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ON QUALITY OF ORDINARY GROUNDWATERS IN THE VISTULA RIVER CATCHMENT AREA

Summary
In the major part of the catchment area of the Vistula River, ordinary groundwater occurs at the greater depths than in western part of the country. This may be explained by differences in evolution of hydrogeological conditions between the areas of the Precambrian and Paleozoic platforms. The catchment area of the Vistula River is characterized by predominance of areas in which the zone of ordinary groundwater is 200 to 800 m thick. The thickness of that zone is, however, highly varying, from some tens to over 1000 m. The Quaternary aquifer is the main one in the scale of the whole catchment area. In about 85%, waters occurring here are characterized by mineralization from 300 to 500 mg/dm3 but in some places the mineralization is up to 1000 mg/dm3 or even higher. The amount of chlorides is usually below 50 mg/dm3 but it may be locally increased (e.g. in Żuławy Wielkie area). In about 20% of cases, general hardness of the waters is over 20°n. The normatives for drinking water are almost always overpassed by the content of iron and manganese.
Waters occurring in the Miocene are markedly coloured which is connected with the presence of brown coals in water-bearing deposits. Waters occurring in Oligocene are characterized by good quality despite of iron content usually above the normative. However, the traces of increased salt content are found in some areas.
Waters occurring in sub-Cenozoic deposits highly vary in mineralization. Typical brines also occur there. The waters are usually of good quality but they may easily become polluted as the deposits are fissured.. The mode of isolation of the major useful groundwater horizons from the influence of agents acting from the surface is variable. Water-bearing fissured Cretaceous rocks are without any isolation throughout large parts of the Lublin Upland. Similar is the case of Quaternary fluvial and sander deposits and, on a smaller scale, some aquifers in the Tatra Mts and Holy Cross Mts, whereas the water-bearing horizons occurring in areas with thick glacial series in northern Poland are usually well isolated.
Intense economic activity resulted in some dozens cases of groundwater pollution. There were recorded spills of oil products, as well as pollutions of water with heavy metals, slat mine waters, municipal as well as industrial sewage. In the last years there was also recorded increase in content of nitrogen compounds in shallow-seated horizons, usually due to intense development in agriculture and horticulture.

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