Radon (222Rn) is a radioactive gas and formed as a result of the radioactive decay of radium. 222Rn relieved from the ground could accumulate in the building and contribute to human exposure. ...Exposure to indoor radon and its decay products contributes to half of the annual dose received by the public from all natural radioactive sources. Radon is recognized as a carcinogenic agent by the WHO and is the second leading cause of lung cancer after tobacco smoke. The radon concentration in buildings and the exposure to radon depend on many factors, but it can be assumed that geology is the main factor influencing the variation of indoor radon. In this regard, the geogenic radon potential (GRP) of the terrain is the probability of the presence of high radon concentration in a building, the genesis of which is directly related to the influence of the earth's surface, and not e.g. from building materials. In addition, there is a concept “radon index”, which is used to characterize GRP. One of the approaches for quantifying the radon index is based on a multivariate cross-tabulation, which includes two parameters – radon concentration in soil gas and gas permeability of the earth layer. Till 2019, complex studies concerning correlation between the measured radon concentrations and bedrock geology in Bulgaria are only scarce and quite general. In the last three years, there are attempts for detailed investigations for evaluation of the bedrock and superficial geology associating with radon potential or/and radon index determinations. Therefore, research works on geogenic radon so far in Bulgaria can be divided into two main groups: regional research works related to the "radon-rock" relationship and local research aimed at determining the radon index at specific sites. In the first group appertain investigations about defining the rock formations in Bulgaria, in their outcrop presence, with possible high radon potential based on geological and published more general “radon–rock correlations” data. Based on that, a GIS based map for the spatial distribution of the particular rock types in accordance with the expected radon potential is made. Also to this group belongs a study concerning spatial sampling design for the use of the polygons (Sliven Province) as the unit of sampling, data collection, and analysis and reduces the number of observations, as well as would optimize the gathering, analysis and systematization of the data for the preparation of a methodology for the preparation of geogenic radon potential map. In the second group appertain investigations of the radon index determination at the two pilot sites affected by fault systems in Sofia.
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, the marble outcrops are fragmented and embedded in non-karstic rocks. They are drained from springs with relatively low flow rates. The largest karst springs drain different hydrodynamic zones of the karst massif of Northern Pirin. From the karst basin of Slavyanka Mountain, only the large subthermal spring near the village of Musomishta falls into the catchment area of the Mesta river. The data on the chemical composition of some of the karst springs are summarized, paying attention to the largest of them. An analysis of the changes in the chemical composition and comparison is made. The changes of the hydrochemical parameters of the springs draining different vertical zones in Northern Pirin are compared. The obtained results prove that the main role in the formation of the chemical composition of karst waters has natural factors - interaction between water and marbles. It was found that the waters are unsaturated to carbonate minerals, which proves that even now there are active processes of karst formation.
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, the outcropped rocks are of major importance. In the considered area most widespread are mainly silicate rocks – about 75% of the total area. These are mainly different types of granites and to a much lesser extent granodiorites, quartz porphyries, quartz porphyrites (58%). Highly metamorphosed rocks such as gneisses, shales, amphibolites are also important – 26%, as well as volcanic (rhyodacites, dacites, ignimbrites and their tuffs) – 5%. These rocks occupy the relatively higher and steeper parts of the catchment area and fractured rocks aquifers are formed in their weathering zones. Given the low solubility of the minerals forming these rocks and their rapid runoff, the waters in them show low TDS content. Due to the processes of chemical weathering, they provide some of the main macrocomponents, determining the chemical type of groundwaters – Na, Ca, Mg, HCO3. Although with a relatively small area (about 5%), the marbles, which are significantly karstified are characterized by the formation of large amounts of water. Active karst processes are the cause for the predomination of hydrogencarbonate-calcium type of waters. Neozoic sandstones, conglomerates and clays (about 8% of the total area) are deposited in lower parts of the river valley, in the range of tectonic grabens. They form a layered aquifer complex, where due to the slower movement of water and longer water-rock contact, groundwater has a relatively higher TDS content. Along with the regional hydrogeological and hydrochemical features, the geological setting is the reason for the probable presence of local hydrochemical anomalies. They are often associated with fractures and pegmatite veins, in which ore manifestations and indications of Pb, Zn, Cu, Fe, W, Mo, Ag, Au, Bi, Sb, as well as talc, asbestos and muscovite have been found. Elevated contents of Fe, Mn and U are found in some places too. The localization of such zones (over 100 in total) will help to correctly clarify the genesis of undesirable deviations in groundwater quality. Thermal water deposits, some of which have conditions for mixing with cold groundwater, are also examined.
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