Aquifer Formation Research Articles

Assessment of interaction between the aquifers by geochemical signatures in an urbanised coastal region of India

Multi-layered coastal aquifers are complex aquifer systems with two or more aquifers divided by the impermeable or semi permeable layers. The objective is to assess the interaction between the aquifers using geochemical indicators in the urbanised multi-layered coastal aquifer of Sankaraparani river basin, India. Hydrogeologically, the coastal part of this region comprises of alluvium formation as upper aquifer and sandstone formation as lower aquifer. Groundwater samples were collected from 33 representative wells during June 2017 and January 2018. Electrical conductivity, pH, and alkalinity were measured in the field while the concentration of major ions was analysed in the laboratory. The groundwater level in the upper aquifer varies from 7.4 to 18 m msl. Na-Cl type groundwater is dominant in the upper aquifer whereas Ca-HCO3 and mixed Ca-Na-HCO3 type groundwater is dominant in lower aquifer. The processes that controls the groundwater chemistry are sulphate reduction, freshening ion exchange, calcite dissolution and conservative mixing of seawater and freshwater. Significantly different values of electrical conductivity, sodium and chloride ratio, base exchange index as well as the different geochemical facies between the upper and lower aquifer indicates the absence of interaction between the aquifers near to the coast. Whereas in the west, the similarity in these confirms the interaction and both the formation function as single aquifer. The groundwater in the upper aquifer is affected by seawater intrusion upto 2 km whereas the lower aquifer is not affected.

Evolution Mechanism of Water-Conducting Channel of Collapse Column in Karst Mining Area of Southwest China

There are many karst collapse columns in coal seam roof in the southern coal field in China, which are different from those in coal seam floor in the northern coal field, due to the stratum characteristics. The karst collapse column in coal seam roof tends to reactivate and conduct water and induce the serious water inrush disaster, when the karst collapse column communicates with the overlying aquifer. In order to reveal the evolution mechanism of water-conducting channel of collapse column in karst mining area of southwest China, the aquifers and water inflow rule in 1908 working face in Qianjin coal mine are analyzed. Besides, the particle size distribution and mineral component of collapse column are researched by the X-ray diffraction test and the screening method, which are the basis for researching the water inrush mechanism in karst collapse column. On this basis, the water inrush of roof collapse column under the influence of mining is researched by establishing the numerical calculation model with the UDEC numerical software. The results show that the water flowing into the 1908 working face comes from the Changxing formation aquifer and Yulongshan formation aquifer above the coal seam, and the proportion of coarse particles and fine particles in collapse column is 89.86% and 10.14%, respectively. With the advance of working face, the water-conducting channel connected the working face with the aquifer, or the surface is formed by collapse pits, karst caves, and collapse column. The research results can be treated as an important basis for the water-preserved mining in southern coal field in China.

Quartz Stressing and Fracturing by Pore Pressure Dropping Down to Negative Pressure

In water-bearing porous rocks, pore pressure variations play a major role in deformation, through dissolution−precipitation and fracturing processes. An often-overlooked variation where pressure falls to negative pressure or tension can operate whenever aquifer formations dry out, for instance, in deep storage (nuclear or industrial wastes, long-term CO 2 mitigation, short-term energetic resources, etc.). This can generate capillary tension within the aquifers. This study investigates the mechanical effect of such in-pore tension in the surrounding crystal field, through laboratory experiments at the one-pore scale. Microthermometric procedures were carried out on synthetic fluid inclusions to generate large tensile stress and were combined with Raman microspectrometry to visualize the resulting stress fields in the host quartz. For comparison, we numerically modeled the stress field by linear elasticity theory. The experiments demonstrate that significant damage is produced in crystalline materials by the pore tension. Despite the induced stress measured by micro-Raman spectrometry to remain moderate, it is able to fracture the quartz. The volume of the cavity is a prominent controlling parameter for the stress amplitude. The crystalline heterogeneities of the solid are another major parameter for localizing the mean weak stress and accumulating overstress. Our results call for bringing pore-scale micromechanics into the safety assessment of the geological storage of various wastes inside depleted aquifers. They also show the magnifying effect of heterogeneities on propagating stress and localizing it along certain directions, promoting the final failure of water-bearing minerals, rocks, or pore networks.

Statistical analyses of groundwater chemistry in the Qingdong coalmine, northern Anhui province, China: implications for water\u2013rock interaction and water source identification

Hydrochemistry of groundwater is important in coal mines because it can be used for understanding water–rock interaction and inrush water source identification. In this study, major ion concentrations of groundwater samples from the loose layer aquifer (LA), coal-bearing aquifer (CA) and Taiyuan Formation limestone aquifer (TA) in the Qingdong coal mine, northern Anhui province, China, have been analyzed by a series of statistical methods for identifying the source of chemical constituents in groundwater and the source of inrush water. The results indicate that the mean concentration of the major ions in the LA were ordered as follows: HCO3− > SO42− > Na+ + K+ > Cl− > Ca2+ > Mg2+ > CO32−, whereas average values of the CA in decreasing order are SO42−, Na+ + K+, HCO3−, Cl−, Ca2+, Mg2+ and CO32−, and the major ion concentrations of the TA have the following order: SO42− > Na+ + K+ > Ca2+ > HCO3− > Cl− > Mg2+ > CO32−, and most of the samples are Na-SO4 and Ca-SO4 types. TDS content in water increases with aquifer depth, whereas the pH values ranged from 7.1 to 8.9, indicating a weak alkaline environment. Two sources (weathering of silicate minerals and dissolution of evaporate minerals) have been identified by principal component analysis responsible for the chemical variations of the groundwater, and their contribution ratios have been quantified by Unmix model. Moreover, based on the Q-mode cluster and discriminant analyses, the samples with known sources have been identified correctly to be 95.7% and 97.6%, respectively, and the samples with unknown sources have been determined with high probability (78–100%).

Natural Radioactivity in Thermal Waters: A Case Study from Poland

A natural radioactivity in thermal water was investigated based on 19 selected thermal waters from Poland. The analysed results show that the radionuclides’ concentrations in the study waters vary over a wide range. The temperature of the waters varies from above 20 °C to above 80 °C. The waters are characterised by different mineralisation, chemical compositions, and belong to different hydrochemical types. There is a good correlation between the water temperature and the depths of the aquifer formations occurrence, suggesting the thermal energy originates from the thermal geogradient. The concentration of radium is well correlated with the water mineralisation. The ratio of radium activity (226Ra/228Ra) in groundwater relates not only the ratio of uranium activity to that of thorium (238U/232Th) in aquifer formation, but also depends on the physical and chemical water properties. Based on the concentration of radon and its transport model, the radiation exposures due to inhalation of 222Rn and its progeny for employees and clients of the spa were assessed. The use of the thermal waters as a drinking resource may be problematic due to the possibility of exceeding the recommended annual committed effective dose 0.1 mSv.

Irrigation Water Susceptibility Indexing Method, Using Pesticide DRASTIC and Water Quality Index, for Basara Basin; Kurdistan Region-Iraq

The increasing use of chemical fertilizers, with spreading industrial and urbanization activities in the whole area of the Basara basin expected to affect the quantity and quality of water from these sources of pollutants. The main aim of this research revolves around the integration of the intrinsic vulnerability Index (VI) through applying the pesticide DRASTIC method, with the irrigation quality index, to assess the irrigation susceptibility Index (SI) for the basin. The quality of groundwater for its suitability for irrigation purposes was measured by its hydro-chemical parameters in this research. Thirty-one water samples were collected in the studied area during the post-monsoon period of the year 2018. Samples have been tested for both physical and chemical parameters. The Geographic Information System (GIS) has been used for this assessment. The results indicate that water movement directions of streams, the geological formation of aquifers, land slope, and contamination sources have a great impact on water quality, vulnerability, and susceptibility index. The pesticide DRASTIC map categorizes the basin into five classes as (very low, low, moderate, high, and very high). Results show that the most vulnerable area to pollution is those that used for intensive agricultural and industrial sectors, besides the areas with high permeability and lands with minimum surface slopes which are intensively used as cultivated areas. The results indicate that the incorporation of both hydrogeological and hydro-chemical datasets enables more realistic evaluations than those of an individual dataset to estimate the groundwater contamination susceptibility of an aquifer. This work offers the decision-makers a clear photo of the quality of irrigation water and the area most vulnerable to contamination. This will be used as the basis for future research to mitigate the effects of vulnerable areas and to establish a new groundwater management strategy in the basin.

Using GIS and Geostatistical Techniques for Mapping Piezometry and Groundwater Quality of the Albian Aquifer of the M’zab Region, Algerian Sahara

The M’zab region is subject to an arid Saharan climate where surface and sub-surface waters are of little importance. The Albian Aquifer, commonly called Continental Intercalary (CI), main component of North Western Sahara Aquifer System (NWSAS/SASS), constitutes the most extensive aquifer formation of the region. In our study area, the CI is identified, as a regional subset, as the Albian Aquifer of M’zab Region (AAMR). Its groundwater resources are considered the only source available to meet the growing needs of drinking water supply, agriculture and industry. This aquifer is heavily exploited by a very large number of wells (more than 750). Its supply is very low, so it is a very low renewable layer. This requires periodic monitoring and control of its piezometric level and its physico- chemical quality. The objective of our study is to know the current state of this aquifer, while studying the variation of its piezometry for the period 2010-2018, and also the chemical quality of its groundwater by analyzing more than 90 samples over the entire study area. The application of geostatistics by kriging and the steps of analysis, modelling and calculation of semivariogram have enabled us to draw up maps of the various hydrogeological and hydrochemical parameters. As a result, twelve thematic maps were gridded using Geostatistical tools of ArcGIS software. The water-level-change map showed a significant drop in the groundwater level over the entire M’zab region and especially around the major cities (Ghardaïa, Berriane, Metlili and Zelfana) with more than 8 meters. Chemical analyses of the Albian groundwater in the study area show the dominance of evaporite facies (Cl--Na+-Ca2+) with low concentrations than the Algerian Standards for Drinking (ASD). All the water quality indices (WQI) that have been mapped reveal that the groundwater samples were suitable for drinking and irrigation with a high quality of water located in the south of the study area.

Advantages of employing multilevel monitoring wells for design of tunnels subjected to multi-aquifer alluvial

For tunnels being excavated through multiple aquifer formations, having precise knowledge of the aquifers’ hydraulic head becomes essential for determining groundwater inflow into the tunnel and analyzing its stability, specifically using multilevel monitoring systems. In the multi-aquifer alluvial section of the Glas tunnel (Iran), since the hydraulic head calculations were based on the data obtained from single-piezometer boreholes, the excavation risk was assessed to be at high level and the tunnel seemed to be unstable, thus an incorrect conclusion was derived from the misleading data. To take cost mitigation measures into account, it was necessary to calculate the hydraulic head at tunnel level accurately. By installing nested and clustered wells the mean hydraulic head was measured to be 70 m, significantly different from the 90 m previously determined by boreholes. Considering the updated value, the groundwater inflow and bulkhead load, formerly calculated as 0.65 m3/s and 9.5 bars, were determined to be 0.49 m3/s and 7.5 bars, respectively.

Baseline monitoring for time-lapse pressure tomography: Initial results from Otway Stage 3

As part of the CO2CRC Otway stage 3 project, time-lapse cross-well pressure tomography methods are being developed to demonstrate unobtrusive, continuous and low-cost monitoring of an injected CO2 plume. Active pressure tomography relies on a robust baseline set of water injections and environmental monitoring to characterise the aquifer in its base state, before CO2 has been injected. Here, we report the initial results from such baseline testing. In late 2019, 4 new monitoring wells were drilled (CRC-4 to 7), in addition to the existing CRC-2 well (where CO2 injection occurred during the stage 2C project) and the CRC-3 well which is the primary CO2 injection well for stage 3. These wells were completed in the Paaratte aquifer formation at depth ≈1500m TVD. Two sets of baseline test sequences were performed, with water injection occurring sequentially at CRC-4, 5, 6 and 7, with all wells (including CRC-2 and 3) continuously monitoring the subsurface pressure. High-quality downhole, surface and weather data were acquired for each sequence, with monitored downhole pressures generally repeatable to within the base environmental noise level. An adjoint Bayesian inversion method was developed to invert for the depth-averaged aquifer petrophysical properties, based on the monitored pressure signals. The Bayesian framework utilised prior aquifer information - interpreted faults and an independently developed geological static model - to inform and constrain the inversion. The resulting baseline model is able to capture the complex time-series pressure propagation across the aquifer subject to the various water injections. Heterogeneous regions of permeability, porosity and aquifer thickness account for the subtle variations in pressure peak arrival time and magnitude observed at the various wells, with spatial variations at a resolution that is a small fraction of the well spacing. The baseline injections and aquifer model provide a robust base for repeat water injections once CO2 has been injected in the next stages of the project.

REVIEW OF THE LAND SUBSIDENCE HAZARD IN PEKALONGAN DELTA, CENTRAL JAVA: INSIGHTS FROM THE SUBSURFACE

Land subsidence is a global threat to coastal areas worldwide, including the North Java coastal area. Of many areas experiencing land subsidence in North Java, the rate of land subsidence in Pekalongan has matched the high subsidence rates usually found in big cities. The rate of land subsidence in Pekalongan far exceeds the sea-level rise, resulting in a looming threat of land loss. The devastating impacts of land subsidence are the manifestation of its subsurface movement. Therefore, it is essential to understand the subsurface to elucidate the mechanism of land subsidence. Previous studies on land subsidence in Pekalongan are mainly related to subsidence rate monitoring and have not elaborated on the subsurface condition. This paper reviews the Pekalongan subsurface geology based on available literature to provide insight into the land subsidence problem. The results revealed that the land subsidence occurs in the recent alluvial plain of Pekalongan, consisting of a 30-70 m thick compressible deposit. Possible mechanisms of land subsidence arise from natural compaction, over-exploitation of confined groundwater, and increased built areas. As the seismicity of the study area is low, tectonic influence on land subsidence is considered negligible. It is expected that the offshore, nearshore, and swamp deposits are still naturally compacting. As the surface water supply is minimal, over-exploitation of groundwater resources from the deltaic and Damar Formation aquifers occurs. In the end, future research direction is proposed to reduce the impacts of the subsidence hazard.

Harvesting geothermal energy with low unit cost installations

In the Netherlands, most geothermal energy is utilized for commercial greenhouse heating and is harvested from aquifers located at depths between 2 and 3 km. Typically, the design consists of two wells: a slanted production well and a slanted injection well that are spaced approximately 1.5 km apart in the aquifer formation. Subsidized exploitation is feasible if high volumes can be produced over long periods of time. This typical solution restricts the use of geothermal energy to high-demand applications in areas with suitable high-quality aquifers. We argue that harvesting geothermal energy is economically feasible almost anywhere in the Netherlands with an alternative concept of low unit cost (LUC) installations. LUC produces at a limited rate from cleverly designed high-quality installations that can be developed at a considerably lower cost. We discuss the LUC concept and its economics based on a project for commercial greenhouse heating in the eastern part of the Netherlands. We carry out a reinterpretation of publicly available 3D seismic and offset well data. The Early Cretaceous Bentheim Sandstone was identified as a suitable aquifer for LUC development. At the proposed well location, the top Bentheim is located at a depth of approximately 1500 m, corresponding to about 61°C. We predict a reservoir thickness of approximately 54 m, with a porosity of up to 25% and sufficient permeability. The LUC concept begins by drilling a pilot hole for static and dynamic aquifer characterization. Based on these test results, we decide on the final architecture and placement of wells. Our calculations show that a 1.5 megawatt thermal (MWth) geothermal plant is economically viable, even without government subsidy.

Impact of subsurface structures on groundwater exploration using aeromagnetic and geoelectrical data: a case study at Aswan City, Egypt

Geological evaluation and groundwater assessment, especially in arid areas, are considerable targets for constructing recent and sustainable development communities. The current work aims to apply an integrated approach to acquire geologic structures and groundwater potentiality at highly deformed area. As a case study, remote sensing (RS), aeromagnetic, and geoelectrical data are conducted to delineate the subsurface structures and hydrogeological regime at Aswan City. Initially, remote sensing data with GIS software are utilized to delineate the surface structures and watershed configuration. Moreover, the reduced to magnetic pole (RTP) aeromagnetic data is processed and interpreted using appropriate filters. In an attempt to demonstrate the subsurface structures and basement relief maps, the RTP map was analyzed considering the RS data which was stated in previous stage. In the light of RTP aeromagnetic results and well logging data, the direct current resistivity (DCR) sounding is executed particularly along paleochannel and flood plain portion. Due to the inversion process problem of DCR field data, advanced solutions and algorithms are applied to improve the property of the results. Based upon overall results mentioned above, the correlation between subsurface structures and aquifer formation can be monitored. The present approach can be applied for groundwater exploration in this and other similar geological and hydrogeological environments around the world.

Effects of coastal lagoon water level on groundwater fluxes of nutrients to the coastal zone of southern Brazil

Abstract Groundwater discharge represents a potentially important source of dissolved nutrients to the coastal ocean. The barrier complex along the coast of southern Brazil separates the Patos Lagoon (PL) from the South Atlantic Ocean and supports the formation of the adjacent surficial aquifers which are connected to both water bodies. Due to the high hydraulic head of the PL regarding the ocean, groundwater flows toward the coastal waters. In this study fresh groundwater nutrient fluxes to the coastal ocean were estimated considering high and low PL water level scenarios. The groundwater fluxes were estimated applying Darcy's Law and the result was 0.043 m3 km−1 day−1. Different low and high PL water level scenarios showed a change in the nutrient availability along barrier. In the lowest PL water level scenario, the nutrient flux concentrations became more significant, which may have had an increase of approximately 25%. In the highest PL water level scenario, concentrations had a decrease of up to 78%. In the molar ratio (106C: 16 N: 1P), P resulted as a potentially limiting nutrient, providing a high primary productive potential to the environment (2735 gC m−2 y−1).

Relationship Between Aquifer Pumping Response and Quality of Water Extracted from Wells in an Active Hydrothermal System: The Case of the Island of Ischia (Southern Italy)

The thermal waters of the Island of Ischia, an active volcano located in Southern Italy, are widely used for supplying numerous spas. Groundwater withdrawals occur mainly through wells in the coastal strip. This study explores the impact of withdrawals on the quality of the waters used in thermal facilities, which is required to be constant in terms of composition and temperature by law. For this purpose, specific investigations were conducted including 155 pumping tests, 124 water temperature measurements during pumping tests, 31 temperature and electrical conductivity logs and periodic chemical analysis of the waters of 21 selected wells. By comparing the response to pumping of the aquifer and the quality of the water extracted from the wells, it turned out that the quality of groundwater supplying spas depends not only on natural phenomena (meteoric recharge, seawater intrusion, and rising of deep hydrothermal fluids) but also relies on the island sector where groundwater is pumped and on the pumping method. The distance of the wells from the coast, the type of aquifer formation intersected by the wells, and the field of groundwater temperature of the hydrothermal system strongly affect the aquifer pumping response, determining the quality of water extracted from wells and its variation over time. In Ischia, techniques and regimes of groundwater withdrawals should adapt to the local aquifer pumping response, more than in another hydrogeological context. The concomitant analysis of drawdown, water temperature, and salinity during pumping turned out to be a valuable tool to define the sustainable yield of the single well.

A study on the application of ATEM in hydrogeological investigation

Airborne time-domain electromagnetic (ATEM) which is suitable for large-scale exploration in complex terrain areas is a high-efficiency, flexible geophysical investigation technique widely applied in various fields of work with broad application prospects. It is difficult to carry out ground geophysical exploration because of the great human disturbance in the study area. By applying ATEM in the air, together with ground geophysical investigation efforts, we were able to greatly improve the hydrogeological research degree of the area and provide useful geophysical data for the fundamental geological research there. The observation system used in our study was an AeroTEM-IV system. The survey data were converted into conductivity depth information, which was used together with existing geological data to examine the electrical structure of the area. By the hydrogeological logging interpretation result, we validated the reliability of the AEM data; comprehensive interpretation was also conducted using airborne magnetic (AM) data to improve the accuracy of the interpretation result. After converting the data across the area, we yielded a three-dimensional data body representing the electrical distribution in the area, with which we inferred the Quaternary formation thickness and aquifer distribution there. Our research and interpretation results confirm that ATEM can be used as a useful means for hydrogeological survey and fundamental geological investigation. It is an effective supplement to ground geophysical exploration.

A new method for estimating hydraulic conductivity in un-screened concrete-lined large-diameter hand-dug wells

The use of large-diameter hand-dug wells as main source of rural water supply for drinking, domestic and irrigation uses in many developing countries has offer an opportunity to developed Darcy-based methods for estimating hydraulic conductivity in screened-lined large-diameter hand-dug wells to determine the yield and discharge potential of the wells. However, in many rural areas of sub-Saharan African countries, the use of un-screened concrete lining is most common method of protecting large-diameter hand-dug wells against collapsing and pollution due to the affordability of the method. The use of un-screened concrete lining prevents horizontal water flow to the well and inflow of water in un-screened concrete well occur through well base, therefore, existing Darcy-based method not suitable to estimate hydraulic conductivity for this well design. This study proposed a new method for estimating aquifer hydraulic conductivity for un-screened concrete-lined large-diameter hand-dug wells. To demonstrate the viability of the new method, field recovery tests were conducted in twelve (12) un-screened concrete lined large-diameter hand-dug wells to estimate apparent hydraulic conductivity (Ka) of aquifer formation. The twelve (12) un-screened concrete wells were screened for the second round of recovery tests to estimate horizontal hydraulic conductivity K. The results showed that the estimated apparent hydraulic conductivity Ka values were lower than the horizontal hydraulic conductivity K values and this show effect of un-screened concrete-lining. A relationship between Ka and K was established to make a correction factor for estimation of K from Ka by a regression analysis which showed a linear regression of 0.78 with a significant strong relationship of 0.00 between Ka and K using a bivariate Pearson correlation coefficient. The new method will be useful to determine well yield most especially in the rural areas of developing countries where un-screened concrete-lined large-diameter hand-dug wells are being practiced.

Numerical investigation of optimum ions concentration in low salinity waterflooding

Injecting low saline water is one of the practices used to improve hydrocarbon production that has recently significantly grown due to its advantages over seawater and chemical flooding. Although many theories and mechanisms have been provided on how additional oil recovery has been achieved utilizing low salinity waterflooding, the principle fundamentals of the mechanism(s) are still ambiguous. This article investigates the potential use of low salinity waterflooding (LSWF) to improve oil production from a sandstone formation. A 3D field-scale model was developed using Computer Modeling Group ( generalized equation-of-state model simulator) based on a mature oil field data. The developed model was validated against actual field data where only 8% deviation was observed. Simulation analysis indicated that multi-component ion exchange is a key factor to improve oil production because it alters rock wettability from oil-wet to water-wet. Simulation sensitivity studies showed that low salinity water flooding provided higher oil production than high water salinity flooding. Moreover, simulation showed early breakthrough time of low salinity water injection can provide high oil recovery up to 71%. Therefore, implementing LSWF instantly after first stage production provides recovery gains up to 75%. The determined optimal injected brine composition concentration for Ca 2+ , Mg 2+ and Na + are 450, 221, and 60 ppm, respectively. During LSWF, a high divalent cations and low monovalent cations’ concentration can be recommended for injected brine and formation aquifer for beneficial wettability alteration. Simulation also showed that reservoir temperature influenced the alteration of ion exchange wettability during LSWF as oil recovery increased with temperature. Therefore, high temperature sandstone reservoirs can be considered as a good candidate for LSWF. Cited as : Ben Mahmud, H., Mahmud, W.M., Arumugam, S. Numerical investigation of optimum lons concentration in low salinity waterflooding. Advances in Geo-Energy Research, 2020, 4(3): 271-285, doi: 10.46690/ager.2020.03.05

Characterisation of fractured carbonate aquifers using ambient borehole dilution tests

Fractured carbonate aquifers derive their transmissivity essentially from a well-developed network of solutionally-enhanced fractures and conduits that can lead to high groundwater velocities and high vulnerability to contamination of water quality. Characterisation of the variation of hydraulic properties with depth is important for delineating source protection areas, characterising contaminant fate and transport, determination of the effectiveness of aquifer remediation, and parameter estimation for models. In this work, ambient open borehole uniform and point injection dilution tests were conducted on observation boreholes in the unconfined Cretaceous Chalk aquifer of East Yorkshire, UK, and interpreted in conjunction with other data via the implementation of a new work flow. This resulted in the characterisation of flow in these boreholes and the inference of properties such as groundwater flow patterns and velocities in the surrounding aquifer formation. Our workflow allowed sections of open boreholes showing horizontal versus vertical flow to be distinguished, and the magnitude of such flows and exchanges with the aquifer to be determined. Flow within boreholes were then used to characterise: i) presence and direction of vertical hydraulic gradients; ii) nature and depth distribution of flowing features; iii) depth interval porosity and permeability estimation of the flowing features from overall borehole transmissivity and geophysical image or caliper logs; iv) groundwater velocity estimation in the surrounding aquifer. Discrete flowing features were distributed across the range of depths sampled by the observation boreholes (typically up to 45–60 mbgl), but the majority were located in the zone of water table fluctuation marked by solutionally enlarged flow features. Quantitative interpretation of both uniform injection (tracer distributed throughout the open borehole section) and point injection (slug of tracer introduced at targeted depth) yielded vertical velocities within the borehole water column in broad agreement with those measured by flow logging. Depth specific fracture kinematic porosities inferred from the ambient dilution data combined with long-interval pump test and geophysical log data ranged between 3.7 × 10−4–4.1 × 10−3 with an average of 2.1 × 10−3; these values were in excellent agreement with those from other methods applied to the same aquifer such as larger scale pumping tests. A new approach to estimation of groundwater velocities from the dilution test data using externally measured hydraulic gradients gave inferred horizontal groundwater velocities ranging between 60 and 850 m/day, in full agreement with those from previously conducted borehole-to-borehole tracer tests. These results confirm that the studied aquifer is karstic, with rapid preferential pathways which have implication for flow and transport modelling, and pollution vulnerability. Our study results indicate that ambient single-borehole dilution approaches can provide an inexpensive and reliable approach for the characterisation of fractured and karstic aquifers.

Aquifer characterization using vertical electrical soundings and remote sensing: A case study of the Chott Ech Chergui Basin, Northwest Algeria

The aim of this study is to provide detailed geological and structural information about groundwater aquifers in the Chott Ech Chergui region using geophysical and remote sensing data. The Chott Chergui region is a large endorheic depression situated in the northwestern part of Algeria. It is submerged in water, and for that reason, it is considered to be a humid zone even though the region is considered to be a semiarid area. The largest quantities of water come from the northern mountains of Saïda and Tlemcen. Some water recharge comes from the Ksour and Amour mountains to the south. Large amounts of this water reach the underground aquifers through a dense fracture network. These water resources are stored in a lithological complex that is composed of three closely related aquifer formations, namely, the continental Tertiary aquifer, the Senonian aquifer and the Aaléno-Bathonian aquifer.The Kheiter and Ain Skhouna areas are known for their gushing water springs that exhibit high flow rates (80 l/s for Ain Skhouna). It is for this reason that we focus on these two regions to understand their flow mechanisms and attempt to construct a conceptual model that illustrates the functional mechanism of the Ain Skhouna spring.This work was accomplished employing a combined approach involving Remote Sensing method and electrical resistivity, specifically, the vertical electrical sounding (VES) technique. The VES technique was used to understand the aquifer geometries and their spatial extents, while the remote sensing results were used to detect some structures and lineaments that favor groundwater exploration. The aquifer geometry was analysed by integrating the results obtained from the interpretations of VES with stratigraphic columns of wells and boreholes using a geographic information system. The results of this study show that three geological levels present aquifer potentialities. The geologic zones are the Aaleno-Bathonian aquifer, which is the most important aquifer in the study area with an average thickness of 250 m, the Senonian aquifer and Tertiary aquifer. The aquifers recharge mainly from fractures in the Saïda and Tlemcen Mountains for the Aaleno-Bathonian aquifer, and from direct infiltration from the accumulated surface waters for the Senonian and Tertiary aquifers. Many water sources are sporadically distributed in the Chott Ech Chergui, but the gushing waters seems to be controlled by E-W accidents, especially in Ain Skhouna hot spring. A schematic model of the spring is presented.

Pit Lake and Drinking Water Intake: Example of Coexistence (Middle Urals, Russia)

The dewatering system of the Lipovsky nickel mining pit (Middle Urals, Russia) has performed a dual role. From 1961 to 1991, while nickel was being mined there, it protected the pit from flooding with groundwater; since 1989, it has been the principal source of drinking water for the town of Rezh (≈ 50,000 residents). After mining ceased, water withdrawal from the drainage wells decreased 2.5 times (to 100 L/s), resulting in a 120 m deep pit lake. A mass balance analysis has shown that water from the pit lake has become the leading source of water intake. However, the concentrations of the water’s basic constituents at the eastern edge of the pit are several times higher than at the western edge. The reason for the significant increase in the water withdrawn by the wells of the western intake is the fact, that during the working of the main ore body, the eastern part of the pit was filled with overburden rock and substandard ore with dispersed sulfide mineralization. Flooding of the pit created a single aquifer between the pit lake and the eastern water intake facility, including an artificial aquifer within the refilled part of the pit. The rise of the groundwater level in the artificial aquifer to an elevation above 150 m (after 1994) led to active chemical weathering of sulfide-containing minerals and dissolution of secondary sulfates, which accounts for the increasing levels of constituents in the eastern part of the pit. The artificial aquifer has become a generator of salts. The dumping of sulfidic wastes and subsequent recovery of the water table have led to the release of sulfate, calcium, and metals into the local groundwater. To prevent the formation of an artificial aquifer, it is necessary to either completely remediate the unflooded portion using non-acid generating material or completely inundate the pit. Partial remediation would be the worst scenario as it could destabilize the hydrogeochemical processes and render long-term coexistence of the drinking water intake and the flooded pit problematic.