Change of groundwater chemistry from 1896 to present in the Mid-Levels area, Hong Kong

In this study, groundwater quality information collected in 1896 (well waters), 1980/1981 (piezometric and seepage samples) and 2002/2003 (seepage samples) in the regions centered by the Mid-Levels area, Hong Kong Island, was compared to illustrate how groundwater quality has changed over a century and the processes controlling it. As shown by saline ammonia and nitrate levels in the late nineteenth century, groundwater was severely polluted by widespread and obvious leakage from poorly designed wastewater collection systems, although groundwater was still a drinking water source for local residents. The extremely high residual chlorines in groundwater demonstrated that large doses of disinfection agents were added to wells at that time. In view of the decline in saline ammonia and nitrate levels, groundwater became less organically polluted in the 1980s probably due to significant improvement of the design of underground sewers. However, more leakage from sources such as salty flushing water and fresh water pipes emerged in the past few decades which added complexity to groundwater chemical systems. Some chemicals were used to identify possible locations of leakages. The temporal variations of the distribution of these chemicals over the area may shed light on the rate of leakage. Leakage from service pipes seems to have improved from the early 1980s to 2002/2003. However, the area is still suffering from widespread and small-scale leakage from service pipes. More efforts should be paid to control small leakages in the future. The findings will be instructive to various government organizations such as the Water Supplies Department and Drainage Services Department to identify possible locations of unobvious leakages in the area.     

Factors affecting the groundwater chemistry in a highly urbanized coastal area in Hong Kong: an example from the Mid-Levels area

Coastal areas of Hong Kong Island are one of the most extensively urbanized areas in the world. Groundwater samples in natural slopes and developed spaces in the regions centered by the Mid-Levels area, Hong Kong Island, were collected and analyzed to investigate the natural and anthropogenic processes affecting the groundwater chemistry. The results presented may be of value to other coastal areas in the world for the identification of possible groundwater contamination sources. Groundwater samples in the natural slopes were in low total dissolved solid (TDS) (<100 mg/l), indicating that the waters were in the early evolutionary stage. Using chloride as a normalizing factor, the “non-marine” components of different major ions in the samples were calculated. The correlation analysis indicated the occurrence of weathering of plagioclase feldspars in the natural slopes. However, the breakdown of biotite and K-feldspar seems to be limited by short groundwater residence time and high resistance to weathering. The high variety in hydrochemical facies may suggest the presence of extremely heterogeneous subsurface geological conditions. In the developed spaces, groundwater samples exhibited a high range of TDS (~100–5300 mg/l) and were mainly dominated by Na–Cl and Na–Ca–Cl water types. Besides water-rock interactions, the groundwater chemistry was significantly affected by leakage from service pipes and the dissolution of concrete materials. Some chemicals were used as signatures to identify the leakage from various service pipes. The area generally suffered from widespread, but small amount of leakages, and no obvious leakage was discovered. The strong correlations among major cations and chloride suggested that even a small amount of leakage from salty flushing water pipes can significantly affect the groundwater chemistry. Groundwater is found to be highly aggressive toward concrete as supported by three commonly used aggressiveness indices. Additional Ca²⁺ may be released to groundwater by corrosion of subsurface concrete materials such as building foundations and basements. The strength of those subsurface engineering structures may be weakened. Besides, excess Ca²⁺ may deposit in the dewatering systems in the area, which may affect their performance in lowering high water tables. The findings regarding leakage from service pipes will be useful for various government organizations such as the Water Supplies Department and Drainage Services Department. Discussion of the behavior of Ca²⁺ is instructional to foundation and slope dewatering designs in the area.     

Preliminary assessment of the impacts of deep foundations and land reclamation on groundwater flow in a coastal area in Hong Kong, China

Many coastal areas have been intensively urbanized because people living and working on or near coastlines are increasing. Land reclamation from the sea and high-rise buildings are common approaches to satisfying the growing needs for more housing and other land use. Coastal areas are usually the ultimate discharge zones of groundwater systems. Using a coastal area in Hong Kong as a case study, this paper discusses the change in a groundwater system due to land reclamation and construction of building foundations in a coastal area. The upper part of the study area is in a nearly natural state, whereas the lower part is probably one of the most extensively developed areas in the world. It is evident that the groundwater flow system in this area has been changed over the last century. The piezometers in the transitional zone between the natural slopes and the urbanized areas indicate significant response to rainfall and obvious upward groundwater flow. To understand these piezometric responses to rainfall, a cross section is selected for detailed study using a two-dimensional multilayered numerical model. The parameters and structure of the aquifer system are calibrated by comparing the simulated and observed water levels. To reproduce the observed behavior of the groundwater system, the model has to include two important characteristics: a highly permeable zone at the rockhead and a reduction in hydraulic conductivity of 14–20 times in the urbanized area. The simulation demonstrates that both land reclamation along the coastline and deep foundations have contributed to the modification of the flow system, but the deep foundations have the most profound impact, especially when a high conductivity zone is present at the rockhead.

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Resumen Muchas áreas costeras han sido urbanizadas de manera intensiva, debido a la presión creciente de la gente que quiere vivir y trabajar en estos sitios. Los terrenos arrebatados al mar y los edificios de gran altura, son las respuestas comunes para satisfacer las necesidades de mas vivienda y usos nuevos para el suelo. Las áreas costeras son comúnmente las zonas de descarga final de los sistemas de agua subterránea. A través de un área costera en Hong Kong, tomada como estudio de caso, este artículo discute el cambio causado en un sistema de agua subterránea, debido a la recuperación de terrenos anteriormente cubiertos por el mar y a la construcción de cimientos de edificios en la zona costera. La parte más alta de la área de estudio está casi en su estado natural, mientras que la parte baja es probablemente una de las áreas más extensas en su tipo y más desarrolladas en el mundo. Es evidente que el sistema de flujo del agua subterránea en esta área ha sido cambiado a lo largo del último siglo. Los piezómetros en la zona transicional, entre los taludes naturales y las áreas urbanizadas, muestran una respuesta notable a la lluvia y un flujo evidente hacia arriba del agua subterránea. Para entender estas respuestas piezométricas a la lluvia, se seleccionó una sección vertical para estudio detallado, utilizando un modelo numérico bidimensional multicapa. Los parámetros y estructura del sistema acuífero son calibrados mediante la comparación de los niveles de agua observados y simulados. Para reproducir el comportamiento observado del sistema de agua subterránea, el modelo ha incluido dos características importantes: Una zona altamente permeable en la parte más elevada y una reducción de 14 a 20 veces en la conductividad hidráulica, dentro de la zona urbanizada. La simulación demuestra que tanto los terrenos recuperados del mar, como las cimentaciones profundas a lo largo de la línea de costa, han contribuido a la modificación del sistema de flujo, pero las cimentaciones profundas han causado el mayor impacto, especialmente cuando se presenta una zona de alta conductividad en la parte más elevada del área.

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Résumé La plupart des zones côtières ont été intensivement urbanisé due à la croissance de la population qui travaille et vive sur les zones littorales. La récupération des terrains sur la mer ainsi que la construction des grandes immeubles sont les moyens usuels utilisés pour satisfaire les demandes accrues de logement. Dhabitude les zones côtières représentent lexutoire final des aquifères. En utilisant la zones côtière de Hong Kong comme un étude de cas cet article analyse les changements dans les systèmes aquifères produits par la récupération des terrains et par les fondations des grandes immeubles. Tendis que la partie supérieure de la zone étudiée se trouve presque à létat naturel, la partie inférieure représente une des zones les plus développée du monde. Il est donc évident que la circulation des eaux souterraines a été modifiée pendant le dernière siècle. Les piézomètres remplacés entre les versants et la zone urbanisée montrent une réponse significative aux précipitations ainsi quune hausse générale des niveaux. Pour mieux comprendre la réponse des niveaux aux plues on a modélisé lécoulement dans une coupe vericale en utilisant un modèle numérique multicouches. Les paramètres et la strucure du système aquifère ont été calés en comparant les niveaux calculés et mesurés. Affin de reproduire les niveaux mesurés le modèle doit considérer deux caratéristiques importantes: une zone périglaciaire à grande perméabilité et une diminution jusqu à vingt fois de la perméabilité dans les zone urbanisées. La simulation a mis en évidence que les récupération des terrains au long du littoral aussi bien que les fondations profondes ont modifié lécoulement mais que les dernières ont limpact le plus important surtout lorsquil sagit de la zone périglaciaire à grande perméabilité.

     

Confined groundwater near the rockhead in igneous rocks in the Mid-Levels area, Hong Kong, China

It is customary in Hong Kong to assume that the hydraulic conductivity of weathered igneous rocks decreases with depth or as the rock mass becomes less weathered. Such a hydraulic conductivity pattern can only lead to an unconfined aquifer. This paper presents a case study in the regions in and around the Mid-Levels area in Hong Kong regarding a possible relatively high hydraulic conductivity (K) zone and confined groundwater along the rockhead. The Mid-Levels area is located at the lower part of the north-facing slopes of Victoria Peak on Hong Kong Island and is prone to landslides. Although this site has a long history of geotechnical studies because of extensive urban development along the coast and public concern on slope stability, hydrogeology of the site remains poorly understood. This paper reexamined the hydraulic conductivity data in 7 boreholes conducted in the 1970s and found that 4 of them indicate an increase in K at the rockhead. Groundwater conditions revealed by tunnel construction at the coast suggest that K close to the rockhead is about 10 times greater than above rockhead. A careful analysis of storm response of a piezometer group with tips in different depths indicates that there was an upward flow from the bedrock to the colluvium. A field study of two overflow standpipes conducted by the authors showed that the water level can be 0.64 and 3.73 m above the ground surface, which illustrates that the deep groundwater is significantly artesian. A search of the archived site investigation reports from the government and private companies has led to an identification of about 24 sites with overflow boreholes, which suggests that overflow phenomenon is quite common in the study area. The paper then concludes that in the study area there is a relatively high K zone along the rockhead and the groundwater in the zone is confined. It is recommended that geotechnical engineers should carry out a more careful field study on an overflow borehole because such a borehole indicates a confined groundwater condition important for slope stability study and foundation design.     

Tracing submarine groundwater discharge flux in Tolo Harbor,Hong Kong (China)

Submarine groundwater discharge (SGD) is an important pathway for groundwater and associated chemicals to discharge to the sea. Groundwater levels monitored along a transect perpendicular to the shoreline are used to calculate SGD flux from the nearshore aquifer to Tolo Harbor, Hong Kong (China). The calculated SGD flux—recharge/discharge measured with Darcy’s Law methods—agrees well with estimates based on geo-tracer techniques and seepage meter in Tolo Harbor during previous studies. The estimated freshwater SGD is 1.69–2.0 m²/d at the study site and 0.3?±?0.04 cm/d for the whole of Tolo Harbor, which is comparable to the river discharge (0.25?±?0.07 cm/d) and precipitation (0.45?±?0.15 cm/d). The tide-driven SGD in the intertidal zone is 13.98–17.59 m²/d at the study site and 2.42?±?0.56 cm/d for the whole of Tolo Harbor. The SGD occurring in the subtidal zone and the bottom of Tolo Harbor is 3.12?±?4.63 cm/d. Fresh SGD accounts for ~5% of the total SGD, while the rest (~95%) is contributed by saline SGD driven by various forces. About 96% of the tide-driven SGD in the intertidal zone occurs in the ebbing tide period because the head difference between the groundwater level and sea level is great during this period. Tide-driven SGD in the spring tide is ~1.2 times that during neap tide. The tidal fluctuation amplitude and tide-driven SGD in the intertidal zone are positively correlated to each other; thus, a spring neap variation of the tide-driven SGD is observed.     

Evolution of the groundwater environment under a long-term exploitation in the coastal area near Zhanjiang, China

Aquifers consisting of unconsolidated sediments in the coastal area near Zhanjiang in southern China are grouped into the shallow, middle-deep and deep aquifer systems. Groundwater exploitation began in the 1950s in this district and has increased from year to year since 1980. Measurements of groundwater levels and monitoring data of groundwater chemistry at some 60 wells since 1981 are examined to analyze the evolution of hydrodynamics and hydrochemistry in the coastal aquifers. The results indicate that groundwater levels in the middle-deep and deep aquifer systems have fallen continuously and the extents of the depression cones in water levels have increased in the past two decades, even though the water levels recovered to some degree during the period of 1997–2001. In 2004, the lowest water levels in the middle-deep and deep aquifer systems were 23.58 and 21.84 m below sea level, respectively. The groundwater has TDS ranging from 40 to 550 mg/L, and is of low pH, commonly varies between 4 and 7. Concentrations of total iron and manganese exceed the concentration limits of the drinking water standards. The hardness is in the range of 10–250 mg/L. Chloride contents of the groundwater range from 10 to 60 mg/L. The chloride and TDS do not show systematically increasing trends. Although the water levels in the exploitation center near the coast are significantly lower than the sea level and the depression cones of water levels in the middle-deep and deep aquifer systems have expanded to the sea, sea water intrusion has not been observed until recently. This phenomenon is quite unique in the coastal area near Zhanjiang.     

Assessment of soil radon potential in Hong Kong, China, using a 10-point evaluation system

Radon and its progenies have been ranked second of being responsible for lung cancer in humans. Hong Kong has four major groups of uranium-rich plutonic and volcanic rocks and is suffering from radon emanated therefrom. However, there is a lack of radon potential maps in Hong Kong to resolve the spatial distribution of radon-prone areas. A ten-point radon potential system was developed in Germany (2005) to predict radon potential using both the in situ geogenic and geographic parameters under hierarchical ranking. Primarily, the ten-point system requires the desk study of the geological environment of sampling sites, which has an advantage of saving resources and manpower in extensive radon potential mapping over the traditional soil radon concentration sampling method. This paper presents a trial of radon potential mapping in Hong Kong to further verify the system. Despite some slight departures, the system demonstrates an acceptable correlation with soil radon concentrations (R ² = 0.62–0.66) from 768 samples of mainly intermediate radon potential. Hong Kong has a mean soil radon concentrations of 58.9 kBqm^?3, while the radon potential from the ten-point system achieves an average of 4.93 out of 10 over the territory. The vicinity of fault zone showed high soil radon concentrations and potentials, which were conducive to uranium enrichment and rapid soil-gas diffusion near faults. High uranium-238 content in soil was found to cause high soil radon concentration with a large R ², 0.84. The Jurassic granite and volcanic crystal tuff cover more than 85 % of the whole Hong Kong area, and they show relatively high radon concentrations (Geometric mean 83 and 49 kBqm^?3, respectively) which are associated with their high uranium contents (Geometric mean 234 and 197 Bqkg^?1, respectively). While indoor radon concentration is an important factor for radon risk assessment, this study has not considered the correlation between indoor radon concentration and radon potential. The reason is that almost all buildings in Hong Kong are high-rise buildings where indoor radon concentrations are governed only by the radium content in the building materials and the ventilation conditions.     

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.     

Study on the groundwater sustainable problem by numerical simulation in a multi-layered coastal aquifer system of Zhanjiang,China

Assessing sustainability of coastal groundwater is significant for groundwater management as coastal groundwater is vulnerable to over-exploitation and contamination. To address the issues of serious groundwater level drawdown and potential seawater intrusion risk of a multi-layered coastal aquifer system in Zhanjiang, China, this paper presents a numerical modelling study to research groundwater sustainability of this aquifer system. The transient modelling results show that the groundwater budget was negative (\(-3826\times 10^{4}\) to \(-4502\times 10^{4 }\,\hbox {m}^{3}/\hbox {a}\)) during the years 2008–2011, revealing that this aquifer system was over-exploited. Meanwhile, the groundwater sustainability was assessed by evaluating the negative hydraulic pressure area (NHPA) of the unconfined aquifer and the groundwater level dynamic and flow velocity of the offshore boundaries of the confined aquifers. The results demonstrate that the Nansan Island is most influenced by NHPA and that the local groundwater should not be exploited. The results also suggest that, with the current groundwater exploitation scheme, the sustainable yield should be \(1.784\times 10^{8}\, \hbox {m}^{3}/\hbox {a}\) (i.e., decreased by 20% from the current exploitation amount). To satisfy public water demands, the 20% decrease of the exploitation amount can be offset by the groundwater sourced from the Taiping groundwater resource field. These results provide valuable guidance for groundwater management of Zhanjiang.     

Some factors affecting TDS and pH values in groundwater of the Beihai coastal area in southern Guangxi,China

Groundwater of low total dissolved solids (TDS) of 10 mg/L and low pH ranging commonly from 4.0 to 7.0 occurs in the unconsolidated unconfined and confined aquifers in the coastal plain near Beihai, Guangxi, China. Minerals in the unconsolidated sediment of Quaternary are predominated by quartz (more than 50%) with small amount of clay minerals, such as kaolinite, illite and chlorite. SiO₂ accounts for most (more than 70%) of the chemical compositions of the sediments. The sediments contain low concentrations of soluble constituents (below 300 μg/g) and are predominated by SO₄. Abundant recharge from low-TDS precipitation and a long time’s dissolution of the unconsolidated sediments containing small amount of soluble compositions lead to low TDS of the groundwater in the area.     

Heat transport in a coastal groundwater flow system near De Panne, Belgium

Temperature distribution and heat transport are studied in a coastal aquifer at De Panne in the western Belgian coastal plain. Field observations include temperature profiles of groundwater in the dunes and temperature measurements at the water table in a profile on the shore. Freshwater–saltwater distribution is known from previous studies. These are used to constrain a density-dependent model simulating the freshwater–saltwater distribution and heat transport using the SEAWAT code. The yearly fluctuation of the groundwater temperature in the phreatic aquifer under the dunes, shore and sea, and the influence of a tidal inlet in the dunes are simulated. The observations show that seawater temperature variations determine the temperature variations on the shore whereas atmospheric temperature changes determine this in the dunes. Yearly temperature fluctuations imposed at the water table propagate mainly vertically in the aquifer with only limited lateral influence. Heat transport is mainly convection dominated. Thickness of the surficial zone is determined by the amplitude of the groundwater temperature at the water table and the groundwater flow. Establishment of a tidal inlet in the dunes results in asymmetric temperature profiles under and in the vicinity of it.     

Degradation of groundwater quality in coastal aquifer of Sabratah area,NW Libya

Overextraction of groundwater is widely occurring along the coast where good quality groundwater is at risk, due to urbanization, tourist development and intensive agriculture. The Sabratah area at the northern central part of Jifarah Plain, Northwest Libya, is a typical area where the contamination of the aquifer in the form of saltwater intrusion, gypsum/anhydrite dissolution and high nitrate concentrations is very developed. Fifty groundwater samples were collected from the study area and analysed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters electrical conductivity, sodium, potassium, magnesium, chloride and sulphate which can be attributed to seawater intrusion. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 30 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high nitrate concentration towards the south of the region. Seawater intrusion and deep salt water upconing result in general high SO₄ ^2? concentrations in groundwater near the shoreline, where localized SO₄ ^2? anomalies are also due to the dissolution of sebkha deposits for few wells in the nearby sebkhas. Upstream, the increase in SO₄ ^2? concentrations in the south is ascribed to the dissolution of gypsum at depth in the upper aquifer.     

Geochemistry of carbonate precipitation from the groundwater in a coastal region

Groundwater samples were collected from a coastal region of Andhra Pradesh to assess the possible conditions of the formation of carbonates. The area experiences a semi-arid climate and is underlain by khondalites, over which the Quaternary sediments occur. The study of the geochemistry of groundwater indicates that groundwater is mostly of fresh, with alkaline nature. The study further suggest that the breakdown of feldspars as kaolinite during rock-water interaction, releases Ca²⁺. Soils/weathered products contribute high CO₂ under the open system. The Ca²⁺ and CO₂ are added to the groundwater through the infiltrating recharge water. They subsequently precipitate as fine-grained carbonates in the weathering profile due to evapotranspiration under a freshwater environment.     

西南某岩溶区地下水系统示踪试验与解析

以西南某典型岩溶区为例,解析示踪试验在岩溶管道连通性以及获取水文地质参数中的应用。选择落水洞为投放点,分别从落水洞西侧和东侧寻找地下水出露点作为接收点,判别落水洞地下径流的实际去向以及落水洞与接收点之间的水力联系。结合Qtracer2软件对示踪试验成果进行定量解析,确定示踪剂回收率、地下水平均流速、最快流速,估算出岩溶管道结构特征和水文地质参数。结果表明：落水洞与接收点JS01、JS03之间不存在直接水力联系;落水洞与接收点JS02存在水力联系且岩溶管道极为发育,含水介质不均匀,地下水运移路径较为通畅,为典型的紊流流态;落水洞地下径流的主要方向是由西向东,但在丰水期雨量较大期间,接收点JS04能够接收到荧光素钠,说明丰水期水位上涨后两者间会有水力联系,导致部分水量向落水洞西侧排泄。     

Tidal effects of groundwater levels in the coastal aquifers near Beihai, China

Four times of observation of the ocean tide and groundwater levels in the coastal aquifers near Beihai, China show that fluctuation in the tide-induced groundwater levels follows the tide, with the highest and lowest water levels corresponding to the high water level syzygy tide and the low water level neap tide. The tidal coefficient is less than 0.5, decreasing approximately exponentially with the distance from the coast. The tide can affect the groundwater levels at observation wells as far as about 4,200 and 3,300 m in the southern and northern coasts in Beihai. Observations and spectrum analyses of the time series of the tide and water levels suggest that the tide and water levels have similar changes with complex fluctuations of a long period of 14.37 days and two short periods of 24.7 and 12.5 h. Time lags of water levels to the tide at observation wells last several hours and increases roughly linearly with the distance from the coast. Mathematic models consisting of a periodic term plus a linear term are established to describe the changes in the tide and the groundwater levels. The periodic terms for the tide and water levels are constructed using finite Fourier’s series consisting of 7 to 11 terms other than a single term of a sine function in earlier work. Computed water levels with the models can fit the observed water levels with reasonable accuracy and satisfactory prediction of the changes in the water levels is also obtained.     

Assessment of hydrochemistry and groundwater quality in the coastal area of South Chennai,India

An attempt has been made to evaluate the water quality in the fast-growing coastal area of South Chennai. Groundwater samples were collected from selected locations and analyzed for major physico-chemical parameters. Experimental results show that the water has alkaline with pH varying from 7.2 to 8.2. Concentrations of Na and Cl were positively correlated with EC and elevated levels of these parameters near the coastal region, especially in the northern end of the study area, indicating the influence of seawater intrusion. Piper diagram identified Na–Cl as the dominant type of water in most of the samples. The presence of Ca–Cl facies in the groundwater suggests the possible ion exchange (Na with Ca) reaction in the aquifer. Molar ratios of Cl/HCO₃ and Mg/Ca showed a higher value (>1) in many samples, which confirmed the influence of seawater intrusion on water quality. The Water Quality Index (WQI) of the study area ranged between 8 and 116, the highest recorded being at Thiruvanmiyur and the lowest at Muttukkadu. However, total hardness values show that 64% of the samples were hard or very hard in nature. The results of SAR, Na%, and PI show that majority of the samples are suitable for irrigation purposes. A comparison of spatial distribution maps of water quality parameters with those of WQI shows that groundwater quality has highly deteriorated in the Thiruvanmiyur region, located on the northeast part of the study area. Good-quality water is found at the southeast part of the study area, namely, Muttukkadu. This study indicates that urbanization and seawater intrusion have heavily affected the groundwater quality of South Chennai coastal area.     

The characteristics and distribution of International Medical Graduates from mainland China, Taiwan, and Hong Kong in the US

As healthcare systems around the world are facing increasing physician shortages, more physicians are migrating from low to high income countries. Differences in medical education and international interaction may have significant effect on physician flows. The Chinese Medical Graduates (CMGs) in the US present an interesting case to examine this effect. This paper evaluated the current number and historical trends of CMGs in the US from mainland China, Taiwan, and Hong Kong comparing their differences and similarities in terms of demographic and geographic characteristics. Since 2000, the number of CMGs in the US showed a consistent upward trend at a rate of approximately 206 additional graduates per year. In 2010, there were 8,797 CMGs in the US. Compared to CMGs from mainland China, CMGs from Taiwan and Hong Kong were much older. Much larger proportion of Taiwan and Hong Kong CMGs were male. However, they were more likely to practice in solo settings than mainland CMGs. The vast majority of CMGs are concentrated in urban areas and no significant differences were found for their distributions in underserved areas. However, a larger proportion of Taiwan and Hong Kong CMGs were in western coastal states; whereas a larger proportion of mainland CMGs were located in eastern coastal states. Fluctuations in CMG numbers in the US reflect the significant differences within the medical education systems among the three. The seemingly homogenous CMGs in the US do show significant differences. Given the magnitude and historical trends of migration of CMGs to the US, further exploration of its causes and impact is needed.     

山东高密地区高F区水文地球化学特征

F中毒是在特定的地理环境中发生的一种生物地球化学性疾病。高密地区F中毒是由饮用水引起的。根据国家饮用水的标准,F〉1mg／L称为高F地下水。高密地区北部六镇地下水的F含量一般为5mg／L,极值达到18．00mg／L,当地居民长期饮用高F水,对身心健康造成了极大的危害。高F地下水的形成受多种因素的影响和制约,高密地区的地势南高北低,最高海拔92m,最低海拔7．5m。地下水主要以大气降水为补给源,水位标高由南向北逐渐降低。通过对高密市的地理、地貌、岩石、水化学类型等特征的分析,阐明了高密市高F地下水的成因,并且提出了合理可行的治理措施。