Jeff Davies

Developing groundwater: A guide for rural water supply

In many rural areas, groundwater is the only feasible way of providing safe, reliable water supplies. However, developing groundwater is not always straightforward. To meet the targets set out in the Millennium Development Goals, more attention needs to be paid to finding and developing groundwater in a sustainable, cost-effective and participatory manner. Developing Groundwater provides a user-friendly guide to this key topic, bringing together for the first time the wide range of techniques required to develop groundwater for community water supplies. This practical manual gives information on effective techniques for siting wells and boreholes, assessing the sustainability of sources, constructing and testing the yield of boreholes and wells, and monitoring groundwater quality. The authors set the technical aspects of rural water supply firmly in their socio-economic context, so that readers can take proper account of community concerns as well as purely engineering questions. Packed with helpful illustrations this book is indispensable for all rural water supply project staff in developing countries.

The scale and causes of the groundwater arsenic problem in Bangladesh

Groundwater is now extensively used for drinking water in Bangladesh and present estimates indicate that there are some 6–11 million tubewells in Bangladesh. It is now apparent that approximately 1/4 of these wells contain arsenic at concentrations exceeding the Bangladesh drinking water standard (50 μg L −1 ). As many as 35 million people may be drinking arsenic-affected groundwater. We discuss a national survey of groundwater quality in Bangladesh that attempted to map the distribution and nature of affected wells. Other solutes measured included Na, K, Ca, Mg, Fe, Mn, P and SO4. The worst-affected part of Bangladesh lies in the south-east of the country where the sediments are of Holocene age and where concentrations of arsenic frequently exceeded 200 μg L −1 . Where sampled, deep groundwaters (>150 m) were only rarely affected as were shallower groundwaters from older sediments including the aquifers underlying the Barind and Madhupur Tracts. Seven groundwater samples from the capital city of Dhaka also suggest that the city is not affected. The arsenic is undoubtedly of natural origin and the problem arises even though the sediments do not contain abnormal quantities of total arsenic. There is no evidence to suggest that the dissolved arsenic is derived from the oxidation of pyrite as some have suggested. Rather it appears that the high concentrations reflect a combination of factors: (i) young sediments undergoing rapid change from an oxidizing to a reducing environment following sedimentburial; (ii) the release of arsenic by one or more mechanisms which are poorly understood at present but which probably involve the desorption and dissolution of arsenic from iron oxides which are quite abundant in many of the worst-affected sediments; (iii) the very low hydraulic gradients throughout much of Bangladesh mean that groundwater flow is very slow which, combined with the ‘young’ age of many of the sediments, means that the natural flushing of the shallow aquifer will be slow allowing any released arsenic to accumulate. The rapid rate of deposition of sediments in Bangladesh and the Bengal Basin means that the chance of a well intercepting arsenic-rich water is likely to be relatively high compared with smaller deltas and other alluvial environments where the sedimentation rate is much lower.

Groundwater conceptual models: implications for evaluating diffuse pollution mitigation measures

The EU Water Framework Directive (WFD) identifies diffuse pollution as a long-term threat to water quality. Farming contributes significantly to this pollution. There is a clear need for mitigation measures and assessment of their efficacy. Accordingly, Demonstration Test Catchments (DTCs) have been established in England to test the effect of changes in agricultural practice on river water quality and ecology. However, the presence of groundwater in these hydrological systems implies a wide range of travel times for pollutants from source to receptor. Unless flow routes are better characterized, it will be difficult to gauge the success of control measures in the short term. Using 3D modelling and supplementary hydrochemical information, this study considers the hydrogeology of several sub-catchments in the Avon DTC, southern England. Data suggest that groundwater ages >25 years exist in parts of the catchments; clearly, observations like these must be used to judge the likely effectiveness of targeted control measures. The revealed hydrogeological complexity of the Avon catchment is unlikely to be unique, so the techniques described here should be applicable to other lowland river systems with moderate to high baseflow indices (>0.5). To support the WFD, groundwater conceptual models should inform the design of effective measures for diffuse pollution mitigation.

Groundwater and data - an African experience

The failure of borewell drilling can often be avoided if data on rural water sources are collected and kept in an accessible format. A landmark project in Malawi demonstrates the value of data gathering and is doing this through involvement with local communities, technical consultants, contractors and the ministry.

Identifying transboundary aquifers in need of international resource management in the Southern African Development Community region

Transboundary aquifer (TBA) management, in part, seeks to mitigate degradation of groundwater resources caused either by an imbalance of abstraction between countries or by cross-border pollution. Fourteen potential TBAs were identified within a hydrogeological mapping programme based on simple hydrogeological selection criteria for the Southern African Development Community (SADC) region. These have been reassessed against a set of data associated with five categories: (1) groundwater flow and vulnerability (which is perceived as the over-arching influence on the activity level of each TBA), (2) knowledge and understanding, (3) governance capability, (4) socio-economic/water-demand factors, and (5) environmental issues. These assessments enable the TBAs to be classified according to their need for cross-border co-operation and management. The study shows that only two of the 14 TBAs have potential to be the cause of tension between neighbouring states, while nine are potentially troublesome and three are unlikely to become problematic even in the future. The classification highlights the need to focus on data gathering to enable improved understanding of the TBAs that could potentially become troublesome in the future due to, for example, change in demographics and climate.RésuméLa gestion des aquifères transfrontaliers vise, pour partie, à réduire la dégradation de la ressource en eaux souterraines causée soit par des prélèvements déséquilibrés entre les pays soit encore par des pollutions transfrontalières. Quatorze aquifères transfrontaliers potentiels ont été identifiés dans le cadre d’un programme de cartographie hydrogéologique basé sur des critères de sélection hydrogéologique simples dans la région de la Communauté de développement de l’Afrique australe (CDAA). Ils ont ensuite été réévalués au regard d’une série de données regroupées en cinq catégories : (1) écoulements souterrains et vulnérabilité (qui est perçue comme d’une influence essentielle sur le niveau d’activité de chaque aquifère transfrontalier), (2) connaissance et compréhension, (3) capacité de gouvernance, (4) facteurs socio-économiques et de demande en eau, et (5) problèmes environnementaux. Ces évaluations permettent de classer les aquifères transfrontaliers en fonction des besoins en coopération et en gestion transfrontalière. L’étude montre que seuls deux des quatorze aquifères transfrontaliers peuvent probablement être la cause de tensions entre états voisins, tandis que neuf sont potentiellement préoccupants et que trois ne deviendront vraisemblablement jamais problématiques même dans le futur. Cette classification souligne la nécessité de mettre l’accent sur la consolidation des données pour permettre une compréhension améliorée des aquifères transfrontaliers qui pourraient de façon potentielle devenir préoccupants dans le futur du fait, par exemple, d’un changement démographique ou climatique.ResumenLa gestión de acuíferos transfronterizos (TBA) busca, en parte, mitigar la degradación de los recursos de agua subterránea causada ya sea por un desequilibrio de la extracción entre países o por la contaminación transfronteriza. Se identificaron catorce potenciales TBAs dentro de un programa de mapeo hidrogeológico basado en un criterio simple de selección hidrogeológica para la región sudafricana de desarrollo comunitario (SADC). Estos han sido reevaluados en función de un conjunto de datos asociados con cinco categorías: (1) flujo de agua subterránea y vulnerabilidad (el cual es percibido como la influencia general sobre el nivel de actividad de cada TBA, (2) conocimiento y comprensión, (3) capacidad de gobernanza, (4) factores socio económicos y demanda de agua, y (5) aspectos ambientales. Estas evaluaciones permiten clasificar a los TBAs de acuerdo con su necesidad de la gestión y cooperación transfronteriza. El estudio muestra que solamente dos de los 14 TBAs tienen potencial para ser motivo de tensión entre estados vecinos, mientras que nueve son potencialmente problemáticos y existen tres de ellos que tienen una baja probabilidad de convertirse en problemáticos aún en el futuro. La clasificación resalta la necesidad enfocarse en la recopilación de datos para permitir la comprensión mejorada de los TBAs que pudieran potencialmente convertirse en problemáticos en el futuro debido a, por ejemplo cambios en la demografía y el clima.ResumoA gestão de aquíferos transfronteiriços (TBA) procura, em parte, mitigar a degradação dos recursos hídricos subterrâneos causada quer pela extração excessiva não balanceada entre países, quer pela poluição transfronteiriça. Catorze TBAs potenciais foram identificados dentro do programa de mapeamento hidrogeológico internacional, com base em critérios simples de seleção para a região da Comunidade de Desenvolvimento do Sul da África (SADC). Isto foi reapreciado em função de um conjunto de dados associados a cinco categorias: (1) fluxo de água subterrânea e vulnerabilidade (o qual é identificado como a influência mais abrangente no nível de atividade de cada TBA), (2) conhecimento e entendimento, (3) capacidade de governância, (4) fatores sócio-económicos/necessidades de água, e (5) questões ambientais. Estas avaliações permitem que as TBAs sejam classificadas de acordo com as suas necessidades para a cooperação e gestão transfronteiriças. O estudo mostra que apenas duas das 14 TBAs têm potencial para ser a causa de tensões entre estados vizinhos, enquanto nove têm potencial para ser problemáticos e três são pouco prováveis como fonte de conflitos, mesmo no futuro. A classificação mostra a necessidade de focar a atenção na recolha de dados, de modo a obter um melhor conhecimento e entendimento dos TBAs que podem potencialmente tornar-se problemáticos no futuro devido a, por exemplo, alterações demográficas e climáticas.

Groundwater supply and demand from southern Africa’s crystalline basement aquifer: evidence from Malawi

Failure of borehole sources in weathered and fractured crystalline basement aquifers in Malawi in southern Africa has been linked with poor borehole design, mechanical failure and badly sited boreholes. However, recent work in Malawi indicates that demand may now exceed long-term resource potential in some places and that this is also a cause of water point failure. An 11-year climate cycle (including a wet and dry period) necessitates overdraft from groundwater storage during the dry-cycle years before episodic rainfall events in the wetter part of the cycle again recharge the aquifers. Data, particularly groundwater hydrograph data, are sparse, but sufficient to evaluate the long-term renewable groundwater potential for both fractured and weathered basement-aquifer types in each of the 15 management areas in Malawi. The groundwater potential or long-term renewable resource (recharge) is given by the sum of Darcian throughflow and dry-season depletion of storage. Estimated rural demand exceeds the renewable resource in the fractured-rock aquifer in two management units and in the weathered-rock aquifer in two other units. Although there is inherent uncertainty in the water-balance estimates, the likelihood that rural demand is exceeding long-term average recharge in some areas is cause for concern.RésuméL’insuffisance du débit des forages dans les aquifères du socle cristallin altéré et fracturé du Malawi (Afrique australe) est liée à une conception défectueuse, un défaut mécanique et une mauvaise implantation de l’ouvrage. Cependant, un travail récent au Malawi indique que la demande peut maintenant excéder la ressource potentielle de long terme en plusieurs emplacements et que c’est aussi une cause d’échec du point d’eau. Un cycle climatique de 11 ans (comprenant une période humide et une période sèche) oblige à une surexploitation de la réserve en eau souterraine pendant les années du cycle sec, avant que les événements pluvieux épisodiques de la partie plus humide du cycle rechargent de nouveau les aquifères. Les données, particulièrement les données d’hydrologie souterraine, sont rares, mais suffisantes pour évaluer le potentiel à long terme en eau souterraine renouvelable des deux types d’aquifères du socle, fracturé et altéré dans chacune des 15 zones de gestion du Malawi. Le potentiel souterrain ou ressource renouvelable à long terme (recharge) est donné par la somme de l’écoulement de Darcy et de la diminution de l’emmagasinement en saison sèche. La demande rurale estimée dépasse la ressource renouvelable de l’aquifère rocheux fracturé dans deux unités de gestion et de l’aquifère rocheux altéré de deux autres. Bien qu’il y ait une incertitude inhérente aux estimations du bilan hydrique, la probabilité que la demande rurale dépasse la recharge moyenne à long terme dans plusieurs secteurs est une cause d’inquiétude.ResumenEl fracaso de las fuentes de agua en pozos de acuíferos del basamento cristalino fracturado y meteorizado en Malawi en África del Sur se asocia a un deficiente diseño de los pozos, a fallas mecánicas y a la mala ubicación de los pozos. Sin embargo, trabajos recientes en Malawi indican que la demanda puede exceder los recursos potenciales a largo plazo en algunos lugares y que esta también es una causa del fracaso de las fuentes de agua. Un ciclo climático de 11 años (incluyendo períodos húmedos y secos) requiere la puesta a disposición del almacenamiento de agua subterránea durante los años del ciclo seco antes que eventos de lluvias episódicas en la parte más húmeda del ciclo produzcan una nueva recarga de los acuíferos. Los datos, particularmente los datos de hidrogramas de agua subterránea, son escasos, pero suficientes para evaluar la renovabilidad potencial de agua subterránea a largo plazo para los acuíferos fracturados y meteorizados del basamento en cada una de las 15 áreas de manejo en Malawi. El potencial de agua subterránea o la renovabilidad del recurso (recarga) a largo plazo está dada por la suma del flujo Darciano y la depleción del almacenamiento en la estación seca. La demanda rural estimada excede el recurso renovable en el acuífero de roca fracturada en dos unidades de manejo y en el acuífero de roca meteorizada en otras dos unidades. Aunque hay una incertidumbre inherente a la estimación del balance de agua, la probabilidad que la demanda rural exceda a la recarga promedio a largo plazo en algunas área es causa de preocupación.ResumoAs falhas no abastecimento de água com base em furos localizados em sistemas alterados e fraturados dos aquíferos cristalinos basais no Malawi, no sul da África, têm sido associadas à conceção deficiente de furos, a falhas mecânicas e à localização desadequada. No entanto, o trabalho recente efetuado no Malawi indica que a procura atual pode ultrapassar o potencial a longo prazo do recurso em alguns lugares, sendo esta também uma causa de falha do recurso nalguns pontos de água. Um ciclo climático de 11 anos (incluindo períodos secos e húmidos) requere a identificação dos principais locais de armazenamento de águas subterrâneas durante os anos de seca, antes de eventos episódicos de precipitação durante a época mais húmida do ciclo recarregarem novamente os aquíferos. Os dados, especialmente de níveis piezométricos, são escassos, mas suficientes para avaliar o potencial de renovação de longo prazo, tanto para as águas subterrâneas em aquíferos basais fraturados, como alterados, em cada uma das 15 áreas de gestão no Malawi. O potencial de recursos de águas subterrâneas ou de recursos renováveis de longo prazo (recarga) é dada pela soma do escoamento de Darcy e pela diminuição do armazenamento na estação seca. A procura de água estimada para abastecimento rural excede o recurso renovável no aquífero em rochas fraturadas em duas unidades de gestão e no aquífero de rochas alteradas noutras duas unidades. Embora haja incertezas inerentes às estimativas de balanços de água, o risco da procura rural de água, a longo prazo, ser superior à recarga média em algumas áreas é já um motivo de preocupação.

Groundwater flow in the South Wales coalfield: historical data informing 3D modelling

The South Wales Coalfield is structurally and lithologically complex. Attempts to understand the regional groundwater flow system have been largely piecemeal, focusing on single collieries or groups of collieries. Inspection of both historical data, gathered during the active mine dewatering phase of the coalfield, and of contemporary post-mining groundwater rebound data, allows a picture of the whole groundwater flow system to be derived, along with the regional water balance. The assessment is aided by application of a 3D visualization model of the geological framework, which includes the piezometry during and after the mining phase and pumping and yield data. Other valuable historical information, which can no longer be replicated, are the analyses of samples of groundwater that entered working mines from specified horizons, rather than present-day analyses of acid mine drainage. It is found that there is little deep regional groundwater flow across the basin, for example towards the sea, and most groundwater flow is of river catchment scale draining to the main rivers that traverse the coalfield. This analysis of the coalfield and the 3D model provide a foundation for future investigation into issues such as dewatering of new opencast pits, in situ gasification or anthracite mining.

The arsenic concentration in groundwater from the Abbey Arms Wood observation borehole, Delamere, Cheshire, UK

Abstract A 150 m observation borehole was drilled in Abbey Arms Wood, Delamere, Cheshire, UK in order to explore the local hydrogeological conditions and to understand better the source of the high concentrations of arsenic in some of the local groundwaters. The borehole was located on an outcrop of the Helsby Sandstone Formation (part of the Sherwood Sandstone Group) and was cored into the underlying Wilmslow Sandstone Formation. The aquifers in the area are unconfined and give rise to low-Fe groundwaters with As concentrations in the 10–50 µg l−1 range. The chemical composition of the sediments is quite uniform down to 150 m. The total arsenic content is in the range from 5 to 15 mg kg−1 and averaged 8 mg kg−1 (n = 60). There is no trend in sediment As concentration with depth, but pore water centrifuged from the core steadily increased in As concentration with depth. The As concentration ranges from 8 µg l−1 at 10 m (unsaturated zone) to 30 µg l−1 at 150 m. The source of the dissolved As remains unclear but the lack of evidence for discrete high-As minerals or zones of mineralization suggests that it is probably derived by desorption from rock-forming minerals in the sandstones, e.g. iron oxides. This may be in response to slightly higher pH (up to 8.0 at depth). If this trend applies throughout the area, restricting the screened interval for abstraction boreholes to the uppermost parts of the saturated zone may reduce As concentrations, but is likely to reduce yields and may also risk encountering groundwaters with high nitrate concentrations.

Movement of petroleum hydrocarbons in sandycoastal soils

In a field trial, oiled beach sand was buried in a coastal dune system in south Wales. A monitoring programme was designed to assess the rate of leaching of inorganic ions and hydrocarbons from the deposit. Active breakdown of the weathered oil occurred within the oiled beach sand, but hydrocarbons from the original material, or arising as a result of degradation, did not follow the same leaching pattern as inorganic ions; they remained within the original deposit. The results suggest that weathered oil coming ashore from spills at sea can be mixed with sand and buried to degrade in coastal soils, without risk of groundwater contamination by hydrocarbons.

Groundwater renewable resource versus demand: ‘good news’ or ‘bad news’ for rural communities?

Government water authorities and aid agencies are receiving conflicting messages about groundwater availability in sub-Saharan Africa. ‘Good news’ articles suggest that groundwater is available in abundance. ‘Bad news’ articles report water-point failure caused by depletion of groundwater storage rather than the more widely recognized mechanical failure of pump or borehole structure. These contradictory messages need to be read in the perspective of the scale of the assessment being described. Although there is plenty of groundwater in Africa, it is neither evenly distributed nor universally accessible. There are places where the groundwater resource renewal cannot keep pace with demographic stress and the local aquifer is drying up; groundwater in Africa is not just a water supply issue but has also become a complex management, maintenance, and regulatory problem. Lessons need to be learnt, not least with regard to the sustainable achievement of the Millennium Development Goals; the key lesson is that go...