Assignment of groundwater level at the wastewater collecting pipe for a landfill groundwater simulation: utilization of the two-dimensional saturated–unsaturated groundwater numerical model

In order to understand the effects of a landfill operation on groundwater flow behavior, a 2D horizontal groundwater simulation model was carried out. The model saved the memory of computer and time consumption, comparing it with the 3D groundwater flow model. However, the greatest difficulty is the assignment of the collecting pipe boundary at the study site. Therefore, a 2D vertical model was applied to calculate the change of the groundwater table above the collecting pipe. This paper focuses on examining the validation of the assignment of the collecting pipe boundary by applying the results of the 2D vertical model. The 2D horizontal model was coupled with the recharge model to solve the partial differential equation of groundwater flow. The finite difference method and iterative successive over relaxation were applied. The drainage volume of leachate collection was summed up in the whole landfill site and compared with the average volume of treated wastewater. The study demonstrated that the results of the 2D vertical model validated and can be applied to the 2D horizontal groundwater flow simulation.     

Is pure groundwater safe to drink?: natural "contamination' of groundwater in Norway

The title of this article is designed to provoke. Naturally occurring parameters are, by definition, not contamination. Nevertheless, nature is not necessarily nice, and naturally occurring trace toxins can be every bit as undesirable as their counterparts derived from human pollution.     

Hydrochemical evolution of groundwater in a riparian zone affected by acid mine drainage (AMD), South China: the role of river–groundwater interactions and groundwater residence time

Investigations were undertaken in the riparian zone near Shangba village, an AMD area, in southern China to determine the effects that river–groundwater interactions and groundwater residence time have had on environmental quality and geochemical evolution of groundwater. Based on the Darcy’s law and ionic mass balances as well as the method of isotopic tracer, the results showed that there were active interactions between AMD-contaminated river water and groundwater in the riparian zone in the study area. River water was found to be the main source of groundwater recharge in the northwestern part of the study area, whereas groundwater was found to be discharging into the river in the southeastern part of the study area throughout the year. End-member mixing analysis quantified that the contributions of river water to groundwater decreased gradually from 35.9% to negligible levels along the flow path. The calculated mixing concentrations of major ions indicated that water–rock reactions were the most important influence on groundwater quality. The wide range of Ca²⁺?+?Mg²⁺ and HCO₃^? ratios and the change of groundwater type from Ca²⁺–SO₄^2? type to a chemical composition dominated by Ca²⁺–HCO₃^? type indicated a change of the major water–rock reaction process from the influence of H₂SO₄ (AMD) to that of CO₂ (soil respiration) along a groundwater flow path. Furthermore, the kinetics interpretation of SO₄^2? and HCO₃^? concentrations suggested that the overlapping time of their kinetics triggered the hydrochemical evolution and the change of major weathering agent. This process might take approximately 8 years and this kinetic time will be continued when a steady source of contamination enter the aquifer.     

Network design for groundwater monitoring – a case study

 The applicability and usefulness of Geostatistics (kriging) as a tool for optimum selection of sites for monitoring groundwater levels has been demonstrated through a case study. The criterion used is the estimation of error variance. Groundwater level data (pre-monsoon 1994) obtained from 32 observation wells of Upper Kongal basin, Nalgonda District, A.P. (India) has been stochastically analyzed. The spatial distribution of water levels and its associated error variance is computed and the locations having maximum error variance are selected as additional sites for augmenting the existing observational well network. Received: 15 june 1998 · Accepted: 14 December 1998     

Sustainable groundwater management——problems and scientific tools

Groundwater is a strategic resource due to its usually high quality and perennial availability. However, groundwater management all over the world often lacks sustainability as evidenced by falling water tables, drying wetlands, increasing sea-water intrusion and general deterioration of water quality. As groundwater cannot be renewed artificially on a large scale, sustainable management of this resource is vital. A number of scientific tools are available to assist in his task. Three items are discussed here. They include methods for the determination of groundwater recharge, groundwater modeling including the estimation of its uncertainty, and thenterfacing to the socio-economic field. Generally the quality of water management work can be largely enhanced with new tools available, including remote sensing, digital terrain models, differential GPS, environmental tracers, automatic data collection, modeling and the coupling of models from different disciplines     

Numerical simulation of the effect of heavy groundwater abstraction on groundwater–surface water interaction in Langat Basin, Selangor, Malaysia

The paper aims at evaluating the interaction between ground and surface water along the Langat River in Malaysia through the development of a numerical simulation. Malaysia has been experiencing a rapid economic growth since the last few decades, driven by many factors such as agriculture, industry, and the like. The demand for water in these sectors has increased so tremendously that surface water has been utilized in conjunction to groundwater. Approximately 18,184 m³ of water per day is obtained from the aquifer to supply to the steel factory. There are also workshops, petroleum stations, and houses in the area thus causing the water quantity and quality to degrade. In terms of quantity, the pumping activity has altered the interaction between the groundwater and surface water. Therefore, a numerical model was proposed and two aquifer layers were simulated, with the first layer being approximately >20 m in depth and the second layer >100 m. The recharge estimated from the tank model was input into the groundwater modeling. The effects of the surface water to the aquifer were included in the simulation by defining the river conductance, river bed, and river level. The calibrated model (error about 0.9 m) was achieved and applied to predict the flow pattern in its natural state without the pumping and with the pumping states. As a result, in the first scenario, the stream was in an effluent condition influenced by the groundwater from the northeast to the west. A hyporheic flow occurred and was observed from the contour map. The flow system was changed in the second scenario when the pumping activity was included in the simulation. The groundwater lost its original function but received leakage from the stream near the pumping sites. The findings of this study will help the local authorities and other researchers to understand the aquifer system in the area and assist in the preparation of a sustainable groundwater management.     

Military uses of groundwater: a driver of innovation?

Military need has been a positive driver to the development of the modern day, and now mature, science of hydrogeology. The important synergy between geology and water supply was appreciated by military men in the mid-nineteenth century but the first real test of this learning only took place in the First World War. German, British and American geologists then mapped water resources and the potential for exploiting groundwater in Belgium and northern France. Technical innovations included deployment of rapid drilling techniques and the promotion of well screens for use in unconsolidated sediments. The mapping techniques were developed further during the Second World War when innovative remote mapping of enemy-occupied territory became an important planning tool to both Allied and German armies. Work in North Africa and other arid and semi-arid terrains promoted insight into the occurrence of groundwater in fresh-water aquifers little replenished by recharge. Mapping of hard rock basement-type environments in the islands of Jersey and Guernsey by German geologists was a concept new to the British Isles. Collectively, these varied initiatives provided part of the foundation for post-Second World War development of modern-day applied hydrogeology.     

Tritium�Chelium groundwater age used to constrain a groundwater flow model of a valley-fill aquifer contaminated with trichloroethylene (Quebec, Canada)

Tritium?Chelium groundwater dating was carried out in a trichloroethylene (TCE)-contaminated valley-fill aquifer system in Quebec, Canada, where a numerical groundwater flow model was developed. Forty seven discrete groundwater and dissolved gas samples were obtained along two flow paths originating from known TCE source zones whose related plumes converge down gradient to form a single plume. Sampling points in monitoring wells were projected onto vertical sections showing particle tracks along the two flow paths. At these points, simulated advective ages obtained from particle tracking were matched to tritium?Chelium ages using different porosity values; the best match was 0.35. Ages were also obtained above and below a prodeltaic silty aquitard in a portion of the aquifer where some source zones are located, which provide groundwater and TCE transit times through the aquitard as well as a mean vertical hydraulic conductivity that agrees with previous estimates used in the model. In certain locations, anomalously old ages associated with high terrigenic ⁴He indicate areas where groundwater from the underlying proglacial unit flows upward into the deltaic sand aquifer through aquitard windows. Upflow locations correspond with increased TCE concentrations, suggesting significant TCE provenance through the proglacial unit originating from a previously unrecognized TCE source zone.     

Performance of alkaline reactive materials in the remediation of acidic groundwater

Acidic groundwater and surface water are common problems in coastal Australia causing massive fish kills, attack of concrete and steel structures, and clogging of waterways. The best solution is the construction of a permeable reactive barrier （PRB） to neutralise the acidic groundwater before entering nearby waterways. A PRB consists of a trench filled with reactive material that intersects the flow-path of a contaminant plume and ameliorates the contaminated groundwater. A PRB is being designed in a pilot scale study in ASS in southeastern Australia. The groundwater is acidic （pH 3） with high A1 （40 mg/L） and Fe （530 mg/L） levels. When the acidic groundwater comes into contact with this PRB, the acid will be neutralized by the alkaline reactive materials and the aluminum and iron will be removed from the groundwater. Twenty-five alkaline materials were tested for use in the PRB, with an emphasis on waste materials, including oyster shells and recycled concrete. Batch tests were used to select the best two reactive materials for use in the column tests. The pH achieved by each material was controlled by the reaction kinetics of the dominant alkaline component.     

Microbial control of mineral–groundwater equilibria:Macroscale to microscale

macroscale processes that perturb general groundwater chemistry and therefore mineral–water equilibria; and microscale interactions, where attached organisms locally perturb mineral–water equilibria, potentially releasing limiting trace nutrients from the dissolving mineral. In the contaminated unconfined glacio-fluvial aquifer near Bemidji, Minnesota, USA, carbonate chemistry is influenced primarily at the macroscale. Under oxic conditions, respiration by native aerobic heterotrophs produces excess carbon dioxide that promotes calcite and dolomite dissolution. Aerobic microorganisms do not colonize dolomite surfaces and few occur on calcite. Within the anoxic groundwater, calcite overgrowths form on uncolonized calcite cleavage surfaces, possibly due to the consumption of acidity by dissimilatory iron-reducing bacteria. As molecular oxygen concentration increases downgradient of the oil pool, aerobes again dominate and residual hydrocarbons and ferrous iron are oxidized, resulting in macroscale carbonate-mineral dissolution and iron precipitation. Feldspars, in contrast, weather exclusively at the microscale near attached microorganisms, principally in the anoxic region of the plume. Native organisms preferentially colonize feldspars that contain trace phosphorus as apatite inclusions, apparently as a consequence of the low P concentration in the groundwater. These feldspars weather rapidly, whereas nearby feldspars without trace P are uncolonized and unweathered. Feldspar dissolution is accompanied by the precipitation of secondary minerals, sometimes on the bacterial cell wall itself. These observations suggest a tightly linked biogeochemical system whereby microbial processes control mineral diagenesis at many scales of interaction, and the mineralogy and mineral chemistry influence microbial ecology. Only the macroscale interaction, however, is easily observable by standard geochemical methods, and documentation of the microscale interactions requires microscopic examination of microorganisms on mineral surfaces and the locally intense diagenetic reactions that result. Received, May 1999/Revised, October 1999/Accepted, October 1999     

Boron isotopic geochemistry of karst groundwater in Guiyang City, China

Boron has two stable isotopes （^10B and ^11B） with relative abundances of about 20% and 80%, respectively. Boron isotopic ratios in natural materials show a huge range of variations, from -70‰ to ＋60‰, when expressed with the classical δ^11B notation. Most of these isotopic variations occur at the surface of the Earth. Hence, boron isotopic composition can be used as a sensitive tracer in geochemical study, for instance, to identify the different sources of contamination and factors controlling the salinity of groundwater. During the last decade, boron isotopes have been used to discriminate between the influences of seawater intrusion and anthropogenic discharge. But few of those researches can precisely identify the different sources of contamination. We measured the boron concentrations and boron isotopic ratios of groundwater samples collected in Guiyang City, as well as the major ions. The results indicate that the major ion composition of the groundwater in the investigated area is mainly controlled by the interactions between water and the dominant rock i.e. carbonates. All the water compositions are characterized by high concentrations of Ca^2＋, Mg^2＋, HCO3^-, SO4^2-, and NO3^-, which are the dominant contaminants. Both dissolved boron concentrations and isotopic ratios show large variations among the ground waters, from 2 μg/L to 90 μg/L and from -6‰ to ＋26‰, respectively. The boron concentrations and isotopic ratios indicate that the river across the studied city has been seriously contaminated by urban discharge. Boron concentrations of fiver water samples varied from 20 μg/L to 140 μg/L, with an average δ^11B value of ＋2.0‰. Using boron isotopic compositions and different geochemical indices allowed us to clearly identify and distinguish the two major sources of contamination, agricultural activity and urban wastewater. Both of the two sources are characterized by high boron concentrations but their boron isotopic compositions significantly differ.     

Hydraulic fracturing: a toxicological threat for groundwater and drinking-water?

This paper deals with the possible impact of hydraulic fracturing (fracking), employed in the exploitation of unconventional shale gas and tight gas reservoirs, on groundwater, which is the most important source of drinking-water in Germany and many other European countries. This assessment, which is part of an interdisciplinary study by a panel of neutral experts on the risks and environmental impact of hydraulic fracturing, is based mainly on data obtained from three ExxonMobil drilling sites in northern Germany. First, the basic technical aspects of fracking and its relevant water fluxes are explained. The type, purpose and fate of the constituents of the fracking fluids are discussed. The chemicals used in the fracking fluids are assessed with regard to their hazardous properties according to the Regulation (EC) No. 1272/2008 of the European Parliament and of the Council on the classification, labelling and packaging of substances and mixtures (CLP regulation) and the German “Water Hazard Classes”. Contamination of groundwater by ingredients of fracking fluids may occur from under ground or may result from above-ground accidents associated with the transport, storage and handling of hazardous substances used as additives in fracking fluids. The degree of groundwater contamination cannot be predicted in a general way. Therefore, different dilutions of the fracking fluid in groundwater are considered. It is shown that the concentrations of most ingredients resulting from a 1:10,000 up to 1:100,000 dilution of the fracking fluid in groundwater are below health-based reference values such as the limit values of the European Drinking Water Directive, the WHO Guideline Values for Drinking-water Quality, and other health-based guide values for drinking-water. Regarding the salinity of fracking fluids, a dilution of 1:1,000 is sufficient to reach concentrations which are acceptable for drinking-water. From the human-toxicological point of view, the constituents of flowback water are more problematic with respect to drinking-water produced from groundwater than those of the fracking fluids. The few reliable data which have become available, as well as hydrogeological considerations, point in the direction of considerable salt concentrations and toxic constituents, e.g., Hg, As, Pb, Zn, Cd, BTX, PAHs, or even radioactive elements. The identification and assessment of reaction products and metabolites, which are produced as a result of the fracking operation and the metabolic activity of microorganisms, are important topics for further research. The recommendations include the need for a better understanding of the environmental impact of fracking operations, especially with regard to the development of sustainable rules for planning, permission, performance and management of fracking, and for the monitoring of groundwater quality around fracked drilling sites.     

Hydrogeology and groundwater ecology: Does each inform the other?

The known, perceived and potential relationships between hydrogeology and groundwater ecology are explored, along with the spatial and temporal scale of these relations, the limit of knowledge and areas in need of research. Issues concerned with the subterranean part of the water cycle are considered from the perspective of the biology of those invertebrate animals that live, of necessity, in groundwater and the microbiological milieu essential for their survival. Groundwater ecosystems are placed in a hydrogeological context including the groundwater evolution along a flowpath, the significance of the biodiversity and of the ecosystem services potentially provided. This is considered against a background of three major components essential to the functioning of groundwater ecosystems, each of which can be affected by activities over which hydrogeologists often have control, and each, in turn, may have implications for groundwater management; these are, a place to live, oxygen and food (energy). New techniques and increasing awareness amongst hydrogeologists of the diversity and broad distribution of groundwater ecosystems offer new opportunities to develop cross disciplinary work between hydrogeologists and groundwater ecologists, already demonstrated to be a field for collaboration with broad benefits.     

Characterization of arsenic-contaminated groundwater and human health risk assessment in Vietnam

The characteristics of arsenic-contaminated groundwater were investigated and the potential risks from groundwater were evaluated in Vietnam. Arsenic contamination in groundwater was found in Ha Nam Province in the northern part of Vietnam. Since groundwater has been used as one of the main drinking water sources in this region, groundwater （n=10） and hair （n=15） samples were collected in the Vinh Tru district, Ha Nam Province, during February of 2006. At the site, the concentrations of anions and silica were analyzed and As（Ⅲ） and As（Ⅴ） species in groundwater were separated with disposable arsenic speciation cartridge. The concentrations of arsenic in groundwater ranged from 13 to 582 μg/L （mean=366 μg/L）. According to the results of arsenic speciation, approximately 90% of arsenic in groundwater existed as As（Ⅲ） species. Average concentrations of iron and manganese were 18 and 0.7 mg/L, respectively. All samples exceeded the Vietnamese drinking water standard of 10μg/L for arsenic and 0.5 mg/L for iron. Also 70% of the groundwater samples were above the Vietnamese drinking water standard of 0.5 mg/L for manganese. However, a real intake of arsenic to human is less than analyzed arsenic concentration because sand filtration units are used to remove iron and arsenic in groundwater in this region. After treatment, arsenic concentrations decreased from 〈1 to 82 μg/L （mean=33 μg/L）. The concentrations of arsenic in hair samples and treated groundwater were compared. Especially, arsenic concentrations in female hair samples and treated groundwater had significantly positive correlation with the Spearman correlation of 0.88 and the P-value of 0.001. Based on the arsenic concentrations in treated groundwater, the assessment of human health risks was conducted.     

Hydrodynamic modeling for groundwater assessment in Sana’a Basin, Yemen

Yemen is a semi-arid country with very limited water resources. Sana’a Basin is located in the central part of Yemen and is the major source of water for drinking and irrigation. High abstraction rates in Sana’a Basin rising from 21.1 million (M) m³ in 1972 to 227.7?Mm³ in 2006, have led to a major decline in water levels and deterioration in groundwater quality. Effective management of groundwater resources in Sana’a Basin can be aided by modelling. FEFLOW was used to build a groundwater flow model for the basin and the model was calibrated under transient conditions for the period 1972–2006. The water balance for transient conditions of the Sana’a Basin in 2006 indicated that the total annual inflow was 116.9?Mm³, and the total annual outflow was 245.8?Mm³. Three scenarios for potential groundwater extraction for the period 2006–2020 are presented. The first represents the present status based on the 2006 extraction rates without introducing any management measures. The second is based on maximum domestic, agricultural and industrial consumption of water resources. The third simulates the effect of water-resource augmentation, i.e. the increase of groundwater recharge, and maximizes sustainability by reducing water consumption. Identified areas of the basin require prompt management action.     

Climate change and groundwater conditions in the Mekong Region–A review

Changes in the climatic system introduce uncertainties in the supply and management of water resources. The Intergovernmental Panel on Climate Change(IPCC) predicts an increase of 2 to 4 °C over the next 100 years. Temperature increases will impact the hydrologic cycle by directly increasing the evaporation of surface water sources. Consequently, changes in precipitation will indirectly impact the flux and storage of water in surface and subsurface reservoirs(i.e., lakes, soil moisture, groundwater, etc.). In addition, increases in temperature contribute to increases in the sea level, which may lead to sea water intrusions, water quality deterioration, potable water shortages, etc. Climate change has direct impacts on the surface water and the control of storage in rivers, lakes and reservoirs, which indirectly controls the groundwater recharge process. The main and direct impact of climate change on groundwater is changes in the volume and distribution of groundwater recharge. The impact of climate change on groundwater resources requires reliable forecasting of changes in the major climatic variables and accurate estimations of groundwater recharge. A number of Global Climate Models(GCMs) are available for understanding climate and projecting climate change.These GCMs can be downscaled to a basin scale, and when they are coupled with relevant hydrological models, the output of these coupled models can be used to quantify the groundwater recharge, which will facilitate the adoption of appropriate adaptation strategies under the impact of climate change.