VOLUME 50 (2)/August 2021

The present study describes the hydrochemistry of ground waters found in the Mesta River Basin, located in the south-western part of Bulgaria. The groundwater’s composition can be expressed as follows: Ca²⁺ > Na⁺ > Mg²⁺ > K⁺; Ca²⁺ > Mg²⁺ > Na⁺ > K⁺ in equivalent units for the cations, and HCO₃^– > SO₄^2– > Cl^– in equivalent units for the anions. The chemical composition of the studied groundwater can be described as calcium-bicarbonate. The calcium ions make up from 17.90% to 38.62% (30.18% on average), and the bicarbonate ions make up from 35.30% to 48.98% (43.70% on average) of all ions. Taken together, the calcium and bicarbonate ions make up from 61.44% to 87.60% (73.88% on average) of all ions. The groundwater itself is of slightly alkaline nature, having pH of 7.3 to 8.6, and TDS of 67 mg/l to 611 mg/l. One groundwater sample from the Mesta River catchment area was found to be of the low-mineralized type (TDS = 193 mg/l) alkaline water (pH = 9.8) in the Mesta Lowlands – the Banichan groundwater mineral source. The water can be described as sodium-bicarbonate, with sodium ions making up to 93.5% of the cations, and bicarbonate ions – 69.6% of the anions. Out of all ions, the sodium ions were found to be 48%, and the bicarbonate ions – 33.86%. The sequence of ions is in the following order: Na⁺ > Ca²⁺ > Mg²⁺ > K⁺, and HCO^₃– > Cl^– > SO₄^2– > CO₃^2–.

The objective was to investigate how water infiltrated into waste dumps at a mine site. The electrical resistivity method of field geophysics was applied to produce 4D imaging of progressive water infiltration into the waste dump. The goal is to test a method for investigating how rain water infiltrates unconsolidated materials in mine waste dumps. This is an important problem when evaluating the water balance in waste dumps and understanding the conditions for contamination of the water flowing through the waste materials. The trial was carried out in one of the two large dumps at Elatsite mine, which are composed of rocks with various fragment size and diverse mineral composition. The investigation was undertaken by discharging salt solution into the waste dump and taking geophysical measurements on a rectangular electrode grid at certain time intervals. The grid consisted of 64 electrodes forming 10×5 m cells and covering a 70×35 m area. As a result, it was possible to record how the infiltration and dispersion of the salt solution developed in space and time. In the last one of the seven surveys, 40 hours after the start of the trial, it was established that the salt solution reached a depth of approximately 40 m. The results could be used for predicting the interaction between water and waste material.