Assessment of advective–dispersive contaminant transport in heterogeneous aquifers using a meshless method

Groundwater solute transport phenomena typically occur in water-bearing zones with heterogeneous solute dispersive characteristics and/or media hydraulic properties. A radial basis function collocation method (RBFCM)-based numerical method was developed in order to investigate the ability of RBFCM to accurately portray solute transport phenomena under heterogeneous conditions. Simulations were performed for 1-D and 2-D transport scenarios in which scale-dependent dispersivity fields were taken into consideration and compared with available analytical solutions. Different radial basis functions (RBFs) were employed for assessing the sensitivity of the present method on the selected RBFs. The simulation results were also compared with the results of MT3DMS which is a modular three-dimensional transport model with alternative solution schemes including the method of characteristics, the implicit central finite difference and the third order total variation diminishing finite volume. The proposed model was also used to simulate a real case condition where solute transport through a two-layer soil medium had been investigated experimentally. The results showed that RBFCM represented a powerful tool for predicting the solute transport occurrence under heterogeneous conditions with high accuracy.     

Factors causing dynamic variations in the saltwater–freshwater transition zone in a beach aquifer, Mangsang, South Korea

Dynamic variation in the saltwater–freshwater transition zone below a seafront beach in South Korea was investigated with long-term monitoring of the groundwater in relation to the precipitation, wave height, and tide. Correlation, spectral analysis, and regression analysis of monitoring data were performed to deduce the relationships between these factors. The general shape of the transition zone was affected by the seasonal groundwater levels, but temporary fluctuations were predominantly affected by local rising-groundwater-level events. The distinct increases in the groundwater level were closely related to the wave height. Different patterns of electrical conductivity (EC) change were detected in the shallow and deep zones, and these differences indicated that the transition zone was highly dynamic. The EC values at shallow depths were temporarily increased by the wave setup and tidal fluctuations during the rising-groundwater events, but the EC at greater depths was reduced by the seaward or downward movement of the relative freshwater. In exceptional cases, during extreme increases in the groundwater level resulting from seawater flooding, the rapid downward flow of the flooding saltwater through the well bore caused synchronous EC fluctuations at all depths.     

Is use of oil-field brine as a dust-abating agent really benign? Tracing the source and flowpath of contamination by oil brine in a shallow phreatic aquifer

In Ohio, 1985 H.R. Bill 501 authorizes the local authorities to issue permits to use oil-field brine surface spreading as a dust and ice control agent. Such permits are usually given without any necessary hydrogeological expertise as to the potential impact on the shallow aquifers, particularly if the brine spreading occurs in a recharge area. One such case occurred recently in the southwestern suburb of the City of Wooster, OH, USA, where a group of home owners were seeking judicial relief when their water wells began yielding salty water as a result of brine spreading on a nearby large open storage area for oil and gas well drilling supplies. The defendant, owner of the storage yard, acted in accordance with the permit issued by the local authorities. Yet, decentralized decision making and an increased emphasis on local and citizen involvement have created a gap between science and society. The local authorities were not required by law to condition the issuance of the permit on an analysis of the potential environmental impact. The decision to issue that permit was made purely on non-scientific grounds. Therefore, the residents had no choice but to embark on a costly process of proving the damages, causation, and liability in court of law. During the protracted, 6-year long conflict, an extensive hydrogeological and hydrochemical data set (including stable isotopes’ analyses along with the complete chemical analyses of major and minor constituents) was amassed at a great cost to both sides. The following article presents the hydrogeological and hydrochemical interpretation of this data set. In addition, the case illustrates a glaring deficiency in the Ohio, 1985 H.R. Bill 501, and one pitfall in the “politically correct” philosophy of delegating decision-making process entirely to the non-professional local authorities.     

Validity evaluation of a groundwater dam in Oshipcheon River,eastern Korea using a SWAT–MODFLOW model

It is assumed that the groundwater dam under consideration is located in the lower Oshipcheon River along Yeongdeok-gun County, Gyeongsangbuk-do Province, eastern Korea. In this study, changes in groundwater level and construction effects of the groundwater dam were analyzed using a SWAT–MODFLOW model designed for integration of surface water and groundwater, and validity analysis before and after construction of the groundwater dam was evaluated. There are an average increase of 0.46 m and a maximum increase of 1.16 m, respectively, at the upstream region due to the groundwater dam. Groundwater levels at the upstream region show an average increase of 0.42 m by the groundwater dam when the water quantity of demand (10,080 m³/day) is pumped. The groundwater dam has potential as an alternative for the surface water dam to secure water resources in the study area.     

Residence time distribution in a large unconfined–semiconfined aquifer in the Argentine Pampas using <Superscript>3</Superscript>H/<Superscript>3</Superscript>He and CFC tracers

The Pampa region in Argentina includes vast unconfined–semiconfined aquifers that local economies depend upon, but detailed knowledge of the associated water resources is still lacking. The Pampeano aquifer in the Pampa plain of Argentina covers around 1.5 million km². In order to achieve a better understanding of the hydrogeological system through the estimation of mean residence times (MRT), water samples were taken from 12 monitoring wells, drilled at different depths in four locations, and analyzed for environmental tracers. The concentrations of ³H, tritiogenic ³He and chlorofluorocarbons (CFCs) can be explained by mixtures of young waters adjusted to exponential piston flow models (EPM) or dispersion models (DM), and different proportions of tracer-free waters (dead water). The sampling site located very close to the water divide shows a dominance of young waters: 85 % of water best represented by a DM model with a MRT of 3 years. For the shallow wells at other sites, best-fitting models result in a DM with MRT between 20 and 35 years, and proportions of dead water between 40 and 60 %. These results lead to important updates in the conceptual model of the Pampeano aquifer. Large proportions of dead water at a few meters depth can be the consequence of upward flows in a multilayered aquifer or diffusive retardation in the inter-bedded clay layers.     

Moessbauer and XRD characterization of contaminated sediments by coal mining drainage in Neath Canal, South Wales, UK

Sediment cores were collected from the upstream of the Neath Canal in South Wales and characterized for their mineral compositions and iron speciation in order to understand the influence of sedimentary properties on the contaminants of heavy metals. The sediments in the canal have been polluted by ocherous precipitate with heavy metals such as arsenic since a major mine water discharge in spring 1993. The sediment core was obtained just from the discharge point in the canal and distinguished into three layers in the field regarding to their physical properties including visible color, sediment particle composition and dryness. X-ray diffraction （XRD） and M6ssbauer spectroscopy revealed vertical variations of minerals and iron species in depth of the sediment profile. The upper layer, reddish-brown, is wet muddy precipitant and is very fine in particle size, consisting mainly of iron oxide and hydroxide. Arsenic is rich in this layer; probably the sorption on iron oxide surface is the main mechanism. The middle layer, 22.0-27.0 cm, is soft deposit in a yellow color and contains sheet silicate, calcite and goethite. The lower part below 27.0 cm is gray to dark gray in color and contains quartz, pyrite, coal particles that are much more similar to normal aquatic sediment. The upper two layers in brown and yellow colors as newly precipitated mud from AMD contain high concentrations of As, Ni under oxic conditions. The lower part as the old canal sediments under reducing conditions contains high Cu and Zn. Chromium is enriched in the limited part of the low layer, just beneath the boundary between the middle and low parts of the sedimentary column, where the redox conditions shifted from oxic to anoxic. It is clear that the distribution of these heavy metals is closely associated with the redox condition reflected in the iron speciation. Thus different treatments are necessary for each layer of the sediment since different mineral and geochemical properties of the sediment will give different impacts on the heavy metals.     

Aquifer vulnerability assessment using GIS and fuzzy system: a case study in Tehran–Karaj aquifer,Iran

Aquifer vulnerability assessment techniques have been developed to predict which areas are more likely than others to become contaminated as a result of activities at or near the land surface. This research focuses on the evaluation of groundwater vulnerability to pollution in an urban area. Among several assessment methods, DRASTIC has been selected for this study. ArcGIS has been used to overlay and calculate different layers and obtain the vulnerability map. In order to show the importance of fuzzy algorithms in classification, both Boolean and fuzzy algorithms were used and compared. The fuzzy algorithm could recognize the areas with low and negligible vulnerability potentials whereas the Boolean model classified them as moderate. Two sensitivity tests, the map removal sensitivity analyses and single-parameter sensitivity analysis, were performed to show the importance of each parameter in the index calculation.     

Mssbauer and XRD characterization of contaminated sediments by coal mining drainage in Neath Canal, South Wales, UK

Sediment cores were collected from the upstream of the Neath Canal in South Wales and characterized for their mineral compositions and iron speciation in order to understand the influence of sedimentary properties on the contaminants of heavy metals. The …     

Significance of river–aquifer interactions for reach-scale thermal patterns and trout growth potential in the Motueka River, New Zealand

To assess whether reaches of the Motueka River (New Zealand) that gain water from groundwater were likely to represent significant cold-water refugia for brown trout during periods of high water temperatures, water temperature was monitored for more than 18 months in two gaining reaches of the Motueka River and three reaches that were predicted to be losing water to groundwater. These data were used to predict brown trout (Salmo trutta) growth in gaining and losing reaches. Groundwater inputs had a small effect on water temperature at the reach-scale and modelling suggests that the differences observed were unlikely to result in appreciable differences in trout growth. Several coldwater patches were identified within the study reach that were up to 3.5°C cooler than the mainstem, but these were generally shallow and were unlikely to provide refuge for adult trout. The exception was Hinetai Spring, which had a mean water temperature of close to 16°C during the period January–March, when temperatures in the mainstem regularly exceeded 19°C. Trout were observed within the cold-water plume at the mouth of Hinetai Stream, which would allow them to thermoregulate when mainstem temperatures are unfavourable while still being able to capitalise on food resources available in the mainstem.     

Delineation of groundwater potential zones using remote sensing,GIS, and AHP technique in Tehran–Karaj plain,Iran

Evaluation of groundwater resources in dry areas without enough data is a challenging task in many parts of the world, including Tehran–Karaj plain in Iran, which includes Tehran, the capital city of Iran and Karaj, one of Iran’s biggest cities. Water demand due to increasing agricultural and industrial activities caused many problems in the field of water resources management. In this study, the potential of groundwater resources was evaluated using remote sensing, geographic information system (GIS), and analytic hierarchy process (AHP) for the first time. Digital Elevation Model from Shuttle Radar Topography Mission was used to generate a slope map and drainage density map. Three Landsat-8 satellite images were utilized to provide lineament density and land cover/land use maps. Geological and soil type maps were provided from the Geological Survey and Mineral Explorations of Iran (GSI). Tropical Rainfall Measuring Mission data were used to prepare average annual precipitation map. Discharge values from 102 pumping wells in the time period of 2002–2014 were used to evaluate the results. Seven data layers were prepared, and the geodatabase was made in GIS. The layers and their classes were assigned weights using AHP method. Finally, the layers were overlaid based on their weights, and the potential map of groundwater resources was generated. The area was classified into five zones with very high, high, moderate, low, and very low potentials. The zones covered 5.95, 32.90, 22.70, 10.20, and 28.25% of the study area, respectively. The results showed good agreement with the field data obtained from discharge wells.     

Rock–water interactions and pollution processes in the volcanic aquifer system of Guadalajara,Mexico, using inverse geochemical modeling

In order to understand and mitigate the deterioration of water quality in the aquifer system underlying Guadalajara metropolitan area, an investigation was performed developing geochemical evolution models for assessment of groundwater chemical processes. The models helped not only to conceptualize the groundwater geochemistry, but also to evaluate the relative influence of anthropogenic inputs and natural sources of salinity to the groundwater. Mixing processes, ion exchange, water–rock–water interactions and nitrate pollution and denitrification were identified and confirmed using mass-balance models constraint by information on hydrogeology, groundwater chemistry, lithology and stability of geochemical phases. The water–rock interactions in the volcanic setting produced a dominant NaHCO₃ water type, followed by NaMgCaHCO₃ and NaCaHCO₃. For geochemical evolution modeling, flow sections were selected representing recharge and non-recharge processes and a variety of mixing conditions. Recharge processes are dominated by dissolution of soil CO₂ gas, calcite, gypsum, albite and biotite, and Ca/Na exchange. Non-recharge processes show that the production of carbonic acid and Ca/Na exchange are decreasing, while other minerals such as halite and amorphous SiO₂ are precipitated. The origin of nitrate pollution in groundwater are fertilizers in rural plots and wastewater and waste disposal in the urban area. This investigation may help water authorities to adequately address and manage groundwater contamination.     

Classification and delineation of groundwater–lake interactions in the Nebraska Sand Hills (USA) using electrical resistivity patterns

Lake?Cgroundwater interactions exhibit a complex three-dimensional (3D) structure that is seldom studied. The utility of waterborne electrical resistivity (ER) surveys is explored for characterization of 3D groundwater flow and solute transport patterns for three lakes in the Nebraska Sand Hills, USA. Waterborne ER surveys, using contrasts between lake and groundwater solutes as natural tracers, are useful for inferring 3D patterns of groundwater flow and solute transport as well as classifying groundwater?Clake interactions. Three unique groundwater flow systems are interpreted under each lake from dense networks of two-dimensional (2D) waterborne ER surveys. A lateral transition from high to low ER values beneath the saline Wilson Lake expresses its flow-through regime, where groundwater salinity indicates changes from groundwater inflow to outflow. Alkali Lake ER profiles reveal a prevalent ER increase with depth over the lakebed area that is characteristic of groundwater discharge lakes. ER profiles beneath Gimlet Lake are the most resistive and indicate pockets of high ER related to fresh groundwater discharge into the lake, supporting a flow-through regime with a short flushing time. These ER patterns correctly classify groundwater?Clake interactions and provide high spatial resolution of mixing patterns for systems with varying water salinity.     

Assessment to the potential mobility and toxicity of metals and metalloids in soils contaminated by old Sb–Au and As–Au mines (NW Portugal)

The main purpose of this study is to assess arsenic and antimony availability in soils, as well as Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn availability in soils derived from the schist–metagraywacke complex close to old Sb–Au mines and in soils developed from Ordovician slates and close to an old As–Au mine in Portugal. The availability was determined using a European certified sequential extraction procedure (BCR). The results demonstrated that metalloids are not readily bioavailable, because they are mainly associated with the residual fraction. Arsenic and antimony proportions in exchangeable fractions are up to 3 and 1%, respectively. However, arsenic is up to 24% in oxy-hydroxide fractions, while antimony is up to 4% in them, demonstrating the highest bioavailability of arsenic compared to that of antimony, as metalloids are weakly bound to the soils in that fraction. Therefore, arsenic tends to be more toxic than antimony in all soils studied. However, the pseudo-total contents show that both metalloids are above the Italian and Dutch guidelines. Therefore, if physico-chemical changes occur arsenic and antimony will show higher potential environmental risk than evidenced by Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn.     

A comparative study of shallow groundwater level simulation with WA–ANN and ITS model in a coastal island of south China

Accurate and reliable prediction of shallow groundwater level is a critical component in water resources management. Two nonlinear models, WA–ANN method based on discrete wavelet transform (WA) and artificial neural network (ANN) and integrated time series (ITS) model, were developed to predict groundwater level fluctuations of a shallow coastal aquifer (Fujian Province, China). The two models were testified with the monitored groundwater level from 2000 to 2011. Two representative wells are selected with different locations within the study area. The error criteria were estimated using the coefficient of determination (R ²), Nash–Sutcliffe model efficiency coefficient (E), and root-mean-square error (RMSE). The best model was determined based on the RMSE of prediction using independent test data set. The WA–ANN models were found to provide more accurate monthly average groundwater level forecasts compared to the ITS models. The results of the study indicate the potential of WA–ANN models in forecasting groundwater levels. It is recommended that additional studies explore this proposed method, which can be used in turn to facilitate the development and implementation of more effective and sustainable groundwater management strategies.     

Development of a Darcy-Brinkman model to simulate water flow and tracer transport in a heterogeneous karstic aquifer (Val d’Orléans, France)

Darcy’s law is the equation of reference widely used to model aquifer flows. However, its use to model karstic aquifers functioning with large pores is problematic. The physics occurring within the karstic conduits requires the use of a more representative macroscopic equation. A hydrodynamic model is presented which is adapted to the karstic aquifer of the Val d’Orléans (France) using two flow equations: (1) Darcy’s law, used to describe water flow within the massive limestone, and (2) the Brinkman equation, used to model water flow within the conduits. The flow equations coupled with the transport equation allow the prediction of the karst transfer properties. The model was tested by using six dye tracer tests and compared to a model that uses Darcy’s law to describe the flow in karstic conduits. The simulations show that the conduit permeability ranges from 5?×?10^?6 to 5.5?×?10^?5?m² and the limestone permeability ranges from 8?×?10^?11 to 6?×?10^?10?m². The dispersivity coefficient ranges from 23 to 53 m in the conduits and from 1 to 5 m in the limestone. The results of the simulations carried out using Darcy’s law in the conduits show that the dispersion towards the fractures is underestimated.     

Mobility and accumulation of selenium and its relationship with other heavy metals in the system rocks/soils–crops in areas covered by black shale in Korea

The purpose of this study is to investigate the enrichment level and dispersion patterns of Se and associated elements in rocks, soils and crops which were collected in the Dukpyung and the Chubu areas covered with black shales of the Okchon Group in Korea. Rock and soil samples were analyzed for Se including multiple elements by ICP, ICP-MS and INAA, and crop samples by INAA. Soil pH and loss-on-ignition (LOI) were also measured.