Hydrochemical changes in a small tropical island’s aquifer: Manukan Island, Sabah, Malaysia

Small islands groundwater are often exposed to heavy pumpings as a result of high demand for freshwater consumption. Intensive exploitation of groundwater from Manukan Island’s aquifer has disturbed the natural equilibrium between fresh and saline water, and has resulted increase the groundwater salinity and leap to the hydrochemical complexities of freshwater–seawater contact. An attempt was made to identify the hydrochemical processes that accompany current intrusion of seawater using ionic changes and saturation indices. It was observed that the mixing between freshwater–seawater created diversity in geochemical processes of the Manukan Island’s aquifer and altered the freshwater and seawater mixture away from the theoretical composition line. This explained the most visible processes taking place during the displacement.     

龙口市地下水信息化管理系统的应用研究

系统采用B/S模式,以远程监测和自动化控制为基础,建设龙口市地下水信息化管理系统,实现地下水数据的在线管理和发布。对系统的结构功能进行了分析,利用计算机技术、自动控制技术、通信技术,探索地下水信息化的管理模式。     

Monitoring and methods to analyse the groundwater quality degradation risk in coastal karstic aquifers (Apulia,Southern Italy)

A multi-methodological approach based on monitoring and spatio-temporal analysis of groundwater quality changes is proposed. The presented tools are simple, quick and cost-effective to give service to all sorts of users. The chief purpose of the monitoring network is the detection of the piezometric or potenziometric level in the aquifer. The spatial and multi-temporal analysis of usual chemical and physical data provides both an assessment of the spatial vulnerability of the aquifer to seawater intrusion, defining a salinity threshold between fresh groundwater and brackish groundwater and of the water quality trend in terms of salinity. The evaluation of the salinity trend or of salinity-correlated parameters highlights the effects of groundwater mismanagement. The multiparameter logging provides a rapid groundwater quality classification for each well. The whole approach allows evaluating the effects of current management criteria and designing more appropriate management targets. The Apulian karstic coastal aquifers have been selected as a case study (Southern Italy). Three types of aquifer zones can be distinguished: (1) areas with low vulnerability to seawater intrusion, (2) areas with high vulnerability and (3) areas with variable vulnerability in which the salt degradation largely depends on the ability to manage the well discharge. The water quality degradation caused by seawater intrusion appears to be a combined effect of an anomalous succession of drought periods observed from about 1980 onwards and increased groundwater pumping, particularly during drought periods. A management criterion based on aquifer zones is proposed.     

烟台市海水入侵程度及影响因素探讨

介绍了烟台市开发区夹河地区20年来海水入侵的现状及过程。基于区内4个监测井点的长期观测资料,讨论了影响海水入侵程度的主要因素,认为烟台市海水入侵程度与区内地下水动态关联密切。在海侵区内,地下水被海水浸染的程度主要受地下水位降深控制,地下水降落漏斗范围内海水对地下水浸染程度随水位下降逐年加剧,而漏斗区外地下水质则多年保持相对稳定。     

Conceptual model of a coastal aquifer system in northern Greece and assessment of saline vulnerability due to seawater intrusion conditions

This paper refers to the development of a conceptual model for the management of a coastal aquifer in northern Greece. The research presents the interpretation and analysis of the quantitative (groundwater level recordings and design of piezometric maps) regime and the formation of the upcone within the area of investigation. Additionally it provides the elaboration of the results of chemical analyses of groundwater samples (physicochemical parameters, major chemical constituents and heavy metals and trace elements) of the area which were taken in three successive irrigation periods (July–August 2003, July–August 2004 and July 2005), in order to identify areas of aquifer vulnerability. The study identifies the areas where ion exchange phenomena occur, as well as the parts of the aquifer where the qualitative degradation of the aquifer system is enhanced. The paper, finally, assesses the lack of any scientific groundwater resources management of the area by the local water authorities, as well as the current practices of the existing pumping conditions scheme as applied by groundwater users.An erratum to this article can be found at     

Geochemical evolution of groundwater in the Maneadero coastal aquifer during a dry year in Baja California, Mexico

Water pumped from 25 shallow wells (<31 m) in the Maneadero unconfined coastal aquifer was studied geochemically in order to determine the short-term compositional variability of the aquifer due to seawater intrusion during a drier than normal year (Fall 2001 to Fall 2002). The groundwater was commonly found to be mixed with seawater, with TDS concentrations in November 2002 ranging from 0.99 to 9.46 g l^–1, having an intermediate Na⁺Cl^– to Ca²⁺Cl^– water-type. Rapid recharge events of short duration, after low and short rainfall events during the study period, are suggested from short-term fluctuations in water quality. Seawater intrusion is progressing faster in the central and southern coastal sections of the aquifer and has recently affected the quality of the sites pumping water to the nearby city of Ensenada. Only one of the wells used for the Ensenada water supply had a TDS concentration lower than the 1.0 g l^–1 official limit. Low flow rates and high residence times of water are inferred to be the cause for high alkalinity in the east-central section of the aquifer. High NO₃ in the east-central aquifer indicates that any NO₃ infiltration due to fertilizer use was only slightly dispersed. After a short rainfall season during winter 2001, a significant decrease was seen for the previously most enriched site. However, concentrations above the 10 mg l^–1 official limit persisted in 2002, affecting one well for urban supply (15.9 mg l^–1). The water from this well is nevertheless mixed with better-quality water from other wells before being distributed through the citys piping system.

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Resumen Se estudió la geoquímica de aguas bombeadas por medio de 25 pozos no muy profundos (<31 m) en el acuifero costero no confinado de Maneadero con el objetivo de determinar la variación de la composición en el corto plazo en el acuifero por la intrusión de agua de mar durante un año más seco de lo normal (otoño 2001 a otoño 2002). Se observó que comúnmente las aguas subterráneas estaban mezcladas con agua de mar, con concentraciones de sólidos totales disveltos (STD) de entre 0.99--9.46 g l^–1 y un tipo de agua intermedia Na⁺Cl^– to Ca²⁺Cl^–. A partir de las fluctuaciones en la calidad del agua en el corto plazo se puede inferir que se dan eventos de recarga rápida de poca duración después de eventos de poca lluvia de poca duración y poco volumen durante el periodo de estudio. La intrusión de agua de mar está progresando más rápido en el centro y sur del acuifero costero y ha afectado recientemente la calidad de los sitios de bombeo de agua para la ciudad de Ensenada. Solamente uno de los pozos usados para el abastamiento de Ensenada tiene un STD por debajo del límite oficial de 1.0 g l^–1. Se presume que las razones lentas de flujo y los tiempos de residencia largos del agua son la causa de la alta alcalinidad en el centro-este del acuifero. Una concentración alta de NO₃ en el este-centro del acuifero indica que cualquier infiltración de NO₃ por aplicación de fertilizantes ha sido poco dispersad. Después de poca lluvia en el invierno de 2001, se observó una disminución importante en la zona previamente más enriquecida. Sin embargo, concentraciones sobre el límite oficial de 10 mg l^–1 continuaron en 2002, afectando a un pozo para suministro de agua urbana (15.9 mg l^–1). El agua extraída de este pozo es mezclada con agua de mejor calidad y se distribuye por el sistema urbano de suministro de agua.

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Résumé Leau de pompage de 25 puits peu profonds (<31 m) situés dans laquifère côtier non-confiné de Maneadero a été étudiée dans le but de déterminer la variation géochimique à court terme qui résulte de lintrusion deau de mer lors dune année plus sèche quà lhabitude (automne 2001 à automne 2002). Leau souterraine est souvent retrouvée mélangée avec de leau de mer, avec des concentrations en résidus solides dissous (RSD) qui sétalent entre 0.99 et 9.46 g l^–1 pour novembre 2002, avec un type intermédiaire en Na⁺Cl^– jusquà Ca²⁺Cl^–. Les processus suggérés pour les fluctuations rapides de la qualité de leau sont des événements de recharge de courte duré suite à de faibles et brèves périodes de précipitations. Lintrusion deau de mer progresse plus rapidement dans les parties centrales et sud de laquifère côtier où la qualité de leau pompée vers la ville de Ensenada a récemment été affectée. Un seul des puits utilisés par la ville de Ensenada pour lapprovisionnement en eau potable a une concentration en RSD sous la limite officielle permise de 1.0 g l^–1. Le temps de résidence élevé et le faible taux découlement de leau souterraine sont présumés être la cause de lalcalinité élevée dans la partie centrale-est de laquifère. La concentration élevée en NO₃ dans cette partie de laquifère indique que la totalité de linfiltration de NO₃ dû à lutilisation de fertilisants ne sest que très peu dispersée. Suite à une courte saison des pluies à lhiver 2001, une diminution substantielle a été notée au site qui était le plus enrichi avant la saison des pluies. Malgré tout, des concentrations dépassant la limite officielle permise de 10 mg l^–1 ont persisté, affectant un puits utilisé pour lapprovisionnement urbain (15.9 mg l^–1). Leau provenant de ce puits est toutefois mélangée avec de leau de meilleure qualité provenant dautres puits avant dêtre distribuée par laqueduc municipal.

     

Salinization properties of a shallow groundwater in a coastal reclaimed area,Yeonggwang, Korea

The need for more agricultural or residential land has encouraged reclamation at the coastal areas of Korea since 1200 ad (approximately). The groundwaters of these reclaimed areas could be expected to reveal hydrogeochemical properties different from those of areas directly affected by seawater intrusion. The purpose of this study, therefore, was to examine the salinization of shallow groundwater in a coastal reclaimed area and to identify the effect of land reclamation on groundwater quality. Major cations and anions, iodide, total organic carbon, δD, δ ¹⁸O and δ ¹³C were measured to assist the hydrogeochemical analysis. Chloride, δD and δ ¹⁸O data clearly show that the Na–Cl type water results from mixing of groundwater with seawater. In particular, the δD and δ ¹⁸O of Ca+Mg–Cl+NO₃ type groundwaters are close to the meteoric water line, but Na–Cl type waters enriched in chloride are ¹⁸O-enriched with respect to the meteoric water line. Meanwhile, carbon isotopic data and I/Cl ratios strongly suggest that there are various sources of salinity. The δ ¹³C values of Na–Cl type groundwaters are generally similar to those of Ca+Mg–Cl+NO₃ type waters, which are depleted in ¹³C with respect to seawater. I/Cl ratios of Na–Cl type groundwater are 10–100 times higher than that of seawater. Because the reclamation has incorporated a large amount of organic matter, it provides optimum conditions for the occurrence of redox processes in the groundwater system. Therefore, the salinization of groundwater in the study area seems to be controlled not only by saltwater intrusion but also by other effects, such as those caused by residual salts and organic matter in the reclaimed sediments.     

A geophysical and geochemical approach for seawater intrusion assessment in the Acquedolci coastal aquifer (Northern Sicily)

Vertical electrical sounding (VES’) surveys and chemical analyses of groundwater have been executed in the coastal plain of Acquedolci (Northern Sicily), with the aim to circumscribe seawater intrusion phenomena. This urbanized area is representative of a more general problem interesting most of Mediterranean littoral areas, where intensive overdraft favors a heavy seawater intrusion through the coastline. Aquifer resistivity seems decisively to be conditioned by the chlorine and magnesium content in the main aquifer of the region. Schlumberger VES’, together with piezometric and chemical–physical information of groundwater, allowed us to perform hydrogeological and geophysical elaborations, to propose the occurrence of a relatively narrow belt marked by fresh–salt water mixing. In the considered plain, pollution risk studies have been already realized by authors with the proposal to identify—by parametric and synthetic zoning of significant hydrogeological elements—the most vulnerable sectors. In detail, an intrinsic vulnerability mapping has been already performed, applying the well-known SINTACS system. This paper intends to give—in this sector of Sicily—an example of integration of different methodologies, showing the role of geophysics to describe the degradation of aquifers on the whole as well as to assess their pollution risk better.     

Groundwater quality of porous aquifers in Greece: a synoptic review

Greece is dependent on groundwater resources for its water supply. The main aquifers are within carbonate rocks (karstic aquifers) and coarse grained Neogene and Quaternary deposits (porous aquifers). The use of groundwater resources has become particularly intensive in coastal areas during the last decades with the intense urbanization, tourist development and irrigated land expansion. Sources of groundwater pollution are the seawater intrusion due to over-exploitation of coastal aquifers, the fertilizers from agricultural activities and the disposal of untreated wastewater in torrents or in old pumping wells. In the last decades the total abstractions from coastal aquifers exceed the natural recharge; so the aquifer systems are not used safely. Over-exploitation causes a negative water balance, triggering seawater intrusion. Seawater intrusion phenomena are recorded in coastal aquifer systems. Nitrate pollution is the second major source of groundwater degradation in many areas in Greece. The high levels of nitrate are probably the result of over-fertilization and the lack of sewage systems in some urban areas.     

Evaluation and numerical modeling of seawater intrusion in the Gaza aquifer (Palestine)

A numerical assessment of seawater intrusion in Gaza, Palestine, has been achieved applying a 3-D variable density groundwater flow model. A two-stage finite difference simulation algorithm was used in steady state and transient models. SEAWAT computer code was used for simulating the spatial and temporal evolution of hydraulic heads and solute concentrations of groundwater. A regular finite difference grid with a 400 m² cell in the horizontal plane, in addition to a 12-layer model were chosen. The model has been calibrated under steady state and transient conditions. Simulation results indicate that the proposed schemes successfully simulate the intrusion mechanism. Two pumpage schemes were designed to use the calibrated model for prediction of future changes in water levels and solute concentrations in the groundwater for a planning period of 17 years. The results show that seawater intrusion would worsen in the aquifer if the current rates of groundwater pumpage continue. The alternative, to eliminate pumpage in the intruded area, to moderate pumpage rates from water supply wells far from the seashore and to increase the aquifer replenishment by encouraging the implementation of suitable solutions like artificial recharge, may limit significantly seawater intrusion and reduce the current rate of decline of the water levels.     

海水入侵对地铁地下结构侵蚀性的统计分析

地下水的腐蚀性严重影响地铁的安全运营,正确评价地下水的腐蚀性是解决问题的关键。以深圳地铁11号线为例,对全线30个工点627个地下水水质分析样本进行统计,得到整条线路地下水腐蚀强弱分布状态。结合线路通过区的填海和海水侵入背景进行分析,得出如下结论:具有典型的海水侵入背景下的地下水侵蚀性与海水侵入(包括填海区)范围密切相关,地铁地下结构宜按干湿交替环境进行钢筋腐蚀等级判别。该研究为滨海城市海水入侵区地铁线路地下水腐蚀性评价提供指导。     

A modeling study of seawater intrusion in Alabama Gulf Coast,USA

A numerical model of variable-density groundwater flow and miscible salt transport is developed to investigate the extent of seawater intrusion in the Gulf coast aquifers of Alabama, USA. The SEAWAT code is used to solve the density-dependent groundwater flow and solute transport governing equations. The numerical model is calibrated against the observed hydraulic heads measured in 1996 by adjusting the zonation and values of hydraulic conductivity and recharge rate. Using the calibrated model and assuming all the hydrogeologic conditions remain the same as those in 1996, a predictive 40-year simulation run indicates that further seawater intrusion into the coastal aquifers can occur in the study area. Moreover, the predicted intrusion may be more significant in the deeper aquifer than the shallower ones. As the population continues to grow and the demand for groundwater pumping intensifies beyond the 1996 level, it can be expected that the actual extent of seawater intrusion in the future would be more severe than the model prediction. Better strategies for groundwater development and management will be necessary to protect the freshwater aquifers from contamination by seawater intrusion.

Simulation of chloride migration rates in Paleo Pennar Delta Region, Coastal Andhra Pradesh, India

 Quaternary alluvial aquifers in the paleo Pennar delta region of Andhra Pradesh (Long. 80°0′ and 80°12′; Lat. 14°40′ and 14°20′) constitute an important coastal strip, with potential fresh groundwater resources and several well fields in operation. The lineament patterns and traces of paleo channels provide basic information on the configuration and boundaries of paleo delta and the possible neotectonic movements in the region. The paleo delta region is essentially characterized by freshwater aquifer systems at the near-surface depths, (up to 50 m from ground level) with transmissivity values in the system ranging from 1200 to 2500 m²/day. This groundwater system has been subjected to heavy draft situation over the last two decades, parlicularly near the outer rim of the delta where an unlined brackish-water canal runs parallel to the coast imparting chloride contamination to the adjoining fresh aquifers. A two-dimensional solute transport model solution was applied to assess chloride migration rates inland under different hydraulic stresses, combining finite difference solution of flow equation and the method of characteristic solution of solute transport equation. Groundwater flow and chloride migration patterns/rates were obtained for different simulated stress events in the delta system, and measures required to protect the freshwater resources ara outlined. Received: 2 January 1997 · Accepted: 4 November 1997     

Evolution of groundwater salinity in the unconfined aquifer of Bou-Areg, Northeastern Mediterranean coast, Morocco

The Bou-Areg plain in the Mediterranean coast at the North-eastern of Morocco is characterized by a semi-arid climate. The aquifer consists of two sedimentary formations of Plio-quaternary age: the upper formation of fine silts and the lower one of coarse silts with sand and gravels. The aquifer is underlain by marly bedrock of Miocene age that dips toward the coastal lagoon of Bou-Areg. The hydrodynamic characteristics vary between 10⁻⁴ and 10⁻³ m/s; and transmissivities range between 10⁻⁴ and 10⁻¹ m²/s. The general direction of flow is SW to NE, toward the lagoon. The aquifer is crossed by the river Selouane, which also ends in the lagoon. The groundwater is characterized by a high salinity that can reach 7.5 g/l. The highest values are observed in the upstream and in the downstream sectors of the aquifer. The temporal evolution of the physico-chemical parameters depends on the climatic conditions and piezometric variations. The analysis of the spatio-temporal distribution of the physico-chemical parameters suggests different sources of groundwater salinization: the seawater intrusion, the influence of marly gypsum-bearing terrains, and the influence of anthropogenic products as the agricultural fertilizers, which cause great nitrate concentrations that vary between 80 and 140 mg/l.     

Evaluation of groundwater quality in coastal areas: implications for sustainable agriculture

Seawater intrusion is a problem in the coastal areas of Korea. Most productive agricultural fields are in the western and southern coastal areas of the country where irrigation predominantly relies on groundwater. Seawater intrusion has affected agricultural productivity. To evaluate progressive encroachment of saline water, the Korean government established a seawater intrusion monitoring well network, especially in the western and southern part of the peninsula. Automatic water levels and EC monitoring and periodic chemical analysis of groundwater help track salinization. Salinization of fresh groundwater is highly associated with groundwater withdrawal. A large proportion of the groundwaters are classified as Na–Cl and Ca–Cl types. The Na–Cl types represent effects of seawater intrusion. The highest EC level was over 1.6 km inland and high Cl values were observed up to 1.2 km inland. Lower ratios of Na/Cl and SO₄/Cl than seawater values indicate the seawater encroachment. A linear relation between Na and Cl represents simple mixing of the fresh groundwater with the seawater. The saline Na–Cl typed groundwaters showed Br/Cl ratios similar to or less than seawater values. The Ca–HCO₃ type groundwaters had the highest Br/Cl ratios. Substantial proportions of the groundwaters showed potential for salinity and should be better managed for sustainable agriculture.     

Environmental isotopic and hydrochemical study of water in the karst aquifer and submarine springs of the Syrian coast

The groundwater of major karst systems and submarine springs in the coastal limestone aquifer of Syria has been investigated using chemical and isotopic techniques. The δ¹⁸O values of groundwater range from ?6.8 to ?5.05‰, while those for submarine springs vary from ?6.34 to +1.08‰ (eastern Mediterranean seawater samples have a mean of +1.7‰). Groundwater originates from the direct infiltration of atmospheric water. Stable isotopes show that the elevation of the recharge zones feeding the Banyas area (400–600 m a.s.l.) is higher than that feeding the Amrit area (100–300 m a.s.l.). The ¹⁸O_extracted (¹⁸O content of the seawater contribution) for the major submarine springs suggests a mean recharge area elevation of 600–700 m a.s.l., and lower than 400 m a.s.l. for the spring close to Amrit. Based on the measured velocity and the percentage of fresh water at the submarine springs outlet, the estimated discharge rate is 350 million m³/year. The tritium concentrations in groundwater (1.6–5.9 TU) are low and very close to the current rainfall values (2.9–5.6 TU). Adopting a model with exponential time distribution, the mean turnover time of groundwater in the Al-sen spring was evaluated to be 60 years. A value of about 3.7 billion m³ was obtained for the maximum groundwater reservoir size.     

鸡西市地下水资源评价研究

地下水资源的正确评价是进行地下水资源科学管理的前提,也是水资源可持续利用的基础。鸡西市缺水由来已久,其中水质性缺水、资源性缺水和工程性缺水并存。在分析研究区地质、水文地质条件基础上,通过选取相关水文地质参数和方法,进而评价地下水资源量和可开采资源量,为地下水资源的合理利用提供科学依据。