Role of some salient geophysical, geochemical, and hydrogeological parameters in the exploration of fresh groundwater in a brackish terrain

. Geophysical, geochemical, and hydrogeological parameters, for example longitudinal unit conductance (S), transverse unit resistance (T), total dissolved solids (TDS) and thickness of the weathered zone (Wz), have been compared for 25 sites of Navalgund taluk in Dharwar District of Karnataka State, India. Interrelation among these parameters has been analyzed quantitatively by the standard statistical technique leading to a suitable mathematical model. The contrasting geophysical, geochemical, and hydrogeological characteristics of the fresh water pockets in the regionally brackish aquifers are compared and illustrated. The study explains the significant bearing of these parameters on exploration, development, and exploitation of fresh groundwater sources in the areas affected by the occurrence of a brackish water aquifer. The importance of such a comparison in raising the confidence to identify a fresh groundwater aquifer in the brackish terrain by quantitative interpretation of resistivity data has been demonstrated.     

Geoelectric model and hydrochemistry of salinity affected lower Atrai floodplain aquifer,NW Bangladesh: An approach for irrigation management

In the salinity affected lower Atrai floodplain aquifer in the NW Bangladesh, geoelectric resistivity survey and hydrochemical analysis are carried out with an aim to identify fresh and saline groundwater zones; investigate the status of salinity; evaluate hydrochemical processes involved and suggest management approaches for irrigation. Here a two-fold aquifer system, inter-layered by silt, clay and silty-clay aquitard and aquiclude is classified as: upper aquifer — spatially affected by salinity of varying degrees; and lower aquifer — generally characterized by high salinity. The aquifer with resistivity values greater than 69 Ωm is safe for irrigation use. Concentrations of major ions vary as: Ca²⁺>Na⁺>Mg²⁺>K⁺ and HCO₃>Cl>NO₃>SO₄ ^2?. Groundwater is dominated by Na-Ca to Ca-Na, HCO₃-Cl-SO₄, Cl-SO₄-HCO₃ and Cl-SO₄ ^2? facies where Ca²⁺, Mg²⁺, SO₄ ^2?, HCO₃ ^?, Cl^? and NO₃ ^2? ion concentrations are statistically dominant and water is of Ca-Mg, HCO₃-SO₄-Cl and NO₃ types. Geochemically, groundwater is hard and saline to fresh water type. Salinity increases with depth, but spatially towards the southern part. Groundwater quality is a product of water-rock interaction, direct mixing and marine spraying, or fall-out of airborne marine salts, where silicate weathering is the primary source of bivalent cations. Sediment provenance of alkaline earth silicates and higher concentrations of alkalis are derived from sources other than precipitation. In general partially or fully salinity affected upper and lower aquifers in the area except in its eastern part are not suitable for tubewell irrigation. As groundwater demand for irrigation is increasing, the saline water has progressively invaded relatively fresher parts of the aquifer by upconning. So, special salinity control management approaches can be adopted through engineering techniques such as groundwater abstraction optimization, as also through scientific behavioral approaches like groundwater demand management, salt tolerant crops production. In this context, surface water conservation and rain water harvesting for domestic and irrigational uses are recommended in the salinity affected area.     

Different isotopic evolutionary trends of δ34S and δ18O compositions of dissolved sulfate in an anaerobic deltaic aquifer system

Concentration and isotope ratios (δ³⁴S_SO4 and δ¹⁸O_SO4) of dissolved sulfate of groundwater were analyzed in a very large anaerobic aquifer system under the Lower Central Plain (LCP) (25,000 km²) in Thailand. Groundwater samples were collected in two different kinds of aquifers; type 1 with a saline water contribution and type 2 lateritic aquifers with no saline water contribution. Two different isotopic compositional trends were observed: in type 1 aquifers sulfate isotope ratios range from low values (+2.2‰ for δ³⁴S_SO4 and +8.0‰ for δ¹⁸O_SO4) to high values (+49.9‰ for δ³⁴S_SO4 and +17.9‰ for δ¹⁸O_SO4); in type 2 aquifers sulfate isotope ratios range from low values (−0.1‰ for δ³⁴S_SO4 and +12.2‰ for δ¹⁸O_SO4) to high δ¹⁸O_SO4 ratios (+18.4‰) but with low δ³⁴S_SO4 ratios (<+12.9‰). Isotopic comparison with possible source materials and theoretical geochemical models suggests that the sulfate isotope variation for type 1 aquifer groundwater can be explained by two main processes. One is the contribution of remnant seawater, which has experienced dissimilatory sulfate reduction in the marine clay, into recharge water of freshwater origin. This process accounts for the high salinity groundwater. The other process, explaining for the modest salinity groundwater, is the bacterial sulfate reduction of the mixture water between high salinity water and fresh groundwater. Isotopic variation of type 2 aquifer groundwater may also be explained by bacterial sulfate reduction, with slower reduction rate than that of the groundwater with saline water effect. The origin of groundwater sulfate with low δ³⁴S_SO4 but high δ¹⁸O_SO4 is recognized as an important topic to be examined in a future investigation.     

Assessment of porous aquifer hydrogeological parameters using automated groundwater level measurements in Greece

In this paper, the hydrogeological parameters of a confined aquifer, such as transmissivity (T), storativity (S) and radius of influence (R), have been assessed using real groundwater level measurements recorded by a monitoring network, consisting of automated municipal water supply boreholes at Nea Moudania aquifer, Chalkidiki, Greece. Particularly, the paper focused on the correlation between the drawdown and the constant flow rate during pumping time. So the Cooper-Jacob and the recovery test method were applied in order to delineate if turbulent head losses occur, as well as the impact of incorrect measurements of the radial distance (r) in the accuracy of estimating S values. The results show that a) the occurrence of a linear correlation between s and Q indicates a negligible turbulent head loss in the pumping wells and thus a reasonable flow rate usage, b) the validity of storativity values could be compromised if the r value is not accurately measured, and c) recovery test method can be used as an indicator of residual drawdown (s’) caused by previous pumping cycles, when the straight line intersecting the logarithmic t/t’ axis has a value greater than 1.     

Integration of geoelectric and hydrochemical approaches for delineation of groundwater potential zones in alluvial aquifer

Geoelectric and hydrochemical approaches are employed to delineate the ground-water potential zones in District Okara, a part of Bari Doab, Punjab, Pakistan. Sixty-seven VES surveys are conducted with the Electrical Resistivity Meter. The resultant resistivity verses depth model for each site is estimated using computer-based software IX1D. Aquifer thickness maps and interpreted resistivity maps were generated from interpreted VES results. Dar-Zarrouk parameters, transverse resistance (TR), longitudinal conductance (SL) and anisotropy (λ) were also calculated from resistivity data to delineate the potential zones of aquifer. 70% of SL value is ≤3S, 30% of SL value is > 3S. According to SL and TR values, the whole area is divided into three potential zones, high, medium and low potential zones. The spatial distribution maps show that north, south and central parts of study area are marked as good potential aquifer zones. Longitudinal conductance values are further utilized to determine aquifer protective capacity of area. The whole area is characterized by moderate to good and up to some extent very good aquifer protective area on the basis of SL values. The groundwater samples from sixty-seven installed tube wells are collected for hydro-chemical analysis. The electrical conductivity values are determined. Correlation is then developed between the EC (μS/cm) of groundwater samples vs. interpreted aquifer resistivity showing R2 value 0.90.     

Delineation of saltwater intrusion into the freshwater aquifer of Lekki Peninsula,Lagos, Nigeria

Recently, the deterioration of water quality in the coastal zones of Lekki Peninsula area of Lagos due to saltwater infiltration into the freshwater aquifer has become a major concern. With the aim of providing valuable information on the hydrogeologic system of the aquifers, the subsurface lithology and delineating the groundwater salinity, vertical electrical resistivity (VES) sounding survey was carried out utilizing surface Schlumberger electrode arrays, and electrode spacing varying between 1 and 150 m. The DC resistivity surveys revealed significant variations in subsurface resistivity. Also, the VES resistivity curves showed a dominant trend of decreasing resistivity with depth (thus increasing salinity). In general, the presence of four distinct resistivity zones were delineated viz.: the unconsolidated dry sand (A) having resistivity values ranging between 125 and 1,028 Ωm represent the first layer; the fresh water-saturated soil (zone B) having resistivity values which correspond to 32–256 Ωm is the second layer; the third layer (zone C) is interpreted as the mixing (transition) zone of fresh with brackish groundwater. The resistivity of this layer ranges from 4 to 32 Ωm; while layer four (zone D) is characterized with resistivities values generally below 4 Ωm reflecting an aquifer possibly containing brine. The rock matrix, salinity and water saturation are the major factors controlling the resistivity of the formation. Moreover, this investigation shows that saline water intrusion into the aquifers can be accurately mapped using surface DC resistivity method.     

Diffuse and concentrated recharge evaluation using physical and tracer techniques: results from a semiarid carbonate massif aquifer in southeastern Spain

In the high-permeability, semiarid carbonate aquifer in the Sierra de Gádor Mountains (southeastern Spain), some local springs draining shallow perched aquifers were of assistance in assessing applicability of the atmospheric chloride mass balance (CMB) for quantifying total yearly recharge (R _T) by rainfall. Two contrasting hydrological years (October through September) were selected to evaluate the influence of climate on recharge: the average rainfall year 2003–2004, and the unusually dry 2004–2005. Results at small catchment scale were calibrated with estimated daily stand-scale R _T obtained by means of a soil water balance (SWB) of rainfall, using the actual evapotranspiration measured by the eddy covariance (EC) technique. R _T ranged from 0.35 to 0.40 of rainfall in the year, with less than a 5% difference between the CMB and SWB methods in 2003–2004. R _T varied from less than 0.05 of rainfall at mid-elevation to 0.20 at high elevation in 2004–2005, with a similar difference between the methods. Diffuse recharge (R _D) by rainfall was quantified from daily soil water content field data to split R _T into R _D and the expected concentrated recharge (R _C) at catchment scale in both hydrological years. R _D was 0.16 of rainfall in 2003–2004 and 0.01 in 2004–2005. Under common 1- to 3-day rainfall events, the hydraulic effect of R _D is delayed from 1 day to 1 week, while R _C is not delayed. This study shows that the CMB method is a suitable tool for yearly values complementing and extending the more widely used SWB in ungauged mountain carbonate aquifers with negligible runoff. The slight difference between R _T rates at small catchment and stand scales enables results to be validated and provides new estimates to parameterize R _T with rainfall depth after checking the weight of diffuse and concentrated mechanisms on R _T during moderate rainfall periods and episodes of marked climatic aridity.     

Geochemical evolution and timescale of seawater intrusion into the coastal aquifer of Israel

This study is an attempt to quantify the geochemical processes and the timescale of seawater intrusion into a coastal aquifer from changes in the major ionic composition of the water and the natural distribution of the cosmogenic isotopes ¹⁴C and ³H. For that purpose, we sampled saline and brackish groundwaters from the Israeli coastal aquifer. A multilayer sampler (MLS) was used to obtain very high resolution (10 cm) profiles across the fresh-saline water interface (FSI).The chemical and stable isotope data revealed three distinct water types (end members) that are located in different zones on the route to the coastal aquifer: (1) slightly modified Mediterranean seawater (SWS); (2) slightly diluted (with up to 20% fresh groundwater) saline groundwater (SDS); and (3) fresh groundwater (FGW).The SWS samples generally show an excess of total alkalinity and total dissolved inorganic carbon (DIC), and a depletion of ¹³C_DIC and ¹⁴C_DIC with respect to normal seawater indicating that anaerobic oxidation of organic matter is the first diagenetic reaction that affects seawater during its penetration into the bottom sediments. SDS waters appear when SWS is slightly diluted, gain Ca²⁺ and Sr²⁺, and is depleted in K⁺, suggesting that the main processes that transform SWS into SDS are slight dilution with fresh groundwater and cation exchange. At the fresh-saline water interface, SDS generally shows conservative mixing with FGW.Inspection of chemical data from coastal aquifers around the world indicates that intensive ion exchange in slightly diluted saline groundwater is a globally important phenomenon of seawater intrusion. Most of our saline groundwater samples contain substantial amounts of ³H suggesting that penetration of Mediterranean seawater and its inland travel to a distance of 50-100 m onshore occurred 15-30 yr ago. This is supported by the ¹⁴C_DIC mass balance that explains the relatively low ¹⁴C_DIC activities in the SDS as influenced by diagenesis and not by simple radioactive decay.     

Estimating transmissivity using empirical and geostatistical methods in the volcanic aquifers of Upper Awash Basin, central Ethiopia

Transmissivity (T) is a basic hydraulic parameter of an aquifer that is utilized in most groundwater flow equations to understand the flow dynamics and is generally estimated from pumping tests. However, the cost of performing a large number of aquifer tests is expensive and time consuming. The fact that specific capacity (S _c) is correlated with hydraulic flow properties of aquifers simplifies parameter estimation mainly because specific capacity values are more abundant in groundwater databases than values of transmissivity and they offer another approach to estimate hydraulic parameters of aquifers. In this study, an empirical relation is derived using 214 pairs of transmissivity and specific capacity values that are obtained from pumping tests conducted on water wells penetrating the complex volcanic aquifers of Upper Awash Basin, central Ethiopia. Linear and logarithmic regression functions have been performed and it is found that the logarithmic relationship predicting transmissivity from specific capacity data has a better correlation (R = 0.97) than the linear relationship (R = 0.79). The two parameters are log-normally distributed, in which the logarithmic relation is also better statistically justified than the linear relation. Geostatistical estimations of the transmissivity were made using different inputs and methods. Measured and supplemented transmissivity data obtained from estimates using the derived empirical relation were krigged and cokrigged, spherical and exponential models were fitted to the experimental variograms. The cross-validation results showed that the best estimation is provided using the kriging procedure, the transmissivity field represented by the measured transmissivity data and the experimental variogram fitted with the exponential model. Based on the geostatistical approach, the transmissivity map of the aquifer is produced, which will be used for groundwater flow modeling of the study area that will follow this analysis.     

电测井在金塔盆地划分咸淡水界面的应用效果

通过分析电测井在金塔盆地划分含水层岩性、咸淡水界面的应用实例,总结出各种岩性含水层在咸、淡水状态下的电阻率特征,论述了涌水量与含水层厚度的关系、矿化度与含水层电阻率的关系,阐明了该方法在指导封井成井的有效性及应用前景。     

Hydrogeologic characteristics of groundwater aquifers in Kathmandu Valley,Nepal

This paper reviews, compiles and comprehensively analyzes spatial variations in hydrogeologic characteristics of shallow and deep groundwater aquifers in Kathmandu Valley. To estimate transmissivity (T) (and then hydraulic conductivity) as a function of specific capacity (SC), an empirical relationship between T and SC is developed for shallow and deep aquifer. The results show that T and SC are log linearly related by an equation T = 0.8857(SC)^1.1624 [R ² = 0.79] in shallow and T = 1.1402(SC)^1.0068 [R ² = 0.85] in deep aquifer. The estimated T ranges from 163 to 1,056 m²/day in shallow aquifer and 22.5 to 737 m²/day in deep aquifer. Finally, mapping of spatial distribution in hydrogeologic characteristics (thickness, T, hydraulic conductivity and storage coefficient) in shallow and deep aquifers are accomplished using ArcGIS9.2 and such maps would be useful in delineating potential areas for groundwater development and simulating groundwater flow in the aquifer system.     

An integrated approach to investigate saline water intrusion and to identify the salinity sources in the Central Godavari delta, Andhra Pradesh, India

The Central Godavari delta is located along the Bay of Bengal Coast, Andhra Pradesh, India, and is drained by Pikaleru, Kunavaram and Vasalatippa drains. There is no groundwater pumping for agriculture as wells as for domestic purpose due to the brackish nature of the groundwater at shallow depths. The groundwater table depths vary from 0.8 to 3.4 m and in the Ravva Onshore wells, 4.5 to 13.3 m. Electrical Resistivity Tomography (ERT) surveys were carried out at several locations in the delta to delineate the aquifer geometry and to identify saline water aquifer zones. Groundwater samples collected and analyzed for major ions for assessing the saline water intrusion and to identify the salinity origin in the delta region. The results derived from ERT indicated low resistivity values in the area, which can be attributed to the existence of thick marine clays from ground surface to 12–15 m below ground level near the coast and high resistivity values are due to the presence of coarse sand with freshwater away from the coast. The resistivity values similar to saline water <0.01 Ω m is attributed to the mixing of the saline water along surface water drains. In the Ravva Onshore Terminal low resistivity values indicated up coning of saline water and mixing of saline water from Pikaleru drain. The SO ₄ ^?2 /Cl^?and Na⁺²/Cl^?ratios did not indicate saline water intrusion and the salinity is due to marine palaeosalinity, dilution of marine clays and dissolution of evaporites.     

Multi-aquifer pumping test to determine cutoff wall length for groundwater flow control during site excavation in Tokyo, Japan

Multi-aquifer pumping tests, using a multi-screen pumping well and multi-level piezometers, were carried out for groundwater flow control in a large-scale excavation site in Tokyo, Japan. The site was underlain by multi-layered confined aquifers. In the tests, pumping was carried out using a multi-aquifer pumping well in which a screen depth was chosen arbitrarily. Changes in groundwater pressure heads in each aquifer were measured at each screen position of the multi-aquifer pumping well. Hydraulic conductivity (K) and specific storage (S _s) of not only aquifers, but also for low permeability layers between the aquifers, were estimated using the Cooper-Jacob method, and calibrated by a finite element method (FEM) groundwater model. Four different cutoff wall lengths were assumed for final excavation depth, and correlations among wall length, pumping discharge and drawdown at the back of the cutoff wall were obtained from simulations using the K and S _s parameters in the FEM model. Then, the most suitable wall length was selected based on the simulated correlations considering environmental condition, construction period and cost of the cutoff wall.     

Origin of groundwater salinity (current seawater vs. saline deep water) in a coastal karst aquifer based on Sr and Cl isotopes. Case study of the La Clape massif (southern France)

In this study a typical coastal karst aquifer, developed in lower Cretaceous limestones, on the western Mediterranean seashore (La Clape massif, southern France) was investigated. A combination of geochemical and isotopic approaches was used to investigate the origin of salinity in the aquifer. Water samples were collected between 2009 and 2011. Three groundwater groups (A, B and C) were identified based on the hydrogeological setting and on the Cl⁻ concentrations. Average and maximum Cl⁻ concentrations in the recharge waters were calculated (Cl_Ref. and Cl_Ref.Max) to be 0.51 and 2.85 mmol/L, respectively). Group A includes spring waters with Cl⁻ concentrations that are within the same order of magnitude as the Cl_Ref concentration. Group B includes groundwater with Cl⁻ concentrations that range between the Cl_Ref and Cl_Ref.Max concentrations. Group C includes brackish groundwater with Cl⁻ concentrations that are significantly greater than the Cl_Ref.Max concentration. Overall, the chemistry of the La Clape groundwater evolves from dominantly Ca–HCO₃ to NaCl type. On binary diagrams of the major ions vs. Cl, most of the La Clape waters plot along mixing lines. The mixing end-members include spring waters and a saline component (current seawater or fossil saline water). Based on the Br/Cl_molar ratio, the hypothesis of halite dissolution from Triassic evaporites is rejected to explain the origin of salinity in the brackish groundwater.Groundwaters display ⁸⁷Sr/⁸⁶Sr ratios intermediate between those of the limestone aquifer matrix and current Mediterranean seawater. On a Sr mixing diagram, most of the La Clape waters plot on a mixing line. The end-members include the La Clape spring waters and saline waters, which are similar to the deep geothermal waters that were identified at the nearby Balaruc site. The ³⁶Cl/Cl ratios of a few groundwater samples from group C are in agreement with the mixing hypothesis of local recharge water with deep saline water at secular equilibrium within a carbonate matrix. Finally, PHREEQC modelling was run based on calcite dissolution in an open system prior to mixing with the Balaruc type saline waters. Modelled data are consistent with the observed data that were obtained from the group C groundwater. Based on several tracers (i.e. concentrations and isotopic compositions of Cl and Sr), calculated ratios of deep saline water in the mixture are coherent and range from 3% to 16% and 0% to 3% for groundwater of groups C and B, respectively.With regard to the La Clape karst aquifer, the extension of a lithospheric fault in the study area may favour the rise of deep saline water. Such rises occur at the nearby geothermal Balaruc site along another lithospheric fault. At the regional scale, several coastal karst aquifers are located along the Gulf of Lion and occur in Mezosoic limestones of similar ages. The ⁸⁷Sr/⁸⁶Sr ratios of these aquifers tend toward values of 0.708557, which suggests a general mixing process of shallow karst waters with deep saline fossil waters. The occurrence of these fossil saline waters may be related to the introduction of seawater during and after the Flandrian transgression, when the highly karstified massifs invaded by seawater, formed islands and peninsulas along the Mediterranean coast.     

川西坳陷新场构造带须家河组超压演化与流体的关系

沉积盆地超压体系是油气勘探与开发过程中一个不容忽视的问题,不仅影响了地质流体的运移和聚集,更为勘探带来安全隐患。以实测地压和油田水化学数据为基础,对川西坳陷新场构造带须四段和须二段现今地层水矿化度与现今压力系数关系进行比较,结合地层水特征系数和阴阳离子关系,综合前人研究结果,对须四段和须二段压力演化史与地层水演化过程进行分析,考察川西坳陷须家河组超压系统演化与地层水演化的耦合关系。结果表明,须家河组超压发育与地层水具有密切的联系:(1)须家河组储层段压力分布范围较广,在弱超压至超强压之间,须二段属于中超压而须四段属于超高压,平面分布中须二段探测井中矿化度随压力系数增加而减少,须四段则相反;(2)在压实过程中,由于流体排驱受阻导致"欠压实"超压的产生,随着超压的不断积聚,局部出现裂缝,导致地层水更加强烈的混合作用和运移;(3)生烃作用导致自生压力增大,地层水离子水岩作用强烈,造成流体包裹体与现今地层水离子成分分异;(4)构造挤压抬升过程中,须四段裂缝不发育,压力进一步升高,须二段则产生泄压,出现了凝析水和水侵现象,造成须四段和须二段现今地层水特征的差异。     

Inverse modelling of aquifer parameters in basaltic rock with the help of pumping test method using MODFLOW software

The origin and movement of groundwater are the fundamental questions that address both the temporal and spatial aspects of ground water run and water supply related issues in hydrological systems. As groundwater flows through an aquifer, its composition and temperature may variation dependent on the aquifer condition through which it flows. Thus, hydrologic investigations can also provide useful information about the subsurface geology of a region. But because such studies investigate processes that follow under the Earth's shallow, obtaining the information necessary to answer these questions is not continuously easy. Springs, which discharge groundwater table directly, afford to study subsurface hydrogeological processes.The present study of estimation of aquifer factors such as transmissivity (T) and storativity (S) are vital for the evaluation of groundwater resources. There are several methods to estimate the accurate aquifer parameters (i.e. hydrograph analysis, pumping test, etc.). In initial days, these parameters are projected either by means of in-situ test or execution test on aquifer well samples carried in the laboratory. The simultaneous information on the hydraulic behavior of the well (borehole) that provides on this method, the reservoir and the reservoir boundaries, are important for efficient aquifer and well data management and analysis. The most common in-situ test is pumping test performed on wells, which involves the measurement of the fall and increase of groundwater level with respect to time. The alteration in groundwater level (drawdown/recovery) is caused due to pumping of water from the well. Theis (1935) was first to propose method to evaluate aquifer parameters from the pumping test on a bore well in a confined aquifer. It is essential to know the transmissivity (T = Kb, where b is the aquifer thickness; pumping flow rate, Q = TW (dh/dl) flow through an aquifer) and storativity (confined aquifer: S = bS_s, unconfined: S = S_y), for the characterization of the aquifer parameters in an unknown area so as to predict the rate of drawdown of the groundwater table/potentiometric surface throughout the pumping test of an aquifer. The determination of aquifer's parameters is an important basis for groundwater resources evaluation, numerical simulation, development and protection as well as scientific management. For determining aquifer's parameters, pumping test is a main method. A case study shows that these techniques have been fast speed and high correctness. The results of parameter's determination are optimized so that it has important applied value for scientific research and geology engineering preparation.     

Hydrogeochemical characteristics of groundwater in coastal phreatic aquifers of Alleppey district,Kerala

Hydrogeochemical characteristics of groundwater in phreatic aquifers of Alleppey district were studied. Factor analysis has been applied to the chemical analysis data of 32 water samples collected from dug wells to extract the principal factors corresponding to the sources of variation in the hydrochemistry. 12 hydrochemical parameters were correlated and statistically examined. Varimax rotation was used to define the factor scores and percentage of variance in the hydrogeochemistry. A four-factor model is extracted and explains over 80.394% of the total groundwater quality variation. Factor-1 has high loading values of Electrical Conductivity (EC), Ca⁺⁺, and Cl⁻, and reflects the signature of saline water. Similarly strong correlation exists between F3 score and pH. The correlation coefficient matrix between EC and Na⁺, Cl⁻, SO₄⁻⁻ is significant. The mineralogy of coastal aquifers and the marine aerosol are playing significant role in the hydrogeochemistry of groundwater in the phreatic aquifer system.     

Arsenic and Antimony in Groundwater Flow Systems: A Comparative Study

Arsenic (As) and antimony (Sb) concentrations and speciation were determined along flow paths in three groundwater flow systems, the Carrizo Sand aquifer in southeastern Texas, the Upper Floridan aquifer in south-central Florida, and the Aquia aquifer of coastal Maryland, and subsequently compared and contrasted. Previously reported hydrogeochemical parameters for all three aquifer were used to demonstrate how changes in oxidation–reduction conditions and solution chemistry along the flow paths in each of the aquifers affected the concentrations of As and Sb. Total Sb concentrations (Sb_T) of groundwaters from the Carrizo Sand aquifer range from 16 to 198 pmol kg⁻¹; in the Upper Floridan aquifer, Sb_T concentrations range from 8.1 to 1,462 pmol kg⁻¹; and for the Aquia aquifer, Sb_T concentrations range between 23 and 512 pmol kg⁻¹. In each aquifer, As and Sb (except for the Carrizo Sand aquifer) concentrations are highest in the regions where Fe(III) reduction predominates and lower where SO₄ reduction buffers redox conditions. Groundwater data and sequential analysis of the aquifer sediments indicate that reductive dissolution of Fe(III) oxides/oxyhydroxides and subsequent release of sorbed As and Sb are the principal mechanism by which these metalloids are mobilized. Increases in pH along the flow path in the Carrizo Sand and Aquia aquifer also likely promote desorption of As and Sb from mineral surfaces, whereas pyrite oxidation mobilizes As and Sb within oxic groundwaters from the recharge zone of the Upper Floridan aquifer. Both metalloids are subsequently removed from solution by readsorption and/or coprecipitation onto Fe(III) oxides/oxyhydroxides and mixed Fe(II)/Fe(III) oxides, clay minerals, and pyrite. Speciation modeling using measured and computed Eh values predicts that Sb(III) predominate in Carrizo Sand and Upper Floridan aquifer groundwaters, occurring as the Sb(OH)₃⁰ species in solution. In oxic groundwaters from the recharge zones of these aquifers, the speciation model suggests that Sb(V) occurs as the negatively charged Sb(OH)₆⁻ species, whereas in sufidic groundwaters from both aquifers, the thioantimonite species, HSb₂S₄ ⁻ and Sb₂S₄ ²⁻, are predicted to be important dissolved forms of Sb. The measured As and Sb speciation in the Aquia aquifer indicates that As(III) and Sb(III) predominate. Comparison of the speciation model results based on measured Eh values, and those computed with the Fe(II)/Fe(III), S(-II)/SO₄, As(III)/As(V), and Sb(III)/Sb(V) couples, to the analytically determined As and Sb speciation suggests that the Fe(II)/Fe(III), S(-II)/SO₄ couples exert more control on the in situ redox condition of these groundwaters than either metalloid redox couple.     

A natural-gradient field tracer test for evaluation of pollutant-transport parameters in a porous-medium aquifer

This paper describes a natural-gradient field tracer test to characterise solute-transport properties in a sand and gravel aquifer in the Hebei Province, northern China. Some laboratory-scale column tests on aquifer material and a local-scale field borehole-dilution test have been conducted previously, but the field test reported herein represents the only large-scale tracer test in the aquifer, which is the sole water supply to the city of Shi Jiazhuang and which is threatened by urban pollution. The aim of the study was to quantify the transport behaviour of nonreactive pollutants in this aquifer. Little quantitative data are available concerning its solute-transport properties; thus, the results of the tracer test are significant and critical for understanding pollutant transport and fate. The in-situ tracer test was carried out in the aquifer using a slug injection of the geochemically conservative, radioactive iodine tracer ¹³¹I. The longitudinal (α _L ) and transverse (α _T ) hydrodynamic dispersivities for solute transport in the field are 1.72 and 0.0013 m, respectively. The ratio of longitudinal dispersivity α _L and the flow length at the field scale is 1:10. The ratio between α _L and α _T from the in-situ test (~1,300:1) demonstrates a dominant longitudinal dispersion in this fluvial sand and gravel aquifer. The tracer test further indicates a relatively short transit time for the aquifer (linear velocities ~13 m/d) under natural-gradient conditions. Electronic Publication     

Managing environmental problems in Cuban karstic aquifers

The study area is located along the Dead Sea Rift, the climate is considered arid in its southern margin near the Dead Sea, which is the lowest water reservoir found on the globe (412 m BSL), to semiarid in its northern part. During the last few decades, the water resources became depleted limiting the natural development of the agricultural settlements, which are the most common type of communities in the region. Previous studies suggested that a large amount of freshwater is lost as the result of salinization processes, which occur when fresh groundwater from the mountain aquifers, flow into the saline clastic Neogene aquifer complex. In order to comprehend this complex system, a detailed outlining of the regional hydrogeological system is essential. Since there are no boreholes, which penetrate the aquiferous rock sequences within the Rift, it was necessary to interpolate a large variety of data from several fields of geosciences. The methods applied included geological mapping, geophysical modeling based on interpretation of seismic profiles and geochemical modeling based on chemical and isotopic analysis of runoff, sediments and groundwater. The combined modeling based on results from the different types of analyses implied to several conclusions relevant to the regional water management policy: (1) groundwater becomes saline as it flows from the margins of the Rift to its center. Therefore, it is recommended to exploit it along the foothills of the rift escarpment. (2) Geophysical modeling indicated that the foothills and the Karstic mountain aquifer extend into the subsurface of the valley and can be farther exploited (up to 15 mm³ per annum) by relatively shallow wells. (3) Several mechanisms of groundwater salinization were deciphered: (a) the dense vertical faulting systems act as potential conduits for saline water, which flow-up from deep-seated sources and penetrate into the fresh aquifers. (b) Fresh groundwater in the clastic aquifer complex is rare, furthermore, two evaporates bodies were encountered (Auja and Zaharat el Qurein), also acting as sources for fresh water salinization. (c) Although the quantity of runoff recharge to the Jordan Valley aquifer complex is negligible, the increase in its salt-content (TDS) turns this negligible freshwater recharge to a significant contributor of salts.