Assessing the ground waters of Bulgaria using a Water Quality Index

The study focuses on the quality of shallow groundwater in Bulgaria based on the content of major ions. To be safe for drinking purposes, their concentrations must not exceed the respective thresholds. The groundwater quality is assessed in terms of health hazard by a groundwater quality index (GWQI or WQI), and the respective map is presented. The results show that for the territory of Bulgaria, this index varies from 13 to 92. The highest values of this index (related to health hazard) are typical for the lower hypsometric zone of the country. The shallow groundwater in the zone of active water exchange is distributed as follows: waters of excellent quality, waters of good quality, waters of poor quality, and waters of very poor quality, covering 3%, 39%, 22%, and 31% of the whole area of the country, respectively. In this study, no estimates have been made for 5% of the territory of Bulgaria, which is characterized by the presence of very hard groundwater.