HYDROGEOCHEMISTRY OF A DEEP GAS-STORAGE CAVERN, CZECH REPUBLIC

Abstract

Groundwater was occasionally found during the construction of a deep gas-storage cavern at approximately 1 km below land surface near Pribram, Czech Republic. The individual groundwater seeps, with a discharge not exceeding 0.01 l/s and T = 3 °C, were usually a strongly alkali natural solution with maximum pH values of 9.9 and TDS concentrations from 0.2 to 0.86 g/l; Na+, HCO3-, and Cl- ions were the major dissolved chemical constituents. Two main groundwater quality groups were defined: Na-Cl and Na-HCO3. Based on the stable isotope (18O/ 16O, D/H), tritium and radiocarbon analyses, some groundwater originated from rainwater infiltrating during the Upper Pleistocene Epoch. Strontium in the groundwater of the crystalline aquifer was isotopically homogenous and equilibrates with strontium in the granite and granodiorite of the gas-storage cavern. Based on the information, the deep groundwater seeps were associated with slow or 'stagnant' groundwater circulation, without direct relation to the recent groundwater of faster circulation near the surface, which is periodically recharged by precipitation. The results of the water-quality monitoring of the deep groundwater seeps have been used in estimating the insulating properties of the neighboring rocks near the gas-storage cavern. This information will be important in the safe operation of the gas-storage cavern.