| dc.description.abstract | Only groundwater sources are used for municipal and individual water supply in Lithuania. In 1994, about 840 thousand m3/d of groundwater was supplied by the municipal water-supply. Water from the main groundwater sources contains about 2-4 mg/1 of iron. Water-supply with iron removing systems contains only 27.7 percent of the whole water content, supplied by water-supply network. Concentration of manganese of our groundwater is up to 0.5 mg/1. There are no special facilities for manganese removal, however its amount decreases together with that of iron in some cases. In the nearest future, 360 thousand m3/d of the output of iron-manganese and 150 thousand m3/d of the output iron removing facilities will be installed in the Lithuanian water supply network. Groundwater for the water-supply system is taken from 10-12 aquifers, the geostructure of which distributes into two complexes of sedimentary rocks: Quaternary (glacial) and Pre-Quaternary. The main factor, determining the hydrogeochemical conditions of iron and manganese development, is the character of connection between aquifer and the atmosphere, i. e. confined watertight bed as well as chemical and biochemical contents of rocks which come into contact with groundwater. The rate of ground flows, water exchange and all the factors mentioned, determine the thermodynamic conditions of aquifers, the regime of gas, temperature, the process of extraction of chemical elements from rocks, dissolving, exchange of ions, crystallizing, etc. Thermodynamic conditions determine more or less the amount of iron and manganese, as well as their forms solution stability. There are 3 types of aquifers, according to their contacts with the atmosphere: 1) open a quifers, 2) semi-open a quifers, 3) close a quifers. This classification is based on intensity of aquifers recharge from run off (or pricipitation). In the yield’s balance of well fields arranged in the open hydrogeological structures, surface flow water and precipitation makes 60-98 percent, in the well fields of semi-open aquifers - 30- 50 percent. The yield of well fields arranged in closed hydrogeological structures is formed by exploiting aquifers and water filtered from neighboring aquifers. The closer an aquifer the greater groundwater mineralization, as well as the concentration of almost all chemical components (except organic substances) and iron bacteria, the less concentration of dissolved oxygen and oxidation-reduction potential. The above mentioned conditions determine high iron and manganese concentrations in closer hydrogeological structures. Besides, the chemical composition of aquifers, watertight bed and recharge sources is important for iron and manganese formation in groundwater utilization. That is why there are abnormal zones in the background of common hydrogeological structures, where specific hydrogeochemical elements determine iron and manganese concentrations, migration forms and stability in groundwater. According to indices, which could determine the technologies of iron and manganese removal from groundwater, five standard groups of Quaternary aquifers and two of Pre-Quaternary ones are distinguished. Zoning of hydrogeochemical conditions was carried out for the substantiation of iron and manganese removing technologies, taking into account prevoius experiments and the information from technical sources. Depending on hydrogeochemical conditions, we propose a preliminary iron and manganese removing technologies in each excepted zone. | eng |
