Hydrogeological models for the conditions causing the occurrence of manganese in wells for groundwater extraction from the terrace of the Vacha River, Southern Bulgaria

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 second one is assumed that there are hydrogeological windows in the aquitard, through which active mass exchange between the two aquifers can take place and manganese can occur in the pumping wells after their exploitation is started.