water Supply Service of Dobrich.

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PART I.- GENERAL INTRODUCTION

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1. OBJECTIVES In the last few decades, the water quality of the karstic aquifers in Bulgaria, and especially in the NE region of the country, has deteriorated significantly as a consequence of agricultural and industrial activities. There is also a possible process of seasonal overexploitation of the aquifers, together with the tendency of a decreasing annual amount of precipitation. For all of these reasons, problems of nitrate pollution have appeared, as well as the probable beginning of seawater intrusion and groundwater depletion. The carbonate aquifers are almost the only source of fresh and drinking water in northeastern Bulgaria, and thus the present study is intended to provide an updated overview of the hydrogeological conditions of the two principal aquifers in the region. One of these aquifers is unconfined and shallow (Upper or Sarmatian Aquifer) and the other is confined and deeper (Deep or Valanginian Aquifer). These two aquifers are described separately. The main objectives of the study are to identify the hydrodynamic and hydrochemical conditions, and the processes of pollution, overexploitation and seawater intrusion in the two main karstic aquifers of the region, wich are heavily influenced by human activities. A better understanding of present conditions and of the reasons for the worsening of water quality and quantity in the most unfavorable areas are required in order to propose and implement measures for restoring and improving groundwater resources. 2. CHARACTERISTICS OF THE STUDY AREA AND PREVIOUS RESEARCHS The study region, with a surface area of some 4600 km2, is located in the NE of Bulgaria, between the geographical coordinates 27º 32' to 28º 42' longitude E and 43º 22' to 44º 00' latitude N. The geographical and political boundaries are: to the north, the border with Rumania; to the east and southeast, the Black Sea; to the south, the Batova River valley; and to the west, the Suha River valley (Figure 1). The most important cities within the area are: Dobrich, Balchik, Kavarna, General Toshevo and Shabla. As Dobrich is situated in the central sector of the study region and is one of the major administrative centres, we refer to the study area as the Dobrich Region (Dobrudja). Photo 1: View of the downtown section of Dobrich.

From an economic point of view, this region is predominantly agricultural; it is the primary producer of wheat and corn in Bulgaria. The area under irrigation forms a relatively small part of the total study area. In addition, livestock installations are numerous, with pig farms predominating in the greatest concentration of the entire Balkan Peninsula. Most industrial activity is centred around the city of Dobrich, although there is also industry in Balchik and Kavarna. The coastal sector bordering the Black Sea registers a relatively high level of tourism, mainly domestic; there is substantial use of numerous spas supplied with thermal waters from the Deep Aquifer. Figure 1. Location of the study area.

The first studies to characterize the hydrogeology and hydrochemistry of the region date from the 1970s and mainly consider the Upper Aquifer (Raykova and Danchev, 1972; Antonov, 1973; Antonov and Danchev, 1980). Later works provide

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hydrogeological descriptions of the principal productive levels of the region (Upper, Deep and other Aquifers), providing data concerning the hydrogeological and hydrogeochemical properties as well as values of hydraulic parameters (Danchev et al., 1981). More recently, an analogic electric model (R-C) was made for the Upper Aquifer to estimate the hidden or less visible discharge (Betsinski et al., 1990). In the late 1980s and early 1990s part of the Bulgarian team responsible for the above project carried out a further study to identify the hydrogeochemical processes underlying the interactions between water and carbonate rocks in the aquifers of the region (Velikov, 1985, 1991, and Velikov et al., 1986, 1989) and to obtain a hydrochemical classification of this water using multivariant statistical analysis (Dimitrov et al., 1993). Many of the hydrogeological results obtained from the project, which are summarized here, together with previously unpublished data, have been published in recent years in various scientific journals and congress reports. These have described the hydrodynamic functioning of the two main aquifers (Pulido-Bosch et al., 1996a, 1996b, 1997) and the environmental problems arising, both in regional terms (Machkova et al., 1997) and at a local scale (Machkova et al., 1995; Velikov et al., 1996 a; Pentchev, 1996). The two main aquifers considered in this study extend to the N, crossing the frontier with Romania: the surface area here, in the part of southern Romania known as Dobrudja, is similar to that of the Bulgarian sector (Iurkiewivz and Oraseanu, 1997). Within the Romanian sector, the waters from the two aquifers mix, both with each other and with those from other deep permeable levels, thus acquiring a marked thermal character, and discharge in the coastal region between Mangalia and Constanza. This sector has also been the object of numerous published hydrogeologic and hydrogeochemical studies, mainly examining the isotopic groundwater composition (Davidescu et al., 1991), the origin of the thermal nature of the groundwater (Feru and Capota, 1991); Feru, 1993), its hydrochemical composition (Marin and Nicolescu, 1993) and the hydrodynamic functioning of the piezometric level (Tenu and Davidescu, 1993; Povara, 1994). All of these studies contribute to further our knowledge of the discharge zone of the main aquifers in the region, thus complementing the data obtained from the Bulgarian sector. 3. CLIMATOLOGY There are 4 meteorological stations in the study area, which measure conventional parameters such as air temperature, humidity, wind velocity and precipitation, at least three times per day. Another 12 stations monitor only daily precipitation. Thus, there is a good coverage of the meteorological information necessary for estimating the volumes of infiltration of rain water, the primary source of recharge in the aquifers. The average annual temperature in the city of Dobrich, over the last 50 years, is 11º C (Bulgarian Hydrometeorological Service, 1983), while the monthly averages fluctuate between -2º C and 23º C during the year. The annual average for the coast is only one degree higher, while the monthly range over the year is somewhat narrower (16º to 17º C). Annual precipitation varies from 380 to 460 mm, increasing from the coastal zone towards the interior of the country (Bulgarian Hydrometeorological Service, 1983). The variations in time have been estimated by linear and quadratic analyses of trends over the last 100 years, showing a clear decrease, which is even more

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accentuated in the coastal zones. Figure 2 shows these analyses of trends for the pluviometric station of Shumen -situated some 30 km west of the study area- for wich a complete series of data is available. In the other pluviometric stations of the area the tendencies are similar, although the series are incomplete. The same figure shows the accumulated curve of differences with respect to the mean. There is a rising trend in the first part of the period and a falling trend in recent years. The adjusted linear model indicates a decrease in annual rainfall of more than 100 mm. Other studies of precipitation trends in Bulgaria report pronounced falls in total annual rainfall during the last 10 years (Sharov et al., 1994). Figure 2. Trend analysis for precipitation recorded at the Shumen pluviometric station.

Annual distribution of the precipitation is quite uniform, with monthly totals of 30 to 60 mm (Figure 3). The monthly maxima in the coastal area occur in October and January, with a secondary maximum from May to July. By contrast, in the central sector of the study area, far from the sea, maximum values are observed between May and July, with a secondary maximum in October (Miklanek and Dimitrov, 1995). Figure 3. Distributions of average monthly precipitation and of potential and actual evapotranspiration, in the coastal area (Varna) and in the central area (Dobrich).

Monthly potential and actual evapotranspiration data, estimated for the meteorological stations by a complex method (Figure 3), between 1976 and 1988, show that only between November and February is there insufficient energy to evaporate the available water. During the other months of the year, the energy is far greater than necessary and evaporation is only limited by water availability. The actual annual evapotranspiration is on the order of 23 to 27 % of the total precipitation, the mean being some 132 mm year-1. The total recharge during the period mentioned was about 80 mm year-1. If the matter is simplified by considering the water budget to be almost zero (hypothesis of stationarity), the quantity of water which flows to the Black Sea and the Romanian part of the aquifer is about 50 mm year-1. 4. GEOLOGY 4.1. General considerations In a large part of the area, its geology is relatively well known from the wells drilled for structural observations, mining investigation (basically coal and petroleum), and for pumping water, which generally reach substantial depths (more than 400 m), but can penetrate to much geater depths (exceeding 4000 m). The study area is located on the Moesian Platform (Iovtchev, 1976), which occupies the entire northern third of the country, to the north of the domain of the Balkan Cordillera and to the south of the domain of the South Carpathians. This platform, which has remained more or less stable since the Hercinian folding, has two main complex structures, one superimposed over the other: a folded and fractured Paleozoic basement (Caledonian complex, Hercinian) and a non-folded cover, which can nevertheless be somewhat fractured, with sedimentary rocks dating from the Permian-Triassic to the Quaternary (Figure 4). Each structural complex presents various tectosedimentary units, but in this area these can be differentiated only by the covering of the following: the lower level, from the Permo-Triassic, does not outcrop and sometimes show intrusions of igneous

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rock; and the upper level, which includes various sublevels form the Middle Jurassic to the Lower Cretaceous, Upper Cretaceous to the Paleogene, and Neogene. Figure 4. Lithostratigraphic synthesis of the study area.

Of special interest to the present study, for their water resources, are certain formations of the upper level of the non-folded covering, specifically of the sublevels ranging from the Middle Jurassic to the Lower Cretaceous (Deep Aquifer) and the Neogene (Upper Aquifer). 4.2. Stratigraphy The description of the materials present in the study area (lithological characteristics, age, thickness, spatial distribution, etc.) begins with the most recent and continues to the oldest materials. Quaternary materials are made up of aeolian Pleistocene sediments (loess), clayey towards the top and in the southern sector, and sandy or mixed with alluvial sediments towards the bottom and in the northern outcrops. These materials cover most of the study area, except the canyon floors, wich are the high-quality cultivated areas. Although there is low permeability, the scant topographical differences mean that canyons are not deeply cut. Occasionally, there are endorreic areas over these materials. The thickness of these varies between 5 and 40 m, thickening towards the north. Photo 2. Panoramic view of the intensively cultivated areas covered by quaternary loess.

The Miocene is represented by various groups of formations, all of paramount importance to the present study. The upper group is comprised basically of two carbonate formations of Sarmatian age (according to the Caucasian chronological scale) or Messinian (according to the international chronological scale), between which lies - only in the sector situated to the N of Balchik and Kavarna and to the W of Shabla - a formation of banded marls and clays (Topolovo formation) which can reach a thickness of 45 to 80 m. The most recent carbonate formation is Karvuna, which consists of organogenic and conchiferous limestone, sometimes compact and sometimes highly porous due to the dissolution of fossil shells. This formation appears only on the southern and eastern edges of the study area, where the greatest thicknesses occur (Cheshitev and Kânchev, 1986), in general from 10 to 50 m. The lower carbonate formation, called Odar, is more extensive, present in practically the entire area, and exposed on the surface in gullies and coastal cliffs. The composition is organogenic, conchiferous, oolithic and detrital limestones with calcarenite interbeds and, more rarely, clays or marls. It is often red-coloured. The thickness of this formation ranges from 30 to 120 m. Photo 3. Outcrops of the Odar formation in the cliffs near Cape Kaliakra.

The Lower Miocene group, from the Aquitanian-Tortonian, comprises 4 formations - Frangja, Evksinograd, Galata and Karapelit- with complex facies as transitions from one to the other. The entire group can be considered an alternation of sands and clays or marls, these latter being generally thicker, with a few intercalations of organogenic limestones and/or thin and rather discontinuous calcarenites. In the southern sector (Balchik) and the southeastern one (the Batova River and the head of the Suha River), where especially clays and/or marls outcrop, thicknesses are greater, of the order of 150 to 200 m. This magnitude is also detected in wells in the Vranino sector (N of Balchik and Kavarna) and in the Shabla-Bulgarevo block (coastal zone ESE of the area). Nevertheless, towards the N of the region, the thickness diminishes, so that this group practically disappears in the middle of the

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northern area, or at most presents a thickness of less than 10 m in the Frangja formation (yellowish-white sands over bluish-grey clays). Miocene materials are unconformably superimposed over a Paleogenic group, which practically does not outcrop in the study area and thus is known only from well drilling data. These data indicate that the group is present only in the southeastern half of the study area, ranging from 40 to 740 m thick, with the thickness increasing towards the E. On the whole, the lithology is highly varied and can be considered as alternating layers of clay and marl (at times very thick), organogenic limestone, marly limestone, sand, sandstone and calcarenite. Manganese concretions also appear at different points. Relevant carbonate intercalation, composed of nummulite and glauconite limestones and called the Aladân formation, dates from the Eocene and is 8 to 30 m thick. These materials are usually confined between marls towards the top and sandstone towards the bottom. Paleogene materials lie unconformably over a group from the Hauterivian to the Upper Cretaceous. In turn, within this group, an unconformity can be discerned separating the Lower from the Upper Cretaceous. Present in depth throughout the region, this group outcrops along the valley of the Suha River and some of the principal tributaries, varying in thickness from 30 to 400 m (increasing towards the W and NW). Essentially, this is a series of alternating marly limestones and limestone marls, more terrigenous or with limestone containing chert and conglomerates of little thickness from the Upper Cretaceous. Nevertheless, a carbonate formation (called the Ruse Formation) intercalates, especially in the northwestern quadrant, outcropping in the northern half of the Suha River valley and major tributaries. These materials, which include organogenic and oolithic limestones, have a porcelain-like texture and are very hard. Thicknesses vary from 30 to 100 m, increasing towards the NW. In this northwestern sector of the region, these limestones lie directly under the Odar formation, infiltrating runoff from the Suha River. In general, the age of this formation is Hauterivian-Barremian. These limestones are only detected in the northwestern sector of this area. Concordantly with the lower part of the previous series are materials from the Malm-Valanginian age. Forming a thick package of limestones (intraclastic, organogenic and aphanitic), dolomite limestone and dolomites, these constitute the Deep Aquifer. These materials are present throughout the region, but outcrop only in the western sector, at certain points, in the valley of the Suha River and some of the most western tributaries. The outstanding formation in these materials is Kaspichan (Cheshitev and Kânchev, 1989), slightly folded (dipping by less than 10°) by adaptation to the play of fault systems. The thickness of this terrain ranges from 400 to 900 m, increasing generally towards the SE. The Middle Jurassic is represented by clayey formations, sandstones, calcarenite and/or limestone marls, with thicknesses of between 5 and 150 m, at times absent in the northwestern sector. Thickness increases in general to the SE. These materials are unconformable with the above mentioned formations. Permian-Triassic materials mainly fill the Hercinian paleorelief, adapted to the morphology of the bottom or folded Paleozoic substratum. Therefore, thicknesses are extremely variable (50 to 4000 m), and can even be absent in the sector known as the Dobrudja Massif (Figure 5), situated in the Kardam-Durankulak-Vranino triangle (this latter to the north of the Balchik-Kavarna sector) and in the massif situated to the west of Dobrich (Figure 5). Triassic is represented by an alternation of carbonate X

and detrital (sand and clay) materials, or of marly materials, all grouped in more or less thick groups. Permian materials consist of a volcano-sedimentary complex, sometimes with intercalations of carbonate and anhydrite materials. In the areas where Permian-Triassic materials are absent or thin, deep wells reach Devonian materials (thick carbonate groups) or carboniferous materials (argillites and sandstones, volcano-sedimentary formations and coal), which are generically called the "Folded Basement". 4.3. Tectonics From a tectonic point of view, these materials have not been affected by Alpine folding. Nevertheless, according to Bergerat and Pironkov (1994), this area provides an accurate register of the main tectonic events that have occurred since the Cretaceous, both in the area itself and in the domains of the Balkan Cordillera and the South Carpathians. At most, fractures are known to exist which can move some blocks with respect to others. The Moesian Platform has remained quite stable since the Hercinian folding. Hercinian basement materials are folded and fractured, making it difficult - because they are completely covered - to identify the structural pattern. Later materials (from Permian-Triassic to at least the Lower-Upper Cretaceous boundary) show a tectonic fracturing which has acted in various periods, with quite different patterns. Bergerat and Pironkov (1994) identified four main stress states, which correspond to at least two significant faulting phases: a Cretaceous phase (Aptian to Maestrichtian), mainly characterized by a NNE-SSW to N-S extension and, to a lesser degree, by an ESEWNW to E-W compression (horizontal maximum stress, with N95 to 120E strike), prior to the collision between the African and Eurasian plates; and secondly, a s.l. Miocene phase, posterior to the Paleocene, at least, characterized by a N-S to NNESSW compression and by an E-W to ESE-WNW extension, concurrent with the Africa-Eurasia collision (Illyrian phase). The same authors have confirmed the existence of a third N-S compression phase (NNW-SSE, according to Shanov, 1990), which they attribute to the Pliocene, affecting materials belonging to this age, as well as those of the Upper Miocene (Sarmatian) and even older (Valachian phase?). From the chronology of these deformations, the first phase must have coincided approximately with the opening of the western oceanic basin of the Black Sea, which occurred as a result of a rifting process that started during the Aptian and which caused the separation of a fragment of the Moesian Platform, currently located in the Istanbul region (Okay et al., 1994). The second phase would correspond to the advance of the domain of the Balkan Cordillera, during the Alpine Folding. Figure 5. Tectonic scheme of the study area.

Despite the tabular arrangement of the Moesian Platform, its internal structuring, due to the effects of multi-phased fracture tectonics, is based on wide depressions and domes. Examples of the latter are to be found to the west of Dobrich (the North Bulgarian Dome, according to Boncev, 1988), where the thickness of the Paleozoic Quaternary series does not exceed 3 km, and the Dobrudja Massif (Ioutchev, 1976), situated to the N of the study area (Figure 5). To the S and SE of these raised blocks lies the Varna - Balchik Miocene basin, elongated towards the N and S. Thus, the top of the Valanginian, which constitutes an excellent seismic reflector, shows a series of horst and grabens, lying within 3 main sets of normal stepped faults (NW-SE, NNESSW and E-W) which cause this surface to range from more than 200 m above sea level to 1000 m below it. These fractures probably cause the dipping of the layers to XI

be in several directions (rollover anticline folds), although in general by no more than 10°. The fracture zone running N-S through Dobrich and the western sector of Balchik has special significance in the apparent normal faulting or flexion in an E-W direction. The fracture zone of Shabla-Bulgarevo is also of special note, forming the western boundary of the horst of Tyulenovo (Figure 5). Some of these fractures have reactivated, during different episodes, affecting even Lower and Middle Miocene materials though apparently not those of the Upper Miocene (Sarmatian). The lateral and vertical distribution of the different stratigraphic formations appear to be strongly determined by this block tectonics, particularly the Cretaceous and Paleogene. 4.4. Geomorphology Approximately the northwestern half of the area corresponds to the hydrographic basin of the Danube, in the lower stretch of the river. The rest of the area is drained by various small basins which empty into the Black Sea. From the standpoint of its morphology, there is no accentuated relief or pronounced slopes, as the area is quite flat, with altitudes from 0 m a.s.l. along the Black Sea to 380 m in the southwest of the region. This monotonous flatness is only interrupted by narrow valleys with depths of up to 200 m from the altitude of the plateau, especially in the southern sector (Batova River) and in the west (Suha River). The altitudes of the plateau rise from the E to the W and from the NE to the SW. The slope of the terrain towards the coast is gentle and steady in the NE sector (Krapetz zone), but abrupt along the rest of the coastline (south of Shabla, Cape Kaliakra and Balchik), where cliffs form a number of inlets. Photo 4. General view of the Dobrudja Plateau from Albena beach.

In addition to the narrow valleys which cut into the plateau, there are at least 13 shallow closed depressions which affect the terrain surface, located mostly between the cities of Dobrich and General Toshevo. These depressions, of karstic origin (dolines or poljes), have an area of more than 1 km2, and can extend over 20 km2. Similar karstic depressions. with diameters of 200 - 600 m, have been observed in SE Romania, to the W of Mangalia, where they are termed Obanes (Feru and Capota, 1991), though in fact several of these correspond to former quarries. Some of these Obanes (such as Kara Oban) present sulphurous hypothermal springs, the origins of which are discussed below, with output flows on occasion exceeding 300 l/s. This part of Romania contains important karstic caves, such as Pestera de la Movile; this is a thermal cave, and was discovered in the course of excavations for hydraulic projects. Photo 5. Karstic forms in the Odar formation, near Bolata.

Iurkiewicz and Oraseanu (1997) consider the Romanian part of the Dobrudja region (which is very similar to the Bulgarian part) to be a platform karst. The main karstification phase recognized probably corresponds to the Upper Pliocene (Povara, 1994); in any case, karstification took place after the terminal Miocene, when there was a marked fall in the level of the Black Sea (Robinson et al., 1996). 5. HYDROGEOLOGY 5.1. Water-bearing formations

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The Quaternary materials which cover a large part of the study area present intergranular porosity. These materials should be considered as forming an unconfined aquifer, with transmissivity values of between 43 and 136 m2/d, and a storage coefficient of between 2 and 5 %, for the case of the Pleistocene loess. Alluvial materials, with little representation in the region, have hydraulic conductivity values of between 70 and 90 m/d, and a storage coefficient of about 23 % (Velikov et al., 1989). These detrital materials are in hydraulic connection with the Upper Aquifer. The Upper Aquifer is one of the most extensive and exploited of the area (Figure 6). It is made up of limestones and calcarenites of the Karvuna and Odar formations; in certain sectors, the two formations can be locally isolated by a layer of low permeability (the Topolovo formation). The generally high level of porosity originates from intergranular spaces (calcarenites), a heterogeneous solution of fossil shell remains (organogenic and conchiferous limestones) and the processes of karstification on fissures and bedding planes; faulting is quite uncommon. Figure 6. Hydrogeological map of the Dobrich region. Photo 6. A detail of the Upper Aquifer (Odar formation) with intergranular porosity, some fissures and small karstic conduits.

The Deep Aquifer, composed of limestone and dolomite from the MalmValanginian, owes its permeability primarily to fracturing and karstification, as primary porosity is almost non-existent. These constitute the most important hydrogeological units in the region, with numerous wells of great depth (Danchev et al., 1981). In Romania (S Dobrudja) it has been shown that the two aquifers constitute - at least locally - a single hydrogeological system. This is the most important of its kind in the entire country, with average resources of around 12-14 m3/s (Iurkiewicz and Oraseanu, 1997). There are interactions not only between the two aquifers, but also between these and the River Danube, the coastal lakes and the irrigation network (including the Danube - Black Sea channel). Among the materials of the Upper Aquifer and the Deep Aquifer is a series of intercalated materials from Hauterivian-Upper Cretaceous, Paleogene and Lower Miocene-Tortonian with highly varied hydrogeological behaviour. Nevertheless, given the confined character of the aquifers, the reduced thickness of the aquifer materials, the predominance of clayey-marly materials, etc., this formation (for most of the region) is considered of low permeability. There are stratigraphic formations of major hydrogeological importance: the Ruse Formation, a fissured and karstified aquifer present only in the northwest of the region, which underlies the Upper Aquifer; and the Aladân Formation, an aquifer of intergranular porosity with fissuring and karstification. In the Romanian sector, situated immediately to the N of the study area, some of these stratigraphic formations intercalated between the two main carbonate aquifers are thicker and, in hydrogeological terms, more important; they have been shown to be hydraulically connected to the aquifers, while the impervious confining materials become less thick. Indeed, some studies (Marin and Nicolescu, 1993) consider the Jurassic, the Cretaceous, the Eocene and even the Paleozoic materials to form a single hydrogeological unit. In this region of Romania, and on the neighbouring seabed, Robinson et al. (1996) found that certain Albian sandstones (with a thickness of up to 300 m) present a mean porosity of 20% and a permeability of 100 - 200 mD, while the sandy marls of the Eocene also have a mean porosity of 20%, but in this case the hydraulic conductivity is only 1 mD. Nevertheless, in the Mangalia region, Feru and Capota (1989) report that some wells tapping the

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Miocene, composed of glauconitic calcarenites and nummulitic limestones, encounter artesian yields of 26 - 52 l/s; high specific yields were also recorded, of the order of 1.8 - 3.7 l/s/m. The hydrogeological behaviour of Middle Jurassic materials can generally be described as practically impervious. These materials can be absent in the NW sector of the area, although these usually constitute the impermeable substratum of the Deep Aquifer. The other geological materials present in depth within the region (Permo-Triassic and Paleozoic basement) include either permeable or impermeable formations. The behaviour of these formations is little known. Data from petroleum wells indicate that Permo-Triassic materials can present strongly saline fossil waters. 5.2 Observation points The observation points correspond exclusively to the Upper and Deep Aquifers (Sarmatian and Valanginian Aquifers repectively, according to the bulgarian nomenclature). Some 50 points were selected for the Sarmatian, most of these being domestic or drilled wells. Approximately ten of the points correspond to springs in the areas of Balchik, Kavarna, the Batova River, Abrit and Botevo (these latter two, on the River Suha). Other monitoring points include the coastal lakes of Durankulak and Shabla, and those in the Bolata region: these are areas of visible discharge. Some 60 points were selected for the Valanginian aquifer, all of which were hydrogeological or research-based boreholes of considerable depth. Only one spring was included that is clearly related to this aquifer, the one at Devtnia, located to the SW of the region and outside it. Many of the wells tapping the aquifer are artesian in the coastal area between Shabla and Balchik, and have no control valves fitted, with the result that water is continuously expelled, and in considerable quantities. 5.3. The Upper Aquifer 5.3.1. Geometrical features The aquifer system, although covered to a fair extent by Quaternary loess (Figure 6), is essentially unconfined. Its structure is tabular, or with a certain dip towards the E (Black Sea), related to the original slope at the time of deposit. Thicknesses range from 30 to 250 m (Figure 7). The minimum thicknesses are found in the western sector, in the Suha River and tributary valleys; in this area the substratum of the aquifer outcrops, due to the deep vertical excavation of these valleys. In the region of Dobrich and General Toshevo, the aquifer rapidly thickens towards the SE, reaching maximum values to the N of Balchik and Kavarna. Towards the E, in general, values again diminish to 50 m near the coast (Figure 7). In the SE of Romania, the aquifer presents thicknesses of 60 to 150 m (Povara, 1994). The eastern boundary of the aquifer system is the Black Sea. Between Cape Kaliakra and Durankulak, the coast has progressively more cliffs towards the S. Along a large part of the eastern coast, the aquifer penetrates beneath the sea, although there is not always contact throughout its entire thickness, as in the case of the southern zone of cliffs. Pentchev (1996) compiled data from the Varna Oceanology Institute (Bulgaria) on the nature of the seabed in the western sector of the study area. These data indicate that, up to 2500 m offshore, the Miocene limestones that comprise the Upper Aquifer outcrop into the seabed, either directly or with a coverage of less than 2 m of sand, silt or clay.

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The southern boundary is defined by the sea between Cape Kaliakra and Kavarna (cliff coast), while farther to the W, towards Balchik, the boundary is the contact with the clay-sandy materials of the Miocene age. This contact rises to the W, entering the deep Batova River valley, which also constitutes the southern limit of the aquifer (Figure 8). Figure 7. Thickness of the Upper Aquifer.

The western boundary is defined essentially by the Suha River, which flows approximately from S to N. Along practically the entire length of this valley, the substratum of the aquifer outcrops due to erosion. This also occurs in the valley which runs from Dobrich towards the NW (Karamandere river). The northern boundary, permeable and of varying thickness, is represented by the border between Bulgaria and Rumania. Figure 8. Hydrogeologic cross-sections through the Upper Aquifer. Lines of sections shown in Figure 6.

The impervious substratum of the aquifer is formed by Lower and Middle Miocene materials towards the S and SE, by Paleogene materials to the NE and by basically marly-clayey materials from the Hauterivian and/or Hauterivian-Upper Cretaceous to the SE. On the other hand, in the entire NW quadrant it is a permeable carbonate formation (the Ruse formation), which constitutes the Sarmatian substratum. 5.3.2. Groundwater table Based on the data of piezometric levels collected at 45 monitoring points, including wells and springs, during the summer of 1988, a map of groundwater potential contour lines has been drawn (Figure 9). There is a wide variation in piezometric level, from a maximum of 200 m a.s.l. to the NE of Dobrich to 0 m on the Black Sea coast. The water table drops towards the W - where the Suha river drains the aquifer - and towards the E, with slight irregularities, as is the case of the Dobrich-General Toshevo zone. Here a depression in the piezometric level of some 10 m can be appreciated, probably due to the intense exploitation of the aquifer in this sector for local agriculture and urban water supply, including Dobrich (about 100,000 inhabitants). With respect to the relationship between the boundaries of the aquifer and piezometric lines, there are three borders - E, W and S - as shown by the existence of several springs near the coast between Balchik and Bulgarevo, as well as along the Suha River. On the eastern border there is also a spring, although most of the discharge is diffuse or hidden. The isopiezes are perpendicular to the northern boundary from Kardan towards the east; given that the aquifer system continues to the other side of the Romanian border, this would be a permeable boundary of varying potential, coinciding roughly with a flow line (exchange of water being almost nil in this sector). The flow system in the Romanian sector, situated immediately to the N of the study area, is very similar to the one described there. Here, too, there is a predominant E-W component and discharge into the Black Sea in the coastal region (Davidescu et al., 1991; Zanfirescu et al., 1994; Povara, 1994). Figure 9. Water table map for June, 1988.

Regarding the evolution in time of the piezometric levels (Figure 10) in the last few years there is no overall tendency throughout the aquifer, since the piezometric level has risen in some sectors and fallen in others. In general, there were small XV

groundwater level fluctuations over the eight-year measuring period, with maxima rarely exceeding 2 m; at most of the monitoring wells, the piezometric level did not vary more than 1 m over the same time period. Figure 10. Water-level hydrographs.

In the Dobrich-General Toshevo sector, the piezometric level has fallen 2 m since 1986 (point 2 in Figure 10). This same downward trend was found on the eastern coast, though the values are lower (1 m at point 3 and 0.4 m at point 5 in Figure 10). In the rest of the aquifer, the level remained either stable or showed a slight increase (0.5 m at point 4 and as much as 1 m at point 7 in Figure 10). Although this increase is small, it is important because it is located in the zone of greater discharge. In Romania, Povara (1994) analyzed the short-term evolution of the phreatic level in an area of 6 km2 around Mangalia. Very small variations in the piezometric level (6 - 18 cm) were reported. As was the case in Bulgaria, these variations did not correlate well with precipitations. 5.3.3. Hydraulic parameters Using data obtained from 27 pumping tests, we conclude that the transmissivity of the carbonate materials which form the Upper Aquifer depends on the degree of karstification. Therefore, the highest values of this parameter are found on the coastal border, where limestones are in contact with the water of the Black Sea. Many authors (Wigly and Plummer, 1976; Back et al., 1979; Sanford and Konikow, 1989; Pascual, 1990) have demonstrated that in a zone where salt water mixes with freshwater, there are favourable conditions for the dissolution of carbonates, and thus the karstification processes in the limestone become accentuated. In this sector the transmissivity values frequently exceed 1000 m2/d, with maximum values of 6500 m2/d. It is noteworthy that, since the aquifer is not directly in contact with the sea, the limestones do not register high values for this parameter along the southern coast. The lowest values, with minima at around 20 m2/d, are found inland, probably coinciding with the least karstified sectors. Figure 11. Specific-capacity map.

As with transmissivity, the highest values for specific capacity (data available for 25 wells) are registered in the coastal zone, with a maximum of 100 l/s/m and with more frequent values at some 25 l/s/m. The lowest specific capacity is about 0.21 l/s/m (Figure 11). The hydraulic gradient in the coastal zone of Krapetz-Durankulak is 0.04 %, while the mean values in the rest of the aquifer are 0.6 %. In SE Romania, in the coastal sector of Mangalia, Feru and Capota (1991) found specific capacity values equivalent to those recorded in Bulgaria, of the order of 7.8 - 15.0 l/s/m. Also in the Romanian sector, Davidescu et al. (1991) obtained isochronous lines by means of 14C water-dating techniques. These authors found that the waters of the Upper Aquifer have an age of 2500 years in the sector furthest from the coast and over 12500 years in the zone nearest the Black Sea and the coastal lakes. Mean flow velocity was found to be very low, at about 0.8 m/year, which gives an effective porosity of around 12%. Applying this same effective porosity value to the part of the aquifer belonging to Bulgaria, and taking into account the above-described data for transmissivity, saturated thicknesses and hydraulic gradients, the results obtained for real flow velocity were not comparable with those of Davidescu et al. (1991). They were, in fact, much higher, at around 1.5 - 25.6 m/year, depending on the greater or lesser proximity to the sea, respectively. Nevertheless, Povara (1994) recorded

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hydraulic conductivity values of 30 - 40 m/day for the Romanian coastal area near Mangalia: these are in better agreement with those obtained for the same aquifer in the Bulgarian coastal zone. We are therefore led to conclude that, in this case, it does not seem advisable to use carbon radioisotope dating methods, among other reasons because in the Romanian sector it seems clear there is a vertical inflow of older thermal waters (proceeding from deep aquifers, mainly the Jurassic Valanginian materials) to the Upper Aquifer, especially in the area nearest the coastal boundary. This vertical inflow, throughs important fractures affecting the study area, is accepted by the above authors and has been described in many studies (Feru and Capota, 1991; Feru, 1993; Tenu and Davidescu, 1993; Marin and Nicolescu, 1993). Povara (1994) reported that, in the proximity of Mangalia, two thirds of the discharge from the Upper Aquifer corresponds to its natural regime, while the remaining third results from deep-level inflows. Evidence of the karstic heterogeneity shown by this aquifer in the areas nearest the coast is provided by the high flow velocity recorded in the location of Mangalia (Romania) by means of tracer-injection tests performed in the Obanes (Feru and Capota, 1991). These authors quote apparent velocities of 89 to 172 m/h. 5.3.4. Physicochemical characteristics To characterize the general hydrogeochemistry of the Upper Aquifer, we studied the analyses of 300 monitoring wells. The final conclusions are based on the analytic data of 30 water samples taken at selected points throughout the study sector, given that these were considered the most representative. The data come from sampling sessions carried out by the National Institute of Meteorology and Hydrology of Bulgaria, between June and September 1984, though results were taken into account from samples collected in September 1986, which offered further information regarding the eastern coastal boundary. The samples were taken from pumpequipped wells, after at least 15 minutes’ extraction, and so the samples would be representative of the water really utilized. The predominant type of water is magnesium bicarbonate, and to a lesser extent, calcium bicarbonate; this is determined by the lithology of the aquifer and by Quaternary detrital covering (Raykova and Danchev, 1972), this latter being rich in magnesium, containing up to 3.64 % MgO. Only on the western coast, where there is widespread contact with the sea, does the type of water change to sodium chloride (this occurs at many, but not all, of the monitoring points). The spatial evolution of the groundwater temperature shows the same distribution pattern as the mean air temperature, ranging between 12º C in the recharge area (Dobrich sector) and 15 to 17º C in the discharge areas (western and southern coastal areas). This temperature increase might be due to the existence of vertical flows from deeper aquifer formations with a greater hydraulic head (Deep Aquifer). In general, in the central sector of the region - the main recharge area - higher values were registered for the concentrations of CO2 (63 mg/l), HCO3- (500 mg/l), Ca2+ (100 mg/l) and Mg2+ (100 mg/l). Values of these ions decrease towards the discharge zones, suggesting a subsaturation in carbonate minerals in these directions as shown by the saturation indices calculated by the WATROCK program (Velikov, 1985). It should be taken into account that the Ca2+ and Mg2+ are subjected to modifying processes such as ionic exchanges and the influence of the loess covering, which cause the concentrations to correlate less well with those of the

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bicarbonates. The Mg/Ca ratio has a mean value of about 1.68 in the aquifer, the two ions showing a very similar spatial behaviour. The sulphate content of the groundwater is generally very low in the entire region (less than 80 mg/l). Only the 1986 sampling, near Cape Kaliakra, registered higher values, around 112 mg/l (Velikov et al., 1989; Dimitrov et al., 1993). In relation to pollution and deterioration in groundwater quality of the aquifer system, the main sources are: - The absence of a sewage network in small municipalities and rural centres, which dump their sewage directly into the aquifer. - Partially treated sewage from large urban areas such as Dobrich and Kavarna being dumped into rivers (such as Suha River), which run dry most of the year. These wastes contain chlorides, sulphates, sulphides, organic and biogenic components, and often heavy metals from industry (which discharges waste through the urban sewage system). - Waste from cattle farms being dumped into dry riverbeds where mainly limestone outcrops. - Excess use of organic fertilizers. - Uncontrolled groundwater exploitation in the coastal zone, which can provoke seawater intrusion in the aquifer. Therefore, the areal distribution of the nitrates and chlorides within the aquifer are related to three main processes of pollution: scattered dumping of urban liquid waste and of unpurified animal waste; excess fertilizer applied in cultivated areas; and incipient sea-water intrusion on the eastern coastal strip. It has been estimated that the surface area of cultivated land exceeds 300,000 ha, of which 20 % is irrigated with groundwater. The nitrate content exceeds 200 mg/l in extensive areas of the aquifer, with maxima at certain points such as the central sector (south of General Toshevo), where values reach more than 600 mg/l. In general, the maximum values are registered in the principal infiltration area of the entire aquifer, coinciding with developed agricultural sectors and with some of the major population centres. In the southern and eastern coastal sectors, except near the discharge area of lake Durankulak, the nitrate values, though not low, are in general below 30 mg/l, thus indicating a major dilution of the polluting charge in the flow sense (Figure 12). Figure 12. Distribution of nitrate concentrations in groundwater for September, 1984.

The highest chloride contents are closely related to local processes of sea-water intrusion near the eastern coast. Mean values for most of the aquifer are around 50 mg/l, which are considered normal for this region. Along a 5 km strip, parallel to the eastern coastline, values exceed 500 mg/l and reach almost 1000 mg/l (Figure 13), signalling the beginning of sea-water intrusion in localized areas of heaviest pumping and easy contact with the sea (the most transmissive areas). Figure 13. Distribution of chloride contents in groundwater for September, 1984.

The map of spatial variation of water conductivity represented in Figure 14 shows that this parameter quite well represents the sectors most affected by one or more of the pollution processes described above, indicating mineralization maxima coincident with nitrate and chloride maxima. Conductivity is about 600 to 700 mS/cm in the XVIII

discharge areas of the Suha and Batova Rivers, increasing in the contact zone between the aquifer and the Black Sea to values of more than 1500 mS/cm (to the north of Cape Kaliakra), or even over 2000 mS/cm in the coastal zone of ShablaKrapetz-Durankulak. The contour lines of these values have not been included in Figure 14, bearing in mind the merely indicative nature of the map, and the scale adopted. All this can be interpreted as a consequence of the incipient process of seawater intrusion, since these values coincide with a high chloride content. There is another anomaly in the natural distribution of conductivity values in the central sector to the south of General Toshevo, where the conductivity reaches values of 1300 mS/cm, probably due to the agricultural contamination of the groundwater, as these values coincide with high nitrate values. Figure 14. Distribution of electrical conductivity of groundwater for September, 1984.

5.3.5. Groundwater system description 5.3.5.1. Inflows The principal source of recharge in this system is the direct infiltration of rain water. As indicated above, the aquifer is largely covered by Quaternary materials, most of which have low permeability (loess). Thus, one fraction of the infiltrated precipitation percolates slowly, while another fraction, falling on more permeable materials, enters the aquifer far more rapidly. As a result, the closed basins act as preferential accumulation areas for rain and runoff. Finally, there is rapid infiltration in sectors where limestones outcrop and along the beds excavated in these outcrops; evidence of this is a baseflow in the Suha River within the study area. Additional recharge results from the return of irrigation water and part of the sewage, as indicated above. Current data do not permit a precise estimation of the average infiltration values, although an order of magnitude may be 50 to 100 mm, which would imply around 350 Mm3/year, equivalent to a continuous flow of 11 m3/s. The other elements of the water budget would constitute a much lower fraction with respect to the total (Figure 15). Figure 15. Diagram of the groundwater hydrologic cycle for the Upper Aquifer.

5.3.5.2. Outflows The main visible natural discharge of the aquifer occurs on the southern border, both along the coast as well as inland following the Batova River, a sector where many streams are located (Figure 6). There is also discharge on the eastern border, although these springs present a substantially smaller flow. The largest springs, with flows of 50 to 150 l/s are located along the Batova River. One of these has the lowest altitude (55 m) of all the springs of the aquifer, and thus constitutes the primary visible discharge of the system (Figure 6). Seasonal fluctuations of the discharge are very low, between 20 and 40 l/s. The springs of the southern coast are located near the cities of Kavarna and Balchik, with the highest flow (70 l/s) measured at Balchik 1 and the smallest (4 l/s) at Balchik 2. On the western border, two springs with flows of 9 and 20 l/s have been monitored. With respect to the evolution of the discharge rate during the last few years, it should be taken into account that there are various actions which have affected the discharge at these points. For example, at the Batova spring, a pumping station with a yield capacity of 25 to 30 l/s was installed in 1982. In Balchik, the pumping of spring water stopped in 1990, and therefore its flow has increased. The naturally-functioning springs show a general tendency towards an increasing flow, XIX

except one spring in Balchik, where the discharge has remained more or less constant over the last 20 years, and the springs on the western boundary (Figure 16). Figure 16. Hydrographs of springs.

In addition to these instances of natural discharge, the outflow to the coastal wetlands of Durankulak and Shabla should be recorded; this is estimated to approach 1000 l/s, an estimate obtained applying Darcy’s law. Another important outflow, and possibly the greatest, is the hidden outflux through the eastern coastal border and, in less quantity, through the southern coastal border. In addition, there must be a hidden discharge through the northern border in the Romanian continuation of the aquifer, of which the most important visible springs are situated on the coastal strip of Mangalia, to the south of Constanza. Photo 7. View of lake Durankulak, an important discharge area of the Upper Aquifer.

Darcy's law, applied to the eastern boundary, for T = 2000 m2/d and a mean hydraulic gradient of 0.5 - 1 ‰, and 70 km of coastline, gives 25-50 Mm3/year. The same procedure can be followed for the other boundaries. Lastly, pumping constitutes another considerable fraction of the discharge. Quantification of pumping is rather complex; however, it is known that the greatest volumes are extracted in the area of Dobrich and Shabla-Krapetz (coastal zone), with more than 300 l/s each. 5.4. The Deep Aquifer Despite its confinement, the Deep Aquifer is exploited more than is the Upper one, especially along the coastal strip where wells tend to overflow and some contain thermal waters; this situation is to be expected within a normal flow scheme (Toth, 1963): this aquifer has a vast surface area and a recharge area situated essentially to the west of and outside the study area. 5.4.1. Geometry and boundaries The deep hydrogeologic system is an aquifer that is confined under materials later in age. The aquifer scarcely outcrops, except at one point on the Suha River and somewhat more along one tributary (Karamandere River) of the left bank of the Suha. This is the sector where the aquifer is situated nearest to the ground surface, the highest parts lie at altitudes of between 0 and 100 m a.s.l. The slope of the aquifer declines gently towards the N, while towards General Toshevo it appears subhorizontal. To the NW of the study area, within the Romanian border, the aquifer declines towards the N and reaches thicknesses of up to 1500 m. There are localized outcrops beside the Danube in the Romanian Plain. To the N of Bucharest, it is confined at a depth of over 2000 m (Iurkiewicz and Oraseanu, 1997). However in SE Romania (South Dobrudja), in the area to the north of Mangalia, the thickness of the aquifer is around 350 m and it lies at just 150 - 200 m below sea level (Feru and Capota, 1991). Somewhat further to the N, near lake Techirghiol, the deep fracture known as Costinesti - Topraisar, which enables the ascent of waters from the depths of the aquifer, marks the boundary with a horst to the S, from which the carbonates of the Jurassic - Valanginian are absent (Tenu and Davidescu, 1993). Towards the E and SE, the aquifer becomes compartmentalized by blocks which are thrown down or rise, depending on deep fractures. In general, the aquifer declines progressively towards the SE and extends, still confined, under the seabed. To the E of the coastline, seismic studies of the seabed (Dachev et al., 1988) reveal that the aquifer remains confined beneath more recent sediments and declines to depths of 2000 m below sea level. At a distance of 60 km E of the coastline, the XX

aquifer lies at a depth of 7000 m below sea level, under recent sediments up to 5000 m thick, due to the effects of listric fault lines associated with the rifting of the western Black Sea. Figure 17. Hydrogeologic sections. Lines of sections shown in Figure 6. Figure 18. Isobathes for the top of the deep aquifer. Figure 19. Isopaches for the confining part of the deep aquifer.

In the continental study area, greatest depths are reached in two troughs: in the sector of the Batova and Balchik Rivers at nearly 1000 m below sea level; and in the Shabla-Bulgarevo trough, at more than 700 m below sea level. The greatest change in the level of the aquifer occurs in the fracture zone of Dobrich (Figures 17, 18 and 19). Some 15 km to the S of Cape Kaliakra, offshore oil wells penetrate the carbonate aquifer at a depth of around 1000 m, confined under Cretaceous and Paleogene sediments. This sector coincides with another horst, evident in the seismic studies (Robinson et al., 1996). Mean thickness is roughly 400 m and the overall variability of the area is not extreme (300-600 m). The maximum thicknesses are towards the S and SE of the study area, while the minima lie in the transition zones between horst and grabens, as occurs to the NE of Dobrich and in Balchik (Figures 17 and 19). This seems to suggest that the narrowing of the aquifer is mainly due to tectonic factors. The lateral extension of this aquifer goes well beyond the boundaries of the study area and therefore it is possible to draw certain conclusions about the confined materials and the impermeable substratum. The former, throughout the area, are composed mainly of marly limestone-marl (except the Ruse Formation in the NW) from HauterivianUpper Cretaceous; nevertheless, towards the SE, materials of very low permeability from Paleogene and Lower Miocene-Tortonian are also found. The thicknesses of these materials, on the whole, are rarely less than 100 m (zones of Karapelit and Krasen-Kardam). This thickness increases considerably in most subsidence troughs (Dobrich: Batova or Balchik River; and Shabla: Bulgarevo), where the thickness can reach 700 m (Figure 20). Figure 20. Isopaches of the deep aquifer.

The impervious substratum is comprised of aquiclude materials (s. l.) from Middle Jurassic, present in almost the entire area except the NW, where, instead, there are Permo-Triassic materials of low permeability. 5.4.2. Groundwater table Figure 21 shows a schematic map of the piezometric surface obtained from the general mean data; despite the imprecision, some considerations can be made on a regional scale. The first noteworthy feature a clear differentiation of the aquifer in two sectors: in the more westerly part, there is a high piezometric level reaching 100 m a.s.l.; in the more easterly part the levels vary from 15 to 20 m a.s.l. The zone of highest levels coincides with a recharge sector of the aquifer, since it outcrops along the bed of the Suha River; in addition, this sector shows intense fracturing, which appears to aid the surface recharge of the aquifer (fracture zone of Dobrich). Such a clear difference between the two sectors indicates that these are hydraulically somewhat disconnected; this would not be a complete disconnection, since practically the only source of inflow possible in the eastern sector is precisely from the surface recharge in the Suha River sector. An explanation for such a disconnection might be a series of faults displacing blocks and thus making difficult XXI

the underground flow between parts; at the same time, there would be a reduced permeable contact section. Groundwater flow would occur in a form that is virtually radial and divergent from such a piezometric dome, indicating an influx of groundwater towards SE Romania (which agrees with the observations of Davidescu et al., 1991), towards the E of the study area and in the direction of the Devtnia springs to the S. In the NE sector of the study area, the piezometric lines indicate the existence of a flow towards the NNE, approximately in the direction of Mangalia (Romania), where there is known to be an important discharge of thermal waters from the carbonate Deep Aquifer (Davidescu et al., 1991). The hydraulic head here is known to be similar to that in the coastal area of the Bulgarian sector. Photo 8. The Devtnia spring. Figure 21. Schematic map of the piezometric surface.

It is also noteworthy that along the coastal border, from Krapetz to Balchik, the piezometric level of the Deep Aquifer remains above sea level, as demonstrated by a series of overflowing wells. These wells have no closure system, and thus the water flows continuously (often directly to the sea) with no regulation. The almost systematic lack of a regulation system in these wells is due to three principal factors: the use of most of these wells for petroleum extraction, mainly in the Tyulenovo oil field; the tourist attraction of having continuously flowing thermal waters; and the common belief that closure systems cause salt precipitation in the filters. Although this latter effect has not been firmly established, it is clear that this situation represents a steady bleeding of the aquifer as well as a waste of great quantities of resources. Thus, in some wells drilled in the Krapetz area, which were originally artesian, the piezometric level has fallen by over 4 m in the last 20 years. In one of these, which was made free-flowing again by excavating a trench, the yield was seen to diminish from 5 to 0.25 l/s in just one year. 5.4.3. Hydraulic parameters Transmissivity values for this aquifer appear to be most closely related to the thickness of the aquifer, since the maximum values (2000 m2/d) coincide with the zone of greatest thickness (in the southern sector). Likewise, in the western part, the minimum transmissivity values (100-200 m2/d) correspond to the thinnest zones of the aquifer. Hydraulic conductivity varies between 6 and 0.5 m/d for aquifer thicknesses of 650 to 230 m. Values for specific capacity range from 18 to 0.2 l/s/m. Such wide variations between data constitute an additional argument in favour of considering this aquifer to be karstic, together with the results of permeability and pumping tests carried out in certain public-works excavations where more karstified levels are clearly visible, heterogeneously located within the limestone mass. On the other hand, the low hydraulic gradients of the boundary near the sea may reflect the contact of freshwater and sea water during its geological history, reflected as greater karstification. With respect to the hydraulic gradient, there is a pronounced difference between the values corresponding to the eastern sector, with very low values (0.02 %), and those found in the western zone with values 35-fold higher (0.75 %). This is due to the presence of a zone of low transmissivity which hinders the groundwater flow, as explained above. Davidescu et al. (1991) quote effective porosity values for this aquifer in the coastal zone of SE Romania of between 5 and 12%. These values, together with those for permeability and hydraulic gradient found in this part of Romania, are in XXII

accordance with the flow velocities estimated by the same authors (actual velocity = 2.6 - 5.4 m/year) from 14C dating techniques and isochronous lines. Employing the same effective porosity, conductivity and hydraulic gradient values in our study area, we obtained comparable real flow velocities (0.2 - 8.8 m/year). Under these conditions, groundwater flow is seen to be very slow, and the waters extracted may be several thousand years old (between 5000 and 25000 years old, according to Davidescu et al., 1991). Nevertheless, it is necessary to be very cautious in interpreting such data obtained by the 14C dating technique, due to the significant limitations of this method (Vallejos, 1997). 5.4.4. Physicochemical characteristics Almost one hundred monitoring points register physicochemical data sufficiently representative of this aquifer for regional conclusions to be drawn. Water temperatures show a spatial distribution in accordance with the geological structure of the area, which determines the depth of flow; in the western and central parts, temperatures are 14 to 17ºC - quite similar to those of the Upper Aquifer -. Temperatures increase towards the east (Figure 22, due to the effect of the geothermal gradient, reaching 32ºC near Balchik, 38ºC near Cape Kaliakra and 41ºC in Shabla. Changes in the general tendency are undoubtedly linked to perturbations induced by the rises and falls of blocks limited by faults. pH values (7.1 to 7.4) did not significantly vary within the study area, although there was a slight tendency to increase towards the coastal zone. In relation to the conductivity of the waters (with an evolution almost identical to the TDS), somewhat more than the western half of the aquifer registers values of less than 700 mS/cm, indicative of a saline content of the waters of the lower half (Figure 23). Towards the east there is a steady rise in this parameter, exceeding 3000 mS/cm at certain points of the coastal border. Figure 22. W-E hydrochemical profiles for the Deep Aquifer, coincident with the hydrogeological section shown in the Figure 17. Figure 23. Distribution of electrical conductivity of the groundwater.

Values of the free CO2 content are generally low, with most of the area registering less than 3 mg/l; nevertheless, levels locally surpass 70 mg/l on the western border. HCO3 concentrations vary from some 500 mg/l on the western border to 300 mg/l on the eastern border (Figure 22, with scattered values of over 600 mg/l. This steady decrease in the direction of the groundwater flow could be related to the distribution of the CO2 itself, combined with the precipitation processes of the calcite. The diminishing solubility of the CO2 with the rise in temperature - in the absence of a continued deep influx - may favour this decline, although it might also contribute to the reduction processes. In this sense, the concentration of sulphates in the waters, registering between 20 and 45 mg/l in most of the aquifer, decreases steadily towards the eastern border to values of less than 10 mg/l, undoubtedly due to the presence of the aforementioned reduction processes; the odour of H2S is evident near the overflowing coastal wells. In SE Romania, controversy exists over the origin of this H2S (concentrations of 2 - 30 mg/l, according to Feru and Capota, 1991), which is present in all the formations found between the Paleozoic and the Miocene (Marin and Nicolescu, 1993). The latter authors discuss various hypotheses regarding this question; taking into account the data obtained from the Bulgarian study area, the most probable explanation is that the thermalism and sulphurous character of the waters derive from the carbonate Deep Aquifer, as we, too, are led

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to believe in this study. According to Feru (1993), the origin of the H2S lies in the reduction of sulphates by anaerobic microorganisms (sulphoreductive bacteria, according to Schoeller, 1956) in the presence of organic matter, rather than the oxidization of sulphur. This sulphate reduction process could be favoured by the presence of organic material in certain parts of the Deep Aquifer; indeed, in SE Romania, Feru (1993) found significant quantities of free methane gas (up to 50%) in the waters of deep wells, submarine springs and the Oban springs of the Mangalia region: N2, CO2 and O2 were present to a lesser degree. Certainly, the limestones and dolomites of the Malm - Valanginian constitute a deposit of gas and hydrocarbons that forms part of one of the first known petroleum provinces in the world. These resources are exploited and investigated in the petroleum field of Tyulenovo, which coincides with the horst of the same name and the Bulgarian and Romanian marine platforms, where there exists evidence of a migrated petroleum, from as far as 10 km to the W, from other stratigraphic levels. According to Robinson et al. (1996), the rocks in which petroleum is found are probably sediments from the Upper Eocene, deposited in a highly anoxic marine environment. Such rocks are currently to be found in the Bulgarian and Romanian marine platforms and towards the abyssal zone of the Black Sea. In such deep undersea zones, the materials are confined at great depth under thousands of metres of more recent materials, and in connection with extensional and rotational structures related to the rifting of the western Black Sea. The petroleum in the Tyulenovo region is highly biodegraded (API = 18.4°) and of low maturity, with a δ13C content of -27 to -28 ‰ (Robinson et al., 1996). Photo 9. Artesian well exploiting the Deep Aquifer, located near Balchik.

Chloride contents are less than 50 mg/l in the western third of the aquifer, but rise notably near the Black Sea to over 1500 mg/l (Figures 22 and 24). Mixing processes of freshwater and saline water (mainly fossil or connate) are apparently the origin of this spatial distribution of the concentrations. Because the aquifer is confined over practically the entire study area, the NO3- contents are low, comprising between 4 and 12 mg/l. Some local values greater than 200 mg/l would be due to the mixing of water from the Upper Aquifer (Machkova et al., 1955) and/or possible pollution through the annular space of the well (Pulido-Bosch et al., 1996, 1997). The anoxic environment that characterizes this aquifer also facilitates the reduction of nitrogenated species. Thus in hydrogeochemical sections perpendicular to the coastal area we detected a progressive reduction in the concentrations of nitrates and a parallel increase in nitrites and ammonia. The reduced ionic species are present in concentrations that on occasion exceed 10 ppm (Figure 22). Figure 24. Distribution of chloride contents in groundwater of the Deep Aquifer.

The study of the chemical equilibrium of the water of the Deep Aquifer, using the WATROCK program (Velikov, 1985), shows that many wells which tap the aquifer present groundwater saturation and even oversaturation with respect to calcite and dolomite, indicating long-standing water-rock contact, and caused by the spatial distribution of the CO2 and HCO3 contents, as well as the progressively increasing water temperature in the flow direction. 5.4.5. Isotopic characterization In order to study the diffusion of some environmental isotopes (2H or D, 18O and 13 C) mainly in the groundwaters of the Deep Aquifer, during May and November 1995

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two water-sampling were carried out, during the high and low flow periods respectively. Some sources representing the Upper Aquifer and a limited number of surface waters were also sampled. Twenty points (mainly boreholes) were investigated (Figure 25), of which 13 points represent the Deep Aquifer, 4 the Upper Aquifer and 2 surface waters (the Batova river and the Durankulak lake, respectively). The spring located at about 3 km from the village of Batovo is assigned to the Paleogene. The points are located in two profiles in a W-E direction, including the recharge zone, the intermediate aquifer part and the drainage zone of the Deep Aquifer. The samples for the δD (deuterium) and δ18O were collected in 50 cm3 glass containers preventing any possible evaporation during transportation and storage. In order to preserve the carbon (13C) isotope ratios of dissolved inorganic carbon in the samples, a precipitation of bicarbonate and dissolved CO2 was performed according to the following procedure: 1 ml 700 g/l NaOH was added to 1 l water and stirred; as the pH was about 11, 16 ml 200 g/l BaCl2 was added to the water and it was stirred again. The settled precipitate was then used in the laboratory for the carbon isotope measurements. All stable isotope determinations were performed in the Laboratory of Stable Isotopes and Radiocarbon Dating at the Institute of Nuclear Research of the Hungarian Academy of Sciences in Debrecen (Hungary) under the supervision of Dr. Ede Hertelendi. The content of Hydrogen and Oxygen heavy isotopes in the natural waters is widely varying: from -400 ‰ to +50 ‰ for D and from -40 ‰ to +8 ‰ for 18O (Feronskii, 1975). The low concentrations of these isotopes are typical of atmospheric and surface waters, while the high concentrations are normal for the sea and ocean waters. The isotope content is virtually constant for the latter water types, while the content of D and 18O in the atmospheric and surface waters is determined by the particular climatic conditions and is quite variable. In general, the isotope content of atmospheric waters follow the relation: δD = 8 x δ18O + 10 (Craig's line) (1) A correlative link between the concentrations of 18O and D in precipitation waters and the annual mean air temperature at the ground (ta) was experimentally established. Thus, the relation is valid for a wide range of temperature and is expressed through the relations (2) and (3): δ18O = 0.695 x ta − 13.6 ‰ (2) δD = 5.6 x ta − 100 ‰ (3) The relations expressed by (2) and (3) are correct only for the coastal regions. Moving away from the sea basin, the continental effect appears, and thus the calculated and experimental results are sometimes identical. Figure 25. Points for isotopic investigation.

In some specific climatic zones (such as the eastern part of the Mediterranean basin) the relation (1) is expressed as δD = 8 x δ18O + 22, while for the European part of the former USSR, relations (2) and (3) take the form of δ18O = 0.4 x ta - 13 ‰ and δD = 2.95 x ta - 100 ‰, respectively (Cheshko et al., 1990). Our opinion is that the relations for the European part of the former USSR can be better used for an approximate estimation of the isotope content of precipitation over the investigated area than relations (2) and (3). Using the annual average air temperature of 10.27 °C XXV

for 1995 in the Dobrich region, the following values for the isotope characteristics of the precipitation waters were obtained: δ18O = −8.89 ‰ and δD = −69.70 ‰. Natural Carbon has two stable isotopes 12C and 13C, which are involved in several migration cycles, together with the radioactive carbon isotope. One of the most important processes in the formation of the isotope content of groundwaters is the dissolving of the limestone due to the presence of carbon dioxide. Other processes include the carbon-acid leaching of silicate rocks, the carbonate decomposition by Fuller’s earth, the sulfate reduction, the oxidation of compounds with a significant carbon content (like methane), carbon input from the atmosphere, etc. A number of different reactions take place in the soils and in the aquifers, but the contribution of each one of these is not clear. Such reactions depends on the general geochemical conditions of the groundwater formation. The bove-mentioned considerations, hoewver, only partially serve to clarify the complex mechanism forming the carbon isotope content in the groundwaters. Of the cosmogeneous radioactive isotopes, only tritium was investigated in this study, and that in a limited number of samples. Its content is within the range 0.2 ± 0.4 TE. The conditions for the tritium cycle related to the groundwaters are directly related to groundwater recharge conditions. The absolute dating of the groundwaters, based on the tritium content and the water cycle, was possible before the period of thermonuclear tests, when the tritium content in the environment was in stable equilibrium. The analysis of the results obtained for the Dobrudja region leads us to the following conclusions: 1 The deuterium content in the ground waters is low (from -92.78 ‰ to 59.95 ‰), which proves their atmospheric origin. 2 The mixing of the groundwaters with contemporary seawaters was not proved. The isotope content of the contemporary seawaters is: -30 ‰ < δD < -25 ‰ and -4 ‰ < δ18O < -3 ‰, depending on the depth (from 0 to 900 m). 3 Five zones could be distinguished In the region studied (Figure 26 and Table 1): - the surface and Upper Aquifer waters are in the first zone. - mixed waters (mainly from the Upper Aquifer) belong to the second zone. - mixed waters (mainly from the Deep Aquifer) are in the third zone. - real Deep Aquifer waters belong to the fourth zone. - Deep Aquifer waters injected by thermal waters are in the fifth zone. Table 1. Zones or groups of waters according to the δ18O/δD relations. Figure 26. Distribution of the sampling points in δ18O ‰ versus δD ‰ coordinate system.

It is quite probable that the groundwaters of the fourth zone have been formed during the Pleistocene (The Ice Age), when the amplitude of the mean annual air temperature varied by 7 - 8 °C. Under these conditions, according to the relations (2) and (3), the following isotopes contents (in view of the geochronologic aspect) were obtained: -12.63 ≤ δ18O ≤ -11.93 ‰ - 92.16 ≤ δD ≤ -86.56 ‰

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5 The small amplitude of δ18O (3.79 ‰) in the investigated region and its negative values are explained by the low degree of water metamorphosis as a solvent, which is proved by the relatively low temperatures and the small isotope exchange potential of the water bearing rocks. 6 Taking into account the above conclusion and according to the type of water bearing rocks, one can deduce that in terms of the geochronologic aspect, multiple cycles of the groundwaters accumulated in the aquifers ocurred and that the rocks are very well flushed. 7 Correlation between the contents of δ13C and CO2 in the Deep Aquifer is established (Figure 27), demostrating the role of carbon dioxide in the formation of the isotope content of the carbonate system groundwaters. Figure 27. Relation between CO2 and δ13C concentrations for the Deep Aquifer.

5.4.6. Groundwater system description The recharge area of the Deep Aquifer, as indicated above, is situated mainly to the W of the study area. Nevertheless, the small limestone outcrops from the MalmValanginian in the Suha River basin appear to contribute to the recharge of the aquifer during the rainy season, as this is the only period when the courses carry water. This is evident from the distribution of the piezometric level and the hydrochemical evolution. The low porosity of the aquifer rock, the fact that the wells penetrate the aquifer formation almost without empty spaces, and the presence of conduits, allow this aquifer to be classified as karstic or conduit flow type (Atkinson, 1977), although there are no data concerning transit velocity, response to external forces, etc. The presence of numerous overflowing Artesian wells, especially along the eastern boundary, with continuous flow over many years, presupposes the existence of a continual recharge and substantial reserves. If the large surface area is taken into account, the latter possibility becomes almost a certainty; the continual recharge apparently originates along the strip that outcrops W of the study zone, where there is an extensive surface area (Cheshitev and Kânchev, 1989) and rainfall in excess of that in the study zone. This is so at least at present; the numerous free-flowing wells in the coastal area have created an ample zone of artificial discharge and thus there is a faster renewal of the water of the aquifer. Under natural conditions, in the absence of these artesian wells, the aquifer, in the short term, behaves like a stagnant aquifer, an “aquitrap” as defined by Mazor (1995), in which the mean age of the waters contained may be of several thousand years, due to the extreme slowness of the flow. Part of the artesianism shown by the aquifer in the coastal area may have originated from the compression of carbonate materials by the increase in effective pressure; this would be a consequence of the exploitation of the aquifer, as suggested by Mazor (1995) in the case of similar aquifers. However, we believe the importance of this phenomenon to be secondary and that there exists a conventional flow arising from the differences in the hydraulic head between sectors. In any case, the discharge area for the whole system has yet to be accurately defined. Due to the aquifer structure which causes the carbonates to reach notable depths, more than 700 m in some sectors, with no loss of hydraulic continuity, waters rise in temperature because of normal geothermal gradients, without necessarily involving positive thermal anomalies. The existence of blocks at unequal depths, added to variations in the sea level between the Cretaceous age and the present, has XXVII

favoured the trapping of salt water in some sectors of the aquifer, as in other Mediterranean areas (Pulido-Bosch et al., 1991). At first sight, the hydrogeochemical evolution of the “apparent flow direction” coincides quite well with that observed for other confined coastal aquifers that terminate in a “cul-de-sac” under the seabed (Lawrence et al., 1976; Edmunds et al., 1979 and 1983). The system drains in four ways: underground lateral outflow to Romania (probably to the Mangalia zone), pumping from wells, overflowing wells having no closure system, and ascending vertical recharge to the Upper Aquifer. This last concept is analyzed below. Quantification of each of the outflow mechanisms is difficult. Applying Darcy´s law to the eastern boundary, the amount of underground discharge towards the Black Sea can be calculated, assuming the following transmissivity and hydraulic gradient values: for 2500-3000 m2/day of T, 0.02 to 0.04 % for the hydraulic gradient and 70 km of boundary length, discharge would be from 10 to 30 Mm3/year. Pumping for irrigation, drinking water and farm use, according to data from questionnaires in 1989, are an estimated 60 Mm3/year. The exact quantity of natural flow in spas and other artesian wells is unknown, though it appears to be around 5 m3/s. 5.5. Relationship between the Upper and Deep Aquifers In addition to the isopache map depicting the confined-semi-confined level which separates the two aquifers, we have drawn a map showing the difference in hydraulic head between the two aquifers (Figure 28) in order to interpret, in an overall manner, those sectors susceptible to recharge by seepage from above ( thin areas of the confining layer and greater water potential in the Upper Aquifer), and vice versa (sectors with greater hydraulic charge in the Deep Aquifer and thinner dimensions of the confining formation). As indicated above, the construction characteristics of the wells which tap both aquifers seem to indicate that there is no water exchange through the well itself, although this conclusion is not absolutely certain. Except for the coastal strip between Tyulenovo and Durankulak, where the Deep Aquifer can attain a hydraulic charge of 10 m more than the Upper Aquifer, in the rest of the study area the hydraulic charge is greater in the Upper Aquifer than in the Deep one. The thickness of the confining level in the coastal sector is between 200 and 400 m, and thus the vertical recharge mentioned above is likely, except very locally, such as along the fractures which permit flow. Several authors have described the interconnection between the Deep and the Upper Aquifers in Romania, between Mangalia and Constanza. The Upper Aquifer has been shown to recharge the Deep Aquifer by virtue of its greater hydraulic head, the lesser thickness of its confining impermeable materials and the presence of deeper thermal saline waters. Povara (1997) made a detailed study of the piezometric levels of the Miocene carbonate aquifer in the Mangalia sector, and discovered areas with abnormally high levels (around 20 - 60 cm) with respect to the regional trend of the water table; a divergent local flow issued from such areas. These anomalous points, some of which coincide with the position of springs in certain Obanes (Feru and Capota, 1991), also present unusually high concentrations of chloride and total dissolved salts (although there is no seawater intrusion, the facies in the Upper Aquifer is sodium chloride, according to Marin and Nicolescu, 1993). These anomalous points are in alignment, signalling the existence of large fractures in a WNW-ESE direction, through which the deep waters may rise. Povara (1994) describes two such fractures, one along lake Mangalia and separating two XXVIII

independent hydrogeological compartments (the Mangalia fault), and another, somewhat further to the N (the Kara Oban fault), which crosses the Mangalia Swamp and continues seawards for several kilometres. On the seabed there are some 30 submarine springs or vents which are aligned, for over 10 km, with one or other of the above-mentioned fractures (Feru and Capota, 1991 Feru, 1993). Figure 28. Differences of hydraulic head between the Upper and Deep Aquifers.

Nevertheless, there does appear to be a more feasible interconnection through the wells themselves, which are well isolated in theory but not in reality. This supposition is equally valid for the descending vertical recharge, theoretically possible in the rest of the area, in which the Upper Aquifer can reach a charge of 170 m more than the Deep Aquifer, although the confining layer is rarely less than 100 m thick; there is clearer evidence for the second case, especially in the form of nitrate concentrations. As already indicated, this ion has a concentration of 15 mg/l in the water of the Deep Aquifer, but can exceed 500 mg/l locally in the Upper Aquifer. Furthermore, in various wells which in theory tap only the Deep Aquifer, more than 200 mg/l have been recorded; this appears to be due to the descending vertical recharge. Such a recharge must be considerable, since to obtain more than 200 mg/l in the mixture, after the subsequent dilution, it is necessary for there to be a substantial flow exchange. 6. SELECTION OF THE PILOT AREAS After examining the results obtained during the first year of the investigation, it was decided to concentrate subsequent activities on the study of two pilot areas, in order to meet the objectives proposed for the project. One factor influencing this decision was the fact that the area included within the general study was too large to enable us to draw detailed and reliable conclusions. Within a total area of more than 4000 km2, it is difficult to analyze the variables affecting the processes of groundwater pollution, particularly when such processes are highly diversified. As the Upper Aquifer was the most affected by processes of pollution and over-exploitation, and as it was also the one with the more suitable infrastructure for study purposes, it was decided to investigate only this one and not the Deep Aquifer, although the interaction and relations between the two aquifers were taken into account. Another relevant factor was that, when the project objectives were drawn up, the economic situation in Bulgaria was considerably more favourable than at present. This situation worsened as the project advanced, to the extent that the control network established in the zone by the National Institute of Meteorology and Hydrology had to be drastically scaled down; as a result, the observation infrastructure was adversely affected and auxiliary personnel were laid off. For the above reasons, it was decided to study the processes of urban and agricultural pollution, together with certain aspects of over-exploitation, in a sector located around the city of Dobrich. This represents the single greatest human and industral concentration in NE Bulgaria, where significant quantities of groundwater are extracted by pumping, both for drinking water and to supply industrial plants. The surroundings of Dobrich contain an important degree of agricultural and livestock activity, with a direct affect on the quality of groundwater, and requiring considerable levels of water extraction for irrigation.

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The pilot area of Shabla - Krapetz - Durankulak will be used for the analysis of the processes of groundwater exploitation and seawater intrusion, as the general study revealed localized problems in groundwater quality at certain pump sites. A further analysis will be made of the risk of intrusion over the whole coastal area; the results may then be used to assist in the task of managing water resources in this region. 7. FINAL CONSIDERATIONS The Upper Aquifer occupies 4600 km2 in NE Bulgaria and is constituted of organogenic, oolithic and detrital limestones and sands of the Messinian age, with a total thickness varying from 40 to 200 m. Most of the area is covered by detritic materials ranging from scarcely permeable (loess) to highly permeable (sands and alluvial silt). The impermeable substrate is composed of marls and clays of varying ages, according to the sector in question. As a whole, the aquifer may be considered one of very weak karstic functioning, probably due to its high porosity, as shown by the scant variations in output flow from the monitoring points. The nature of the Quaternary coverage is of great hydrogeochemical importance, while the principal sources of pollution are seen to be related to agricultural activities, corralled livestock and urban wastewaters. Such pollution is apparent in the high nitrate contents of the waters from many wells. Seawater intrusion, as a contaminant process, seems to have become established in some sectors on the eastern boundary. The study area presents relatively complex stratigraphic characteristics - changes in the thickness and facies of the water bearing materials - which lead to a certain hydrogeological complexity. The small amount of tectonic activity consists of some fracturing, on occasion accompanied by tilting. There is no evidence of the existence of significant endokarstic forms, though closed surface depressions (dolines) covering a large area are relatively common. From a climatic viewpoint, there appears to have been a decrease in rainfall, which, though most notable in the last 10 years, affects a much longer period (50 years), in a cycle of 95 years, of which the 45 years represent a wet cycle. Nevertheless, the hydrogeological data available do not definitively reflect a generalized fall in the piezometric levels or in the flows of the springs monitored. From a hydrochemical standpoint, the dominant anion is bicarbonate; sodium can become the dominant cation in the eastern sector, but magnesium and/or calcium predominate in the rest of the aquifer. The origin of the magnesium appears to be related to the mineralogical composition of the Quaternary covering, which has an abundance of MgO (3.7%), although part of the magnesium may proceed from the aquifer itself (dolomite limestone ?). The conceptual model of the carbonate aquifer would be closer to diffuse flow (Shuster and White, 1971; Atkinson, 1977) than to karstic flow, in the strict sense, although there could be more transmissive conduits, at least locally. The former flow could be explained by the pronounced porosity of the rock, while evidence of the possible karstification lies in the dispersion of the specific capacity values of the wells (from 0.5 to 100 l/s/m). The discharge evolution over time of the springs shows very little variation, indicating the great inertia of the system. With respect to the functioning of the large aquifer, the great spatial variation of the recharge should be stressed, depending on the absence or existence of a detrital covering and its nature. In the areas covered by loess, recharge is scant and slow, XXX

while in other areas, covered with highly permeable sands and alluvials, influx is far greater in both volume and speed. In the closed basins and along the river beds there is rapid infiltration; finally, throughout the carbonate outcrops, infiltration is also substantial and quick. All of these factors have influenced the spatial and temporal variation of the hydrogeochemistry in the area. High nitrate contents in the water measured in large sectors of the aquifer indicate pollution that is basically linked to the agricultural activities of the area, although livestock stabling also has an effect, as does the dumping of unpurified or partially purified urban waste; the dumping of solid urban sewage constitutes another source of pollution. The limestones, dolomitic limestones and dolomites of the Malm - Valanginian in the Dobrich region comprise a confined karstic aquifer with a thickness of 300 to 600 m, extending over an area of 4600 km2 . Within the study area, it only outcrops in two small sectors, and thus is well protected from pollutants; nevertheless, the probable existence of pollution has been detected in the wells connecting it to the Upper Aquifer, where the water has a high nitrate content. In the same respect, evidence of seawater intrusion and/or “fossil” salt waters has been found along the eastern boundary. Finally, it is a noteworthy fact that numerous artesian wells, some with thermal waters, drain off part of the hydric resources, with no use being made of them except in a few cases of spa resorts. The unequal values obtained for transmissivity and specific flow, together with substantiated transmissive conduits next to the limestone strip, which is practically without voids, characterize this formation as a karstic aquifer, although available data do not provide detailed knowledge of the degree of functionality of the existing karstic network (Bakalowicz, 1979; Crampon and Bakalowicz, 1994). The continuous overflow in many wells indicates large reserves and voluminous, steady recharge. Nevertheless, this flow only occurs very slowly, producing a significant oxygen deficit in the groundwater and important effects on the chemistry of this environment, particularly concerning the reduction in certain ionic species. Under these circumstances, the behaviour of the aquifer takes on the characteristics of an “aquitrap”, at least on a short time scale. The Deep Aquifer can be considered a karstic aquifer of great potential, whose resources could be better utilized. In addition to the numerous wells that lack efficiency, there are thermal waters which could be used for heating and irrigating greenhouses and thereby offer geothermal energy for agricultural production during the cold season. The notable increase in the chloride content of the water in the eastern third is attributed to a present-day and/or past marine influence related to paleokarstification and to fractures which permit the blockage of fossil water in the grabens. It is also known (though we have not stressed this fact) that some wells extract water with a higher saline content than that of sea water. Future sampling, together with isotope determinations (Gonfiantini and Araguas, 1988; Price and Herman, 1991) will provide the identification of these waters and their origin, together with information about the processes which take place deep in the aquifer and along at least two profiles parallel to each other and perpendicular to the sea.

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The studies carried out have shown the vertical downward recharge from the Upper Aquifer, evidenced by the unusually high nitrate contents of the water in the Deep Aquifer. The connection between the aquifers appears to be through the well itself. It would then be desirable in the future to employ drilling techniques which would avoid the interconnection between the two aquifers and the contamination of the deep waters with nitrate contents coming from the Upper Aquifer.

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PART II.- PILOT AREA OF DOBRICH

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1. INTRODUCTION In accordance with the above-stated project objectives and the pilot areas selected, the Dobrich pilot area consists of a 20 x 20 km square around the city of Dobrich (Figure 29). The terrain is almost flat with a slight general slope to the N, cut by the Dobrich gully in a N-S direction. The altitude of the pilot area ranges from 175 to 300 m a.s.l. Dobrich is the largest town in the region, with over 100,000 inhabitants, and forms an industrial and agricultural centre with a fairly well developed infrastructure. Thus, most of the groundwater problems related to pollution and overexploitation in this region are concentrated here. Figure 29. Scheme of location of the Dobrich pilot area.

1.1. Objectives The two main goals of the study were to examine processes of groundwater overexploitation in highly urbanised conditions together with groundwater pollution caused by sources such as: - Concentrated/point sources, i.e. domestic and industrial wastewater, livestock farms (pig, calf and poultry farms), landfills and dumps. - Diffusion/nonpoint sources, i.e. agriculture, acid rain, air pollution deposits. 1.2 . Methodology 1.2.1. Hydrogeology It was decided to adopt several approaches to achieve the above objectives: - The establishment of an observation network to monitor relevant physical and hydrochemical characteristics providing information about the temporal and spatial variability of such characteristics. - The use of tracer tests and data from previous pumping tests to determine the hydraulic parameters of the Upper Aquifer. - Statistical data processing and analysis, using time-series, uni- and multivariate methods to evaluate trends, spatial distributions of data and parameters, links between different characteristics and variables. - The use of empirical formulas and pre-defined models to calculate some parameters of the water balance and pollutant dissemination. These methodological approaches are described below, together with the presentation of the activities carried out and the results obtained. 1.2.2. Hydrochemistry 1.2.2.1. Collection and Preservation of Water Samples Water samples for analysis were collected and preserved carefully to ensure that the most representative samples for the corresponding aquifers were obtained (Velikov, 1986; Committee of Standardisation,1989; APHA - AWWA - WPCF, 1989). Samples from wells were collected after the pump had been running long enough (under temperature or electric conductivity control) to deliver water representative of the groundwater feeding the well. If no pump was available then specially designed samplers were used, though the analytical results represent the water composition only at the monitoring point and not the groundwater body as a whole.

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Polyethylene containers for the inorganic determinations and glassware for the organic, both thoroughly washed with 1:1 HCl and 1:1 HNO3 were used to minimise the effect of interferences. Preservation methods were limited to pH control, chemical addition and refrigeration (storage at low temperature of 3-4 °C). The metal cations for instance were collected in a separate clean bottle of 200 ml acidified with nitric acid to a pH below 2. Because a desirable immediate analysis was not possible for every characteristic, some determinations had to be obtained in situ. These were: Temperature, pH, ∆pH, Eh, dissolved gases (CO2, O2, H2S), neutralising capacities, NH4+, NO2-. The specific electric conductivity (κ) was also measured. The principles of the chemical and instrumental methods used to achieve reliable hydrochemical results are briefly described in the following epigraph. All chemical substances used were from the German firm MERCK. If not otherwise stated, the photometrical measurements were provided with the photometer MERCK SQ 118. 1.2.2.2. Hydrochemical parameters determined in situ Appearance: the presence of colour, turbidity, suspended solids, odour, taste, floating material, etc. was stated briefly and only for the colour (spectral absorption coefficient) and turbidity some numerical values were obtained using photometric determinations. Temperature: the temperature measurements were made with a good mercury-filled Celsius thermometer in a metal case having a scale marked for every 0.1 °C and a minimum thermal capacity to permit rapid equilibration. It was checked periodically against a certified precision thermometer. pH value: the pH values were determined by potentiometric measurements using a combined SEIBOLD E12 electrode incorporating glass and reference silver/silver chloride electrodes and a WTW pH 90 meter accurate and reproducible to a 0.1 pH unit and with temperature compensation. ∆pH index: a negative ∆pH index indicates a tendency of the water to dissolve CaCO3 and a positive index indicates a tendency to deposit calcium carbonate. The index was calculated according to: ∆pH = pHb - pHa, where pHb is the pH value before and pHa is the pH value after adding marble powder to the sample. Eh (redox potential): the Eh value was measured potentiometrically using a combined SEIBOLD EP electrode incorporating platinum and reference silver/silver chloride electrodes and a METROHM Herisau E588 mV meter. Special attention was paid to avoid the influence of the atmospheric oxygen when measuring Eh of deep groundwater samples with reductive properties. Eh was calculated from the measured electromotive force after adding the standard potential of the reference electrode for the corresponding temperature. Specific Electric Conductivity (κ): an immersion form conductivity cell containing platinized electrodes with an LDI instrument of SEIBOLD-Kappl-Vienna capable of measuring conductivity with an error not exceeding 1 % were used. The temperature correction was made and the results were reported at 20 °C in mS/cm or µS/cm. Neutralising capacities (HCO3-, CO2, CO32-): the acid neutralising capacity (alkalinity) was determined by direct titration of 100 ml water sample with 0.1 M hydrochloric acid against phenolptaleine (Kk8.3 = p value) or methylorange (Kk4.4 = m value). The XXXV

base neutralising capacity was determined by direct titration of 100 ml water sample with 0.02 M sodium hydroxide only against phenolptaleine (Ko8.3 = negative p value). From these neutralising capacities the concentrations of the corresponding forms of the dissolved carbon dioxide were calculated: a) if the sample pH was greater than 8.3 and m>2p, then: CCO2 = 0, CCO3 = p, CHCO3 = m - 2p b) if 4.4 < pH< 8.3, then: CCO3 = 0, CHCO3 = Kk4.4 = m, CCO2 = Ko8.3 = -p. Dissolved oxygen (DO): oxygen-sensitive membrane electrode of polarographic type with a gold cathode and a silver anode polarised by an external source of applied voltage in an appropriate WTW OXI 90 meter were used. In this temperature and pressure-compensated instrument the “diffusion current” is linearly proportional to the DO concentration in mg/l. An accuracy of ± 0.1 mg/l DO was obtained. Dissolved sulfide (H2S/HS-): taking into account the sample pH, the unionised hydrogensulfide may be easily calculated. Hydrogensulfide reacts with N,N’-dimethyl1,4-phenylene-diammonium-dichloride to colourless leucomethylene blue which is then oxidised by ferric sulfate to methylene blue. Sulfamic acid prevents interference through nitrite. A MERCK SQ 118 photometer (test kit number 14779) and measurements at 665 nm against blank were used. Ammonium: here the sensitive Nessler reaction was used for higher NH4+ concentrations (above 2 mg/l), while for the lower NH4+ contents the reaction with a chlorinating agent in an alkaline medium to form monochloramine was used and then with thymol to form 2,2’-isopropyl-5,5’-methylindopnenol (the Berthelot’s reaction) were used. Hardness formers were kept in solution by a simultaneous addition of potassium sodium tartrate. The interference of H2S/HS- was eliminated by precipitation of S2- in alkaline medium with a few drops of 10 % Zn(OOCCH3)2. All ammonium nitrogen was given as a NH4+ although a well known pH-dependent equilibrium exists between NH4+ and NH3. Nitrite: here the Griess reaction was used which involves the conversion of NO2- with sulfanilic acid to form 4-diazo-benzenesulfonic acid. This subsequently condenses with 1-naphtylethyleneamine dihydrochloride to provide a magenta azo dye. The measurements were made using a comparator or photometer at 525 nm against blank. 1.2.2.3. Hydrochemical parameters determined in the laboratory Unless otherwise stated the laboratory measurements were performed in the Laboratory of Hydrochemistry at the University of Mining and Geology of Sofia. Sulfate: SO42- ions, for concentrations below 100 mg/l (Velikov, 1986), react with barium ions in acidified aqueous solutions to form slightly soluble barium sulfate. The resulting turbidity is measured by photometry at 440 nm after filter turbid samples through a 0.45 µm membrane filter. The barium-sulfate crystals formed partially a deposit on the bottom of the cell during the 10 minute reaction time. It is therefore important to shake the cell content shortly before the measurements in order to distribute the crystals in the solution uniformly. For sulfate concentrations above 100 mg/l the classical gravimetric method or the ICP AES (Spectroflame Analytical Instruments) was used.

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Chloride: the determination of the Cl- concentrations was performed by argentometric titration with silver (I) nitrate in neutral or slightly alkaline medium in the presence of potassium chromate as indicator. Nitrate: in the presence of chloride in a strongly sulfuric acid containing solutions, nitrate reacts with a phenol derivative to form red-violet indophenol dye that is determined photometrically at 515 nm against blank. Phosphate: in a solution acidified with sulfuric acid ortho-phosphate ions and molybdate ions form a molybdophosphoric acid. Ascorbic acid reduces this to phosphomolibdenum blue, which is determined photometrically at 712 nm against blank. Calcium, magnesium and hardness: the main “contributors” to the water hardness were determined complexometrically with ethylenediamintetraacetic acid disodium salt : Ca2+ + Mg2+ together at pH 10 in the presence of erio-chrom-black T and separately Ca2+ at pH 12-13 in the presence of calcone. The magnesium was then calculated from the difference. Sodium and potassium: the amounts of sodium and potassium were determined separately using the Flapho 40 flame photometer at a wavelength 589 nm (Na+) and 770 nm (K+) isolated by the use of interference filters. The water samples were sprayed into the gas flame and excitation was provided under carefully controlled and reproducible conditions. Other metal ions: all other metal ions (such as Li, Al, B, Cr, Mn, Fe, Cu, Zn, Sr, Cd, Ba, Hg, Pb and U) and As were determined in the water samples preserved with HNO3 using atomic emission spectrometry with inductively coupled plasma (apparatus from “Spectroanalytical Instruments”). For some metal cations with lower contents an atomic absorption spectrometer (Perkin Elmer 3030) was also used. Silicic acid (H4SiO4): water soluble silicate (“dissolved silicic acid”) reacts in an ammonium heptamolibdate/sulfuric acid medium to form β-silicomolybdic acid. The photometric measurements were performed at 630 nm against blank. The analogous phosphorous compound which may be present was selectively eliminated with tartaric acid. Chemical oxygen demand (COD): the chemical oxygen demand is a measure of the oxygen equivalent of the organic matter content of the water samples acidified with sulphuric acid that is susceptible to oxidation by a strong chemical oxidant {KMnO4 permanganate oxidizability (PO) or K2Cr2O7 - COD}. COD was measured only for samples with PO greater than 2.6 mg/l. Pesticides: the pesticide determinations were performed by using a Hewlett Packard 5890 gas chromatograph with electron capture and NP detectors and with capillar column HP-5 (30 m/0.32 mm) at the Institute of Plant Protection in Kostinbrod near Sofia under the supervision of Dr. Ana Balinova. 2. GENERAL DESCRIPTION OF THE AREA 2.1. Geology In the surroundings of the Dobrich pilot area, the outcropping levels of the carbonate series of the Upper Miocene (Sarmatian, according to the Caucasian chronological scale) correspond to materials of the Odar formation, composed of XXXVII

organogenic limestones with a high degree of secondary porosity arising from dissolution. Below this formation there are very localized outcrops of sandy materials belonging to the Frangja formation, together with carbonate facies of the Karapelit formation. The existence of the latter at ground level is restricted to those sectors where erosion produced by the River Suha, to the W of Dobrich, has uncovered the upper levels of the Miocene. The whole group is covered by an extensive layer of Quaternary loess which, in this sector, attains a thickness of around 10 m. The data obtained from geological columns indicate a certain spatial heterogeneity of the Upper Miocene materials, which comprise the lithological group of greatest hydrogeological interest in the region. The thickness of the group increases from W to E, from barely 20 m near Odrintsi, on the banks of the River Suha, to over 50 m in the eastern area, near Metodievo. Figure 30 illustrates the variation in thickness of the Upper Sarmatian limestones lying above the group of clays, marls and sandstones in the Frangja formation of the Lower Sarmatian. The marked and abrupt increase in thickness is apparent to the E of Dobrich following a line running approximately N-S. Figure 30. Thickness of the carbonate Miocene materials (Sarmatian) in the Dobrich pilot area.

Notable spatial heterogeneity is also present at the altitude of the bottom of the Odar formation, which might be indicative of the block tectonics that affected the Moesian Platform, with a succession of horsts and grabens; these also had a slight effect on the materials forming the Upper Miocene. In this respect, the Dobrich region forms a graben structure, with a relative fall of 60 m in the carbonate wall of the Odar formation. This fall resulted from a group of normal faults, originating during the Pliocene Epoch, aligned approximately in a NE-SW direction, and also detectable at other points on the Moesian Platform. Figure 31 shows how the depth of the Upper Sarmatian wall ranges from 200 m a.s.l. inthe northern sector (Rosenovo) and in the southern sector (Stefanovo) to 140 m a.s.l. in the Dobrich depression. The greatest density of isolines roughly coincides with the above mentioned tectonic pattern. Figure 31. Altitude above sea level of the bottom of the carbonate materials of the Upper Miocene (Sarmatian) in the Dobrich pilot area.

2.2. Hydrogeological features As stated above, the Upper Aquifer was the object of study in the pilot area. The main hydrogeological characteristics of this aquifer were described in the first part of this Report (Section 5.3). Here, it is only necessary to remark upon the two principal features of the aquifer in the zone nearest to Dobrich, taking into account that certain purely hydrogeological considerations will be examined later, such as the specific results derived from the studies carried out in this area. In the Dobrich area, the Upper Aquifer is comprised almost entirely of the organogenic limestones of the Odar formation; present to a much smaller degree are the sandstones of the Frangja formation and the carbonates of the Karapelit formation. The thickness of this permeable group, on average, does not exceed 45 m. These materials only outcrop in the valleys of the principal rivers: the Suha and the Karamandere (which passes through Dobrich). Within the pilot area, the beds of these valleys are sometimes occupied by the impervious substrate of the aquifer (basically, Cretaceous materials), though the extension of such outcrops is relatively small in comparison with the total area studied. Most of the outcrops in this zone correspond to Quaternary loess.

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The depth of the piezometric level varies between 0 and 30 m. Certain aspects concerning the spatial and temporal evolution of the piezometric level are discussed below, but here it is only necessary to note that the whole pilot area lies within a drawdown cone arising from the exploitation of groundwater in the surroundings of Dobrich; thus the groundwater flow is radial and convergent towards the city. The hydraulic gradient here is of around 0.4 - 0.5 %. The data available were obtained from various pumping tests performed in the area, and show average hydaulic conductivity values of about 30 m/day, although, due to the heterogeneity of the carbonate materials, recorded values vary widely, between 5 and 280 m/day. Taking into account the saturated thicknesses observed in the pilot area (around 30 m), the transmissivity of the aquifer is quite high, at about 500 - 1000 m2/day. The variations in piezometric levels during some of the pumping tests revealed mean storage coefficient values of around 3 %. Tracer tests with 131I were performed to determine the hydraulic parameters at certain outstanding points of the aquifer within the pilot area; boreholes 21 and 22 (Figure 33) were selected for this experiment. At the latter borehole, a further test was performed, using the “mise a la masse” electric method. These experiments were carried out by a specialist company contracted for this purpose. In preparation for the tracer tests, the following well logs were obtained: gamma ray, resistivity, thermometry, calipmeter and gamma-gamma. Photo 10. Works during the tracer test carried out at the well no. 22 (Dobrich park).

The values for hydraulic conductivity at well 21, calculated by tracing the entire depth with 131I, varied from 1.29 to 0.46 m/day, with a mean value of 0.56 m/day. The values obtained at well 22 were much higher, at 10.5 m/day in the 42-47 m depth segment, 1.95 m/day at 29-34 m and 3.2 m/day mean value for the 30-47 m depth segment. Thus there was found to be a marked vertical variation in hydraulic conductivity, which provides more evidence of karstification within the aquifer. Furthermore, these data also lead us to conclude that hydraulic conductivity values are locally low to very low. 3. MAIN SOURCES OF POLLUTION There are three main sources of groundwater contamination in the studied region: agriculture, animal breeding and urban areas. A brief description and characterisation of these sources follows. 3.1. Agriculture Agriculture may be considered the main source of pollution in this region, for two reasons. Firstly, because there is an excessive use of fertilizers, with organic and inorganic substances, and thus the groundwater in the aquifer is enriched in NO3- and HPO42- ions. Consequently, in the cultivated area of about 300000 ha, NO3concentrations of 200 mg/l and even up to 600 mg/l (in the central part of the region south of General Toshevo) were found. In some local sites (Malka Smolnitsa) the NO3- concentration reached its highest value of 930 mg/l during our observations. HPO42- reaches values commonly in the order of 0.2 -0.5 mg/l, but rarely up to 5.0 mg/l (Sveshtarovo). Similarly to NO3-, values for HPO42- are excessively high in the recharge areas, wich include not only agriculturally-developed regions but also small population centres. Secondly, agrochemical treatment with herbicides and XXXIX

insecticides, often with a long half-life, also causes pollution from some complex organic compounds. Thus, in Malka Smolnitsa, Paskalevo and Almaliy Lindan, metolachlor and acetochlor having concentrations between 0.01 and 0.09 µg/l (for Almaliy-metolachlor up to 6.4 µg/l) were detected. Photo 11. Cultivated areas in the Suha river valley, near the pilot zone of Dobrich.

3.2. Animal breeding Animal breeding is very well developed in the studied region and its solid and liquid wastes, which are either not purified or only partly treated, are significant point sources of contamination for the groundwater of the Upper Aquifer. In the 10 km zone around Dobrich concentrated contaminants come from the Stozher and Stefanovo pig-breeding farms. The lagoons of the Stozher pig-breeding farm are found 3 km NW of the village of Stozher and 1.5 km S of the village of Draganovo. They are built over the jointed and karstified limestones of the Sarmatian complex, which permits the waste water to infiltrate directly. At present the pigbreeding farm is being privatised and no pigs are being bred but the future owners will probably be involved in the same activity. The complex has its own water source from the Valanginian aquifer. The lagoons of the Stefanovo pig-breeding farm are located 1.5 km W of the village. They are built on loess materials but are continuously overflowing by around 1 l/sec. The waste water flows down the valley, passes along the village of Branishte and reaches a point W of the village of Plachidol where it sinks. During heavy rainfall the water reaches the drill wells of the Primortsi pumping station, one of the main suppliers of drinking water to Dobrich. Photo 12. Waste water purification plant of a pig-breeding farm located to the north of the pilot area of Dobrich.

There are many dunghills in the proximity of the dairy-, sheep- and poultrybreeding farms. The bigger ones, which have a more serious effect on groundwater pollution, are those situated SW of the village of Opanets, S of Riltsi quarter, E of the village of Pobeda, E of the village of Minkovo, the dairy farm at the village of Branishte where pigs are now being bred, NE of the village of Opanets, E of the village of Smolnitsa, the northern end of the village of Kozlodouytsi, N of the village of Paskalevo and N of the village of Vrachantsi. Figure 32. Time plot of certain hydrochemical parameters measured at Kozloduytzi pig breeding farm.

Figure 32 shows the time evolution of some hydrochemical characteristics of the waste water from the Waste Water Purification Plant (WWPP) of Kozlodouytsi “Pitimpex” pig breeding farm. In fact even such partly treated wastes are a real groundwater pollution source since these wastes go into dry riverbeds (valleys) where mainly Sarmatian limestones outcrop. 3.3. Urban areas The urban areas such as Dobrich and General Toshevo and the industries developed there, which are related mainly to the processing of agriculture products, are the third main source of pollution because of the lack of sewerage and modern systems for solid and liquid waste treatment. The waste water from Dobrich is delivered to the WWPP located near the village of Vrachantsi. A small portion of the waste water flows down the valley. All residential districts are provided with sewerage. The house and rainfall drainage systems are XL

built close to each other so that due to failures, pipe displacements, etc., it is possible for part of the house drainage water to mix with the rainfall drainage water underground and then flow down the valley. The sewerage of ZENA Co. - Dobrich is discharged into the valley. The system has not been operating for several years for economic reasons. In 1994 it used a total of 29,290 m3 of water. The Dobrich WWPP operates under the conditions shown in Table 2. Table 2. Characterisation of the Dobrich Waste Water Purification Plant. Photo 13. The Dobrich Waste Water Purification Plant. Photo 14. The solid waste dump of Dobrich.

This plant features a final, biological, treatment stage when the water intake is classified as third category. Its nominal capacity is 60000 m3/day. A further consideration is that several large companies discharge their waste water into the sewerage system; the characteristics of this are described in Table 3. Table 3. Waste water characteristics of the industries in Dobrich with greatest potential for pollution (average annual values).

There are waste dumps near every village. Big waste dumps are those near Dobrich, located N of the village of Bogdan, S and N of the village of Vrachantsi, S of the village of Pobeda, etc. Contaminated water flows down the valley from the southern end of Dobrich to the northern end of the village of Vrachantsi, and part of this infiltrates into the aquifer. The drill well N of the Riltsi pumping station has not been put into service because of this waste water pollution in the valley. Table 4 presents some hydrochemical characteristics of the polluted water flowing in this valley at different points. Table 4. Hydrochemical characteristics of polluted surface water as a groundwater contamination source.

The Onogour and Brestnitsa water dams are some 40 km from Dobrich in a N-NW direction (Brestnitsa is near the Bulgarian-Romanian border). Even in Brestnitsa the NH4+, HPO42- and permanganate oxidazability (PO) are too high. That is why this surface water flow in the valley is an important groundwater pollution source so that even the existing WWPP is of little help in this respect. Such valleys are common in other parts of the studied region (e.g. the valley near Stefanovo, Branishte and Plachidol). 3.4. Recommendations Strict agrochemical control of the use of fertilisers and pesticides, a modern solid and liquid treatment plant as well as a sewerage system are strongly recommended in order to minimize the possible impact of agriculture, breeding farms and urban sites on groundwater quality, especially that of the Upper Aquifer. 4. MONITORING FRAMEWORK The following criteria were taken into account during the establishment of the experimental monitoring network: - The observation points should be representative of the Upper (Sarmatian) Aquifer with respect to the location of point and non point pollution sources, as well as the influence of water intake.

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- The spatial distribution of the points should be relatively uniform over the pilot area. - The technical conditions of the points, including equipment, the well, the the gully cross-section themselves, etc. should be sufficient to enable sampling, level and discharge measurements, in situ determination of hydrochemical parameters, carrying out of various experimental activities on.

spring, secure certain and so

- Easy access to the point. - Possibilities for fast transportation of the samples to the chemical and isotope determination laboratories. The establishment of the monitoring network was carried out in two steps: -

The available historical data about groundwater surveys, small scale hydrogeological maps created for certain case studies, lithological columns, regime data, scientific publications and technical reports were reviewed.

- Field investigations and acquaintance with the real situation of the terrain in the area. 4.1. The evolution of piezometric levels The hydrogeological/hydrological monitoring network was established according to the above criteria and started operation in January, 1995. It comprised 19 points including 16 wells in the Upper aquifer, 2 springs in the coastal zone and 1 at the gully crossing Dobrich (Table 5 and Figure 33). Table 5. Points for measuring water tables and discharges. Figure 33. Scheme of the experimental monitoring network.

The groundwater tables and gully discharges were measured monthly during the period January, 1995 to June, 1996. The preliminary survey showed that most of the existing boreholes representing the Upper Aquifer are located in Dobrich or its surroundings. There were no such boreholes in most of the villages in the pilot area. A significant number of the existing boreholes were not suitable for the purposes of the experimental monitoring network because of the fitted pumps and cables inside or because they were sealed. Neither was it possible to use the wells located on the territory of the industrial plants that were closed because of the economic crisis in Bulgaria. Thus, some of the observation points located in the villages were shallow wells, as shown in Table 5. The measurement of the groundwater level was done by piezometer type HWK-AG2/1761, while the temperature was measured by a glass and mercury thermometer with a metal cover. This type of equipment is used in the basic hydrological network of the Bulgarian Hydromet service. The gully which crosses the town of Dobrich was used as a point to measure the surface water flow and its quality (point number 3 in Figure 33). The runoff is formed by direct precipitated waters, small springs existing on its slopes, domestic waste waters from some parts of the town not equipped with a sewerage pipeline, together with waters drained from the landfill of the town located to the S. The flow velocity was measured by a current meter type GR-55/1090, as used in the basic hydrological/hydrogeological network of the Bulgarian Hydromet service.

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Two springs were included in the network as mentioned above to characterise the discharge zone of the Upper aquifer. They were measured by the volume/time method four or six times per month. The information gathered during the 18 month experimental period was preprocessed including data entry, quality check, calculation of the absolute altitudes of the groundwater levels etc., using a PC type microcomputer. It was further postprocessed using different types of tables, graphs and simple statistical estimates. The analysis shows that the piezometric levels presented a relatively low variability during the experimental period (January, 1995 - June, 1996). This is due to the fact that the karst is almost totally covered by loess with a thickness of less than 10 m, which is “filtering” the time variations of the infiltration inputs. It is also important to mention here that the hydraulic characteristics of the aquifer are not uniform, neither horizontally nor vertically, and it is stratified into sub-layers with different permeabilities. The amplitudes of the levels range from 0.2 to 3 m (Figure 35). Most of the wells have amplitudes of less than 1 m. The highest amplitudes are observed in the wells located in the NW of the area (1, 2 and 4) varying within the range 2 - 3 m. They are shallow wells situated in an agricultural area where, during the spring and summer, water is used for irrigation, farming and domestic purposes. The other two wells located to the E-SE of the town have amplitudes of 1.8 - 2 m, probably because of the higher permeability in this zone. There is no clear seasonal component here. Most of the wells have clear positive tendencies, probably due to the high precipitation amounts during the spring and autumn, 1995 (Figure 34), being significantly higher than the mean. Those tendencies are probably related to the decreased consumption in the area because of the present economic crisis. Figure 34. Time plot of the actual monthly precipitation totals, their means and the monthly observations of the Dobrich gully discharges. Figure 35. Time plots and trends of the piezometric levels.

To analyse some more general characteristics of the water level variations, seasonal means of the monthly values were calculated. They were further plotted over the scheme of the pilot area (Figure 36), to enable the analysis of the spatial variations. These plots were subsequently prepared to elucidate the evolution of the areal distribution of the groundwater tables (Figure 37). The depression of the piezometric levels has an approximately conic form with its lowest part located in the area of Dobrich. The picture is virtually constant, at least during the period under investigation. The depression is slightly lower during the spring of1995 and in June, 1996, probably because of the higher precipitation total during the previous periods. This shows the relative equilibrium of the positive and negative components of the water balance. Figure 36. Piezometric levels means for winter, 1995. Figure 37. Seasonal means of the groundwater levels.

For a more precise analysis of the evolution of the piezometric levels, the differences between the monthly values were calculated and further considered (e.g. the level in January, 1995 minus the level in February, 1995; the level in February, 1995 minus the level in March, 1995; and so on). Those differences were plotted to illustrate the time periods when the monthly variations were more dynamic (Figure 38). Figure 38. Differences between the monthly piezometric levels.

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It is evident that the differences for most of the observation points are less than 20 cm. This probably means that the response of the aquifer to a unit precipitation input is heavily transformed by the covering system and/or that the space redistribution of the unit precipitation signal is quite fast because of the high transmissivity of the aquifer. Larger differences exist in a very few cases. These occur mainly in the spring and summer, when the recharge processes are more active. Another analysis of the evolution of piezometric levels is to give the areal plots of the differences between the seasonal averages of the levels (Figure 39). In general, positive anomalies indicate depletion zones and corresponding time periods, while negative anomalies indicate the recharge zones and periods. During the winter and spring of 1995, recharge processes prevailed over the whole pilot area. The opposite type of depletion processes prevailed during the period autumn, 1995 - winter, 1996. The other four situations mix recharge and depletion at different locations of the pilot zone. The strongest gradients are to the NW, because of the higher amplitudes there, as mentioned above. It appears that in Dobrich and its surroundings the seasonal differences are in most cases quite small. Thus, it may be concluded that there are no strong seasonal variations in the piezometric levels in this part of the pilot area. Figure 39. Seasonal differences of the groundwater levels.

The spring discharges and water temperature present quite small variations within the period under investigation. The ratio of the maximum and minimum discharges is close to 1, which is not typical for karst springs. There is no clear seasonal component, while a slight tendency to increase was seen in the Kavarna spring hydrograph. Another slight, but decreasing, tendency was found for the Obrochishte spring (Figure 40). Figure 40. Time plots of the spring discharges.

4.2. Considerations about the water budget in the pilot area As mentioned above, the depression in the water table around Dobrich is fairly stable, and might even be assumed to be stationary. The most difficult aspect of calculating the balance is the determination of the flows through the boundaries of the pilot area. In a real situation, and over time, such flows could vary in volume and direction, depending both on the situation outside and inside the pilot area, in terms of intake, infiltration rates and other water balance input and output. In the case in question, there could be assumed to be a simple stationary gradient flow across the boundaries of the pilot area. Thus, the components of the water balance can be calculated by simple empirical formulas, always bearing in mind that is only a first approximative step. Under these premises, the equation of the water balance is: E = S ± ∆V where E represents the input, S, the output and ∆V, the variation in water storage within the hydrogeological system. During 1995, water reserves in the aquifer rose and thus ∆V was positive. Assuming a generalized rise in the phreatic level of some 20 cm and a mean storage coefficient of 3 %, ∆V is approximately equal to 2 Mm3/year. The following may be considered to represent the input to the system:

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E=G+I+D where G is the flow of water from outside the pilot area towards the centre of the drawdown cone, I is the rainfall infiltration rate and D is recharge effected by domestic wastewaters where no sewage pipelines exist. The system output could be represented as follows: S = Sv + In where Sv is the amount of water flowing from the Upper to the Deep Aquifer and In is the total input. The above components can now be evaluated. G, the flow from outside the pilot area, can be estimated by applying Darcy’s Law to each of the boundaries. A length of 16 km was assumed for the southern boundary, together with a mean hydraulic gradient of 0.006 and a mean transmissivity of 500 m2/day; thus, an input of 17.5 Mm3/yr is obtained. Input through the southern part of the eastern boundary may be considered negligible, at least for the southern part, as this coincides with a flow line (a region of zero interchange); along the rest of the boundary, input is calculated at 3.3 Mm3/yr. Using the same procedures and reasoning, a value of 3.5 Mm3/yr was obtained for the northern boundary, while the input along the western boundary was considered inappreciable as, to a large degree, this coincided with another flow line. Therefore, the hidden lateral input (G), proceeding from outside the pilot area, may be estimated at about 24 Mm3/yr. According to the information given in the first section, I, the infiltration, could be 50 mm per year or more, affecting an active infiltration area of some 400 km2. Thus, total infiltration inflow would be around 20 Mm3/year. The recharge of the Upper Aquifer by domestic wastewater, D, was estimated from data provided by the local water suppy company, and the volume calculated for 1995 was 0.8 Mm3. The intake, In, was calculated from the same source at 7 Mm3 for 1995. In addition to this quantity, water was also pumped for industrial use and irrigation, estimated for 1995 at 12 Mm3. Thus, In is estimated at about 19 Mm3/yr. Finally, if the flow is assumed to be stationary and the water balance close to zero, there only remains one unknown component of the balance equation, that is, the amount of water flowing from the Upper to the deep Aquifer, Sv. The residual of the equation is almost 24 Mm3/year, a fairly significant amount which probaly contributes to the existence of the water table depression around Dobrich. There are two possible mechanisms for this significant leakage from the Upper Aquifer. The first is related to natural conditions: fault zones and the existence of localized aquitard between the two aquifers. The second possibility concerns anthropogenic factors, i.e. badly-constructed deep boreholes that enable water to flow between the two aquifers. Justifications for this latter hypothesis include the following facts: - The piezometric levels of the Upper Aquifer are higher than those of the Deep one in the Dobrich pilot area. - There exist two (unpublished) piezometric maps of the region. In the first, dated 1958, there is no water depression around Dobrich, while in the second, produced in 1988, the depression is shown but it is less deep (only 10 m) than at present.

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- The number of deep wells (deeper than 500 m) in the town and its surroundings has increased dramatically over the last 15 years to a current figure of over 70. - Investigation has revealed that, for many reasons, the technical implementation of the wells was unsatisfactory, enabling the possibility of artificial links between the two aquifers. 4.3. Quality control wells 4.3.1. Experimental monitoring network The experimental hydrochemical monitoring network comprises 19 sampling points (Table 6 and Figure 33). Sixteen of those points represent the Upper Aquifer. Part of them are shallow dugwells situated at the villages around Dobrich. It was necessary to use such shallow wells, because of the reasons given in 2.4.1. Points 23, 25, 26 and 27 are situated in the industrial zone of the town, representing industrial activities like meat and milk processing plants, a cooking oil plant and so on. Points 10, 12 19, 28 and 29 are situated in the agricultural areas around the town (Figure 33). Most of the points are situated in the villages around the town where no sewage pipeline or waste water purification facilities exist. There are additional pollution sources close to these villages such as stock-breeding farms and related small enterprises. During the selection of the sampling points we tried to couple them with the water level observation wells. This was an important approach that enabled a more precise study of the links between water level variations and those of the hydrochemical parameters, as discussed below. The Balchick spring (Nº. 33), situated in the coastal zone, was selected as representative of background hydrochemical characteristics. Point Nº. 5 is situated at the output channel of the Dobrich waste water purification station. The purification station disgorges the processed waste waters into the Dobrich gully. These waters, together with the gully runoff, could be traced to the N, where several small reservoirs have been constructed for secondary processing of the polluted waters. On flowing N, these waters could partially or entirely infiltrate the limestone outcropping along the gully bed. Photo 15. Deep borehole in the Pumping Station of Primortsi, near Dobrich.

Precipitation waters were also sampled at the Dobrich synoptic station in order to assess possible inputs of chemical components from the atmosphere. It was found that these waters were fairly clean during the period under investigation and thus this point will not be further considered. In September, 1995, the composition of rainfall water was: pH, 6.2; Na, 1.23 mg/l; K, 0.39 mg/l; Ca, 2.4 mg/l; Mg, 0.25 mg/l; Cl, 1.5 mg/l; SO4, 6.93 mg/l; NH4, 0.2 mg/l; NO3, 0.6 mg/l; Mn, 0.018 mg/l; Zn, 0.019 mg/l; and Fe, Pb, Al, As, Cd, Cr, and Cu, were less than 0.035 mg/l. Table 6. Groundwaters sampling points.

All the points were sampled monthly. The following parameters were determined in situ: T (water temperature), pH, ∆pH (pH before and after adding marble powder to the water sample), κ (conductivity), tests for NO2, NH4 and CO2. The macro and micro components (HCO3, SO4, Cl, NO3, HPO4, Ca, Mg, Na, K, F, O2, H (hardness), Fe, Mn, Sr, H4SiO4) were determined at the hydrochemical laboratory of the University of Mining and Geology, Sofia. Pesticide pollution was studied by two during November, 1995 and March, 1996 all. During the first campaign we focused the most polluted wells (points 2, 4 and XLVI

seasonal sampling campaigns carried out (Table 7). Sixteen points were sampled in on water supply pumping stations and on 6). Only pumping stations were sampled

during the second campaign. Sample analysis was performed at the specialised laboratory of the Institute for Plant Protection at the town of Kostinbrod, Bulgaria. Table 7. Pesticide sampling sites.

4.3.2. Spatial distribution of hydrochemical characteristics The first step in processing the data collected by the pilot area experimental observation network was the pre-processing of data including data entry, quality check, calculation of different characteristics such as ion balance, the preparation of different types of graphs and the illustration of the spatial and temporal variability of the hydrochemical parameters observed. For these purposes, two types of graphs were chosen: areal plotting of the parameters in the area around Dobrich using a base map similar to Figure 33; time plots of the relevant parameters for all observation points in the pilot area. From the areal distribution of the hydrochemical characteristics, the results of the studies with respect to groundwater composition show that the processes of congruent dissolution and mineral leaching in the zone of aeration (soil cover, loess) play a basic role in the formation of groundwater composition, under the strong influence of the human factor (active pumping from the aquifer combined with nonpoint-, and to a lesser degree point-, pollution). Figure 41 shows the minimum, mean and maximum pH values with an apparent absolute and relative minimum for the points in and around Dobrich, possibly due to anthropogenic influences. We also performed some marble tests in situ to check the aggressiveness of the groundwater (measuring pH before and after adding marble powder to the water sample). Almost every time and for every point the delta pH values were between -0.01 and -0.20, which demonstrates the under-saturated behaviour of the water with respect to calcite. Figure 41. Spatial distribution of minimum, average and maximum pH values observed during the period January ,1995 - June, 1996. Figure 42. Spatial distribution of minimum, average and maximum κ values observed during the period January ,1995 - June, 1996.

Figure 42 shows the area distribution of electrical conductivity values. A clear tendency can be observed towards a decrease in electrical conductivity (and, naturally, its determining mineralization and prevailing macro-components) from NW to SE with a small "island" of increased values in and around Dobrich. As regards the hydrochemical type, the hydrocarbonate-water type is predominant in the area, in some cases containing higher concentrations of chloride and nitrate ions (along the line Malka Smolnitsa-Vrachantsi-Paskalevo). The nitrate content at point Nº.4 (Vrachantsi, the well in the village centre) is so high that the water has changed into nitrate-type water. A similar phenomenon can be observed at the point in Malka Smolnitsa (Nº. 2). Bearing in mind that these are shallow wells, which are not protected, although pumped actively and that the composition data should be accepted with some reservations, it is still possible to suggest that the upper part of the Sarmatian is more polluted than the deeper one. Thus, an index showing the larger extent of the pollution of the upper part of the aquifer could be found in our measurements made in July, 1996, in the well no. 24, near Strelbishte (Figure 43), where the nitrate concentration values decrease from 160 mg/l at the top of the water column to 18 mg/l at the bottom.

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In the cation part of the waters examined (Figure 43), irrespective of the uniform geolithological conditions of the Sarmatian aquifer, a greater variety is observed. Figure 43. Spatial distribution of minimum, average and maximum Mg/Ca ratio values observed during the period January ,1995 - June, 1996.

For example, in the water from well Nº.12 - Dobrich-Primortsi, well Nº.25 Dobrich-Dobrudja Textile Factory, well Nº.11 - Paskalevo, near the village centre, Nº.10 - Minkovo, Nº.19 Dobrich Almaniy, Nº17 Bogdan, Nº11 Sveshtarovo magnesium ions predominate, the Mg/Ca ratio being from 1.01 to 5.40. This anomaly can be explained by the peculiarities in the mineral composition of the loess sediments and soil cover. In the heavy part of the loess fraction 0.01 amphibole and tremolite predominate, and the 0.005 fraction is composed mainly of the minerals montmorillonite, hydromuscovite, vermiculite and chlorite, which, when leached, release Mg ions. The data from the bulk analysis of the carbonate and leached chernozems are presented in Figure 44 (Raykova and Danchev, 1972). Figure 44. Time plot of certain soil characteristics.

Obviously, due to the high thickness of the aeration zone, the composition of the infiltrating water, before reaching the zone of Sarmatian limestones, is formed during its downward movement as a result of incongruent dissolution of the rock-forming minerals, and is enriched primarily in HCO3, magnesium and partly Ca and Na ions, whereas in the zone of carbonate depositions only Ca2+ and HCO3- ions are added. In the areas where the loess cover is thin and typical chernozems occur (where the ratio Ca/Mg >1) Ca ions predominate in the groundwater composition. Time plots of several hydrochemical parameters are shown in Figure 45 as an example of this case. Figure 45. Time plot of certain hydrochemical characteristics for point Nº 2.

4.3.3. Temporal distribution of the hydrochemical characteristics The results of the investigations show that the sulphate ions are the least changeable, both spatially (Figure 46) and in time (Figure 47). At almost all points their concentrations change within narrow limits, with no abrupt variations, throughout the year. The only exceptions are the points at Vrachantsi Nº. 4 and at Nº. 17 (Bogdan), where higher contents of this ion were recorded during the autumn-winter periods. Figure 46. Spatial distribution of minimum, average and maximum SO42- values observed during the period January ,1995 - June, 1996. Figure 47. Time plots of the sulphates for certain sampling points.

The concentrations of Na ions (points Nos.12, 23, 28, 10, 9, 19, 17, 2 and 11) are slightly changeable in time, and the potassium concentrations are, as a rule, quite low except for the water sources along the line from point Nº 2 - Malka Smolnitsa (up to 73 mg/l) - Almaliy (No 19 ), probably due to specific agrochemical activity. The waters contain mineralizations, often up to 650-900 mg/l; the time variations of the specific electrical conductivity, as an integral expression of the mineralisation, show more seasonal changes (Figure 48). With respect to the total hardness of groundwaters, they are usually hard to very hard, the hardness decreasing, by analogy to calcium and magnesium, from NW (28.3 °d) to SE (6.15 °d). Figure 48. Time plots of electric conductivity for certain sampling points.

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As mentioned above, high concentrations of NO3- ions are contained in the waters of all the water sources examined (Figure 49). Particularly high concentrations of these ions were recorded at points Nº.2, Malka Smolnitsa, up to 930 mg/l, Paskalevo - 300 mg/l, Vrachantsi - 567 mg/l, Almaliy (102 mg/l ), etc. At these sampling points (with the exception of Vrachantsi), lindan, metolachlor and acetochlor in concentrations between 0.01 and 0.09 µg/l (for Almaliy-metolachlor up to 6.4 µg/l) were also detected. Figure 49. Spatial distribution of minimum, average and maximum NO3- values observed during the period January ,1995 - June, 1996.

The time changes in the nitrate concentrations at each point vary within a very wide range, with some clearly established periods of rises and falls (Figure 50). The presence of this type of pollutants is probably related to the large number of animal and poultry farms, waste heaps and dung-hills, which are not properly isolated; their waste products, through the actions of precipitation and surface waters, actively pollute the groundwater. Figure 50. Time plots of electric conductivity at certain sampling points.

In all the water sources studied, the presence of HPO42- ions was found, though not in high concentrations, usually in the order of 0.1-0.5 mg/l. Exceptions to this are the points at Sveshtarovo (Nº. 11), Minkovo (Nº. 10), where the HPO42concentrations reach 5 mg/l and 1.5 mg/l, respectively. The NH4+ and NO2- concentrations measured are significant for the possible organic pollution of the waters and, with the exception of the high values in the gully above and below the Dobrich purification station (points 3 and 5, respectively), NH4+ and NO2- were detected mainly at points 25, 4, 16, 17, 2 and 11. At these points the permanganate oxidizability and the COD were also high. Of the other microcomponents, strontium (0.4 - 1.5 mg/l), fluor (0.2 - 1.4 mg/l) and sometimes zinc (0.08 - 0.4 mg/l) were detected, but at values below the maximum permissible levels. 4.3.4. Consideration of some hydrodynamic aspects. Relations between groundwater levels and hydrochemical parameters Our investigations have shown that statistical methods enable the evaluation of some tendencies and trends over the last two years concerning hydrodynamic and hydrochemical characteristics. To avoid the undesirable influence of outliers, especially in the hydrochemical information, for some purposes the series were filtered using the moving average method. To estimate possible links between the groundwater dynamics characteristics (the levels, in this case) and the hydrochemical parameters (the concentrations), the pairwise correlation matrix of the levelsconcentrations was calculated. Subsequently, the significant correlation coefficients were selected, using the significance level a = 0.05. From 10 points in the region, where hydrodynamics (levels) and hydrochemistry were studied, such significant relationships were found for only 7 of them (Figures 51 to 57). On examining the evolution of groundwater levels, two cases were recognised: a tendency to increasing groundwater (which is the predominant case), and a decreasing tendency (which was observed at a few points). The relation between the variations in hydrochemical characteristics and levels will be considered separately for those two cases.

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Increasing tendency for groundwater levels: as mentioned previously, the period studied (January, 1995 - June, 1996) was quite humid. The total precipitation was above the mean (Figure 34) and thus it is quite logical for the predominant tendency of groundwater levels in the region to be increasing. For 6 of the 7 points under consideration, the tendency is for the levels to increase (Figures 51 to 56). This tendency is related to a decrease in the values of such important hydrochemical characteristics as mineralisation and nitrates (5 of 6 cases) and, to a lesser degree of the hardness. It is very likely that the "refreshment" of the groundwater is due to the decrease in the use of nitrate fertilizers in recent years (for economic reasons) and to the fact that nitrates migrate with the groundwater flow. This is not true for the phosphates, which migrate relatively slowly from the unsaturated zone into the aquifer and so their tendency is increasing in all 6 cases (Figures 51 to 56). For the chlorides and permanganate oxidizability, no common tendency or relationship was found. The point at Malka Smolnitsa represents the highest local pollution in the region. Even with a tendency towards increasing groundwater levels, the nitrates and the mineralisation here tend to rise, probably because of a strong and continuous pollution source in this village. Figure 51. Time plots of the trends of some hydrochemical characteristics versus water levels trends for the Dobrich-park point. Figure 52. Time plots of the trends of some hydrochemical characteristics versus water levels trends for Plachidol point. Figure 53. Time plots of the trends of some hydrochemical characteristics versus water levels trends for the Riltzi point. Figure 54. Time plots of the trends of some hydrochemical characteristics versus water levels trends for the Paskalevo point. Figure 55. Time plots of the trends of some hydrochemical characteristics versus water levels trends for the Stefanovo point. Figure 56. Time plots of the trends of some hydrochemical characteristics versus water levels trends for the M. Smolnitsa point.

Tendency towards decreasing groundwater levels: this tendency was found in very few points. Only one point, Sveshtarovo (Figure 57), represents this case among the set of points considered. In this case this is probably due to the local depression related to the exploitation of the aquifer by the nearby Primortsi pumping station. In such a process of decreasing groundwater levels, there is usually an increasing tendency for most hydrochemical parameters. Here, surprisingly, there is no significant tendency towards an increase in all hydrochemical parameters. There was observed to be a decreasing trend in mineralisation and hardness, but increasing levels of nitrates and ammonium - which is somewhat significant of groundwater pollution occurring in this region. Figure 57. Time plots of the trends of some hydrochemical characteristics versus water levels trends for the Sveshtarovo point.

5. FINAL CONSIDERATIONS The monitoring network used is capable of detecting "hot-spots" or local sources of groundwater contamination by nitrates in the region. These sources are mainly located in the NW sector of the Dobrich district, along the Malka SmolnitsaVrachantsi-Paskalevo line and in the stream where the wastewater from Dobrich flows towards the N-NW. There is an alarming presence of herbicides (metholachlor L

and acetochlor) and pesticides (lindane) at some points, where the nitrate concentration is greatly above the maximum permissible levels. Also, the groundwater in the upper part of the aquifer is much more polluted than the deeper part. Although the main source of groundwater pollution is the excessive use of fertilizers and pesticides, there also exist other potential sources of contamination such as uncontrolled urban waste dumps and the infiltration of waste water both from farms and from the town of Dobrich. This latter waste water flows into the limestone aquifer to the NE of the town. A treatment plant has been established here, but it is inadequate for the volume of waste water produced. The piezometric configuration of the area, in which the flow is towards the main points of extraction for the supply of urban drinking water, together with the karstic nature of the aquifer, means that the sector of Dobrich is highly vulnerable to groundwater pollution. Nevertheless, the analysis of the scarce historical data available since fifties, as well as the recent detailed information, shows that a significant overexploitation of the Upper Aquifer do not exist in this area. Moreover, due to the recent economic decrease, the groundwater intakes are significantly reduced. The observed sligth advance of the groundwater table depletion around the town of Dobrich is a result of the artificial discharge of the Upper Aquifer into the Deep one. The approximate estimate of the water balance components of the Upper Aquifer in the piezometric level depression zone around Dobrich shows that most losses are related to the filtration from the Upper to the Deeper Aquifer. This significant flow value is quite probably due to the high number of badly isolated deep boreholes constructed during the last fifteen years. It is strongly recommended that these boreholes should be checked and their technical conditions improved. This would raise the water table around Dobrich, saving energy currently used for transferring water from the coastal zone and reducing the risk of pollution of the Deep Aquifer.

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PART III.- KRAPETZ PILOT AREA

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1. INTRODUCTION 1.1. Objectives The coastal zone of the Upper Aquifer is of particular interest for studying the hydroecological conditions in an area where the groundwaters are the only water supply source. In this zone the complex impact of different factors, natural and human, on the quantity and quality of groundwaters is possible. On the one hand there is the influence of the villages with their wastes and agricultural activities; on the other, there exists groundwater overexploitation with the consequent risk of seawater intrusion. From the whole coastal zone, the area of Durankulak - Krapetz and Lake Durankulak was chosen as a pilot area for investigation. It extends over part of the Black Sea coastal zone (Figures 58 and 59) and has an area of about 200 km2. The region has not been sufficiently studied from an ecological point of view, although some aspects of groundwater salinization and protection have been approached in research reports and papers (Raykova and Danchev, 1972; Antonov and Danchev, 1980; Balev, 1981; Pentchev, 1983; Galabov and Pentchev, 1986; Galabov et al., 1989; Velikov et al., 1989; Pentchev, 1992 a and 1992 b; Pentchev, 1993; Pentchev and Petrov, 1993; Naidenov, 1994). The lake is a protected zone in accordance with the requirements of the Ramsar Convention (02/02/1971). In this respect, the detailed study of hydrogeological conditions in the pilot area is of particular interest as it is also directly related to the hydroecological conditions in the lake and adjacent territories. The pilot area can also be considered a model for the whole coastal zone of the Upper Aquifer with respect to the methods of studying the environmental aspects of water quality deterioration. Figure 58. Area under investigation. Figure 59. Pilot area map. Photo 16. Panoramic view of the Durankulak lake.

The pilot area is a typical agricultural area, in which 10 villages are situated. The larger villages (more than 1000 inhabitants) are Krapetz, Vaklino, Durankulak and Z. Stojanovo. The average population density is about 40/km2 but during the tourist season this is doubled. Wheat, maize and sunflowers are the main crops grown in the region and in the bigger villages vegetable cultivation is practiced. Cattle breeding is well developed and poultry, pigs and other farm animals are also bred. The climate is moderate-continental and is strongly influenced by the Black Sea. During the cold half-year air masses are transferred from the W or the NW, though sometimes cold masses from the N enter and cause heavy snowfall. The average January air temperature is between minus 0.8 and 1.5 °C, while the average July air temperature is between 20.8 and 21.6 °C. The total annual precipitation for the region is 466 mm/year (Figure 60), which is considerably lower than that for Bulgaria as a whole, around 673 mm/year (Institute of Meteorology and Hydrology, 1990). Figure 60. Average precipitation amounts.

1.2. Methodology 1.2.1. Indices, frequency and methodology of the monitoring activities The selection of the indices and the frequency of the monitoring observations and sampling are based on: 1) the peculiarities of the hydrogeological conditions of the region; 2) the potential groundwater pollution sources; 3) the possibilities for LIII

seawater intrusion in the coastal zone; 4) the groundwater exploitation regime for water supply and irrigation; 5) the available financial resources for monitoring and laboratory analyses of water samples. The following indicators were adopted for the survey of the monitoring network: 1) static water levels (SWL) in the monitoring points (hydraulic indices); 2) components of the chemical composition and qualities of groundwater (hydrochemical indicators) temperature, pH, redox potential (Eh), specific electrical conductivity (SEC), total dissolved solids (TDS), total hardness (TH), permanganate oxidizability (PO), COD, SAK, chlorides, sulphates, bicarbonates, nitrates, nitrites, phosphates, ammonia, sodium, potassium, calcium, magnesium, silica. The frequency of the observations and samplings were selected as follows: a) SWL in the monitoring points - measuring each month by a standard electric level meter; b) Hydrochemical indicators - sampling twice a year - in May (before the start of irrigation) and September (after the finish of irrigation). In order to compare the results of the separate monitoring points (MP), the testing of the hydrochemical indicators was performed at a depth of 1 - 1.5 m below SWL (without a preliminary water pumping). At this sampling depth, the data for chemical composition and the quality of groundwater refer to the higher part of the Upper Aquifer, i.e. to the interface between the aeration zone and the zone of saturation. All water samples were taken with a standard sampler. The hydrochemical determinations were made in situ (for fast-changing parameters such as pH, Eh, dissolved gases) and under laboratory conditions (for the remaining characteristics after preservation, if necessary). Standardised methods and equipment were used. 1.2.2. Estimation of groundwater contamination and pollution sources: impact assessment A new methodological approach to estimate the degree of groundwater contamination was developed, based on the so-called Contamination Percentage Index (CPI), defined as: CPI (%) = [( Cgw / Clim ) - 1] . 100 where Cgw is the concentration of a certain chemical component (or characteristic) in the groundwater; and Clim is the concentration of the same chemical component (or characteristic) limited in the groundwater standard. Accordingly, a new Impact Percentage Index (IPI) is accepted for assessment of the hydrogeological impact of the existing sources of groundwater contamination. The parameter is calculated as: IPI (%) = [( Cp / Cbg) - 1] . 100 where Cp is the concentration of a certain chemical component (or characteristic) in the groundwater in the area affected by pollution sources; and Cbg is the natural (background) concentration of the same chemical characteristic in the unaffected areas of the aquifer. It is not advisable to use groundwater components or characteristics (for instance NH4, NO2, H2S, Eh, etc.) which: a) are too changeable in time (and have to be determined in situ, which is not possible in every case); b) are strongly dependent on the local hydrogeochemical conditions (near the contamination sources); c) have no prescribed maximum permissible level in the corresponding national or international standards.

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The contamination assessments (CPI) can be applied in regard to the main groundwater constituents (Cl, SO4, NO3, Ca, and Mg) and water mineralisation characteristics (TDS or SEC) included in the standards for drinking water indices. The impact assessments (IPI) should be made in regard to: a) all main groundwater constituents (Cl, SO4, HCO3, NO3, Na, K, Ca, Mg); b) the characteristics of the water mineralisation (TDS or SEC); c) other specific and relevant groundwater chemical characteristics for special cases. In groundwater contamination and impact studies it is advisable to use averaged hydrochemical data from the following two characteristic water points groups: - Group A - water points situated far from the potential contamination sources, where the chemical composition of the water is representative of that in the aquifer under study. - Group B - water points situated in the zone of potential contamination sources where the water composition is typical of the affected parts of the aquifer. The degree of contamination or impact can be estimated by the scale proposed in Table 8. Table 8. Degree of contamination and impact.

In many cases it is possible to obtain a negative degree of contamination although an average or even significant impact score is observed and vice versa. This is so because the CPI parameter only gives the deviation of the groundwater quality from the drinking water standard while the IPI gives the changes of groundwater composition in relation to the reference level. From this viewpoint the IPI parameter should be preferentially used for groundwater protection purposes because it gives an earlier indication of possible contamination processes in the aquifer. So, when the IPI > 50 %, it is advisable to set up a monitoring network. If ∆IPI > 0, where ∆IPI = IPIn - IPIn-1 (n is a relevant year or month of sampling), it is necessary to begin appropriate activities to limit contamination even if the groundwater quality is within the limits of the drinking water standard (CPI < 0 %). In cases when CPI > 0 %, but IPI < 0 %, the authorities can allow the use of the corresponding well (water source) for water supply purposes taking into account the purification technologies applied. 2. GENERAL DESCRIPTION OF THE AREA 2.1. Geology 2.1.1. Stratigraphy In lithological terms, down to a depth of 250 m the region is fairly simple (Figure 61). The top part comprises a Quaternary loess material with a thickness ranging from several tens of centimetres (in the eastern part) up to 15-20 metres (in the western part). In the Vaklino Gully and along the southern bank of Lake Durankulak there is no loess and the Sarmatian limestones outcrop. South and north of the lake the thickness of the loess gradually increases and at some places the loess deposits occur under the sea level (Balev, 1981). Figure 61. Hydrogeological vertical scheme.

The deposits of the Upper Miocene (Sarmatian) lie under the loess. They make up the so-called Karvuna and Odar formations. The differences between the two formations are mainly facial. The Odar formation is characterised by sandy and LV

oolithic limestones, and the Karvuna one by shelly limestones. At intervals among the limestones there are irregular interlayers of marls. The limestones are commonly thin-layered, with clearly expressed interstices, porous, jointed, cavernous and karstified. Most clearly expressed is the horizontal interbed karstification. Vertical karstification has also developed, but to a lesser extent. The vertical and horizontal development of the karstification process results from the repeated change in the sign of the epirogenic movements in the region during the Pliocene and the Quaternary (Antonov, 1973) and of the fluctuations of the sea level during the same period. The total thickness of the Miocene sediments is about 150 metres. Oligocene clays and marls, which comprise the so-called Avren formation, lie under the Miocene limestones. The thickness of the clays is over 90 m and they act as a regional aquitard for the overlying groundwater. 2.1.2. Geomorphology In geomorphologic terms the region is a low plateau, slightly hilled and sloping towards the Black Sea. The largest dry valley is the Vaklino Gully (Figure 59), which has a comparatively well-defined valley character (cut into the limestone platform), the incision being in the order of 10 metres. The gully opens in the NE direction into Lake Durankulak. The hydrographic network in the region is poorly developed. There is no surface runoff in the dry valleys and only after short-term pouring rain or intensive thaw does water run through them for several hours. The temporary runoff is quickly drained (sinks) in highly karstified limestones outcropping in the valley bottoms and replenishes groundwater in the Upper Aquifer. 2.2. Hydrogeological features 2.2.1. Water-bearing formations A basic hydrogeological unit in the region is the Upper Aquifer (Sarmatian carbonate). This was formed in the karstified limestones of the Karvuna and Odar formations, and extends far outside the territory of the studied region (Pulido-Bosch et al., 1997). In the Upper Aquifer an unconfined groundwater flow has formed in a W-E general direction, towards the Black Sea. The coastal zone coincides with the natural drainage zone of the aquifer where, in the lower parts of the relief, and particularly along the strike of the Vaklino Gully, a considerable number of downward karst springs rise. The latter are captured by water pumps for water supply and irrigation needs. A significant particularity of the hydrogeology of the region is the presence of Lake Durankulak. This has the status of a wet zone in accordance with the requirements of the Ramsar Convention (02/02/1971). The lake basin was formed in the Miocene limestones, its bed extending to 21 m below sea level. The basin is filled with marsh silts and clays with thicknesses of up to 18 m, which form a good isolation from direct seawater intrusion. The lake is separated from the Black Sea by a sandbar and is replenished by subaquatic springs from the Upper Aquifer. The water level in the lake is about 0.5 - 0.8 m above that of the Black Sea. In very humid years part of the lake water seeps through the sandbar into the sea, while in dry periods (and/or when there is increased pumping from the wells situated near the lake) a seawater inflow through the sandbar occurs. Thus, in hydrogeologic terms Lake Durankulak is a natural collector of fresh groundwaters which can be used as an additional source of water in the peak periods of irrigation, providing certain precautions are taken. 2.2.2. Hydraulic parameters LVI

The analysis of archive data for 10 pumping wells, bored for different purposes in the pilot area (Balev, 1981) shows (Table 9) a relatively high heterogeneity with respect to the hydraulic conductivity of the Upper Aquifer in a lateral extent. Based on the existing pumping test data (obtained only with piezometers) and on the recent pumping tests of new wells in the pilot area carried out during 1995 - 1996 (Tables 10 and 11) the empirical relationship between the transmissivity (T) and specific capacity (SC) of pumping wells has been examined. The latter is shown in Figure 62 and can be used for an approximate determination of aquifer transmissivity in cases where the pumping test data only contains the SC parameter. Table 9. Pumping test results (based on reference data). Table 10. Aquifer parameters in the Krapetz site. Table 11. Aquifer parameters in the Smin site. Figure 62. Relationship between transmissivity and specific capacity.

Transmissivity isolines were drawn, based on the data from the pilot area (Figure 63). The highest transmissivities were found to be near the sea coast and in the vicinity of Lake Durankulak (over 2000 m2/d), where the main water catchments are constructed. Far from the sea coast, transmissivities are around 1000 m2/d or less. In this part of the aquifer, the presence of clay lens and solid limestones in some parts of the hydrogeological cross section probably interferes with the existing hydraulic connection between karst caves and channels. Figure 63. Transmissivity isolines in m2/d.

2.2.3. Groundwater exploitation Groundwater withdrawal in the region is carried out by means of a considerable number of water catchments for irrigation and domestic water supplies. There are 7 pumping stations (Figure 64), 4 units of which (PS-1, PS-2, PS-4 and PS-7) are for the supply of drinking water (equipped with wells) and 3 units (PS-3, PS-5 and PS-6) are used for irrigation (equipped with horizontal drainage galleries). Figure 64. Location of pumping stations (PS) in the pilot area.

The data on groundwater exploitation during 1995 are given in Table 12 and are shown graphically in Figure 65. In past years (1984 - 1989), groundwater withdrawal for irrigation was of 3.2 to 4.8 Mm3/year. The irrigation pumping stations are very close to Lake Durankulak and as a result of active water pumping during the irrigation period, indications of salinization of the lake water and a notable drawdown of lake levels were repeatedly observed. In order to improve the present ecological condition of the lake, since 1990 groundwater withdrawal for irrigation has been limited to 1.5 Mm3/year. The rate of groundwater exploitation in 1995 is shown in Figure 65. For drinking water supply, total pumping is about 0.95 Mm3/year. The withdrawal from local wells in populated areas does not exceed 0.1 Mm3/year. Annually, about 2.5 Mm3/year are pumped from the territory of the pilot area, 37.8 % of which is for drinking water supply and 62.2 % for irrigation. Table 12. Groundwater exploitation in the pilot area. Figure 66. Groundwater exploitation (1995).

3. GROUNDWATER POLLUTION IN THE AREA 3.1. Main sources of pollution LVII

3.1.1. General characterisation of the pollution sources in the pilot area There is no industry in the area. Sewerage is also absent from the villages and the waste waters from the cattle farms are collected in primitive septic pits. The solid wastes are accumulated in local dunghills without underlying clay strata. The cultivated lands had been treated with nitrate and phosphate fertilisers each year up to 1992. As a result of the economic recession and the closing of cooperative farms from 1992, the application of fertilisers has been greatly reduced. The cultivated lands have been treated by nitrate fertilisers (30 kg/1000 m2) only in the Durankulak (12 000 000 m2) and Z. Stojanovo lands (6 000 000 m2). Taking into account the specificity of the infrastructure and economic activity in the pilot area, the main contaminants of groundwater can be categorized as follows: fertilisers and chemicals for treating cultivated lands; waste waters and solid wastes from the urban zones. The main interest from a scientific point of view is to study the general degree of impact of the above-mentioned pollution sources on the quality of groundwater in the Upper (Sarmatian) Aquifer. 3.1.2. General assessment of groundwater contamination in the pilot area For a general assessment of the degree of groundwater contamination in the pilot area, the hydrochemical data from the monitoring network and some additional water points in the villages have been used. The results from the chemical analyses of water samples are summarised in Tables 13, 14 and 15. Table 13. Groundwater chemical composition in the urban sites. Table 14. Groundwater chemical composition outside the urban sites. Table 15. Groundwater chemical composition at the pumping stations.

The distributions of TDS, SEC, chlorides and nitrates in the sampled water points are shown in Figures 66, 67, 68 and 69. From these Figures it is obvious that groundwater contamination is localised in urban areas, where the groundwater is unsuitable for drinking water supply (in accordance with the corresponding national standard). The village of Smin is an exception (water sampling point MP-7) where the groundwater is fully potable. Outside the villages, the quality of groundwater is within the limits of the drinking water standard. Figure 66. Distribution of TDS in the pilot area. Figure 67. Distribution of SEC in the pilot area. Figure 68. Distribution of Cl in the pilot area. Figure 69. Distribution of NO3 in the pilot area.

The CPI values (%) for the different characteristics of the groundwater composition in the area are shown in Table 16. Figure 70 shows the bars of average CPI values. It is obvious that in non-urban sites and pumping stations (according to the scale in Table 7) the groundwater has a negative degree of contamination in terms of all characteristics. These are also within the limits of the drinking water standard. Table 16. CPI Values (%) in the pilot area. Figure 70. Average CPI Values in the pilot area.

In the urban sites the situation is quite different. The degree of contamination in the villages is positive for four different characteristics. The level of nitrate LVIII

contamination is dramatically high in almost all urban sites. The IPI parameter values (%) from water points in urban areas and from pumping stations are shown in Table 17. Figure 71 shows the bars of average IPI values. Table 17. IPI Values (%) in the pilot area. Figure 71. Average IPI values in the pilot area.

It is clear that the environmental impact of urban sites on the groundwater corresponding to these areas is classified as drastic for the following parameters: nitrates (1484 %), Mg (233 %), chlorides (128 %) and sulphates (119 %) and significant for SEC (90 %) and TDS (79 %). For the mentioned indices, IPI has positive values of 80 to 100 % for the water sample tested. The impact of urban sites on the groundwater in pumping stations is less extreme than in the urban areas but is significant for Mg (109 %), Cl (81 %), NO3 (29 %), TDS (25 %) and SEC (11 %). All mentioned IPI indices are positive in 100 % of the water samples investigated. It is interesting that nitrate contamination was not evident in two of the villages Smin (MP-7) and Granichar (MP-12) (Table 16), despite the fact that the degree of nitrate contamination in all other villages was very high. If evaluation is performed solely on the basis of CPI, an erroneous conclusion may be reached, i.e. that contamination sources are absent in these urban areas or that the geological conditions prevent deep-level contaminant movement. The observed IPI values (Table 17) for the same water samples prove that there does exist groundwater contamination on the borders of the mentioned urban areas, because IPI for nitrates is 108 % at MP-7 and 45 % at MP-12. It may be considered the contamination is at an initial stage and thus the nitrate concentration values recorded are within the limits of the drinking water standard (the CPI values are negative). This is probably because of the local clay lens situated in the Sarmatian limestone which is a barrier to the deep infiltration of contaminated surface water. 3.1.3. Conclusions Groundwater contamination is localised on the borders of urban areas, where water quality is unsuitable, as defined by the drinking water standard. A high level of nitrate groundwater contamination is obvious in almost all urban sites within the pilot area. The degree of contamination as shown by the other characteristics of groundwater chemical composition (if any) is insignificant to average. Urban sites strongly influence groundwater composition within and across the territory of such sites as regards nitrates (1484 %), Mg (233 %), chlorides (128 %) and sulphates (119 %); the impact is also significant in relation to SEC (90 %) and TDS (79 %). The impact is lower at the pumping stations but is still evident for Mg (109 %), Cl (81 %), NO3 (29 %), TDS (25 %) and SEC (11 %). The methodology developed for groundwater contamination assessment (applying the CPI parameter) and the urban site impact assessment (applying the IPI parameter) can be successfully used as a working tool in other similar cases. The IPI parameter should be preferentially used for general groundwater contamination assessments in populated areas. Application of the IPI parameter can clearly show whether there is a worsening of groundwater quality in relation to the background level. Furthermore, the IPI parameters can help, in each concrete case, in the selection of the most sensitive indicator of groundwater contamination - this will be the chemical characteristic for which the IPI value increases even if that of the CPI does not.

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3.2. Case studies of local groundwater contamination and urban impact 3.2.1. Vaklino experimental site 3.2.1.1. Description of the site Hydrogeological conditions: a characteristic feature of the site (Figures 72 and 73) from the geomorphologic point of view is the presence of the Vaklino Gully, which crosses the village of Vaklino and ends in Lake Durankulak. The gully's bed has rounded shapes, up to 150-200 m wide, and shallow slopes. From a topographic viewpoint, it is confined at 20 m a.s.l. Its depth is only 10-15 m and its slope length is about 4/100. The gully's bed at its entry into Lake Durankulak is about 1 m a.s.l. and at the borders of the village it is about 15 m. The soil layer in the gully is just 1-2 m, if there is any. At several places there is no soil at all and there is only karstified limestone of the Sarmatian outcropping to the surface. There is no permanent water flow in the gully. Such as there is only appears after intense rainfall or snowthaw. At the end of the Vaklino Gully, before the lake, there is a boggy zone with thick vegetation. With an area varying according to the season, at high groundwater levels (in the spring), the bog almost reaches the water pumping station of PS-2. All surface water from the high part of Vaklino and the water from the deep well B-0 (tapping the Deep or Malm-Valanginian Aquifer) discharges into the Gully. Several private shaft wells for irrigation and local needs have been built along the gully. These are 5-12 m deep and have 1-2 m water column. Their exploitation is periodical and pumping rates are not high, usually around 3-4 l/s. Figure 72. Location of the Vaklino site. Figure 73. Hydrogeological cross-section.

Aquifer permeability evaluation: to evaluate the tested wells, some single water pumping tests (without observation wells) were carried out at the test site (Figure 72), providing values for the specific well capacity (SC). The data from the water pumping tests are summarized in Table 18. On the basis of the SC values obtained it is possible to calculate some approximate values for the transmissivity (T) of the aquifer, taking into account that T is a function of SC. Table 18. Pumping test data from the Vaklino site.

It is evident that in the study area the aquifer is essentially heterogeneous as regards the permeability of the Sarmatian limestones. Outside the Gully borders, the transmissivity is comparatively low (data from MP-5 and MP-6), and SC does not exceed 3 l/s/m. In the Vaklino Gully, the permeability increases by one order (data from SW, DW-1 and DW-2), and SC rises to 31.25 l/s/m in DW-2. From the assessments made it is clear that the higher karstified zone, along the Vaklino Gully, acts as a natural drainage channel for the groundwater in this site. This is why the hydraulic conductivity of the Upper Aquifer in the zone, situated near and to the W of MP-6, is of greatest importance for a possible migration of contaminants to the Pumping Station (Figure 72). Main groundwater catchments: in the site under investigation there are two pumping stations exploiting the Upper Aquifer: PS-2 (for drinking water supply) and PS-3 (for irrigation). PS-2 is situated on the left slope of the Vaklino Gully at 1.5 km from Vaklino. It has two water supplying wells. - Shaft Well (SW) with the following parameters: 9 m depth; elevation of the mouth 6.40; elevation of the SWL - 1.4 m a.s.l.; pump capacity - 40 l/s.

LX

- Drilling Well (DW) with the following parameters: 42 m depth; 0.3 m in diameter, SWL - 4.2 from the mouth; elevation of the mouth - 5.20; elevation of the SWL 1.00 m a.s.l.; pump capacity -16 l/s. The wells of PS-2 are built near the mouths of some karst springs which in the past discharged from the Upper Aquifer at 1.40 - 1.50 m a.s.l. The waters from the springs were replenished by Lake Durankulak. After the exploitation of PS-2 started in 1956, the springs ran dry and the bog narrowed in the direction of the lake. The average annual yield of groundwater from PS-2 (for 1981-1995) was about 19-20 l/s, which on the whole is similar to the average annual discharge of the springs in the past. PS-3 is also situated in the zone of natural discharge of the Upper Aquifer. There is a drainage channel, which is used as a water source. The channel is unlined and is dug from the limestone, which almost outcrops to the surface. The drainage channel is 750 m long and follows the right slope of the gully. Its average depth is about 2 m and the cross section is 8-10 m2. It can supply up to 80-100 l/s with supply restricted to 8 hours per day in the peak moments of the irrigation period. There is a direct hydraulic connection between the SW and the drainage channel, probably due to the karst channel system. This is shown by the fast reaction of the SW when the drainage channel is pumped for water supply. From the sanitary point of view this fact is of essential importance for the drinking water supply and the evaluation of the contamination originating from Vaklino. Groundwater contamination sources: the main contamination sources of the groundwater are the waste water from Vaklino, the solid and liquid wastes from the stock farms and the fertilising of the cultivated lands. The population of this village is about 1100 inhabitants. About 1800 cattle and small farm animals are bred here. There is no sewerage, and so the waste water is collected in septic pits. All the lands along the Vaklino Gully are intensively used for vegetable growing and cattle breeding. Up to 1990, to the W of the village (in the opposite direction to groundwater flow), about 5 000 000 m2 were fertilised intensively at an average rate of 30 kg/1000 m2. There is a farm to the SW of the village which in the past was an intensive local contaminant (until 1995). About 600 animals were bred there, and both sodium and phosphate fertilisers were applied (in an unsuitable way). From 1990 to 1996 no fertilisers were applied, because of the economic recession in the region, and the exploitation of the latter farm has been abandoned. The thickness of the loess covering is about 20-25 m in the high parts of the village. The loess provides a certain protective layer against the direct infiltration of waste waters into the karstified limestone of the Sarmatian. Despite this, the natural protection of the groundwater is insufficient along the Vaklino Gulley, because the limestone outcrops almost to the surface. 3.2.1.2. Experimental studies and results Water samples were taken regularly from the water supplying wells of PS-2, in order to evaluate the main characteristics of any organic pollution of the groundwater. These evaluations have a direct connection with the sanitary protection of the water sources. Analysis of existing archive data (Pentchev and Petrov, 1993) shows that in the past, rising concentrations of ammonia and nitrate were recorded in the groundwater. After 1991, a certain increase in the frequency of the non standard LXI

samples connected with an increased concentration of these characteristics was observed. As a result of the recession in the region, the water supplied from the drainage channel for irrigation was stopped after 1991. Table 19 shows the results of a detailed study of the region near the pump stations (Pentchev and Petrov, 1993) carried out to identify the origin of the ammonia and the nitrites in the water supplying the PS-2 wells. It is clear that, in comparison with the other water points, the concentrations of ammonia and nitrites in the water sources of PS-2 are very high while the concentrations of nitrates and PO are relatively low. This suggests the presence of a local source of organic pollution, near the pumping stations. This source is interpreted as being of natural origin and connected with the anaerobic biodegradation of the vegetation. The ammonia and nitrite ions probably derive from the bog, which is situated very close to the water-supplying wells. They also come from the drainage channel, which forms a basin of stagnant water when water is not being pumped. The increased nitrate concentrations in the region of Vaklino and particularly in the Vaklino Gully (water points B-2, B-4 and B-5) show that the influence of the village on the environment is critical and that there is a risk of human pollution of the water obtained from the pump station. Table 19. Results from hydrochemical sampling in 1993.

During August 1995, SWL levels were measured and water samples taken from 11 characteristic water points of the Upper Aquifer, to evaluate the impact of the village of Vaklino on the quality of the groundwater in the test region. The study was carried out in a manner analogous to that of 1993 except that there were more water points and more hydrochemical characteristics were analysed. Table 20 shows the results of the in situ SWL and hydrochemical measurements and the results of the laboratory analysis of the water samples are given in Table 21. Table 20. Data for hydrochemical parameters (in situ ) in the Vaklino site. Table 21. Data from laboratory analysis in the Vaklino site.

Control samplings from MP-5 and MP-6 were taken during June, 1996 to determine whether there is any kind of vertical zonality of the hydrochemical parameters of the groundwater. The results from the determinations are summarised in Table 22 and show that the chemical characteristics of the groundwater in the Upper Aquifer, outside the urbanised regions, do not vary, to a depth of 30 m below the water table: thus, there are no indications of any hydrochemical vertical zonality. Table 22. Hydrochemical sampling of MP-5 and MP-6.

Comparison of the data from Table 22 and those from Table 20 shows a tendency for an insignificant decrease in nitrate concentrations - of few mg/l in the period September1995 - July1996. This decrease is probably related to the lower use of fertilisers in recent years and denitrification processes within the aquifer. 3.2.1.3. Data interpretation and discussion The method developed in epigraph 1.2.2. to assess the impact of the village of Vaklino on groundwater quality was used. Evaluations are based on the average data concerning the chemical composition in the following characteristic groups of water points (Table 21): - Monitoring water points (MP), situated outside the urbanised zone and reflecting the composition of the groundwater in the parts of the aquifer which are not directly affected by Vaklino.

LXII

- Shaft wells (SW), situated in the urbanised zone and reflecting the composition of the groundwater in the parts of the aquifer which are affected by Vaklino. - Pump stations (PS), situated outside the urbanised zone in aquifer zones which might be affected by Vaklino. The data for the main components of the groundwater in the different groups MP, SW and PS, were calculated by averaging the values of the concentrations at the water points with indices MP, B and PS, respectively (Table 21). The bar-diagrams of these concentrations (in meq/l and in % meq), generated with the HG program, are shown in Figures 74 and 75. Figure 74 shows that Vaklino has an evident influence on the composition of the groundwater in the urbanised zone. This appears in the almost doubling of the sum of meq concentrations in the shaft wells (SW) in comparison with the monitoring water points (MP). As can be seen in Figure 75, this provokes a change in the chemical type of the water, from HCO3-Na at MP to HCO3/Cl-Na/Mg at SW. A similar impact was detected at the water points of the pump stations (PS) but on a smaller scale. The sum of the meq in relation to those at the MP increased by almost 18 % but on the whole the chemical type of the water was unchanged. Figure 74. Average major chemical constituents of groundwater at the monitoring points (MP), pumping stations (PS) and shaft wells (SW) belonging to the Vaklino site. Figure 75. Distribution of the major chemical constituents of groundwater at the monitoring points (MP), pumping stations (PS) and shaft wells (SW) belonging to the Vaklino site.

The values of the CPI parameter (%) for the groundwater chemical characteristics in the water point studies are shown in Table 23 while the bars of average CPI values are shown in Figure 76. It can be seen that in the region of MP and PS the degree of contamination of the groundwater, according to the scale in Table 8, is negative and for almost all of the hydrochemical characteristics there is a certain reserve until the limits of the standard for drinking water are reached. Table 23. CPI Values (%) at the Vaklino site. Figure 76. Average CPI values at the Vaklino site.

The degree of contamination in the SW area is different. Nitrate contamination is undoubtedly extreme at all parts of the urban region (416 % average). With respect to SEC and TDS, contamination is absent or its rate is insignificant to average. The IPI parameter values (%) for the characteristics of groundwater composition at the tested water points are shown in Table 24, and the bars of the average IPI values are given in Figure 77. It can be seen that at the borders of the urban area of Vaklino, the impact is established for almost all the characteristics of groundwater chemical composition. The degree of contamination is extreme for nitrates (1089 %), magnesium (242 %), sulphates (186 %) and chlorides (114 %) and significant for SEC (88 %), TDS (74 %) and calcium (56 %). Table 24. IPI values (%) at the Vaklino site. Figure 77. Average IPI values at the Vaklino site.

The impact of the village of Vaklino on the pump station region is lower but the degree of contamination is still severe with respect to magnesium (109 %) and nitrates (101 %). The impact is negative or inconsiderable to average with respect to the other chemical characteristics. In order to assess the pollution risk to the drinking water supply, the program SURFER was used to create detailed maps of the experimental site: map of SWL isolines (Figure 78); map of SEC isolines (Figure 79); LXIII

map of TDS isolines (Figure 80); map of NO3 isolines (Figure 81); map of Cl isolines (Figure 82); map of SO4 isolines (Figure 83). Figure 78. SWL isolines at the Vaklino site. Figure 79. SEC isolines at the Vaklino site. Figure 80. TDS isolines at the Vaklino site. Figure 81. NO3 isolines at the Vaklino site. Figure 82. Cl isolines at the Vaklino site. Figure 83. SO4 isolines at the Vaklino site.

The input data for these maps cover the period up to August 1995 and are summarised in Table 25. Table 25. Input data for the isoline maps.

The following conclusions can be drawn from the hydrochemical maps: - In all the maps there is a contaminated plume in the aquifer, located in the urbanised zone and adjoining parts of the Vaklino Gully. At the borders of this plume, the groundwater is not suitable for drinking water supply with respect to TDS, SEC, NO3 and Cl. The contaminated plume has an irregular shape and extends in the direction of the gully, sinking towards Lake Durankulak. At the borders of the Vaklino Gully, maximum concentrations of all chemical components and characteristics are obtained in areas where the loess coverage is thinnest. - The concentrations of the components studied are minimum and close to those of the non contaminated parts of the aquifer in the region of the pumping station. The groundwater is suitable for drinking water supply in terms of all constituent concentrations (except ammonia and nitrites). A hydrodynamic network, including 6 water flow tubes used to assess the structure of groundwater flow at the borders of the test site, was constructed, and is shown in Figure 78. This reveals that the structure of the groundwater flow is mainly influenced by water pumping at PS-2 and has the following particularities: - One part of the groundwater inflow to PS-2 passes through flow bands N-1 and N2. These traverse the urbanised zone and the Vaklino Gully. From the sanitary protection point of view this, too, is unfavourable because the highest concentrations of TDS, NO3 and Cl were found at the borders of these water flow bands (Figures 80 and 82). - Another part of groundwater flow to PS-2 passes through flow bands N-4 and N-5. These go through the boggy area at the end of the Vaklino Gully and through Lake Durankulak. The pollution of the drinking water with products (ammonia and nitrites) from the anaerobic decay of plants from the bog area and the possible increase in chlorides when salinization occurs in Lake Durankulak is effected via these bands. - The third part of groundwater flow to PS-2 occurs by flow bands N-3 and N-6, which go through areas with no natural or technogenic sources of groundwater pollution. The composition of the groundwater in these bands is relatively close to the natural one. The above considerations lead us to conclude that the most important risk factor for the pollution of PS-2 is the urbanised zone of Vaklino, which is situated in the recharge zone of the water supply wells. However, the influence of the urbanised zone is local and at the current pollutant loading rate it

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does not reduce the quality of the water at the pump station below the limits of the standard for drinking water supply. 3.2.1.4. Conclusions The environmental impact of Vaklino on the composition and quality of the groundwater in the Upper Aquifer is produced by the waste water at the borders of the urbanised zone and by the agrochemical treatment of cultivated lands. The composition of the groundwater changes as a result of this influence and some constituents of the water are below the limits for drinking water supply and irrigation. The most dramatic consequence is the increase in the average concentration of nitrates at the borders of the urbanised zone (up to 12 times) and in the region of the pumping station (two times). A two-fold increase in TDS at the borders of the urbanised zone is also evident. Moreover, this increase is accompanied by changes to the hydrochemical type of the water - from HCO3-Na in the undisturbed regions to HCO3/Cl-Na/Mg. As a result of the impact of the village of Vaklino, there is a contaminated plume in the upper sides of the Upper Aquifer, which has a local distribution and coincides with the borders of the urbanised zone. The water in this plume is not suitable for drinking water supply with respect to TDS, SEC, NO3 and Cl . The contaminated plume extends in the direction of the gully sink and almost reaches the water supplying pumping station. The maximum pollution of the groundwater is in the region of the gully in the places where the loess coverage is thinnest. From the sanitary protection viewpoint, the urbanised zone is the greatest risk factor for the PS-2 water supply pumping station, which is situated at the recharge zone of the water supply wells. Nevertheless, the influence of the urbanised zone on PS-2, under present exploitation conditions, does not provoke critical states in which the water falls below the limits of the standards for the supply of drinking water. 3.2.2. Krapetz experimental site 3.2.2.1. Description of the site In this region (Figure 84) a characteristic geomorphologic feature is the presence of a shallow valley 3 km to the W of the village of Vaklino, falling towards the sea with an average slope of 1/100. The valley has rounded shapes and from a topographic point of view it lies on the 25 m contour line. Figure 84. Location of the Krapetz site.

The valley is filled with eolian deposits (loess and loess clays) which are 12-13 m thick in the western part and 4-5 m in the eastern one. There are no outcroppings of the Sarmatian limestone except in the area near the sea where limestone outcrops on the coastal strip. In the valley there is no permanent surface water flow even after intensive rainfalls or snowthaw. Along the valley and in the village of Krapetz many shaft wells (over 40) 10-15 m in depth and with a water column of 1-2 m, used for irrigation and local needs, have been bored. The exploitation of these wells is periodic (during the summer) and the discharge is not high - up to a few l/s. In the study site a pumping station has been built for drinking water supply (PS-1), including three water supplying wells (DW-1, DW-2 and DW-3) together with two non equipped drill wells (MW-1 and MW-2, which is MP-2 in the monitoring network). From the existing wells providing PS-1 with drinking water, only DW-1, with an average discharge of nearly 8 l/s, is exploited throughout the year. Groundwater from LXV

DW-2 and DW-3 is pumped for irrigation only during the summer. The deep wells of MW-1 and MW-2 are not exploited because salinization of the water occurs at the time of water pumping and TDS reaches 4 - 5 g/l. The main groundwater contamination source is the waste water from Krapetz, solid and liquid wastes from the stock farms and fertilisers applied to the cultivated lands. Two thousand inhabitants live in the village, a figure which triples during the resort season. Waste water is collected in septic pits. All the land in the valley and in the village is used for vegetable cultivation with intensive fertilising. Up to 1990, in the area to the W of Krapetz, 6 000 000 m2 had been fertilised with an average quantity of 30 kg/1000 m2. Because of the economic recession from 1990 to 1996 only land on the borders of the urban area was treated with nitrate fertilisers during this period. The thickness of the loess covering at the borders of the urban area is about 5-10 m. It performs a certain protective function against the direct infiltration of waste water into the karst limestone of the Upper Karst Aquifer but is not a barrier against nitrates, especially in conditions of intensive fertilising of the cultivated lands. An additional factor worsening groundwater quality is the salinization provoked by seawater intrusion into the coastal zone, due to the proximity of the village to the sea. This salinization mainly occurs during the summer when the total yield of groundwater for irrigation on the borders of urban area reaches 40 - 50 l/s For an assessment of the main characteristics of the organic contamination of groundwater with direct relation to sanitary protection of the water sources, water samples are taken regularly from PS-1. Analysis of the data presented from 1985 to 1995 shows that the water extracted was always within the limits of the drinking water standards with respect to NH4, NO2, NO3 and PO. A certain increase in Cl, respectively of TDS and SEC, above the limits of the drinking water standard was recorded in isolated cases, mainly during the summer. This cannot be considered contamination but rather a partial groundwater salinization as a result of seawater intrusion into the coastal zone. However, on the borders of Krapetz the groundwater is often of low quality and falls below the drinking water standard with respect to many hydrochemical characteristics. In this case the impact of the urban area on the quality of groundwater is bilateral, producing contaminants from economic activity on the one hand and activating seawater intrusion during the irrigation period on the other. 3.2.2.2. Study results and discussion To assess the urban impact of Krapetz on groundwater quality, a detailed hydrochemical sampling from 5 shaft wells on the borders of the urban area and from MP-2 in the PS-1 region during May and September 1995 was performed. Water samples were obtained in such a way as to form a transverse hydrogeological section with respect to the coastline. The results from the analyses made in situ and in the laboratory are shown in Tables 26 and 27. Table 26. Data for hydrochemical parameters (in situ) at the Krapetz site (September 1995). Table 27. Data from laboratory analysis at the Krapetz site (September 1995).

To establish whether there is any vertical zonality of the hydrochemical parameters in the aquifer, samples were taken from the only deep drilled well in the region (MP-2), at two depths, 30 and 60 m. Table 28 shows the results from the chemical analyses, from which it is clear that in the pumping station region highly

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mineralised water lies under the fresh water. This is probably the result of seawater intrusion into the coastal area and is discussed in greater depth in epigraph 5. Table 28. Data from the laboratory analysis of MP-2 at two different depths.

Water samples were taken from SW-2 at the borders of the urban area every month during 1996 in order to assess the seasonal variations in chemical groundwater composition. The results of the chemical analyses are shown in Table 29. Table 29. Results of monthly samplings from SW-2 (1996).

The method to assess the urban impact previously developed for the village of Vaklino was applied in this case. The assessments are based on the average data on chemical composition for the following two groups of water samples in the Krapetz site (Table 27): - Pumping station (PS), situated outside the urban zone and reflecting the groundwater composition in undisturbed parts of the aquifer, free from the direct impact of the village of Krapetz. - Shaft wells (SW), situated on the borders of the urban zone and reflecting the groundwater composition in the parts of the aquifer directly affected by the impact of Krapetz. The respective bar-diagrams of the concentrations (in meq/l and % meq) generated with the HG program are shown in Figures 85 and 86. From Figure 85 it is clear that the impact of Krapetz on groundwater composition in the urban zone is critical. This is evident in the almost twofold increase in the meq concentration sum in shaft wells (SW) over that in the wells of the pumping station (PS). It is obvious from Figure 86 that the impact of the village changes the chemical type of the water in SW - from HCO3-Na to Cl-Na. Figure 85. Average principal chemical constituents of groundwater in the pumping station (PS) and shaft wells (SW) corresponding to the Krapetz site. Figure 86. Distribution of the major chemical constituents of groundwater in the pumping station (PS) and shaft wells (SW) corresponding to the Krapetz site.

The CPI value (%) parameter for each characteristic of the groundwater composition in the sampled water points is shown in Table 30, while Figure 87 shows the bars of average CPI values. It is clear that the groundwater at the pumping station site presents a negative degree of contamination and that for all chemical characteristics (except TDS) there is a considerable margin before reaching the maximum permissible value of the drinking water standard. However, with respect to some characteristics, the groundwater contamination on the borders of the urban zone is obvious. There is undoubtedly a drastic degree of NO3 contamination in all parts of the village. With respect to the other chemical characteristics, there is either no contamination (SO4, Ca and Mg) or its degree is average to significant (Cl, TDS and SEC). Table 30. CPI Values (%) at the Krapetz site. Figure 87. Average CPI values at the Krapetz site.

The values of the IPI (%) parameters for each chemical characteristic of the groundwater composition at the sampled water points are shown in Table 31, while Figure 88 shows the bars of average IPI values. It is evident that the village of Krapetz produces a severe degree of impact on the groundwater at the borders of LXVII

the urban zone due to nitrates (821 %), chlorides (183 %), sulphates (124 %) and SEC (112 %); there is also a significant degree of impact caused by TDS (68 %) and magnesium (60 %). Table 31. IPI Values (%) at the Krapetz site. Figure 88. Average IPI values at the Krapetz site.

3.2.2.3. Conclusions The environmental impact of Krapetz on the composition and quality of the groundwater within the Upper Karst Aquifer is similar to that of Vaklino. As a result of this impact, the groundwater composition changes and the values of some chemical characteristics are above the permissible levels for drinking water supply and irrigation. The most important consequences of the mentioned impact are expressed in the nine fold increase in average nitrate concentrations at the urban area boundaries. A rise in TDS to almost double the previous levels at the borders of the urban zone is related to a change in the hydrochemical type, from HCO3-Na in undisturbed regions to Cl-Na in disturbed ones. As a result of the impact of Krapetz, a contaminated plume is rising in the superficial parts of the Upper Karst Aquifer. This contaminated plume has a local distribution, and on the whole coincides with the borders of the urban zone. With respect to TDS, SEC, NO3 and Cl, the groundwater at the borders of this plume is not suitable for drinking water supply. The contaminated plume extends in the direction of the natural groundwater flow towards the sea. From the point of view of the sanitary protection of the water supply pumping station PS-1, in terms of its present exploitation for the urban zone of Krapetz, there is no immediate danger of worsening groundwater quality. The urban zone is outside the recharge zone of the water supply wells. But if the quantity of water pumped from PS-1 increases significantly, the impact of the urban zone could provoke critical conditions, resulting in the groundwater from the pumping station falling below the limits of the drinking water standard. 4. MONITORING FRAMEWORK 4.1. Piezometric evolution 4.1.1. Description of the monitoring network and results To identify the behaviour and qualities of groundwater in the pilot area, a local monitoring network was set up in early 1995, comprising 13 water points. To select the monitoring points (MP), the following requirements were taken into account (Pentchev et al., 1993): - MP should be comparatively regularly distributed in the pilot area; - MP should be at sufficiently large distances from the operating water-supply systems (beyond the daily fluctuations of the groundwater levels, induced by the switching on and off of the pumps); - MP should be well protected from direct pollution and not used for any purposes other than monitoring the levels, content and qualities of the groundwater.

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The location of the monitoring points is shown in Figure 89, and the their main characteristics are summarized in Table 32. Figure 89. Location of monitoring points in the area. Table 32. Data for monitoring points (MP).

The meanings of the abbreviations in Table 32 are as follows: - SW, shaft well with a large diameter (1-2 m), constructed by excavating the rock and surrounding the shaft with stone masonry; - DW, drill well, constructed by drilling and casing with pipes and filters; - ML, lath to measure the surface water level; - MC, municipal contamination; - ACP, agrochemical pollution; - SWI, seawater intrusion. Table 32 shows that the monitoring points can be divided into two main groups: - Group A.- MP for monitoring of MC (located within the boundaries of the urban sites); - Group B.- MP for monitoring of ACP and SWI (located outside the villages). The main data for SWL observations at the monitoring points are summarized in Table 33. Table 34 gives the SWL values in absolute elevations above sea level. Table 33. Regime observations of the monitoring network. Table 34. Static Water Levels (SWL) at the monitoring points.

The principal results of the laboratory analyses of main groundwater components at the monitoring points and the other hydrochemical parameters (in situ) are summarized in the appendices. 4.1.2. Assessment of the seasonal variations of the water table of the Upper Aquifer For an assessment of the seasonal variations of groundwater levels at each MP, the empirical relation D = F (Time) is used, where: - D = SWL - mean SWL; - Time = the moment when the respective SWL are measured (from the start of the monitoring observations). - mean SWL = the average value of SWL for the total (annual) period of monitoring observations. The use of the index D is to be preferred to SWL, because the data is normalised about D = 0 (corresponding to SWL = SWL mean) and data from monitoring points with substantially different SWL values can be analysed in a graph, without distorting the preliminary information. Table 35 shows the D values for the respective monitoring points and Figure 90 shows the changes in these on an annual basis. The graph in Figure 90 does not include the observations for MP-2 and MP-11 (which are located close to the functioning pumping stations) or MP-13 (Lake Durankulak, which is pumped in the summer period). This was in order to eliminate the possible impact of human factors on the groundwater regime. The following conclusions can be deduced from Figure 90:

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- Maximum groundwater level is reached about the beginning of May and the minimum is reached at the end of August. - The water table of the Upper Aquifer has approximately uniform movement in time, and the SWL changes are mainly due to climatic factors (infiltration rates). This allows us to make a general assessment of the groundwater flow structure in the studied region on the basis of the average annual SWL values at the monitoring points. Table 35. Differences between SWL and mean SWL at the monitoring points. Figure 90. Alteration of D values at the monitoring points versus time from the start of observations.

Statistical analysis of the monthly observations of SWL in the monitoring network shows that the natural fluctuations of groundwater levels at the individual monitoring points have low amplitudes, from 0.11 to 0.47 m (Table 36), and are obviously not affected by human factors. The standard deviation was between 0.04 and 0.14 m. Table 36. Statistics of SWL (data in Table 34).

4.2. Recharge, resources and degree of overexploitation of the aquifer 4.2.1. Determination of annual infiltration and average infiltration velocity The collected data on the changes in SWL at MP (Table 34) enables the annual infiltration (Ian) and the average infiltration velocity (Ivel) to be determined for the period February 1995 - February 1996, using the INF methodology and computer program (Galabov and Pentchev, 1986). The calculations were carried out for each monitoring point separately, by using the alteration of SWL as a function of time from the beginning of observations. For all calculations, the coefficient of specific storage of the Upper Aquifer Ss = 0.08 was used, which is sufficiently accurate to be accepted as representative within the boundaries of the pilot area. Table 37 summarises the final results of the calculations of Ian and Ivel for the observation period, while Figure 91 shows the annual infiltration values at the separate monitoring points. Figure 92 shows an isoline map of infiltration recharge in the territory of the pilot area - drawn on the basis of data for annual infiltration at the separate monitoring points. From this Figure, as well as from Figure 91, it is clear that the smallest values of Ian (from 32 to 48 mm) are obtained at monitoring points MP-11, MP-2, MP-8 and MP-1, located in the coastal area, which generally coincides with the drainage area of the Upper Aquifer. At the remaining MP, located inside the pilot area, the quantity of infiltration is approximately equal (about 60-70 mm) which is indicative of a comparatively uniform recharge of groundwater. Only MP-3 is an exception, where the infiltration is significantly higher (98 mm) than at the remaining inner MP. The higher infiltration can be explained by the location of MP-3 within the boundaries of the Vaklino Gully, where the temporary surface flow (after heavy rainfall) is wholly lost in karstified limestones. Table 37. Calculated values of annual infiltration and average infiltration velocity. Figure 91. Annual infiltration at the monitoring points. Figure 92. Isolines of annual infiltration (in mm) inside the pilot area.

For the pilot area in general an average annual infiltration Ian = 62 mm (from all MP data) is obtained, which on the whole is not a very significant value, being indicative of an obstructed natural recharge of the Upper Aquifer. This is explained by the presence of a thick loess layer (20 - 30 m thick) extended over the Sarmatian

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limestone, which obstructs the direct seepage of rainfall to the depth of the saturation zone. For an approximate determination of the coefficient of infiltration recharge Kinf of the Upper Aquifer at the borders of the pilot area (where the surface runoff is negligible) the following formula is used: Kinf = Ian / Pan = 62 / 466.9 = 0.132 = 13.2 %

(4.1)

where Pan is the average annual precipitation amount (466.9 mm in the pilot area Figure 60). It is seen that in an annual cycle, about 87 % of the rainfall falling on the pilot area evaporates and only 13 % infiltrates through the aeration zone to supply the groundwater. This is harmful from the point of view of the natural resources of the Upper Aquifer but favourable in terms of groundwater vulnerability. 4.2.2. Assessment of natural groundwater resources and degree of overexploitation The water balance method is used to assess the natural groundwater resources in the pilot area . This is based on the formula: Qgw = 2.74 (Pan - Ean) x A - Qr

(4.2)

where Qgw is the average annual groundwater outflow from the pilot area (natural groundwater resources) in m3/d; Pan is the average annual precipitation in mm; Ean is the average annual evaporation in mm; Qr is the average annual river outflow in m3/d; A is the aquifer area considered in km2. Qgw = 2.74 (Pan - Ean) x A = 2.74 Ian x A

(4.3)

where Ian is the average annual infiltration in mm. Inserting Ian = 62 mm and A = 200 km2 in (4.2) produces Qgw = 33976 m3/d = 393 l/s. The latter value, for natural resources of the Upper Aquifer, is approximate but may be taken as being sufficiently accurate for a general assessment of the degree of groundwater overexploitation in the pilot area to be made, using the following formula : OEi = [ PUMPgw / Q gw ] -1

(4.4)

where OEi is an index of groundwater overexploitation in %; PUMPgw is the average annual groundwater withdrawal in the pilot area. The gradation shown in Table 38 describes the degree of aquifer overexploitation: Table 38. Gradations of aquifer overexploitation.

With existing groundwater pumping during 1995-1996, with an average annual withdrawal PUMPgw = 2.51 x 106 m3/year = 79.6 l/s (Figure 65) the OEi = - 80 % is obtained from formula 4.4. On the basis of this value, it can be concluded that the Upper Aquifer as a whole is in a condition of negative overexploitation (i.e. it is exploited below the limits of the estimated natural resources ). 4.2.3. Estimation of the risks of local groundwater overexploitation in the coastal zone The following procedure, based on the classical methods of flownet analysis (Pentchev et al., 1990), was elaborated to estimate the risk of groundwater overexploitation in the coastal area. - Based on the existing data from pumping tests, transmissivity isolines in the pilot area were drawn up using the computer program SURFER.

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- Based on the average annual SWL values at the monitoring points, an isoline map of SWL was drawn up and the hydrodynamic network constructed by means of the program SURFER. The different subregions in the coastal area of the aquifer are separated by the dividing flow lines. - Groundwater discharge Dgw was calculated for each flow tube according to Darcy’s law. The calculations were made between two contiguous SWL isolines situated outside the pumping station area - in the opposite direction to groundwater flow. Based on the calculated tube discharge, the natural groundwater resources at the borders of each subregion were determined by the formula: Qgw = Σ Dgw - Based on formula 4.4, the local overexploitation index OEi (%) was determined for each subregion by inserting the data on total groundwater pumping (PUMPgw) in the respective subregion. Figure 93 shows an isoline map of the mean groundwater levels on which the flow lines of the groundwater flow to the sea are graphically represented. The hydrodynamic network obtained includes nine flow tubes in the direction of the coastal zone. Using the above methodology, the discharge from each tube (between hydroisohypses 3 and 4) was calculated and the natural groundwater resources of the coastal zone assessed. The data for this zone, divided into three subregions (Figure 93) are summarised in Table 39. This shows that, at present, conditions suggesting significant local overexploitation of the aquifer cannot be said to exist. Total groundwater pumping for the whole coastal zone is only about 21 % of natural groundwater resources and OEi = -79 %. Figure 93. Groundwater flow network in the coastal zone of the pilot area. Table 39. Data for groundwater resources and exploitation in the coastal area.

The distribution of pumping is spatially irregular in the three subregions, being highest in the vicinity of Lake Durankulak. If more groundwater than the estimated resources is pumped (for instance during the irrigation period), then a local degree of overexploitation can occur. Such a phenomenon has occurred in the past (19841985), when groundwater pumping for irrigation in the Lake Durankulak subregion was 4.8 Mm3/year (152 l/s), which corresponds to PUMPgw = 160 l/s in the subregion and to OEi = 60 %. As a result of this overexploitation, there was a significant decrease in the lake water level. The consequence was the salinization of the lake and the deterioration of hydroecological conditions. Similar seasonal local overexploitation and groundwater salinization takes place almost every year in the village of Krapetz. 4.3 Conclusions Maximum groundwater levels in the Upper Karst Aquifer are reached about the beginning of May and the minimum level is reached at the end of August. The movement of the water table is approximately uniform in time and the SWL changes are mainly due to climatic factors (infiltration rates). For the pilot area in general, an average annual infiltration of 62 mm was calculated. In the annual cycle, 86.8 % of rainfall falling onto the pilot area evaporates and only 13.2 % goes to supply the groundwater. The overexploitation

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index for the pilot area as a whole is - 80 %. This means that the Upper Aquifer is exploited below the limits of its natural resources.

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Current total groundwater pumping in the coastal zone is only about 21 % of the natural groundwater resources and OEi = -79 %. The OEi distribution between the different subregions of the coastal zone is spatially irregular, being highest in the subregion of Lake Durankulak (OEi = -40 %). In the past (1984-1985) an OEi = 60 % in that subregion was recorded. 5. SEAWATER INTRUSION 5.1. General considerations The Upper Aquifer is the main source of drinking water supply and irrigation in NE Bulgaria and has been an exploitation site since the early 1950’s. The main water pumping stations for drinking water supply and irrigation, which extract groundwater from the Upper Aquifer, are located in the coastal 10 km strip coinciding with the natural groundwater drainage area. Research articles and reports (Balev, 1981; Galabov et al., 1989) describe single cases of salinization of water pumping stations in the coastal zone but until now no generalisation has been made about the scope of intrusion under the existing conditions of exploitation. This is the reason why the conditions for the occurrence and development of seawater intrusion in the Upper Aquifer are of particular interest from a scientific and practical point of view. The assessments made in this unit are based on the studies carried out during 1986-1987 (Galabov et al., 1989), updated and subsequently supplemented during 1995 -1996 in connection with the implementation of the international project CIPA CT-93-0139. The study aims to make a general presentation of the issue concerning the seawater intrusion in the entire coastal zone of the Upper Aquifer at the existing exploitation rate. The detailed investigations and results obtained in the Durankulak Krapetz pilot area, where the risk of seawater intrusion has been proven, are also discussed. 5.2. General assessment of the extent of seawater intrusion From a hydrological point of view the conditions for the occurrence of seawater intrusion in the coastal zone of the Upper Aquifer (Figure 94) are as follows: Southwest of Cape Kaliakra the Upper Aquifer lies above sea level and has no direct hydraulic connection with the sea. It is drained through gravity springs, most of which have been tapped for water supply needs. In this area there are no natural conditions for seawater intrusion. In the area N of Cape Kaliakra, near the border with Romania, the conditions for the occurrence of the Upper Aquifer are quite different, and this can be considered an area of high seawater intrusion potential. The limestones here are part of the large Kavarna-Shabla graben and have a considerable thickness. The strata dip to the E and sink gradually into the seawater area. Under natural conditions the groundwater is drained through gravity springs in the coastal drowned valleys (in the area of Shabla, Ezerets and Durankulak lakes) and by submarine springs under the sea bed. An essential geological factor affecting the potential for the development of seawater intrusion is the condition of the submarine shore slope. In places where the limestones are covered by weakly permeable deposits (silts, clays, etc.) the contact between the fresh and salt waters moves seaward and as a result the risk of seawater intrusion is reduced. The type of karstification in the coastal zone is also of

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particular importance for the development of the intrusion. The areas where karstification is associated with faults and manifestations of conduit-type karst, the intrusion can occur at a considerable distance inland. Conversely, in the presence of weak karstification with manifestations of diffuse-type karst, the risk of intrusion decreases and only the water pumping stations adjacent to the shore line are influenced. From this point of view the region under study can be divided into three subregions characterised by their specific features. 5.2.1. Kaliakra-Shabla Subregion This subregion comprises the coastal line N of Cape Kaliakra up to Cape Shabla. According to data from the Institute of Oceanology - Varna (unpublished) up to 100300 m from the shore the limestones outcrop directly in the sea area and further seaward along the shore slope they lie under a 2 m thick layer of sands and silts. The karstification is local and associated mainly with the zones of tectonic faults which have caused the block faulting of the Upper Aquifer within the boundaries of the Tyulenovo horst (Anonymous, 1994). There is only one site in this subregion (Bolata Site) where there are wells built for drinking water supply and irrigation. They are 20-25 m deep and are located approximately 700-800 m from the sea. In the past (1962-1986) there were many indications of water salinization, especially during the peak irrigation periods (in August). After 1986 water pumping for irrigation was suspended but even today at times (during periods of higher levels of water consumption) chloride concentrations above the drinking norms can be observed. 5.2.2. Shabla-Krapetz Subregion This subregion comprises the coastal line N of Cape Shabla near the village of Krapetz. Here the conditions for limestone outcrops along the shore slope opposite the Ezerets and Shabla lakes vary considerably from those in the other subregions. It has been proven (Institute of Oceanology - Varna) that up to 300-800 m from the shore line the limestones are covered by clays over 2 m thick which further on outcrop directly along the shore slope. The karstification of the limestone plate is everywhere and comprises nearly the whole thickness of the hydrological section. The karstification process is most intensive (with manifestations of conduit-type karst) in the area of the Shabla and Ezerets lakes, coinciding with the zone of natural discharge of the Upper Aquifer in this subregion. A large number of pumping stations for drinking water supply have been built in this subregion. In the Shabla water supply area alone, over 40 pumping wells (Pentchev, 1992), having a depth of 30-40 m and sited about 1500-2000 m from the sea, are being exploited. Since the commencement of the exploitation no indications of salinization have been observed in the water, even during peak irrigation periods (Anonymous, 1970). 5.2.3. Krapetz-Durankulak Subregion This subregion comprises the coastal line N of Krapetz up to the border with Romania. Opposite Krapetz, along the entire length of the profiles (Institute of Oceanology - Varna), up to 2500 m from the coastal line, the limestones outcrop directly in the sea area and there are no sea floor deposits. Opposite Lake Durankulak, up to 800-1000 m from the shore, the limestones are covered only by carbonate sands with a thickness of 20-30 cm and they outcrop directly seaward along the shore slope. The karstification of these limestones is similar to that in the LXXVII

Shabla-Ezerets subregion and is particularly well-developed in the immediate proximity of Lake Durankulak (Balev, 1981; Naidenov, 1994). In the subregion under study three pumping stations for local drinking water supply as well as a number of shaft wells and drains for irrigation have been built. All the shaft wells in the territory of Krapetz are partially salinized (Galabov, et al., 1989) and the water is not suitable for irrigation. There have also been indications of slight salinization in the pumping well of the Krapetz water supply station which is 30 m deep and is situated at a distance of 1700 m from the shore line. From the information presented above it can be concluded that in the ShablaEzerets subregion there are better conditions than in the other areas for groundwater exploitation, since the contact between the fresh and salt waters has moved considerably seaward. 5.3. Sites with proven seawater intrusion Analysis of the existing archive regime data (unpublished) on the composition and qualities of the groundwater in the pumping stations for drinking water supply shows that the extent of salinization is related primarily to the local groundwater extraction for irrigation. Figure 95 shows the maximum values of the basic indices (Todd, 1987) for seawater intrusion - Cl, TDS and SEC, recorded at the pumping wells of the water supply stations Bolata, Shabla and Krapetz during 1986-1996. For convenience Cl, TDS and SEC are given in percentages in relation to the same indices in the seawater. It is obvious that for the existing level of exploitation a certain degree of chloride salinization of the drinking water sources (caused by possible seawater intrusion) can be observed only at the Bolata pumping station (over 5 % sea water) and partly at the Krapetz pumping station (over 1 % sea water). Such a regularity can also be observed in the percentages of the indirect indices for seawater intrusion (TDS and SEC). Figure 96 show meq concentrations of the main chemical constituents and their percentage in the chemical composition of pumped groundwater. The averaged values of the same components in the Black Sea water are given for comparison. Figure 95. Values of maximum salinity. Figure 96. Concentration of the major chemical constituents.

It is clear that while in groundwater pumped at the Shabla site the chlorides comprise only 7.54 % meq of the composition, at the Krapetz site they increase to 17.46 % meq and at the Bolata site they reach 31.49 % meq. In the latter case the chemical type of groundwater is very close to that of seawater, in which the chlorides are 45.60 % meq. Such a regularity, though in an inverse order and not so wellexpressed, can be noted for the bicarbonates. In the literature a number of criteria have been proposed to assess the extent of seawater intrusion, based on the relationships between separate basic ions in the water. Under the particular conditions of this study (where there is insignificant nitrate content) the best indication for seawater intrusion (Revelle, 1941) is the criterion rCl/(rHCO3+rCO3), where r is concentration in meq. At values of rCl/(rHCO3+rCO3) > 1.6 the intrusion (in the area of the Bulgarian coast) is considered to be proven in the water sample (Velikov, 1991). Table 40 shows that seawater intrusion causing chloride salinization of the fresh groundwater, even within the limits of a few percent, leads to a radical change in the LXXVIII

chemical type of the water in the Upper Aquifer. It changes from bicarbonatemagnesium (Shabla site) into bicarbonate-sodium (Krapetz site) and finally becomes a chloride-sodium type (Bolata site). At the same time, the quality of the water for drinking water supply and irrigation deteriorates, mostly as a result of the higher values of chlorides, TDS and the SAR index. Table 40. Hydrochemical characteristics and indices for the extent of seawater intrusion.

The data presented in Table 40 lead to the conclusion that for practical purposes in the coastal zone of the Upper Aquifer it is sufficient to use the simplified criterion Clgw/Clsw > 5 % (chloride salinity). The designations in the latter are as follows: Clgw chlorine concentration in groundwater; Clsw - chlorine concentration in the Black Sea. 5.4. Seawater - freshwater relationship in the Durankulak - Krapetz pilot area 5.4.1. Verification of the criteria for groundwater salinization within the pilot area boundaries The present hydrochemical investigations of the existing wells in the pilot area show increased mineralization zones in the Upper Aquifer near the sea coast, probably due to sea water intrusion into the aquifer. These increased mineralization zones have been found in the upper part of the aquifer (1-2 m below the SWL). Figures 97, 98 and 99 show isoline maps characterising the level of groundwater mineralization in the top part of the aquifer - constituting TDS, chlorides and SEC. The maps were created on the basis of field data from sampling of the monitoring network (Figure 89) during September, 1995 and some additional wells situated in the villages. Zones with higher mineralization, chlorides and electric conductivity, caused by seawater intrusion in the coastal area, are clearly distinguished. Figure 97. TDS isolines. Figure 98. Cl isolines. Figure 99. SEC isolines.

For rapid assessment of groundwater salinization, a SEC parameter is usually used, because of its easy measurement in the field. From this point of view, the empirical relationship between SEC, Cl and TDS in the pilot area is of essential interest. On the basis of the data obtained (Table 41), the relationship between SEC, Cl and TDS seems to be essentially linear on a log - log scale, as shown in Figure 100. For approximate assessments of the Cl and TDS on the basis of the corresponding SEC data, the following empirical relations can be applied log (SEC) = 0. 6735 log (Cl) - 3.1895

(5.1)

log (SEC) = 1.1691 log (TDS) - 8.0802

(5.2)

where SEC is in mS/cm, and Cl and TDS - in mg/l. Table 41. Data for assessment of empirical relationship between SEC, TDS and Cl. Figure 100. Empirical relation between SEC and Cl or TDS.

The empirical relations between SEC, TDS and Cl can be applied to the determination of the degree of groundwater salinization by means of a chlorine salinity index (% seawater) and relations (5.1) and (5.2). Bearing in mind that the concentration of Cl in the Black Sea is 9830 mg/l on average, the following criteria to determine the designation and type of groundwater on the NE Bulgarian coast are presented (Table 42).

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Table 42. Criteria for determination of groundwater salinization types, caused by seawater intrusion (NE Bulgarian Coast).

5.4.2. Experimental investigations at Krapetz site The lack of deep wells in the coastal zone does not allow a regional assessment of the fresh - seawater relationship and the salt wedge development into the aquifer on the basis of experimental hydrochemical parameters (SEC, Cl) to be made. The only site where a local evaluation could be made is in the vicinity of the village of Krapetz (Figure 84). At the studied site (Figure 101) a pumping station for drinking water supply (PS-1) including three water supplying wells (DW-1, DW-2 and DW-3) and two non-equipped drill wells - MW-1 and MW-2 (which is MP-2 in the monitoring network) has been built. Of the existing wells of PS-1 for drinking water supply, only DW-1 with an average discharge of nearly 8 l/s is exploited throughout the year. Groundwater from DW-2 and DW-3 is pumped for irrigation only during the summer. The deep wells MW-1 and MW-2 are not exploited because salinization of the water occurs at the time of water pumping and TDS reaches 4 - 5 g/l. Figure 101. Situation of the wells at the Krapetz pumping site.

Table 43 summarises the results of pumping tests carried out in the wells and their principal constructive parameters. Table 44 gives the results of hydrochemical samples, taken during the time of pumping tests, and also the results of sampling at two different depths in MW-2. Table 43. Parameters of wells at the Krapetz site. Table 44. Hydrochemical data from pumping and monitoring wells.

From Table 44 it can be seen, that during the pumping test of the deep well MW-1 in 1989, salinized waters with a chloride content of 2042 mg/l, or 21 % chlorine salinity, were extracted. Salinization begins at the start of pumping and gradually increases from 1426 up to 2042 mg/l at the end of pumping. In the shallow wells PW1, PW-2 and PW-3 (which are in regular exploitation) salinization above 2.5 % seawater in pumped water has never been registered. The presence of the salinized water lying under freshwater is proved by the logging of conductivity carried out in both deep wells (MW-1 and MW-2), and water samples taken at two different levels in MW-2 as well (Tables 28 and 44). The results of these tests are shown in Figure 102. On the basis of these values, a hydrogeological cross section (Figure 103) illustrating the freshwater-saltwater relationship in the top parts of aquifer has been constructed. Figure 102. Logs of conductivity from deep wells at the Krapetz pumping site. Figure 103. Cross section at the Krapetz pumping site.

Figures 102 and 103 show that the upper 13-14 m of the aquifer thickness are filled with fresh water, with SEC < 1.7 mS/cm and chlorine salinity under 2.5 % seawater. Below the freshwater body, down to 39 m under SWL, typical brackish water with SEC < 10.5 mS/cm lies in the aquifer and chlorine salinity does not exceed 38 % seawater. The results of hydrochemical sampling of MW-2 at two different depths (30 and 60 m under terrain, or 9 and 39 m below the SWL) confirm the absence of typical seawater down to the bottom of the well. The seawater probably lies at a considerable depth, near the bottom of the aquifer. This is the main reason why the productive well DW-1 has never really been salinized during the period of 20 years’ exploitation. The lack of considerable salinization of DW-1 can

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also be explained by the essential anisotropy in hydraulic conductivity of the aquifer, probably related to the specific development of karstification processes in the area. Figure 104 shows the theoretical boundary between seawater and freshwater, predicted by the Ghyben-Herzberg relation: ps z = pf (z + hf) where ps and pf are salt water and fresh water densities, g/cm3; hf is the fresh water hydraulic head relative to mean sea level; z is the vertical thickness of the fresh water lens below mean sea level at the borehole site. The calculations were made for MW-2 site at ps = 1.012 g/cm3, corresponding to TDS = 17.5 g/l of the Black Sea water; pf = 1.000 g/cm3, corresponding to TDS = 1.2 g/l of the fresh groundwater and hf = 0.21 m (mean SWL - Table 36). For z in MW-2 the value of 17.5 m is obtained, which corresponds to an interface depth of 41.2 m under the terrain. Figure 104. Groundwater salinization in cross section 2-2. Figure 105. Groundwater salinization in cross section 3-3. Figure 106. Groundwater salinization in cross section 4-4.

It can be seen that the Ghyben-Herzberg relation does not give a good approximation of the actual relationship between sea and fresh water in this region. The main reason is that the model cannot explain the range of mixing (salinized) zones observed (with a thickness of over 30 m). Therefore, for an approximate assessment of the vertical groundwater salinization, the chlorine salinity isolines are empirically constructed by interpolation between real data in water points (by use of the SURFER contouring program). The isolines corresponding to 5, 35, 50, 75 and 95 % seawater are shown in Figure 104. If we assume that isoline 50 % corresponds to the interface between fresh and saline water, the length of the salt wedge along the bottom of the aquifer should be no more than 3 km from the shoreline. The methodology developed is used to analyze some initial reference data concerning the salinization of Lake Durankulak and the groundwater in neighbouring territories. The investigations were carried out in two borehole cross sections (3-3 and 4-4 - Figure 59) situated laterally to the Black Sea. Hydrochemical sampling of the test boreholes was performed seasonally (in the period 1964 - 1966) by a standard sampler at different depths - at 1-2 m below the SWL, in the middle of the water column in the borehole, and at 1-2 m above the bottom of the borehole. The control of salinization was achieved using the chlorine content and the dry residue (DR) of groundwater. After concluding the investigations (1968) all boreholes were closed and sealed with cement. Figures 105 and 106 show the freshwater-seawater relationship based on the isolines of chlorine salinity (in % towards seawater). The data used are referred to October, 1966. Although some differences between the different cross sections (Figures 104, 105 and 106) can be found, in general the presence of a thick layer of brackish water (40 - 60 m) is clearly proved everywhere. 5.5. Conclusions From a hydrogeologic point of view the conditions for the occurrence of seawater intrusion in the coastal zone of the Upper Aquifer vary considerably. South of Cape Kaliakra, the Upper Aquifer occurs at a level higher than the sea level and in this

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region there is no natural potential for seawater intrusion. North of Cape Kaliakra, up to the boundary with Romania, the bedding conditions of the Upper Aquifer and its outcrops in the sea area favour the occurrence of seawater intrusion. An essential geological factor influencing the possibilities for the development of seawater intrusion is the outcropping of limestones in the submarine shore slope. From this point of view the coastal zone of the Upper Aquifer, N of Cape Kaliakra, can be divided into three subregions, each with its specific characteristics related to the potential risk of seawater intrusion. The best conditions, in relative terms, for groundwater exploitation exist in the Shabla-Ezerets subregion where the contact between the fresh and salt waters is further seaward as compared with the other areas. At the existing rate of groundwater exploitation, a certain salinization related to seawater intrusion has been proven only at the Bolata site (over 5 % chloride salinity) and partly at the Krapetz site (over 1 % chloride salinity). The salinization, despite being within low limits, has brought about a radical change in the chemical type of the water from the Upper Aquifer. This has changed from bicarbonate-magnesium (at the Shabla site) into chloride-sodium type (Bolata site). With increasing groundwater exploitation in the coastal zone of the Upper Aquifer, the potential problem of seawater intrusion could turn into a real one. In this respect, the Durankulak-Krapetz subregion is the most endangered area, where the most unfavourable geological conditions and the highest needs of groundwater for irrigation exist. The present investigations carried out in the coastal zone of the DurankulakKrapetz subregion (pilot area) show that given the existing rate of groundwater exploitation, the salinization of upper parts of the coastal zone has extended to 2.5 3.5 km inside the aquifer. This is clearly shown by the presence of a brackish water layer (wedge), having a thickness of 40-60 m and situated below the fresh groundwater everywhere in the coastal zone of the aquifer. In this sense, it is clear that neither the model of the Ghyben-Herzberg static system nor the sharp interface model of a system having fluid flow can give a good approximation of the freshwaterseawater relationship in this area. Under the most unfavourable conditions relating to seawater intrusion is Lake Durankulak, which has the status of a wet zone. The major groundwater sources for irrigation are concentrated in very close proximity. In this sense, the evaluation of the optimal groundwater extraction in the region would be of particular interest to ensure the preservation of the hydroecological conditions in the lake and the adjacent territories.

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PART IV.- GENERAL CONCLUSIONS AND RECOMMENDATIONS

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1. CONCLUSIONS There are two main karstic aquifers in the region of Dobrich (Dobrudja): the Upper, comprising Sarmatian materials, and the Deep Aquifer, composed of MalmValanginian Age materials. Both aquifers are formed of carbonate materials, but have different hydraulic characteristics and are subject to different phenomena related to the quality and quantity of the groundwater they contain. As regards the Upper Aquifer, though certain extractions of specific characteristics (such as domestic wells of little depth) contain water with a relatively high content of nitrates and pesticides and which is more highly mineralized than the mean level within the aquifer, in general it can be said that the water obtained is of good quality and suitable for supplying the urban drinking water system. The main source of pollution, occurring throughout the region, is the large-scale use of organic fertilizers in agriculture. The surplus nitrogen that is not taken up by the crops is diverted to the groundwater, which in this aquifer is not deep below the surface. The use of such fertilizers was especially intense some years ago; at present, with the economic crisis currently affecting the region, very limited use is being made of fertilizers. The existence of numerous livestock farms, particularly pig farms, comprises another source of pollution for the groundwater of this aquifer, as the strongly pollutant lye that is produced frequently infiltrates the aquifer. The same is true of the dumping of solid urban waste, mainly to the south of Dobrich, which takes place over the aquifer and without any treatment or precautions being taken. The lye from such dumps has been seen to enter both the groundwaters of the Upper Aquifer and the surface water of the river flowing through Dobrich. The dumping of urban sewage comprises a relatively unconcentrated problem in this area, as the population of Dobrich is clustered in numerous suburbs and outlying developments. The liquid urban waste generated in Dobrich is less of a problem due to the existence of a wastewater treatment plant, although this only performs a secondary treatment before expulsion to the river and hence to the aquifer. Overexploitation of the Upper or Sarmatian Aquifer, in the strict sense, cannot be said to exist, at least in the study area. A marked decline in the phreatic level has been recorded in Dobrich, with levels up to 20 metres lower than 15 years ago. This is due to three principal factors: the diminution in the mean precipitation during this period; the excessive spatial concentration of wells; and the steady increase in the volume of exploitation over time. At most, there might be considered a seasonal overexploitation, more pronounced in dry periods, which might last several years. On the coast, there are high levels of extraction concentrated in certain localized areas, which also produce marked falls in the phreatic level, though less so than in the surroundings of Dobrich. In the coastal region, the main problem in water extraction is the incipient process of salinization of the groundwater arising from saltwater intrusion, although this process is not generalized along the whole coast. Concerning the Deep or Malm-Valanginian Aquifer, the quality of its water is extremely high, thanks to the deep-level confinement that protects it from pollution processes of human origin. Nevertheless, as part of its very nature, there exist natural hydrogeochemical processes that make the water relatively unsuitable for human consumption, with the presence of undesirable compounds such as H2S and NH4+, together with a higher degree of mineralization. These processes do not affect the whole of the aquifer within the study area, but rather those sectors closest to the coast, coinciding with a region of thermal activity, the influence of petroleum deposits LXXXIV

and, probably, the existence of fossil or connate waters trapped within the geological structure. The level of water extraction from the Deep Aquifer is quite high, either produced by pumping or from the numerous Artesian wells in the coastal area. Here, the water is used to a very limited extent in spa resorts, though with virtually no control system, and is rapidly lost to the sea, thus producing a considerable waste of hydric resources. The only balance to this discharge of the Deep Aquifer is a limited and distant recharge; the immediate consequence of this situation is the slow but steady fall in piezometric levels. In a large part of the region, the two aquifers are isolated and function independently. Nevertheless, a certain degree of interconnection has been detected at certain points, usually based on the draining of the Upper Aquifer towards the Deep one, but also perhaps on a flow from the Deep to the Upper when the former is higher than the latter (this only being possible in the coastal region). The first case, of a drainage from the Upper to the Deep Aquifer, might be accompanied by a relatively high concentration of nitrates in the water from the former, when this pollutant is present in large quantities in the waters of the Upper Aquifer and where there exist badly designed deep wells tapping the two aquifers. Such unsatisfactory wells could lead to an interconnection between the two aquifers. 2. RECOMMENDATIONS Although, in recent years, the application of fertilizers to crops and the use of groundwater for irrigation have diminished as a result of the unfavourable economic conditions affecting the country, in order to maintain the quality of the groundwater in the Upper or Sarmatian Aquifer and avoid the effects of nitrate pollution, fertilizers should be applied under strict agronomic control to prevent the origination of nitrate surpluses that are unnecessary for crop development. The principal pig farms should be equipped with a plant to treat the liquid waste produced, as does occur in some instances; alternatively, the biomass could be used and transformed into biogenic gas to be employed, for example, for the generation of electricity. The Dobrich solid waste dump needs to be totally redesigned and located in an area that is less liable to contaminate ground and surface waters, using modern methods of control and follow-up. Such measures are justified by the volume of waste produced. As soon as possible, tertiary treatment of the Dobrich waste waters should be introduced: in this respect, it is strongly recommended that the numerous urban developments surrounding the city of Dobrich should be equipped with treatment stations to perform at least secondary treatment of wastewater. To reduce the effects of the extraction of groundwater from the Sarmatian Aquifer in the surroundings of Dobrich, it would be beneficial to: prevent leaks from the distribution network and encourage economy in the use of hydric resources; obtain a greater dispersal of wells, locating them according to hydrogeological criteria in such a way as to avoid interactions, thus reducing the descent in the phreatic level and hence energy requirements.

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REFERENCES

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Anonymous (1970). Regime observations on the levels and chemical composition of the groundwater and lake in the region of the town of Shabla during the pumping in the irrigation period. Vodokanalproekt Ltd. Unpublished technical report, Sofia (in Bulgarian). Anonymous (1994). Explanation text towards the geological map of Bulgaria in 1/100 000 scale: part - Dobrich. Committee of Geology, Sofia (in Bulgarian) Unpublished technical report, Sofia (in Bulgarian). Antonov, H. (1973). The miocene aquifer of Dobrudja and its use for water supply. VII Session of Hydrogeology and Engineering Geology, Sofia. Proceedings: 3-14. (in Bulgarian) Antonov, H. and Danchev, D. (1980). Groundwaters in Bulgaria. Technika, Sofia, 340 p. (In Bulgarian). APHA - AWWA - WPCF (1989). Standard Methods for Examination of Water and Wastewater. Washington. Atkinson, T.C. (1977). Diffuse flow and conduit flow in limestone terrain in the Mendip Hills, Somerset (Great Britain). Journal of Hydrology, 35: 93-110. Back, W. (1992). Coastal karst formed by ground-water discharge, Yukatan, Mexico. In "Hydrogeology of selected karst regions", IAH, 13: 461-466. Back, W., Hanshaw, B.B., Pyle, T.E., Plummer, L.N. and Weidie, A.E. (1979). Geochemical significance of ground-water discharge and carbonate solution to the formation of Caleta Xel Ha, Quintana Roo, Mexico. Water Resources Research, 15: 1521-1535. Bakalowicz, M. (1979). Contribution de la géochimie des eaux à la connaissance de l’aquifère karstique et la karstification. Thèse Univ. Paris VI. Lab. Sout. CNRS, Moulis. 269 p. Balev, H. (1981). Hydrogeological and engineering geological exploration in the area of the Durankulak irrigation field. Vodproekt, Ltd. Unpublished technical report, Sofia (in Bulgarian). Bergerat, F. and Pironkov, P. (1994). Déformations cassantes et contraintes crétacées à actuelles dans la plate-forme moesienne (Bulgarie). Bull. Soc. géol. France, 165,5: 447-458. Betsinski, P., Machkova, M., Zavileyski, O., Dimitrov, D. and Zaharieva, K. (1990). Modelling of the groundwater recharge of the rivers in North-East Bulgaria. Institute of Meteorology and Hydrology of Sofia, State Institute of Hydrology of Leningrad, Technical Report. (In Russian). Boncev, E. (1988). Notes sur la tectonique alpine des Balkans. Bulletin de la Societé Géologique de France, 8, 4, 2: 241-249. Bulgarian Hydrometeorological Service (1983). Meteorological yearbook of Bulgaria. Institute of Meteorology and Hydrology of Sofia: 26-134. (In Bulgarian). Cheshitev, G. and Kânchev, I., eds. (1989). Geological Map of P.R. Bulgaria, scale 1:500,000. Supreme Technical Council, Sofia. Cheshko, A.L. et al. (1990). Deuterium and Oxygen 18 in the precipitations, surface and groundwaters of the Kamchatka and Kuril islands. Water Resources, Academy of Sci. USSR, 16. (In Russian). LXXXVII

Committee of Standardisation (1989). Bulgarian Standard Methods for Examination of Waters and Soils. Sofia (in Bulgarian). Crampon, N. and Bakalowicz, M. (1994). Basic and applied hydrogeological research in french karstic areas. EU, Action COST 65, 161 p. Custodio, E. (1986). Hidroquímica del Karst. Jornadas sobre el Karst en Euskadi, 2: 131-180. Donostia-San Sebastián. Dachev, C., Stanev, V. and Bokov, P. (1988). Structure of the Bulgarian Black Sea area. Bollettino di Geofisica Teorica ed Applicata, 30: 79-107. Danchev, D., Damyaniv, A., Nikolov, E., Benderev, A. and Gushkov, I. (1981). Regularities in the distribution of groundwater in the southeast of Dobrudja and Ludogorieto region. Annals of the High School of Mining and Geology, 21: 140-153. (In Bulgarian). Davidescu, F.D., Tenu, A. and Slavescu, A. (1991). Environmental isotopes in Karst Hydrology. A lay-out of problems with exemplifications in Romania. Theoretical and Applied Karstology, 4: 77-86. Dimitrov, D.; Velikov, B. and Machkova, M. (1993). Processing of Groundwater Hydrochemical Data by Means of Cluster and Discriminant Analyses. Hidrogeología, 8: 25-39. Edmunds, W.M. and Lloyd, J.W. (1979). Application de la géochimie dans les études hydrogéologiques au Royaume - Uni. Bull. BRGM, 2ème série, sec.III, 3: 319-333. Edmunds, W.M. and Walton, N.G. (1983). The Lincolnshire limestone: hydrochemical evolution over a ten-year period. Journal of Hydrology, 61: 201-221. Feronskii, V.J. (1975). Natural isotopes of the hydrosphere. Nedra, Moscow (in Russian). Feru, M.U. (1993). Considérations sur la genèse et la circulation des eaux thermominérales karstiques de la zone de Mangalia (Roumanie). Theoretical and Applied Karstology, 6: 189-197. Feru, M.U. et Capota, A. (1991). Les eaux thermominérales karstiques de la zone de Mangalia (Roumanie). Theoretical and Applied Karstology, 4: 143-157. Fidelibus, M.D. and Tulipano, L. (1991). Mixing phenomena due to sea-water intrusion for the interpretation of chemical and isotopic data of discharge waters in the Apulian coastal carbonate aquifer (Southern Italy). In: Hydrogeology of Salt Water Intrusion". IAH, 11: 317-327. Galabov, M. and Pentchev, P. (1986). Solution of applied hdrogeological problems by computers (procedures, programs, examples). Technica, Sofia, 374 p. (in Bulgarian). Galabov, M. and Pentchev, P. (1987). Forecasting the optimum groundwater withdrawal in the vicinity of the town of Shabla in connection with the possibilities for seawater intrusion: Report NPP-HIMG. Unpublished technical report, Sofia (in Bulgarian). Galabov, M., Pentchev, P., Velikov, B., and Damyanov, A. (1989). Development of strategy for groundwater protection of the Bulgarian coastal aquifers against seawater intrusion: Report no. 1130, Research Centre of UMG. Unpublished technical report, Sofia (in Bulgarian).

LXXXVIII

Giménez, E. (1994). Caracterización hidrogeoquímica de los procesos de salinización en el acuífero costero de la Plana de Castellón (España). Tesis Doct. Univ. Granada, 336 p. Gofiantini, R. and Araguas, L. (1988). Los isótopos ambientales en el estudio de la intrusión marina. TIAC’88, 1: 135-190. Institute of Meteorology and Hydrology of Sofia (1990). Climatic Handbook of Bulgaria (In Bulgarian). Iovtchev, I., ed. (1976). Tectonic Map of P.R. Bulgaria scale 1: 500,000. Main Authority of Geodesy and Cartography, Sofia. Iurkiewicz, A. and Oraseanu, I. (1997). Karst terrains and major karst systems in Romania. In Günay, G. and Johnson, A.I. (eds.) Karst waters and environmental impacts. Ed. Balkema, Rotterdam: 471-478. Lawrence, A.R.; Lloyd, J.W. and Marsh, J.M. (1976). Hydrochemistry and groundwater mixing in part of the Lincolnshire limestone aquifer, England. Ground Water, 14, 5: 320-327. Machkova, M.; Velikov, B.; Dimitrov, D.; Pulido-Bosch, A.; Lopez-Chicano, M. and Calvache, M.L. (1995). Hydrogeochemical conditions of the Sarmatian (the Dobrich pilot area case study). Geology and mineral resources, 9-10, 1995: 32-37. Machkova, M.; Dimitrov, D.; Pulido-Bosch, A.; Calaforra, J.M.; Calvache, M.L; LopezChicano, M.; Pentchev, P. and Velikov, B. (1997). Main hydrogeological problems in the karstic aquifers of NE Bulgaria. In Günay, G. and Johnson, A.I. (eds.) Karst waters and environmental impacts. Ed. Balkema, Rotterdam: 53-58. Marin, C. and Nicolescu, T. (1993). The geochemistry of groundwater from southeastern Dobrogea, Romania. Trav. Inst. Spéol "E. Racovitza", 32: 229-247. Mazor, E. (1995). Stagnant aquifer concept Part 1. Large-scale artesian systems Great Artesian Basin, Australia. Journal of Hydrology, 173: 219-240. Miklanek, P. and Dimitrov, D. (1995). Evaluation of the Evapotranspiration in NorthEast Bulgaria using the complex methods. Bulgarian Journal of Meteorology and Hydrology, 5: 26-33. Naidenov, D. (1994). Rehabilitation and improvement of the ecological conditions in the area of the Durankulak lake in relation with criteria of Ramsar convention. Report no. 34/93, Ministry of Environment. Unpublished technical report, Sofia (in Bulgarian). Okay, A.I., Sengör, A.M.C. and Görür, N. (1994). Kinematic history of the opening of the Black Sea and its effect on the surrounding regions. Geology, 22: 267-270. Pascual, M. (1990). Hidrogeoquímica del macizo carbonatado de Garraf: Análisis de los procesos relacionados con la mezcla de aguas subterráneas dulces y saladas en el litoral de Calafell-Bellvei (Tarragona). Thesis Universidad Politécnica Cataluña. 241 p. Pentchev, P. (1983). Study of the influence of built-up areas as a source of groundwater contamination in karst areas. European Regional Conference on Speleology, Sofia, 2: 533-540. (in Russian). Pentchev, P. (1992 a). Sanitary - protection areas around the pumping wells for drinkable water suply in Shabla site. Report no. PKE 4/92, HYDROCOMP. Unpublished technical report, Sofia (in Bulgarian). LXXXIX

Pentchev, P. (1992 b). Determining the sanitary - protection zones of the Vaklino Pumping Station by mathematical modeling. Report no. PKE3/92, HYDROCOMP. Unpublished technical report, Sofia (in Bulgarian). Pentchev, P. (1993). Hydro - ecologycal assessments and a project for sanitary protection zones of the Drainage Tunnel - Balchik. Report no. PKE14/93, HYDROCOMP. Unpublished technical report, Sofia (in Bulgarian). Pentchev, P. (1996). A general assessment of the seawater intrusion in the Sarmatian karst aquifer. Geology and mineral resources, 9-10, 1996: 19-23. Pentchev P., Borissov, S., Velikov, B., Lakov, A., and Spassov, K. (1990). Hydrogeology and Engineering Geology fundamentals. Technika, Sofia, 336 p. (in Bulgarian). Pentchev, P. and Petrov, K. (1993). Assessment of the ammonia and nitrite contamination and development of a strategy for cleaning up the Vaklino Pumping Field. Report no. PKE16/93, HYDROCOMP. Unpublished technical report, Sofia (in Bulgarian). Pentchev, P., Velikov, B., Angelova, R., and Kovatchev, S. (1993). Development of methodology and instruction for groundwater monitoring in Bulgaria: Part 2. Instruction. Report no. KG 70/93, HYDROCOMP. Unpublished technical report, Sofia (in Bulgarian). Price, R.M. and Herman, J.S. (1991). Geochemical investigation of salt-water intrusion into a coastal carbonate aquifer: Mallorca, Spain. Bulletin Geologic Society of America. 103, 10: 1270-1279. Pulido-Bosch, A.; Lopez-Chicano, M.; Calvache, M.L.; Calaforra, J.M.; Machkova, M.; Dimitrov, D.; Velikov, B. and Pentchev, P. (1996). Principales características de los acuíferos carbonatados de la región de Dobrich (Bulgaria). Revista Sociedad Geológica España, 9, 3-4: 143-156. Pulido-Bosch, A.; Lopez-Chicano, M.; Calvache, M.L.; Calaforra, J.M.; Machkova, M.; Dimitrov, D.; Velikov, B. and Pentchev, P. (1996). Consideraciones sobre el flujo en el acuífero kárstico profundo de la región de Dobrich (NE de Bulgaria). In Morell, I. and Fagundo, J.R. (eds.) Contribuciones a la investigación y gestión del agua subterránea. Colecció Summa, Ciències experimentals, Ed. Universitat Jaume I, 4: 67-85. Pulido-Bosch, A; Machkova, M.; Lopez-Chicano, M.; Calvache, M.L.; Dimitrov, D.; Calaforra, J.M.; Velikov, B. and Pentchev, P. (1997). Hydrogeology of the Upper Aquifer, Dobrich Region (Northeastern Bulgaria). Hydrogeology Journal, 5, 2: 75-85. Pulido-Bosch, A., Navarrete, F., Molina, L. and Martinez-Vidal, J.L. (1991). Quantity and quality of groundwater in the Campo de Dalias (Almeria, SE Spain). Water Science Technology, 4 (11): 87-96. Povara, I. (1994). Characteristics of the water table topography in the southern part of the romanian Black Sea coast. Theoretical and Applied Karstology, 7: 127-132. Raykova, B. and Danchev, D. (1972). Hydrogeological and hydrochemical characterization of the groundwaters in the southeast of Dobrudja region. Bulletin of the Institute of Meteorology and Hydrology of Sofia, 20: 137-161. (In Bulgarian). Revelle, R. (1941). Criteria for recognition of sea water in groundwaters. Trans. Amer. Geophysical Union, 22: 593-597. XC

Robinson, A.G., Rudat, J.H., Banks, C.J. and Wiles, R.L.F. (1996). Petroleum geology of the Black Sea. Marine and Petroleum Geology, 13, 2: 195-223. Sanford, W.E. and Konikow, L.F. (1989). Simulation of calcite dissolution and porosity changes in saltwater mixing zones in coastal aquifers. Water Resources Research, 25, 4: 655-667. Schoeller, H. (1956). Géochimie des eaux souterraines. Application aux eaux des gisements de pétrole. Editorial Technip, 213 p. Shanov, S. (1990). Tectonic stress fields in Northeast Bulgaria. Geologica Balcanica, 20, 4:37-47. Sharov, V. and Koleva, K. (1994). Droughts in Bulgaria. Final project Report, VI19/91, Institute of Meteorology and Hydrology of Sofia. (In Bulgarian). Shuster, E.T. and White, W.B. (1971). Seasonal fluctuations in the chemistry of limestone springs: a possible mean for characterizing carbonate aquifers. Journal of Hydrology, 14: 93-128. Tenu, A. and Davidescu, F. (1993). Relations entre le Lac Techirghiol (Dobroudja du sud, Roumanie) et les aquifères adjacents. Theoretical and Applied Karstology, 6: 163-174. Todd, D.K. (1987). Groundwater Hydrology. Ed. John Wiley & Sons, New York, 535 p. Toth, J., (1963), A theoretical analysis of groundwater flow in small drainage basins. Journal of Geophysics Research, 68: 4795-4812. Vallejos, A. (1997). Caracterización hidrogeoquímica de la recarga de los acuíferos del Campo de Dalías a partir de la Sierra de Gádor (Almería). Tesis Doctoral Univ. Granada, 264 p. Velikov, B. (1985). Estimation hydrochimique des interactions eau-roches carbonatées. XXI Congrès International de Technique Hydrothermale. 2: 170-179. Varna, Bulgaria. Velikov, B. (1986). Hydrochemistry of groundwaters. Ministry of Higher Education, Sofia (in Bulgarian). Velikov, B. (1991). Hydrochemische Untersuchungen und Kriterien von Meerwasserintrusion in Aquiferen an der Schwarzmeerküste. Vom Wasser, 76: 235250. Velikov, B., Damyanov, A. and Pentchev, P. (1989). Hydrogeological conditions and hydrochemical characteristics of sea water intrusion in aquifers near the Black Sea coast of Bulgaria. Proceedings 40 years Department of Hydrogeology and Engineering Geology, UMG, Sofia: 102-112 (in Bulgarian). Velikov, B.; Machkova, M. and Dimitrov, D. (1986). Hydrochemical investigations of the groundwaters of the North-East of Bulgaria. HUMG Yearbook, 32, 6: 133-148. Velikov, B.; Machkova, M. and Dimitrov, D. (1989). Estudio hidroquímico de las aguas subterráneas de la región noreste de Bulgaria. Hidrogeología, 4: 13-24. Velikov, B.; Dimitrov, D.; Machkova, M.; Pulido-Bosch, A.; Lopez-Chicano, M. and Calvache, M.L. (1996 a). Hydrogeochemical regime observations on the groundwater

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in the area of Dobrich - Northeast Bulgaria. Geology and mineral resources, 8, 1996: 3-7. Velikov, B., Pentchev, P., and Pulido-Bosch, A. (1996 b). About some hydrochemical characteristics of groundwaters in Northeast Bulgaria. National Symposium on Quality and Purification of the Drinkable Waters in Bulgaria, Slantchev Briag, Bulgaria: 118-123. (in Bulgarian) Wigley, T.M.L. and Plummer, L.N. (1976). Mixing of carbonate waters. Geochimica et Cosmochimica Acta, 40: 989-995. Zanfirescu, F., Moldoveanu, V., Dinu, C., Pitu, N., Albu, M. and Nash, H. (1994). Vulnerability to pollution of karst aquifer system in southern Dobrogea. In: International Hydrogeological Symposium on Impact of industrial activities on groundwater. Constanza, Romania: 592-603.

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