Regional characterization of the vulnerability of the unconfined groundwaters in Bulgaria

Groundwater vulnerability to contaminant infiltration from the surface, and to state deterioration, is related to the spatial distribution of rocks with diverse porosities, flow characteristics and unsaturated zone thickness. For the present regional assessment of groundwater vulnerability, it is considered most appropriate to adopt a method based on spatial differences in the geological and tectonic, and related hydrogeological, conditions in Bulgaria. The objective of the present study is to compile a vulnerability map of the unconfined groundwater in the country. This groundwater type is very important for drinking water supply, and it is at the highest risk of contamination. The groundwater on the territory of the Republic of Bulgaria has been divided into seven vulnerability classes, based on the corresponding hydrogeological units. The map is based on the geological map of Bulgaria in scale 1:100 000. It shows that groundwater is of low vulnerability over a large part of the country’s area (57%). Medium to medium-high groundwater vulnerability is defined for approximately 31% of the total area, while high and very high vulnerability are defined for 7% and 5%, correspondingly.