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Speleothem-like deposits that develop underground in urban areas are an archive of the environmental impact of anthropic activities that has been little studied so far. In this paper, the sulfate content in shallow groundwater from northern Paris (France) is compared with the sulfur content in two 300-year-old urban carbonate deposits that grew in a historical underground aqueduct. The present-day waters of the aqueduct have very high sulfur and calcium contents, suggesting pollution from gypsum dissolution. However, geological gypsum levels are located below the water table. Sulfur content was measured by micro-X-ray fluorescence in these very S-rich carbonate deposits (0.5 to 1% of S). A twofold S increase during the second half of the 1800s was found in both samples. These dates correspond to two major periods of urbanization above the site. We discus three possible S sources: anthropic sources (industries, fertilizers…), volcanic eruptions and input within the water through gypsum brought for urbanization above the studied site (backfill with quarry waste) since the middle of the 19th century. For the younger second half of the studied section, S input from gypsum brought during urbanization was confirmed by the study of isotopic sulfur composition (δ 34 S=+15.2‰ at the top). For the oldest part, several sulfur peaks could be related to early industrial activity in Paris, that caused high local air pollution, as reported in historical archives but also to historical gypsum extraction. This study provides information on the origin and timing of the very high SO 4 levels measured nowadays within the shallow groundwater, thus demonstrating the interest in using carbonate deposits in urban areas as a proxy for the history of urbanization or human activities and their impact on water bodies.2- levels measured nowadays within the shallow groundwater, thus demonstrating the interest in using carbonate deposits in urban areas as a proxy for the history of urbanization or human activities and their impact on water bodies., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Abstract: Chemical (Na, K, Mg, Ca, Cl, SO4, HCO3, Si, Al, Fe, Mn, TOC) and isotopic (18O[H2O], 2H[H2O], 3H[H2O], 14C[DIC], 13C[DIC], 34S[SO4], 18O[SO4]) data were obtained on groundwater collected from fractures inside the consolidated argillaceous formation of Tournemire (Aveyron) and from the aquifers surrounding this formation. Because of the very low transmissivity of such fractures (10−10 m2 s−1), specific devices were developed, for limiting out-gassing and air-contamination of groundwater during the sampling. Two modelling approaches are proposed to account for the chemical evolution of fracture groundwater from Na–Cl–HCO3 to Na–SO4 type. The first one is based on mineral equilibria only and the second one also takes into account the ion-exchange reactions. The two modelling approaches are able to reproduce K+ concentrations and they led to an almost constant pCO2 (10−2.6 atm), which only depends on equilibrium with the calcite–dolomite–kaolinite–quartz assemblage. The modelling of Na+, Ca2+ and behaviours is improved by taking the ion-exchange reactions into account. In some boreholes, the time evolution of the chemical composition of fluids was greatly influenced by SO4 reduction combined with oxidation of dissolved organic C. The isotopic composition of aqueous SO4 in fracture groundwater confirms that SO4 reduction processes have occurred since the drilling of these boreholes, but also previously, during the natural evolution of groundwater. These redox reactions constitute a source of aqueous inorganic C that has to be considered in the computation of groundwater “ages” with 14C. For the studied fracture groundwaters, the maximum age estimates range from 17 to 29ka. This shows that fractures may induce relatively fast groundwater flow, compared to the very long migration times that are calculated by only considering diffusive transport in the rock microporosity. [Copyright &y& Elsevier]

Boron is biologically an essential element but is toxic at high concentrations to plants (above approximately 1 mg/L in irrigation water) and probably to humans: The EU Drinking Water Directive fixes a threshold of 1 mg/L and the World Health Organisation (WHO) set a recommended limit at 0.3 mg/L now increased to 0.5 mg/L. Because of this potential toxicity and the need of implementation of EU regulation on national level, the study of the boron levels in both ground- and surface water is of great significance for water management. In Greece, a significant number of thermal, mineral and superficial water springs are found especially in Northern Greece, that present high boron values rendering such water unacceptable according to the European standards. Nevertheless, such ground waters or borehole water with high temperature and high boron content are used for irrigation and drinking purposes, and could therefore have an antagonistic effect on crop yield and health. In order to study the boron contamination and to elucidate the origin of B, we collected a number of hot and fresh water all over Greece. In all the water sampled, the boron concentration exceeds the limit of 0.3 mg/L, which is the former recommended WHO limit. Moreover, in the irrigation water examined, the boron concentration exceeds the value of 0.75 mg/L, which is the limit for sensitive plants (for plants of moderate and plants of high tolerance, these values vary between 0.75–3 and > 3 mg/L respectively). In all cases, elevated boron could be attributed to natural sources, geothermal activity and/or seawater intrusion into the aquifers. This finding has important implications for water management: In a setting of high natural geochemical background values, source control of the pollution is not possible and water managers have to cope with a local to regional geochemical anomaly that implies boron specific water treatment or mixing with unpolluted resources to bring concentrations down. [ABSTRACT FROM AUTHOR]

In a semi-arid to arid climate context, dependency on groundwater resources may lead to overexploitation and deterioration of water quality. The Continental Intercalaire (CI) aquifer is one such continental-scale aquifer (more than a million of km 2 ), which is mainly confined, poorly recharged but intensely abstracted. To date, the management of this resource relies on hydrogeological modelling and key parameters such as recharge/discharge rate and groundwater dynamics. We use a combination of residence time indicators ( 14 C, 36 Cl, 4 He) and stable isotopes of water ( 2 H and 18 O) to give greater constraint on the groundwater residence time in the CI. In previous studies, 14 C measurements and steady state modelling indicate a residence time of less than 100 ka whereas in others, 36 Cl measurements and transient scenarios modelling suggest a longer residence time (>500 ka). In this study, most of the 14 C measurements are below the limit of detection, establishing residence times greater than 40 ka and confirming the necessity of strict sampling protocols to exclude all air and AMS measurements when low 14 C concentrations are expected. In the Tunisian recharge area, detectable 14 C indicate sporadic recharge episodes (3–7 ka and 29–43 ka), whereas 4 He and 36 Cl concentrations in central areas suggest very old (<2 Ma) groundwaters. In these central areas, chlorine concentration can reach more than 2 g/l. Since 36 Cl concentrations are up to 4 time less than the initial input, we are confident there is no excessive deep 36 Cl production. We characterise five distinct flowpaths reaching the Tunisian discharge area using their isotopic signatures. According to our mixing model, the average contribution from the main recharge area, the Algerian Atlas Mountains, is around 88%. This value is close to hydrogeological models. Conversely, the contribution from the Dahar Mountains is lower than in the hydrogeological modelling (2% against 10%) whereas the Tinhert shows a greater contribution (10% against 1%). Increase of abstraction from the CI can potentially activate the circulation of old brackish groundwaters and dramatically decrease the water quality in the whole system. [ABSTRACT FROM AUTHOR]

Abstract: Following the explosion of reactor 4 at the Chernobyl power plant in northern Ukraine in 1986, contaminated soil and vegetation were buried in shallow trenches dug directly on-site in an Aeolian sand deposit. These trenches are sources of radionuclide (RN) pollution. The objective of the present study is to provide constraints for the Chernobyl flow and RN transport models by characterising groundwater residence time. A radiochronometer 3H/3He method (t 1/2 =12.3a) and anthropogenic tracers including CFC and SF6 are investigated along with the water mass natural tracers Na, Cl, 18O and 2H. The groundwater is stratified, as evidenced by Na and Cl concentrations and stable isotopes (18O, 2H). In the upper aeolian layer, the Na–Cl relationship corresponds to evapotranspiration of precipitation, while in the underlying alluvial layer, an increase in Na and Cl with depth suggests both water–rock interactions and mixing processes. The 3H/3He and CFC apparent groundwater ages increase with depth, ranging from ‘recent’ (1–3a) at a 2m depth below the groundwater table to much higher apparent ages of 50–60a at 27m depth below the groundwater table. Discrepancies in 3H/3He and CFC apparent ages (20–25a and 3–10a, respectively) were observed during the 2008 campaign at an intermediate depth immediately below the aeolian/alluvial sand limit, which were attributed to the complex water transfer processes. Extremely high SF6 concentrations, well above equilibrium with the atmosphere and up to 1112pptv, are attributed to significant contamination of the soils following the nuclear reactor explosion in 1986. The SF6 concentration vs. the apparent groundwater ages agrees with this interpretation, as the high SF6 concentrations are all more recent than 1985. The persistence of the SF6 concentration suggests that SF6 was introduced in the soil atmosphere and slowly integrated in the groundwater moving along the hydraulic gradient. The apparent age distribution in the lumped parameter models suggests an exponential or piston flow model in the upper geological section, followed by more pronounced mixing processes in the lower section. [Copyright &y& Elsevier]