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.     

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.     

香港九龙复活破火山的鉴别及其地质意义

香港主城区座落在香港岛一九龙地区的九龙花岗岩体上,该花岗岩体平面形态呈直径约11km的圆形,周边火山岩群山环绕,构成特殊的圆形盆地地貌,以往曾有人认为是陨石坑。笔者根据前人地质资料分析并经实地考察,认为该地貌形态实为大致以尖沙咀为中心的一个大型晚中生代复活破火山机构,九龙花岗岩体为破火口塌陷后侵位的中央侵入体,周围火山地层产状围斜内倾,发育环形断裂（主要为高角度正断层）和放射状断裂,具典型复活破火山特征,可称之为“九龙复活破火山”。     

Changes to the groundwater system, from 1888 to present, in a highly-urbanized coastal area in Hong Kong, China

Historical groundwater levels in a coastal region of Hong Kong Island (China) were reviewed and compared with data collected recently to reveal changes to the groundwater regime over the last century. The coastal springs and seeps have disappeared and the lower boundary of the seepage zone has moved uphill. Groundwater was found to be flowing upward along the boundary of natural slopes and urbanized areas. Artesian flows were commonly noted in the deep piezometers in the lower urbanized areas. Moreover, an overall rise in water levels in a 10-year period was observed in the urbanized areas, except in areas with good drainage. Extensive urbanization since the 1950s has included large-scale land reclamation, deep foundations of high-rise buildings, an underground transport system, water mains and horizontal drains in slopes; the effect has been a slow but gradual increase in the water level of the hillslope groundwater system. Further urbanization activities such as the westward extension of the underground transport system and new major drainage systems in the slopes, should be assessed for possible further changes to the groundwater system. The results presented here may serve as reference for other highly-urbanized coastal areas in the world.     

香港地区边坡防护与治理

自开埠以来香港地区边坡事故一直不断。香港政府多年来积极进行边坡的防护治理,成效显著。讨论了香港地区岩土边坡破坏的主要原因、防治滑坡的工程措施及边坡管理系统。香港的边坡防治经验值得内地借鉴。     

香港花岗岩地貌地质旅游的开发

地质旅游利用现有的地质资源，以一种崭新的角度去发展可持续性的旅游景点。香港地少人多，发展旅游吸引点是极度困难的。香港陆地约有30％为花岗岩覆盖，其中的一半已在城市之下，其余的则拥有相当吸引人的地质景象，有极大潜力发展地质旅游。除吸引地质生态有关游客外，在花岗岩地区开发地质旅游，更容易普及地球科学，同时增强公众对地质地貌之欣赏能力，提高环保及地质保护意识。不过，于香港花岗岩区发展地质旅游所遇到的困难亦不少，主要来自规划、行政及安全的问题，当中需要政府、地区民众及地质旅游工作者并肩合作，寻求最佳解决方法。     

香港五号干线前期工程大直径钻孔桩塌孔事故的处理

主要介绍在香港五号干线前期工程石围角至柴湾角段的灌注桩桩墙施工中的塌孔事故的处理。     

香港九龙破火山的地层结构与划分讨论

香港岛—九龙半岛地区以往火山地层的划分主要依据岩性特征,基本不考虑火山构造和火山岩相的鉴别,由于陆相火山岩区特有的岩性岩相时空上的复杂多变,导致地层组越划越多,不能合理进行区域地层对比,更无法通过火山地层划分恢复古火山活动过程。笔者等在该地区开展了野外路线地质调查和火山构造—火山岩相研究,鉴别出九龙复活破火山机构,在此基础上确定火山地层主要由同一期普林尼式喷发形成的冷却单元构成,有类似的地层结构,结合年龄资料和区域地质对比,它们基本上可归入同一地层组;同时,分析了陆相火山地层的划分方法,指出岩石地层单位划分不能作为主要方法;冷却单元或流动单元才是合理划分陆相火山地层的基本单位。     

香港山泥倾泻防灾减灾管理体系

香港曾因频繁的斜坡重力活动发生人员财产重大灾害损失,1977年将斜坡安全纳入政府职责后,建立了一套全面统一的管理体系,这使事故及人员伤亡数量大大降低,为世界斜坡安全管理提供了成功案例。基于实地考察访问、交流研讨和文献资料查询,梳理并总结香港斜坡管理体系、经验模式,为内地相应地区和相关部门的防灾减灾体系建设提供借鉴。     

人工边坡绿化种植技术及其在香港的应用

在人工边坡上进行绿化种植不仅美化环境，而且有控制冲蚀和稳定斜坡的作用，设计人员应考虑将植被作为所有土和风化岩石的人造斜坡的基本保护方法。香港在边坡绿化种植方面积累了成功的经验。文章概述了在人工边坡表面进行绿化种植的基本原理及其综合效应，详细介绍香港地区的人工边坡绿化种植技术，包括设计思路、设计过程、施工技术和维护管理等方面，并为当前中国内地人工边坡绿化种植技术的推广和研究提出了建议。     

Geochemical characteristics of the slip zones of a landslide in granitic saprolite,Hong Kong: implications for their development and microenvironments

Geochemical investigations of the slip zones of a landslide in granitic saprolite revealed that they have signatures distinct from their host materials. These distinctions include stronger Si depletion, higher Al enrichment, greater LOI, significant fixations of Mn, Ba and Ce, stronger negative Eu anomalies, and greater accumulations of other rare earth elements (REE). Altogether, these geochemical characteristics indicate that: (a) the slip zones have greater abundance of clays, consistent with field and microscopic observations; (b) concentration of clay size particles within the slip zones may have been from downward leaching and deposition, and lateral transportation of Al-Si solutions and colloids through pores and fractures within the saprolite; and (c) there were prevailing oxidation and poor drainage, and occasional reduction conditions within the slip zones. It was concluded that geochemical analyses could be effective in gathering clues for understanding the development and nature of slip zones in landslide investigations.     

Impact of human activities on quality and geochemistry of groundwater in the Merdja area,Tebessa, Algeria

Chemical data are used to clarify the hydrogeological regime in the Merdja area in Tébessa, as well as to determine the status of water quality in this area. Groundwater from the aquifer in the Merdja area can be divided into two major groups according to geographical locations and chemical compositions. Water in the center part of the area of study is characterized by the dominance of chloride, sulfate, sodium, and potassium; whereas waters in the limestone aquifers in the west are dominated by the same cations but have higher concentrations of bicarbonate. Stable isotopes show that the Tébessa aquifers contain a single water type, which originated in a distinct climatic regime. This water type deviates from the Global Meteoric Water Line (MWL), as well as from the Mediterranean meteoric water line. The water is poor in tritium, and thus can be considered generally older than 50 years. Piezometric map suggests that water is moving from the west towards the center of the studied area, and from east towards center. Degradation of water quality can be attributed to agricultural fertilizers in most cases, although the wadi El Kebir River is a contributor to pollution in the middle part of the studied area.     

Vulnerability mapping of shallow groundwater aquifer using SINTACS model in the Jordan Valley area, Jordan

Jordan Valley is one of the important areas in Jordan that involves dense agricultural activities, which depend on groundwater resources. The groundwater is exploited from an unconfined shallow aquifer which is mainly composed of alluvial deposits. In the vicinity of the Kafrein and South Shunah, the shallow aquifer shows signs of contamination from a wide variety of non-point sources. In this study, a vulnerability map was created as a tool to determine areas where groundwater is most vulnerable to contamination. One of the most widely used groundwater vulnerability mapping methods is SINTACS, which is a point count system model for the assessment of groundwater pollution hazards. SINTACS model is an adaptation for Mediterranean conditions of the well-known DRASTIC model. The model takes into account several environmental factors: these include topography, hydrology, geology, hydrogeology, and pedology. Spatial knowledge of all these factors and their mutual relationships is needed in order to properly model aquifer vulnerability using this model. Geographic information system was used to express each of SINTACS parameters as a spatial thematic layer with a specific weight and score. The final SINTACS thematic layer (intrinsic vulnerability index) was produced by taking the summation of each score parameter multiplied by its specific weight. The resultant SINTACS vulnerability map of the study area indicates that the highest potential sites for contamination are along the area between Er Ramah and Kafrein area. To the north of the study area there is a small, circular area which shows fairly high potential. Elsewhere, very low to low SINTACS index values are observed, indicating areas of low vulnerability potential.     

Analysis of rainstorm-induced slide-debris flows on natural terrain of Lantau Island, Hong Kong

Lantau Island, the largest outlying island of the territory of Hong Kong, experienced a severe rainstorm on 4–5 November 1993, which induced >800 slope failures on natural terrain there. Detailed field investigations were carried out to study the failure modes, in relation with various influencing factors. It was found that the occurrence of slide-debris flows has a close relationship with bedrock geology, slope gradient, vegetation cover and micro landform. The failure modes of slide-debris flows may be classified into translational slides and rotational slides, and the former are predominant. Analysis of the hydrological response of colluvial slopes during the rainstorm indicated that the majority of the failures were caused by the development of a perched water table in the thin surface layer of colluvium of volcanic origin due to infiltration during the heavy rain. Undisturbed soil samples from south Lantau have been subjected to anisotropically consolidated undrained compression tests at comparatively low stress levels. Constant deviatoric stress path tests (CQD) simulating the stress path in the field at in situ stress levels have been performed to investigate soil behavior. The CQD test results indicate that the material of slopes at undisturbed state is brought to dilation because of the increase in pore water pressure caused by infiltration of rain water. For a translational slide, the displacement, resulting from dilation, may destroy cohesion along the failure surface and locally within the interior of the slide. The surplus water during the intense rainstorm was able to equilibrate the reduction in pore pressure caused by dilation, and the dilation and displacement may be further increased. The strain-softening after significant strains triggered debris flow mobilization. However, for a rotational slide, the increase in pore water pressure caused by surplus water infiltration during the intense rainstorm could not equilibrate the reduction in pore pressure caused by dilation, much or even all of the sliding block could not mobilize into a debris flow.     

Late Jurassic to Early Cretaceous volcanism of Hong Kong: Insights from the Ping Chau Formation

The vast expanse of Mesozoic igneous rocks in Hong Kong contain important geological records of late Mesozoic magmatic events and tectonic processes from the coastal region of Southeast China. Of these,the Ping Chau Formation in the northwestern New Territories is the youngest known stratum. We perform a detailed study of the volcanic rocks of the Ping Chau Formation utilizing zircon U-Pb dating,with major and trace elements geochemistry. LA-ICP-MS zircon U-Pb data reveal Early Cretaceous age from two volcanic rock samples, with zircon crystallization from magmas at 140.3 ± 0.8 Ma and 139.3 ± 0.9 Ma,respectively. These rocks have high contents of total alkalis(Na_2O + K_2O = 5.58-9.45 wt.%), high-field-strength elements and light rare earth elements, conspicuous negative Eu anomalies, and depletions in Nb, Ta, Ti, Sr, Ba and P. Using this data, in combination with previous studies on the late Mesozoic volcanic belt in Southeast China, we propose that the volcanic rocks of the Ping Chau Formation probably originated from deep melting of the crust in a back-arc extensional setting induced by the subduction of the paleo-Pacific Plate. This formation represents the final stages of Early Cretaceous volcanic activity in Hong Kong, as associated with large-scale lithospheric extension, thinning and magmatism. Our results provide new information that can be used in evaluating the significance of Early Cretaceous volcanism and tectonics in Southeast China.     

香港西贡粮船湾组火山岩石柱区次生节理研究

在香港世界地质公园西贡火山岩区,白垩纪粮船湾组发育有目前世界已知面积最大的流纹质碎斑熔岩石柱群。在详细的野外地质调查基础上,对粮船湾组火山岩石柱区的次生节理进行了研究,并探讨了柱状节理岩体的构造变形特征及过程。粮船湾组火山岩石柱区次生节理主要包括陡倾的纵节理及缓倾的横节理。前者多具有共轭剪节理的特征,形成于不同方向的挤压构造环境下;后者切割早期构造面理,形成于重力垮塌的构造环境,多发展为正滑断层。粮船湾组火山岩石柱总体上受次生节理改造明显,共轭节理反演的构造应力环境表明石柱区在140 Ma左右经历了快速的构造转换,主挤压应力由近NE-SW向转换为近NW-SE向,可能与莲花山断裂的构造活动相关。     

香港国家地质公园粮船湾组火山岩岩石学研究

在香港国家地质公园西贡火山岩园区,核心地质景观是白垩纪粮船湾组(Kkh)火山岩优美的六方形石柱(柱状节理),它们的岩石类型长期存在熔岩和火山碎屑岩之争。笔者等经野外调查和薄片岩石学研究,确认粮船湾组火山岩实属一种特殊的熔岩——流纹质碎斑熔岩,以普遍的柱状节理、斑晶具有碎斑结构和珠边结构、基质发育霏细结构和流动构造为特征;它们不仅代表了香港地区中生代最晚期火山喷发的产物,而且构成了西贡破火山机构的中央侵出相岩穹。推断粮船湾组火山岩石柱是地球上已知面积最大的流纹质碎斑熔岩石柱群(～150 km2),目前所见的火山岩石柱仅是长期剥蚀后的残余部分。     

Assessment of groundwater pollution due to tannery industries in and around Dindigul, Tamilnadu, India

The overexploitation of groundwater in some parts of the country induces water quality degradation. The untreated industrial effluents discharged on the surface causes severe groundwater pollution in the industrial belt of the country. This poses a problem of supply of hazard free drinking water in the rural parts of the country. There are about 80 tanneries operating in and around Dindigul town in upper Kodaganar river basin, Tamilnadu, India. The untreated effluents from the tanneries have considerably affected the quality of groundwater in this area. To assess the extent of groundwater deterioration, a detailed analysis of groundwater quality data has been carried out. The concentration of cations such as Calcium (Ca²⁺), Magnesium (Mg²⁺), Sodium (Na⁺) and Potassium (K⁺), and anions such as Bicarbonate (HCO₃^–), Sulphate (SO₄^2–), Chloride (Cl^–) and Nitrate (NO₃^–) in the groundwater have been studied. Apart from these constituents, pH, electrical conductivity (EC), total dissolved solid and total hardness (TH as CaCO₃) were also studied. The correlation of these constituents with the EC has been carried out. The highest correlation is observed between EC and chloride with a correlation coefficient of 0.99. Progressive reduction in correlation coefficients for Mg²⁺, (Na⁺ + K⁺), Ca²⁺ and SO₄^2– are observed as 0.91, 0.87, 0.86 and 0.56, respectively. It is found that the quality of groundwater in the area under investigation is deteriorated mainly due to extensive use of salt in the leather industries.     

Comparison of organic pollutants in urban deposits of Guangzhou and Hong Kong metropolitan areas

With the rapid development of industrialization and urbanization in the Pearl River Delta region, organic as well as inorganic pollution is becoming a major environmental concern. Urban deposits including road dusts, corresponding gully sediments and topsoils proved to be useful tools for assessing the level and distribution of contaminants in metropolitan areas. Most of the previous studies utilizing urban deposits, however, focused on inorganic pollutants, while data on organic pollutants are rare. In this study, therefore, the organic pollutants in urban deposits of Hong Kong and Guangzhou were systematically investigated in terms of their abundance, composition and distribution. The road dusts, gully sediments and vehicular tunnel dusts as well as soils from different urban locations with variable traffic volumes （less than 1000 to more than 75000 AADT） were examined. The results indicated that vehicle-emitted particles were the major source of organic pollutants, while the contributions from background soils were very limited. Surprisingly, the soil in a remote island of Hong Kong with no vehicular traffic has also shown signs of pollution from vehicular particles likely through dry-wet atmospheric deposits. In general, the characteristics of organic pollutants in urban dusts from both cities are comparable although there were also some significant differences. For example, the amount of extractable organic matter in urban deposits of Hong Kong was significantly higher than that of Guangzhou. Differences in their extractable asphaltene contents not only reflected the differences in quality and types and fuels used in these cities, but also sample residence times, and thus different extents of weathering processes.     

Distribution and concentrations of anthropogenic platinum group elements in the surface environment of Hong Kong

Ecotourism environmental impact assessment is a traveling activity relevant influence prediction and appraisal. And the setting-up of the index system is very important to implement the appraisal of environmental impact of ecological travel. According to the index system, natural ecological environment, humane social environment, the environment of tourist resources and the atmosphere of capacity of tourist environment, four major systems form the first index. Each system formed the second index of several key elements. In addition, it is a key step to appraise the sureness of the factor weight, which influences the rationality of the result directly. Daily method of weighting has the Delphi＇s and the AHP. According to ＂Grade form of characteristic value of Standard of rating for quality of tourist attractions＂ which the National Tourism Administration issues, the paper takes the Jingshan mountains ecological tourist zone as an example and adopts AHP to weight the factors mainly, assisted with the Delphi＇s by the help of computer. The Jingshan ecological tourist zone is good. The result of calculation, comprehensive value of 8.35 after establishment, shows that it doesn＇t change dramatically, attributing to the index of natural ecological environment like atmosphere, quality of surface water, acoustics environment and vegetation coverage. Improvement of traffic states and sanitation caused by the project in the region increases the comprehensive value, while the water and soil loss in partial area caused by construction decrease.