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Report IMo. IfiEA R - 3621-F TITLE Isotopic investigation on the evolution of groundwater dynamics in the principal aquifers in the southern Dobrudja FINAL REPORT FOR THE PERIOD 1983-12-01 - 1986-11-30 AUTHOR(S) Dr. Tenu, ft. INSTITUTE Institute of Meteorology and Hydrology, Bucharest, Romania INTERNATIONAL ATOMIC ENERGY AGENCY DATE December 198(í i INSTITUTE OP METEOROLOGY AND HYDROLOGY Bucharest - Romania ISOTOPIC INVESTIGATION ON THE EVOLUTION OF GROUNDWATER DYNAMICS IN THE PRINCIPAL AQUIFERS IN THE SOUTHERN DOBRUDJA Contraot IAEA number J621/RB - Final report - Bucharest - 1986 INSTITUTE Oí1 METEOROLOGY AND HÏDROLOGÏ Bucharest - Romania LIST OF SIGNATURES Head of Institute: Dro I. Draghici VA\^ Chief Scientific Investigator; Dr A. Tenu Additional Scientific Staff: F.D. Davidescu Ana Slaves cu Other Staff: M. Cunescu G. Mihordea ÂJp^ CONTENTS: % I» INTRODUCTION 4 2« P3GI0NAL GEOLOGICAL AND HÏ.DROGEO LOGICAL CONDITIONS 5 2ol. Physiografical framework 5 2c2. Geological background 6 2.2.1. Bed rock ? 2.2o2. Sediment cover 7 2.2„3. Tectonics 20 2,3« Hydrogeological considerations 20 2.3.1° Short history of the research 21 2.3°2o Presentation of the aquifers 22 2.3.3» Elements of hydrochemistry 30 3. EXPERIMENTAL RESULTS AND DISCUSSIONS 37 3.1. Sampling network 37 3.2. Experiments 37 3o3o Validity of results 39 3.4-. Isotopic composition of meteoric waters ............ 40 3«5. Iso topic composition of surface waters ...„. 42 3.6. Isotopic composition of groundwaters 44 3.6.1. Globally-spacial characterization „ 44 3.6.2. The Sarmatian aquifer „. 47 3.6.3. The Barremian-Jurassic aquifer 51 3.7. Certain considerations on the age 14 correction methods of C 62 4O CONCLUSIONS 66 fy?*?'& .'~'*í*f&&^<^y APPENDED TABLES CONCERNING THE EXPERIMENTAL RESULTS ....... 68 TABLE I - Groundwater chemistry in the Sarmatian formation o 69 TABLE II - Groundwater chemistry in the Barremian-Jurassic formation 71 TABLE III - PRECIPITATIONS: Meteorological station Constantza 74 TABLE IV - SURFACE WATER: results of isotope analysis (sampling May 1984) 77 TABLE V - SURFACE WATER: results of isotope analysis (sampling May 1985) « 78 TABLE VI - SURFACE WATER: results of isotope analysis (sampling May 1986) <, 79 TABLE VII - GROUNDWATER: results of isotope analysis (sampling May 1984) e 80 TABLE VIII - GHOUNDWATER: results of isotope analysis (sampling May 1785) « 82 TABLE IX - GROUNDWATER; results of isotope analysis (sampling May 1986) 85 TABLE X - GROUNDWATER: results of § 15C and radio carbon analysis 88 TABLE XI - Table for chemical parameter computation required in radiocarbon correction 90 14. TABLE XII - Table for the computation of initial C activity (A,.) by means the Fontes-Garnier method ...? 93 TABLE XIII i- Comparative table of the ages computed by various methods 97 REFERENCES 100 1. INTRODUCTION This work has been issued in the Institute of Meteorology and Hydrology, Bucharest - Romania in terms of the research contract 5621/fiB concluded with the International Atomic Energy Agency in Vienna. The extent of the contract was over three years, covering the time span: December, 1, 1983 - November, 30, 1986. The objective of the research was the application of environmental isotope technique to the hydrogeological study of Southern Dobrudja, a region fully justifying an isotopic study at a regional scale both due to the importance of ground aquifers and to the rate of anthropic changes. Among the major objectives considered, the following are worth mentioning: - delimiting the recharge areas of the Sarmatian and the Barremian-Jurassic aquifers; - determining certain hydrodynamics regional parameters of the two aquifers; - assessing the modifications undergone in the general framework of the regional isotopic distribution range with time, consequence to the surface waters influences. The approach of this study was a complex one which provided both a thorough understanding of the natural background (geology, tectonics, hydrogeology, hydrochemistry) and a judicious selection of the network of water points, as well as an efficient testing each year. The total number of determinations performed in situ, or in the laboratory, occasioned by this contract, was about 1,000 mostly devoted to analyses of environmental isotopes *H, D, 0, ^C and C As this paper is the final report of the research contract it covers the analytical results presented in the annual progress reports as well. - 5 - 2. REGIONAL GEOLOGICAL AND HTDROGEOLOGICAL CONDITIONS 2.1. Physiographical framework The area being investigated lies south-eastern Romania, namely the southernmost third of Dobrudja. It is bordered by the Danube in the west, the Bulgarian frontier in the south, the Black Sea in the east and the Capidava-Ovidiu fault in the north. From a morphologi- cal stand point, the region looks like a flat plateau domina- ting by its steep walls the Danube course and the Black Sea in the west and in the east, respectively. In point of alti- 20" tude, the region generally covers the O 120 240Km range 50-150 m, gra- dually higher towards the south-southwest ¡ Fig.l. Map showing the survey area. where the altitude rea- ches 207 m in the neigj bourhood of the border. As far as the hydrography of the region is concerned, it should be mentioned that the south Dobrudjan plateau shows the poorest network of permanent and half-permanent rivers in the entire Romania, i.e. practically 0 Km/Km . The valleys are generall shaped as canyons with steep symmetrical walls mainly reaching the Black Sea towards the east and the Danube towards the west. In the area adjacent to the littoral, there are some natural lakes of great economic, balneological and touristic impor- tance among which, mention should be made of the Lake Siutghiol, Lake Techirghiol and Lake Mangalia. They occurred consequence to certain genetical mechanisms in old estuaries, lagoons, etc. (ARIADNÁ BREIER, 1976). j Even more important than the natural hydrographical network is the network of canals in the area. Mention should be - 6 - first made of the great canal linking the Danube and the Black Sea, • open to navigation on its main course following the old track of of the Oarasu valley between Cernavoda and Basarabi (with the northern branch: Poarta Alba - Midia - Navodari still in work). There are also numerous canals making up the irrigation system which covers at present about 3,000 Km (i.e. 70% of south Dobrudja s surface). It is here, in the littoral area and the southern part of the region that the thermal regime recorded the highest values of the mean multiannual temperature in Romania - above 11°C. The multiannual average of the temperatures in January covers the tange from -2°C to +1°C, gradually increasing from the Danube to the Black Sea shore where it reaches the multiannual minima, -25° at Mangalia, while the multiannual average in July was 22-24°C with maxima up to 38,5°C at Constantza. The average multiannual amounts of precipitations recorded were something between 370 mm in the littoral zone (Mangalia, Constantsa) and 470 mm towards the south-west where the relief formations are higher in the neighbourhood of the Bulgarian border« These precipitation amounts are unevenly distributed in time and space and the rainfalls are of torrential type. Evaportion amounts to 850-950 mm which accounts for the half-arid climate in the region. The winds prevailing in the region blow from the north all the year round and at times, from the west; the annual average wind-speed exceeds 4-5 m/s. 2.2. Geological background Southern Dobrudja stands out from the adjacent region as a platform sharing the Carpathian foreland characteristics and defines itself as a self-contained geological-structural unit.. It is separated from Wallachian Platform by the Danube fault in the west, from the central Dobrudjan massif in the north by the Capidava- Ovidiu fault, while toward the east, it is continued with the Black Sea shelf. The basement of this unit consists of a crystalline bedrock covered by a thick unfolded pack of sediments deposits of various ages. The stratigraphical sequences outcrop either in land patches or. in the Danubian cliffs and the steep slopes of the valleys. Fig. 2 - Map of Southern Dobrud^a showing locations of the structural drillings and the geological cross-sections. WLrnavoda 1- The well having provided Í5061 structural data and the \ 5026 indicative; 2- Geolo- /J Medgidia - Castelu ical section line -*s ochirleni T^rS&=*^®*SQS3 Fig. 3). Basarabi 5052 Techirghioj Lake 5033 Plopeni Lake *\ TaHageac Lake 5057 Mangalia ¡IV 15081 «ti - 8 - 2.2.1, Bed rook As the geological studies revealed, the basement of the south Dobrudjan platform was consolidated during the Karelian oro- genesis. This basement does not outcrop; it was identified at vary- ing depths only at the time of drilling in the areas west from the Siutghiol Lake (Palazu Mara - Coco su), at Cernavodä - Tortonfonu - Medgidia - Basarabi (Fig.3, section 2-2' and 3-5') ûn'd west from the Techirgiol Lake (Topraisar-Tuzla). It consists in granite gnais overlopped by mesómetamorphic crystalline schists and green schists. A significant uplift of the basement with mesozonal schists along the axis and green schists along the flank was revealed by the drillings at Palazu Mare (according to G. VASILESCU et al., 1964, the Jurassic/crystalline boundary is at 550 m depth). Another area of basement uplift in the fault ridge was identified et Tuzla - Topraisar by geophysical studies and by drilling. 2,2.2. Sediment cover In Southern Dobrudja the sediment cover lies in Silurian, devonian, triassic, Jurassic, cretaceous, tertiary and quaternary deposits characterized by a system of weak folds and numerous simple and angular unconformities* The Silurian, developed in the southern half of the south Dobrudjan platform was detected at 418 m depth in the area Tuzla and at 1,200 m around Mangalia (Pig.3» section 2-2').

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