Aleksey Benderev

• Professor at Bulgarian Academy of Sciences

In 2022, the Karst Commission of the International Association of Hydrogeologists (KC-IAH) launched the implementation of the project "The Most Important Springs from Karst Aquifers (MIKAS)". The main task of the project is to unite scientists from different countries working in the field of karst, in order to identify and assess the most important...

The article describes the main types of drainage waters within the Grantcharitsa tungsten deposit: acid mine drainage, neutral to slightly acidic mine drainage, waters draining the oxidation zone of the deposit and underground waters of the meadow soils located above the oxidation zone. It is shown that the acid mine drainage accompanied by the pre...

Radon as a daughter product from the radioactive uranium family, is present in all rocks and soils in the geosphere. Its half-life (3.82 d) allows the element to migrate from the terrestrial environment to the surface. This migration can be intensified through preferential degassing pathways, such as faults or fracture systems Geogenic radon potent...

The aim of the study is to determine whether it is possible to define subtypes of the type R9 Dobrudja sinking rivers. The river sections pass through the recharge zones of three karst aquifers. It establishes a permanent or temporary lack of runoff in these areas, as well as after leaving them. This defines a necessity on preparation of explorator...

Seasonal variations of drainage waters and ochreous products of their discharge from the closed abandoned old gallery at the Grantcharitsa scheelite deposit (Bulgaria) were studied by field and laboratory methods for the period 2019–2023. The drainage is generated under anoxic conditions and is inherently diluted (EC = 100–202 µS/cm) with S (6–12 m...

In connection with the preparation of a Global and National list under the MIKAS Project of the most important karst springs, it is necessary to evaluate and compare them according to several criteria. The aim of the present study is to determine the ecological status of pre-selected more important karst springs in Bulgaria, which will facilitate...

Environmental spread of radon gas (222Rn) has been intensively investigated in the last few years due to its harmful effects on human health. A concept of radon index is used to characterize the geogenic radon potential of the terrain, as the latter gives the probability of the presence of radon gas concentration in a building, the genesis of which...

RELATION BETWEEN INDOOR RADON CONCENTRATIONS AND GEOGENIC RADON POTENTIAL Bistra K. Kunovska1*, Todor Y. Yordanov1, Desislava K. Djunakova1, Dimitar I. Antonov2, Sava N.Kolev2, Kremena G. Ivanova1, Aleksey D. Benderev2 1 National Centre of Radiobiology and Radiation Protection, 3 Georgi Sofyiiski, Str., 1606 Sofia, Bulgaria 2 Geological Institute,...

Hydrogeological conditions in karst areas reflect the high velocities of groundwater movement in open or material-filled channels. Usually they remain hidden under the ground, and only high flow rates of the flowing underground water reveal them. An example is one of the largest karst springs in Bulgaria – Glava Panega in the village of Zlatna Pane...

The northern part of the Municipality of Brezovo falls within the range of a fractured massif, which predetermines the presence of springs with a limited flow rate, insufficient for water supply for the villages there, which necessitates the localization of suitable locations for boreholes drilling. After a complex assessment of the geological-hydr...

In June 2022, the Karst Commission of the International Association of Hydrogeologists (IAH) initiated, under the auspices of UNESCO, the adoption and implementation of the project „Most Important Karst Aquifer Karst Springs (MIKAS)”. The project is completely implemented on a voluntary basis and is based on the knowledge and professional experienc...

Mining is a significant industrial and economic activity, but it can also result in ore waste that contains several potentially toxic elements (PTEs). Furthermore, the wide range of observed transfer and accumulation factors suggests that not only the soil element concentrations but also the soil characteristics are important for uptake, which is r...

One of the goals of the study is to establish the conditions that affect the water quality in the catchment area of the Mesta River (Southwest Bulgaria). This will help to distinguish the anthropogenic impact from natural factors, with geological setting in first place. For the formation of the chemical composition of the waters in regional aspect,...

Karst has a wide distribution, both throughout the world and in Bulgaria. The groundwater formed in it are important for providing water for the population and for the existence of a number of ecosystems. Considering the importance of karst springs, an international project "Most Important Karst Aquifer Springs" – MIKAS was started. The project aim...

The object of research is the Iskrets spring, one of the large and important karst springs in Bulgaria. A characteristic feature of its regime is the temporary interruptions of its outflow. The purpose of the research is to establish the probable causes and mechanism for these interruptions. After analyzing the hydrogeological situation and data fr...

The study deals with the evaluation of the dynamic of the radon index in one pilot site based on second-time pilot investigations of the radon index in Bulgaria. In situ measurements of the radon concentration in soil gas, and soil permeability at three polygons: one over and two – close to fault zone have been performed in October 2020 and October...

The study assesses the role of the various potential and active sources of impact on the quantity and quality of surface and groundwater in the area of the Regional Landfill for Solid Household Waste in Yambol. The focus is on the geological and hydrogeological characteristics of the terrain and the anthropogenic load on the catchment basin of the...

The presented study examines the problem caused by the groundwater pollution in the alluvial aquifer complex formed in the terrace of the Vacha River. Two working hypotheses are considered. In the first one is accepted that the aquitard is regionally well sustained and limits the penetration of Mn-contaminated waters into the lower aquifer. In the...

The thermal waters and the historical heritage in the area of Hisarya were the focus of the field trip held during the XXII International Congress of the CBGA in Plovdiv.

Mesta river is a cross-border river with Greece, whose catchment area includes parts of Rila, Pirin and the Rhodope Mountains. The karst is developed in pre-Paleozoic marble that forms isolated outcrops with different basins. The largest of them forms two alpine karst basins located in Northern Pirin and Slavyanka Mountains. In the Rhodopes region,...

Natural radon (222Rn) is a radioactive noble gas that occurs in every rock or soil due to the content of radium (226Ra), part of the 238U family, in the lithosphere. One of the indicators for evaluating the impact of radon on a certain area/terrain, including on the biota, is the so-called geogenic radon potential. Different types of rocks and soil...

The regional hydrogeological conditions in Northern Bulgaria determine the existence of a large artesian basin consisting of layered aquifers. The groundwater temperature increase with depth and the conditions in the deeper layers are favourable for the formation of stratified hydrothermal reservoirs with potential for heat extraction. Although it...

The artesian borehole R-30–Staro Oryahovo with total depth of 1740 m gives waters of chlorine–sodium type with a mineralization of 31 g/L from formations of Paleogene age. These waters contain high concentrations of iron and because of this, intense precipitation of iron compounds takes place at and around the wellhead. To clarify the ongoing proce...

The development of a methodology for the geogenic radon potential (GRP) mapping based on soil gas radon and soil gas permeability field measurements is among the main objectives in the determination of “radon priority areas” in Bulgaria. One of the key elements of the methodology is to define as accurately as possible, areas of risk for the presenc...

A distinct increase in the concentration of W in the topsoil (from 19–20 to 71 ppm) is found in the vertical profile of the alluvial soil at the Grantcharitsa deposit. The distribution of W, Fe, and C is well correlated, which indicates a significant role of organic material and iron oxides/hydroxides formed in the soil in the chemical behavior of...

Studies have been carried out to establish the impact of Medetska River on the pollution of Topolnitsa River, as a result of mining activities discontinued in the past. The results of monitoring observations of water quantities and chemical composition, in the confluence area of the two rivers, are summarized and analyzed. A laboratory experiment w...

The purpose of the present study is to evaluate the environmental impact of a surface spill of groundwater with high total dissolved solids content by clarifying the extent of contamination in the soil layer near the borehole R1 – Barzina. The overall tendency for limitation of the migration of chloride pollution in the immediate vicinity of the fo...

The presented study is aimed towards determining the reasons for manganese pollution of drinking water extracted from the terrace of Vacha River. The results show that this is due to the seepage of from the artificial lake, formed after the construction of a small hydropower plant. Another possible reason is the natural accumulation in the upper pa...

Natural radon (222Rn) is a radioactive noble gas that occurs in every rock or soil due to the content of radium (226Ra), part of the 238U family, in the lithosphere. Different types of rocks and soils possess different 226Ra content and different permeability. Radon has high mobility and is driven by diffusion and convection with the soil gas throu...

The present research is related to one of the basic component of the environment – waters with study area the Ogosta river catchment. It is based on the investigation of water samples collected during field research in the river monitoring area and laboratory analysis. The research is focused on the state of the pollution and quality of the water....

Sofia, the capital of Bulgaria, is situated in a region rich in thermal waters, which were a major factor for the establishment and development of the city. The thermal spring in the city center of Sofia has been in use since ancient times. As the city expanded rapidly in the 19th and 20th centuries, it absorbed many other sources of thermal water....

INTRODUCTION The radon gas relieved from ground could accumulate in the building and contribute to human exposure. Exposure to indoor radon and its decay products contributes half of the annual dose received by the public from all natural radioactive sources [1]. Radon is recognized as a carcinogenic agent by the WHO and is the second leading cause...

The objective was to investigate how water infiltrated into waste dumps at a mine site. The electrical resistivity method of field geophysics was applied to produce 4D imaging of progressive water infiltration into the waste dump. The goal is to test a method for investigating how rain water infiltrates unconsolidated materials in mine waste dumps....

The described exotic rock block (60×80×13–15 cm) was found at 290 m depth in a lower–middle Badenian gypsum layer in the Koshava mine, NW Bulgaria, near the Danube River. It is greyish-black, granular, with layered structure and layers composed of α-quartz rosettes covered with organic matter (kerogen-like type with high contents of Ge, Mo and B),...

The study deals with pilot investigations of the radon index in Bulgaria. In situ measurements of the radon activity and soil permeability at 3 sites one over and two-close to fault zone have been performed. The results show that higher radon content is detected in the fault zone.

The presence of arsenic in the Ogosta River Valley's alluvial sediments is subject to historical contamination due to upstream located ore-factories, tailing ponds, and even industrial accidents from the past. In recent years, there have been several types of research focused on different aspects of the contaminated alluvial sediments in the floodp...

Radon (222Rn) is a natural gas produced by the radioactive decay of uranium-bearing rocks and soils in the Earth’s crust. Geology is one of the main factors controlling source and distribution of radon. Most rocks and soils possess small amount of uranium, but there are particular types of bedrocks and unconsolidated deposits characterized by highe...

The safety and accident free exploitation of hydraulic facilities depends on geological and hydrogeological conditions of terrains where they are built. Such facilities have one of the most serious problems when they are located in a karst environment. In Bulgaria, there have been a number of cases of refusal to build dam walls at the preliminary e...

The study of intra-earth processes requires a comprehensive approach, which should be based on the understanding different nature and origin depth of terrestrial processes. In this regard, the problem of the relationship between seismicity and heat flow in the lithosphere is of interest. We analyzed seismic observation data in Bulgaria from 1981 to...

After Bulgaria’s accession to the European Community, a process of harmonization of national legislation with the European Union has started. This has led to the introduction of the term “groundwater bodies”, sometimes resulting in conflicts between hydrogeologists and water management experts. Some examples are considered in this respect, relating...

The preliminary data show that the all studied waters in the area of the Grantcharitsa deposit (surface, mine and underground) are low mineralized. It was found that W, As and U as critical chemical elements for the local inhabitants, occur in the waters of the Grantcharitsa River in low concentrations (U) or their contents are below the detection...

The Repository for Radioactive Waste in Novi Han, Lozen Mountain (Bulgaria), dates from the early 1960s. In the present study, the complex geoenvironmental setting of the repository site was analysed from the viewpoint of assessment of potential radionuclide migration from the repository to the geosphere. Thus, components of the mass transport fiel...

Study region: Lom depression, Bulgaria. Study focus: A multi-tracer investigation was applied to identify the recharge conditions and isotope hydrological character of four aquifers in the Lom depression (Northwest Bulgaria) using environmental isotopes (δ18O, δ2H, δ13C, 3H, 14C) and noble gases. The radiocarbon age model of Ingerson and Pearson w...

As a result of historical mining activities, some layers in the Ogosta Valley`s floodplain sediments are highly enriched in arsenic (As). Reductive release of iron (Fe) and As in the floodplain soil could be expected under reducing conditions, which would lead to an increase of the more toxic As species in the soil pore water. Therefore, it is impo...

Bulgaria is relatively rich in geothermal water of temperature in the range of 25ºC-100ºC and the total flow-rate exceeds 3,000 L/s. Generally, there are more than 170 geothermal fields: 102 of them are state-owned and the rest of them – belong to some municipalities. Up to 72% of the total known flow-rate from the reservoirs has a comparatively lo...

This paper presents the methodology and results of the national radon survey in Bulgaria and its spatial variability. The measurements were carried out in 2778 dwellings using CR-39 track detectors over two successive 9 and 3-month periods from April 2015 to March 2016. The arithmetic (AM) and geometric (GM) means of annual indoor radon concentrati...

The chemical composition of thermal waters has an important role in their use as a shallow geothemal source. One of the chemical components that may have a negative impact is iron. Its presence in the water can lead to both chemical and biocorrosion, as well as filling of the wells and facilities associated with the use of thermal waters. The aim o...

“Shipkovo” thermal water field is one of the few in the country formed in karstified carbonate rocks. Initially, there was a natural spring with elevated temperature, located at the boundary of Triassic karstified limestones and dolomites and Lower Cretaceous terrigenous rocks, sinking in depth to the east. Later, drilling operations were carried o...

The Dobrudzha Coal Deposit is characterized by complex geological, tectonic and hydrogeological conditions. The formed aquifers and complexes, on the one hand, hinder the possible exploitation of the coal deposit, on the other hand they are important for drinking water supply in the area. The aim of the present study is to develop a 3D hydrodynamic...

The ground surface relief, geological settings, river network and hydrogeological conditions along the Bulgarian-Greek border are analysed. As a result three transboundary aquifers are identified: the alluvial aquifer in Maritsa River valley and the Neogene porous aquifer Svilengrad-Orestiada in the eastern part of the border, and the karst aquifer...

A major issue in groundwater and surface water management and monitoring is transboundary groundwater flow between neighbouring countries. The subject of our study is the assessment of the groundwater flow across the state border between Bulgaria and Greece, which is characterized by complex natural features. We present a study on the factors that...

The Velingrad geothermal field is one of the largest in Bulgaria. Its water is widely used for balneo­ logy, spa tourism, sports, heating and other purposes. An interesting problem related with the operation of ther­ mal water is the process of scaling or corrosion of equipment when the water passes through it. Specifically, for the geothermal fiel...

The area of Kamchiya River's inflow into the Black Sea has an important role not only as a natural landmark, but also as a leading factor for the national economy. It has been subjected for many years to oil and gas exploration, as well as to extraction of deep, highly mineralized waters containing chemical elements of industrial value. There are c...

The Arda River is the main river course in the mountain range Rhodopes located in Southern Bulgaria. Its river basin is characterized by highly variable relief and diversified geological and hydrogeological conditions. The groundwater is recharged mostly from precipitation and forms baseflow of the Arda River and its tributaries. The aim of the stu...

Karst groundwater is widespread in Northwestern Bulgaria. In the higher parts of the Balkan mountain range (Stara Planina) and Fore Balkan typical karst basins are found built mainly from Mesozoic carbonate sediments, whereas in the flat platform part the typical aquifer in the Neogene (Sarmatian) deposits is formed. The drainage of these carbonate...

In relation with a study of the arsenic pollution of groundwater in the Ogosta Valley, a monitoring station was built in the floodplain in the upper reaches of the river not far from the town of Chiprovtsi. The monitoring took place at three adjacent sites including a hydrometric river gauge and two tube wells located closer and further from the ri...

The studied area is located in the vicinity of Rashid branch, part of the Nile Delta. This region is part of one of the most important aquifers in the world. The review of published information indicates that the existing zone of interaction between groundwater and sea salt water is complicated by the variable lithological composition in vertical a...

This work is an environmental isotope investigation of groundwater samples from a multi-layered aquifer system in the Lom depression of Danubian Plain in Bulgaria. Our previous studies in the Carpathian-Pannonian Region had been convinced through groundwater researches using noble gas temperatures that the recharge temperature difference between th...

The karst springs group "Toplitsa" are located in Gotse Delchev karst basin. The aquifer consists of karst marbles-part of Dobrostan formation and encircles the Paleogene Teshovo pluton. Geological conditions give a reason that the groundwater movement is throw faults between karst and pluton and springs can be classified as karst fault springs. Mo...

The paper describes the hydrochemistry of Iskrets Spring, which is one of the largest karst springs of Bul- garia. The spring's water has a composition expressed in equivalent units for cations: Ca2+ > Mg2+ > (Na++K+) and for anions: HCO3— > SO42— > NO3— > Cl—. Calcium and bicarbonate account present approximately 75% of the ions. The correlations...

This work is an environmental isotope investigation of groundwater samples from a multi-layered aquifer system in the Lom depression of Danubian Plain in Bulgaria. Our previous studies in the Carpathian-Pannonian Region had been convinced through groundwater researches using noble gas temperatures that the recharge temperature difference between th...

In the recent years there has been a steady increase in the concentrations of arsenic in the Kobilyak karst spring. After a complex research, the Ogosta River was found to be the source of pollution, and the reason is the accelerated lateral and bottom erosion of the river, which relieves the infiltration of river waters into the karst limestones a...

A strategy for a safe slope design is needed to mitigate the risk of a significant landslide initiation in the Elatsite open-pit mine in Central Bulgaria. This strategy should be based on detailed information about the water dynamics and the interplay of hydrology with various factors, such as the mountain geomorphol-ogy, engineering infrastructure...

23. 09-25. 09. 2016 г. Abstract: The article provides an overview of the concepts and methods applied for evaluation of the risk for chemical contamination of groundwater and their consistency with the concept of ecological risk assessment. The aim of this study is selection of indicators for estimation of the specific risk for arsenic pollution of...

The article provides an overview of the concepts and methods applied for evaluation of the risk for chemical contamination of groundwater and their consistency with the concept of ecological risk assessment. The aim of this study is selection of indicators for estimation of the specific risk for arsenic pollution of groundwater in contaminated rive...

The geological structure of Bulgaria is a complex mosaic of plates and orogenic structures, characterized by deep faulting and lithofacial and magmatic contrasts. Three types of reservoirs are found in the country: stratified (northern Bulgaria), fractured, and mixed, where mineral water from a fractured reservoir is secondarily accumulated in a yo...

The study presents the results of a decade-long investigation of the environmental status in the area of the KCM smelter (Plovdiv, Bulgaria). All pollution sources, pathways and targets in the area are recognized and their roles in the overall environmental status are evaluated. The range and direction of seasonal dynamics of all analyzed factors i...

The purpose of study is to estimate the role of karst springs in the formation of the flow of the Bulgarian rivers that are right tributaries of the Danube River. The study area includes the region from the Danube River to the main ridge of the Balkan (Stara Planina), representing a major water divide that separates the Black Sea catchment area fro...

The object of the study is evaluation of the groundwater recharge to the river runoff in the Vitosha Nature Park. This mountain area with widespread rock aquifers is poorly studied in terms of hydrogeology. An updated Hydrogeological map is prepared based on the map produced in 1975 on scale 1: 200 000. Delineation of the aquifers, aquifer complexe...

The territory of Northern Bulgaria is an object for searching oil and natural gas. Essential aspect of these activities is prediction and estimation of impact on groundwater and its protection. Many factors and all sources should be studied in detail in order to avoid any negative impact on groundwater during study and exploitation of oil and natur...

The territory of Northern Bulgaria is an object for searching oil and natural gas. Essential aspect of these activities is prediction and estimation of impact on groundwater and its protection. Many factors and all sources should be studied in detail in order to avoid any negative impact on groundwater during study and exploitation of oil and natur...

Sofia, the capital of Bulgaria is undergoing significant development in recent years. The number of residents has increased significantly during the last decades, which has given a significant impact on the expansion of the urban environment. The water and particularly groundwater have important implications for the city since its founding until no...

The region of the Western Balkan is characterized by its complex geology and the presence of polymetallic ores. Iron and base metal (Pb-Ag) deposits are located in the upper valley of the Ogosta River near the town of Chiprovtsi. The local Fe-ores are rich in arsenic and copper, while the Pb-Ag ores contain much zinc and cadmium. The former mining...

This paper presents the outcome of a feasibility study on underground coal gasification (UCG) combined with direct carbon dioxide (CO₂) capture and storage (CCS) at a selected site in Bulgaria with deep coal seams (>1,200 m). A series of state-of-the-art geological, geo-mechanical, hydrogeological and computational models supported by experimental...

The article describes the methods of hydrodynamic observations for monitoring tectonic processes in real time and seismic isolation component. The developed methods are used to extract the geodynamic component of observation data to examine patterns of its distribution in space and time over large areas in the process of preparation of strong earth...

Vitosha is the first natural park in Bulgaria and on the Balkan Peninsula. The “Development of Water and Water Resource System Balance for the Territory of the Vitosha Natural Park” is the first comprehensive study of its kind on the water resources of the Vitosha Mountain and the possibilities of their use for the purposes of the integrated manage...

The territory of Bulgaria is rich in thermal water of temperature in the range of 20 °C–100 °C. Electricity generation from geothermal water is not currently available in the country. Direct thermal water use nowadays is mainly for balneology, space heating and air-conditioning, greenhouse heating, geothermal ground source heat pumps (GSHP), direct...

Dobrudzha coal deposit is located in a tectonically disturbed zone in north-eastern Bulgaria. It has not been exploited till now due to the great depth of occurrence (1200 ÷ 1400 m) and very complicated geological and hydro geological conditions. Several storey arranged aquifers are discovered in the region. Each of them has a specific chemical com...

Flooded abandoned coal mines are a potential source of geothermal energy, which could be used for heating and cooling of energy efficient buildings. Cherno More Coal Mine is located in SE Bulgaria and has been closed for more than 20 years. It represents a large human-induced subsurface reservoir which consists of three interconnected coalfields ("...

The aim of the study is to evaluate the potential recharge to the ground- water for the chosen study area – the Ogosta River basin in Northwestern (NW) Bulgaria. Various techniques are used for quantifying groundwater recharge. Some of them are based on water budget methods. The Budyko-type curves al- low partitioning of the long-term precipitation...

Bulgarian territory is rich in thermal water of temperature in the range of 20-100°C. The highest water temperature (98°C) is measured in Sapareva banya geothermal reservoir. Electricity generation from geothermal water is not currently available in the country. The major direct thermal water use nowa-days covers: balneology, space heating and air-...

Bulgarian territory is rich in thermal water of temperature in the range of 20 o C-100 o C. Direct thermal water use nowadays is for balneology (prevention, treatment and rehabilitation, bathing and swimming pools), space heating and air-conditioning, greenhouses, geothermal ground source heat pumps (GSHP), direct thermal water supply, bottling of...