Top Aquifer Research Articles

BCH modelling studies on biocementation process in mitigating leaks from a CO2 sequestrated aquifer

BCH modelling studies on biocementation process in mitigating leaks from a CO2 sequestrated aquifer

Influence of top water on SAGD steam chamber growth in heavy oil reservoirs: An experimental study

Steam-assisted gravity drainage (SAGD) is one efficient and mature technology for recovering heavy oil and bitumen resources. The key underlying mechanism is the growth of the steam chamber after injecting steam. However, due to the complex geological environment, the thief zones exist and have a prejudicial effect on the development of the steam chamber, thus impacting the ultimate heavy-oil recovery. In this work, our objective is to investigate the effect of a top-water thief zone (i.e., water zone overlies the oil sand) on SAGD performance and further to understand the crucial mechanisms that control the heat loss during steam injection. A large-scale three-dimensional experimental apparatus is used to carry out the SAGD process with a top aquifer. Based on the similarity criterion, the field-scale model is transformed into a laboratory elemental model. To evaluate the SAGD performance quantitatively, the dynamic growth of the steam chamber is measured using the thermal detectors and the production data is recorded. The results show that the steam chamber exhibits three distinguished stages, that is, upward spread, lateral extension, and downward development in the presence of top-water zone. The bottom-water zone has less impact on the steam-chamber growth. The existence of a confined top-water zone, however, significantly affects SAGD performance, especially the lateral expansion of the steam chamber. The lateral propagation of the steam front is hindered by the top thief zone due to the heat exchange with the top water. Once the steam chamber reaches the boundary, the accumulation of energy in the water thief zone, in turn, can reduce the remaining oil saturation along the topwater–oil interface. This study provides us some key insights into the development of heavy oil resources with top thief zones when implementing SAGD technology.

Water inflow characteristics of coal seam mining aquifer in Yushen mining area, China

The Yushen mining area is located in the arid and semi-arid regions of western China. Coal mining activities in this mining area face the challenges of water resource pollution. In this study, in order to study the water inflow law of aquifer caused by coal mining activities, the overlying strata of the mining seam are divided into four aquifer groups according to the geological and hydrogeological characteristics in Yushen mining area. Three categories of aquifer water inflow are proposed by considering the depth of the mining coal seam: the water-conducting fractures formed by coal mining disturbance, the distribution of aquiclude, and the water inflow characteristics, i.e., (1) shallow seam—damaged aquifuge—direct water inflow (SDD), (2) medium seam—single aquifuge—longitudinal water inflow (MSL), and (3) deeply buried seam—two aquifuges—small water inflow (DTS). Then, the aquifer water loss numerical models of three kinds of actual mines in the study area are established by numerical simulation. The simulation results show that due to the water-conducting fractures that developed in the Sandy aquifers, the top aquifer of the mining face is dry. Although the water-conducting fractures only extend into the bedrock aquifers, the groundwater flow of the Sandy porous aquifer is basically unchanged due to the protection by the key soil layers and the secondary mudstone aquifuges for the DTS group. In the MSL group, in which the water-conducting fractures are extend into the interior of the bedrock aquifer as a result of stratified mining of the coal seam, the groundwater flow of the sandy aquifer little change. However, when the full height of the coal seam was mined, it will cause a large influence on the sandy aquifers because the water-conducting fractures have entered the bottom of the weathered bedrock aquifer. This paper quantitatively analyzes the impact of coal mining on aquifer groundwater and provides basic data for coal mining and water resources protection in western China.

Prediction model of water yield property based on GRA, FAHP and TOPSIS methods for Ordovician top aquifer in the Xinwen coalfield of China

In North China, the exploitation of deep coal seams is seriously threatened by water inrush from Ordovician limestone. Predicting the water yield property of the Ordovician limestone aquifer has been an important and challenging task. Based on accessible geological and hydrological data, a water yield property index (WYPI) model, which integrated four factors including the water inflow of borehole, fault impact factor, drilling fluid consumption and burial depth of the Ordovician top aquifer, was proposed for predicting the spatial distribution of the water yield property of the upper Majiagou group limestone in the Ordovician top (Ordovician top aquifer) in the Xinwen coalfield, Shandong, China. The grey relative analysis (GRA) and fuzzy analytic hierarchy process (FAHP) methods were combined to objectively determine the weights of each factor. Then, the technique for order performance by similarity to ideal solution and the weights calculated by the GRA and FAHP were used to establish the WYPI model. The water yield property zone map, which was built using the WYPI values, displayed three water yield property zones. The WYPI model was further verified by taking into account practical engineering data, which were considered effective in predicting the zonation of the water yield property of the Ordovician top aquifer in the Xinwen coalfield, Shandong, China.

Hydrogeochemical Characteristics and Groundwater Inrush Source Identification for a Multi‐aquifer System in a Coal Mine

Correct identification of water inrush sources is particularly important to prevent and control mine water disasters. Hydrochemical analysis, Fisher discriminant analysis, and geothermal verification analysis were used to identify and verify the water sources of the multi‐aquifer groundwater system in Gubei coal mine, Anhui Province, North China. Results show that hydrochemical water types of the Cenozoic top aquifer included HCO3–Na+K–Ca, HCO3–Na+K–Mg and HCO3–Na+K, and this aquifer was easily distinguishable from other aquifers because of its low concentration of Na++K+ and Cl–. The Cenozoic middle and bottom aquifers, the Permian fissure aquifer, and the Taiyuan and Ordovician limestone aquifers were mainly characterized by the Cl–Na+K and SO4–Cl‐Na+K or HCO3–Cl–Na+K water types, and their hydrogeochemistries were similar. Therefore, water sources could not be identified via hydrochemical analysis. Fisher model was established based on the hydrogeochemical characteristics, and its discrimination rate was 89.19%. Fisher discrimination results were improved by combining them with the geothermal analysis results, and this combination increased the identification rate to 97.3 % and reasonably explained the reasons behind two water samples misjudgments. The methods described herein are also applicable to other mines with similar geological and hydrogeological conditions in North China.

Fluoride Concentration in Groundwater of Khapa Town, Saoner Tehsil, Nagpur District – A Case Study

Fluoride is known to contaminate groundwater in many countries notably India, Sri Lanka, China, rift valley countries in East Africa, Turkey and parts of South Africa. Sporadic incidence of high fluoride content in groundwater has been reported in 19 states and union territories across the country (CGWB 2010; Pol 2012). The fluoride occurrences in top aquifer system are endemic in many parts of Andhra Pradesh, Tamil Nadu, Karnataka, Gujarat, Rajasthan, Punjab, Haryana, Bihar and Kerala (Agarwal et al. 1997; Latha et al. (1999); Gopalakrishnan et al. (2012). The toxicity of fluoride is generally influenced by high ambient temperature, alkalinity, calcium and magnesium contents in drinking water (BIS 1991). High level of fluoride posses serious health hazards to humans and irreversible damage to plants. The present study was carried out to assess the fluoride concentration of groundwater in the selected villages around Khapa town of Nagpur district.

Quantitative estimations of aquifer properties from resistivity in the Bolivian highlands

Abstract Resistivity data constitute the largest part of the available information to assess the hydrogeological characteristics of the aquifer system near Oruro, in the central part of the Bolivian Altiplano. Two aquifers are part of this system; top unconsolidated sediments storing fresh water in their granular voids, overlying fractured hard rock formations where saline water was detected in connection to some faults. This study proposes an indirect and cost-effective way to estimate aquifer hydraulic properties for the groundwater management in the region. Hydraulic conductivity and transmissivity in the top aquifer were estimated using an empirical linear relationship between hydraulic conductivity and resistivity. This latter parameter, as well as the aquifer thickness, were obtained from the inverted models corresponding to the geoelectrical tests performed in the study area (electrical resistivity tomography, transient electromagnetic soundings and vertical electrical soundings). The highest estimated transmissivity values are ∼4.0 × 10−2 m2/s located in the centre of the study area, the lowest values are ∼3.4 × 10−3 m2/s, located around thermal intrusions to the south and where the top of the bedrock is shallow (∼20 m depth) to the west. The methodology presented in this study makes wider use of resistivity measurements to identify promising groundwater production sites.

Electrical resistivity mapping of oil spills in a coastal environment of Lagos, Nigeria

Three years after the oil spillage and pipeline explosion that claimed about 100 human lives at Ijegun Community of Lagos–Nigeria, a combination of carefully designed 2D Electrical Resistivity Profilling and Vertical Electrical Sounding methods was deployed to map and characterise the subsurface around the contaminated site. Data acquired were processed, forward modelled and tomographically inverted to obtain the multi-dimensional resistivity distribution of subsurface. The results of the study revealed high resistivity structures that indocate the presence of contaminant (oil plumes) of different sizes and shapes around the oil leakage site. These high resistivity structures are absent in the tomograms and resistivity-depth slices computed for Iyana—a linear settlement not affected by oil spillage. The five geo-electric layers and the resistivities delineated in the area are the top soil layer, 220–670 Ωm; clayey sand layer, 300–1072 Ωm; top sand layer, 120–328 Ωm; mudstone/shale layer, 25–116 Ωm and the bottom sand layer, 15–69 Ωm. The base of the first four geo-electric layers corresponds to 3.9, 8.4, 27.2 and 34.6 m respectively. The two groundwater aquifers delineated correspond to the third and fifth geo-electric layers. The top aquifer has been infiltrated by oil plumes. The depth penetrated by the oil plume decreases from 32 m to about 24 m across the survey profiles from the two ends. It was concluded that the contaminant plumes from the oil spillage are yet to be completely degraded as at the time of the study. It is recommended that the contaminated site be remediated to remove or reduce the contaminant oil in the subsurface.

Hydrochemical Characteristics and Groundwater Source Identification of a Multiple Aquifer System in a Coal Mine

Hydrochemical analysis and Bayesian discrimination were used to identify groundwater sources for multiple aquifers in the Panyi Coal Mine, Anhui, China. The results showed that the Cenozoic top aquifer water were HCO3−Na+K−Ca and HCO3−Na+K−Mg types, which distinguished it from the other aquifers due to its low Na+ + K+ and Cl− concentrations. The Cenozoic middle and Cenozoic bottom aquifer waters were mainly Cl−Na+K and SO4−Cl−Na+K types. The water types in the Permian fractured aquifer changed from Cl−Na+K to HCO3−Cl−Na+K and HCO3−Na+K moving away from the Panji anticline. In addition, HCO3 − concentrations increased and Ca2+ concentrations decreased with depth in the aquifer. The Taiyuan limestone aquifers were of Cl−Na+K, SO4·Cl−Na+K, and HCO3·Cl−Na+K types, and are very difficult to distinguish from the other aquifers. The precision of the Bayesian discrimination based on groundwater chemistry was 86.09%. Water chemistry indicators in the Permian fractured aquifer were moderately to highly variable and moderately to strongly correlated, spatially. The water chemistry spatial distribution indicates that the Permian fractured aquifer is recharged by the Cenozoic bottom aquifer near the Panji anticline, which reduces the accuracy of Bayesian discrimination in that area.

Flow Characteristics of Steam and Gas Push in the Presence of Heat Thief Zones Overlying Oil Sands Deposits

This paper presents the effects of the top water-bearing zone on the performance of the steam and gas push, i.e., nitrogen as a non-condensable gas injected with steam into an oil sands deposit. The flow characteristics of fluid mixtures are examined in the presence of different-sized water-bearing formations overlying oil sands deposits, i.e., a finite aquifer with no-flow boundaries and an infinite aquifer with continuous mass flux. The performance efficiency is investigated by respectively implementing the cumulative steam to oil ratio, a simple thermal efficiency parameter, and the oil production on the surface. The top water-bearing area serves as a heat thief zone and negatively impacts bitumen recovery; furthermore, it increases the cumulative steam to oil ratio while decreasing the simple thermal efficiency parameter, as well as the oil production rate. When the steam chamber encounters the top aquifer, a severe heat loss occurs. As increasing mol % of nitrogen, the producing time with energy efficiency increases but the chamber growth is limited. The specific operational conditions would be possible for the finite-sized aquifer, while the continuous water influx and the significant heat loss obstructs the thermal processes for the infinite aquifer.

Hydrogeochemical analysis of multiple aquifers in a coal mine based on nonlinear PCA and GIS

Hydrogeochemical characteristic analysis of multiple categorical aquifers, including the delineation of hydrogeochemical spatial distributions, can provide a basic understanding of the groundwater flow system necessary for the prevention and control of groundwater damage associated with coal mines. Nonlinear principal component analysis (PCA) was used to analyse the groundwater chemical characteristics of water samples from five aquifers in Gubei Coal Mine, Anhui Province, China. In particular, Ca2+, Mg2+, Na+ + K+, HCO3−, Cl−, SO42−, and pH were analysed. To analyse the spatial distribution of groundwater chemistry in this Permian fractured aquifer, interpolation of principal component 1 (PC1) scores obtained from the nonlinear PCA was performed using the inverse distance weighting (IDW) method. Additionally, concentrations of the hydrogeochemical variables were plotted against depth. The relationships between water samples, variables, and water samples with variables were simultaneously analysed by nonlinear PCA. The results show: (1) nonlinear PCA explains more variability than standard PCA in the first two principal components (PCs); (2) the Cenozoic top aquifer has low concentrations of Na+ + K+ and Cl−; the Cenozoic middle aquifer and Cenozoic bottom aquifer are characterised by high concentrations of Ca2+ and Mg2+ and low concentrations of HCO3−; the shallow groundwater of the Permian fractured aquifer is recharged by the Cenozoic bottom aquifer, while other parts have high concentrations of HCO3− and low concentrations of Ca2+ and Mg2+. The Taiyuan limestone aquifer has similar groundwater chemistry to that of the Cenozoic bottom aquifer, and thus it may be recharged by the Cenozoic bottom aquifer in outcropping Taiyuan Formation strata; (3) the wide south-western and north-western areas of the Permian fractured aquifer may be recharged by the Cenozoic bottom aquifer; and (4) concentrations of Ca2+ and Mg2+ in the Permian fractured aquifer are negatively correlated with sampling depth, while the concentrations of Na+ + K+ and HCO3− are positively correlated with sampling depth, which verifies that the shallow groundwater of this Permian fractured aquifer is recharged by the Cenozoic bottom aquifer. The findings demonstrate that combining nonlinear PCA with GIS can be a powerful approach for conducting spatial nonlinear analysis of hydrogeochemical characteristics.

Hydrogeological Issues Concerning the Thar Lignite Prospect

The paper is concerned with the hydrogeological appraisal of the proposed mining operations in theThar lignite field in Sindh, Pakistan. The Thar coalfield covers an area of approximately 9000km2 andcontains three lignite seams lying at depth of 130m to 250 m. In the Thar lignite field, the presence ofthree main aquifers induces pore pressure in the rock mass surrounding the lignite seams and makes highwall slopes potentially unsafe. It is, therefore, necessary to dewater the rock mass before commencingmining excavations. The paper describes the proposed mine dewatering scheme to facilitatedepressurising of the rock mass surrounding the mining excavations. Inflow prediction of groundwater tothe surface mining excavation was carried out using a SEEP/W finite element software package. Thesimulation results show that the ground water inflow from the Top aquifer is 114m3/d, from theIntermediate confined aquifer is 141m3/d and from the Bottom confined aquifer is 1.28 x 105 m3 /d. Theseresults were compared with the analytical solutions which indicated that the relative error of estimation ofinflow quantities varies from 3.4 % to 6.4%.

Impact of CO2 Injection in Deep Saline Aquifers: A study on Pressure Evolution in Stratified Formation of Qianjiang sag, China

In order to mitigate the adverse impacts of climate change, CO2 captured from carbon emitters like coal-fired power plants may be stored in deep saline aquifers. This action may cause pressure changes, which affect subsurface volumes. The main purpose of this study is to evaluate the pressure changes during CO2 sequestration in CO2 storage formation embedded in a sequence of aquifers and aquitard of the Qianjiang depression area. In order to demonstrate the transient pressure, we have conducted TOUGH2 modeling of CO2 injection into closed formations of different thicknesses assuming impermeable boundaries. A 2-D radially symmetric model was developed to represent a CO2 storage site in the Qianjiang depression area. The storage formation into which CO2 is injected is 120 m thick and located at a depth of about 1530 m below the ground surface. The CO2 injection thickness was 25m from the bottom of the storage formation. Carbon dioxide is injected into a zone of 71 m radial extent representing a few distributed wells. Injection occurs at an annual rate of 1* 10 7 tonnes of CO2 representing six times the CO2 rate captured from a medium-size-coal-fired power plant. The simulation runs cover a time period of 100 years altogether, comprising the 20-year injection period and 80-year post-injection period. Our simulation results indicate that interlayer pressure propagation through a sequence of aquitard/aquifer will not affect the top aquifer except for the case when seal permeability was 9 * 10-18 m2, after 100 years the pressure perturbation reached the upmost aquifer .Placing a barrier (fault) at a distance of 10 km have shown that the flow barrier started affecting pressures after about 1 month and 24 days and the pressure increase were very high, about 150 bars after 20 years.

Groundwater responses to artificial recharge of rainwater in Chennai, India: a case study in an educational institution campus

This paper reports the response of the groundwater in the St Peter’s Engineering College campus, Avadi, near Chennai, India. Artificial recharge of rainwater was done through roof top harvesting methods during 2004 to 2007. Based on a hydro geological survey of the campus, eleven bore well were sunk for augmenting water supply to the campus. The lithology of each bore well was also recorded. A percolation pond in 1 ha area on the south eastern side of the campus was dug to collect and store the rainwater harvested from rooftops of the campus buildings. The survey also assisted in the identification and location of about 70 number of recharge wells in the campus. Pumping test was conducted in well no:3 to assess the hydraulic conductivity and calculate other aquifer parameters during 2005. A three layer hydro geological model of the aquifer was applied in Visual Modflow ver 4.1 environment and the model fit was 84% between observed and predicted values (R2 = 0.844). Significant increase in water level in the top aquifer during 2007 was recorded when compared to 2004. The flow profiles in the middle and deep aquifer showed responses, through changes in the direction of flow to the pumping wells (5, 6 in 2004 and 2, 3 in 2007). In 2007, with improved recharge, changes in the direction of groundwater flow and discharge of water from the aquifer in the southern part of the campus can be noticed. The flow directions in the three aquifer layers also indicated that the northern part of the study area serves as an effective recharge zone for the St Peter’s Engineering College Campus. Rainwater harvesting and recharge studies form important part in groundwater restoration and management in intensely urbanized cities/townships. Keywords: Rainwater harvesting methods, Aquifer recharge, Groundwater flow, Aquifer test pro, Visual Modflow.

THE AZNALCÓLLAR PIT LAKE – WATER QUALITY AND OPTIONS OF CONTROL

The Aznalcollar mine is well known since the disaster in 1998. A dam of the tailings impoundment broke and about 4 million m 3 of acidic water and 2 million m 3 of sludge contaminated the river system Rio Agrio-Rio Guadiamar- Rio Guadalquivir with heavy metals. A lot of research has been done to quantify the consequences of the disaster for the river system and to prove the success of the remediation measures. But little is known about the state and the perspectives of the rising lake in the former mine pit. Parts of the Aznalcollar pit have been used to dump waste rock from the neighboring pit Los Frailes. Additionally, tailings material and contaminated soil from the river system were deposited in the former mine pit. Consequently, the pit lake sediments are very heterogeneous and highly enriched in heavy metals reaching ore-grade concentrations for some elements. Actually, the pit lake water level is regulated by pumping to stay at least 6 m below the natural groundwater level. The water is acidic (pH 3.6) and has high concentrations of metals (e.g. 800 mg/L Zn, 200 mg/L Mn, 100 mg/L Al, 2000 µg/L Cd). The major concern is that the contaminated lake water may enter the river system and the top aquifer when the lake reaches its natural water level. Based on recent knowledge, options of future remediation of the lake water quality are discussed.

Steady groundwater flow through many cylindrical inhomogeneities in a multi-aquifer system

A new approach is presented for the simulation of steady-state groundwater flow in multi-aquifer systems that contain many cylindrical inhomogeneities. The hydraulic conductivity of all aquifers and the resistance of all leaky layers may be different inside each cylinder. The approach is based on separation of variables and combines principles of the theory for multi-aquifer flow with principles of the analytic element method. The solution fulfills the governing differential equations exactly everywhere; the head, flow, and leakage between aquifers may be computed analytically at any point in the aquifer system. The boundary conditions along the circumference of the cylinder are satisfied approximately, but may be met at any precision. Two examples are discussed to illustrate the accuracy of the approach and the significance of inhomogeneities in multi-aquifer systems. The first application simulates the vertical and horizontal, advective spreading of a conservative tracer in a homogeneous aquifer that is overlain by an aquifer with cylindrical inclusions of higher permeability. The second application concerns the three-dimensional shape of the capture zone of a well that is screened in the bottom aquifer of a three-aquifer system. The capture zone extends to the top aquifer due to cylindrical holes of lower resistance in the separating clay layers.

Two exact solutions for a cylindrical inhomogeneity in a multi-aquifer system

Two new exact solutions are presented for steady-state, uniform flow through a cylindrical inhomogeneity in a multi-aquifer system. The solutions are valid for an arbitrary number of aquifers, and all aquifer properties may change from outside to inside the cylinder. The first problem concerns flow in a confined aquifer. The second problem is similar to the first problem, but now the cylinder is bounded on top by a lake with a semi-permeable bottom and a fixed water level; a constant amount of water may be extracted from the lake. The equations are derived in a radial coordinate system and make use of the known solution for uniform flow through a cylindrical inhomogeneity in a single aquifer, and the general theory for flow in leaky, multi-aquifer systems. Separate equations are presented for the head, flow, and leakage inside and outside the cylinder; a complete set of linear equations is presented to solve for the coefficients in the solutions. For each solution a specific example is presented for flow in a system with three aquifers. Rather complicated leakage patterns are obtained when inside the cylinder the transmissivity of the top aquifer is increased, the transimissivity of the middle aquifer is decreased, and the transmissivity of the bottom aquifer is kept constant.

Simulating groundwater flow in multi-aquifer systems with analytical and numerical Dupuit-models

Analytic Dupuit solutions for multi-aquifer flow are compared to exact solutions for two-dimensional flow in the vertical plane to determine the error in discharge that is introduced by adopting the Dupuit approximation. Specifically, the problem of flow in the bottom aquifer of a two-aquifer system is studied where flow is caused by a piecewise constant head in the top aquifer. The difference between the exact and Dupuit solutions is small if the leakage factor (a characteristic length of the aquifer system) is large relative to the thickness of the aquifer, even for anisotropic hydraulic conductivities. The accuracy of discharges obtained with a Dupuit solution improves when the aquifer is divided up in a number of layers, separated by leaky layers representing the vertical resistance to flow of the aquifer. In a second comparison, analytic Dupuit solutions are compared to numerical Dupuit solutions obtained with the finite difference method to determine reasonable cell sizes and domain sizes for finite difference models. Accurate discharges were obtained with the finite difference method when the cell size is chosen equal to or smaller than the smallest leakage factor and the domain size is at least six times the largest leakage factor. Both a two-aquifer system (with one leakage factor) and a three-aquifer system (with two leakage factors) were studied.

Risk hazard mapping of groundwater contamination using long-term monitoring data of shallow drinking water wells

Long-term monitoring data from over 10 000 shallow drinking water wells in the county of Osnabrück (2121 km 2) were used for generating regionalized time-averaged maps of top aquifer contamination. Using these approach local impacts can be distinguished from wide spread contamination with agrochemicals (nitrate, pesticides). Spatial databases of land-use patterns, livestock figures, soil and meteorological data are stored in a Geographical Information System (ARC/INFO). They were overlayed with regionalized aquifer contamination to facilitate the hazard mapping of top aquifer contamination.

Salinity study of coastal groundwater aquifers in north Kelantan, Malaysia

The salinity of the ground water along the coastal aquifers of north Kelantan was investigated using both geophysical and hydrogeochemical methods. In the geophysical method, a geoelectrical sounding technique was employed using ABEM SAS 300C terrameter. A total of 53 sounding stations had been established and resistivity values of the ground water in different aquifers were determined. Salinity ofthe ground water was interpreted using a classification made by Flathe (1974). Based on this classification, ground water with resistivity values of less than 45 Ohm-m is considered as saline or brackish water and those of greater than 45 Ohm-m is fresh water. The results show that the ground water of the first top aquifer is fresh with resistivities ranging from 47 Ohm-m to 164 Ohm-m except in an area along the coast where the water is brackish. The ground water of the second aquifer generally has resistivity lower than 45 Ohm-m and has been classified as brackish water. Resistivity map of the second aquifer indicates that the brackish water covers an area of up to about 6 kilometres from the coastal line. Only few resistivity data were obtained for the third aquifer and values are generally low (ranging from 56 to 72 Ohm-m) indicating that the ground water is relatively fresh. Salinity of the groundwater in all of the aquifers was also studied by analysing their chloride content. Ground water with chloride concentration of less than 250 mg/l is classified as fresh water and those having higher concentration of chloride is considered brackish or saline. Results of the water analysis show that the chloride concentration of the first aquifer is low and averages to only 15.8 mg/l. The fresh water/ saline water interface in this aquifer is generally located directly in the coastal area, or very close to it. The concentration of chloride in the second aquifer is high with values ranging from 500 to 3,600 mg/l and covers an area of up to about 6 kilometres from the coast. Beyond this area, the concentration of chloride appears to be low, with values ranging from 2 to 110 mg/l. Continuous monitoring of its chloride content (Haryono, 1997) indicates'little changes with time inferring that the high salinity is not due to seasonal sea water intrusion. The analysis also reveals low concentrations of sulphate which suggest that the groundwater of the second aquifer may represent fossilised sea water. The chloride content in the third aquifer is generally low with values ranging from 2 to 210 mg/l and thus the ground water in this aquifer is considered fresh and good for domestic use.