Aquifer Units Research Articles

Drinking Water Supply Options in Arsenic and Salinity Affected Areas of Bangladesh: A Case Study

Widespread groundwater arsenic contamination in south, south-western and north-eastern regions and high salinity in the south-western coastal region are the two major challenges for drinking water supply in Bangladesh. In this study, we assessed various water supply technologies used for mitigating arsenic and salinity in Laksam of Cumilla and Assasuni of Satkhira district. Water samples were analyzed for Arsenic, Iron, Chloride (indicator for salinity) and FC from different water extraction systems (shallow, deep and Tara tubewells), groundwater arsenic treatment units (SIDKO and READ-F), rainwater harvesting systems (RWH), pond sand filters (PSF), and managed aquifer recharge units. Most shallow tubewells, both in Laksam and Assasuni, have been found to produce arsenic contaminated water. But water from deep and Tara tubewells have been found arsenic-free, though high concentration of iron was observed in the wells in Laksam. Rainwater harvesting systems, PSF and MAR units in Assasuni have been found to provide water free from the common chemical contaminants but suffer from high bacterial contamination. Deep tubewell appear to be the most preferred option where a suitable aquifer is available. The community-scale groundwater treatment systems would require strong operation and maintenance support from the service providers to be successful.
 Environ. Sci. & Natural Resources, 12(1&2): 215-223, 2019

Borehole inventory, groundwater potential and water quality studies in Ayede Ekiti, Southwestern Nigeria

This study aims at determining the state of government provided boreholes, evaluating groundwater potential and quality assessment within the Ayede Ekiti community. 12 Vertical Electrical Soundings (VES) were conducted using Schlumberger array in order to determine geoelectric layers and fracture attributes. Also, 12 water samples were collected from the study area to evaluate physicochemical characteristics of the groundwater. The study revealed average values of total depth of boreholes, static water levels and water column in the boreholes to be 18.77 m, 6.77 m and 11.99 m respectively. 70% of the boreholes are either abandoned, damaged or with evidence of corrosion and encrustation. Geophysical investigation revealed weathered layer thickness ranging from 1.3 to 34.7 m with two regimes of fracture at 40–50 and 75–80 m. The frequency of curve types obtained shows 16.67%, 33.33%, 25%, 8.33%, 8.33% and 8.33% for AK, HA, KH, AA, QH and HK respectively while weathered and fractured basement are identified as the two types of aquifer unit. Results of water analysis unveiled that dominance cations are in order Ca2+ > Na+ > K+ > Mg2+while anions are in the order of HCO3− > Cl− > SO42−. Three types of hydrochemical facies present are CaHCO3 > NaHCO3 > CaCl in 66.67%, 25% and 8.33% respectively. The Wilcox plot suggests the suitability of the groundwater samples for irrigation purposes when compared with the World Health Organization standards. Despite potential for groundwater and good quality of analyzed samples, the problem of water in this community is traceable to inadequacy in exploration, shallow boreholes with consequent seasonal water availability.

Aquifer system and groundwater potency in coastal area of Kretek, Bantul Regency, Indonesia

The existence of groundwater in coastal areas really needs attention because of its vulnerability to sea water intrusion. Utilization and good management are needed to maintain its sustainability. The purpose of this research is to determine the aquifer system in the study area and to calculate the groundwater potency. The aquifer system is determined by processing geoelectric sounding data using Rockworks 16 software. Groundwater potency is calculated using a static approach. The safe yield of groundwater is calculated by multiplying of groundwater fluctuation, village area and the specific yield. Water requirement is calculated base on domestic, livestock and tourism water requirement. The results showed that the Kretek District had two aquifer units, namely the fluvio marin plains and sand dunes. In the fluvio marin plains, most of the constituent material is sand with clay as inserts, while in the aquifer unit the sand dune has constituent material in the form of unconsolidated sand originating from the Merapi Volcano. The groundwater potency of the study area is 234,448,0000 m3/year and the safe yield is 11,772,400 m3/year. With the water requirement for domestic, livestock and tourism are 555,044 m3/year, the groundwater potency in the study area is still sufficient. However, it is recommended that the well drilling does not exceed a depth of 40 meters, because at several locations there has been detected an interface. In addition, in several locations there were also detected connate water originating from ancient marines during the deposition process of the fluvio marin plains in the past.

Geophysical and Contamination Assessment of Soil Spatial Variability for Sustainable Precision Agriculture in Omu-Aran Farm, Northcentral Nigeria

The Spatial and temporal variability of soil properties (fluid composition, structure and water content) and hydrogeological properties employed for sustainable precision agriculture can be obtained from geoelectrical resistivity methods. For sustainable precision agricultural practices, site-specific information is paramount, especially at the planting season. An integrated one-dimensional (1D) and two-dimensional (2D) electrical resistivity surveys have been adopted to characterize the subsoil parameters and delineate the aquifer unit of large farm area, especially in precision agricultural practices. Also, contamination assessment reveals the soil quality status of farmlands. This study aims to determine the site-specific soil parameters of a commercial farm in Omu-Aran, Northcentral, Nigeria. The subsoil features from the geoelectrical resistivity surveys indicate 3 to 4 distinctive lithology to a depth of 43.4 m into the subsurface of the farm. The ID (Vertical Electrical Sounding) and 2D resistivity inversion models results have revealed the heterogeneity nature of the topsoil also known as the stone zone comprising of reworked clayey soil and sandy gravelly soil, the weathered/saprolite zone (gravelly sandy/ sandy soil), the fractured basement and the fresh basement rock. Contamination factor (Cf), pollution load index (PLI) and Nemerow integrated pollution index (NIPI) were used to assess the contamination index on the farmland. Toxic elements such as arsenic, cadmium, chromium, cobalt, lead, manganese, nickel, and zinc have low to moderate contamination in the farm. The depth of investigation (≤ 3m) covers the upper root zone of significant crops grown in the area. The findings can assess soil contamination, delineate basement features, subsoil variability, soil profiling, and determine the subsoil hydrological properties.

CARACTERIZAÇÃO HIDROGEOQUÍMICA DOS AQUÍFEROS DA REGIÃO DA APA CARSTE DE LAGOA SANTA, MG

Estudo hidrogeoquímico foi realizado envolvendo a região da Área de Proteção Ambiental Carste de Lagoa Santa, 504km2, a norte do município de Belo Horizonte. As litologias aquíferas envolvidas foram a sequência pelito-carbonática da Formação Sete Lagoas, metapelitos da Formação Serra de Santa Helena e granito-gnaisses do Complexo Belo Horizonte. A primeira divide-se em Membro Pedro Leopoldo, inferior, encerrando calcários impuros, com intercalações pelíticas, e Membro Lagoa Santa, superior, contendo calcários puros. As águas são bicarbonatadas cálcicas, secundariamente bicarbonatadas mistas a sódicas, quando associadas ao embasamento e coberturas. As concentrações de Ca2+ e Si4+ foram fundamentais para a distinção entre as unidades aquíferas carbonáticas e não carbonáticas, permitindo também identificar águas mistas, elucidar sobre o meio de recarga e compartimentar horizontal e verticalmente o sistema aquífero. A heterogeneidade litológica conferida ao membro inferior levou a sua subdivisão em 4 tipos hídricos, enquanto as águas do Mb. Lagoa Santa são homogêneas, refletindo a sua homogeneidade litológica. A alta produtividade dos poços profundos deve-se à dissolução de porções rochosas mais puras e à localização próxima a falhamentos e de contato litológico entre os membros, enquanto nas nascentes é controlada pela intensidade dos processos de carstificação dos calcários mais puros do Membro Lagoa Santa.

Groundwater dynamics in the Vietnamese Mekong Delta: Trends, memory effects, and response times

Study RegionVietnamese Mekong Delta. Study focusThis study investigates the trends of groundwater levels (GWLs), the memory effect of alluvial aquifers, and the response times between surface water and groundwater across the Vietnamese Mekong Delta (VMD). Trend analysis, auto- and cross-correlation, and time-series decomposition were applied within a moving window approach to examine non-stationary behavior. New hydrological insightsOur study revealed an effective connection between the shallowest aquifer unit (Holocene) and surface water, and a high potential for shallow groundwater recharge. However, low-permeable aquicludes separating the aquifers behave as low-pass filters that reduce the high‐frequency signals in the GWL variations, and limit the recharge to the deep groundwater. Declining GWLs (0.01−0.55 m/year) were detected for all aquifers throughout the 22 years of observation, indicating that the groundwater abstraction exceeds groundwater recharge. Stronger declining trends were detected for deeper groundwater. The dynamic trend analysis indicates that the decrease of GWLs accelerated continuously. The groundwater memory effect varied according to the geographical location, being shorter in shallow aquifers and flood-prone areas and longer in deep aquifers and coastal areas. Variation of the response time between the river and alluvial aquifers was controlled by groundwater depth and season. The response time was shorter during the flood season, indicating that the bulk of groundwater recharge occurred in the late flood season, particularly in the deep aquifers.

A novel method for the quantification of industrial and municipal waste materials for environmental hazard assessment

A novel methodological approach was developed to quantified the volume of industrial waste desposal (IWD) site, combined with municipal waste materials (MWM), through the integration of a non-invasive, fast, and less expenssive RES2-D Electrical Resistivity Technique (ERT), using Wenner-Schlumberger electrode array geophysical method with Oasis Montaj software. Underground water bearing structures, and the eco-system are being contaminated through seepage of the plumes emanating from the mixtures of the industrial waste materials (IWM), made of moist cemented soil with municipal solid wastes (MSW) dumped at the site. The distribution of the contiminant hazardous plumes emanating from the waste materials' mixtures within the subsurface structural lithological layers was clearly map and delineated within the near-surface structures, using the triplicate technique to collect samples of the soil with the waste mixtures, and the water analysis for the presence of dissolved ions. The deployed method helped to monitor the seepage of the contaminant leachate plumes to the groundwater aquifer units via the ground surface, through the subsurface stratum lithological layers, and hence, estimation of the waste materials' volume was possibly approximated to be 312,000 m3.In summary, the novel method adopted are as presented below:•The novel method is transferable, reproduce-able, and most importantly, it is unambiguous technique for the quantification of environmental, industrial and municipal waste materials.•It helps to map the distribution of the plumes emanating from the waste materials' mixtures within the subsurface structural lithological layers that was clearly delineated within the near-surface structures underlain the study site.•The procedure helped in the monitoring of leachate contaminants plumes seepages into the surface water bodies and the groundwater aquifer units, via the ground surface, through to the porous subsurface stratum lithological layers.

Upper Elk Point subgroup paleogeography and evaporite distribution with implications for evaporite dissolution, karstification, and carbonate diagenesis in northeastern Alberta

Abstract Lithostratigraphic correlation and mapping of formations and units within the Upper Elk Point subgroup provide updated information on their extent and distribution within the province of Alberta. Together with detailed bed-scale evaporite mapping of three evaporite minerals — halite, anhydrite, and gypsum — within evaporitic successions for net-thickness maps, these data allow new representations of the paleogeography of these units across the province. Paleogeographic maps of the Keg River, Prairie Evaporite and Muskeg formations reveal new details on the location of the La Crete sub-basin in northern Alberta, and the distribution and nature of Keg River Formation buildups and the overlying evaporite strata within this depositional realm. Net-evaporite mapping gives a robust picture of the distribution of Upper Elk Point subgroup evaporites, and allows for a detailed characterization of heterogeneities, halite dissolution, and sulphate karstification. Mapping of gypsum reveals that rehydration of anhydrite to gypsum (gypsification) through meteoric inflow is most pronounced within the La Crete sub-basin in northeastern Alberta, particularly where thick anhydrite deposits are associated with interbuildup basinal areas east of the Prairie Evaporite halite dissolution scarp. This association provides an explanation for the location of where active gypsification, dissolution and associated karstification is occurring and where it can be expected to occur. The process of gypsification, and ultimately sulphate dissolution, is requisite for the formation of porous dedolomite zones within the carbonates of the Prairie Evaporite Formation. Dedolomitized beds are recognized as aquifer units that are known to have contributed to Devonian-sourced, high-salinity water inflows to mine pits in the mineable oil sands area. Evidence is provided for a top-down advancement of halite and sulphate dissolution in all evaporites in northeastern Alberta. Circular, chain-like karst lakes are likely surficial expressions of the meteoric conduits for top-down karstification of sulphates east of the Prairie Evaporite halite dissolution scarp, similar to that observed in the well-documented sulphate karst district of Wood Buffalo National Park.

Quality of Surface Water and Groundwater in Iraq

Insufficiency of water resources in the Middle East Region represents vital factors that influence the stability of the region and its progress. Expectations indicate that the condition will be dimmer and more complicated, especially in Iraqi territory. Iraq, which is situated in the Middle East, it covers an area of 433,970 square kilometers and populated by about 32 million inhabitants. Iraq greatly relies in its water resources on the Tigris and Euphrates Rivers as a surface water resources, and several productive groundwater aquifers in which from the hydrogeological point of view divided into several major aquifer units including Foothill, Al-Jazira, Aquifer System, Mandali-Badra-Teeb, Mesopotamian and Desert Aquifer system. Recently, Iraq is suffering from water shortage problems. This is due to external and internal factors affecting the water quality of water resources; they are controlled and uncontrolled factors. The uncontrolled factors are climate change and its consequences, such as reduction of precipitation and temperature increasing. The controlled factors have a significantly negative influence on water resources, but their effects involve more specific regions. The controlled factors are mainly represented by building dams and irrigation projects within the upper parts of the Tigris and Euphrates catchments, Al-Tharthar Scheme, waste water, solid wastes and wastes from wars, which has a significant effect on surface water in Iraq because about 80% of the water supply to Euphrates and Tigris Rivers come from Turkey. In addition, the pressures resulting from the high demand for water resources, and the continued decline in their quantity rates have led to major changes in the hydrological condition in Iraq during the past 30 years. The decrease in surface water levels and precipitation during these three decades reflects the drop in the levels of water reservoirs, lakes, and rivers to the unexpected levels. The level of main country’s water source, Tigris, and Euphrates Rivers has fallen to less than a third of its natural levels. As storage capacity depreciates, the government estimates that its water reserves have been reduced precariously. According to the survey from the Ministry of Water Resources, millions of Iraqi people have faced a severe shortage of drinking water. Since of the importance of water for human life and the need to monitor temporal and spatial changes in quality and quantity, there is a need to develop a general Iraqi Water Quality Index (Iraq WQI) to monitor surface water and groundwater and classify it into five categories, very good, good, acceptable, bad and very bad, in terms of suitability for domestics, irrigation and agriculture depending on the Iraqi and WHO standards for drinking water. In addition, strict establishment for the regular quantitative monitoring surface water and groundwater setting and processes. Prospects are more negative for all riparian countries. This implies that solving these problems requires actual and serious international, regional, and national cooperation to set a prudent plan for water resources management of the two basins. Iraq being the most affected country should seriously set a prudent, scientific, and strategic plan for the management and conservation of its water resources. Keywords: Pollution, Water Quality, Waste, Surface water, Groundwater, Iraq.

Seasonal Comparison of Potential Groundwater Aquifer in Ijebu-Ife, South-West, Nigeria, using Dipole-Dipole Array and Electromagnetic Methods

Seasonal comparison of potential groundwater aquifer unit using integrated geophysical methods at Ijebu-Ife, Ogun State, South-west, Nigeria was investigated. The fieldwork employed two seasons (dry and wet seasons). The electromagnetic method employed the Very low frequency and its data was acquired during the dry and wet seasons along with five profiles of Dipole-dipole array covering 500 m length using ABEM WADI VLF equipment and was processed using the KAROUS-HJELT software. The 2 – D Dipole-dipole data were also acquired along with five (5) traverse for both seasons making a total number of ten (10) and was processed with DIPROFWIN software. The results of the Integrated Dipole-Dipole and VLF-EM data identified three geoelectric layers based on its electrical resistivity and conductivity distribution. The study identified a clayey sand horizon which constitutes a good aquifer zone. The study reveals in, comparison, that during the dry season, all layer resistivities are high with low depth while during the wet season; all layer resistivities are low with high depth. Also, conductivity during the wet season is high at high depth than conductivity which is low at low depth during the dry season. The study concluded that, in water exploration, drilling of water should be done during the dry season in other to locate the exact depth of water.
 

Natural Hydrogeochemical Background Levels in the Carste Lagoa Santa Protection Unit, Minas Gerais, Brazil

The identification of hydrogeochemical anomalies in karst water resources represents a crucial step in Brazil's water management plans. Accelerated urban and industrial development occurs in the region that includes the Carste Lagoa Santa Protection Unit, State of Minas Gerais, which may negatively impact its water quality. This paper establishes Natural Background Levels (NBL) of waters collected from deep tubular wells and springs for Si4+, Ca2+, Mg2+, Na+, K+, HCO3−, SO42, Cl− to understand sources of possible geogenic and anthropogenic anomalies. Areas with surpassed thresholds were compared with geological, hydrogeochemical, and land use data. Every parameter, except for chloride, showed elevated concentrations due to lithologic origin. The NBLs for waters of wells and springs are, respectively, 17.9 and 12.7 mg/L (silica), 97.0 and 91.5 mg/L (calcium), 4.9 and 2.9 mg/L (magnesium), 6.2 and 3.8 mg/L (sodium), 1.0 and 0.3 mg/L (potassium), 285.5 and 254.6 mg/L (bicarbonate), 9.4 and 13.6 mg/L (sulfate). Chloride, analyzed only in groundwater, presented 6.7 mg/L indicating a possible influence of upstream urban areas of Lagoa Santa and Pedro Leopoldo municipalities. Volatile and Semivolatile Organic Compounds were also analyzed, but all of them were below the detection limit. This work is important to comprehend the NBL of major elements, reveal geogenic anomalies, and distinguish carbonate aquifer units from the impure ones.

Modelling aquifer parameters using surficial geophysical techniques: a case study of Ovwian, Southern Nigeria

Vertical electrical sounding (VES), pumping test and grain size distribution techniques have been used to model the hydraulic parameters in Ovwian, Nigeria. Twenty-two depth soundings were carried out with a maximum current electrode separation of 400 m to delineate the aquifer layers while the pumping test and grain size distribution procedures were conducted by drilling two boreholes where thirteen representative soil samples were collected at an interval of 3.048 m. The field data obtained from the resistivity sounding were modelled using the Win Resist software and the results when correlated with borehole log identified five geoelectric units made up of the topsoil, clayey sand, sandstone, fine grain sand and coarse grain sand. The sands of the third and fourth geologic layers constitute the aquiferous units with depth which varied between 6 and 42 m while the aquifer resistivity ranged between 100 and 2100 Ωm. The pumping test was analysed using the Copper Jacob method and the results revealed that the hydraulic conductivity and transmissivity of the aquifer from the reference well are 30.467 m/day and 495.072 m2/day, respectively. These results together with results from the vertical electrical soundings were used to model the hydraulic conductivity and transmissivity values for the area. This showed that the hydraulic conductivity of the area ranged from 28.595 to 38.435 m/day, with a mean value of 30.757 m/day while the transmissivity ranged from 185.697 to 1310.636 m2/day, with a mean of 495.752 m2/day. The grain size distribution analysis also revealed the hydraulic conductivity value of 1.46–171.94 m/day with an average of 38.880 m/day, while transmissivity ranged from 23.725 to 2794.025 m2/day with an average values of 631.738 m2/day. The close approximations of the results revealed the reliability of the VES, pumping test and grain size distribution analysis in the estimation of aquifer hydraulic parameters for groundwater resource development. Analyses of the results obtained in this study suggest that the aquifer is prolific and highly permeable with a high degree of rechargeability.

Environmental hazard assessment of industrial and municipal waste materials with the applications of RES2-D method and 3-D Oasis Montaj modeling: A case study at Kepong, Kuala Lumpur, Peninsula Malaysia

Environmental hazards, industrial, and municipal wastes geochemical and geophysical assessments were carried out at an industrial waste disposal (IWD) site at Bukit Kepong, Kuala Lumpur, Malaysia. RES2-D geophysical method was applied, capable of identification and quantification of the industrial wastes; buried hazardous materials (BHM) and their effects on the subsurface stratum, from the moderately saturated zones, to fully saturated zones housing the aquifer units underneath the water table. Six RES2-D survey profiles were respectively acquired along E-W, and N-S directions. The perpendicular arrangement of the RES2-D survey lines, was tenaciously designed to make possible, the industrial waste materials (IWM)and municipal solid waste (MSW) quantification, with sufficient length of survey lines set at 200 m, and electrode spacing of 5 m, to cover as much details segments of the IWM and MSW as possible. The six RES2-D inversion results, helped in the subsurface stratum classification into three layers, namely; soft layers, which encompasses the waste materials, with varied resistivity values i.e., 0–100 Ω-m, at 10–15 m depths. The consolidated layers produced varied resistivity values i.e., 101–400 Ω-m, at 15–20 m depths. The bedrock has the highest resistivity values i.e., 401–2000 Ω-m, at depths > 20 m. The estimated volume of the waste materials was 312,000 m 3, using 3-D Oasis Montaj modeling via rectangular prism model generated from the inverted RES2-D. Results from the geochemical analysis helped in the validation of the site as a potential contaminated zone with severe health effects.

Geophysical and geochemical assessments of the environmental impact of Abule-Egba landfill, southwestern Nigeria

There have been reports of cases of groundwater contamination in the areas around the Abule-Egba landfill site, Lagos, Nigeria. Based on this, geophysical and geochemical investigations were carried out to ascertain the cause(s) of the pollution and the extent of its impact on surrounding soils and groundwater within the area. A total of eleven vertical electrical sounding were conducted on two profiles established within the landfill area. Electrical resistivity tomography was conducted using a dipole–dipole array. The investigation results showed that the anomalously low resistivity values (> 40 Ω-m) observed from the surface to the depth of about 13 m on the generated geosections are due to leachate pollution of the aquifer units. On the borehole logs, a sand formation which ordinarily should possess a moderately resistive property was found to correspond to all the low resistivity zones characterized by leachate pollution. Geochemical results as observed from the wells within the landfill site show higher concentration of ions such as nitrate which is a diagnostic of leachate solution, as confirmed from geophysical analysis.

Geology and Aquifer Sensitivity of Quaternary Glacial Deposits Overlying a Portion of the Mahomet Buried Bedrock Valley Aquifer System

To characterize the distribution of Holocene and Late Quaternary deposits and to assess the contamination potential of the Mahomet Aquifer, surficial geologic and aquifer sensitivity maps of the Gibson City East 7.5-Minute Quadrangle were created. Geologic data, extent, and thickness of the geologic materials were coupled with LiDAR topographic data and analyzed using ESRI’s ArcGIS 10.6.1. Aquifer sensitivity to contamination was calculated based on the depth to the first aquifer unit, aquifer thickness, and the lithology of the aquifer materials. The surficial geologic mapping identified five lithostratigraphic units: the Cahokia Formation, the Equality Formation, the Henry Formation, and the Yorkville and Batestown Members of the Lemont Formation. The southeast to northwest trending Illiana Morainic System is the most prominent feature in the study area and delineates the maximum extent of the glaciers during the Livingston Phase of glaciation. Postglacial deposits of the Cahokia Formation, alluvium, interfinger, and overlie with glacial outwash of the Henry Formation along channels and drainage ways downslope of the moraine. The areas of least sensitivity are located over the Illiana Morainic System, whereas the greatest potential to contamination occurs where the thickest deposits of the Henry Formation and Cahokia Formation lie at or just below the land surface.

Evaluation of groundwater potential of bedrock aquifers in Geological Sheet 223 Ilorin, Nigeria, using geo-electric sounding

Electrical resistivity data acquired in one hundred and ten (110) locations using vertical electrical sounding method of Schlumberger array have been used to study the hydrogeological properties and groundwater storage potential of bedrock aquifers in an area covered by Geological Sheet 223 Ilorin, Nigeria. The aim of the study was to identify productive aquifer zones for citing boreholes for community water supply. The data acquired were processed and interpreted using auxiliary curve matching and computer automation method to delineate the different geo-electric layers, their resistivities, thicknesses, and depths. Geo-electrical layers were interpreted to their equivalent geological layers using borehole lithological logs from the study area. Then, the hydraulic conductivity, transmissivity, fracture contrast, reflection coefficient were estimated and plotted in the form of 2D maps to describe the spatial variations of these parameters in the area. The results of the study revealed the presence of three to five geo-electric layers. The geo-electric layers, from top to the bottom, corresponds to the topsoil layer, lateritic layer, weathered rock layer, fractured rock layer, and the fresh basement rock. Lateritic and/or fractured rock layers were not delineated in some places. The weathered and fractured rock layers, where present, correspond to the aquifer units. The thickness of the fracture aquifer ranges from 0.6 to 33.6 m while the thickness of the weathered aquifer ranges from 1.4 to 49.3 m. The transmissivity, T , and hydraulic conductivity, K , range from 3 to 1200 m2/day and 1 to 48 m/day, respectively. The reflection coefficient and fracture contrast map showed the presence of water-bearing fractures and shared some similarities with T and K maps. A mathematical model for predicting groundwater potential, {text{GW}}_{text{P}} , of weathered aquifer in the basement complex terrain was proposed in this study. The consistencies between the overall groundwater potential map and aquifers parameters distributions maps suggest the appropriateness of the proposed mathematical model for predicting groundwater potential of weathered rock in the basement complex area of Nigeria. The western, northwestern, and central parts of the study area, having {text{GW}}_{text{P}} greater than 0.6 (60%), were recommended for groundwater development through boreholes drilled to a depth ranging between 75 and 100 m.

Vulnerability assessment of hydrogeologic units in parts of Enugu North, Southeastern Nigeria, using integrated electrical resistivity methods

Aim/objectives: This research is geared towards integrating Vertical Electrical Soundings (VES) and Electrical Resistivity Tomography (ERT) profiles constrained with geoelectric sections and borehole logs to assess the vulnerability of the aquifer units employing Aquifer Vulnerability Indexing (AVI) method.Method: The dataset used in this study comprises of fifty VES, five ERT profiles surveyed in parts of Enugu north in Enugu state, two geoelectric sections and three borehole logs. The computer and manual interpretation of VES resistivity data using WinResist software gave values of resistivity, depth and thickness of each geoelectric layer using half current electrode spacing of 1.0 to 450.0m and maximum current electrode spacing of 900 m. 2D imaging data from the measured field resistance values were processed using RES2DINV32 version 3.71.115 software. The geoelectrical sections show the variation of resistivities with depth along transcent lines. The geohydraulic parameters were also estimated. Finding: Interpreted VES data revealed five to six geoelectric layers and fundamental parameters generated were used to estimate the values of hydraulic conductivity (s ) and hydraulic resistance (C) of the covering layers ranging from 0.010 to 0.769 mday􀀀1 and 40.47 to 8292.0 day􀀀1 respectively.This research revealed high hydraulic conductivity in the western part implying good groundwater potential with moderate to high protective capacity while areas with low hydraulic conductivity correspond to areas with high resistivity indicating little or no pore space and total devoid of water. The hydraulic resistance quantifies groundwater vulnerability using AVI and reveals that the area of study is characterized by low to high AVI with moderate AVI dominanting.Originality and novelty: The estimated geohydraulic properties from resistivity data and their spatial spread are promising and could increase the depth of knowledge on groundwater vulnerability within and around the study area. Keywords: VES; ERT; AVI; hydraulic conductivity; hydraulic resistance

Using isotope data to characterize and date groundwater in the southern sector of the Guaraní Aquifer System

ABSTRACT The Guaraní Aquifer System (SAG) is the largest transboundary aquifer in Latin America, extending beneath parts of Brazil, Paraguay, Argentina, and Uruguay. This paper presents the results of recent hydrogeological studies in the southern portion of the SAG. Locally, the abundance of surface water bodies precluded the use of conventional hydrological tools to characterize groundwater flows. Geological, hydrochemical and environmental isotope investigations were integrated to postulate a revised hydrogeological conceptual model. The revised geological model has provided a better definition of the geometry of the aquifer units and outlined the relevance of regional faults in controlling flow patterns. The new potentiometric map is consistent with groundwater flow from the SAG outcrops to the centre of the Corrientes Province, where upwards flows were identified. Hydrochemical and isotope data confirmed the widespread occurrence of mixing. Noble gas isotopes dissolved in groundwater (4He and 81Kr/Kr) provided residence times ranging from recent recharge up to 770 ± 130 ka. Groundwater age modelling confirmed the role of the geological structures in controlling groundwater flow. The southern sector of the SAG is a multilayer aquifer system with vertical flows and deep regional discharge near the Esteros del Iberá wetland area and along the Paraná and Uruguay rivers.

A national border-based assessment of Malawi’s transboundary aquifer units: Towards achieving sustainable development goal 6.5.2

Study regionMalawi. Study focusThe adoption of the United Nations Sustainable Development Goal 6 in 2016 has triggered countries across the globe to assess and improve management and use of water resources. Monitoring of these resources is becoming increasingly important, and the management of transboundary water resources, in particular groundwater aquifers, required to meet SDG target 6.5.2, is lagging behind. It is vital to assess and manage these resources in a sustainable manner within an integrated water resource management approach. Transboundary aquifer assessments have largely focused on the regional scale which is not sufficient for countries to manage their transboundary aquifers effectively. This paper focuses on results of a national transboundary aquifer unit assessment in Malawi as a case study to support the countries plans for achieving Sustainable Development Goal 6.5.2.New hydrological insights for the region: We have identified 38 new transboundary aquifer units shared between Malawi and its neighbours. These results can form the basis for future transboundary aquifer management between Malawi and its neighbouring countries. We also highlight the current limitations of transboundary aquifer assessments and management that should be addressed to achieve SDG 6.5.2. These include institutional mechanisms, limited cross-border data sharing, limited groundwater monitoring, and a need to revisit the wording of the transboundary-focused SDG target and its indicators.

Contribution of the resistivity method to the determination of the fault zone and the hydro-geophysical characteristics of the aquifer system in Tataouine (Southern Tunisia).

Southern Tunisia aquifer's systems including Tataouine region has suffered since long time by over-exploitation resulting in a subsequent drop of the piezometric level. Consequently, the overexploitation of these layers poses various problems in term of quality and quantity. Therefore, to better recognize these hydraulic potentialities and evaluate their extensions in this region, a geophysical survey, using the electrical resistivity method was carried out to determine the structure, the configuration of these aquifer systems and to investigate the subsurface layering and evaluation of the aquifer characteristics. Applying the schlumberger array, a total of 335 Vertical Electrical Soundings were conducted along 4 profiles, using a maximum current electrode separation ranging between 500 and 600 m. Qualitatively and quantitively interpretation were both obtained and represents the outcomes from the study field. The qualitative interpretation is based on isoapparent resistivity maps, and the geoelectrical pseudosection analysis. It shows that Tataouine Basin is formed by alternating conductive and resistant anomalies related to the lateral and vertical variation of lithology in the study area. As well, quantitative interpretation using calibration, electrostratigrafic sections and isopach maps shows a clay-sandstone series of the Triasssic, Bathonian and Cretaceous. Theses series, with average low resistivity values, and low percentage of clay present some porosity and constitute the main aquifer unit in the study area. In addition, the carbonate unit shows in certain zone a sight fracking and high resistivity values composed of the aquifers such as; Triassic dolomite, Krachoua limestone, and marl-limestone of upper Jurassic. Furthermore, most of these aquifer units are communicating with each other through the tectonic discontinuities.