Conditions and processes of precipitation of iron compounds upon discharge of high-mineralized artesian water from artesian borehole R-30, Staro Oryahovo, Bulgaria.

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 processes, samples of precipitates and overflow water were taken. It was shown that the predominant form of iron in the water before reaching the surface is Fe2+-85-90% and FeCl+-4-11%. The calculated saturation index for a number of Fe2+-containing minerals showed that hydroxides and sulfates of Fe2+ are the possible candidates for sources of iron in the water. The reductive dissolution of wide spread Fe3+-containing minerals (hematite, goethite) was assumed as a possible alternative process releasing Fe2+ into water. At the surface, due to the contacts with the atmospheric oxygen, the environment is sharply changed to oxidizing one thus forming a geochemical barrier and causing mass precipitation of Fe3+ oxides. Simultaneous Fe2+ oxidation, hydrolysis of Fe3+ and co-precipitation with silica and other components are assumed as the major processes causing the formation of low-crystalline Si-containing ferrihydrite or ferrihydrite-like phase. After formation, the precipitated gels due to the processes of aging and continued interaction with the outflowing water have suffered the further change including the formation of goethite. It was shown that due to the intensive precipitation processes, the iron migration to the surface is limited to a very small area and does not affect adjacent agricultural territories with Fe.

Analysis of the spatial variation of indoor radon concentrations (national survey in Bulgaria).

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 concentration were 111 ± 105 Bq/m3 and 81 Bq/m3 (GSD = 2.15), respectively. The distribution of data has been accepted to be log-normal. Two hypotheses have been investigated in the paper. The first one was a spatial variation of indoor radon concentration and the second was spatiality of the factor that influences radon variation. The indoor radon concentrations in the 28 districts have been significantly different, which prove the first hypothesis. The influence of the factors, geology (geotectonic unit, type of rock, and faults distance of the measuring site), type of the region, and the presence of the basement in the building on radon spatial variation, was examined. The analyses have been shown that they significantly affect radon variations but with a relatively small contribution in comparison to the radon variation between district. Furthermore, the significance and contribution of the investigated factors were different in each district, which confirmed the second hypothesis for their spatiality.