Genesis of boron in groundwater in a water supply borehole in the village of Dobri Dol, Plovdiv region, Bulgaria

This study investigates the elevated boron concentrations in groundwater from a water supply well in the village of Dobri Dol, Plovdiv region, Bulgaria. While surrounding water sources show low boron levels (0.02–0.06 mg/L), the well consistently exhibits values exceeding drinking water limits (1.27–2.1 mg/L). A comprehensive hydrogeological, hydrochemical, and statistical analysis was conducted, including sampling from multiple aquifers, field inspections, geophysical surveys, and hydrochemical modeling. The chemical composition of groundwater was assessed across 18 regional sources and analyzed for 56 elements. Partial Least Squares–Discriminant Analysis was used to identify distinguishing chemical patterns. The results ruled out anthropogenic contamination and support a geogenic origin of boron. Evidence indicates that the elevated boron levels in the well are due to upward migration of mineralized water through fault-related pathways from deeper Paleogene volcanic-sedimentary rocks, similar to those in the distant Merichleri geothermal area. Visual Minteq modeling confirmed that boron in the Dobri Dol water exists predominantly as H₃BO₃. The findings suggest no surface-related contamination and conclude that natural geological-hydrogeological processes are responsible for the boron anomaly.