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An efficient preconcentration technique based on ultrasonic-assisted ionic liquid-based dual microextraction (UA-ILDµE) method has been developed to preconcentrate the lead (Pb +2 ) in ground and stored rain water. In the current proposed method, Pb +2 was complexed with a chelating agent (dithizone), whereas an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) was used for extraction purpose. The ultrasonic irradiation and electrical shaking system were applied to enhance the dispersion and extraction of Pb +2 complex in aqueous samples. For second phase, dual microextraction (DµE phase), the enriched Pb +2 complex in ionic liquid, extracted back into the acidic aqueous solution and finally determined by flame atomic absorption spectrometry. Some major analytical parameters that influenced the extraction efficiency of developed method, such as pH, concentration of ligand, volume of ionic liquid and samples, time of shaking in thermostatic electrical shaker and ultrasonic bath, effect of back extracting HNO 3 volume, matrix effect, centrifugation time and rate were optimized. At the sample volume of 25 mL, the calculated preconcentration factor was 62.2. The limit of detection of proposed procedure for Pb +2 ions was found to be 0.54 μg L −1 . The validation of developed method was performed by the analysis of certified sample of water SRM 1643e and standard addition method in a real water sample. The extraction recovery of Pb +2 was enhanced ≥ 2% with shaking time of 80 s in ultrasonic bath as compared to used thermostatic electrical shaker, where for optimum recovery up to 10 min was required. The developed procedure was successfully used for the enrichment of Pb +2 in ground and stored rain water (surface water) samples of an endemic region of Pakistan. The resulted data indicated that the ground water samples were highly contaminated with Pb +2 , while some of the surface water samples were also have higher values of Pb +2 than permissible limit of WHO. The concentration of Pb +2 in surface and ground water samples was found in the range of 17.5–24.5 and 25.6–99.1 μg L − 1 respectively. [ABSTRACT FROM AUTHOR]

During the March-May 2014 Colorado River Delta pulse flow, approximately 102 × 10 6 m 3 (82,000 acre-feet) of water was released into the channel at Morelos Dam, with additional releases further downstream. The majority of pulse flow water infiltrated and recharged the regional aquifer. Using groundwater-level and microgravity data we mapped the spatial and temporal distribution of changes in aquifer storage associated with pulse flow. Surface-water losses to infiltration were greatest around the Southerly International Boundary, where a lowered groundwater level owing to nearby pumping created increased storage potential as compared to other areas with shallower groundwater. Groundwater levels were elevated for several months after the pulse flow but had largely returned to pre-pulse levels by fall 2014. Elevated groundwater levels in the limitrophe (border) reach extended about 2 km to the east around the midway point between the Northerly and Southerly International Boundaries, and about 4 km to the east at the southern end. In the southern part of the delta, although total streamflow in the channel was less due to upstream infiltration, augmented deliveries through irrigation canals and possible irrigation return flows created sustained increases in groundwater levels during summer 2014. Results show that elevated groundwater levels and increases in groundwater storage were relatively short lived (confined to calendar year 2014), and that depressed water levels associated with groundwater pumping around San Luis, Arizona and San Luis Rio Colorado, Sonora cause large, unavoidable infiltration losses of in-channel water to groundwater in the vicinity. [ABSTRACT FROM AUTHOR]

Landslides reactivated by groundwater variations are usually characterized by low displacement rate with deformations essentially concentrated within a narrow shear zone above which the unstable soil mass moves like a rigid body. A simplified method was recently proposed by Conte and Troncone [1] for a preliminary evaluation of the mobility of these landslides. In the present study, this method is extended by incorporating a calibration procedure for a direct evaluation of some parameters which are difficult to obtain experimentally. Some case studies are analysed to validate the present approach. [ABSTRACT FROM AUTHOR]

We collected samples from sea water, runnel water, beach pore waters, water from the unconfined surficial aquifer discharging at the beach face, groundwater, and rainwater from the Aquitanian coast in order to determine the flux of dissolved inorganic nitrogen (DIN), phosphorus and silica from terrestrial submarine groundwater discharge (SGD). The flux of fresh groundwater was obtained from a water balance calculation based on precipitation and evapotranspiration and assessment of the coastal watershed from hydrograph separation. Waters with intermediate salinities between sea water and freshwaters are found all along the 240-km-long coast, indicating that SGD is ubiquitous. The estimated fresh water flux is 2.25 m 3 d − 1 m − 1 longshore. Terrestrial SGD provides a DIN flux of 9·10 6 mol each year to the adjacent coastal zone. This flux is about four times lower than the release of DIN due to tidally driven saline SGD. The freshwater DIN flux is low because the upland land use consists almost exclusively of pine forest. Dissolved organic nitrogen represents more than 60% of the total dissolved nitrogen flux. Dissolved iron, phosphorus and silica have much higher concentrations in the anoxic forest aquifer than in the fresh-water end-member of the subterranean estuary sampled in the upper beach aquifer. This suggests that the salinity gradient of the estuary does not correspond to a redox gradient. The redox front between anoxic groundwater and fresh oxic waters occurs below the soil-depleted foredune/yellow dune. Anoxic P- and Si-rich waters seep directly on the beach face only in the north Gironde, where the foredunes are eroded. This study reveals the role of the sandy foredune aquifer in biogeochemical fluxes from SGD, which is to dilute and oxidize waters from the unconfined surficial upland aquifer. [ABSTRACT FROM AUTHOR]

Annual U.S. expenditures of $2B for site characterization invite the development of new technologies to improve data quality while reducing costs and minimizing uncertainty in groundwater monitoring. This work presents a new instrument for time-integrated sampling of environmental fluids using in situ solid-phase extraction (SPE). The In Situ Sampler (IS2) is an automated submersible device capable of extracting dissolved contaminants from water (100s–1000s mL) over extended periods (hours to weeks), retaining the analytes, and rejecting the processed fluid. A field demonstration of the IS2 revealed 28-day average concentration of hexavalent chromium in a shallow aquifer affected by tidal stresses via sampling of groundwater as both liquid and sorbed composite samples, each obtained in triplicate. In situ SPE exhibited 75 ± 6% recovery and an 8-fold improvement in reporting limit. Relative to use of conventional methods (100%), beneficial characteristics of the device and method included minimal hazardous material generation (2%), transportation cost (10%), and associated carbon footprint (2%). The IS2 is compatible with commercial SPE resins and standard extraction methods, and has been certified for more general use (i.e., inorganics and organics) by the Environmental Security Technology Certification Program (ESTCP) of the U.S. Department of Defense. [ABSTRACT FROM AUTHOR]

Nitrate concentrations in groundwater frequently exceed permissible levels for potable water in intensive agricultural regions. It is critical to develop highly efficient techniques for the removal of nitrate at low cost, without the addition of chemicals. In this study, we report on an advanced and efficient approach, referred to as electrodeionization (EDI), for effectively removing and concentrating nitrate with low energy consumption. An additional merit of this process was that hardness ions, such as Ca 2+ and Mg 2+ , were also simultaneously removed from the dilute compartment and recovered in concentrate compartment. Furthermore, the limiting current was systematically investigated and the impacts of different applied currents, water flow rates, and ratios of cationic and anionic exchange resins on the performance of nitrate removal were studied. When treating actual groundwater samples, the EDI system exhibited an excellent removal rate for all ions (>90%) under a low and constant cell voltage. The results confirmed that the EDI process is suitable for the continuous and highly efficacious removal and recovery of nitrate and hardness ions in ground water. [ABSTRACT FROM AUTHOR]

Canola ( Brassica napus ) is an oil-seed crop that is adapted to the northern High Plains of the USA and is considered a viable rotational and biofuel crop. However, decreased ground water allocations have necessitated determining the impact of limited irrigation on canola productivity. The objectives of this research were to determine the effects of a range of irrigation from none to fully irrigated on yield, oil content, soil water changes and water productivity of spring canola. The study was conducted for four growing seasons at three locations in western Nebraska. Two sites had sandy soils whereas the other was a silt loam. Glyphosate tolerant canola was planted late March to early April. Cumulative irrigation treatments were 0, 100, 200, and 300 mm of water with the highest rate adjusted to be non-ET limiting. Canola extracted soil water from depths greater than 1.2 m in both fine textured and sandy soils making it a good alternative for deficit irrigation. Canola responded well to irrigation during dry years but showed little response in above average precipitation years. A water use efficiency of 7.6 kg mm −1 with a threshold of 123 mm was observed. Canola seed yield ranged from 440 to 3280 kg ha −1 with 165 and 582 mm of cumulative ET. During drier years, canola exhibited peak values in water use at 8–9 weeks after planting. Deficit irrigation reduced ET and yield and hastened maturity during drier years. Oil content was increased by irrigation during drier years with no effect shown when precipitation was above average. Oil content ranged from 30 to 50% depending on year and irrigation level. The water response provided benefits of not only higher yield, but also higher oil content which makes deficit irrigated canola an attractive alternative production and biofuel crop for this region. [ABSTRACT FROM AUTHOR]

Different magnesium (Mg) containing nanoparticles, magnesium hydroxide, (Mg(OH) 2 ), magnesium oxide (NMgO) and activated magnesium oxide (AcMgO) were tested, in a first step, to identify a highly efficient adsorbent for groundwater (GW) defluoridation. Consequently, the NMgO, which was the most suitable material, was impregnated on a granular matrix (sand) to produce a reactive filtration material (GSN). Amongst the different features (surface area, total pore volume, pH pzc mineralogical assemblage and particle size) of the investigated magnesia species, only the particle size had profound influence on defluoridation efficiency. Kinetic analysis showed that the defluoridation process was limited by pore diffusion while experimental evidences showed that both specific and non-specific mode of interaction were the underlying mechanism of the process. In the defluoridation system, the thermodynamic parameters (Δ G ) of precipitation of magnesium fluoride (MgF 2 ) was negative but no MgF 2 peak was observed in the XRD pattern of the spent GSN. The defluoridation efficiency of the GSN in a real groundwater system at different initial F − concentrations was comparable with that of simulated water. The evaluation of the quality characteristics of the treated water showed that Mg 2+ that leached from the GSN enhanced the total hardness while the concentrations of Ca 2+ was greatly reduced. Reduction in the magnitude of the total inorganic carbon content of the GW was observed. [ABSTRACT FROM AUTHOR]

This study investigates the performance of granular dead anaerobic sludge (GDAS) bio-sorbent as permeable reactive barrier (PRB) in removing lead from a contaminated shallow groundwater. Batch tests have been performed to characterize the equilibrium sorption properties of the GDAS and sandy soil in lead-containing aqueous solutions. A 1D advection–dispersion equation, solved by computer solutions Multiphysics 3.5a software which is based on finite element method, has been used to simulate the equilibrium transport of Pb+2ions within groundwater. This equation has taken into account the pollutant sorption onto the GDAS and sandy soil which is performed by Langmuir equation. Numerical results proved that the PRB plays a potential role in the restriction of the contaminant plume migration. These results also show that the thicker PRB is better than the thinner ones in lead treatment and the barrier starts to saturate with contaminant as a function of the travel time. A good agreement between the predicted and experimental results was recognized with root mean square error not exceeded the 0.0499. [ABSTRACT FROM PUBLISHER]

The possibility of using zero-valent iron (ZVI) as permeable reactive barrier (PRB) to remove zinc from a contaminated groundwater was investigated. Batch equilibrium tests were carried out. The effects of many parameters such as contact time between adsorbate and adsorbent (0–240 min), initial pH of the solution (4–8), sorbent dosage (1–12 g/100 ml), initial metal concentration (50–250 mg/l), and agitation speed (0–250 rpm) were studied. The best values of these parameters that achieve the maximum removal efficiency of Zn+2(=91%) were 3 h, 5, 10 g/100 ml, 50 mg/l, and 200 rpm, respectively. Langmuir isotherm model gives better fit for the sorption data of Zn+2ion by ZVI than Freundlich model under the studied conditions. Finite difference method and COMSOL Multiphysics 3.5a software, which is based on finite element method, were used to simulate the one-dimensional equilibrium transport of zinc through sandy aquifer with and without presence of PRB. The predicted and experimental results proved that the PRB plays a potential role in the restriction of the contaminant plume migration. A reasonable agreement between these results was recognized with root mean squared error not exceeded the 0.1487. [ABSTRACT FROM PUBLISHER]

The Pampean plain is the most productive region in Argentina. The Pampeano Aquifer beneath the Pampean plain is used mostly for drinking water. The study area is the sector of the Pampeano Aquifer underlying the Del Azul Creek basin, in Buenos Aires province. The main objective is to characterize the chemical and isotopic compositions of groundwater and their origin on a regional scale. The methodology used involved the identification and characterization of potential sources of solutes, the study of rain water and groundwater chemical and isotopic characteristics to deduce processes, the development of a hydrogeochemical conceptual model, and its validation by hydrogeochemical modelling with PHREEQC. Groundwater samples come mostly from a two-depth monitoring network of the “Dr. Eduardo J. Usunoff” Large Plains Hydrology Institute (IHLLA). Groundwater salinity increases from SW to NE, where groundwater is saline. In the upper basin groundwater is of the HCO 3 -Ca type, in the middle basin it is HCO 3 -Na, and in the lower basin it is ClSO 4 –NaCa and Cl–Na. The main processes incorporating solutes to groundwater during recharge in the upper basin are rain water evaporation, dissolution of CO 2 , calcite, dolomite, silica, and anorthite; cationic exchange with Na release and Ca and Mg uptake, and clay precipitation. The main processes modifying groundwater chemistry along horizontal flow at 30 m depth from the upper to the lower basin are cationic exchange, dissolution of silica and anorthite, and clay precipitation. The origin of salinity in the middle and lower basin is secular evaporation in a naturally endorheic area. In the upper and middle basins there is agricultural pollution. In the lower basin the main pollution source is human liquid and solid wastes. Vertical infiltration through the boreholes annular space during the yearly flooding stages is probably the pollution mechanism of the samples at 30 m depth. [ABSTRACT FROM AUTHOR]

Trace organic compounds (TOrCs) in municipal wastewater effluents that are discharged to streams are of potential concern to ecosystem and human health. This study examined the fate of a suite of TOrCs and estrogenic activity in water and sediments in an effluent-dependent stream in Tucson, Arizona. Sampling campaigns were performed during 2011 to 2013 along the Lower Santa Cruz River, where TOrCs and estrogenic activity were measured in aqueous (surface) and solid (riverbed sediment) phases. Some TOrCs, including contributors to estrogenic activity, were rapidly attenuated with distance of travel in the river. Those TOrCs that are not sufficiently attenuated and percolate to ground water have in common low biodegradation probabilities and low octanol–water distribution ratios. Independent experiments showed that attenuation of estrogenic compounds may be due in part to indirect photolysis caused by formation of organic radicals from sunlight absorption. Hydrophobic TOrCs may accumulate in riverbed sediments during dry weather periods, but riverbed sediment quality is periodically affected through storm-related scouring during periods of heavy rainfall and runoff. Taken together, evidence suggests that natural processes can attenuate at least some TOrCs, reducing potential impacts to ecosystem and human health. [ABSTRACT FROM AUTHOR]

The economic evaluation of defluoridation of Sahara groundwater is presented for three processes: electrodialysis, reverse osmosis and the electrochemical bipolar reactor (EBR). The economic study was accomplished for a drinking water unit production of 100 m3/h. One of the findings was that the costs per cubic metre of treated water obtained with different processes were not too costly for the states of the North African region. The results also indicated that the most efficient process uses the EBR, followed by the electrodialysis and reverse osmosis process. However, the water produced by the first process does not have the required quality for drinking water; therefore, it has to be utilised for agricultural purposes. On the other hand, the electrodialysis unit do produce quality drinking water and appears to be an interesting solution to the fluorisis disease. Reverse osmosis method technique provides higher quality of drinking water with a salinity not exceeding 0.1 gsalts/l. [ABSTRACT FROM PUBLISHER]

Summary A bibliometric analysis was conducted to evaluate groundwater research from different perspectives in the period 1993–2012 based on the Science Citation Index-Expanded (SCIE) database. The bibliometric analysis summarizes output, categorical, geographical, and institutional patterns, as well as research hotspots in global groundwater studies. Groundwater research experienced notable growth in the past two decades. “Environmental sciences”, “water resources” and “multidisciplinary geosciences” were the three major subject categories. The Journal of Hydrology published the largest number of groundwater-related publications in the surveyed period. Major author clusters and research regions are located in the United States, Western Europe, Eastern and Southern Asia, and Eastern Australia. The United States was a leading contributor to global groundwater research with the largest number of independent and collaborative papers, its dominance affirmed by housing 12 of the top 20 most active institutions reporting groundwater-related research. The US Geological Survey, the Chinese Academy of Sciences, and the USDA Agricultural Research Service were the three institutions with the largest number of groundwater-related publications. A keywords analysis revealed that groundwater quality and contamination, effective research technologies, and treatment technologies for water-quality improvement were the main research areas in the study period. Several keywords such as “arsenic”, “climate change”, “fluoride”, “groundwater management”, “hydrogeochemistry”, “uncertainty”, “numerical modeling”, “seawater intrusion”, “adsorption”, “remote sensing”, “land use”, “USA”(as study site), and “water supply” received dramatically increased attention during the study period, possibly signaling future research trends. [ABSTRACT FROM AUTHOR]

Summary High As groundwater has been found in shallow aquifers of the flat plain of the Hetao basin, but little is known about As concentration in deep groundwaters around piedmont areas, which are the major drinking water resources. One hundred and three groundwater samples from wells with depths >50 m and seven samples from one multi-level monitoring well (89 m in depth) were analyzed for chemical compositions and 18 O and D isotopes to examine the geochemical processes controlling As mobilization. According to hydrogeological setting, chemical and isotopic characteristics of deep groundwater, three distinguished hydrogeochemical zones are delineated, including Recharge-Oxic Zone (Zone I), Groundwater Flow-Moderate Reducing Zone (Zone II), and Groundwater Flow-Reducing Zone (Zone III). Zone I is located in proximal fans in the recharge area with oxic conditions, where low As groundwater generally occurs. In Zone II, located in the intermediate between the fans and the flat plain with Fe-reduction predominated, groundwater As is moderate. Zone III lies in the flat plain with the occurrence of SO 4 2 - reduction, where high As groundwater is mostly found. This indicates that release of As to groundwater is primarily determined by reduction sequences. Arsenic is immobilized in O 2 / NO 3 - reduction stage in Zone I and released in Fe-reducing conditions of Zone II, and displays a significant elevated concentration in SO 4 -reducing stage in Zone III. Dissolution of carbonate minerals occurs in Zone I, while Ca 2+ and Mg 2+ are expected to precipitate in Zone II and Zone III. In the multi-level monitoring well, both chemical and isotopic compositions are dependent of sampling depths, with the similar trend to the hydrogeochemical zonation along the flow path. The apparent increases in δD and δ 18 O values in Zone III reveal the possibility of high As shallow groundwater recharge to deep groundwater. It indicates that deep groundwaters in proximal fans have low As concentrations and are considered as safe drinking water resources in the Hetao basin. However, high As concentration is frequently observed in deep groundwater in the flat plain, which should be routinely monitored in order to avoid chronic As poisoning. [ABSTRACT FROM AUTHOR]

Summary Exploitation of groundwater from shallow, high prolific Holocene sedimentary aquifers has been a main element for achieving safe drinking water and food security in Bangladesh. However, the presence of elevated levels of geogenic arsenic (As) in these aquifers has undermined this success. Except for targeting safe aquifers through installations of tubewells to greater depth, no mitigation option has been successfully implemented on a larger scale. The objective of this study has been to characterise the hydrostratigraphy, groundwater flow patterns, the hydraulic properties to assess the vulnerability of low-arsenic aquifers at Matlab, in south-eastern Bangladesh, one of the worst arsenic-affected areas of the country. Groundwater modelling, conventional pumping test using multilevel piezometers, hydraulic head monitoring in piezometer nests, 14 C dating of groundwater and assessment of groundwater abstraction were used. A model comprising of three aquifers covering the top 250 m of the model domain showed the best fit for the calibration evaluation criteria. Irrigation wells in the Matlab area are mostly installed in clusters and account for most of the groundwater abstraction. Even though the hydraulic heads are affected locally by seasonal pumping, the aquifer system is fully recharged from the monsoonal replenishment. Groundwater simulations demonstrated the presence of deep regional flow systems with recharge areas in the eastern, hilly part of Bangladesh and shallow small local flow systems driven by local topography. Based on modelling results and 14 C groundwater data, it can be concluded that the natural local flow systems reach a depth of 30 m b.g.l. in the study area. A downward vertical gradient of roughly 0.01 down to 200 m b.g.l. was observed and reproduced by calibrated models. The vertical gradient is mainly the result of the aquifer system and properties rather than abstraction rate, which is too limited at depth to make an imprint. Although irrigation wells substantially change local flow pattern, targeting low-As aquifers seems to be a suitable mitigation option for providing people with safe drinking water. However, installing additional irrigation- or high capacity production wells at the same depth is strongly discouraged as these could substantially change the groundwater flow pattern. The results from the present study and other similar studies can further contribute to develop a rational management and mitigation policy for the future use of the groundwater resources for drinking water supplies. [ABSTRACT FROM AUTHOR]

Summary Extensive arsenic (As) enriched groundwater is known to occur in the aquifers of the Chaco-Pampean Plain of Argentina. Previous studies speculated that the As mobilization in these groundwaters was a direct result of their elevated pH and oxidative conditions. The volcanic glass layers present in the aquifer matrix were hypothesized as one of the possible sources of As to the groundwaters. Here, we examine the groundwater chemistry of the Santiago del Estero province of Chaco-Pampean Plains of Argentina, and test these hypotheses by using hydrogeochemical modeling within the framework of the regional geologic–tectonic setting. The study area is located in the active foreland of the Andean orogenic belt, which forms a continental arc setting, and is dotted with several hot springs. Rhyolitic volcanic glass fragments derived from arc volcanism are abundant within the aeolian–fluvial aquifer sediments, and are related to the paleo-igneous extrusion in the vicinity. Hydrogeochemical analyses show that the groundwater is in predominantly oxidative condition. In addition, some of the groundwaters exhibit very high Na, Cl − and SO 4 2 - concentrations. It is hypothesized in this study that the groundwater chemistry has largely evolved by dissolution of rhyolitic volcanic glass fragments contained within the aquifer sediments along with mixing with saline surface waters from, adjoining salinas, which are thought to be partially evaporated remnants of a paleo inland sea. Flow path modeling, stability diagrams, and thermodynamic analyses undertaken in this study indicate that the dominant evolutionary processes include ion exchange reactions, chemical weathering of silicate and evaporites, in monosialitization-dominated weathering. Geochemical modeling predicts that plagioclase feldspar and volcanic glass are the major solids phases that contribute metal cations and dissolved silica to the local groundwaters. Co-influxed oxyanions, with similar ionic radii and structure (e.g. Mo, Si, V, PO 4 3 - ), compete with As for mineral surface site, leading to As mobilization to the groundwaters (without considering the influence of microbial activities). Further, the transition of the Ca-rich groundwater to Na-rich groundwater, by mixing with water from the salinas and/or evaporative concentration, might also have led to counter-ion effects (a type of ion exchange reactions), and hence, further enrichment of groundwater by As. Some of the As may also have been contributed from mixing of meteoric water with magmatic-sourced water in the geothermal springs. [ABSTRACT FROM AUTHOR]

Summary Groundwater arsenic (As) of geogenic origin in the western Alps is generally associated with aquifers in crystalline rock. The External Crystalline Massifs (ECM) are in particular noted for occurrences of elevated concentrations of As in groundwaters. The present study is based on As in groundwaters that have been measured in the ECM in both France and Switzerland. Arsenic-bearing sulfide minerals, such as pyrite, arsenian pyrite, and arsenopyrite, are the most likely sources of As leached within the crystalline ECM rocks. While it is not known how As concentrations vary with time at all of the reported water sources, we measured on a weekly basis the concentration of As at one thermal source over a period of one year and found the As concentrations to be variable; however, the cause of the variability is at present not understood. Even though many studies have applied δ 34 S SO4 as a tool for understanding As mobilization in the ECM, there is no consensus at present. Finally, we present some perspectives on the possible effects of climate change and anthropogenic activities on As mobility in the ECM. In particular, droughts have the potential to increase As concentrations in groundwaters. [ABSTRACT FROM AUTHOR]

Land subsidence in the Bandung basin, West Java, Indonesia, is characterized based on differential interferometric synthetic aperture radar (DInSAR) and interferometric point target analysis (IPTA). We generated interferograms from 21 ascending SAR images over the period 1 January 2007 to 3 March 2011. The estimated subsidence history shows that subsidence continuously increased reaching a cumulative 45 cm during this period, and the linear subsidence rate reached ∼12 cm/yr. This significant subsidence occurred in the industrial and densely populated residential regions of the Bandung basin where large amounts of groundwater are consumed. However, in several areas the subsidence patterns do not correlate with the distribution of groundwater production wells and mapped aquifer degradation. We conclude that groundwater production controls subsidence, but lithology is a counteracting factor for subsidence in the Bandung basin. Moreover, seasonal trends of nonlinear surface deformations are highly related with the variation of rainfall. They indicate that there is elastic expansion (rebound) of aquifer system response to seasonal-natural recharge during rainy season. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nitrate in 28% of tested groundwater exceeded WHO's maximum contaminant level. [•] Cropland and landfill were the two largest sources of nitrate in groundwater. [•] A high resolution map of reactive nitrogen leakage to groundwater was constructed. [•] Anthropogenic factors explained majority of groundwater nitrate source variation. [•] Source appointment results matched well with the sampling data of groundwater nitrate. [ABSTRACT FROM AUTHOR]

The effects of some commonly used pH conditioners, viz., lime, banana ash, the carbonate and the bicarbonate of sodium and potassium and their binary mixture, on simultaneous removal of arsenic and iron ions from water have been studied. KHCO3 has been found to be the most suitable pH conditioner for the purpose. About 80 mg/L KHCO3 can remove both arsenate and iron ions from initial 250 µg/L and 20 mg/L to below their respective guideline values of the WHO for drinking water, retaining the final pH in the acceptable range for drinking. The simultaneous removal of arsenate and iron by the pH-conditioners decreases in the order: Lime > KHCO3 > NaHCO3 > K2CO3 > Na2CO3 > ash. However, lime requires post-treatment correction of highly alkaline pH. The arsenate ion is removed predominantly through goethite or ferrihydrite in the presence of the bicarbonates and through ferric hydroxide in the presence of the more alkaline pH-conditioners. KHCO3 is more advantageous over the more basic substances including NaHCO3, because with it, one not only needs the smallest dose but also can avoid careful adjustment of the dose for regulating the initial and the final pH. The paper clearly demonstrates the potential of KHCO3 to substitute the currently used pH-conditioners, viz., ash, lime and NaHCO3 for simultaneous removal of arsenate and iron ions. [ABSTRACT FROM AUTHOR]

Abstract: The widely applied model for groundwater dating using 14C proposed by Fontes and Garnier (F&G) (Fontes and Garnier, 1979) estimates the initial 14C content in waters from carbonate-rock aquifers affected by isotopic exchange. Usually, the model of F&G is applied in one of two ways: (1) using a single 13C fractionation factor of gaseous CO2 with respect to a solid carbonate mineral, εg/s, regardless of whether the carbon isotopic exchange is controlled by soil CO2 in the unsaturated zone, or by solid carbonate mineral in the saturated zone; or (2) using different fractionation factors if the exchange process is dominated by soil CO2 gas as opposed to solid carbonate mineral (typically calcite). An analysis of the F&G model shows an inadequate conceptualization, resulting in underestimation of the initial 14C values (14C0) for groundwater systems that have undergone isotopic exchange. The degree to which the 14C0 is underestimated increases with the extent of isotopic exchange. Examples show that in extreme cases, the error in calculated adjusted initial 14C values can be more than 20% modern carbon (pmc). A model is derived that revises the mass balance method of F&G by using a modified model conceptualization. The derivation yields a “global” model both for carbon isotopic exchange dominated by gaseous CO2 in the unsaturated zone, and for carbon isotopic exchange dominated by solid carbonate mineral in the saturated zone. However, the revised model requires different parameters for exchange dominated by gaseous CO2 as opposed to exchange dominated by solid carbonate minerals. The revised model for exchange dominated by gaseous CO2 is shown to be identical to the model of Mook (Mook, 1976). For groundwater systems where exchange occurs both in the unsaturated zone and saturated zone, the revised model can still be used; however, 14C0 will be slightly underestimated. Finally, in carbonate systems undergoing complex geochemical reactions, such as oxidation of organic carbon, radiocarbon ages are best estimated by inverse geochemical modeling techniques. [Copyright &y& Elsevier]

This paper presents a spatially explicit model for simulating the fate of nitrogen (N) in soil and groundwater and nitrous oxide (N2O) production in groundwater with a 1 km resolution at the European scale. The results show large heterogeneity of nitrate outflow from groundwater to surface water and production of N2O. This heterogeneity is the result of variability in agricultural and hydrological systems. Large parts of Europe have no groundwater aquifers and short travel times from soil to surface water. In these regions no groundwater denitrification and N2O production is expected. Predicted N leaching (16% of the N inputs) and N2O emissions (0.014% of N leaching) are much less than the IPCC default leaching rate and combined emission factor for groundwater and riparian zones, respectively. [Copyright &y& Elsevier]

Abstract: Due to its size and to its strategic importance as a huge transboundary aquifer, the Continental Intercalaire (C.I.) has been widely studied, making use of the most classical groundwater research approaches as well as the latest techniques. Investigations focused more on the shared parts and neglected the Great Occidental Erg sub-basin occurring exclusively in Algeria. The present research deals with recent hydrochemical and isotope results obtained for that sub-basin. The latter has seen major developments and an increase in water demand during the last two decades. The Occidental sub-basin occurs in an arid region limited by the Atlas Mountains (north), Tademaït plateau (south), Saoura valley (west) and the M’Zab uplift (east). Rainfall is relatively high only in the mountainous recharge area (Saharan Atlas). Rainfall decreases southward with decreasing altitude, from ∼200 mm to 20 mm yearly in the discharge area. The sub-basin is characterized by a dense run-off network (wadis flowing southward from the southern Atlas foothills). The C.I. reservoir is contained in the continental formations of the lower Cretaceous. The aquifer is mostly unconfined, unlike the eastern part. Its depth increases from north to south. It has a shape of a depression that disappears further south where it becomes confined. TDS increases southward along the recognized flowpath. Sample points align parallel to the halite dissolution line on a Cl–Na plot, confirming the origin of those elements. Major elements increase with the increase of TDS. Moreover, a good correlation between calcium and sulfates suggests gypsum and anhydrite leaching as water flows underground. Isotopically speaking, groundwater are enriched and exhibit large variations in stable isotopes (18O and 2H). They are distributed along an evaporation line corresponding to a mixing of two end-members: the Erg aquifer that feeds the C.I. in the north, and unaffected C.I. groundwater in the south. In the west, Saoura valley alluvial aquifer samples align in the continuation of the evaporated C.I. line, mirroring the intermingling of two aquifers during wadi Saoura flooding. Radiocarbon data showed that appreciable amount of 14C in the C.I. is traceable only up to few distances from the aquifer exposure zones up north (Atlas escarpments). The confined part of the reservoir shows depleted stable isotopes data and low 14C content, reflecting the absence of modern water at the discharge zone. [Copyright &y& Elsevier]

The industrial solvent trichloroethylene (TCE) is among the most ubiquitous chlorinated compounds found in groundwater contamination. The objective of this pilot-scale study was to apply the combined biosparging and enhanced in situ bioremediation technology to remediate TCE-contaminated groundwater at a TCE-spill site. A biosparging well was installed inside the TCE plume for oxygen supplement. Primary substrate (cane molasses) was injected into the TCE plume through the biosparging well to enhance the rate of TCE cometabolism. Three monitoring wells were installed in series downgradient of the biosparging well along the groundwater flow path. Results of polymerase chain reaction and nucleotide sequence analysis revealed that no appropriate TCE-degradation enzymes were observed in site groundwater. Thus, aerobic-activated sludge containing TCE-degraders collected from an industrial wastewater treatment plant were injected into the biosparging and three monitoring wells as an inoculum to provide microbial consortia for TCE biodegradation. After sludge injection, TCE-degraders (type I and II methanotrophs) and TCE-degrading enzymes (e.g. toluene monooxygenase, phenol monooxygenase) were detected in the injection and downgradient monitoring wells and remained in the aquifer during the 140-day pilot-scale study. Results indicate that significant TCE removal was observed (with TCE concentration dropped from 210 to 18 µg/L in substrate injection well). This reveals that appropriate substrates and inocula are required to effectively enhance the aerobic co-metabolic rate of TCE. Results from this study indicate that the enhanced in situ bioremediation is a promising technology to remediate TCE-contaminated groundwater. [ABSTRACT FROM AUTHOR]

Abstract: Samples of groundwater, surface water, snow and precipitation were collected to identify potential end-members for aquifer recharge in an unconfined esker aquifer connected to nearby surface waters. Concentrations of Ca2+, Cl−, NO3–N and SiO2 and electrical conductivity were determined in these water samples. Time series, ANOVA followed by HSD test and biplots were used to investigate temporal and spatial variations in surface water and groundwater chemistry. Examination of the spatial and temporal variations in groundwater solutes revealed that water quality was similar in perched groundwater and the main aquifer. The exception was NO3–N concentration, which increased in the perched groundwater with rising groundwater level, indicating a nitrogen source from the overlying airport. In the main aquifer, solute concentrations generally decreased during and immediately after snowmelt periods, indicating the importance of snowmelt input for groundwater quality. Groundwater solute concentrations generally decreased with declining groundwater level. During the spring melt period, the surface water level rise higher than groundwater level and the Cl− concentration in groundwater decreased showing a seasonal surface water intrusion. During the anomalously warm period in winter (T>0°C) the solute concentration decreased, implying that groundwater quality may be sensitive to future warming. [Copyright &y& Elsevier]

Abstract: Airborne electromagnetic methods (AEM) are used extensively in groundwater investigations, often in combination with high-resolution seismic data. Despite the frequent use of this mapping strategy, only a few cases are found in the literature. In this study, comparisons and interpretations were made based on AEM (SkyTEM) and high-resolution seismic data from an area covering 10km2 in the western part of Denmark. As support for the interpretations, an exploration well was drilled to provide lithological and logging information in the form of resistivity and vertical seismic profiling. Based on the resistivity log, synthetic SkyTEM responses were calculated with a varying number of gate-times in order to illustrate the effect of the noise-level. At the exploration well geophysical data were compared to the lithological log; in general there is good agreement. The same tendency was recognised when SkyTEM results from the area were superposed onto seismic sections. Comprehensive geological knowledge is necessary in order to introduce layer boundaries from one method interactively in the data handling of the other. However, in cases where resistivity transitions are positively correlated to reflections, SkyTEM data supports the interpretation of weak reflections, and can also support the correlation of reflections both internally and between seismic lines. Besides contributing lithological information, the AEM survey provides gross three-dimensional structural information, whereas seismic data contributes with more detailed structural information in two dimensions. [Copyright &y& Elsevier]

Abstract: Airborne geophysical methods have been used successfully in groundwater exploration over the last decades. Particularly airborne electromagnetics is appropriate for large-scale and efficient groundwater surveying. Due to the dependency of the electrical conductivity on both the clay content of the host material and the mineralisation of the water, airborne electromagnetics is suitable for providing information on groundwater resources, water quality, aquifer conditions and protection levels. Frequency-domain helicopter-borne electromagnetic systems are used to investigate near-surface groundwater occurrences in detail even in rough terrain and populated areas. In order to reveal the subsurface conductivity distribution, the quantities measured, the secondary magnetic fields, are generally inverted into resistivity–depth models. Due to the skin-effect the penetration depths of the electromagnetic fields depend on the system characteristics used: high-frequency data describe the shallower parts of the conducting subsurface and the low-frequency data the deeper parts. Typical maximum investigation depths range from some ten metres (highly conductive saltwater saturated sediments) to several hundred metres (resistive hard rocks). In urban areas there are a number of man-made sources affecting the electromagnetic measurements. These effects on the secondary field values are discussed on the basis of synthetic data as well as uncorrected and corrected field data. The case histories of different hydrogeological setups in Indonesia, The Netherlands and Germany demonstrate that airborne electromagnetics can be applied to groundwater exploration purposes even in urban areas. [Copyright &y& Elsevier]

Abstract: In the paper Visual MODFLOW, the international standard visualization software, is applied to set up the mathematical model which is used for groundwater flow numerical simulation in Balasu water source. The calibration and validation results of the numerical model indicate that the model can reflect the actual hydrogeological conditions, and can be applied in predicting the future groundwater flow conditions. The prediction results show that scheme 4 is optimal which is necessary for ensuring the safety and the normal operation of Balasu water source. [Copyright &y& Elsevier]

The amount of available groundwater in a catchment changes quickly, and the amount of water that users can take sustainably depends on where and when it is taken. However, rights to water tend to be fixed, and obtaining rights to water incurs high transaction costs. As a result, water catchments are over-allocated worldwide. In this paper, I show how a catchment manager could match users' rights to the available water, in near real time, despite uncertain future inflows, while making effective use of all available hydrological data. The solution uses the framework of a smart market. A smart market is a periodic auction cleared with the help of an optimization model. In addition to market clearing, this model allows a convenient means to adjust initial rights, and the auction revenue reflects the available water relative to users'' rights. When the auction is revenue neutral, the catchment may be viewed as allocated perfectly. I suggest several ways in which a catchment manager can find this revenue-neutral allocation, assuming the manager has authority to adjust initial rights. [Copyright &y& Elsevier]

Summary: The basic advantages of the multi-cell groundwater models are the parsimony, speed, and simplicity that make them ideal for hydrological applications, particularly when data are insufficient and/or repeated simulations are needed. However, the multi-cell models, in their basic version, are conceptual models and their parameters do not have physical meaning. This disadvantage may be overcome by the Narasimhan and Witherspoon’s integrated finite difference method, which, however, demands that the cells’ geometry conforms to the equipotential and no-flow lines. This restriction cannot be strictly satisfied in every application. Particularly in transient conditions, a mesh with static geometry cannot conform constantly to the varying flow kinematics. In this study, we analyse the error when this restriction is not strictly satisfied and we identify the contribution of this error to the overall error of a multi-cell model. The study is experimental based on a synthetic aquifer with characteristics carefully selected so as to be representative of real-world situations, but obviously the results of these investigations cannot be generalized to every type of aquifer. Nonetheless these results indicate that the error due to non-conformity to the aforementioned restriction plays a minor role in the overall model error and that the overall error of the multi-cell models with conditionally designed cells is comparable to the error of finite difference models with much denser discretization. Therefore the multi-cell models should be considered as an alternative option, especially in the cases where a discretization with a flexible mesh is indicated or in the cases where repeated model runs are required. [Copyright &y& Elsevier]

Vegetation growth models often concentrate on the interaction of vegetation with soil moisture but usually omit the influence of groundwater. However the proximity of groundwater can have a profound effect on vegetation growth, because it strongly influences the spatial and temporal distribution of soil moisture and therefore water and oxygen stress of vegetation. In two papers we describe the behavior of a coupled vegetation–groundwater–soil water model including the competition for water and light. In this first paper we describe the vegetation model, compare the model to measured flux data and show the influence of water and light competition in one dimension. In the second paper we focus on the influence of lateral groundwater flow and spatial patterns along a hillslope. The vegetation model is based on a biophysical representation of the soil–plant–atmosphere continuum. Transpiration and stomatal conductance depend both on atmospheric forcing and soil moisture content. Carbon assimilation depends on environmental conditions, stomatal conductance and biochemical processes. Light competition is driven by tree height and water competition is driven by root water uptake and its water and oxygen stress reaction. The modeled and measured H2O and CO2 fluxes compare well to observations on both a diurnal and a yearly timescale. Using an upscaling procedure long simulation runs were performed. These show the importance of light competition in temperate forests: once a tree is established under slightly unfavorable soil moisture conditions it can not be outcompeted by smaller trees with better soil moisture uptake capabilities, both in dry as in wet conditions. Performing the long simulation runs with a background mortality rate reproduces realistic densities of wet and dry adapted tree species along a wet to dry gradient. These simulations show that the influence of groundwater is apparent for a large range of groundwater depths, by both capillary rise and water logging. They also show that species composition and biomass have a larger influence on the water balance in eco-hydrological systems than soil and groundwater alone. [Copyright &y& Elsevier]

Abstract: The objective was to quantify leaching of the widely used low-dosage sulfonylurea herbicides rimsulfuron and its primary degradation products IN70941 ([N-(4,6-dimethoxypyrimidin-2-yl)-N-((3-ethylsulfonyl)-2-pyridinyl)urea]) and IN70942 ([N-((3-ethylsulfonyl)-2-pyridinyl)-4,6-dimethoxy-2-pyrimidineamine]) at two sandy research fields in Denmark. Water was sampled monthly from the vadose and groundwater zones at the two sites (Tylstrup and Jyndevad) over a 4–6-year period following application of rimsulfuron. No rimsulfuron was detected in the water samples. At the Jyndevad site, IN70941 was detected in the vadose zone at a depth of 1m for as long as three years in annual average concentrations exceeding the EU limit value for drinking water of 0.1μgL−1. At the Tylstrup site, IN70941 was detected at a depth of 2m in concentrations just below 0.1μgL−1. The groundwater concentration of IN70941 occasionally exceeded 0.1μgL−1 at the Jyndevad site, but is only detected on one occasion (and at a low concentration) at the Tylstrup site. At both sites IN70941 was relatively stable and persisted in the soil water for several years, with relatively little degrading further to IN70942. Thus, the concentration of IN7092 was much lower and apart from four samples from the Jyndevad site, never exceeded 0.1μgL−1. Nevertheless, our findings show that degradation products of rimsulfuron can leach through sandy soils in relatively high concentrations and could potentially contaminate vulnerable aquatic environments. In view of this risk, IN70941 and IN70942 should be included in pesticide monitoring programmes, and their long-term ecotoxicological effects should be investigated further. [Copyright &y& Elsevier]

Abstract: This paper reviews all available stable isotopic data concerning precipitation and spring water in Greece, from the 1960s until today. Spatial variability is investigated in order to provide basic information and identify the locally significant parameters that affect isotopic distributions. The area of interest was partitioned into eight sections according to geographical location and climatic characteristics. The distance of the station from the sea and the altitude are the main factors imprinted in the isotopic signature of precipitation. Local meteoric water meteoric line (LMWL) for precipitation and spring water were calculated for each section and for Greece as a whole. Precipitation LMWLs differ from the Global Meteoric Water Line (GMWL) in various ways across Greece. Elevated deuterium excess values are observed, probably due to water vapour originating from the Aegean or the Mid-eastern Mediterranean. Spring LMWLs are more or less consistent throughout the country. Furthermore, a high resolution map of precipitation and freshwater spring (Cl− <200ppm and T <25°C) δ 18O reveals several interesting features such as an orographic shadow effect induced by the Pindos Mountains, a strong climatic signal in southern Greece and a local city-microclimate effect around Athens. [Copyright &y& Elsevier]

Abstract: The Palaeogene history of the Almazán basin is that of a non-marine basin sediments derived from fluvial distributary systems and lateral playa–lakes. The coeval uplifting of the Cameros Massif and the Aragonian Branch of the Iberian Chain during Alpine compression exposed Triassic evaporites, which became the main source of sulphates to the playa–lake system, as recorded by the Bordalba Formation. This unit exhibits the classical facies distribution of gypsum-precipitating playa–lakes, which can be grouped into two main settings: 1) distal alluvial/mud flat and 2) saline mud flat/ephemeral lake. The stable isotope data for gypsum from the distal alluvial/mud flat areas (12.2<δ18OSMOW <16.5; 10.8<δ34SCDT <13.0‰) lie within the range of values of neighbouring Triassic gypsum (or are slightly lower for δ34SCDT). This agrees with palaeogeographical interpretations suggesting that the Triassic evaporites were the source of gypsum for the Almazán basin. The slightly lower values could be explained in terms of a minor contribution through the oxidation and dissolution of Palaeozoic-derived sulphides. The isotopic values for gypsum of the saline mud flat/ephemeral lake environments (19.8<δ18OSMOW <23.82; 15.6<δ34SCDT <19.9‰) are higher than those of the distal alluvial/mud flat. The higher δ18OSMOW in the saline mud flat/ephemeral lake environments is interpreted as being a consequence of the progressive evaporation of shallow groundwaters from proximal to distal areas. The heavier values for the δ34SCDT in the saline mud flat/ephemeral lake environments are interpreted as reflecting the activity of sulphate-reducing bacteria, which is evidenced by spheroidal dolomite aggregates on gypsum crystals and by the grey colours of the gypsum facies. [Copyright &y& Elsevier]

Summary: This study presents a hybrid spectral method (HSM) to estimate flow uncertainty in large-scale highly nonstationary groundwater systems. Taking advantages of spectral theories in solving unmodeled small-scale variability in hydraulic conductivity, the proposed HSM integrates analytical and numerical spectral solutions in the calculation procedures to estimate flow uncertainty. More specifically, the HSM involves two major computational steps after the mean flow equation is solved. The first step is to apply an analytical-based approximate spectral method (ASM) to predict nonstationary flow variances for entire modeling area. The perturbation-based numerical method, nonstationary spectral method (NSM), is then employed in the second step to correct the regional solution in local areas, where the variance dynamics is considered to be highly nonstationary (e.g., around inner boundaries or strong sources/sinks). The boundary conditions for the localized numerical solutions are based on the ASM closed form solutions at boundary nodes. Since the regional closed form solution is instantaneous and the more expensive perturbation-based numerical analysis is only applied locally around the strong stresses, the proposed HSM can be very efficient, making it possible to model strongly nonstationary variance dynamics with complex flow situations in large-scale groundwater systems. In this study the analytical-based ASM solutions was first assessed to quantify the solution accuracy under transient and inner boundary flow conditions. This study then illustrated the HSM accuracy and effectiveness with two synthetic examples. The HSM solutions were systematically compared with the corresponding numerical solutions of NSM and Monte Carlo simulation (MCS), and the analytical-based solutions of ASM. The simulation results have revealed that the HSM is computationally efficient and can provide accurate variance estimations for highly nonstationary large-scale groundwater flow problems. [Copyright &y& Elsevier]

Abstract: Groundwater is a vital natural resource for provision of potable water in both the urban and rural environment. Pollution of groundwater may come from urbanization, industrial development, agricultural and mining activities, and also from natural sources. The soil strata have the capacity to attenuate contaminants in the water passing through it. The chemical composition of groundwater is an indicator of its suitability as a source of water for human and livestock consumption, and for many other purposes. In order to ensure safe drinking water for the people in the Volta Region of Ghana, the CommunityWater and Sanitation Agency (CWSA) in 2003 contracted the CSIR Water Research Institute to carry out groundwater quality assessment of boreholes that had been dug for the rural communities in the Volta Region of Ghana. Major water quality parameters like pH, conductivity, alkalinity, hardness, Ca2+, Cl−, NO3-N, NO2-N, SO4 2− , SiO2, PO4-P, NH3-N, were determined. Most of the parameters were within the WHO guide values for drinking water. Some parameters, however, gave occasional extreme values in few places. For example, an extreme value of 475 mg/L in NO3-N, far exceeding the WHO guideline value of 10 mg/L, was recorded in a station in the Akatsi district, and similar values elsewhere. The pH values were very satisfactory, ranging from 5.13 to 8.37 for all the three districts in question. Only very few pH values fell below pH 6. [Copyright &y& Elsevier]

Abstract: Determination of chromium in groundwater samples containing iron may pose analytical problems due to sorption and fixation of chromium species onto Fe(III) hydroxides. Parks et al. (Water Res. 2004, 38, 2827) hypothesized that chromium species trapped inside Fe(III) hydroxides i.e. “fixed chromium” may not be soluble by HNO3 digestion (APHA method 3030 B). In such cases, hydroxylamine digestion is required to release “fixed chromium”. To verify the hypothesis, we carried out this study on groundwater samples containing chromium and iron, using different methods of APHA and EPA. The results showed the presence of “fixed chromium”, ranged between 0.1 and 19.2μg L−1, contributing 0.2 to 14.1% towards true total chromium. Digestion of samples with HNO3 released Cr(III) bound to organic complexes, but not the “fixed chromium”. The hydroxylamine digestion released “fixed chromium”, but not the Cr(III) bound to organic complexes. Microwave digestion of samples with HNO3 +HCl was effective for the release of both “fixed” and “Cr(III)-organic complexes”. Cr(III) was only adsorbed onto suspended matter, whereas Cr(VI), and Cr(III)-organic complexes were not adsorbed onto suspended matter due to their solubility. Sample pH, buffering capacity, and matrix have a significant influence on the adsorption and fixation of chromium species onto Fe(III) hydroxides. [Copyright &y& Elsevier]

Abstract: We tested two methods for dating groundwaters that cannot be reliably measured by 36Cl dating alone, one based on groundwater flow velocity plus distance along a flow path and the other based on 4He accumulation rates calibrated with 36Cl dates. We sampled groundwaters along six inferred regional groundwater flow paths in the Great Artesian Basin (GAB) of Australia. We selected three groundwater paths where the decrease in 36Cl was largely controlled by cosmogenic 36Cl radioactive decay without a significant increase in chloride concentration. The extrapolated groundwater velocities were 0.133±0.018 m/y to 0.433±0.140 m/y. The estimated residence time of 1.06×106 y at the discharge area around Lake Eyre was comparable to the estimate of (1–2.2)×106 y in previous studies. On the other hand, our estimated 4He accumulation rates for the selected three groundwater flow paths (1.85±0.31×10−11 to 1.51±0.63×10−10 ccSTP/cm3∙y) were approximately 2–15 times lower than previously reported rates for the central GAB. Our estimated rate of 1.51×10−10 ccSTP/cm3∙y−1 in the western GAB is compatible with previous estimates based on 81Kr ages. The groundwater residence time estimated from the 4He accumulation rate was approximately 7×105 y near the discharge area at Lake Eyre. Finally, both estimations were mutually compatible with a 30% error. [Copyright &y& Elsevier]

Abstract: The primary objective of this work was to evaluate a chemically modified cellulose for the sorption efficiency and selectivity to remove cadmium from spiked high-hardness groundwater. Heterogeneous esterification of cellulose with succinic anhydride in toluene under basic conditions has proceeded very efficiently to yield the succinylated cellulose (SC) with fairly high DS value, as confirmed by FTIR and solid-state MAS 13C NMR spectroscopies. Deprotonation of the free carboxylic acid group was achieved by alkaline treatment of SC with saturated NaHCO3 aqueous solution. Batch experiments were carried out on the resulting sodic material (NaSC) to examine its cadmium-removing capability in both distilled water (DW) and spiked groundwater (GW). The results obtained from the sorption characteristics (kinetics, isotherms and pH effect) have revealed that NaSC material is particularly effective in removing cadmium from both DW and GW solutions, with a maximum uptake of 185.2 and 178.6mgg−1, respectively. These comparable sorption capacities strongly suggest that NaSC sorbent is highly selective to heavy metal over alkaline earth cations (Ca2+ and Mg2+) and therefore less susceptible to interference from background ions, naturally present in groundwater. On the other hand, cadmium sorption is shown to decrease with a decrease in pH which is indubitably inherent to the competing proton during the ion-exchange process. Furthermore, the material has proven to be efficiently regenerable by using a NaCl brine solution. Thus, the use of the sorbent sequentially to the first regeneration led to nearly no attenuation in the material''s capacity for cadmium-removal. Finally, the sorption effectiveness of NaSC is compared to those of other low-cost sorbents so far reported in the literature. [Copyright &y& Elsevier]

Abstract: The aim of this paper was to explore new factors that might be reasons for the occurrence of fluoride-rich groundwater in the area around a construction site. During the construction of two deep shafts of the Mizunami Underground Research Laboratory (MIU) in Mizunami city, central Japan, a large quantity of groundwater with high fluoride concentration was charged into the shafts. Chemical investigation carried out during the excavation revealed that fluoride concentrations in the area around the MIU site greatly exceeded those prescribed by Japanese standards. Therefore, the origin of fluoride ion was experimentally investigated. Samples were collected from the core of a deep borehole drilled in the study area. The weathering - and alteration levels of the collected granites varied greatly. Granitic powders were used to measure fluoride content in the granitic rock mass. The fluoride content ranged between 200 and 1300 mg/kg. The powders were reacted with purified water for 80 days. The results of water–rock interaction showed granitic rock to be one of the main sources of fluoride-rich groundwater in Mizunami area. Fluoride concentrations in these solutions that were shaken for 80 days varied between 2 and 7 mg/l. This change may have occurred as a result of the spatial distribution of fluoride ions in the granite mass as evidenced by mineralogical analysis of fluoride content in several specimens. X-ray powder diffraction analysis of the rock before- and after the water–rock interaction tests manifested that the presence of fluorite mineral was relatively small compared to other minerals. The degree of weathering and alteration might be an additional factor causing dissolution of fluoride-rich minerals. However, it was difficult to interpret the change in fluorite composition by X-ray diffraction analysis. [Copyright &y& Elsevier]

Abstract: Monitoring of contaminant concentrations, e.g., for the estimation of mass discharge or contaminant degradation rates, often is based on point measurements at observation wells. In addition to the problem, that point measurements may not be spatially representative, a further complication may arise due to the temporal dynamics of groundwater flow, which may cause a concentration measurement to be not temporally representative. This paper presents results from a numerical modeling study focusing on temporal variations of the groundwater flow direction. “Measurements” are obtained from point information representing observation wells installed along control planes using different well frequencies and configurations. Results of the scenario simulations show that temporally variable flow conditions can lead to significant temporal fluctuations of the concentration and thus are a substantial source of uncertainty for point measurements. Temporal variation of point concentration measurements may be as high as the average concentration determined, especially near the plume fringe, even when assuming a homogeneous distribution of the hydraulic conductivity. If a heterogeneous hydraulic conductivity field is present, the concentration variability due to a fluctuating groundwater flow direction varies significantly within the control plane and between the different realizations. Determination of contaminant mass fluxes is also influenced by the temporal variability of the concentration measurement, especially for large spacings of the observation wells. Passive dosimeter sampling is found to be appropriate for evaluating the stationarity of contaminant plumes as well as for estimating average concentrations over time when the plume has fully developed. Representative sampling has to be performed over several periods of groundwater flow fluctuation. For the determination of mass fluxes at heterogeneous sites, however, local fluxes, which may vary considerably along a control plane, have to be accounted for. Here, dosimeter sampling in combination with time integrated local water flux measurements can improve mass flux estimates under dynamic flow conditions. [Copyright &y& Elsevier]

Abstract: Hydrological, geochemical and environmental isotope data from groundwater wells at Ruprechtov natural analogue site were evaluated to characterize the flow pattern and C chemistry in the system. The results show that water flow in the Tertiary sediments is restricted to 1–2m thick zones in the so-called clay/lignite horizon with two different infiltration areas in the outcropping granites in the western and south-western part of the investigated area. Generally the flow system is separated from the underlying granite by a kaolin layer up to several tens of metres thick. Differences in stable isotope signatures in the northern part of the site indicate very local connections of both flow systems via fault zones. The observed increase of δ13C values and decrease of 14C activities in dissolved inorganic C during evolution of the groundwater from the infiltration area to the clay/lignite horizon was modelled using simple open- and closed-system models as well as an inverse geochemical model (NETPATH), which included changes in other geochemical parameters. The results from both types of models provided some insights into timescales of groundwater flow, but mainly revealed that additional sources of C are active in the system. These are very likely biodegradation of dissolved and sedimentary organic C (DOC and SOC) as well as the influx of endogenous CO2. The occurrence of microbial degradation of SOC in the clay/lignite layers is indicated by the increase of biogenic DIC, DOC, and phosphate concentrations. The impact of microbial SO4 reduction on this process is confirmed by an increase of δ34S values in dissolved from the infiltration area to the clay/lignite horizon with an enrichment factor of 11‰. The very low DOC concentrations of 1–5mgC/L in the clay/lignite horizon with an organic matter content up to 50% C is probably caused by very low availability of organic matter to the processes of degradation and DOC release, demonstrated by extraction experiments with SOC. [Copyright &y& Elsevier]

An important step in the procedure of building an environmental model is the transformation of a conceptual model into a numerical simulation. To simplify model construction a framework is required that relieves the model developer from software engineering concerns. In addition, as the demand for a holistic understanding of environmental systems increases, access to external model components is necessary in order to construct integrated models. We present a modelling framework that provides two- and three-dimensional building blocks for construction of spatio-temporal models. Two different modelling languages available in the framework, the first tailored and the second an enhanced Python scripting language, allow the development and modification of models. We explain for both languages the interfaces allowing to link specialised model components and thus extending the functionality of the framework. We demonstrate the coupling of external components in order to create multicomponent models by the development of the link to the groundwater model MODFLOW and provide results of an integrated catchment model. The approach described is appropriate for constructing integrated models that include a coupling of a small number of components. [Copyright &y& Elsevier]

Abstract: This paper presents the development of a hybrid bi-level programming approach for supporting multi-stage groundwater remediation design. To investigate remediation performances, a subsurface model was employed to simulate contaminant transport. A mixed-integer nonlinear optimization model was formulated in order to evaluate different remediation strategies. Multivariate relationships based on a filtered stepwise clustering analysis were developed to facilitate the incorporation of a simulation model within a nonlinear optimization framework. By using the developed statistical relationships, predictions needed for calculating the objective function value can be quickly obtained during the search process. The main advantage of the developed approach is that the remediation strategy can be adjusted from stage to stage, which makes the optimization more realistic. The proposed approach was examined through its application to a real-world aquifer remediation case in western Canada. The optimization results based on this application can help the decision makers to comprehensively evaluate remediation performance. [Copyright &y& Elsevier]

Abstract: Growing population and wealth, agricultural expansion, changing land use, and mechanized irrigation increase the demand on water resources. Groundwater accounts for about 20% of global water use, with agriculture the largest consumer. Groundwater CO2 partial pressures are typically ∼10–100 times higher than atmospheric, so CO2 degassing is an unavoidable consequence of groundwater extraction. For regional studies, very good estimates of groundwater CO2 in clastic aquifers can be calculated for temperate-climate regions from:where the constant is the sum of the negative logarithm (base 10) of the Henry''s Law constant for CO2 and first association constant for H2CO3 at 13 °C, and titration alkalinity can be substituted for activity of HCO3 −. Groundwater CO2 is not uniformly distributed in groundwater, being most variable near the water table, lowest at intermediate depth, and highest in deep aquifers where non-potable water is typical. Geochemical speciation modeling is required to assess CO2 released when groundwater equilibrates with the atmosphere. A suite of potable water types were modeled for this purpose, with the result that current groundwater production is estimated to release ∼0.01 to 0.03 Pg C year−1, similar to CO2 from volcanic emissions and ∼200 times less than other human-sourced CO2 emissions. Determination of dissolved CO2 depends on accuracy of pH measurements: CO2 released due to groundwater use may be underestimated if reported pH measurements do not represent in situ pH. [Copyright &y& Elsevier]

Abstract: The biological and physical controls on microbial processes that produce and consume N2O in soils are highly complex. Isotopomer ratios of N2O, with abundance of 14N15N16O, 15N14N16O, and 14N14N18O relative to 14N14N16O, are promising for elucidation of N2O biogeochemistry in an intact ecosystem. Site preference, the nitrogen isotope ratio of the central nitrogen atom minus that of the terminal nitrogen atom, is useful to distinguish between N2O via hydroxylamine oxidation and N2O via nitrite reduction. We applied this isotopomer analysis to a groundwater system in a temperate coniferous-forested ecosystem. Results of a previous study at this location showed that the N2O concentration in groundwater varied greatly according to groundwater chemistry, i.e. NO3 −, DOC, and DO, although apportionment of N2O production to nitrification or denitrification was ambiguous. Our isotopic analysis (δ15N and δ18O) of NO3 − and N2O implies that denitrification is the dominant production process of N2O, but definitive information is not derived from δ15N and δ18O analysis because of large variations in isotopic fractionations during production and consumption of N2O. However, the N2O site preference and the difference in δ15N between NO3 − and N2O indicate that nitrification contributes to total N2O production and that most measured N2O has been subjected to further N2O reduction to N2. The implications of N2O biogeochemistry derived from isotope and isotopomer data differ entirely from those derived from conventional concentration data of DO, NO3 −, and N2O. That difference underscores the need to reconsider our understanding of the N cycle in the oxic–anoxic interface. [Copyright &y& Elsevier]

Abstract: Hydrogeological investigations conducted by the Geological Survey of Canada in the Lake Saint-Martin region of Manitoba have confirmed earlier reports of naturally elevated F− and B concentrations in local groundwaters. Fluoride and B concentrations are highly correlated (r 2 =0.905) and reach 15.1mg/L and 8.5mg/L, respectively. Virtually all groundwaters with F− concentrations greater than the drinking water limit of 1.5mg/L are from wells within the Lake Saint-Martin impact structure, a 208Ma complex crater 23km in diameter underlying a large part of the study area. The high-F− groundwaters can be classified into two groups according to their anionic and isotopic compositions. Group I samples consist of Na-mixed anion groundwaters, with Cl greater than 100mg/L and highly depleted 18O compositions indicative of recharge under much cooler climatic conditions than at present. Samples belonging to this group exhibit a striking relationship to crater morphology, and are found in an arcuate belt within the southern rim of the impact structure. Group II high-F− samples consist of Na–HCO3–SO4 groundwaters, with little Cl, and less depleted 18O compositions. Samples belonging to this group are associated with groundwaters recharged locally, on a low ridge within the impact structure. This paper traces the probable source of high-F− groundwaters to phosphatic pellets in shales of the Winnipeg Formation, a regional basal clastic unit which sub-crops at shallow depth beneath the crater rim as a result of more than 200m of structural uplift associated with the impact event. This extensive aquifer is known elsewhere in southern Manitoba for its naturally-softened groundwaters and locally elevated F− concentrations. Group I groundwaters are interpreted as discharge from the Winnipeg Formation where it abuts against crater-fill deposits. Group II high-F− groundwaters are interpreted as modern recharge from within the impact structure, displacing Group I groundwaters. Thus, elevated F− and B concentrations observed in groundwaters of the Lake Saint-Martin area represent the geochemical signature of upwelling from a deep regional aquifer. The previously unsuspected discharge zone occurs within an isolated sub-crop of the aquifer formed as a result of structural uplift caused by the impact event. [Copyright &y& Elsevier]

Abstract: This work is aimed at investigating the weathering processes of the granodiorites cropping out in a small catchment of the Sila Massif. The mineral constituents in this granodiorite are plagioclase, often zoned with a Ca-rich core and a Na-rich rim, quartz, chlorite, K-feldspar, white mica and epidote. During this study, dolomite was discovered in local stream sediments, as separate monomineralic grains, probably resulting from erosion of veins cutting the crystalline rocks. Prevailing dissolution of foreign dolomite and a Ca-rich plagioclase is suggested by the Ca–Mg–HCO3 chemical composition of local groundwaters and stream waters, which is rather unexpected for waters interacting with granitoid rocks. These qualitative observations are quantitatively confirmed by reaction path modelling of the weathering processes occurring in the study area, which was carried out using the EQ3/6 software package, version 8.0, and the Double Solid Reactant Method. Indeed, it was possible to ascertain that the release of both major dissolved constituents and several trace elements (Ba, Co, Cr, Fe, Mn, Ni, Pb, Sr, V and Zn), from rocks to waters, is chiefly controlled by the dissolution of foreign dolomite and the Ca-rich core of zoned plagioclases. [Copyright &y& Elsevier]

Geochemical and microbiological techniques were used to assess water-quality impacts from the land application of treated municipal wastewater in the karstic Wakulla Springs basin in northern Florida. Nitrate-N concentrations have increased from about 0.2 to as high as 1.1 mg/L (milligrams per liter) during the past 30 years in Wakulla Springs, a regional discharge point for groundwater (mean flow about 11.3 m3/s) from the Upper Floridan aquifer (UFA). A major source of nitrate to the UFA is the approximately 64 million L/d (liters per day) of treated municipal wastewater applied at a 774 ha (hectare) sprayfield farming operation. About 260 chemical and microbiological indicators were analyzed in water samples from the sprayfield effluent reservoir, wells upgradient from the sprayfield, and from 21 downgradient wells and springs to assess the movement of contaminants into the UFA. Concentrations of nitrate-N, boron, chloride, were elevated in water samples from the sprayfield effluent reservoir and in monitoring wells at the sprayfield boundary. Mixing of sprayfield effluent water was indicated by a systematic decrease in concentrations of these constituents with distance downgradient from the sprayfield, with about a 10-fold dilution at Wakulla Springs, about 15 km (kilometers) downgradient from the sprayfield. Groundwater with elevated chloride and boron concentrations in wells downgradient from the sprayfield and in Wakulla Springs had similar nitrate isotopic signatures, whereas the nitrate isotopic composition of water from other sites was consistent with inorganic fertilizers or denitrification. The sprayfield operation was highly effective in removing most studied organic wastewater and pharmaceutical compounds and microbial indicators. Carbamazepine (an anti-convulsant drug) was the only pharmaceutical compound detected in groundwater from two sprayfield monitoring wells (1–2 ppt). One other detection of carbamazepine was found in a distant well water sample where enteroviruses also were detected, indicating a likely influence from a nearby septic tank. [Copyright &y& Elsevier]