WORLD BANK TECHNICAL PAPER NO. 390 0 ~~~~WTPS390 Work in progress for public discussion C :%a Groundwater in Urban Development Assessing Management Needs and Formulating Policy Strategies x;3 Stephen Foster Adriani Lawrence Bri'aiI Morris RECENT WORLD BANK TECHNICAL PAPERS No. 325 Bacon, Besant-Jones, and Heidarian, Estimating Construction Costs and Schedules: Experience with Power Generation Projects in Developing Countries No. 326 Colletta, Balachander, and Liang, The Condition of Young Children in Sub-Saharan Africa: The Convergence of Health, Nutrition, and Early Education No. 327 Valdes and Schaeffer in collaboration with Martin, Surveillance of Agricultural Price and Trade Policies: A Handbookfor Paraguay No. 328 De Geyndt, Social Development and Absolute Poverty in Asia and Latin America No. 329 Mohan, editor, Bibliography of Publications: Technical Department, Africa Region, July 1987 to April 1996 No. 330 Echeverria, Trigo, and Byerlee, Institutional Change and Effective Financing of Agricultural Research in Latin America No. 331 Sharma, Damhaug, Gilgan-Hunt, Grey, Okaru, and Rothberg, African Water Resources: Challenges and Opportunities for Sustainable Development No. 332 Pohl, Djankov, and Anderson, Restructuring Large Industrial Firms in Central and Eastern Europe: An Empirical Analysis No. 333 Jha, Ranson, and Bobadilla, Measuring the Burden of Disease and the Cost-Effectiveness of Health Interventions: A Case Study in Guinea No. 334 Mosse and Sontheimer, Performance Monitoring Indicators Handbook No. 335 Kirmani and Le Moigne, Fostering Riparian Cooperation in International River Basins: The World Bank at Its Best in Development Diplomacy No. 336 Francis, with Akinwumi, Ngwu, Nkom, Odihi, Olomajeye, Okunmadewa, and Shehu, State, Community, and Local Development in Nigeria No. 337 Kerf and Smith, Privatizing Africa's Infrastructure: Promise and Change No. 338 Young, Measuring Economic Benefitsfor Water Investments and Policies No. 339 Andrews and Rashid, The Financing of Pension Systems in Central and Eastern Europe: An Overview of Major Trends and Their Determinants, 1990-1993 No. 340 Rutkowski, Changes in the Wage Structure during Economic Transition in Central and Eastern Europe No. 341 Goldstein, Preker, Adeyi, and Chellaraj, Trends in Health Status, Services, and Finance: The Transition in Central and Eastern Europe, Volume I No. 342 Webster and Fidler, editors, Le secteur informel et les institutions de microfinancement en Afrique de l'Ouest No. 343 Kottelat and Whitten, Freshwater Biodiversity in Asia, with Special Reference to Fish No. 344 Klugman and Schieber with Heleniak and Hon, A Survey of Health Reform in Central Asia No. 345 Industry and Mining Division, Industry and Energy Department, A Mining Strategyfor Latin America and the Caribbean No. 346 Psacharopoulos and Nguyen, The Role of Government and the Private Sector in Fighting Poverty No. 347 Stock and de Veen, Expanding Labor-based Methods for Road Works in Africa No. 348 Goldstein, Preker, Adeyi, and Chellaraj, Trends in Health Status, Services, and Finance: The Transition in Central and Eastern Europe, Volume II, Statistical Annex No. 349 Cummings, Dinar, and Olson, New Evaluation Procedures for a New Generation of Water-Related Projects No. 350 Buscaglia and Dakolias, Judicial Reform in Latin American Courts: The Experience in Argentina and Ecuador No. 351 Psacharopoulos, Morley, Fiszbein, Lee, and Wood, Poverty and Income Distribution in Latin America: The Story of the 1980s No. 352 Allison and Ringold, Labor Markets in Transition in Central and Eastern Europe, 1989-1995 No. 353 Ingco, Mitchell, and McCalla, Global Food Supply Prospects, A Background Paper Prepared for the World Food Summit, Rome, November 1996 No. 354 Subramanian, Jagannathan, and Meinzen-Dick, User Organizationsfor Sustainable Water Services No. 355 Lambert, Srivastava, and Vietmeyer, Medicinal Plants: Rescuing a Global Heritage No. 356 Aryeetey, Hettige, Nissanke, and Steel, Financial Market Fragmentation and Reforms in Sub-Saharan Africa (List continues on the inside back cover) WORLD BANK TECHNICAL PAPER NO. 390 Groundwater in Urban Development Assessing Management Needs and Formulating Policy Strategies Stephen Foster Adrian Lawrence Brian Morris The World Bank Washingon, D.C. Copyright C 1998 The Intemational Bank for Reconstruction and Development/THE WORLD BANK 1818 H Street, N.W. Washington, D.C. 20433, U.S.A. All rights reserved Manufactured in the United States of America First printing March 1998 Technical Papers are published to communicate the results of the Bank's work to the development community with the least possible delay. The typescript of this paper therefore has not been prepared in accordance with the proce- dures appropriate to formal printed texts, and the World Bank accepts no responsibility for errors. Some sources cited in this paper may be informal documents that are not readily available. The findings, interpretations, and conclusions expressed in this paper are entirely those of the author(s) and should not be attributed in any manner to the World Bank, to its affiliated organizations, or to members of its Board of Executive Directors or the countries they represent. 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Cover artwork used with permission of the British Geological Survey. ISSN: 0253-7494 Stephen Foster is assistant director of the British Geological Survey, visiting professor of contaminant hydrogeol- ogy at the University of London, and chair of the Intemational Association of Hydrogeologists: Burdon Commission on Developing Nations. Adrian Lawrence and Brian Morris are principal hydrogeologists at the British Geological Survey, Nottingham. Library of Congress Cataloging-in-Publication Data Foster, Stephen S. D. Groundwater in urban development: assessing management needs and formulating policy strategies / Stephen S. D. Foster, Adrian R. Lawrence, Brian L. Morris. p. cm. - (World Bank technical paper; no. 390) ISBN 0-8213-4072-7 1. Groundwater-Developing countries. 2. Urban hydrology- Developing countries. I. Lawrence, Adrian R., 1951- . II. Morris, Brian L., 1947- . III. Title. IV. Series. TD327.F67 1997 333.91'0415'091724-dc2l 97-41737 CIP Contents Foreword ........................................v Acknowledgments ............................................... vii Abstract ................................................ ix Executive Summary ............................................... xi 1. Interdependence of Groundwater and Urbanization ................................................1 Subsurface Dimensions of Urban Development .........1......................................1 Stages and Patterns of Urban Evolution ................................................3 Inter-Related and Conflicting Processes ...............................................5 Urban Groundwater in Hydrogeological Context ................................................6 2. Analysis of Urban Hydrogeological Processes ............................................... 11 Urban Influences on Groundwater Recharge and Quality ............................................... 11 Effects of Uncontrolled Groundwater Abstraction ............................................... 22 3. Urban Groundwater Management Issues ............................................... 27 Analysis from Different Perspectives ............................................... 27 Evolution of Problems ............................................... 30 Underlying Causes of Management Problems ............................................... 34 4. Improving Groundwater Resource Management ............................................... 39 Institutional Framework and Social Dimension ............................................... 39 Technical Management Objectives and Targets ............................................... 40 Achieving Management Targets ............................................... 40 The Way Forward: Political Realism and Practical Steps ............................................... 52 References and Bibliography ............................................... 55 Boxes 1.1 Groundwater Occurrence .9 1.2 Groundwater Flow Systems .10 2.1 Urban Groundwater Contamination by Canal Seepage-Hat Yai, Thailand .15 2.2 Groundwater Contamination by Pathogens-Merida, Mexico .19 2.3 Downward Leakage of Contamination Induced by Pumping-Santa Cruz, Bolivia .20 3.1 Separation of Water Supply and Wastewater Disposal in Vulnerable Aquifers-Merida, Mexico 29 3.2 Deep Groundwater Quality Degradation Induced by Pumping-Hat Yai, Thailand .32 3.3 Industrial Wastewater Reuse for Irrigation: Problems and Potential Solutions-Le6n, Guanajuato, Mexico .33 3.4 The Problem of Unregulated Private Abstraction-Bangkok, Thailand .35 3.5 Long-Term Groundwater Quality Threat Posed by On-Site Sanitation in an Arid-Zone, Urban Environment-Sana'a, Yemen .38 4.1 Reduction of Urban Groundwater Abstraction in a Command Economy to Control Land Subsidence-Tianjin, China .42 iii iv Table of Contents Groundwater in Urban Development 4.2 Conjunctive Use of Water Resources: Worth More than the Sum of the Parts .............. ....................... 45 4.3 Regulatory and Economic Instruments to Reduce Groundwater Abstraction- Jakarta, Indonesia ...................................................................... 47 4.4 Complementary Relation between Public and Private Groundwater Abstraction- Santa Cruz, Bolivia ...................................................................... 48 4.5 Proactive Response to Excessive Groundwater Abstraction-Queretaro, Mexico ............ .................. 49 4.6 Protection Zones for Periurban Groundwater Sources-Bridgetown, Barbados ................................. 54 Figures 1.1 Interaction of Groundwater Supply and Wastewater Disposal in a City Overlying a Shallow Aquifer .......................................................................1 1.2 Evolution of Water Supply and Wastewater Disposal for a Typical City Underlain by a Shallow Aquifer .......................................................................4 1.3 Population Growth and Water Demand in the Mexico City Metropolitan Area .............. .....................5 2.1 Hydrological Equivalent Rates of Circulation in Water Supply Mains in Urban Areas .......... ........... 13 2.2 Potential Range of Subsurface Infiltration Caused by Urbanization ............................ ......................... 17 2.3 Processes that Promote Contaminant Attenuation in Groundwater Systems ............... ....................... 22 2.4 Evolution of Groundwater Quality Problems in a Typical Coastal, Alluvial Aquifer System following Rapid Urbanization ...................................................................... 26 3.1 Interaction between Urban Services and Facilities through the Underlying Groundwater System ...................................................................... 27 3.2 Urban Evolution from the Perspective of Groundwater Resources ................................ ....................... 31 Tables ES.1 Groundwater-Using Cities Considered in Assessing Management Needs and Formulating Policy Strategies ...................................................................... xii 1.1 Balancing Initial Benefits and Long-Term Costs in the Urban Use of the Subsurface Environment .......................................................................2 1.2 Characteristics of Principal Urban Hydrogeological Environments ................................... .....................7 2.1 Impacts of Urban Processes on Infiltration to Groundwater ................................................................... 11 2.2 Sources of Aquifer Recharge in Urban Areas and Their Implications for Groundwater Quality ...................................................................... 12 2.3 Classification of Groundwater Quality Problems ................................... ................................... 18 2.4 Hydrogeological Enviromnents and Their Associated Groundwater Pollution Vulnerability ....... ............................................................... 23 2.5 Summary of Activities that Might Generate a Subsurface Contaminant Load .............. ...................... 24 2.6 Susceptibility of Hydrogeological Environments to Adverse Side-Effects During Uncontrolled Exploitation ...................................................................... 25 3.1. Urban Groundwater Problems and Management Requirements .36 4.1 Urban Groundwater Supply Management: Objectives, Problems, and Mitigation Measures.41 4.2 Practical Steps toward Defining and Promoting an Urban Groundwater Resources Managem.ent Policy.53 Foreword Pivotal to World Bank policy on urban development and urban water resources is the definition of im- proved and sustainable management strategies. Groundwater resources in and around the urban centers of the developing world are exceptionally important as a source of relatively low-cost and generally high- quality municipal and domestic water supply. Management strategies need to recognize and to address the complex linkages that exist between groundwater supplies, urban land use, and effluent disposal. This paper, prepared by senior staff of the British Geological Survey (BGS), grew out of research projects promoted by the United Kingdom's Department for International Development (formerly the Overseas Development Administration). These projects, focusing on the various impacts of rapid urbanization on groundwater, were undertaken in collaboration with the governments of Bolivia, China, Mexico, and Thai- land. It provides a review of the current status of urban groundwater resources in the developing world, an assessment of resource management needs, and the first steps to take in formulating policy strategies. The target audience includes senior water supply and environmental managers concerned with devel- oping and managing the urban infrastructure, especially in rapidly developing cities dependent on ground- water, and the staff of the international support agencies responsible for financial and technical assistance in this area. The hope is that the paper will focus attention on urban groundwater issues, will form a valuable reference for urban infrastructure decisionmakers, and will promote more proactive management of ground- water resources and protection of groundwater supplies. Anthony Pellegrini John Briscoe Director Senior Water Adviser Transportation, Water and Urban Development Environmentally and Socially Sustainable Development v Acknowledgments The idea of preparing a World Bank technical paper based on the results of the United Kingdom's Depart- ment for International Development projects on the impact of rapid urbanization on groundwater origi- nated from Carl Bartone, principal environmental engineer of the World Bank's Transportation, Water and Urban Development Department, who also coordinated the production of this paper. The Department for International Development financed the work involved in producing the paper. John Hodges and Alistair Wray, senior staff of its Engineering Division, are thanked for their support and interest in the initiative, which was commissioned with the British Geological Survey. A number of national organizations played key roles in collecting data on urban groundwater for the cases used to illustrate the paper. These include the Mexican National Water Commission; the Thailand Ministry of Public Health, Environmental Health Division; and the following water companies and envi- ronmental bureaus: the Water Supply and Sewerage Cooperative of Santa Cruz (SAGUAPAC) in Bolivia, the Potable Water and Sewerage Service of Le6n (SAPAL) in Mexico, and the Tianjin Bureau of Geology and Mineral Resources (TBGMR) in China. The authors wish to acknowledge the assistance of numerous World Bank staff in issue identification, data collection, policy discussion, and editorial review, including John Briscoe, Paula Stone, David Hanrahan, David Grey, Geoffrey Read, Heinz Ungar, Ulrich Koeffner, Larry Simpson, Augusta Dianderas, Awa Busia, and Prasad Gopolan. Helpful comments on the manuscript were received from Marcus Moench and Henry Salas; and earlier support from Richard Helmer, Chief of Urban Environmental Health in the World Health Organization, is acknowledged. The authors also wish to thank the following British Geological Survey colleagues for their input into this and related projects: John Chilton, Brian Adams, Marianne Stuart, Roger Calow, and Daren Gooddy. Gill Tyson drafted all the figures and designed the layout of the text boxes. Finally, the authors are grateful to Lilian Lyons of the World Bank who oversaw the production of this book; and to Rebecca Kary and the staff at Alpha-Omega Services, Inc., who copy-edited and desktop published this paper. vii Abstract Groundwater is of major importance in providing mains water supply, and is intensively exploited for private, domestic, and industrial use in many urban centers of the developing world. At the same time, the subsurface has come to serve as the receptor for much urban and industrial wastewater and for solid waste disposal. There are increasingly widespread indications of degradation in the quality and quantity of ground- water, either serious or incipient, caused by excessive exploitation and/or inadequate pollution control. The scale and degree of degradation varies significantly with the susceptibility of local aquifers to exploitation- related deterioration and their vulnerability to pollution. This paper is based on the investigation or review of the situation in a substantial number of developing cities worldwide. It aims to raise the awareness among policymakers of hydrogeological processes in urban areas, to highlight key urban groundwater issues, to provide a framework for the systematic consideration of the groundwater dimension in urban management, and to formulate approaches for more sustainable management of groundwater resources in urban areas. ix Executive Summary Whatever befalls the earth, befalls the sons of the earth. If men spit upon the ground, they spit upon themselves. All things are connected like the blood which unites onefamily. from The Great Chief (Seathle) Sends Word (to the "white chiefs" in Washington, D.C.), 1855 Groundwater plays a fundamental role in shaping the economic and social health of many urban areas in the developing world. No comprehensive statistics exist on the proportion of urban water supply world- wide derived from groundwater, but more than 1 billion urban dwellers in Asia and 150 million in Latin America probably depend directly or indirectly upon well, spring, and borehole sources. Due to its rela- tively low cost and generally high quality, groundwater has often been the preferred source for reticulated public water supplies and is widely exploited for private domestic and industrial uses. Urbanization and industrialization have a profound effect on urban groundwater resources, which are inextricably linked with land use and effluent and waste disposal practices in a complex fashion. The diag- nosis of groundwater-related urban management problems presented in this paper draws on the assess- ment of the current situation in many cities across the developing world (table ES.1). The table indicates the importance of groundwater and the range of problems that threaten the sustainability of its use. Improved management of urban groundwater resources is urgently needed to mitigate actual and po- tential derogation caused by excessive exploitation and inadequate pollution control. Unless groundwater is protected, in terms of both quantity and quality, there will be increased scarcity of water supply and escalating water supply costs with potential impacts on human health. Many industries require good qual- ity and high reliability of water supply that if not available may cause them to locate elsewhere, thereby causing economic stagnation. The principal aims of this policy paper are * To highlight key urban groundwater issues and management needs. * To raise awareness and understanding of hydrogeological processes in urban areas. * To provide a framework for the proper and systematic consideration of the groundwater dimension in urban management. * To suggest options for more sustainable development and management of groundwater in urban areas. Chapter 1 provides a brief introduction to the importance and behavior of groundwater in general terms, and to the close interdependence and interaction between urbanization and groundwater in many situations. Although the paper is primarily a policy document, Chapter 2 provides a considerable amount of tech- nical detail to enable nonspecialists to appreciate the behavior of groundwater systems in urban areas be- cause * Those concerned with urban water supply and environmental management often have a poor un- derstanding of groundwater. * To be effective, regulatory controls and economic instruments need to be lodged in a sound hydrogeological framework (so that they work with nature and not against it). xi Table ES.1: Groundwater-Using Cities Considered in Assessing Management Needs and Formulating Policy Strategies City Country Information Role of Groundwater City Country Information Role of Groundwater status groundwater problems status groundwater problems Latin America Asia Buenos Aires Argentina 3 miin * urb poll Dhaka Bangladesh 2 ss } gwl Mar del Plata Argentina 2 maj sal int Beijing China 3 min * urb poll Salta Argentina 3 maj urb poll Shenyang China 2 maj * gwl,d-s poli Santa Cruz Bolivia 1 ss * urb poll Jinzhou China 2 maj d-s poll Cochabamba Bolivia 3 maj * gwl Tianjin China 1 maj sub Santiago Chile 2 mini urb poll,d-s poll Shijiazhuang China 3 maj urb poll,d-s poll Cali Colombia 3 mini * urb poll Lucknow India 3 maj * urb poll San Jos6 Costa Rica 1 maj d-s poll Nagpur India 3 maj * urb poll Guatemala City Guatemala 2 maj d-s poll Jakarta Indonesia 3 min * sal int San Pedro Sula Honduras 2 maj * urb poll Bandung Indonesia 2 maj * urb poll Mexico DF Mexico 2 maj sub Semarang Indonesia 2 min * gwl,urb poll Le6n-Guanajuato Mexico 1 maj * d-s poll Surakarta Indonesia 3 maj * urb poll Chihuahua Mexico 2 ss gwl,d-s poll Manila Philippines 2 min * sal int Queretaro Mexico 2 maj sub,urb poll Cebu City Philippines 3 maj * sal int,urb poll Merida Mexico 1 maj * urb poll Jaffna Sri Lanka I ss * sal int,urb poll Managua Nicaragua 2 maj urb poll Bangkok Thailand 2 maj * sal int,urb poll,sub Lima Peru 2 maj gwl Hat Yai Thailand 1 mrin sal int,urb poll Ica Peru 3 ss'* urb poll Hanoi Vietnam 3 maj urb poll El Tigre Venezuela 2 ss urb poll Sanaa Yemen 2 maj gwl,urb poll Caribbean Basin Africa Nassau Bahamas 2 maj * sal int,urb poll Abidjan C6te Ivoire 3 min * urb poll Bridgetown Barbados 1 ss urb poll Cairo Egypt 3 min urb poll Bermuda Bermuda 1 maj urb poll Dakar Senegal 3 min * urb poll Santo Dorningo Dominican 2 ss * sal int,urb poll Lusaka Zambia 3 maj * gwl,urb poll Republic t Major private domestic/industrial use. d-s poll Downstream groundwater pollution. gwl Failing groundwater levels. maj Major source of public supply. min Minor source of public supply. SS Sole source for public supply. sal int Aquifer saline intrusion. sub Land subsidence. urb poll Groundwater pollution within urban area. 1 Full survey data. 2 Useful summary document. 3 General background only. Groundzwater in Urban Development Executive Summary xiii Urbanization has a major impact on recharge to, and groundwater flow within, aquifers beneath cities. This is a result of a combination of factors, such as: * Importation of large quantities of water. * Modifications to pluvial drainage. * Extensive use of the ground for effluent discharge and waste disposal. * Abstraction of large volumes of groundwater for water supply. The consequences include aquifer depletion, saline intrusion, and land subsidence. Furthermore, in most developing cities population growth precedes the development of infrastructure to handle wastewater. This tends to lead to widespread contamination of shallow groundwater by domestic and industrial effluents. Given the large storage capacity of most aquifers and the long residence times of groundwater within them, there is often a major time lag before the problems of groundwater pollution become fully apparent. The net outcome is increasing water scarcity with escalating long-run marginal costs for water supply. The traditional use of low-cost, minimally treated, groundwater for public water supply in urban areas is being threatened, and in some hydrogeological environments health risks are increasing. Consequently, those responsible for managing groundwater need to be aware of the causes of aquifer degradation, how hydrogeological environments vary with regard to susceptibility to uncontrolled exploi- tation and vulnerability to anthropogenic pollution, and the long-term implications for water resources. Chapter 3 presents three somewhat different perspectives on the subsurface environment in cities, namely: * Water supply provision and regulation. * Wastewater and solid waste disposal. * Engineering infrastructure development and maintenance. These three functions are very different and can often be in conflict. The chapter illustrates such con- flicts using a number of specific examples from around the world. Sustainable development and effective management of groundwater in urban areas must reconcile dif- ferent interests: maintaining well yields, safeguarding the water quality, handling solid waste and liquid effluents effectively, and protecting the engineering infrastructure. Various hydrogeological processes may threaten these objectives. In particular, problems of aquifer saline intrusion, land subsidence, and ground- water pollution occur, which result from two underlying processes: * Overabstraction of groundwater resources. * Excess subsoil contaminant loading relative to its natural assimilation capacity. Appropriate specialists will need to diagnose each individual case to identify priority areas for con- straining groundwater abstraction and to establish priority targets for controlling the subsurface contami- nant load. Chapter 4 is dedicated to formulating policy strategies to eliminate or to mitigate these problems. It reviews the requirements in terms of an appropriate institutional framework, recognizing that the imple- mentation of sustainable policies for allocating and protecting groundwater resources will often require building public awareness and promoting stakeholder dialogue so as to create the necessary sociopolitical consensus. Management measures have to target the control of groundwater levels and/or subsurface contami- nant loading. These targets may be achieved by a range of measures, both regulatory controls and economic instruments. However, the optimum balance will depend on the hydrogeological environment concerned, the prevailing institutional framework, and the obvious need to promote regulation through self-interest. Another important aspect highlighted is the need to obtain a realistic balance and effective control of both public and private exploitation of groundwater in urban areas if serious negative consequences for all groundwater users are not to arise, and if scarce, high-quality groundwater is to be conserved for potable and sensitive uses. xiv Executive Summary Groundwater in Urban Development Cities evolve in space and time, consequently, patterns of groundwater use, waste disposal, and indus- trial development change. Thus, management measures must be flexible and should be reviewed regularly. Controlling incipient trends relating to imbalance of groundwater recharge or excess contaminant loading will be much easier than dealing with more mature problems. In some megacities, especially in the more arid regions, only partial remediation may be possible. Policies aimed at helping medium-sized cities to avoid the problems currently observed in some megacities may well be the highest priority. A companion volume is planned, which will provide an outline guide to the methodologies of (rela- tively) rapid groundwater assessment and the associated (minimal) data requirements. These methodolo- gies will focus on defining the magnitude and status of groundwater resources; determining their suscepti- bility to side-effects during exploitation; and assessing groundwater pollution hazard, aquifer pollution vulnerability, and subsurface contaminant load. 1 INTERDEPENDENCE OF GROUNDWATER AND URBANIZATION Subsurface Dimensions of Urban Development The provision of water supply, sanitation, and drainage is a key requirement of the urbanization process. Furthermore, the subsurface plays an important role in all three of these elements of infrastructure develop- ment and in the disposal of industrial effluent and solid waste (figure 1.1, table 1.1). Thus in the develop- ment of urban infrastructure, the subsurface environment is a key consideration, and the presence or ab- sence of permeable subsoil and shallow groundwater are key factors. Figure 1.1. Interaction of Groundwater Supply and Wastewater Disposal in a City Overlying a Shallow Aquifer Water Supply Wastewater Disposal Re-use I I Surface Pluvial Sewage Water Drainage (Piped) ± Treatment , , , ~~~~Use 1 Peri-urban Urban Wells On-site Sanitation and Errigation Wellfields Industrial Effluent Disposal i X \ (Excess Flows) Groundwater Abstraction Aquifer Provision of Water Supply Where cities overlie productive aquifers, groundwater is almost invariably the first water resource to have been tapped. This is because groundwater is * Generally of excellent natural quality, and thus offers significant savings in treatment costs compared to an equivalent surface water source. * More secure as a source of supply during extended dry periods than most surface water resources. 1 2 Interdependence of Groundwater and Urbanization Groundwater in Urban Development * Suitable for public supply and private use independently, at least during the early stages of develop- ment. * Attractive in terms of capital investment because development can progress in stages with rising water demand. Table 1.1. Balancing Initial Benefits and Long-Term Costs in the Urban Use of the Subsurface Environment Function of subsurface Initial benefits Long-term costs Water supply source * Low capital cost * Excessive abstraction can lead to * Staged development possible - abandonment/reduced * Initial water quality better efficiency of wells * Private and public supply can - saline intrusion risk in coastal develop separately cities - subsidence risk in susceptible environments On-site sanitation receptor * Low-cost communuity-built . Sustainability of groundwater facilities possible abstraction threatened * Permits rapid expansion under if contaminant load exceeds sanitary conditions aquifer assimilation capacity * Uses natural attenuation capacity of subsoil Pluvial drainage receptor * Low capital costs * Contamination from industrial/ X Conserves water resources commercial areas and major * Less flood risk along highways downstream watercourses * Roof runoff provides dilution of urban contaminants Industrial effluent/solid * Reduced manufacturing costs * Noxious effluent may prejudice waste disposal groundwater quality * System favors irresponsible attitude to waste stream management Most urban aquifers are exploited by hand-dug wells or drilled boreholes. Hand-dug wells are typically less than 20 meters deep with diameters of 1 meter or more. Their water is abstracted by small pumps or manually. Water supply boreholes are mechanically drilled, usually of smaller diameter than hand-dug wells, but much deeper (ranging from 20 to 200 meters or more in depth). Boreholes are lined with steel, plastic, or glass fiber casing, and their groundwater is abstracted by electric- or diesel-powered pumps. Sections of screen may be required to support and retain unconsolidated strata while permitting free entry of groundwater from permeable horizons, but in some well-consolidated aquifers linings are unnecessary. Sanitation Measures The subsurface also plays a key role in urban wastewater disposal because of the widespread use of unsewered sanitation. Due to high cost, mains sewerage installation invariably lags behind population growth and the provision of mains water supply. On-site wastewater disposal (via septic tanks, cesspits, or pit latrines) for high-density settlements may be semipermanent, especially in low-income districts where municipal au- thorities struggle to provide a functioning service. Groundwater in Urban Development Interdependence of Groundwater and Urbanization 3 Pluvial Drainage While urbanization always leads to impermeabilization of the land surface, the net effect on an underlying groundwater system depends on the plavial (stormwater) drainage arrangement that accompanies con- struction. The ground conditions and rainfall regime, in turn, exert a major influence over the need for (and size of) stormwater drains to remove excess water from the land surface. Where the subsoil infiltration capacity is adequate, the ground is the most economical receptor for urban runoff, thereby avoiding the need for costly surface drainage measures. Industrial Effluent Discharge The subsurface is often a major receptor for industrial effluents, either directly from casual disposal to the ground or indirectly as seepage from treatment lagoons or infiltration from surface watercourses or canals. Much of the industrial expansion that sustains urban growth relies implicitly on the subsurface to dispose of unwanted by-products. A further factor is spillage and/or leakage to the ground of hydrocarbon fuels and liquid chemicals stored in tanks at industrial sites and throughout urban areas. Solid Waste Disposal As part of the urbanization process, municipal authorities and private entities eventually arrange for the collection of solid wastes. In most cases they dispose of these wastes using landfills or open dumps, which, if not controlled, generate leachates that infiltrate the ground and can impact seriously on groundwater supplies at the local scale. Stages and Patterns of Urban Evolution All cities evolve from small settlements (figure 1.2). In the industrial economies this evolution normally took place over centuries, but in the developing world, where most of the world's population growth is currently occurring, urban growth rates are unparalleled in human history. From 1800 to 1910 the popula- tion of Greater London grew from 1.1 to 7.3 million, yet some Latin American and Asian cities have re- corded similar growth rates in just a few decades (figure 1.3). A common feature of many developing cities has been the appearance of informal settlements located on marginal land or in burgeoning periurban districts. The proportion of urban poor in these settlements is typically between 30 to 60 percent of the overall urban population, and estimates indicate that by the year 2000 more than 1 billion people will be living in such settlements. If cities are to provide adequate water supply, sanitation, drainage, and waste disposal to all their residents, municipal authorities need to evalu- ate critically how to manage the subsurface more sustainably, because these communities increasingly de- pend upon it, both for water supply and as a waste receptor. The effects of urban water supply and wastewater disposal are not limited to the geographic area occu- pied by the city itself. This is because cities, especially those undergoing major expansion, are intimately linked with their hinterlands. For instance, as cities grow, water supplies that were originally obtained from shallow underlying aquifers may no longer be sufficient, either because the available resource is too limited or because pollution has caused its quality to deteriorate. The extra water resources required can be tapped from deeper aquifers or, more often, can be drawn from aquifers or surface water bodies in the city's hinter- land (figure 1.2), invariably at an ever-increasing distance and marginal cost. These water supplies normally have a competing prior use, notably agriculture, and serious conflicts may arise as a result. Similarly, as cities expand they may envelop their own periurban wellfields (figure 1.2), thus, ground- water quality may deteriorate progressively, either because of direct urban encroachment or because of infiltration from polluted surface watercourses in downstream riparian areas. Such expansion will inevita- 4 Interdependence of Groundwater and Urbanization Groundwater in Urban Development Figure 1.2. Evolution of Water Supply and Wastewater Disposalfor a Typical City Underlain by a Shallow Aquifer N~~ _ 5.it~ , i. WaterTabiE.i. -^ . $ (a) Early settlement * Water supply obtained from shallow urban wells and boreholes. * Wastewater discharged to ground. * Pluvial drainage to ground or watercourse.