Distribution of tritium-helium groundwater ages in a large Cenozoic sedimentary basin (North German Plain) (original) (raw)
Related papers
Water Resources Research, 1998
The 3 H-3 He dating method is applied in a buried-valley aquifer near Dayton, Ohio. The study area is large, not all sampling locations lie along well-defined flow paths, and existing wells with variable screen lengths and diameters are used. Reliable use of the method at this site requires addressing several complications: (1) The flow system is disturbed because of high pumping rates and induced infiltration; (2) tritium contamination is present in several areas of the aquifer; and (3) radiogenic helium concentrations are elevated in a significant number of the wells. The 3 H-3 He ages are examined for self-consistency by comparing the reconstructed tritium evolution to the annual weighted tritium measured in precipitation; deviations result from dispersion, tritium contamination, and mixing. The 3 H-3 He ages are next examined for consistency with chlorofluorocarbon ages; the agreement is poor because of degradation of CFCs. Finally, the 3 H-3 He ages are examined for consistency with the current understanding of local hydrologic processes; the ages are generally supported by hydrogeologic data and the results of groundwater flow modeling coupled with particle-tracking analyses.
Tritium/3He dating of shallow groundwater
Earth and Planetary …, 1988
Combined tritium/ 3 He data from three multi-level sampling wells (DFG 1, DFG 4, DFG 7) located at Liedern/ Bocholt, West Germany, are presented and principles of the tritium/ 3 He method in shallow groundwater studies are discussed. The 3 He excess produced by radioactive ...
GEOCHEMICAL JOURNAL
Based on previous studies in Hungary the average groundwater recharge is 50 to 100 mm/yr on sandy soils in the Great Hungarian Plain, while much higher values between 150 and 200 mm/yr have been determined in karstic regions using tritium-based techniques (Groundwaters in Hungary, Ministry for Environment and Water, Guide, 2006). Other studies provided 60 mm/yr and 82 mm/yr average recharge rates based on steadystate water balance models and numerical flow models in the Nyírség area during the period 1961-1990 (Ács and Simonffy, 2012). In this study, our approach has been the application of the two environmental tracers tritium and 3 H/ 3 He to determine the apparent ages of water. In December 1998 well nests were constructed at Méntelek and Fischerbócsa, allowing tritium-depth profiles to be measured based on samples from six and 11 different depths respectively. The simple tritium-peak method was applied by Deák after the 1998 field measurements to estimate the average groundwater recharge at the two investigated test sites on the Danube-Tisza Ridge (Deák, 2006). The first rough
1] Springs and gaining streams are locations where groundwater flow paths naturally converge and discharge as a flow-weighted mixture of water from the contributing aquifer. The age of that water is therefore a good measure of the mean transit time (MTT) of the contributing aquifer. The question examined in this paper is whether tritiogenic helium-3 and tritium ( 3 He trit -3 H) can be used to estimate MTT in these settings. To answer that question two factors must be considered: (1) the loss of 3 He from discharging groundwater as it becomes exposed to the atmosphere, and (2) the accuracy with which MTT can be determined from flow-weighted 3 He trit -3 H concentrations. These concepts were tested at the Fischa-Dagnitz system (springs and emerging stream), which is part of the southern Vienna Basin aquifer. Conducting a gas tracer test, gas exchange coefficients (l) were established for helium-4 ( 4 He) and krypton-84 ( 84 Kr), and derived for helium-3 ( 3 He) and neon-20 ( 20 Ne). By simulating measured groundwater inflow and gas transport in the stream, groundwater inflow concentrations for 3 He, 4 He, 20 Ne, and 84 Kr were estimated. Correcting for the various sources of He, the tritiogenic helium-3 ( 3 He trit ) concentration of inflowing groundwater was estimated at 8.3 tritium units (TU). The flow-weighted groundwater concentration of 3 H, determined from 22 stream water samples, was estimated at 9.8 TU. Assuming that the relationship between flow amount and transit time at Fischa-Dagnitz is characterized by a hybrid dispersion-exponential age model, the 3 He trit -3 H ratio (8.3/9.8 = 0.85) defines a MTT of 8 years. The validity of this estimate was evaluated by comparison to a long-term 3 H time series that exists for Fischa-Dagnitz. The likely range of MTT's derived from the measured 3 H time series is 11 to 14 years. (2010), Age dating base flow at springs and gaining streams using helium-3 and tritium: Fischa-Dagnitz system, southern Vienna Basin, Austria, Water Resour. Res., 46, W07503,
The origin of helium in deep sedimentary aquifers and the problem of dating very old groundwaters
Noble gases, inert elements having isotopes produced by the decay of long half-life radionuclides, offer a powerful approach for tracing fluid circulation and dating groundwa-ters.The (U + Th)-4He water ages-calculated from the accumulation rate in water of radio-genic 4He produced by decay of U and Th contained in the aquifer rocks-is frequently higher than the hydrological ages. This discrepancy is generally interpreted by two contrasting models: (i) heterogeneities of the aquifers, which allow water stagnation and accumulation of large amounts of radiogenic 4He, or (ii) addition of 4He produced in deeper regions of the continental crust. In this contribution, we propose that the apparent contrast between (U + Th)-4He ages and hydrological ages in the Paris Basin reflects the mixing of different types of water, having different residence times. We show, using the helium isotopic signatures of waters, that this mixing occurs between three aquifers, the Middle Jurassic, the Triassic and the Palaeozoic basement, which have contrasting helium contents and heterogeneous chemical compositions and permeabilities. The difference of radiogenic 4He/4~ ratios between the aquifers of Triassic and Middle Jurassic strongly suggests that a significant fraction of helium is produced in the aquifer rocks. This implies residence times for groundwaters circulating in the Middle Jurassic carbonate aquifer much longer than those obtained from hydrological studies. Independent fluid age estimates, based on the ground palaeotemperatures recorded in the same groundwaters by the atmosphere-derived noble gases, seem to confirm the presence of very old groundwaters in the Paris Basin.
Journal of Hydrology, 2004
Multi-tracer study of the Malm (Upper Jurassic) limestone aquifer in north-western part of Cracow, Poland, revealed the existence of much older waters than those estimated from Darcy's law. The following environmental tracers were used: 3 H, 14 C, d 13 C, d 18 O, d 2 H, 4 He, Ne, Ar, Kr, Xe, 3 He/ 4 He and 40 Ar/ 36 Ar in combination with water chemistry. The natural drainage of unconfined parts of the aquifer is by springs and streams, with a dominant presence of modern and pre-bomb era Holocene waters, whereas the confined part is drained only by upward leakage through thick Miocene clays in river valleys, mainly in the Vistula (Wisła) river valley. As a consequence, the confined part contains much older waters. Their glacial ages are indicated by d 18 O and d 2 H values significantly more negative than those found for modern recharge and by noble gas temperatures reduced by ca. 4.5 8C when compared to the present-day mean annual air temperatures. Quantitative age interpretation of 14 C is regarded unreliable due to isotope exchange between dissolved and solid carbonates as suggested by d 13 C values of DIC in the range of 2 0.6 to 2 6.1‰ for the confined part of the aquifer. Similarly, quantitative 4 He dating turned out to be unreliable, though 4 He excess values (0.93-5.45 £ 10 26 cm 3 STP/g) and very low 14 C contents (0.0-5.5 pmc) suggest glacial ages. Changes in hydrochemistry also indicate a long-lasting water -rock interaction probably dominated by diffusion-controlled exchange with overlying and underlying formations. Admixture of older water ascending from underlying formations is observed at two sites. That older water is also supposed to be of Quaternary age as the 40 Ar/ 36 Ar of the mixture remains equal to the atmospheric ratio. Great tracer ages are shown to result mainly from the delay of solute velocity with respect to the velocity of mobile water, caused by diffusive exchange between mobile water in the fissures (porosity of 0.0001-0.001) and stagnant water in the matrix (porosity of , 0.06). This stagnant water in the porous matrix is the main water reservoir in the Malm aquifer. In the erosion structures of the Malm limestones, close to the Cracow centre on the southern side of the Vistula river, Tertiary sands are deposited under clay cover. Prior to this study, the origin and age of mineral water exploited from these sands was controversial. However, tracer data indicated meteoric water recharged at the end of the last glacial, and excluded an admixture of connate 0022-1694/$ -see front matter q .pl (K. Różański). marine water from adjacent formations. In one well a 10% admixture of modern water was observed with the mean age of about 30 years as determined from the lumped-parameter modelling of the tritium data. The recharge is supposed to take place indirectly through nearby Malm horsts and/or by seepage through Miocene clays in unidentified areas, with dissolution of evaporites as the main source of chemical components. The glacial ages of waters in the confined parts of the Malm aquifer and in Tertiary sands indicate their low vulnerability to anthropogenic pollution. q
Groundwaters from the Tithonian/Kimmeridgian, Oxfordian and Upper Dogger aquifers, within the eastern part of the Paris basin (France), were characterised using 3H, 14C and 36Cl, and noble gases tracers, to evaluate their residence times and determine their recharge period. This information is an important pre- requisite to evaluating the confinement properties of the Callovo-Oxfordian clay formation sandwiched between the Oxfordian aquifer and the Dogger aquifer, currently being investigated by the French nuclear waste management agency (Andra) for radioactive waste disposal. Data presented in this paper are used to test 4 hypotheses. (1) The Oxfordian limestone is isolated from the overlying Tithonian/Kimmeridgian surface aquifer. This first hypothesis is supported by the presence of measurable 3H activities in groundwaters from the surface aquifer (6–11 TU), and by its absence in groundwaters derived from deeper aquifers (<3 TU), as well as by geochemical data from earlier studies. (2) The Callovo-Oxfordian clay sequence in the vicinity of the URL serves as an effective barrier to advective flow and transport between the underlying Upper Dogger aquifer and the overlying Oxfordian limestone aquifer. This second hypothesis is supported by relatively low concentrations of Cl (3.5–78 mg.L-1), Na (15–145 mg.L-1), Br (0.08–0.4 mg.L-1) and 4Herad (0.2–2.3 ccSTP.g-1) and slightly higher 36Cl/Cl ratios (2.7–59x10-15 at.at-1) in groundwaters from the Oxfordian aquifer, compared to those from the Upper Dogger aquifer (345–4027 mgCl.L-1 ; 402–2390 mgNa.L-1 ; 1.8–22.2 mgBr.L-1 ; 1.6–37.2 ccSTP He g-1 ; 1–5x10-15 at36Cl.at -1Cl). (3) Groundwaters from the Oxfordian aquifer, in the vicinity of URL are pre-Holocene, with residence times exceeding 10 ka. Geochemical and isotopic lines of evidence for this hypothesis include:(a) delta13C values measured on Oxfordian aquifer waters that are close to delta13C of the aquifer matrix, reflecting strong isotopic exchange over several thousand years; (b) noble-gas temperatures that indicate recharge temperatures between 3 and 8.6°C, lower by 2–7°C than the modern average temperature in this area ; (c) radiogenic 4He concentrations between 0.16x10-5 and 2.3x10-5 ccSTP.g-1 of water, about 2–3 orders of magnitude greater than the 4He concentration of air-equilibrated water. (4) Groundwater residence time for the Upper Dogger aquifer in the vicinity of the URL probably exceed several hundred thousand years. Such long residence times are indicated by the accumulation of radiogenic He-up to 37x10-5 ccSTP.g-1 assuming a closed system.Primary contributors to uncertainties in interpretation of the data presented in this paper are the lack of: – well-defined 36Cl/Cl input ratio; – knowledge about the 4Herad sources for Oxfordian and Dogger aquifers; – knowledge about transport processes occurring through the Dogger aquifer, and the extensive dilution of initial 14C activities by dissolution/exchange with aquifer matrix. Overall, however, although the data presented in this paper remain semi-quantitative due to inevitable intrinsic limitations of the methods, none contradict the hypotheses of long residence times and aquifer isolation in the vicinity of the URL.
Geologija. Geografija
Radioactive decay and mixing leads to tritium activity decrease in groundwater. In south-eastern Lithuania, the unconfined layer and precipitation water tritium activity decrease rate is dominated by radioactive decay for the period of 1980–2013. Confined aquifers are vastly affected by mixing; therefore, it is hard to predicted tritium activity values. To achieve it, the monitoring type of sampling must be applied in order to calculate tritium activity gradient value. Moreover, gradient values in different sampling points along the water pathway must be similar. It is a necessary condition when comparing theoretical decay curves with actually calculated. Only the shallowest confined aquifer (ag II–III md-gr) in this study met these conditions. An additional method for modelled data interpretation was tritium peak analysis. According to the modelled tritium peak, a few possible dating water age alternatives exist. The data analysis suggests that no certain water age could be deter...