Regional application of complex groundwater quality indices and mapping for the territory of Bulgaria with possibilities for their use

The aim of this study is to perform a spatial complex hydrochemical analysis of groundwater quality in Bulgaria and compile a map. For this purpose, data for the chemical composition (Ca²⁺, Mg²⁺, Na⁺, Cl^–, SO₄^2–, NO₃^–, HCO₃^–, TDS, EC) of fresh groundwater (having shallow circulation) for the year 2015 have been summarized. These are the waters most vulnerable to incoming contaminants infiltrating from the surface and, at the same time, these are the waters of importance for the provision of potable water supply. The Groundwater Quality Index has been used to assess the water quality for domestic usage. An assessment of the potential groundwater’s corrosive activity has also been made. For this purpose, the Langelier Saturation Index and the Potential to Promote Galvanic Corrosion were determined as well. The galvanic corrosion of water in respect to lead (expressed as the chloride-sulphate mass ratio) has not been determined and mapped on the territory of Bulgaria, nor has the Langelier index for fresh groundwater. For the year of 2015, the groundwater of the territory was classified as being in acceptable (76 to 90), and good (90 to 95) condition in terms of the Groundwater Quality Index. In terms of the Langelier Saturation Index and the Potential for Galvanic Corrosion, the territory of the country can be characterized by low to moderate potential (for galvanic corrosion), and according to LSI it can be classified in three categories – potentially corrosive, indeterminate, and scale forming.