Multiple Aquifer System Research Articles

Structure-controlled groundwater flow and salinization paths in the Bet She’an and Harod Valleys, Israel

The Bet She’an and Harod Valleys are regional recipients and mixing zones for groundwater draining to these valleys from a multiple aquifer system. This aquifer system includes two different carbonate aquifers, several groundwater-bearing basalt flows and deep-seated pressurized brine, the upflow of which causes salinization of fresh groundwater bodies. These aquifers drain through two groups of springs. Due to lack of information on the subsurface structure of the valley the flow-paths of groundwater feeding the springs, the initial distribution of salinities along the valley and particularly, the inflow-paths of the brines, have never been understood but were assumed to be fault-controlled. The interpretation of seismic profiles and analysis of gravity anomalies revealed the subsurface structure of the valley and namely the occurrence of a dense network of faults which branch out from those delineating the Jordan-Dead Sea Rift. The faults formed a series of uplifted and down-warped horst-and-graben structures. By joint analysis of structural, hydrological and geochemical evidence, it occurs that groundwater flow-paths leading to the springs emerging in the middle of the Bet She’an Valley are determined by structural elements such as major faults and fault-controlled structures. The penetration of the pressurized Ca-chloride Rift brines and their inflow into fresh groundwater bodies occurs prevalently along the faults outlining the western margins of the Dead Sea Rift Valley and at their intersection with outbranching NW–SE-striking faults.

The utility of gravity and water-level monitoring at alluvial aquifer wells in southern Arizona

Coincident monitoring of gravity and water levels at 39 wells in southern Arizona indicate that water-level change might not be a reliable indicator of aquifer-storage change for alluvial aquifer systems. One reason is that water levels in wells that are screened across single or multiple aquifers might not represent the hydraulic head and storage change in a local unconfined aquifer. Gravity estimates of aquifer-storage change can be approximated as a one-dimensional feature except near some withdrawal wells and recharge sources. The aquifer storage coefficient is estimated by the linear regression slope of storage change (estimated using gravity methods) and water-level change. Nonaquifer storage change that does not percolate to the aquifer can be significant, greater than [Formula: see text], when water is held in the root zone during brief periods following extreme rates of precipitation. Monitor-ing of storage change using gravity methods at wells also can improve understanding of local hydrogeologic conditions. In the study area, confined aquifer conditions are likely at three wells where large water-level variations were accompanied by little gravity change. Unconfined conditions were indicated at 15 wells where significant water-level and gravity change were positively linearly correlated. Good positive linear correlations resulted in extremely large specific-yield values, greater than 0.35, at seven wells where it is likely that significant ephemeral streamflow infiltration resulted in unsaturated storage change. Poor or negative linear correlations indicate the occurrence of confined, multiple, or perched aquifers. Monitoring of a multiple compressible aquifer system at one well resulted in negative correlation of rising water levels and subsidence-corrected gravity change, which suggests that water-level trends at the well are not a good indicatior of overall storage change.

Are the lower subaquifers of the Mediterranean coastal aquifer of Israel blocked to seawater intrusion? Results of a TDEM (time domain electromagnetic) study

Kafri, U. and Goldman, M. Are the lower subaquifers of the Mediterranean coastal aquifer of Israel blocked to seawater intrusion? Results of a TDEM (time domain electromagnetic) study. Isr. J. Earth Sci. 55: xx-xx. The TDEM (time domain electromagnetic) method was employed to delineate a low resistivity seawater intrusion into the multiple aquifer system of the Mediterranean coastal aquifer of Israel. The upper (A, B) subaquifers of the aquifer have been known for a long time to be intruded by seawater along the entire coastal plain. It was sug- gested in the past and supported by sparse hydrogeological information that the lower (C, D) subaquifers are blocked to the sea and thus might escape seawater intrusion. The results of the survey, in conjunction with existing borehole information, al- lowed delineating large areas along the central and southern coastal aquifer, where the lower subaquifers solely occupy relatively fresh water (below 1000 mg/l Cl) close to the seashore. The largest of these areas is an approximately 20 km strip between north Ashdod and Bat Yam. According to the low TDEM resistivities obtained at appropri- ate depths, the lower subaquifers at other areas seem to be locally blocked to the sea or vice versa intruded by seawater.

Effect of a contaminated site (the San Giuliano landfill, Venice, Italy) on the interaction between water bodies in a coastal aquifer system.

A complex multiple aquifer system affected by a contaminated site and exposed to tidal effects was investigated to develop the hydrogeological conceptual model of the study case. Two water bodies were identified, from top to down: a surface aquifer unaffected by tidal events, and a semiconfined aquifer partly communicating with the brackish lagoon waters. By using the Cl(-)/SO4(2-) ratio and the DOC (Dissolved Organic Carbon) concentration, as well as by applying the kriking to the piezometric levels results, the groundwater flow directions and the hydraulic gradients within the investigated aquifers were also identified. Based on the overall results, a schematic of the conceptual model for the whole aquifer system was provided which allows to visualize the communication between the different water bodies.

Hydrogeologic and geomorphic settings of the Lower Subansiri Basin, Assam, India

Geomorphic settings of an area provide valuable supplementary information regarding groundwater recharge, their occurrence and distribution. The geomorphic settings of the Lower Subansiri Basin can broadly be represented by three distinct geomorphic units viz., structural hills, piedmont zone and alluvial plain. While the elevation, slope, lithology, drainage pattern and various relevant morphometric parameters vary from one geomorphic unit to another, the conditions of recharge and discharge, occurrence and distribution of groundwater also differ in different units. The structural hills occupying only 4.5% of the area along the north-western boundary represent a high run-off zone characterised by steep slope and fairly dense parallel to sub-parallel drainage. The piedmont zone, built up by the coalescence of alluvial fan deposits, represents 7.7% of the area occurring in a long and narrow NE-SW trending steeply sloping belt along the foothills of Arunachal Pradesh. Owing to high permeability, this zone hardly retains any water and hence forms a high recharge zone with relatively deeper groundwater level. The alluvial plain, covering 87.8% of the basin area and characterised by a gentle slope, serves both as recharge and discharge areas where groundwater occurs relatively close to the ground surface.
 Panel diagrams prepared for the Lower Subansiri Basin showing the thickness and extent of granular zones display that the unconsolidated alluvial sediments are primarily composed of sands of various grade and gravel with minor amounts of silt and clay. The sand-gravel isolith maps showing the cumulative thickness of the granular zones down to the depth of 40 m reveal that the subsurface formations in a major part of the alluvial plain of the Lower Subansiri Basin are entirely represented by granular zones. The granular zone in most parts of the area forms one single aquifer system where groundwater mostly occurs under unconfined to semi unconfined conditions. Due to the presence of thin clay and/or sandy clay lenses at shallow depths, however, the single aquifer system gets locally dissipated into multiple aquifer system where, barring the uppermost aquifer, groundwater mostly occur under semiconfined to confined conditions. The overall regional variation of depth to water level, from the piedmont zone in the north and north-west to the alluvial plain of the south and southeast, is controlled by the prevalent geomorphic settings of the area. The disposition of water table contours of the area indicates that the configuration of groundwater table closely controls to that of general topography of the area. The steeper hydraulic gradient observed to be present in the north and north-east indicates the possible control of the characteristically distinguished geomorphic setting, i.e., topography, relief and lithology.

An unstructured mesh finite volume method for modelling saltwater intrusion into coastal aquifers

In this paper, a two-dimensional finite volume unstructured mesh method (FVUM) based on a triangular background interpolation mesh is developed for analysing the evolution of the saltwater intrusion into single and multiple coastal aquifer systems. The model formulation consists of a ground-water flow equation and a salt transport equation. These coupled and non-linear partial differential equations are transformed by FVUM into a system of differential/algebraic equations, which is solved using backward differentiation formulas of order one through five. Simulation results are compared with previously published solutions where good agreement is observed.

Density-dependent groundwater movement in sediments overlying salt domes - the Gorleben site example

In the multiple-aquifer system in the sediments above the Gorleben salt dome, an upper fresh-water body is underlain by saline water. The salinity of the water generally increases with depth. The salt dome is crossed by a subglacial erosion channel, in which the lowermost aquifer is locally in contact with the caprock or the salt itself. Saturated brines are found in these areas. Information on the flow system can be derived from the observed density distribution. Two-dimensional numerical studies have been conducted to determine the transient density distribution and the associated flow field. They have demonstrated the sensitivity of the system to changes in the hydrogeological structure, initial density distribution, and modeled time period (palaeohydrogeological effects). A few of the calculated present density distributions compare well with measured field data.

Application of Flowmeter and Depth‐Dependent Water Quality Data for Improved Production Well Construction

Ground water production wells commonly are designed to maximize well yield and, therefore, may be screened over several water-bearing zones. These water-bearing zones usually are identified, and their hydrogeologic characteristics and water quality are inferred, on the basis of indirect data such as geologic and geophysical logs. Production well designs based on these data may result in wells that are drilled deeper than necessary and are screened through zones having low permeability or poor-quality ground water. In this study, we examined the application of flowmeter logging and depth-dependent water quality samples for the improved design of production wells in a complex hydrogeologic setting. As a demonstration of these techniques, a flowmeter log and depth-dependent water quality data were collected from a long-screened production well within a multilayered coastal aquifer system in the Santa Clara-Calleguas Basin, Ventura County, California. Results showed that the well yields most of its water from four zones that constitute 58% of the screened interval. The importance of these zones to well yield was not readily discernible from indirect geologic or geophysical data. The flowmeter logs and downhole water quality data also show that small quantities of poor-quality water could degrade the overall quality of water from the well. The data obtained from one well can be applied to other proposed wells in the same hydrologic basin. The application of flowmeter and depth-dependent water quality data to well design can reduce installation costs and improve the quantity and quality of water produced from wells in complex multiple-aquifer systems.

Reconstruction of natural groundwater flow paths in the multiple aquifer system of the northern Negev (Israel), based on lithological and structural evidence

The Judea Group, a limestone and dolomite karstic aquifer of late Albian–Turonian age, is one of the most important sources of water in Israel. In the western part of the country, the Judea Group aquifer is also known as the Yarkon–Taninim basin. In the northern Negev, the Judea Group is a recipient for fresh water flowing southward from the Hebron Mountains and of brackish paleowater flowing northward from Sinai. Very little is known of the hydraulic properties of this aquifer. In order to outline assumed natural flow paths that existed in this karstic environment prior to groundwater exploitation, use was made of lithological, structural, and paleomorphological features. A detailed hydrogeological conceptual model of the Judea Group aquifer in northern Negev was established by the geological interpretation of high-resolution seismic reflection and by analysis of lithological evidence from boreholes. Isopach, isolith-contour, and isolith-ratio maps were compiled for the main lithological components. Increase in transmissivity values is inversely proportional with the cumulative thickness of argillaceous components. The lithological and hydraulic evidence provides the basis for subdividing the subsurface into distinctive permeability zones for the upper and lower sections of the aquifer; for outlining possible preferential groundwater flow paths for both subaquifers; and for improving understanding of groundwater-salinty variations that result from lithological variability, direction of groundwater flow paths, groundwater flow rates, and the duration of rock/water interactions. In an earlier conceptual model of the basin, the Judea Group aquifer was regarded as a continuous and undisturbed entity. The present study reveals an intricate groundwater flow pattern that is controlled by lithological and structural factors that create zones of preferential flow. This interpretation bears on the overall evaluation of groundwater resources and their management and exploitation.

Sensitivity Analysis of Flow in Multilayered Leaky Aquifer Systems

The sensitivity of drawdown prediction to the uncertainty in estimating the hydraulic properties of multiple leaky aquifer systems is studied by first-order sensitivity analysis. A new set of dimensionless parameters is suggested to reduce the amount of sensitivity coefficient calculations. The procedure is illustrated for three aquifer configurations pumped by one well: one aquifer with impermeable boundaries (Theis case), one aquifer with two aquitards, and two aquifers with one aquitard. The results allow one to assess the relative contribution of uncertainty of each hydraulic property on the accuracy of predicting drawdown and to reduce the number of parameters that influence uncertainty. The methodology and results may be employed when margins of confidence of the predicted drawdown are needed.

The interaction of two major old water bodies and its implication for the exploitation of groundwater in the multiple aquifer system of the central and northern Negev, Israel

In the Beer Sheva region of the Negev desert, the only significant fresh groundwater is contained within the Judea Group carbonate aquifer. It is found that this aquifer holds two distinctly different old water bodies. One such groundwater body has evolved in equilibrium with the carbonate aquifer rocks after being recharged during the Holocene in the Hebron Mountains north of the study area. At present, modern recharge, as denoted by the tritium and radiocarbon contents, is very minor. A subtle ‘piston effect’ generated by contemporary replenishment is discussed in representative hydrographs in Beer Sheva wells. Another groundwater body identified in the Judea Group aquifer derives from the underlying Kurnub Group aquifer. The regional artesian Kurnub Group aquifer (Nubian Sandstone) contains an older and brackish groundwater body which has been recharged in Sinai during Pleistocene pluvials. Faulting in the Beer Sheva region facilitated hydrologic contact between the two aquifers. Exploitation of the Judea Group has released confining pressures and resulted in the intrusion of Kurnub Group water into the overlying Judea Group carbonate aquifer. This process is most significant in those wells drilled close to major faults where salinity increases with pumping. The intruding water originating from the Kurnub Group sandstone aquifer has not yet equilibrated chemically with the carbonate host. The low pH and high temperatures that have been encountered indicate continuing and very recent intrusion. In the Beer Sheva area, in the absence of direct significant modern recharge (as determined from tritium and 14C values), all waters should be considered as paleowaters that are being mined. A complete revision of the hydrologic concept by which the multiple aquifer system can be exploited is required, to take into account the fact that the fresh Judea Group groundwater is actually an old (Holocene) water body intruded by brackish and older (Pleistocene) water along fault zones.

Pumping test data analysis in wells with multiple or long screens

A computer method is presented to estimate the drawdown and the flow rate development in wells with multiple or long screens. The mathematical model involves the following processes: unsteady, quasi-three-dimensional laminar flow in a multiple leaky aquifer system, laminar and/or turbulent radial flow in the skin zone including the screens, turbulent axial flow and change of the kinetic energy in the screen pipe, and the effect of well storage. The numerical accuracy was checked against analytical (Theis, Wikramaratna) and semianalytical (numerical Laplace-inversion) solutions. The low error of numerical drawdown and flow rate simulation, achieved during testing, is acceptable in most of the practical cases. Two case studies demonstrate the calibration of aquifer and screen parameters. The method may also be used as an approximate tool to analyse the three-dimensional flow around wells with long, partially penetrating screens in thick, vertically heterogeneous aquifers. Analysis of the approximation error and some results of practical application are given.

The Nubian Sandstone aquifer in the central and northern Negev, Israel: delineation of the hydrogeological model under conditions of scarce data

The Cl − content of ground water in the central and northern Negev ranges between 250 mg 1 −1 in the Beer Sheva area and 1600 mg 1 −1 near the Egyptian border, where the water is also thermal with high concentrations of sulphates and iron. During the last few years, groundwater resources in the heavily populated Beer Sheva area have become endangered by a continuing process of salinization. In the course of the present work, it was found that, in the study area, ground water flows through a multiple aquifer system including the Jurassic-Lower Cretaceous Kurnub Group and the Upper Cretaceous Judea Group aquifers. Because of the absence of impermeable beds at the boundary between the two groups, brackish ground water flows from the Kurnub Group into the overlying Judea Group aquifer. Moreover, numerous faults discovered in the subsurface facilitate lateral inflow of Kurnub ground water into the Judea aquifer. By interpreting new lithostratigraphic data from the Kurnub Group and seismic surveys made in the study area, it is shown that the Kurnub aquifer extends far beyond the hitherto known boundaries and contains an additional estimated volume of 51 × 10 9 m 3 of paleowater. The limiting factors of its exploitability are groundwater depth and salinity. The rational exploitation of the Kurnub paleowater may prevent salinization of the overlying Judea Group aquifer.

Quasi‐Three‐Dimensional Optimization Model of Jakarta Basin

An optimization model for the control of saltwater intrusion in the Jakarta Multiple aquifer system is presented. The optimization model incorporates a quasi‐three‐dimensional, finite‐difference simulation model of the aquifer system. The ground‐water systems are hydraulically coupled via leakage into or out of each aquifer. Finite‐difference methods are used to generate the hydraulic‐response equations of the ground‐water basin relating, for each aquifer, the freshwater and saltwater heads, the location of the interface, and the pumping and recharge schedules. The optimization model minimizes the total squared volume of saltwater in each aquifer of the ground‐water system; the control variables of the model are the location and magnitude of ground‐water pumping and recharge. The model is required to satisfy the current water demand in the basin. The optimization model is solved using MINOS, a projected Lagrangian algorithm, and a modified gradient procedure based on Box's algorithm. The underlying simula...

Definition of groundwater flow patterns by environmental tracers in the multiple aquifer system of southern Arava Valley, Israel : Rosenthal, E; Adar, E; Issar, A S; Batelaan, O J HydrolV117, N1/4, Sept 1990, P339–368

Definition of groundwater flow patterns by environmental tracers in the multiple aquifer system of southern Arava Valley, Israel : Rosenthal, E; Adar, E; Issar, A S; Batelaan, O J HydrolV117, N1/4, Sept 1990, P339–368

Definition of groundwater flow patterns by environmental tracers in the multiple aquifer system of southern Arava Valley, Israel

The present paper describes a model for identification and semi-quantitative evaluation of the different water bodies replenishing groundwater in the southern Arava Rift Valley. The potential sources of recharge into the alluvial aquifer of the valley were assessed by multivariable cluster analysis of environmental tracers such as dissolved ions and stable isotopes. This data was also used to determine the flow pattern to the valley and, within its alluvial aquifer, to the natural outlet of the Red Sea. Spatial variations in the chemical compositions of groundwater and of their isotopic ratios are explained as the result of differential rates of replenishment of various water bodies flowing to the Arava. The alluvial aquifer of the southern Arava Valley is recharged by the following water bodies: (1) lateral subsurface flow caused by infiltration of water from flash floods occurring in the neighbouring mountain massifs; (2) upward and lateral groundwater flow from sandstone and carbonate aquifers in the Negev and Edom mountains; and (3) leakage from deep-seated brine reservoirs. A complete groundwater flow pattern based upon hydrological, hydrochemical and isotopic data is presented in a compartmental configuration.

Hydrochemical changes induced by overexploitation of groundwater at common outlets of the Bet Shean-Harod multiple-aquifer system, Israel

The Bet Shean and Harod Valleys are regional recipients and mixing zones for groundwaters draining into them from a multiple-aquifer system which includes carbonate and basalt aquifers and deep-seated reservoirs of brine. The aquifers drain through two types of outlets — unique and common. The latter type is mainly conditioned by the occurrence of fault blocks acting as connecting media between the aquifers. Ca-chloride brines originating from deep-seated and confined reservoirs, leak along the major faults and contaminate the relatively fresh groundwaters originating from the regional aquifers. During the last two decades, the salinity of groundwaters at the outlets of aquifers and in springs discharging into the valleys, have increased as the result of overexploitation. The changes in the chemical composition of these waters indicated inflow of dilute Ca-chloride brines which replace at an ever increasing rate the fresh water of the area. The inflow of brines is limited to fault zones and seems to be controlled by the counterpressure of the overlying fresh water. Overexploitation diminishes this counterpressure, thus facilitating the progressive upflow of brines.

Ca-chloride brines at common outlets of the Bet Shean-Harod multiple-aquifer system, Israel

The Bet Shean and Harod Valleys are regional recipients and mixing zones for groundwaters draining into them from a multiple-aquifer system, which includes carbonate and basalt aquifers and deep-seated reservoirs of brine. The outlets of the three aquifers are located at the mountain border separating the valleys from the Gilboa and Ramot Issakhar Mts. The aquifers drain through two types of outlets — unique and common. The latter type is mainly conditioned by the occurrence of fault blocks acting as connecting media between the aquifers. Upon reaching the interconnecting zones, fresh groundwater flowing from carbonate and basalt aquifers intermix, losing their hydrochemical identities. Ca-chloride brines originating from deep-seated and confined reservoirs, leak along the deep-seated faults characterizing the common outlet zones and contaminate the relatively fresh mixing products originating from the three regional aquifers. Two types of dilute Ca-chloride brines were identified in the study area. The Devora type is a hot and hypersaline source brine which was identified at great depth and under very high hydrostatic pressures. This brine could be the residual product of seawater that evaporated during the Cambrian-Cretaceous continental interval and subsequent prolonged interaction with surrounding carbonate rocks. The Neve Ur-type brine seems to be genetically related to the Neogene inland Sdom Sea that preceeded the contemporary Dead Sea.

Hydrochemistry of groundwater at unique outlets of the Bet Shean-Harod multiple-aquifer system, Israel

The Bet Shean and Harod Valleys are regional recipients and mixing zones for groundwater draining to these valleys from a multiple-aquifer system which includes carbonate and basalt aquifers and deep-seated reservoirs of brine. The outlets of these aquifers are located at the mountain border separating the valleys from the Gilboa and Ramot Issakhar Mts. The aquifers drain through two types of outlets — unique and common. The latter type is mainly conditioned by the occurrence of fault blocks acting as connecting media between the aquifers. Ionic ratios of groundwaters flowing through different carbonate aquifers have not sufficient contrast to facilitate precise identification of source aquifers. In the case of basalt aquifers, the ratios are unequivocal and sufficient contrast enables such an identification.

Saltwater intrusion in aquifers: Development and testing of a three‐dimensional finite element model

A three‐dimensional finite element model is developed for the simulation of saltwater intrusion in single and multiple coastal aquifer systems with either a confined or phreatic top aquifer. The model formulation is based on two governing equations, one for fluid flow and the other for salt transport. Density coupling of these equations is accounted for and handled using a Picard sequential solution algorithm with special provisions to enhance convergence of the iterative solution. Flexibility in the formulation allows for either three‐dimensional simulations or quasi three‐dimensional simulations, where flow and transport in aquitards are treated using one‐dimensional analytical and/or numerical approximations. Spatial discretization of three‐dimensional regions is performed using a vertical slicing approach designed to accommodate complex geometry with irregular boundaries, layering, and/or lateral discontinuity. This approach is effectively combined with the use of simple linear elements such as rectangular and triangular prisms, and composite hexahedra and pentahedra made up of tetrahedra. For these elements, computation of element matrices can be performed efficiently using influence coefficient formulas that avoid numerical integration. New transport influence coefficient formulas are presented for rectangular and triangular prism elements. Matrix assembly is performed slice by slice, and the matrix solution is achieved using a slice successive relaxation scheme. This permits a fairly large number of nodal unknowns (of the order of five to ten thousand) to be handled conveniently on small or medium‐size minicomputers. Flexibility of the formulation and matrix handling procedures also allows two‐dimensional and axisymmetric problems to be solved efficiently using single slice representations. Four examples are presented to demonstrate the model verification and utility. These problems represent a fair range of physical conditions. Where possible, simulation results are compared with previously published solutions.