Intermediate Aquifer Research Articles

Contribution of the time domain electromagnetic method to the study of the Kalahari transboundary multilayered aquifer systems in Southern Angola

AbstractThe Cunene Province (Southern Angola) is facing recurrent and pluriannual droughts. Surface water supply could be reinforced using the groundwater resources of the multilayered aquifer systems (MAS) hosted in the siliciclastic sediments of the Kalahari Group. The MAS were first identified in the early 2000s in Northern Namibia and recently in the Cunene Province, by studies of the PLANAGEO project based on modern processing and reinterpretation of legacy data from the 1960s and 1970s (electrical resistivity data and deep boreholes). This article presents the results of a time domain electromagnetic (TDEM) survey conducted in the Cunene Province to: (i) contribute to the design of the hydrogeological conceptual model of the transboundary MAS, namely their geometry and extension; (ii) validate the reprocessing of the legacy data; and (iii) guide the future location of boreholes. Results depict the geometry of the sedimentary basin and the characterization of the MAS, with particular emphasis on the intermediate and deep aquifers. The borehole siting, based on the interpretation of the new TDEM data and the legacy data (clay markers in borehole logs), was successful, with a good agreement between estimated and observed horizons of the deep aquifers. However, the presence of clayey layers, a clay-rich matrix in the detrital deposits and saline/brackish groundwater led to uncertainties in the interpretation of the electrical transects. As such, recommendations are made to improve future data collection and mapping of the MAS.

Hydrogeochemical appraisal, sources, quality and potential health risk assessment in Holocene and Pleistocene aquifers in Bangladesh.

This study integrated hydrochemical analysis, isotopic analysis, the integrated water quality index (IWQI), and the health risk assessment model to analyze hydrochemical characteristics, quality, and nitrate health risks in a typical agricultural and industrial (i.e., Holocene and Pleistocene) simultaneously affected byanthropogenic activities, as well as to explore the recharge mechanisms of the groundwater. The shallow groundwater is mainly Ca-HCO3- and deep groundwater is mainly Na-HCO3- types. In shallow and intermediate aquifers (Holocene), rainfall recharge is seen, but in deep aquifers (Holocene) and the Madhupur tract (Pleistocene), there is no evidence of recent recharge from the stable isotopic (δ2H‰ and δ18O‰) composition of groundwater. Anthropogenic sources significantly impacted the groundwater chemistry of shallow and intermediate aquifers more than geogenic sources. Most metalloids, and metals (As, and Cr, Fe, Ni, Pb, and Mn) and NO3- exceed the WHO-2011 and BD acceptable limit from shallow and intermediate groundwater. PCA analysis revealed the contamination of shallow and intermediate aquifers by metalloids, metals and from various anthropogenic activities. Based on the IWQI, HPI, HEI, and DC, groundwater samples from shallow and intermediate aquifers are unsuitable for oral consumption. The NPI shows that the metalloids, and metals are responsible for groundwater pollution in a descending order of As > Fe > Pb > Ni > Cr > Mn. Health risk assessment indicates oral and dermal consumption of contaminated water from shallow and intermediate aquifers can pose carcinogenic and non-carcinogenic health risks for both the adults and the children. The HQ and HI values of shallow and intermediate groundwater indicates higher non-carcinogenic risk. Carcinogenic risk through oral and dermal consumption follows an order of As > Ni > Cr > Pb and Ni > Cr > As > Pb, respectively. Compared to adults, children are more susceptible to both carcinogenic and non-carcinogenic risks. Potential threats to the health of people living in the study region need immediate attention from the public, government, and the scientific community.

Exploration of trace elements in groundwater and associated human health risk in Chattogram City of Bangladesh

The study aimed to evaluate trace metals in the groundwater of Chattogram City located on the southeastern coast of Bangladesh and assess their potential health risks. Given the city's unique characteristics as both a coastal and industrial hub in Bangladesh, a knowledge gap persists particularly in the assessment of trace metals. A random sampling technique was applied to collect one hundred and seventeen groundwater samples from different wards of the city to analyze some trace metals (Cr, Cd, Fe, Cu, Mn, Pb, and Zn) and the quality of the collected water samples was evaluated using different indices, such as Heavy Metal Evaluation Index (HEI), Groundwater Quality Index (GWQI), Heavy Metal Pollution Index (HPI), and Degree of Contamination (Cd). The average concentration of all the studied metals except Fe, Mn, and Cd satisfied the Bangladesh drinking water standards. The Fe, Mn, and Cd content were observed higher in shallow wells (depth 10–150 ft) followed by intermediate (151–300 ft) and deep wells (>300 ft). However, the Cr, Cu, and Zn content did not significantly change with aquifer depth. The spatial distribution map showed that the highest values of Mn and Cu were observed in the west-northern region of the city. Metal As was only found in shallow and intermediate aquifers. The HEI suggested that about 9 % of samples fall into the higher degree of pollution category similar to the GWQI, while 37 % and 42 % of samples exhibited a higher degree of pollution in the case of HPI and Cd, respectively. The positive correlations and loadings found in the statistical analysis indicated that Fe, Mn, and Cu originated from the same sources. A variety of industrial activities might be ascribed to this type of pollution. However, an average Hazard Quotient (HQ) through ingestion was found to be greater than 1 for Cd, and the Carcinogenic Risk (CR) values for children were identified as two-fold higher than that of adults. Raising social awareness, avoiding the usage of groundwater without proper treatment, and strict regulations and monitoring by the concerned authority are recommended in the study.

Geochemistry of Arsenic and Salinity-Contaminated Groundwater and Mineralogy of Sediments in the Coastal Aquifers of Southwest Bangladesh

This study aimed to develop a geochemical database by thoroughly analyzing groundwater and sediments from coastal aquifers of southwest Bangladesh. Moreover, we investigated the source of sediment deposition and the mechanisms behind the presence of arsenic and salinity in groundwater. The seasonal distribution patterns of arsenic among the shallow and deep coastal aquifers were found to be 45.12 µg/l and 20.65 µg/l during dry and wet seasons, respectively. Moreover, the groundwater salinity distribution ranged from 3262.88 mg/l to 1930.88 mg/l during the dry and wet seasons. Cored sediment samples showed fine to medium sands of 92%, with silt and clay particles. The petrographic study of authigenic and heavy minerals revealed that the mineral grains were subangular to angular, indicating their textural immaturity of coastal sediments. The reactivity of goethite (FeOOH) and siderite (FeCO3) minerals suggests that the aquifers were subjected to slightly oxidized to moderately reducing conditions, with ORP values ranging from +50.40 mv to −149.5 mv. Such redox conditions could potentially result in the enrichment and mobility of arsenic in the groundwater. Although arsenic concentrations in deep aquifers are relatively low, higher salinity values are found in both shallow and intermediate coastal aquifers.

Multi-isotopic and hydrochemical evidence of water resources evolution and recharge estimation in the tropical coastal aquifer

The study integrates hydrochemical and isotopic (δ18O, δ2H, 3H, and δ13C) techniques to investigate water evolution in the North Kelantan River basin. Groundwater facies were mainly classified as Ca–Mg–Cl, Ca–Mg–Cl–HCO3, and Na–Cl during the rainy season and shift toward Ca–Mg–HCO3 and Na–Ca–HCO3–Cl during the dry season in surface water and shallow aquifer, while facies in intermediate and deep aquifers were classified as Na–HCO3 and Na–Cl. The δ18O and δ2H compositions of most groundwater samples have not deviated significantly from NKMWL (δ2H = 8.4 δ18O + 11.5) with slightly depleted isotopic values due to the humid climate. Isotopically, evaporation does not impact recharged water significantly. However, shallow aquifers are slightly enriched than deep aquifers of the study area. The estimated recharge was 20.17% and 22.52% of annual rainfall based on the CMB and δ18O values, respectively. The recharge mainly occurs during the wet season and is influenced mostly by the amount of rain. Aquifers clustered in distinct groups based on their isotopic signatures and hydrochemical results. The decomposition of organic matter is the primary carbon source in the study area. Building on this, by utilizing isotope hydrology to study water resources, we can gain a deeper insight into the susceptibility of groundwater in coastal aquifers of monsoonal tropical humid regions.

Hydrochemical and isotopic characteristics of the Lodwar Alluvial Aquifer System (LAAS) in Northwestern Kenya and implications for sustainable groundwater use in dryland urban areas

Groundwater is a crucial resource for dryland regions such as this, where surface water resources are limited and unreliable. This paper presents a study of the Lodwar Alluvial Aquifer System (LAAS) in northwestern Kenya and its hydrochemical and isotopic characteristics, with the goal of understanding how to sustainably manage the groundwater system. As a result, the paper focuses on elucidating the hydrogeochemical and river-groundwater interaction (using environmental isotopes and major ion chemistry) of an aquifer that is located in the north-western dryland of Kenya. The study utilised environmental isotopes of oxygen-18 (18O), deuterium (2H), and tritium (3H) as tracers for establishing recharge sources and origin of groundwater. A sampling campaign involving 112 water samples was conducted to establish isotopic compositions of rain, spring, surface water (rivers, scoop holes, dams and lake) and groundwater at the peak of the wet season in May 2018. The tritium values in the study area ranged from 1.1 to 2.4 TU. Considering the median values of δ18O and δ2H in surface water and groundwater samples, four clusters emerge based on the degree of enrichment; Cluster 1 comprises the lake water (δ18O = +6.01, δ2H = +41.9); Cluster 2 is the Turkwel and Kawalase river water with slightly positive relative to VSMOW and with different δ2H values (+7.6‰ versus −9.8‰). The third cluster is the groundwater of the Shallow Alluvial Aquifer (SAA) and the Deep Aquifer (DA) (δ18O = −0.96‰ and −0.70‰; and δ2H = +0.4‰ and +0.6‰, respectively). The last cluster comprises the most isotope-depleted waters of water pans, scoop holes, Intermediate Aquifer (IA) and Turkana Grit Shall Aquifer (TGSA) with median values ranging from −2.87‰ to −2.48‰ for δ18O and −8.6‰ and −16.4‰ for δ2H. While the SAA is mainly recharge by the Turkwel River, a relationship is observed between the values deuterium in the Kawalase (−9.6‰ VSMOW) and IA (−8.6‰ VSMOW). Understanding recharge sources and aquifer vulnerability of similar strategic aquifers helps scientists appropriately advise policymakers and the water community who develop sustainable water use, aquifer protection and conservation strategies. In addition, the study contributes scientific evidence of isotopic compositions of groundwater in the Horn of Africa. Furthermore, the evidence of surface water-groundwater interaction presents a case of a fragile dryland ecosystem. Future work will involve the installation of piezometers in strategic aquifer zones to monitor groundwater levels in relation to river gauging data to quantify the amount of recharge and establish the impacts of rainfall variability in the upstream catchment.

Hydraulic head fluctuations in an intermediate depth coastal surface aquifer

Tides and storm surges are important drivers of groundwater circulation and fluxes in coastal aquifers. However, few field studies have characterized the response of the coastal aquifer to both forcings. Here, three years of hydraulic head observations in a roughly 20-m deep barrier island surface aquifer are used to investigate the inland propagation of fluctuations driven by ocean water-level changes owing to diurnal and semi-diurnal tides and storm-induced surge and wave-driven setup. Similar to prior observations, the observed rate of amplitude attenuation of the hydraulic head fluctuations is higher than the inland increase in phase lag for the tidally-driven head fluctuations. Additionally, tidal hydraulic head fluctuations deeper in the aquifer lead those nearer the surface of the aquifer. In contrast, storm surges with periods of several days have similar rates of amplitude attenuation and inland increase in phase lags, and hydraulic head fluctuations are roughly depth uniform. A nonlinear, intermediate aquifer-depth theory (not previously compared with field observations) describes the inland and vertical changes of tidal amplitudes and phase lags, and collapses to the linear solution for long period fluctuations, consistent with the storm surge observations. The diffusivity estimated by fitting intermediate depth solutions to the observed tidal amplitude attenuation and rate of inland phase lag is consistent with the aquifer properties, providing a method to characterize aquifers using coastal head observations. Numerical model simulations neglecting capillary effects, hysteresis, and vertical layering (which can cause discrepancies between amplitude attenuation and phase lag evolution) are similar to the observations and support the importance of the depth of the aquifer relative to the wavelength of the hydraulic head fluctuations.

Petrophysical and hydrogeological characterization of coastal aquifer using geophysical logs in Lekki Peninsula, Lagos, Nigeria

The coastal aquifers of Lekki Peninsula, Lagos are increasingly threatened by saline water invasion. In this study, the characterization of the petrophysical properties of the coastal aquifers in Lekki Peninsular through analysis of geophysical logs was carried out. The methodology involved editing, interpolation, depth shifting and normalization of gamma ray and resistivity logs from twelve water wells. Log analysis was employed to map aquiferous units and determine their petrophysical properties which include clay volume, porosity, permeability, water resistivity, total dissolved solid and water quality. These properties were further subjected to cross plot analysis. The results identified three aquifers. Aquifer 1 is mostly unconfined shallow phreatic aquifer characterized by 11–35% porosity. The TDS ranges from of 4.63 mgL−1 – 50.33 mgL−1. The intermediate Aquifer 2 is characterized by significant thickness (25–75 m), clay volume (0.22–0.54) excellent porosity (16–27%), permeability (99–110 mDarcy), water resistivity (25–175 Ωm) and total dissolved solids of <30.00 mgL−1. The deep Aquifer 3 lies at 153–255 m depth and has total dissolved solids value of 10.63 mgL−1 and 26% porosity. Cluster analysis shows 67% of wells that penetrated Aquifer 2 encountered saline to brackish water while 40% found aquitard with poor petrophysical properties. Water wells in the study area should target aquifer 3 as Aquifer 2 is prone to saltwater intrusion due to over-pumping. This study furnishes information that enables sustainable future exploration, exploitation, monitoring and management of groundwater reserve in Lekki Peninsula.

Hydrogeochemical evaluation, groundwater contamination and associated health risk in southern Tangail, Bangladesh

Water pollution is a worldwide concern that has growing severe in developed and developing nations. Increasing groundwater pollution threatening both the physical and environmental health of billions of people as well as economic progress. Consequently, hydrogeochemistry, water quality and potential health risk assessment is crucial for water resource management. The study area comprises Jamuna Floodplain (Holocene deposit) area in the west and the Madhupur tract (Pleistocene deposit) area in the eastern part. Total 39 groundwater samples were collected from the study area and were analyzed for physicochemical parameters, hydrogeochemical, trace metals, and isotopic composition. The water types are mainly Ca–HCO3- to Na–HCO3- types. The isotopic compositions (δ18O‰ and δ2H‰) analysis traces the recent recharge in Floodplain area from rainwater and no recent recharge in Madhupur tract. The concentration of NO3−, As, Cr, Ni, Pb, Fe, and Mn in shallow and intermediate aquifer at the Floodplain area exceed the WHO-2011 permissible limit and is lower at deep Holocene and Madhupur tract aquifer. The integrated weighted water quality index (IWQI) exposed groundwater from shallow and intermediate aquifer are unsuitable for drinking and deep Holocene aquifer and Madhupur tract are suitable for drinking purposes. PCA analysis confirmed that anthropogenic activity is dominant in shallow and intermediate aquifers. The non-carcinogenic and carcinogenic risk for adults and children is due to oral and dermal exposure. The non-carcinogenic risk evaluation revealed that the mean hazard index (HI) values range from 0.009742 to 16.37 for adults and 0.0124–20.83 for children, respectively, and most groundwater samples from shallow and intermediate aquifers exceed the permissible limit (HI>1). The carcinogenic risk ranges from 2.71 × 10−6-0.014 for adults and 3.44 × 10−6-0.017 for children via oral consumption and 7.09 × 10−11-1.18 × 10−6 for adults and 1.25 × 10−10-2.09 × 10−6 for children via dermal exposure. Spatial distribution shows the presence of trace metal and associated health risk is high in shallow and intermediate aquifer (Holocene) than in the deep (Holocene) Madhupur tract (Pleistocene). The study implies that effective water management will ensure safe drinking water for the future generation of people.

Hydrochemical Characterization and Quality Assessment of Groundwater in Hatiya Island, Southeastern Coastal Region of Bangladesh

Groundwater is a vital source of fresh water for drinking and agricultural purposes in the region of Hatiya Island, Bangladesh, yet it is subject to contamination by natural and anthropogenic activities. Over time, the contamination has resulted in a variety of negative effects on human health. This research aims to examine groundwater hydrogeochemical characterization and suitability for irrigation and drinking purposes on different indices utilizing a combined geochemical method, multivariate statistical approaches, and geospatial analysis. Results of hydrogeochemical analyses of 15 groundwater samples from the intermediate aquifer (60–90 m depth) represent the order of cations, anions, and metal concentrations as Na+ &gt; Mg2+ &gt; Ca2+ &gt; K+, Cl− &gt; SO42− &gt; HCO3− &gt; NO3−, and Fe &gt; I &gt; Br &gt; Mn &gt; As, respectively. Saltwater intrusion has been determined to be the most important hydrogeochemical process influencing the chemistry of groundwater. Principal component analysis, Pearson’s correlation matrix, and hierarchical cluster analysis indicate that groundwater quality is highly governed by geogenic influences. This information has been evaluated using a drinking water quality index map, which found that six (40%) of the groundwater samples are suitable for human consumption, whereas the other nine (60%) are unfit for drinking. The analysis of irrigation quality parameters revealed that eight (54%) of the groundwater samples are in excellent or good condition for agricultural uses; however, the other seven (46%) samples are unsuitable.

3D electrical structure definition of aquifer systems in the Kalahari basin in Southern Angola based on legacy data reprocessing

The Kalahari-Ohangwena transboundary aquifer system, recently identified in Northern Namibia, comprises 3 major aquifers with very different characteristics. The shallowest is discontinuous and with limited reserves, but it has local importance in water supply for the population, since it is easy to reach, and often presents good hydrochemical quality. An intermediate deeper aquifer is characterized by high salinity while the deepest aquifer, also mostly saline, can present zones with fresh water. However, the latter is located at considerable depths and is shaped by the bottom of the basin basement. There hasn't been a systematic hydrogeological data acquisition for decades in this area of Angola, but legacy electrical resistivity data reprocessing from geophysical surveys conducted >50 years ago in the Cunene Province allowed the construction of a quasi-3D geoelectrical model for the Angolan side of KOH aquifer system in the Cuvelai-Etosha basin. This model is based on 482 vertical electrical soundings carried out in 1966–67, using the Schlumberger array, that contribute to confirming the presence of the Kalahari-Ohangwena aquifer system in Angola. The obtained quasi-3D model highlights the geoelectrical features of hard bedrock and is validated with other hydrogeological and geophysical information. The quasi-3D electrical resistivity data is interpreted using selected boreholes and two time-domain electromagnetics transects carried out in Namibia, in the 2000s. Although both geophysical data acquisitions were >40 years apart, the results show a very good correlation between the deeper aquifer and the aquitard separating the intermediate aquifer from the deeper aquifer either with the results from Namibia or the borehole data. This is a direct result of the lack of alteration in the hydraulic conditions over these decades, without significant anthropogenic activity and negligible extraction from deep wells. Based on this analysis, the original dataset was considered a reliable source and this quasi-3D model was validated. Furthermore, the model can be considered in the future as an important tool for groundwater resources management, as well as a good starting point for further hydrogeological research in the province of Cunene.

A potential source of low-manganese, arsenic-safe drinking water from Intermediate Deep Aquifers (IDA), Bangladesh

Elevated manganese (Mn) concentration in many drinking water tubewells in Bangladesh has made access to safe drinking water more critical despite providing arsenic (As) safe water to millions of people after decades of efforts to achieve latter. This study evaluates the potential of the Intermediate Deep Aquifer (IDA) in the Matlab area of Bangladesh as a source of As-safe and low-Mn groundwater. Based on observations from depth-specific piezometer nests, drinking water tubewells were installed at a targeted depth of 120 m in the Matlab region, an As-hot spot in the country. Water chemistry analysis of 243 Intermediate Deep Tubewells (IDTW) provided promising results which support the strategy of exploiting the IDA as a safe source for drinking water tubewells. Arsenic, manganese and other trace elements, along with the major ions, were analyzed by high-precision ICP-OES and ion chromatography. The Bangladesh drinking water standard for As (50 μg/L) was exceeded only in 3 wells (1%) while 99% (n = 240) of the wells were found to be safe. More than 91% (n = 222) were within the WHO guideline value of 10 μg/L. For Mn, 89% (n = 217) of the wells showed the concentration within or below the former WHO guideline value of 0.4 mg/L with a mean and median value of 0.18 and 0.07 mg/L respectively. Similar high permeability sand units at this depth range, if available could be targeted by the local tubewell drillers for tapping water at half the cost of deep tubewell installation, which will be quite encouraging for the local community, considering their affordability for installation of As-safe and low-Mn drinking water tubewells. This study's results could also be important for other relevant stakeholders, including the policy makers, implementing agencies and the water sector development partners, as well as water supply projects elsewhere in the world with similar hydrogeological settings.

Groundwater quality evaluation and health risk assessment in coastal lowland areas of the Mekong Delta, Vietnam

This study provides a comprehensive assessment of groundwater quality in the Mekong Delta (Vietnam) and their potential risks to human health. The dataset consists of 282 groundwater samples collected in dry and rainy seasons between 2017 and 2018. Multiple physio-chemical parameters, groundwater quality index (GWQI), and irrigation water quality indices (IWQI) were employed to evaluate the suitability of groundwater resources for drinking and irrigation purposes. Thereupon, the hazard quotient (HQ), and total hazard index (HI) were used to assess the non-carcinogenic risks to different demographic groups. GWQI indicates that groundwater samples are excellent (41.5%), good (40.4%), poor (17%), and very poor (1.1%) classes for drinking purpose. The total hazard index (HI) indicated that 15.2%, 8.5%, 7.4%, and 7.1% of samples express non-carcinogenic health threats to infants, females, children, and males. Irrigation water quality indices (IWQI), namely, EC, sodium adsorption ratio (SAR), residual sodium bicarbonate (RSBC), soluble sodium percent (SSP), permeability index (PI), and magnesium hazard (MH), reveal that 82.2%, 94%, 20.2%, 69.6%, 45.4% and 12.8% of samples have EC < 2250 μS/cm, SAR <26, RSBC <1.25, SSP <60%, PI > 75%, and MH < 50%, respectively, which are suitable for irrigation use. Wilcox diagram shows that 17.54% of total groundwater samples exceed the permissible levels of salt-tolerant crops and solidity hazards in the study area. Furthermore, high concentrations of nitrate (>50 mg/L) and chloride (>1000 mg/L) were detected in the shallow, intermediate, and deep aquifers. GWQI and IWQ maps imply that groundwater in the South-western area is suitable, whereas groundwater in the central area is not recommended for any purpose. These findings provide useful insights into the vulnerable groundwater system of the coastal lowland area of the Mekong Delta related to human activities (agricultural practices, dam construction) and global climate change impacts. Accordingly, appropriate management strategies for water resources and mitigation solutions are imperatively needed to ensure the sustainability of the groundwater resource and the protection of public health in the Mekong Delta.

Groundwater quality evaluation and human health risks assessment using the WQI, NPI and HQnitrate models: case of the Sfax intermediate aquifer, Sahel Tunisia.

Groundwater is a vital natural resource required to satisfy the domestic and agricultural needs. In general, human health is linked to the quality of the consumed water. For instance, long-term exposure to high nitrate levels in groundwater may cause problems. Hence, the present study was conducted to assess the nitrate contamination of groundwater as well as its related health risks for the inhabitants of the Sfax region, Sahel Tunisia. Irrigation groundwater suitability has been evaluated with sodium content (%Na), electrical conductivity (EC), magnesium hazard (MH), sodium adsorption ratio (SAR), permeability index (PI), Kelly's ratio (KR) and soluble sodium percent (SSP). The results indicate that the selected groundwater is characterized by low to moderate quality for irrigation. Furthermore, the drinking water quality index (DWQI) was assessed using potential of hydrogen (pH), total dissolved solids (TDS), magnesium (Mg2+), calcium (Ca2+), sodium (Na+), chloride (Cl-), sulfate (SO42-), potassium (K+), bicarbonate (HCO3-) and nitrate (NO3-). The results indicate that 3.63% of samples have good quality of water, while 41.82% have poor to very poor water quality and the rest (54.55%) are unfit for drinking. The nitrate pollution index (NPI) model revealed that about 42% of the samples present significant to very significant type of pollution. Based on human health risk assessment, the children are at higher risks compared to the other affected groups. The obtained results could be used as a basic document for realistic management of groundwater quality and to provide an overview for decision-making authorities to take necessary actions.

Engineering Site Investigation for Foundation Design and Construction in Shale and Sandstone Derived Soils of Okitipupa Area, Southwestern Nigeria

Geotechnical and geo-electrical investigations of Okitipupa has been carried out with the major objectives of establishing the subsoil/geology, evaluate the geotechnical properties and recommend appropriate foundation alternatives for building foundation construction. Seven borings were carried out with hand auger at two cone penetration test locations, and representative samples were collected and analyzed in the laboratory in accordance with relevant geotechnical engineering standards. In addition, six vertical electrical soundings (VES) were also conducted using Schlumberger configuration. The result of VES delineates three major geologic sequence comprising the topsoil/caprock, sand surficial aquifer, and sand intermediate aquifer. The topsoil has resistivity range of 242 – 1503 ohm-m and thickness of 3.4 - 20.9 m composed of clay sand and sand. This layer is capable of supporting shallow foundation such as simple spread, raft of reinforced concrete, with recommended allowable bearing pressure of 100 KN/m2 at depths of 1.0 m and 3.2 m in the northern and southern part of the study area respectively. The estimated settlement are less than 50 mm using foundation width of 0.6 m, but could be reduced by almost 50% if the width is greater than or equal to 2 m. The groundwater level is very deep (&gt;10 m) and may not likely threatens the integrity of the foundation structures. The estimated allowable bearing capacity for strip footing (203 – 980 KN/m2), square footing (608 – 2940 KN/m2) within 1.4 m depth is appropriate. The capacity of driven (deep foundation) circular piles of diameters 400mm, 500mm, and 600mm, the recommended pile capacity varies at depth of 5 m (69 – 124 KN), 10 m (225 – 378 KN), and 15 m (470 – 766 KN), while that of bored circular pile ranges from (36 – 75 KN), 10 m (93 – 180 KN), and 15 m (170 – 317 KN).

Isotopes (δ18O, δD and 3H) variations in groundwater with emphasis on salinization in the state of Punjab, India

The state of Punjab has a dominant agrarian economy and is considered India's bread basket. However, it is now under the problem of falling agro-economy primarily because of pervasive depletion of groundwater levels and deteriorating groundwater quality in south-west Punjab, but increasing salinity is a major concern. The irrigation requirements of crops are fulfilled by groundwater and canal water but the introduction of canal irrigation has led to waterlogging and subsequent salinization rendering large fertile-land areas becoming unproductive mainly in the south-western part of Punjab. There was an apprehension that excessive withdrawal of groundwater might have caused a reversal of natural groundwater flow pattern that might have caused ingress of saline water into fresh groundwater region of central Punjab. To address the apprehension related to the rise in groundwater salinity and its subsequent ingression in the fresh-water zone and suggest suitable management solutions, a study was undertaken to analyse the data related to salinity, isotopes, land-use and land cover (LULC) along with field and laboratory experimental results. The depth-wise isotope analysis shows that there is a large variation in isotopic signatures of shallow and intermediate aquifers and it decreases with the depth of aquifers (150–250 m). It appears that very deep groundwater (>250 m) is relatively isolated and does not show a large variation or mixing effect. Tritium analysis shows that dynamic groundwater is actively recharged through canal, river, and/or rain. The presence of modern groundwater at deeper depth indicates a good interconnection between shallow and deep groundwater. Interpretations of the results show that the canal is the main source of groundwater recharge in south-west Punjab and the evaporation process is responsible for increasing the salinity hazard. In the central parts of Punjab, groundwater and rain are the main sources of groundwater recharge, while rain is the main source of groundwater recharge in the Kandi area. In the south-west Punjab, some primary salinity has formed as a result of mineral dissolution which has further increased due to evaporative enrichment.

Environmental isotopes and noble gas ages of the deep groundwater with coupled flow modelling in the Baltic artesian basin

In this study, modelled groundwater actual flow times in intermediate and deep aquifers, covered by regional scale impermeable aquitards, were compared with 4He and 81Kr age dating results. To improve the reliability of the steady state 3D groundwater flow model, the isotopic ages of deep groundwater were compared to the MODPATH modelled travel times. The highest helium values in groundwater reservoirs coincide with fault zones in the crystalline basement and sedimentary cover near Rapakivi granite massifs. Insights into isotope-geochemical anomalies of the Baltic Artesian Basin intermediate and deep groundwater support their main distribution peculiarities in the flow path towards the Baltic Sea coast lowland and seabed depression as the regional groundwater discharge area.

The effect of hydrogeological and hydrochemical dynamics on landslide triggering in the central highlands of Ethiopia

The volcanic terrain at the western margin of the Main Ethiopian Rift in the Debre Sina area is known for its slope stability problems. This report describes research on the effects of the hydrogeological and hydrochemical dynamics on landslide triggering by using converging evidence from geological, geomorphological, geophysical, hydrogeochemical and isotopic investigations. The chemical characterization indicates that shallow to intermediate aquifers cause groundwater flow into the landslide mass, influencing long-term groundwater-level fluctuations underneath the landslide and, as a consequence, its stability. The low content of total dissolved solids and the bicarbonate types (Ca–Mg–HCO3 and Ca–HCO3) of the groundwater, and the dominantly depleted isotopic signature, indicate a fast groundwater flow regime that receives a high amount of precipitation. The main causes of the landslide are the steep slope topography and the pressure formed during precipitation, which leads to an increased weight of the loose and weathered materials. The geophysical data indicate that the area is covered by unconsolidated sediments and highly decomposed and weak volcanic rocks, which are susceptible to sliding when they get moist. The heterogeneity of the geological materials and the presence of impermeable layers embodied within the highly permeable volcanic rocks can result in the build-up of hydrostatic pressure at their interface, which can trigger landslides. Intense fracturing in the tilted basalt and ignimbrite beds can also accelerate infiltration of water, resulting to the build-up of high hydrostatic pressure causing low effective normal stress in the rock mass, giving rise to landslides.

Vulnerability Evaluation of Groundwater of N’Djamena City: Contribution of the Parametric Methods GOD and SI

The purpose of this work is to study the vulnerability of the Quaternary aquifer that lies beneath the N’Djamena city Chad. The subsoil of N’Djamena city Chad is made up of a multilayered aquifer in which there are two main aquifers located respectively at a depth of about 10 and 60 m, between the two there is an intermediate aquifer at about 30 m depth. It is this latter water table, generally captured by human-powered pumps, that is the subject of this study. Because of anarchic garbage dumping, wastewater discharge, latrines scattered throughout the city, chemical fertilizers and herbicides used on the banks of Chari River and its tributary the Logone for market gardening, the quality of the water in this aquifer is highly threatened. Moreover, it has been noting that the sources of pollution are constantly increasing in conjunction with the growth of the population, so the knowledge and protection of groundwater are necessary. We have therefore carried out a study of intrinsic vulnerability using two mapping methods (GOD and SI), as mapping is recognized as an effective tool for decision support in the case of safeguarding water resources. The results obtained by the GOD method show that 38% of the study area is covered by high vulnerability, 29% by moderate vulnerability, 21% by low vulnerability and 21% by the very low vulnerability. With the SI method, 54% of the study area is covering by low vulnerability and 46% by the low and moderate vulnerability. The coincidence rate of low nitrate values in groundwater with areas of very low and low vulnerability is 91% and 76% for the GOD and SI methods, respectively. Although these observations validated the different maps obtained, the SI approach seems to be the most adequate for vulnerability tracing in our study area.

Anthropogenic basin closure and groundwater salinization (ABCSAL)

Global food systems rely on irrigated agriculture, and most of these systems in turn depend on fresh sources of groundwater. In this study, we demonstrate that groundwater development, even without overdraft, can transform a fresh, open basin into an evaporation dominated, closed-basin system, such that most of the groundwater, rather than exiting via stream baseflow and lateral subsurface flow, exits predominantly by evapotranspiration from irrigated lands. In these newly closed hydrologic basins, just as in other closed basins, groundwater salinization is inevitable because dissolved solids cannot escape, and the basin is effectively converted into a salt sink. We first provide a conceptual model of this process, called “Anthropogenic Basin Closure and groundwater SALinization” (ABCSAL). We examine the temporal dynamics of ABCSAL using the Tulare Lake Basin, California, as a case study for a large irrigated agricultural region with Mediterranean climate, overlying an unconsolidated sedimentary aquifer system. Even with modern water management practices that arrest historic overdraft, results indicate that shallow aquifers (36 m deep) exceed maximum contaminant levels for total dissolved solids on decadal timescales. Intermediate (132 m) and deep aquifers (187 m), essential for drinking water and irrigated crops, are impacted within two to three centuries. Hence, ABCSAL resulting from groundwater development constitutes a largely unrecognized constraint on groundwater sustainable yield on similar timescales to aquifer depletion in the Tulare Lake Basin, and poses a serious challenge to groundwater quality sustainability, even when water levels are stable. Results suggest that agriculturally intensive groundwater basins worldwide may be susceptible to ABCSAL.