This study presents the behavior of nitrate in the recharge zone of Tursko well-field (south Wielkopolska, Poland). The presence of a contaminant plume derived from land drainage systems was documented. The contamination is reflected mainly by the high concentration of nitrate ([80 mg/l). It was documented that the contaminant plume migrates in the aquifer along a flow path from the contamination source to the well-field. The factor that retards nitrate migration is bacterial denitrification. As a result of the denitrification, the nitrate concentration decreases systematically along flow lines, but the concentration of other parameters-products of denitrification (sulfate and total hardness)-increases. The occurrence of denitrification was confirmed by measuring the gaseous excess of N 2 (the product of denitrification) and by using the isotopes of 15 N and 18 O dissolved in nitrate. These methods also enable the intensity of denitrification to be assessed. Keywords Land drainage systems Á Groundwater nitrate contamination Á Gaseous nitrogen N 2 Á Nitrogen and oxygen isotopes Á Denitrification
Applications of the Helium (He) method known so far consisted mainly of 4He measurements using a special mass spectrometer. 4He measurements for groundwater dating purposes can be replaced by total He (3He+4He) concentration measurements because the content of 3He can be ignored. The concentrations of 3He are very low and 3He/4 He ratios do not exceed 1.0·10(-5) in most cases. In this study, the total He concentrations in groundwater were determined using the gas chromatographic (GC) method as an alternative to methods based on spectrometry measurement. He concentrations in groundwater were used for the determination of residence time and groundwater circulation. Additionally, the radiocarbon method was used to determine the value of the external He flux (JHe) in the study area. Obtained low He concentrations and their small variation within the ca. 65 km long section along which groundwater flows indicate that it is likely there is relatively short residence time and a strong hydraulic connection between the aquifers. The estimated residence time (ca. 3000 years) is heavily dependent on the great uncertainty of the He concentration resulting from the low concentrations of He, the external 4He flux value adopted for calculation purposes and the 14C ages used to estimate the external 4He flux.
We discuss a study designed to elucidate the genesis and inflow conditions at riverbank filtration wells located on a mountain river. This article seeks to identify the most important drivers of spatio-temporal dynamics of water flow in the hyporheic exchange zone, in natural conditions and conditions disturbed by the water abstraction. In our study we try to contribute to further understanding the dynamics of groundwater mixing with river water in the hyporheic exchange zone. We focus on understanding river/aquifer interactions at the scale of reach of an intake, especially the unidirectional water flows induced by water abstraction. To understand these issues, a two-day field hydrogeological experiment was conducted based on a pumping test of increasing intensity. At each pumping stage, groundwater and river samples were collected to determine the concentration of noble gases, CFCs, SF6, stable isotope content, and the chemical composition of the water. The study results indicate a short pressure propagation time (of the order of several hours) between the intake and the river, which already results in the inflow of water from the riveraquifer mixing zone at low rates of water abstraction by the intake. As pumping rates increase, the conditions of mixing and inflow of water to individual wells stabilize or approach stabilized conditions in less than 1-2 days. The share of river water in the water flux flowing into the intake does not exceed 12%, whereas the ratio of river water to groundwater in the mixing zone is estimated at 1 to 7 or more. The range of the river-aquifer mixing zone may reach up to 170 m from the river and this range can be identified with a good approximation as coinciding with the range of the zone of hyporheic exchange in the study area.
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