Adjacent Aquifer Research Articles

Geological and hydrogeological environment in Tianjin with potential geohazards and groundwater control during excavation

This paper discusses the geological and hydrogeological features of Quaternary deposits in Tianjin as well as the geohazards related to groundwater hydrology in this region. The soft soil deposits, comprising silt, sand, silty clay and clay, are composed of four aquifer groups. In the first aquifer group, one phreatic aquifer and two confined aquifers have relationships with underground construction in the urban area. These three aquifers are separated by two aquitards and collectively form a multi-aquifer system. During geotechnical construction, potential geohazards present are related to the groundwater, which include water-in-rushing, quicksand and piping hazards. To prevent the aforementioned geohazards, dewatering is conducted; however, groundwater pumping may result in large settlements of the surrounding ground. To reduce pumping-induced settlement, the dewatering–waterproofing system has been adopted. According to the characteristics of the subsoil, excavation depth and the surrounding environment, the dewatering system can be divided into five patterns. In the first four patterns, when pumping is conducted in the excavation pit, the groundwater head in the adjacent aquifers outside the pit decreases due to the leakage effect of the aquitards located between the aquifers. In the fifth pattern, waterproof curtain has cut off the aquifers completely and dewatering in the pit cannot result in settlement around excavation pit. To avoid geohazards related to groundwater hydrology, countermeasures recommended include construction of an effective waterproof curtain, selection of a reasonable excavation dewatering pattern and withdrawal of required groundwater.

The effects of floods on the temperature of riparian groundwater

AbstractThe transition area between rivers and their adjacent riparian aquifers, which may comprise the hyporheic zone, hosts important biochemical reactions, which control water quality. The rates of these reactions and metabolic processes are temperature dependent. Yet the thermal dynamics of riparian aquifers, especially during flooding and dynamic groundwater flow conditions, has seldom been studied. Thus, we investigated heat transport in riparian aquifers during 3 flood events of different magnitudes at 2 sites along the same river. River and riparian aquifer temperature and water‐level data along the Lower Colorado River in Central Texas, USA, were monitored across 2‐dimensional vertical sections perpendicular to the bank. At the downstream site, preflood temperature penetration distance into the bank suggested that advective heat transport from lateral hyporheic exchange of river water into the riparian aquifer was occurring during relatively steady low‐flow river conditions. Although a small (20‐cm stage increase) dam‐controlled flood pulse had no observable influence on groundwater temperature, larger floods (40‐cm and >3‐m stage increases) caused lateral movement of distinct heat plumes away from the river during flood stage, which then retreated back towards the river after flood recession. These plumes result from advective heat transport caused by flood waters being forced into the riparian aquifer. These flood‐induced temperature responses were controlled by the size of the flood, river water temperature during the flood, and local factors at the study sites, such as topography and local ambient water table configuration. For the intermediate and large floods, the thermal disturbance in the riparian aquifer lasted days after flood waters receded. Large floods therefore have impacts on the temperature regime of riparian aquifers lasting long beyond the flood's timescale. These persistent thermal disturbances may have a significant impact on biochemical reaction rates, nutrient cycling, and ecological niches in the river corridor.

Assessing the effect of chlorinated hydrocarbon degradation in aquitards on plume persistence due to back-diffusion

This modeling study aims to investigate how reactive processes in aquitards impact plume persistence in adjacent aquifers. For that purpose the migration of a trichloroethene (TCE) plume in an aquifer originating from dense non-aqueous phase liquid (DNAPL) source dissolution and back-diffusion from an underlying reactive aquitard was simulated in a 2D-numerical model. Two aquitard degradation scenarios were modeled considering one-step degradation from TCE to cis-dichloroethene (cDCE): a uniform (constant degradation with aquitard depth) and a non-uniform scenario (decreasing degradation with aquitard depth) and were compared with a no-degradation scenario. In the no-degradation scenario, a long-term TCE tailing above the Maximum Contaminant Level (MCL) caused by back-diffusion after source removal was observed. In contrast, in the aquitard degradation scenarios, TCE back-diffusion periods were shorter, whereby the extent of back-diffusion reduction depended on the aquitard degradation depth and the rate. For high degradation rates (half-life: 30–80days), an aquitard degradation depth greater than 65cm prevented TCE plume persistence after source removal but generated a long-term tailing above the MCL for the produced cDCE. For slow degradation rates (half-life: <200days), TCE was only partially degraded after source removal, independent of the aquitard degradation depth, leading to a long-term dual contamination of the aquifer by cDCE and TCE. A sudden enrichment of 13C in TCE and cDCE was observed after source removal in the uniform and non-uniform degradation scenarios that was distinct from δ13C patterns observed when aquifer degradation occurs (continuous enrichment of 13C along the plume axis) and for when there is absence of degradation (no change of isotope ratios). This demonstrates that δ13C measurements in the aquifer can be used as a diagnostic tool to demonstrate aquitard degradation, which simplifies the identification of reactive processes in aquitards, as aquifers are usually easier to monitor than aquitards.

Assessing hydrothermal groundwater flow path using Kohonen's SOM, geochemical data, and groundwater temperature cooling trend.

Assessing groundwater flow path in a thermal aquifer, such as El Hamma aquifer, southeastern Tunisia, and its lateral communication with the adjacent Jeffara-Gabes aquifers, is a very complex operation which requires the integration of several approaches to understand and explain the reality of phenomenon. In this study, geochemical and isotopic data, Kohonen self-organizing map, temperature cooling trend, and kriging techniques were used to assess groundwater flow path in hydrothermal aquifer of El Hamma-Gabes, Tunisia. For this objective, 32 sampled wells are analyzed for major ions, electric conductivity, pH, total dissolved solids, and stables isotopes (δ2H and δ18O). Geochemical diagrams reveal that groundwater chemistry was controlled by evaporation, and rock-water interaction with a dominant water facies was Cl·SO4-Na·Ca-Mg. Kriging techniques were used to highlight groundwater flow path. Kohonen self-organizing map shows that the waters are clustered into three classes according to chemical and isotopic composition. These clusters represent a hydrothermal groundwater class from the Continental Intercalaire aquifer, a shallow groundwater class corresponding to Jeffara-Gabes aquifer and mixed water class. Groundwater cooling trend and stable isotopes indicate that groundwater flow is toward west to east part of study area, indicating a recharge of Jeffara aquifer from El Hamma thermal aquifer.

Pump Hydro Energy Storage systems (PHES) in groundwater flooded quarries

Pump storage hydroelectricity is an efficient way to temporarily store energy. This technique requires to store temporarily a large volume of water in an upper reservoir, and to release it through turbines to the lower reservoir, to produce electricity. Recently, the idea of using old flooded quarries as a lower reservoir has been evoked. However, these flooded quarries are generally connected to unconfined aquifers. Consequently, pumping or injecting large volumes of water, within short time intervals, will have an impact on the adjacent aquifers. Conversely, water exchanges between the quarry and the aquifer may also influence the water level fluctuations in the lower reservoir. Using numerical modelling, this study investigates the interactions between generic flooded open pit quarries and adjacent unconfined aquifers, during various pump-storage cyclic stresses. The propagation of sinusoidal stresses in the adjacent porous media and the amplitude of water level fluctuations in the quarry are studied. Homogeneous rock media and the presence of fractures in the vicinity of the quarry are considered. Results show that hydrological quarry – rock interactions must be considered with caution, when implementing pump – storage systems. For rock media characterized by high hydraulic conductivity and porosity values, water volumes exchanges during cycles may affect significantly the amplitude of the water level fluctuations in the quarry, and as a consequence, the instantaneous electricity production. Regarding the impact of the pump – storage cyclic stresses on the surrounding environment, the distance of influence is potentially high under specific conditions, and is enhanced with the occurrence of rock heterogeneities, such as fractures. The impact around the quarry used as a lower reservoir thus appears as an important constraining factor regarding the feasibility of pump – storage systems, to be assessed carefully if groundwater level fluctuations around the quarry are expected to bring up adverse effects. Results highlight opportunities and challenges to be faced, to implement pump – storage hydroelectricity systems in old flooded open pit quarries.

Suitability for developing riverside groundwater sources along Songhua River, Northeast China

ABSTRACTRiverbank filtration is a natural water treatment technology that consists of extracting water from rivers by pumping wells located in the adjacent alluvial aquifer. It is vital to choose the most appropriate from multiple potential candidate sites, which is a complex procedure and seldom paid attention to. In this study, a method system including multicriteria evaluation indexes was developed with which the suitability of bank filtration along the Songhua River of China for developing riverside groundwater sources was assessed. The system was comprised of main suitability indexes for water quantity, water quality, interaction intensity between surface water and groundwater, and the exploitation condition of aquifer condition, weights of which were determined by specialist marking methods. Based on this assessment system, the suitability of the study area was divided into five grades. Results show that riversides along Lalin River, Hulan River, and the middle part of Songhua River are suitable for developing riverside groundwater sources.

Investigation of seepage flow path(s) in the right embankment of Sheshpeer Dam, the Zagros Region, Iran

Gar and Bare Anticlines are located in the Zagros mountain range, southern Iran. The cores of the anticlines are comprised of the calcareous Sarvak formation sandwiched between two impermeable marly formations, namely Pabdeh-Gurpi at the top and Kazhdomi at the bottom. Sheshpeer spring with an average discharge rate of 3.2 m$$^{3}$$ s$$^{-1}$$ emerges from the Gar Anticline, forming the Sheshpeer River. To the west, the Sheshpeer River is delimited by the Albian aged calcareous Sarvak formation, while the Santonian-Oligocene impermeable deposits of the marly Pabdeh-Gurpi formation constitute the eastern limit. Sheshpeer Dam is currently under study and under construction. Parts of the Sheshpeer riverbed lie directly on the Sarvak formation and its water seeps into the adjacent karst aquifer at a rate of approximately 340–650 l s$$^{-1}$$ which will increase undoubtedly after reservoir impoundment. In addition, two tracing tests, for determination of underground seepage flow path(s) were accomplished. However, no dye tracer was detected in any source of ground water located downstream of the reservoir. Interestingly, water levels of the studied boreholes have dropped during drilling operations indicating the existence of a deep karst aquifer in the region. Finally, the seepage flow direction was investigated and assumed to be most likely parallel to Gar Anticline which strikes toward the adjacent Bare Anticline based on the dye tracing, borehole permeability, water table profiles, water budget, hydrochemistry of water resources and due to the presence of extensive crushed zones on the southern flank of the Gar Anticline.

Evaluating the reliability of time series analysis to estimate variable riparian travel times by numerical groundwater modelling

AbstractThe transition zones between rivers and adjacent riparian aquifers are locations of high biogeochemical activities that contribute to a removal of potentially hazardous substances in the aquatic system. The potential of the removal processes depends highly on subsurface water travel times, which can be determined by using the propagation of electrical conductivity (EC) signal from the river into the riparian aquifer. Although this method has been applied and verified in many studies, we observe possible limitations for the usage of EC fluctuation analysis. Our findings are based on EC time series analyses during storm events and artificial hydropeaks induced by watermill operations. Travel times derived by cross‐correlation analysis were compared with travel times calculated based on backward particle tracking of a calibrated transient numerical groundwater flow model. The cross‐correlation method produced only reasonable travel times for the artificial hydropeaks. In contrast, cross‐correlation analysis of the EC data during natural storm events resulted in implausibly negative or unrealistically low travel times for the bulk of the data sets. We conclude that the reason for this behaviour is, first, the low EC contrast between river and groundwater in connection with a strong damping of the infiltrating river EC signal into the subsurface during storm events. Second, the existence of old and less‐mineralized riparian water between the river and the monitoring well resulted in bank‐storage‐driven EC breakthrough curves with earlier arrival times and the subsequent estimation of implausible riparian travel times.

Review: Water–rock interactions and related eco-environmental effects in typical land subsidence zones of China

Land subsidence is common in some regions of China. Various eco-environmental problems have arisen due to changes in water–rock interactions in these subsided areas, for which a comprehensive understanding of the hydrogeological setting is needed. This paper presents the general status of land subsidence in three typical subsided areas of China through the compilation of relevant data, and reviews some typical changes in the water–rock interactions in subsided areas along with related eco-environmental issues. It is found that the subsidence development and distribution are controlled by the groundwater-withdrawal intensity externally, and by the thickness and compressibility of unconsolidated sediments internally. The physical changes and related effects of water–rock interactions in subsided areas include: (1) the decreased ground elevation that caused floods, waterlogged farmland, etc.; (2) the differential subsidence that caused ground fissures; and (3) the change of seepage field that caused substantial reduction of the water resource. Chemically, the changes and related effects of water–rock interactions include: (1) the change to the chemical environment or processes due to the hydrogeologic structure alteration, which caused groundwater pollution; and (2) hydrologic mixing (seawater intrusion, artificial recharge; exchange with adjacent aquifers or aquitards), which degraded the groundwater quality. Further research on the subsided areas in China is suggested to reveal the mechanisms regarding biological and gaseous (meteorological) changes from the perspective of interacting systems among water, rocks, biological agents and gases.

Geochemistry, Hydraulic Connectivity and Quality Appraisal of Multilayered Groundwater in the Hongdunzi Coal Mine, Northwest China

This study assessed the geochemistry and quality of groundwater in the Hongdunzi coal mining area in northwest China and investigated the mechanisms governing its hydrogeochemistry and the hydraulic connectivity between adjacent aquifers. Thirty-four groundwater samples were collected for physicochemical analyses and bivariate analyses were used to investigate groundwater quality evolution. The groundwater in the mine was determined to be neutral to slightly alkaline, with high levels of salinity and hardness; most samples were of SO4·Cl–Na type. Fluoride and nitrate pollution in the confined aquifers were identified, primarily sourced from coals. Natural geochemical processes, such as mineral dissolution, cation exchange, and groundwater evaporation, largely control groundwater chemistry. Anthropogenic inputs from agricultural and mining activities were also identified in both shallow unconfined aquifers and the deeper confined aquifers, respectively. It was determined that the middle confined aquifer has a high hydraulic connectivity with the lower coal-bearing aquifer due to developed fractures. Careful management of the overlying aquifers is required to avoid mine water inrush geohazards and groundwater quality deterioration. The groundwater in the mining area is generally of poor quality, and is unsuitable for direct human consumption or irrigation. Na+, SO42−, Cl−, F−, TH, TDS, NO3−, and CODMn are the major factors responsible for the poor quality of the phreatic water, while Na+, SO42−, F−, and TDS are the major constituents affecting the confined groundwater quality. This study is beneficial for understanding the impacts of coal mine development on groundwater quality, and safeguarding sustainable mining in arid areas.

Insights into arsenic retention dynamics of Pleistocene aquifer sediments by in situ sorption experiments

The migration of arsenic (As) enriched groundwater into Pleistocene aquifers as a consequence of extensive groundwater abstraction represents an increasing threat to the precious water resources in Asian delta regions. Pleistocene aquifer sediments are typically rich in FeIII-(hydr)oxides and are capable to adsorb high amounts of As. This results in a pronounced accumulation of As in Pleistocene aquifers, where high As groundwater infiltrates from adjacent Holocene aquifers. However, As retention by Pleistocene aquifers over long-term time scales remains largely unknown. We studied As sorption in situ by placing natural Pleistocene sediments and pure mineral phases directly inside groundwater monitoring wells at a study site near Hanoi (Vietnam). This in situ exposure allows for constant flushing of the samples with unaltered groundwater and the establishment of undisturbed sorption equilibria similar to those in local aquifer sediments, which is not readily attainable in traditional laboratory sorption experiments. The groundwaters in our experimental wells were characterized by different As concentrations (0.01–6.63 μmol/L) and redox states, reaching from suboxic to anoxic conditions (Eh of +159 to −4 mV). Results show that adsorption is the dominant As retention mechanism, independent from the respective groundwater chemistry (i.e. concentrations of dissolved P, HCO3− and Si). Whilst most of the As sorbed within the first week, sorption further increased slowly but consistently by 6–189%, respectively, within six months. Hence, the As sorption behavior of Pleistocene aquifer sediments should be determined over longer periods to avoid an underestimation of the As sorption capacity. Accompanying desorption experiments revealed that about 51% of the sorbed As was remobilized within six months when exposed to low As groundwater. We therefore conclude that a considerable proportion of the As accumulated in the aquifer sediments is prone to remobilization once the As concentrations in migrating groundwater decline. Remobilization of As should be considered in local water management plans to avoid contamination of precious groundwater resources with this As legacy.

Contaminant transport in a small deformation aquitard affected by the delayed drainage phenomenon

AbstractThis paper presents a formulation accounting for the effect of delayed drainage phenomenon (DDP) on the breakthrough of contaminant flux in an aquitard, by considering the movement of soil particles, porosity variation, hydraulic head variation, and transient flow during the consolidation. The water flow equation in an aquitard was based on the Terzaghi's consolidation theory, and the contaminant transport equation was derived on the basis of the mass balance law. Two cases were used to illustrate the effect of DDP on the contaminant transport in an aquitard of small deformation. It is found that the breakthrough time of contaminant in an aquitard is very long, which is mainly ascribed to the low permeability of aquitard and sorption of soil particles. It is also found that the increase of depletion, which is in general induced by the increase of thickness and specific storativity and the decrease of hydraulic conductivity, enhances the impact of DDP on the contaminant transport in an aquitard. A larger delay index (τ0) of DDP gives a greater delay breakthrough time (DBT) of solute transport in an aquitard, which controls the difference of the breakthrough time of contaminant transport in aquitards with and without the occurrence of DDP. For the cases where advection plays a dominant role during the process of solute transport, τ0 is almost linearly correlated with DBT, and the ratio of DBT over the breakthrough time without consideration of DDP also approximately shows a linear relationship with the ratio of specific storativity to porosity, given a fixed drawdown in the adjacent aquifer with the sorption being ignored.

The role of hydrogeological setting in two Canadian peatlands investigated through 2D steady-state groundwater flow modelling

ABSTRACTThis study investigated how hydrogeological setting influences aquifer–peatland connections in slope and basin peatlands. Steady-state groundwater flow was simulated using Modflow on 2D transects for an esker slope peatland and for a basin peatland in southern Quebec (Canada). Simulations investigated how hydraulic heads and groundwater flow exported toward runoff from the peatland can be influenced by recharge, hydraulic properties, and heterogeneity. The slope peatland model was strongly dominated by horizontal flow from the esker. This suggests that slope peatlands are dependent on the hydrogeological conditions of the adjacent aquifer reservoir, but are resilient to hydrological changes. The basin peatland produced groundwater outflow to the surface aquifer. Lateral and vertical peat heterogeneity due to peat decomposition or compaction were identified as having a significant influence on fluxes. These results suggest that basin peatlands are more dependent on recharge conditions, and could be more susceptible to land use and climate changes.

Jahani Salt Diapir, Iran: hydrogeology, karst features and effect on surroundings environment

The Jahani Salt Diapir (JSD), with an area of 54 km2, is an active diapir in the Simply Folded Belt of the Zagros Orogeny, in the south of Iran. Most of the available studies on this diapir are focused on tectonics. The hydrogeology, schematic model of flow direction and hydrochemical effects of the JSD on the adjacent water resources are lacking, and thus, are the focus of this study. The morphology of the JSD was reevaluated by fieldwork and using available maps. The physicochemical characteristics of the springs and hydrometric stations were also measured. The vent of the diapir is located 250 m higher than the surrounding glaciers, and covered by small polygonal sinkholes (dolines). The glacier is covered by cap soils, sparse trees and pastures, and contains large sinkholes, numerous shafts, several caves, and 30 brine springs. Two main groups of caves were distinguished. Sub-horizontal or inclined stream passages following the surface valleys and vertical shafts (with short inlet caves) at the bottoms of nearly circular blind valleys. Salt exposure is limited to steep slopes. The controlling variables of flow route within salt diapirs are the negligible porosity of the salt rocks at depth more than about ten meters below the ground surface and the rapid halite saturation along the flow route. These mechanisms prevent deep cave development and enforce the emergence points of brine springs with low flow rates and small catchment area throughout the JSD and above the local base of erosion. Tectonics do not affect karst development, because the distributions of sinkholes and brine springs show no preferential directions. The type of spring water is sodium chloride, with a TDS of 320 g/l, and saturated with halite, gypsum, calcite and dolomite. The water balance budget of the JSD indicates that the total recharge water is 1.46 MCM (million cubic meter)/a, emerges from 30 brine springs, two springs from the adjacent karstic limestone, and flows into the Firoozabad River (FR) and the adjacent alluvium aquifer. The FR cuts through the northern margin of the salt diapir, dissolving the glacier salts at the contact with JSD, increasing the halite concentration of the 17.7 MCM/a of the FR from 100 mg/l to 12,000 mg/l. This is a permanent process because the active glacier flows rapidly down the steep slopes into the river gorge from the nearby vent. The possible relocation of the FR channel would enhance the FR water quality, but disrupt the natural beauty of the diapir.

Discharge and environmental isotope behaviours of adjacent fractured and porous aquifers

The combined use of hydrogeological and hydrogeochemical methods can provide relevant information about the characteristics of aquifers in studies focused on groundwater protection and management. In the present study, spring discharge monitoring coupled with stable and unstable water isotopes was used to compare the behaviour of adjacent fractured and porous aquifers hosted in a 4.5 km2 area along the same slope in the northern Apennines, Italy. Based on stable isotope analyses of four springs, a plausible local meteoric water line and a local vertical isotopic gradient were identified. Additionally, tritium contents revealed a recent meteoric origin for groundwater via infiltration in the area. The results of monthly stable isotope monitoring, hourly spring discharge monitoring, hourly rainfall monitoring, and statistical analyses (time series analysis) suggested that although the adjacent aquifers exhibited pronounced geological and hydrogeological differences, few discrepancies were observed regarding groundwater infiltration and release processes. Notably, they exhibited similar temporal delays associated with the response to precipitation events due to the roles of macro-fractures and macro-porosity. Groundwater circulation was characterized by piston and memory effects in both the fractured and porous aquifers, and these effects reflect the roles of micro-fractures/fissures and micro-porosity. The study highlights the relevant contributions of isotopes in studies that focus on spring vulnerability and aquifer processes. Moreover, results obtained in the Pietra di Bismantova site are useful to increase hydrological knowledge on the quite relevant aquifers hosted in Epi-ligurian rock slabs and the surrounding slope deposits in the northern Apennines of Italy.

The shallow structure of a surface-rupturing fault in unconsolidated deposits from multi-scale electrical resistivity data: The 30 October 2016 Mw 6.5 central Italy earthquake case study

We report the results of a shallow electrical resistivity investigation performed across a normal fault that ruptured the surface displacing with average ~0.05m vertical offset alluvial fan deposits (<23kyr old) within an intermontane fault-bounded basin following the 30 October 2016 Mw 6.5 earthquake in central Italy. We adopted a multi-scale geophysical approach, by acquiring three 2-D electrical resistivity tomography (ERT) profiles centred on the coseismic ruptures, and characterized by different spatial resolution and investigation depth. Below the fault scarp, the ERT models show a narrow (~10m wide) and steeply-dipping moderately-resistive region (100–150Ωm), which we interpret as the electrical response of the fault zone displacing layers of relatively high-resistivity (300–700Ωm) values. We explain the electrical signature of the retrieved fault zone as due to an increment of permeability caused by coseismic fracturing, and to the subsequent water migration from adjacent shallow aquifers squeezed by compaction induced by seismic waves. By using a statistically-based classification of electrical units, we estimate that the shallowest alluvial fan layer is affected by 2.7±0.9m vertical offset, which is consistent with the measured 2.3–2.8m morphologic offset of the top fan surface, and suggesting a post-12 kyr throw-rate of 0.23±0.08mm/yr. Similarly, we evaluate a post-23 kyr throw of 5.1±1.7m, indicating a Late Pleistocene throw-rate of 0.22±0.07mm/yr, in accordance with available paleoseismic data. We further hypothesize a minimal total fault throw >30m, which likely accrued since the Middle Pleistocene (possibly in the last 350–500kyr). The investigated fault structure is therefore an important splay characterized by a thick and highly permeable damage zone in unconsolidated deposits, and which ruptured the surface during several tens of strong (M>6) earthquakes.

3D Geological Model of Potential CO2 Storage: Abandoned Oil and Gas Field LBr-1in the Vienna Basin

Successful CO2 storage in abandoned oil and gas fields, building the underground gas storages, and enhanced oil and gas recovery require a functional 3D static geological model of the storage complex with the real geometry and conditions. Abandoned oil and gas field Lanzhot-Brodske North (LBr1) on the territory of the Czech Republic was selected for the preparation of a pilot research project of the geological CO2 storage. It is situated in the Northern part of the Vienna Basin, close to the Czech-Slovak border. The 3D-model includes a separate northern part of the LBr1 field. The 3D model is designed to serve as an input for the dynamic model and makes it possible to experiment and test simulations of the CO2 storage in a more-or-less real geological environment. The model documents areal and vertical extent of the storage complex, geological structure formed by the Lab reservoir horizon, trap seal built by the overlying clays, overlying and adjacent strata, aquifers, faults, natural and artificial migration paths. Further information provided by the model consists of the reservoir volume, pore space, reservoir properties, fluid distribution, and saturation by the pore fluids. A simplified 3D-model of the reservoir overburden offers a basis for risk analysis of potential fluid migration into shallower aquifers.

Processes governing arsenic retardation on Pleistocene sediments: Adsorption experiments and model‐based analysis

AbstractIn many countries of south/south‐east Asia, reliance on Pleistocene aquifers for the supply of low‐arsenic groundwater has created the risk of inducing migration of high‐arsenic groundwater from adjacent Holocene aquifers. Adsorption of arsenic onto mineral surfaces of Pleistocene sediments is an effective attenuation mechanism. However, little is known about the sorption under anoxic conditions, in particular the behavior of arsenite. We report the results of anoxic batch experiments investigating arsenite (1–25 µmol/L) adsorption onto Pleistocene sediments under a range of field‐relevant conditions. The sorption of arsenite was nonlinear and decreased with increasing phosphate concentrations (3–60 µmol/L) while pH (range 6–8) had no effect on total arsenic sorption. To simulate the sorption experiments, we developed surface complexation models of varying complexity. The simulated concentrations of arsenite, arsenate, and phosphate were in good agreement for the isotherm and phosphate experiments while secondary geochemical processes affected the pH experiments. For the latter, the model‐based analysis suggests that the formation of solution complexes between organic buffers and Mn(II) ions promoted the oxidation of arsenite involving naturally occurring Mn‐oxides. Upscaling the batch experiment model to a reactive transport model for Pleistocene aquifers demonstrates strong arsenic retardation and could have useful implications in the management of arsenic‐free Pleistocene aquifers.

Unstable convection flow as a controlling process of increasing salinity in the saline lake coastal aquifers: case of Maharlu Lake coastal aquifer

Deterioration of freshwater aquifers adjacent to saline lakes is a serious environmental and water resources management problem. Generally, different phenomena including saltwater intrusion, upconing, free and forced convection flow can lead to the salinization of fresh aquifers in the vicinity of saline lakes. The severity of this problem depends on hydrogeological and hydrogeochemical conditions of coastal saline lake aquifers. Accordingly, Maharlu Lake in the southeast of Shiraz plain is one of these saline lakes and has an important impact on its adjacent fresh aquifers so that the salinity of these aquifers has increased in recent years. Since the lake has special conditions such as very flat and low permeable floor and variable water level fluctuation during a year, with the onset of the rainy season after a long-term well pumping in the adjacent aquifer, the lake water covers a wide extent of the lake area in a short time. Then, because of the higher permeability of the surface of the lake in its southeast margin, conditions for convection flow are provided there. In this study, salinity distribution in one of the aquifers (Bokat aquifer) in the southeast of the lake is investigated using resistivity tomography along several profiles. Interpretation of inverse models of these profiles showed that convection flow is an important process in increasing the salinity of fresh aquifer. Comparison of the results of geo-tomography sections with convection index map of the Bokat aquifer showed that getting closer to the lake, free convection flow becomes the dominant process in the salinity distribution. In addition, in farther distances relative to the lake, due to increasing the pumping rate of the extraction wells, forced convection flow is an important process.

Effect of pumping on hydrologic system of a young satellite city in south Bengal Basin through numerical modelling: past, present and future

Hydrogeologic analysis based on groundwater modelling was used to evaluate the past, present and possible future states of the groundwater system that will supply water to a future population of more than 1.5 million of the newly developed urban centre of Rajarhat New Town (RNT). This city is located in the north eastern fringe of Kolkata megacity. Pumping of groundwater beneath this satellite city will modify the subsurface hydrologic system. Drastic changes in head distribution patterns, recharge areas of the RNT aquifer and outflow areas of arsenic-affected wells in adjacent contiguous aquifer under current and future development conditions indicate that human impacts far outweigh topographic and geologic forces on the groundwater flow system. Interference effects were also observed in wells of the nearby urban centres. Future groundwater abstraction in RNT may lead to further reduction in groundwater levels in the neighbouring Kolkata megacity and may increase the rate of transport of contaminants to the RNT aquifer.