Aquifer Range Research Articles

Groundwater Potential of the Jakarta Groundwater Basin using the Darcy Equation Method

The annual increase in population leads to a growing demand for water. To control groundwater utilization in a directed manner is to extract groundwater according to groundwater potential. The research aims to analyze the groundwater potential in the Jakarta Groundwater Basin in terms of quantity and quality. The method used is primary data analysis by determining quantity potential using the Darcy equation method with additional calculations of groundwater volume and quality potential based on drinking water quality standards from the Republic of Indonesia Minister of Health Regulation no. 2 of 2023 and WHO of 2022. The dynamic potential for unconfined aquifers ranges from 2,663–1,372,901 m³/year, while for confined aquifers range from 184,991–1,895,288 m³/year. The static potential for unconfined aquifers ranges from 266,852–3,252,654 m³, while for confined aquifers ranges from 1,317,862–30,620,266 m³. Based on groundwater quality standards for drinking water from the Minister of Health and WHO for the parameters pH, TDS, Na⁺, Cl⁻, SO₄²⁻ and NO₃⁻, there are 15 samples from 53 samples of unconfined aquifer and 36 samples from 75 samples of confined aquifer that meet standards.

Podzemní vody hluboké struktury regionálního rozsahu: Pasohlávky–Laa an der Thaya

The regions of South Moravia in Czech Republic and Lower Austria are well-known for their use of thermal mineral waters for balneological purposes. Mineral waters are exploited from a Jurassic aquifer by two about 1.5 km deep wells MUS-3G (Pasohlavky, Czech Republic) and Laa TH Nord 1 (Laa an der Thaya, Austria). This Jurassic aquifer buried below the Neogene foredeep overlies a crystalline basement of Bohemian Massif and continues to the southeast below the Western Carpathians. Jurassic sediments which are mainly composed of autochthonous carbonates increase their thickness in this direction due to the decline of the crystalline basement. Because of this decline, there are two developments of Jurassic sediments, the shallower on the northwest and the deeper on the southeast. The zone between these two developments is known as the Mušov transition zone. For sustainable mineral water resources development, a groundwater flow pattern and recharge are evaluated. This evaluation includes both the hydrogeologic structure of Jurassic carbonates and hydraulically continuous underlying and overlying rocks. Because of the considerable depth of this hydrogeologic structure, which ranges from 100 to 3 000 metres below sea level, this study was based mostly on archive reports related to deep wells at the study area. The extent of studied units was identified on well-log data and geophysical survey interpretation. The resulting groundwater level contour map is based on the spatial distribution of hydraulic heads ranging approx. from 180 to 220 metres above sea level (masl) that were derived from pressure and water density conditions at the Jurassic aquifer. The general direction of groundwater flow is from northwest and southeast to the drainage zone (hydraulic head approx. 170–190 masl) identified in the middle of the studied area, which is identical to a course of the Mušov transition zone and parallel to the course of Dyje river (water table 170–180 masl). The northwestern part of the studied hydrogeological structure also differs from the southeastern part in a lower total mineralization which indicates active inflow of fresh water. The study was also enhanced by a spatial distribution of hydraulic parameters of all modelled units. These parameters were derived from hydrodynamic tests. The hydraulic conductivity values for the major Jurassic aquifer range from 6.0 × 10-4 to 1.3 × 10-9 m/s. The occurrence of the higher hydraulic conductivity near the drainage zone indicates the presence of a well-developed drainage network.

Mantle-derived fluids in the continental-scale Nubian aquifer

The Nubian aquifer of northeastern Africa is one of the largest confined fossil-water aquifer systems in the world. It is central for ongoing water needs and future development goals of Egypt, Libya, Sudan and Chad. Groundwater extraction and consumptive use over the past 40 years have led to a continuous decline of water level and to the reduction and/or cessation of natural flow in artesian wells and springs. This study introduces new noble gas and stable isotope geochemical data from deep groundwater supply wells of the main oases of the Western Desert of Egypt (Bahariya, Farafra, Dahkla, and Kharga) and places these data in the context of a regional compilation of published hydrological and hydrochemical data. Helium isotopes, stable isotope compositions for water (δ2H; δ18O) and dissolved inorganic carbon (δ13C), salt compositions, and [CO2] suggest deeply derived fluid inputs. Highly variable groundwater temperatures (20–56 °C) also suggest the presence of geothermal inputs that mix with aquifer water. Nubian water displays high PCO2 (up to three orders of magnitude higher than atmosphere) and hydrochemical analysis using δ13C suggests up to ~30% of the CO2 is derived from deep geologic sources. Helium isotope (3He/4He) ratios of samples obtained from the Nubian aquifer range from crustal values of 0.02RA (where RA reflects the 3He/4He in air or 1.384 × 10−6) to values of up to 0.36RA (2.5% mantle helium) in Dahkla Oasis of Egypt and up to 1.4RA (17% mantle helium) in Libya. Correlations among excess heat, increases in [CO2], δ13C, and 3He/4He indicate that small volumes of deeply sourced fluids carrying mantle-derived volatiles are leaking into the Nubian aquifer. Geothermal water apparently ascend along faults and shear zone conduits and mix with regional groundwater. The origin of these volatiles may be partial melts in low velocity upper mantle beneath the aquifer and young magmatism surrounding the Nubian aquifer. Fluid-rock interactions along flowpaths can explain variable associations and correlations among the tracers. Variability of composition and temperature suggest complex fluid mixing within the Nubian aquifer, the existence of fault-bounded hydrologic sub-basins, and a connection between tectonics and water quality. Better understanding of the sources and admixtures of deep geothermal fluid inputs is needed for informed water management.

Estimation of Hydrogeological Parameters by Using Pumping, Laboratory Data, Surface Resistivity and Thiessen Technique in Lower Bari Doab (Indus Basin), Pakistan

Determination of hydrological properties of the aquifer is of fundamental importance in hydrogeological and geotechnical studies. An attempt has been made to refine the hydraulic conductivity values computed from the pumping test by utilizing the hydraulic values computed in the laboratory. This study uses hydraulic conductivity computed in the laboratory of rock samples, pumping test data in conjunction with the empirical equations, and vertical electric sounding (VES) to determine the hydraulic properties of Lower Bari Doab (LBD) in the Indus Basin of Pakistan. The utilized dataset comprises pumping test results (Kpump) from 17 water wells, hydraulic conductivity values (Klab) of different grain size subsurface lithologies, and 50 VES stations. To this end, the investigated area is divided into 17 polygons by using the Thiessen technique, and equal distribution/weight of conductivities values is assigned to 17 polygons (one polygon around each water well where pumping test is conducted). The true resistivity ranging from 20–90 ohm-m along with an average thickness of the aquifer is computed using the VES data for each polygon. A novel approach has been developed to estimate the hydraulic conductivity of the aquifer by combining laboratory data and pumping test which is used to compute the other hydraulic properties. The calculated hydraulic conductivity, transmissivity, and tortuosity values of the aquifer range from 4.4 to 85.6 m/day, 674 to 8986 m2/day, and 13 to 20, respectively. The porosity ranges from 32 to 45% and the formation factor values fall in the range 4 to 12. Higher hydraulic conductivities were encountered in the southern portion of the area near the junction of the rivers, and it increases with an increase in porosity. The aquifer having T > 5700 m2/day and K > 40 m/day, yields a large quantity of water whereas the portion of an aquifer with T < 1100 m2/day and K < 13 m/day are combatively low yield aquifer. The results of the resistivity method show that the subsurface geological material, as depicted from true resistivity, is composed of layers of sand, clay, and silt mixed with gravel/sand. This study improves the understanding of the aquifer and will help in the development and management of groundwater resources in the area including the prediction of future behavior of the aquifer.

Geophysical Investigations and Aquifer Characteristics of the Benin Formation at Agbarho, Delta State, Nigeria

Groundwater investigations were carried out at Agbarho using geophysical survey method to delineate the aquifer and subsurface lithology. Three (3) vertical electrical sounding were conducted with a maximum current electrode spacing of 300m. The data acquired were subjected to partial curve matching and computer processing. The results delineated five geoelectric layers for the area, which include; topsoil, silty sand, silty clay, fine sand, medium grain sand and coarse sand. The Dar-Zarrouk parameter revealed an aquifer system that has a resistivity values ranging from 503.9-966.9ohm-m, an average hydraulic conductivity of 7.73 m/day, and transmissivity in the range of 156.24-181.44m2/day. The depth to the aquifer range from 13.2-42.7m and the aquifer thickness is between 7-36.7m. Results from seven down-hole logs revealed the presence of silty sand, fine sand and fine-medium grained sand. The transmissivity values from pumping test range from 162.29-286.56m2/day and storativity is from 0.001-0.00838. The aquifer is capable of yielding useful quantity of water to the wells and sustainable groundwater management plan can be develop for the area.

Relationship between rain and groundwater in the hydrogeological sectors of the South Basin of Ciego de Ávila

Introduction: Groundwater constitutes the main source of water in the province of Ciego de Ávila, Cuba; especially in agriculture, which occupies the main economic line, however the overexploitation of aquifers in the southern basin of the province puts the sustainability of this important resource at risk, which is renewed through the natural recharge of rainfall. Objective: To determine the relationship between precipitation and groundwater levels in the hydrogeological sectors CA-II-2 and CA-II-3 of the Ciego de Ávila South Basin, which can constitute a way for the efficient use of water for irrigation purposes in this area of ​​great agricultural importance. Methodology: In the development of the research, different methodologies were used: selection of the most representative rain gauges, calculation of effective precipitation, determination of accumulated monthly and annual rainfall; as well as the annual rainfall of the wet and dry periods, completion of rainfall series by the linear regression method, use of the HidroEsta 2 program to obtain the mean hiperanual rainfall and the historical mean levels, absolute minimum and maximum of all the selected wells. The mean rainfall of the area of ​​the sectors was determined with the Isohyet method and the charts of hiperanual limnigrams were constructed using the BARHIS software. Results: The investigation showed that the average rainfall in the area is 1303.6 mm, higher than the historical average for the province. The water levels in the aquifer range between 0.84 and 12.98 m; where 7.21 m is the absolute average value. The year 1988 had great variations in rainfall, levels and the exploitation of groundwater. This study suggests the need to take measures that contribute to the rational use of groundwater in this overexploited basin due to the intensive use of water resources in agricultural irrigation. Conclusions: The study carried out was able to verify that the average rainfall in the area is 1303.6 mm, higher than the historical average for the province. The water levels in the aquifer range between 0.84 and 12.98 m, with absolute averages of 6.52 and 7.21 m respectively. The year 1988 presented high variability in rainfall, underground levels and the exploitation of groundwater.

Potential of Shallow Groundwater for Household Level Irrigation Practices in Tahtay Koraro Woreda, Tigray, Northern Ethiopia

This paper deals with the results of a pilot study conducted to estimate the shallow groundwater resource potential and irrigation capacity at the household level in Tahtay Koraro Woreda, northwestern zone of Tigray, Ethiopia. The potential evapotranspiration and actual evapotranspiration of the study area are estimated to be 1484 mm/year and 814 mm/year respectively. The runoff is approximately calculated to be 280 mm/year and the annual groundwater recharge is estimated to be 29 mm/year. The total annual groundwater abstraction for human, livestock, and irrigation is estimated to be 25 mm/year. It should be noted that the groundwater recharge rate is expected to remain constant while the total annual groundwater discharge is expected to increase from year to year. This relation when projected over a long period may result in a negative groundwater budget which can result in depletion of groundwater (lowering of groundwater levels), reduced baseflow to streams, and deterioration of water quality. The computed values for hydraulic conductivity of the aquifers range from 1.63 m/day to 7.27 m/day with an average value of 4.9 m/day and transmissivity from 48.9 m2/day to 218.1 m2/day with an average value of 147.14 m2/day. The aquifers in the highly weathered basalt and highly weathered siltstone – sandstone intercalation have transmissivity values ranging from 99 m2/day to 218.1 m2/day with an average value of 157 m2/day and are grouped into the moderate potentiality aquifers category. The aquifers in the slightly weathered and fractured metavolcanics grouped under low potentiality based on the lower transmissivity values (<50 m2/day). The study area has low to moderate groundwater potentiality, hence, large-scale groundwater pumping is not possible. Therefore, the current activity of using hand dug wells for household-level irrigation is the best way of using groundwater for irrigation and other uses as well. Increasing the depth of the existing hand dug wells that are constructed in highly weathered basalt and highly weathered siltstone – sandstone intercalation can also enhance the yield of the hand dug wells. It is recommended to use water-saving irrigation technologies rather than increasing the number of wells. This will also help in increasing the irrigation area. Groundwater recharge enhancement structures such as trenches, percolation ponds, and check dams be constructed in scientifically selected localities to further enhance the groundwater potential.

GEOPHYSICAL INVESTIGATION OF GROUNDWATER CONTAMINATION USING DC RESISTIVITY TECHNIQUE AT THE MALE HOSTEL OF ISA KAITA COLLEGE OF EDUCATION DUTSIN-MA, KATSINA STATE, NIGERIA

A geophysical investigation involving Vertical Electrical Sounding (VES) using the Schlumberger array was carried out at the Isa Kaita College of Education specifically at the Male Hostel. The aim of the investigation is to explore the groundwater contamination of the area with the objectives: to determine the depth to basement of the study area, to determine the aquifer thickness, to determine the depth to aquifer, to determine the conductivity of the aquifer and to determine the thickness of topsoil and its variation in resistivity. A total of four (4) vertical electrical soundings were carried out using Schlumberger configuration. Terrameter signal averaging system (SAS) model 300 was the instrument used. The survey area is dominated by mainly four layers, namely: Topsoil, Weathered basement, fractured basement. The value of VES 03 and VES 04 have high electrical conductivities which likely shows they are contaminated, The topsoil resistivity along the profile ranges from approximately 1 to 154, The depth to basement (basement topography) Varies from 4.94 m to 7.59 m, The thickness of aquifer range from 1 m to 6.8 m. Therefore VES 02 has high Potential for groundwater because it has retaining capacity and good aquifer thickness and is therefore recommended for borehole establishment. It is recommended that the management of Isa Kaita College of Education should provide a concrete dumping site to avoid leaching of waste in ground thereby contaminating the groundwater.

Discharge of groundwater flow to Potter Cove on King George Island, Antarctic Peninsula

Abstract. There are only a small number of recent publications discussing glacial runoff in Antarctica, and even fewer of them deal with the groundwater flow discharge. This paper focuses on the groundwater flow aspects and is based on a detailed study performed on a small hydrological catchment, informally called Potter basin, located on King George Island (KGI; Isla 25 de Mayo), South Shetland Islands, at the northern tip of the Antarctic Peninsula. The basin is representative for the rugged coastline of the northern Antarctic Peninsula and is discussed as a case study for the possible future evolution of similar basins further to the south. A conceptual hydrogeological model has been defined using vertical electrical soundings (VESs), geological and hydrogeological surveying methods, geomorphological interpretation based on satellite imagery, permeability tests, piezometric level measurements, meteorological, geocryological and glaciological data sets. The transmissivities of the fluvial talik aquifer and suprapermafrost aquifer range from 162.0 to 2719.9×10-5 m2 s−1 and in basaltic fissured aquifers from 3.47 to 5.79×10-5 m2 s−1. The transmissivities found in the active layer of hummocky moraines amount to 75.23×10-5 m2 s−1 and to 163.0×10-5 m2 s−1 in the sea deposits, and in the fluvioglacial deposits, they were observed between 902.8 and 2662.0×10-5 m2 d−1. Finally, the groundwater flow discharge was assessed to 0.47 m3 s−1 (during the austral summer months of January and February), and the total groundwater storage was estimated to 560×103 m3. The Antarctic Peninsula region has experienced drastic climatological changes within the past five decades. Under the Intergovernmental Panel on Climate Change scenarios, a further warming of the polar regions can be expected as polar amplification of our changing climate. Although the basin in consideration is small and results are valid only during austral summers with surface air temperatures above the freezing point, it serves as model study that can be regarded as representative for the western coastline of the Antarctic Peninsula further south under expected future warming, with surface air temperatures periodically surpassing freezing point. This data can be used to adjust glacial mass balance assessments in the region and to improve the understanding of coastal sea water processes, and their effects on the marine biota, as a consequence of the global climate change.

Concentration of Iron(II) in Fresh Groundwater Controlled by Siderite, Field Evidence

Iron(II) concentrations in fresh groundwater in Dutch aquifers range from absent up to 50 mg/l. Evaluation of extensive chemical data sets learned that the maximum logarithmic concentration of iron(II) in aquifers, between ± 6.5 < pH < ± 8, is a linear function of pH, governed by Siderite. It is a broad relation due to oversaturation with respect to Siderite and to variation in alkalinity. Iron(II) is continuously supplied to groundwater by reduction of hydrous ferric oxides (HFO), until becoming saturated with respect to Siderite, and from then on, HFO reduction and Siderite precipitation occur simultaneously. In Dutch aquifers, the electron supply rate (equivalent to the organic matter oxidation rate) apparently exceeds the HFO electron uptake rate (equivalent to the HFO reduction rate) and the excess supply is taken up by sulfate (equivalent to the sulfate reduction rate): HFO reduction, sulfate reduction and FeS precipitation occurring simultaneously, where the presence of Siderite prevents a dip in the iron(II) concentration. After sulfate becomes exhausted, the excess electron supply is transferred to methane production: HFO reduction and methane production occurring simultaneously. This evaluation also demonstrated that the organic matter oxidation rate and the HFO reduction rate decrease over time. The results of this study are also relevant for the behavior of As and of Co, Ni and Zn in groundwater, as HFO, Pyrite and Siderite may contain variable contents of these elements.

Groundwater recharge and water table response to changing conditions for aquifers at different physiography: The case of a semi-humid river catchment, northwestern highlands of Ethiopia

Groundwater recharge estimation, aquifer response to meteorological variables, and evapotranspiration calculations have been performed on a semi-humid catchment, in northwestern Ethiopian plateau. The Soil Moisture Balance (SMB), WetSpass water balance model, Water Table Fluctuation (WTF), and Chloride Mass Balance (CMB) methods are applied to estimate the groundwater recharge. Accordingly, 431 mm, 462 mm, and 477 mm recharge amounts are estimated as mean annual value, respectively, using SMB, WetSpass, and CMB methods. Based on the WTF method, the annual recharge rates of the volcanic aquifers range from 157 mm to 760 mm. The SMB and WetSpass methods are less effective for the flat physiographic area, where the recharge rate is storage controlled rather than precipitation amount. The calculated high recharge for maintain-front aquifers using WTF is attributed to extra rising due to lateral groundwater flow, which restricts the reliability of the method for such aquifer geometries. High groundwater level rising rate (121 mm/day) has been observed for the steeply sloping, low rates (11 mm/day) for the flat floodplain, and intermediate rate (52 mm/day) for the gently sloping volcanic aquifers. Similarly, receding rates of 3.18 mm/day were found for the steeply sloping, 0.40 mm/day for the floodplain, and 1.14 mm/day for the gentle sloping aquifers. The recession, in all of the topographies, is happening with second-order polynomial decay function. A strong connection between the shallow and deep groundwater aquifers is noted. Storage change in the relatively deeper volcanic aquifers is due to vertical groundwater flow from the overlying alluvial aquifer. This indicates that the recharge mechanism is local, and may be the reason for the low aquifer productivity of the Dangila wellfield. Diurnal water table fluctuation is detrended from the receding trend of the dry period, and evapotranspiration from the groundwater is estimated at 28% of total ET.

The effect of geochemical processes on groundwater in the Velenje coal basin, Slovenia: insights from mineralogy, trace elements and isotopes signatures

This study investigated the mineralogical and isotopic composition of groundwater and precipitation to identify and constrain geochemical processes within stacked Pliocene and Triassic aquifers in the Velenje coal basin. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopic analysis revealed that suspended matter in the Pliocene aquifer consists of feldspars and quartz, while dolomite, calcite and feldspars are present in the aquifer dewatering Triassic strata. The concentrations of trace elements in Triassic and Pliocene aquifers range from highest to lowest Zn > Fe > Ni > Al > Ba > Mn > B>Li > Mo > As with the majority of trace element concentrations below international drinking water health guidelines. Multivariate principal component analysis indicated that concentrations of Mn, Ba, Eu, Cs, Y, Li and T, pH, conductivity and dissolved oxygen in samples were the best chemical parameter for distinguishing the two aquifers. A significant positive correlation (p < 0.05) was found between Ni, Mn, Co, Zn, As and Mo. Groundwater in the Pliocene aquifer likely has an external source of carbon based on the δ13CCO2 values (− 12.3 to − 3.6‰). The groundwater also has detectable levels of dissolved methane with isotopic values (− 77.7 to − 51.4‰ δ13CCH4; − 247 to − 162‰ δ2HCH4) consistent with microbial methanogenesis. The groundwater in the Triassic aquifer has tritium values (up to 4.1 TU 3H) characteristic of modern recharge (< 50 years), while the lack of detectable 3H (0 TU) in the Pliocene aquifer is consistent with longer residence times.

Determination of Groundwater Potentials in Crystalline Basement Areas of Bauchi Local Government Area, Bauchi

Developing groundwater is generally an excellent option for sustainable water supplies in Bauchi due to the ephemeral nature of surface water. However, the large variability in geological and hydrological conditions have a profound influence on the availability of groundwater across the study area. The rationale for this research is to contribute at least, in terms of providing empirical data towards sustainable development of groundwater resource, particularly in the Crystalline Basement hydrogeological unit of Bauchi area. Aquifer properties of wells within the Crystalline Basement were estimated from a constant-rate pumping test of 10 sampled wells by fitting mathematical models (type curves) to drawdown data through curve matching. Generally, yields of sampled boreholes within the crystalline basement aquifer range from 8.64 m 3 /d to 120.96 m 3 /d with an average of 52.36 m 3 /d. The total yield of the boreholes is about 661.83.m 3 /day. This can sustain a population of 26,473 based on water supply standard of 25 litres per day for rural communities (Babatola, 1997). Considering the total population of 12,218 people (NPC, 2014) that are currently using the water points in comparison to water supply standard of 25 litre per person per day, this shows that the aquifers from the 10 sampled boreholes have relatively enough groundwater in terms of yield to meet the water need of the population. However, any significant increase in population growth may result in water scarcity in these areas, as the Crystalline Basement aquifers generally have low yielding capacity. Also, the crystalline basement aquifer properties evaluated reveal that the transmissivity values range from 2.55 m 2 /day to 111.0 m 2 /day with an average of 38.94m 2 /day (Table 5). According to Offodile (2002), a transmissivity range of 5 to 50 m 2 /day could be regarded as high potential in crystalline rock situations. By the above standard, the crystalline basement aquifers in the area are classified as aquifers of negligible to high potentials. The specific capacities of boreholes in the study area were computed and the results show that they vary between 1.30 to 691.2 m 2 /d/m. Keywords: Crystalline Basement, Groundwater, Pumping Test, Aquifer, Transmissivity, Bauchi State, Nigeria DOI : 10.7176/JEES/9-7-02 Publication date :July 31 st 2019

Application of Multi-Isotopes and Geochemical Modeling for Delineating Recharge and Salinization Sources in Dahab Basin Aquifers (South Sinai, Egypt)

The Dahab watershed comprises three aquifers; the alluvial Quaternary, the Early Cambrian sandstone, and the fractured Pre-Cambrian basement aquifers. The Dahab watershed is located in the southeastern part of the arid Sinai Peninsula, where low precipitation and groundwater over-exploitation deteriorate the groundwater quality in the alluvial coastal plain aquifer located downstream. Multi-isotopes including δ18O and δ2H, 87Sr/86Sr, δ81Br and δ11B coupled with groundwater geochemistry were utilized to assess the recharge source(s), water-rock interaction, and seawater mixing to aid sustainable groundwater management strategies. Br and Cl concentrations, used to measure groundwater salinity, were low in the upstream groundwater, while higher concentrations were observed in the deep drilled wells located downstream, in the main well field. The δ18O and δ2H isotopes were depleted in the upstream aquifers, but enriched in the shallow coastal aquifer, indicating slight evaporation and seawater intrusion. Higher mean values of 87Sr/86Sr and δ81Br were observed in the fresh groundwater from high in the watershed (87Sr/86Sr = 0.707716 and δ81Br = +2.05‰), while lower mean values were observed in the saline groundwater located downstream in the main well field (87Sr/86Sr = 0.706631 and δ81Br = +0.11‰). The cumulative mass balance mixing curves and the geochemical NETPATH model confirm the change of groundwater quality from the upper to lower watershed caused by the leaching and evaporation processes, as well as mixing with seawater. The corrected 14C age dating and stable isotopes show that the Quaternary and Pre-Cambrian basement aquifers contain modern groundwater, while the Early Cambrian aquifer holds paleo-groundwater, which has received considerable recharge from recent precipitation. The mixing ratiosin the Quaternary coastal aquifer range between 5% and 13% seawater to 95% and 87% fresh groundwater, respectively. These results indicate that future groundwater withdrawal must be well managed in order to limit further salinization. Groundwater withdrawal from the Quaternary coastal aquifer must be below the natural average recharge in order to be sustainable.

Application of electrical resistivity method in estimating geohydraulic properties of a sandy hydrolithofacies: a case study of Ajali Sandstone in Ninth Mile, Enugu State, Nigeria

Geoelectric investigation using vertical electrical sounding (VES) (Schlumberger electrode configuration) was carried out in 14 locations at Ninth Mile area, southeastern Nigeria to determine the variations and interrelationship of some geoelectric and geohydraulic parameters of a sandstone hydrolithofacies. The measured resistivity data were interpreted using manual and computer software packages, which gave the resistivity, depth, and thickness for each layer within the maximum current electrodes separation. The aquifer resistivity values range from 86.56 to 4753.0 Ωm with 1669.40 Ωm average value. The values of water resistivity from borehole locations close to the sounding points range from 79.49 to 454 .55 Ωm and averaging about 264.7 Ωm. Porosity values of the sandy aquifer range from 30.19 to 34.20%. Fractional porosity values range from 0.3019 to 0.3292, while the tortuosity values vary between 2.91 and 22.85. The geohydraulic parameters estimated vary across the study area. Formation factor ranges from 0.28 to 15.29, hydraulic conductivity ranges from 1.21 to 66.54 m/day which, however, influences the natural flow of water in the aquifer while tortuosity values range from 2.91 to 23.27. The contour maps clearly show the variation of these parameters in the subsurface and the plots show their relationship and high correlation coefficients with one another. The results of this study have revealed the geological characteristics of the subsurface aquifer, established the influence on the amount of groundwater, and proposed a strategy for the management and exploitation of groundwater resources in the area and other aquiferous formations.

High arsenic groundwater in the Guide basin, northwestern China: Distribution and genesis mechanisms

High arsenic (As) groundwater has been found in Pliocene confined aquifers at depths from 100 to 300 m of the Guide basin, but little is known on the main hydrogeochemical processes leading to its elevated concentrations. Ninety-seven water samples and fifty-three sediment samples were collected for chemical and/or isotopic analysis. Concentrations of As in groundwater of confined aquifer range from 9.9 to 377 μg/L (average 109 μg/L), which generally show a sharply increasing trend along with NH4+, HCO3−, CO32− and TOC along the inferred flow path, while NO3−, SO42−/Cl− and redox potential (Eh) have decreasing trends. Results of sequential extraction show that As bound to amorphous and crystalline Fe oxide minerals are the main As forms, accounting for around 50% of total As in sediments. Reductive dissolution of As-bearing Fe(III) oxide minerals under reducing conditions in confined aquifers lead to the mobilization of As in groundwater. In addition, alkaline environment and high concentrations of HCO3− and CO32− may make contributions to As enrichment in groundwater. High As groundwater in confined aquifer continuously flows out on the ground surface through tens of artesian wells, which may potentially contaminate low As groundwater in unconfined aquifer. Thus, further investigation is needed to evaluate long-term variations of water chemistry of low As groundwater and assess vulnerability of unconfined aquifer to As contamination.

Quality of natural waters in carbonate aquifers at a densely populated Odukpani area of cross river state, Southern Nigeria

The study area, Odukpani is underlain by cretaceous sediments of the Calabar Flank. The main aquifers are fractured black shales that are inter-bedded with calcareous sandstones. The aquifers range...

87Sr/86Sr Ratios in Shallow and Deep Aquifers and Thermal Water from the Eastern Boundary Fault of the Northern Upper Rhine Graben at the Heidelberg Basin, Germany

Strontium isotopic ratios are important tracers of hydrological processes such as water-rock interaction and the detection of the ascent of deep fluids at hydraulically active faults. The 87Sr/86Sr ratios have been measured in shallow and deep aquifers (n=19) and thermal water at the Eastern Boundary Fault (EBF) of the northern Rhine Graben Rift in Germany. 87Sr/86Sr ratios and Sr contents from Quaternary groundwater conducting sediments of the shallow aquifers range from 0.70896 to 0.70965 and 0.23 to 0.67 mg/l, respectively. Strontium contents of the shallow groundwater are low and highly variable in their 87Sr/86Sr ratios. No unequivocally hints of ascending deep fluids at the EBF fault have been found in the shallow aquifers of the Heidelberg Basin. However, groundwater from production wells of up to 205 m deep aquifers and the 1100 m deep thermal well show radiogenic 87Sr/86Sr ratios and high Sr contents in the range from 0.70984 to 0.71074 and 0.39 to 319 mg/l, respectively. The radiogenic Sr ratios are clear indications for ascending deep fluids into deep aquifers at the EBF fault of the northern upper Rhine Graben.

Determination of the origins and recharge rates of the Sfax aquifer system (southeastern Tunisia) using isotope tracers

The origin of groundwater in the Sfax aquifer system was studied using environmental isotopic tracers (δ18O, δ2H, and 3H). In total, 164 water samples were analyzed for stable isotopes: 73 collected from the Sfax shallow aquifer, 63 from the Sfax middle aquifer, and 28 from the Sfax deep aquifer. Recent recharge of the groundwater in the Sfax aquifer was identified using tritium concentrations in 82 groundwater samples from different depths. The isotopic ratios of the shallow aquifer range from −5.55 to −1.59 ‰ for δ18O and from −38.38 to −14.19 ‰ for δ2H, and the isotopic ratios in the middle aquifer range from −6.86 to −2.97 ‰ for δ18O and from −44.18 to −22.38 ‰ for δ2H. The deep aquifer exhibited markedly lower isotopic values, ranging from −6.70 to −5.70 ‰ for δ18O and from −42.40 to −38.89 ‰ for δ2H. The mixing proportions inferred from stable isotopic mass balance calculations suggest that the deep aquifer contributes significantly to the middle aquifer through geologic structures and may reach 100 % in the Menzel Chaker region. The isotopic mass balance model also indicates that the middle groundwater aquifer may contribute up to 100 % of the shallow Plio-Quaternary aquifer, particularly in the western and northeastern parts of the study area, between Bir Ali ben Khalifa and Djebeniana. The tritium data support the existence of recent recharge. The tritium and stable isotope data clearly indicate the presence of mixing processes, especially in the northwestern and coastal portions of the study area. A conceptual model is established, explaining the pressure differences that generate vertical leakage, which is a reasonable mechanism for flow between the aquifers.

Chloride as tracer of solute transport in the aquifer–aquitard system in the Pearl River Delta, China

A 1D numerical model is constructed to investigate the impact of sedimentation and sea level changes on transport of Cl− in the aquifer–aquitard system in the Pearl River Delta (PRD), China. The model simulates the evolution of the vertical Cl− concentration profiles during the Holocene. Sedimentation is modeled as a moving boundary problem. Chloride concentration profiles are reconstructed for nine boreholes, covering a wide area of the PRD, from northwest to southeast. Satisfactory agreement is obtained between simulated and measured Cl− concentration profiles. Diffusion solely is adequate to reproduce the vertical Cl− concentration profiles, which indicates that diffusion is the regionally dominant vertical transport mechanism across the aquitards in the PRD. The estimated effective diffusion coefficients of the aquitards range from 2.0 × 10–11 to 2.0 × 10–10 m2/s. The effective diffusion coefficients of the aquifers range from 3.0 × 10–11 to 4.0 × 10–10 m2/s. Advective transport tends to underestimate Cl− concentrations in the aquitard and overestimate Cl− concentrations in the basal aquifer. The results of this study will help understand the mechanisms of solute transport in the PRD and other deltas with similar geological and hydrogeological characteristics.