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There is an increasing need for accurate groundwater-level (GWL) prediction to support effective seasonal water management. It is desirable for forecasting tools to be not only accurate but also ac...

Datos suplementarios en: https://doi.org/10.1016/j.jhydrol.2020.125580, Precipitation measurements are performed mostly by simple automatic rain gauges installed at a certain level above the ground surface, but these methods are often affected by significant measurement errors due to the deformation of the wind field above the rain gauge orifice. In recent years precision lysimeters have emerged, providing an efficient means to improve rainfall measurements and to check the reliability of the standard devices. This article reports comparative rainfall measurements by different devices including a precision lysimeter, two tipping bucket rain gauges and one weighing rain gauge. Rainfall and meteorological data were collected within 3–4.5 years of operation using intervals of 1, 10 and 30 min for registration providing a large data set of exclusively rainfall precipitation without snow and without the effect of freezing. Results show very good agreement of lysimeter, tipping bucket 1 and the weighing pluviometer measurements without any need of precipitation correction, whereas tipping bucket 2 rain gauge underestimated precipitation., Unidad de Sevilla, Instituto Geológico y Minero de España, España, Departament d’Enginyeria Civil i Ambiental, Universitat Politècnica de Catalunya, España

A tailing impoundment situated in the mining district of La Carolina (Spain), which stores waste resulting from the washing of Pb and Ag sulphides, was studied 30 years after it was abandoned. Fibre optic sensors were installed to record humidity, temperature, electrical conductivity and oxygen content in the pores down to a depth of 35.5 m. The oxygen profiles show an oxidised thickness of 5 m, meaning that the speed of the advancing oxidation front is estimated as 15 cm year−1. Sediment samples were obtained from different depths, and parameters such as pH, carbonates and metal(loid)s, among others, were analysed. High concentrations of As (> 500 mg kg−1), Fe (> 34,000 mg kg−1), Mn (> 900 mg kg−1), Pb (> 8000 mg kg−1) and Zn (> 5000 mg kg−1) were found. A piezometer was installed to enable the water inside the tailing pond to be sampled, and this presented high contents of SO42− (> 2400 mg L−1), Fe (> 28,000 μg L−1), Mn (> 7800 μg L−1) and Zn (> 7000 μg L−1), suggesting that the mineral leaching was related to the oscillations in the water table. The water from two drainage adits situated at the foot of the impoundment was also analysed, as well as surface water both upstream and downstream from it. The speciation-saturation models applied for these water samples indicated that in spite of the contamination potential of the impoundment, the deterioration in the quality of the river water is mainly due to the discharge from mining drains and the dissolution processes of precipitates accumulated along the riverbanks.

Groundwaters from shallow aquifers and surface water from rivers of the southern part of Poopo Lake basin within the Bolivian Altiplano have significant quality problems such as high salinity and high concentrations of arsenic (As). The extent of As contamination is observed in the studied groundwater over large parts of the study area. Surface-waters are generally alkaline (pH 8.2–8.7) and oxidizing with dissolved oxygen (DO) concentrations in a range of 2.5–6.6 mg/L The water chemistry is predominantly of Na–Cl–HCO 3 –type, with concentrations of dissolved As in the range of 8.6–117 µg/L with As(V) as the main aqueous species. The concentration of Li varies in the range of 1.1–4.4 mg/L, while other trace elements occur in low concentrations. Groundwaters have a very large range of chemical compositions and the spatial variability of As concentrations is considerable over distances of a few km; dissolved As in groundwater spans over 4 orders of magnitude (3–3497 µg/L), while concentrations of Li have a range of 0.05–31.6 mg/L. Among the investigated drinking-water wells, 90% exceed the WHO guideline value of 10 µg As/L. Electrical conductivity ranges between 295 and 20,900 µS/cm; high salinity is resulting from evaporation under ambient semi-arid climatic conditions. The pH values of the groundwaters are generally slightly alkaline (5.5–8.7) and universally oxidizing, under these conditions As(V) is the prevalent specie. Groundwater As correlates positively with pH, electrical conductivity, Cl − , Na + , HCO 3 − , Ca 2+ and SO 4 2 − . Weathering/dissolution of carbonates, evaporites, halite and plagioclase minerals incorporate Na + and HCO 3 − in solution with consequent pH and alkalinity increase; these are favorable conditions for high mobility of As species. Stable isotopic signatures indicate recharge at the Altiplano with seasonal effects. All surface water and some groundwater samples are enriched due to evaporation, which probably increased concentration of dissolved As.

Summary Many density-dependent groundwater flow simulations rely on a linear equation of state that relates the fluid density to the total dissolved solute content (TDS). This approach ignores non-linear volume of mixing effects, as well as the impact of any chemical reactions. These effects can be considered by using geochemical codes that implement algorithms that calculate the density of a fluid based on the concentration of individual solute species. While in principle such algorithms could be used in-lieu of a linear equation of state in a groundwater model, the computational overhead is such that the use of a more simplified equation of state is preferred. This requires that the assumption of linearity as well as the appropriate value of the linear slope have to be determined. Here, published density measurements of 7 chemically-distinct salt lake brines are compared with densities calculated by PHREEQC-3, confirming the applicability of PHREEQC’s algorithm to salt lake brines, as well as to seawater brines and artificial brines from laboratory experiments. Further, calculations with PHREEQC-3 are used to assess the impact of mineral precipitation reactions during evaporative concentration. Results show that the density–TDS relationship is essentially linear over a wide concentration range, and that slopes range between 0.64 and 0.75, with the upper end of the range applying to Na–CO 3 –Cl brines and the lower end to Na–Cl brines. Mineral precipitation of highly-soluble evaporate minerals such as halite and trona limit TDS, and may lead to considerable errors in coupled flow simulations based on a linear equation of state at high concentrations. Misrepresentation of the slope may lead to an error of up to 20% in the calculated length of the brine nose bordering a salt lake, or of the Rayleigh number, which indicates if a density stratification is stable or not.

Environmental isotope techniques, hydrogeochemical analysis and hydraulic data are employed to identify the main recharge areas of the Mt. Vulture hydrogeological basin, one of the most important aquifers of southern Italy. The groundwaters are derived from seepage of rainwater, flowing from the highest to the lowest elevations through the shallow volcanic weathered host-rock fracture zones. Samples of shallow and deep groundwater were collected at 48 locations with elevations ranging from 352 to 1,100m above sea level (a.s.l.), for stable isotope (δ18O, δD) and major ion analyses. A complete dataset of available hydraulic information has been integrated with measurements carried out in the present study. Inferred recharge elevations, estimated on the basis of the local vertical isotopic gradient of δ18O, range between 550 and 1,200m a.s.l. The isotope pattern of the Quaternary aquifer reflects the spatial separation of different recharge sources. Knowledge of the local hydrogeological setting was the starting point for a detailed hydrogeochemical and isotopic study to define the recharge and discharge patterns identifying the groundwater flow pathways of the Mt. Vulture basin. The integration of all the data allowed for the tracing of the groundwater flows of the Mt. Vulture basin. Se emplearon técnicas isotópicas ambientales, análisis hidrogeoquímicos y datos hidráulicos para identificar las principales áreas de recarga de la cuenca hidrogeológica del Mt. Vulture, uno de los más importantes acuíferos del sur de Italia. Las aguas subterráneas provienen de la infiltración del agua de lluvia, flujo desde las elevaciones más altas a las más bajas a través de zonas de fracturas someras de rocas reservorio volcánicas meteorizadas. Se recolectaron muestras de aguas subterráneas someras y profundas en 48 sitios con alturas en el intervalo que va de 352 a 1,100 m por sobre el nivel del mar (m s.n.m), para análisis de isótopos estables (δ18O, δD) e iones mayoritarios. Se integró una completa base de datos de la información hidráulica disponible con las mediciones llevadas a cabo en el estudio presente. Las alturas de recarga deducidas, estimadas sobre la base de gradiente isotópico vertical local de δ18O, oscilaron entre 550 y 1,200 m s.NM El patrón isotópico del acuífero Cuaternario refleja la separación espacial de diferentes fuentes de recarga. El conocimiento de la configuración hidrogeológica local fue el punto de partida para un estudio isotópico e hidrogeoquímico detallada para definir el esquema de la recarga y descarga identificando las trayectorias de flujo subterráneo de la cuenca del Mt. Vulture. La integración de todos los datos permitió el seguimiento de los flujos de las aguas subterráneas de la cuenca del Mt. Vulture., Department of Geological Sciences, University of Basilicata, Italia, Department of Chemistry, University of Basilicata, Italia, Unidad de Sevilla, Instituto Geológico y Minero de España, España, Institute of Geological Sciences, Freie Universität Berlin, Alemania, Unit Potsdam, Isotope Laboratory, Alfred Wegener Institute for Polar and Marine Research, Alemania, Department of Structural Engineering, Geotechnical Engineering, Engineering Geology, University of Basilicata, Italia

A finite element model was set-up to determine degradation rate constants for p-TSA during rapid sand filtration (RSF). Data used for the model originated from a column experiment carried out in the filter hall of a drinking water treatment plant in Berlin (Germany). Aerated abstracted groundwater was passed through a 1.6m long column-shaped experimental sand filter applying infiltration rates from 2 to 6mh(-1). Model results were fitted to measured profiles and breakthrough curves of p-TSA for different infiltration rates using both first-order reaction kinetics and Michaelis-Menten kinetics. Both approaches showed that degradation rates varied both in space and time. Higher degradation rates were observed in the upper part of the column, probably related to higher microbial activity in this zone. Measured and simulated breakthrough curves revealed an adaption phase with lower degradation rates after infiltration rates were changed, followed by an adapted phase with more elevated degradation rates. Irrespective of the mathematical approach and the infiltration rate, degradation rates were very high, probably owing to the fact that filter sands have been in operation for decades, receiving high p-TSA concentrations with the raw water.

This study reports the impact of hydrological conditions on salinisation and nitrate concentrations of a coastal aquifer located at the Mediterranean Sea, southern Spain. Eighty-two samples of ground- and surface water taken during two extreme hydrological events between 1994 and 1996 at 25 different wells were evaluated with regard to hydrochemistry, focusing on nitrate concentrations and salinisation, which constitute the main hazard of this aquifer. Furthermore, hydrochemical data were analysed by principal component analysis (PCA). Additionally, in 2007 13 ground- and surface water samples taken at 12 different locations were analysed for stable isotopes of D/18O, and one sample was analysed for 15N. Since 1993 until present saltwater intrusion was observed only during dry hydrological conditions in 1994; it showed an irregular salinisation pattern probably related to locally elevated hydraulic conductivities. Nitrate concentrations increase significantly during wet hydrologic conditions owing to uptake of nitrate by rising groundwater. Stable isotopes of groundwater reveal an Atlantic origin of the precipitation that recharges the aquifer and a minor amount of groundwater recharge by the water coming from the La Viñuela reservoir, which is used for irrigation over the aquifer. 15N isotopes point to a considerable input of nitrates derived from organic fertilisers., Institute of Geological Sciences, Freie Universitát Berlin, Alemania, Instituto del Agua, Universidad de Granada, España, Unidad de Murcia, Instituto Geológico y Minero de España, España, Departmento de Geología, Universidad de Málaga, España, Alfred Wegener Institute, Alemania

The microbial degradation of pharmaceuticals found in surface water used for artificial recharge is strongly dependent on redox conditions of the subsurface. Furthermore the durability of production wells may decrease considerably with the presence of oxygen and ferrous iron due to the precipitation of trivalent iron oxides and subsequent clogging. Field measurements are presented for oxygen at a bank filtration site in Berlin, Germany, along with simplified calculations of different oxygen pathways into the groundwater. For a two-dimensional vertical cross-section, oxygen input has been calculated for six scenarios related to different water management strategies. Calculations were carried out in order to assess the amount of oxygen input due to (1) the infiltration of oxic lake water, (2) air entrapment as a result of water table oscillations, (3) diffusive oxygen flux from soil air and (4) infiltrating rainwater. The results show that air entrapment and infiltrating lake water during winter constitute by far the most important mechanism of oxygen input. Oxygen input by percolating rainwater and by diffusive delivery of oxygen in the gas phase is negligible. The results exemplify the importance of well management as a determining factor for water oscillations and redox conditions during artificial recharge.

Summary This research reports the characterisation of ground- and surface-water interaction in the Fuente de Piedra Salt lake basin in southern Spain by a combined approach using hydraulic, hydrogeochemical and stable isotope data. During three sampling campaigns (February 2004, 2005 and October 2005) ground- and surface-water samples were collected for stable isotope studies ( 18 O, D) and for major and minor ion analysis. Hydraulic measurements at multilevel piezometers were carried out at four different locations around the lake edge. Conductivity logs were performed at four piezometers located along a profile at the northern lake border and at two deeper piezometers in the Miocene basin at a greater distance from the lake. To describe processes that control the brine evolution different hydrogeochemical simulations were performed. Hydrogeochemical data show a variety of brines related to thickness variations of lacustrine evaporites around the lake. Salinity profiles in combination with stable isotope and hydraulic data indicate the existence of convection cells and recycled brines. Furthermore restricted ground-water inflow into the lake was detected. Dedolomitisation processes were identified by hydrogeochemical simulations and different brine origins were reproduced by inverse modelling approaches.

Summary This paper reports the hydrogeochemical modelling of reactions that take place during the uptake of weathering products by a rising watertable into a partly oxidized pyrite bearing sediment. The anoxic material used for the column, which is 2 m long, was taken from a core while drilling into a pyrite bearing sediment with an average pyrite content of 0.04 wt%. After packing the column it was drained and maintained in an unsaturated state over a period of 107 days to allow oxygen supply and pyrite weathering. During this period oxygen breakthrough curves were measured. After 108 days the column was flooded with distilled anoxic water from the bottom to the top with an average water table rise of 5 cm per day. The chemical composition of the pore water in the saturated zone as well as the water saturation and the oxygen contents have been monitored over the profile of the column. The compositions of the water samples at different depths of the column were modelled with PHREEQC, defining a one-dimensional reactive transport model regarding the mixing process between the incoming flooding water and the residual pore water of the drained period. Kinetic relations were implemented to account for source terms of acids and acid generating components released during the drained period. This study showed that the evolution of the rising water table can be characterized by almost immediate uptake of gypsum and by kinetically controlled dissolution of pyrite weathering products in combination with mixing processes and dispersion.

Numerical modeling approaches with varying complexity were explored to investigate coupled groundwater flow and geochemical processes in saline basins. Long‐term model simulations of a playa system gain insights into the complex feedback mechanisms between density‐driven flow and the spatiotemporal patterns of precipitating evaporites and evolving brines. Using a reactive multicomponent transport model approach, the simulations reproduced, for the first time in a numerical study, the evaporite precipitation sequences frequently observed in saline basins (“bull's eyes”). Playa‐specific flow, evapoconcentration, and chemical divides were found to be the primary controls for the location of evaporites formed, and the resulting brine chemistry. Comparative simulations with the computationally far less demanding surrogate single‐species transport models showed that these were still able to replicate the major flow patterns obtained by the more complex reactive transport simulations. However, the simulated degree of salinization was clearly lower than in reactive multicomponent transport simulations. For example, in the late stages of the simulations, when the brine becomes halite‐saturated, the nonreactive simulation overestimated the solute mass by almost 20%. The simulations highlight the importance of the consideration of reactive transport processes for understanding and quantifying geochemical patterns, concentrations of individual dissolved solutes, and evaporite evolution., Working group Hydrogeology and Landscape Hydrology, Carl von Ossietzky Universität, Alemania, Hydrogeology group, Freie Universität, Alemania, School of the Environment, Flinders University, Australia, National Centre for Groundwater Research and Training, Flinders University, Australia, Unidad de Sevilla, Instituto Geológico y Minero de España, España, CSIRO Land and Water, Australia, School of Earth and Environment, University of Western Australia, Australia

The groundwater downstream of a former sewage irrigation farm in Berlin is contaminated with ammonium (NH4+) and para-toluenesulfonamide (p-TSA), besides other anthropogenic pollutants. In the field, in situ removal of NH4+ by gaseous oxygen (O2) and air injection is currently being tested. A laboratory column experiment using aquifer material and groundwater from the site was performed to determine whether this remediation technology is also feasible to reduce high p-TSA concentrations in the anoxic groundwater. First, the column was operated under anoxic conditions. Later, compressed air was introduced into the system to simulate oxic conditions. Samples were collected from the column outlet before and after the addition of compressed air. The experiment revealed that whereas p-TSA was not removed under anoxic conditions, it was almost fully eliminated under oxic conditions. Results were modelled using a transient one-dimensional solute transport model. The degradation rate constants for p-TSA increased from 2.8E-06 to 7.5E-05 s–1 as a result of microbial adaption to the change of redox conditions. Results show that O2 injection into an anoxic aquifer is a successful strategy for p-TSA remediation, Institute of Geological Sciences, Freie Universität Berlin, Alemania, Department of Biology and Environmental Sciences, Carl von Ossietzky Universität Oldenburg, Alemania, Unidad de Sevilla, Instituto Geológico y Minero de España, España, DVGW-Technologiezentrum Wasser, Alemania, Department of Laboratories, Berliner Wasser Betriebe, Alemania

We characterize the precipitation and groundwater in a mountainous (peaks slightly above 3000 m a.s.l.), semi-arid river basin in SE Spain in terms of the isotopes 18O and 2H. This basin, with an extension of about 7000 km2, is an ideal site for such a study because fronts from the Atlantic and the Mediterranean converge here. Much of the land is farmed and irrigated both by groundwater and runoff water collected in reservoirs. A total of approximately 100 water samples from precipitation and 300 from groundwater have been analysed. To sample precipitation we set up a network of 39 stations at different altitudes (800–1700 m a.s.l.), with which we were able to collect the rain and snowfall from 29 separate events between July 2005 and April 2007 and take monthly samples during the periods of maximum recharge of the aquifers. To characterize the groundwater we set up a control network of 43 points (23 springs and 20 wells) to sample every 3 months the main aquifers and both the thermal and non-thermal groundwater. We also sampled two shallow-water sites (a reservoir and a river). The isotope composition of the precipitation forms a local meteoric water line (LMWL) characterized by the equation υD D 7Ð72υ18O C 9Ð90, with mean values for υ18O and υD of 10Ð28‰ and 69Ð33‰, respectively, and 12Ð9‰ for the d-excess value. To correlate the isotope composition of the rainfall water with groundwater we calculated the weighted local meteoric water line (WLMWL), characterized by the equation υD D 7Ð40υ18O C 7Ð24, which takes into account the quantity of water precipitated during each event. These values of (dυD/dυ18O), Instituto del Agua, Universidad de Granada, España, Oficina de Granada, Instituto Geológico y Minero de España, España, Institute of Geological Sciences, Freie Universit¨at Berlin, Alemania, Alfred Wegener Institute, Alemania