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Hydrogeology of fluvial sediments in the area of the Skorkov and Sojovice water supply systems: evaluation of groundwater flow and chemistry based on new data from monitoring wells
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The Sojovice and Skorkov water supply systems, fed by local infiltration to calcareous sandstones, fluvial aquifer and induced recharge from the Jizera River have been affected by high nitrate content in recent years.
Twelve new wells (Fig. 1) revealed low saturated thickness of alluvial aquifer (average 3.6 m, just 2 m close to river, Table 1), which may limit amount of water derived from river recharge. As the river water has a low nitrate content (˜10 mg/l), while local groundwater is rich in nitrate due to intense agricultural activity (114-210 mg/l) this decreases the dilution of local groundwater by river water infiltration. Based on dilution technique in boreholes the ambient groundwater flow in fluvial aquifer is 0.5-1 m/day.
Groundwater table oscillation depends on the distance from river (Fig. 2). In a well situated 10 m from the river the water table is dominantly controlled by river level oscillation. With increasing distance from the river the oscillation is increasingly damped, so that the water level peaks are longer, less pronounced and the amplitude of water oscillation is decreasing. River water was detected in larger fraction only in wells situated less than 130 m far from the river. Using a simple hydraulic model the water table in well V1 was predicted from oscillation of water table in the Jizera River (Fig. 3).
Sinusoidal variation of groundwater temperature with minimal and maximal temperature delayed 100-160 days after minimal and maximal air temperatures at ground surface indicates that groundwater temperature is affected by conductive heat transport (Fig. 4).
Based on groundwater chemistry the water from fluvial aquifer cannot be distinguished from water from surficial zone of Cretaceous calcareous sandstones (Fig. 5, Table 2). Relatively low content of potassium, sodium and chloride in ground waters with high nitrate content indicates that the nitrates are dominantly derived from agriculture, not from sewage.References
