| Authors |
Elena FILIMONOVA, Natalia KHARITONOVA, Vasiliy LAVRUSHIN, Alexey MASLOV, Ekaterina BARANOVSKAYA, Anna KORZUN, Elena MAKSIMOVA, Arslan SARTYKOV, Elena BAIDARIKO |
| Abstract |
The Caucasian mineral water (CMW) region is the unique region within Russia where various types of mineral groundwaters widely spread. The Essentuki mineral groundwater basin is the most famous area located in the central part of the CMW region. In spite of the study of mineral groundwater has more than 200-year history, many aspects are not specified yet. The mineral waters from Essentuki area widely used not only as a spa but as bottled waters. The Essentuki mineral groundwater basin (EMGW) involves the unique wide variety of mineral waters having different temperatures (from cold to medium thermal), TDS, pH, chemical, and gas composition. TDS changes from fresh (0,5-0,9 g/l) to high-salinity (10-13 g/l) and strongly depends on the chemical composition of water. According to the main anion, the chemical type of groundwater varies from HCO3 to Cl- HCO3 or SO4- HCO3. Based on gas content, the mineral groundwaters within the Essentuki basin could be still water or high-pCO2 sparkling water, sometimes H2S rich aqua. This study was undertaken to identify the source of water and gas phases in mineral groundwaters from EMGW. According to geological and hydrological settings, EMGW basin is located in extension structure, consisting of narrow horsts and grabens, restricted north-eastern faults. Faults and surrounding them fractured rocks served in the past and present time as vertical channels to fluid migration between layers and from basal complex to sedimentary cover and as lateral channels to speeding migration inside aquifers. Thus, hydrochemical inversion appeared and continued to exist at present in the cross-section of EMGW basin. The geological basin consists of a two-stage structure: basal complex and carbonate-terrigenous sedimentary cover with a total thickness of 1500-1800 m, declined in the north-eastern direction. Increase in the depth of layers, removal the recharge area consequently change the chemical and gas composition. The significant stratum of Neogene clays overlays Palaeogenic and Upper-Cretaceous carbonate sediments, conserving high-salinity groundwater. In the southern part of monocline subjacent Lower-Cretaceous aquifer appears on the surface without overlaying sediments and recharge by precipitation. Constant fresh flow causes stepwise freshening in lateral migration in a north-eastern direction. Magmatic granitic laccolite-peaks also set in a north-eastern direction, create thermal, hydrochemical and gaseous anomalies and generate CO2. At this moment Essentuki mineral groundwater basin is characterized by the increased seismic intensity, in the recent past active volcanic activity, unstable geodynamic regime, the particular community of mineral and thermal water in this region. Groundwater pumping in the EMGW basin began in 50th years XX century from Quaternary and Upper-Cretaceous aquifers, and the pumping rate reaches up to 310-380 m3/d and 310-410 m3/d respectively. Withdrawal Palaeogenic mineral water also began in 50th years with the small rate of 10-20 m3/d and increases in 80th years up to 35-40 m3/d. Lower-Cretaceous aquifer use joined to others in 70th years with the average rate of 60-80 m3/d. In 80th years Quaternary aquifers stopped using due to bacteriological contamination. In 90th years mineral groundwater withdrawal considerably decreased, the recent times demand in mineral water spa is growing, and pumping rates are also rising. The groundwater levels primary have been lowered, but in some wells, the phenomena is observed. The groundwater levels after pumping are higher than before, and this is caused by "thermogaslift effect"– formation the gas-cap due to high gaseous factor (20 l/l). The chemical and gas composition changing depends on geological conditions (occurrence of fractures, the closeness of granitic laccolite-peaks, depth of aquifer, etc.) and pumping rate. |