Hydrology of part of the Oramiriukwa River basin,southeast of Owerri,Imo State,Nigeria

The Oramiriukwa River is within the sandy coastal plain strata of the Benin formation (Miocene–Recent). The base flow is very high ranging from 79.13–98.56%, which is caused by the excellent hydraulic interconnection between the river and the adjacent unconfined aquifer. Recharge rates are high, estimated to range from 1.8×10¹²–2.5×10¹² m³/year. Coastal sands are medium-to-coarse grained, moderately-to-poorly sorted, angular to subangular, with lenses of clay and clayey fine-grained sands. The coastal sands and clay lenses form aquifer and aquitard systems, which are unconfined to semi-confined. Groundwater recharge potential is high. Runoff from precipitation is low. Groundwater and surface water are fairly acidic; pH ranges from 5.5–6.1 (groundwater) and 5.8–6.5 (surface water), and hardness is generally low. Chemical analysis and percentage sodium show that groundwater and surface water are somewhat potable after some pH modification of the surface water. The waters are good for agricultural use, especially for irrigation and poultry water supply. However, pollution from landfill leachate is serious. Electronic Publication     

Using groundwater levels to estimate recharge

Accurate estimation of groundwater recharge is extremely important for proper management of groundwater systems. Many different approaches exist for estimating recharge. This paper presents a review of methods that are based on groundwater-level data. The water-table fluctuation method may be the most widely used technique for estimating recharge; it requires knowledge of specific yield and changes in water levels over time. Advantages of this approach include its simplicity and an insensitivity to the mechanism by which water moves through the unsaturated zone. Uncertainty in estimates generated by this method relate to the limited accuracy with which specific yield can be determined and to the extent to which assumptions inherent in the method are valid. Other methods that use water levels (mostly based on the Darcy equation) are also described. The theory underlying the methods is explained. Examples from the literature are used to illustrate applications of the different methods. Electronic Publication     

Groundwater flow through Pleistocene glacial deposits in the rapidly urbanizing Rouge River–Highland Creek watershed,City of Scarborough,southern Ontario,Canada

The city of Scarborough lies on the eastern margin of the Greater Toronto Area of southern Ontario, Canada, along the northern coastline of Lake Ontario. The City has a population of 500,000 and is presently one of the fastest growing communities in Canada. The City is expanding northwards onto rural land on the south slope of the large Pleistocene glacial Oak Ridges Moraine system. The moraine system is underlain by a thick (150 m) succession of tills, sands and gravels and is a regionally-significant recharge area for three principle aquifer systems that discharge to numerous watercourses that flow to Lake Ontario. Protection of deeper aquifers from surface-generated urban contaminants is a particular concern. A groundwater flow model using Visual MODFLOW was developed for the 350-km² Rouge River–Highland Creek (RRHC) drainage basin using an extensive GIS-based collection of subsurface geological, geophysical and hydrogeological data, maps of land use and surficial geology. The RRHC model was calibrated against point water level data, known potentiometric surfaces of the principal aquifers and baseflow measurements from streamflow gauging stations and determined to be within acceptable limits. Water balance calculations indicate that 70% of the basin recharge (106,000 m³/day) enters the Upper Aquifer along the crest and immediate flanks of the Oak Ridges Moraine. To the south, Upper Aquifer water moving through fractured till aquitards accounts for more than 75% of recharge to deeper aquifers. Water quality data confirm previous observations that urban- and rural-sourced contaminants (chlorides and nitrates) present in Upper Aquifer waters are moving rapidly into deeper aquifers. Some 83% of total RRHC recharge water is ultimately discharged as baseflow to creeks draining to Lake Ontario; the remainder discharges to springs and along eroding lakeshore bluffs. Model results demonstrate that deeper aquifers are poorly protected from urban contaminants and that long-term protection of ground and surface water quality has to be a priority of municipal planners if the resource is not to be severely degraded. Electronic Publication     

Hydrogeological mapping as a basis for establishing site-specific groundwater protection zones in Denmark

The water supply in Denmark is based on high-quality groundwater, thus obviating the need for complex and expensive purification. Contamination from urban development and agricultural sources, however, increasingly threatens the groundwater resource. In 1995 the Danish Government thus launched a 10-point plan to improve groundwater protection. In 1998 this was followed by a decision to instigate spatially dense hydrogeological mapping of the groundwater resource within the 37% of Denmark designated as particularly valuable water-abstraction areas. The maps will be used to establish site-specific groundwater protection zones and associated regulation of land use to prevent groundwater contamination. Traditional mapping based solely on borehole data is too inaccurate for this purpose. The work will take 10 years and cost an estimated DKK 920 million, equivalent to 120 million euro (€). To fund this, consumers will pay a € 0.02 surcharge per m³ of drinking water during the 10-year period. This review of the Danish strategy to protect the groundwater resource demonstrates why dense mapping with newly developed geophysical measurement methods in large contiguous areas accords geophysics a highly central role in the forthcoming hydrogeological mapping. It is illustrated by examples of spatially dense, large-scale geophysical mapping carried out in the Aarhus area.

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Resumen El abastecimiento de agua en Dinamarca está basado en agua subterránea de alta calidad, evitando de esta manera la necesidad de una purificación compleja y cara. Sin embargo, la contaminación a través del desarrollo urbano y de fuentes agrícolas, ha incrementado la amenaza para el recurso de agua subterránea. Entonces en 1995 el gobierno lanzó un plan de 10 puntos para mejorar la protección del agua subterránea. Este fue seguido en 1998 por la decisión para promover una cartografía hidrogeológica espacialmente detallada, para el recurso agua subterránea dentro del 37% de las áreas de extracción consideradas por Dinamarca con una importancia especial. Los mapas serán usados para establecer zonas específicas de protección para puntos de agua subterránea y una regulación asociada al uso del territorio, para prevenir la contaminación del agua subterránea. La cartografía tradicional basada exclusivamente en datos de la perforación es muy inexacta para este propósito. Este trabajo tomará 10 años y costará aproximadamente DKK 920 millones, equivalentes a 120 millones de Euros (€). Para financiar esto los consumidores pagarán un sobreprecio de € 0.02 por m³ de agua potable durante un periodo de 10 años. Este análisis de la estrategia Danesa para proteger el recurso agua subterránea, demuestra porque la cartografía detallada, hecha con nuevos avances en métodos de medición geofísica, aplicados a grandes áreas aledañas, otorgan a la geofísica un papel altamente importante en el futuro de la cartografía hidrogeológica. Esto está ilustrado con ejemplos de cartografía geofísica a gran escala y espacialmente detallada, llevados a cabo en el área de Aarhus.

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Résumé Lalimentation en eau au Danemark suppose une haute qualité des eaux souterraines, en éliminant ainsi le coûteux processus dépuration. Néanmoins, la qualité des sources souterraines est menacée par la pollution provoquée par le développement urbain et agricole. En 1995 le gouvernement danois a lancé un plan en 10 points pour améliorer la protection des eaux souterraines. En 1999 ce plan a été suivi par la décision de promouvoir une cartographie hydrogéologique à grande densité sur 37% du territoire du Danemark où se trouvent des zones de captages importantes. Les cartes seront utilisées pour établir les zones de protection des eaux souterraines, en tenant compte des conditions locales du site ainsi que des règlements conjoints dutilisation des territoires, afin de prévenir la pollution des eaux souterraines. La cartographie traditionnelle, basée seulement sur les données des forages, est trop imprécise pour ce but. Les travaux vont durer 10 ans avec un coût estimé à 120 millions deuros (€). Pour ces travaux les consommateurs vont payer une surcharge de € 0.02 par m³ deau potable, ceci pendant 10 ans. Cette révision de la stratégie du Danemark concernant la protection des ressources en eaux souterraines a démontré les raisons pour lesquelles on a accordé un rôle central aux nouvelles méthodes géophysiques dans la future cartographie hydrogéologique de vaste régions. On présente un exemple de cartographie géophysique réalisée dans la région dAarhus.

     

The persistence of the water budget myth and its relationship to sustainability

Sustainability and sustainable pumping are two different concepts that are often used interchangeably. The latter term refers to a pumping rate that can be maintained indefinitely without mining an aquifer, whereas the former term is broader and concerns such issues as ecology and water quality, among others, in addition to sustainable pumping. Another important difference between the two concepts is that recharge can be very important to consider when assessing sustainability, but is not necessary to estimate sustainable pumping rates. Confusion over this distinction is made worse by the Water Budget Myth, which comprises the mistaken yet persistent ideas that (1) sustainable pumping rates cannot exceed virgin recharge rates in aquifers, and (2) that virgin recharge rates must therefore be known to estimate sustainable pumping rates. Analysis of the water balance equation shows the special circumstances that must apply for the Water Budget Myth to be true. However, due to the effects recharge is likely to have on water quality, ecology, socioeconomic factors, and, under certain circumstances, its requirement for numerical modeling, it remains important in assessments of sustainability.An erratum to this article can be found at     

Arsenic in groundwater of the Bengal Basin, Bangladesh: Distribution, field relations, and hydrogeological setting

Arsenic contaminates groundwater across much of southern, central and eastern Bangladesh. Groundwater from the Holocene alluvium of the Ganges, Brahmaputra and Meghna Rivers locally exceeds 200 times the World Health Organisation (WHO) guideline value for drinking water of 10 µg/l of arsenic. Approximately 25% of wells in Bangladesh exceed the national standard of 50 µg/l, affecting at least 25 million people. Arsenic has entered the groundwater by reductive dissolution of ferric oxyhydroxides, to which arsenic was adsorbed during fluvial transport. Depth profiles of arsenic in pumped groundwater, porewater, and aquifer sediments show consistent trends. Elevated concentrations are associated with fine-sands and organic-rich sediments. Concentrations are low near the water table, rise to a maximum typically 20–40 m below ground, and fall to very low levels between about 100 and 200 m. Arsenic occurs mainly in groundwater of the valley-fill sequence deposited during the Holocene marine transgression. Groundwater from Pleistocene and older aquifers is largely free of arsenic. Arsenic concentrations in many shallow hand-tube wells are likely to increase over a period of years, and regular monitoring will be essential. Aquifers at more than 200 m below the floodplains offer good prospects for long-term arsenic-free water supplies, but may be limited by the threats of saline intrusion and downward leakage of arsenic.

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Resumen El arsénico ha contaminado gran parte de las aguas subterráneas en el Sur, centro y Este de Bangla Desh. Su concentración en las aguas subterráneas del aluvial Holoceno de los ríos Ganges, Brahmaputra y Meghna supera localmente en un factor 200 el valor guía del arsénico en el agua potable, establecido por la Organización Mundial de la Salud (OMS) en 10 µg/L. Aproximadamente, el 25% de los pozos de Bangla Desh superan el estándar nacional de 50 µg/L, afectando al menos a 25 millones de personas. El arsénico ha llegado a las aguas subterráneas por la disolución reductora de hidróxidos férricos a los que se adsorbe durante el transporte fluvial. Los perfiles del arsénico en las aguas subterráneas bombeadas, agua de poro y sedimentos del acuífero muestran tendencias coherentes. Las concentraciones elevadas están asociadas a arenas finas y sedimentos ricos en materia orgánica. Las concentraciones de arsénico son bajas cerca del nivel freático, se incrementan hasta un máximo que se localiza generalmente a entre 20 y 40 m bajo la cota del terreno, y disminuyen a valores muy pequeños entre alrededor de 100 y 200 m. El arsénico se encuentra sobretodo en las aguas subterráneas existentes en la secuencia de sedimentación que tuvo lugar en el valle durante la transgresión marina del Holoceno. Las aguas subterráneas del Pleistoceno y acuíferos más antiguos están mayoritariamente libres de arsénico. Es probable que las concentraciones de arsénico aumenten en los próximos años en muchos pozos de tipo tubo perforados manualmente, por lo que será esencial efectuar un muestreo regular. Los acuíferos ubicados a más de 200 m bajo las llanuras de inundación ofrecen buenas perspectivas de abastecimiento a largo plazo sin problemas de arsénico, pero pueden estar limitados por las amenazas de la intrusión salina y de la precolación de arsénico desde niveles superiores.

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Résumé Larsenic contamine les eaux souterraines dans la plus grande partie du sud, du centre et de lest du Bangladesh. Les eaux des nappes alluviales holocènes du Gange, du Brahmapoutre et de la Meghna dépassent localement 200 fois la valeur guide donnée par lOMS pour leau de boisson, fixée à 10 µg/l darsenic. Environ 25% des puits du Bangladesh dépassent la valeur standard nationale de 50 µg/l, affectant au moins 25 millions de personnes. Larsenic a été introduit dans les nappes par la dissolution par réduction doxy-hydroxydes ferriques sur lesquels larsenic était adsorbé au cours du transport fluvial. Des profils verticaux darsenic dans leau souterraine pompée, dans leau porale et dans les sédiments des aquifères montrent des tendances convergentes. Les concentrations élevées sont associées à des sédiments à sable fin et riches en matières organiques. Les concentrations sont faibles au voisinage de la surface de la nappe, atteignent un maximum typiquement entre 20 et 40 m sous le sol, puis tombent à des niveaux très bas entre 100 et 200 m. Larsenic est surtout présent dans les eaux souterraines de la séquence de remplissage de vallée déposée au cours de la transgression marine holocène. Les eaux souterraines des aquifères pléistocènes et plus anciens sont très largement dépourvus darsenic. Les concentrations en arsenic dans de nombreux puits creusés à la main doivent probablement augmenter au cours des prochaines années ; aussi un suivi régulier est essentiel. Les aquifères à plus de 200 m sous les plaines alluviales offrent de bonnes perspectives pour des alimentations en eau sans arsenic à long terme, mais ils peuvent être limités par les risques dintrusion saline et la drainance descendante de larsenic.

     

Fracture hydraulic conductivity in the Mexico City clayey aquitard: Field piezometer rising-head tests

A regional lacustrine aquitard covers the main aquifer of the metropolitan area of Mexico City. The aquitards hydraulic conductivity (K) is fundamental for evaluating the natural protection of the aquifer against a variety of contaminants present on the surface and its hydraulic response. This study analyzes the distribution and variation of K in the plains of Chalco, Texcoco and Mexico City (three of the six former lakes that existed in the Basin of Mexico), on the basis of 225 field-permeability tests, in nests of existing piezometers located at depths of 2–85 m. Tests were interpreted using the Hvorslev method and some by the Bouwer-Rice method. Results indicate that the distribution of K fits log-Gaussian regression models. Dominant frequencies for K in the Chalco and Texcoco plains range between 1E–09 and 1E–08 m/s, with similar population means of 1.19E–09 and 1.7E–09 m/s, respectively, which are one to two orders of magnitude higher than the matrix conductivity. In the Mexico City Plain the population mean is near by one order of magnitude lower; K=2.6E–10 m/s. The contrast between the measured K and that of the matrix is attributed to the presence of fractures in the upper 25–40 m, which is consistent with the findings of previous studies on solute migration in the aquitard.

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Resumen El acuífero principal del Área Metropolitana de la Ciudad de México está recubierto por un acuitardo regional lacustre, cuya conductividad hidráulica es fundamental para evaluar la protección natural de las aguas subterráneas contra los contaminantes presentes en superficie y su respuesta hidráulica. Este estudio analiza la distribución y variación de dicha conductividad en las llanuras de Chalco, Texcoco y Ciudad de México (tres de los seis lagos que existían al principio en la Cuenca de México) a partir de 225 ensayos de campo en piezómetros múltiples existentes, ubicados entre 2 y 85 m de profundidad. La interpretación de los ensayos se ha realizado mediante el método de Hvorslev y—algunos—el de Bouwer-Rice. Los resultados indican que la distribución de la conductividad se ajusta a modelos de regresión lognormales. Las frecuencias dominantes en las Llanuras de Chalco y Texoco están comprendidas entre 1^–9 y 10^–8 m/s, con medias de población similares de 1.19×10^–9 y 1.70×10^–9 m/s, respectivamente, que son dos órdenes de magnitud mayores que el valor de la matriz. En el Llano de México, la media es casi un orden de magnitud inferior (2.60×10^–10 m/s). Se atribuye este contraste entre la conductividad hidráulica medida y la de la matriz a la presencia de fracturas en el tramo superior situado entre 25 y 40 m, cosa que es coherente con estudios previos de migración de solutos en el acuitardo.

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Résumé Un imperméable régional dorigine lacustre recouvre le principal aquifère de la zone urbaine de la ville de Mexico. La conductivité hydraulique K de cet imperméable est fondamentale pour évaluer la protection naturelle de laquifère, contre les différents contaminants présents en surface, et sa réponse hydraulique. Cette étude analyse et les variations de K dans les plaines de Chalco, Texcoco et Mexico (trois des six anciens lacs qui existaient dans le Bassin de Mexico), sur la base de 225 essais de perméabilité sur le terrain, réalisés en grappes dans des piézomètres existants entre 2 et 85 m de profondeur. Les essais ont été interprétés avec la méthode de Hvorslev et certains avec la méthode de Bouwer-Rice. Les résultats indiquent que la distribution de K sajuste à des modèles de régression log-gaussiens. Les valeurs de K les plus fréquentes dans les plaines de Chalco et de Texcoco sont entre 1E–09 et 1E–08 m/s, avec des moyennes similaires de 1.19E–09 et 1.7E–09 m/s respectivement, qui sont dun ou deux ordres de grandeurs supérieures à la conductivité de la matrice. Dans la plaine de Mexico, la moyenne est proche dun ordre de grandeur en moins, avec 2.6E–10 m/s. Ce contraste entre le K mesuré et celui de la matrice est attribué à la présence de fractures dans les 25–40 m supérieurs, ce qui est en accord avec les études précédentes sur la migration de solutés au travers de limperméable.

     

Vertical migration of municipal wastewater in deep injection well systems,South Florida,USA

Deep well injection is widely used in South Florida, USA for wastewater disposal largely because of the presence of an injection zone (“boulder zone” of Floridan Aquifer System) that is capable of accepting very large quantities of fluids, in some wells over 75,000 m³/day. The greatest potential risk to public health associated with deep injection wells in South Florida is vertical migration of wastewater, containing pathogenic microorganisms and pollutants, into brackish-water aquifer zones that are being used for alternative water-supply projects such as aquifer storage and recovery. Upwards migration of municipal wastewater has occurred in a minority of South Florida injection systems. The results of solute-transport modeling using the SEAWAT program indicate that the measured vertical hydraulic conductivities of the rock matrix would allow for only minimal vertical migration. Fracturing at some sites increased the equivalent average vertical hydraulic conductivity of confining zone strata by approximately four orders of magnitude and allowed for vertical migration rates of up 80 m/year. Even where vertical migration was rapid, the documented transit times are likely long enough for the inactivation of pathogenic microorganisms.     

Effect of agricultural land use on the chemistry of groundwater from basaltic aquifers, Jeju Island, South Korea

Geochemical processes were identified as controlling factors of groundwater chemistry, including chemical weathering, salinization from seawater and dry sea-salt deposition, nitrate contamination, and rainfall recharge. These geochemical processes were identified using principal component analysis of major element chemistry of groundwater from basaltic aquifers in Jeju Island, South Korea, a volcanic island with intense agricultural activities. The contribution of the geochemical processes to groundwater chemistry was quantified by a simple mass-balance approach. The geochemical effects due to seawater were considered based on Cl contributions, whereas the effects due to natural chemical weathering were based on alkalinity. Nitrogenous fertilizers, and especially the associated nitrification processes, appear to significantly affect groundwater chemistry. A strong correlation was observed between Na, Mg, Ca, SO₄ and Cl, and nitrate concentrations in groundwater. Correspondingly, the total major cations, Cl, and SO₄ in groundwater were assessed to estimate relative effect of N-fertilizer use on groundwater chemistry. Cl originates more from nitrate sources than from seawater, whereas SO₄ originates mostly from rainwater. N-fertilizer use has shown the greatest effect on groundwater chemistry, particularly when nitrate concentrations exceed 6–7 mg/L NO₃–N. Nitrate contamination significantly affects groundwater quality and 18% of groundwater samples have contamination-dominated chemistry.     

Identifying and quantifying urban recharge: a review

The sources of and pathways for groundwater recharge in urban areas are more numerous and complex than in rural environments. Buildings, roads, and other surface infrastructure combine with man-made drainage networks to change the pathways for precipitation. Some direct recharge is lost, but additional recharge can occur from storm drainage systems. Large amounts of water are imported into most cities for supply, distributed through underground pipes, and collected again in sewers or septic tanks. The leaks from these pipe networks often provide substantial recharge. Sources of recharge in urban areas are identified through piezometry, chemical signatures, and water balances. All three approaches have problems. Recharge is quantified either by individual components (direct recharge, water-mains leakage, septic tanks, etc.) or holistically. Working with individual components requires large amounts of data, much of which is uncertain and is likely to lead to large uncertainties in the final result. Recommended holistic approaches include the use of groundwater modelling and solute balances, where various types of data are integrated. Urban recharge remains an under-researched topic, with few high-quality case studies reported in the literature. Electronic Publication     

The changing role of hydrogeology in semi-arid southern and eastern Africa

Much of southern and eastern Africa is semi-arid and heavily groundwater dependent. Borehole drilling commenced over a hundred years ago with magnetic and electrical resistivity surveys for borehole siting being introduced from 1936. Formalised training of hydrogeologists led in the 1970s to an almost standard approach to hydrogeological investigation and a period of stability followed, during which some major investigations were carried out. A period of decentralisation and fragmentation has since taken place in many parts of southern and eastern Africa, and groundwater monitoring and management are inadequate in many countries. All but six of the 14 SADC (Southern African Development Community) member states reportedly have an adequate monitoring network in place. However, groundwater demand is increasing and hydrogeologists need to promote the use of appropriate methodologies as an essential part of tackling the severe issues now facing the water sector in the region.     

Recharge processes: piston flow vs preferential flow in semi-arid aquifers of India

Study of groundwater recharge processes is vital for quantification of total natural recharge to the aquifers. One of the recharge processes demonstrated earlier by tracer experiments in the unsaturated zone is that of piston flow movement of soil moisture. Based on this recharge process, environmental tritium, chloride and injected tritium studies have been carried out extensively in various geological environs of India. The purpose of this paper is to evaluate the validity of the piston flow concept in different geological environs viz. consolidated fractured and weathered granites, semi-consolidated sandstones and unconsolidated alluvial tracts, and quantify the contribution from this process as well as that from the preferential flow mechanism using different tracers. Analysis of tracer data demonstrates that the preferential flow recharge process contributes very significantly (an average of 75% of total recharge) in the case of fractured granites and is important (an average of 33% of total recharge) for semi-consolidated sandstones, whereas the preferential flow recharge component is minimal in unconsolidated alluvial tracts (piston flow model is applicable). These findings necessitate re-evaluation of the total natural recharge potential of the above mentioned geological environs in view of the significant preferential flow recharge that is evidenced and estimated. Electronic Publication     

Numerical simulation of groundwater flow in regional rock aquifers, southwestern Quebec, Canada

The St. Lawrence Lowlands platform, Quebec, Canada, is a densely-populated area, heavily dependent on groundwater resources. In 1999, the Geological Survey of Canada initiated a large-scale hydrogeological assessment study over a 1,500 km² region northwest of Montreal. The objectives were to define the regional groundwater flow, and to give quantitative estimates of the groundwater dynamic parameters and of the available groundwater resources. The applied approach consisted of defining the hydrogeologic framework, hydraulic properties of the aquifer units, and groundwater dynamic components. Lower Paleozoic sedimentary rocks represent regional aquifer units. Coarse Quaternary fluvio-glacial sediments locally overlay the rock sequence and constitute an interface aquifer unit. Fine marine sediments confine most of the regional aquifers. Collected GIS based information was synthesized in a finite element numerical model. The regional saturated steady-state flow was calibrated under current stress conditions assuming an equivalent porous medium approach. Water budget calculations show that the total groundwater flow in regional aquifers amounts to 97.7 Mm³/y. Infiltration from precipitation provides 86.6% of the groundwater supply, while 9.6% comes from subsurface inflow and the remaining 3.8% is induced recharge from surface waters. Discharge from regional aquifers occurs through flow to streams (76.9%), groundwater withdrawal (18.4%), and underground outflow (4.7%).

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Resumen La plataforma de Tierras Bajas San Lorenzo, Quebec, Canadá, es un área densamente poblada que depende fuertemente de recursos de agua subterránea. En 1999 el Servicio Geológico de Canadá inició un estudio de evaluación hidrogeológica a gran escala sobre un área de 1,500 km² en la región noroeste de Montreal. Los objetivos fueron definir el flujo regional de agua subterránea y aportar estimados cuantitativos de los parámetros dinámicos de agua subterráne y de los recursos disponibles de agua subterránea. El enfoque aplicado consistió en definir el marco hidrogeológico, propiedades hidráulicas de las unidades acuíferas, y los componentes dinámicos de agua subterránea. Rocas sedimentarias del Paleozoico Inferior representan unidades regionales de acuíferos. Sedimentos fluvio-glaciares Cuaternarios gruesos sobreyacen localmente la secuencia rocosa y constituyen una unidad acuífera interfacial. Sedimentos marinos finos confinan la mayoría de acuíferos regionales. Información colectada basada en SIG se sintetizó en un modelo numérico de elemento finito. El flujo regional saturado en régimen permanente se calibró bajo condiciones de stress asumiendo un enfoque de medio poroso equivalente. Los cálculos de balance hídrico muestran que el flujo total de agua subterránea en acuíferos regional alcanza 97.7 Mm³/año. Infiltración a partir de lluvia aporta el 86.6% del abastecimiento al agua subterránea, mientras que el 9.6% proviene de entradas subsuperficiales y el restante 3.8% consiste de recarga inducida a partir de aguas superficiales. La descarga proveniente de acuíferos regionales ocurre a través de flujo a ríos (76.9%), utilización de agua subterránea (18.4%), y salida subterránea (4.7%).

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Résumé La plateforme Lowllands du Saint-Laurent, Québec, Canada, est une aire densément peuplée, dépendant grandement des ressources en eau souterraine. En 1999, le Service Géologique du Canada a initié une étude hydrogéologique à grande-échelle sur 1500 km² au Nord-Ouest de Montréal. Le sobjectifs ont été de définir la dynamique de lécoulement régional, et de donner des estimations quantitatives des paramètres dynamiques des ressources disponibles en eau souterraine. Lapproche utilisée consista à définir le cadre hydrogéologique de travail, les propriétés hydrauliques des unités aquifères, et les composantes dynamiques des eaux souterraines. Les roches sédimentaires du Paléozoïque Inférieur représentent les unités aquifères régionales. Les sédiments marins fins confinent la plus grande partie des aquifères régionaux. Les informations de base, collectées dans un SIG, ont été synthétisées dans un modèle numérique aux éléments finis. Lécoulement permanent régional, en zone saturée, a été calibré en conditions de stress en assumant une approche de milieu poreu équivalent. Les calculs du bilan hydrologique montrent que lécoulement total des eaux souterraines dans les aquifères régionaux atteind 97,7 Mm³/an. Linfiltration à partir des précipitations apporte 86.6% de leau souterraine exploitée; sachant que 9,6% proviennent découlement de subsurfaces, et que les 3,8% restants proviennent de la recharge via les eaux de surface. Le débit pompé des aquifères régionaux apparaît à travers lécoulement des cours deau, le rabattement des eaux souterraines (18.4%), et lécoulement ascendant (4.7%).

     

The role of some regional factors in the assessment of well yields from hard-rock aquifers of Fennoscandia

The attributes of about 13,600 hard-rock water wells were arranged in three profiles parallel to gradients of typical regional factors. These factors are thought to be of importance to groundwater yield from wells in the Fennoscandian crust and were subjected to a statistical analysis. The regional factors comprise annual rate of postglacial crustal uplift and annual average precipitation, whereas soil type, soil depth, and bedrock type are considered sub-regional and local factors. There is no clear trend in well yield along the regional gradients. The results of the statistical analysis indicate that for the typical regional variables, the rate of postglacial uplift and average annual precipitation explain not more than 11% of the observed variation in well yields. Some of these factors, and other factors not included in this study, work in opposite directions and may cancel each other out. It is concluded that other, more local factors, such as well depth, proximity to fracture-related lineaments and topography, have a greater influence on well yields in this area.

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Resumen Se ha recogido los atributos de aguas subterráneas con 13.600 años de antigüedad en tres perfiles perpendiculares a los gradientes de los factores regionales típicos, las cuales son captadas por pozos perforados en rocas duras. Se cree que estos factores tienen importancia en el rendimiento de los pozos realizados en la corteza de Fenoscandia, y han sido analizados estadísticamente. Los factores regionales comprenden la tasa anual de alzamiento postglacial y la precipitación media anual, mientras que el tipo y la profundidad del suelo, y el tipo de roca madre, son tratados como factores sub-regionales y locales. No se aprecia una tendencia clara en el rendimiento de los pozos a lo largo de los gradientes regionales. Los resultados del análisis estadístico indican que, para las variables regionales típicas, la tasa de alzamiento postglacial y la precipitación media anual explican como mucho el 11,2% de las variaciones observadas en el rendimiento de los pozos. Algunos de estos factores, así como otros no incluidos en el estudio, son de signo opuesto y pueden llegar a compensarse. Se concluye que factores diferentes, de escala más local, tales como la proximidad a lineamientos correlacionados con fracturas o la topografía, pueden afectar de forma más importante al rendimiento de los pozos en esta zona.

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Résumé Les propriétés d'environ 13,600 puits d'extraction d'eau souterraine dans le socle ont été réparties selon trois profils disposés perpendiculairement aux gradients de facteurs régionaux typiques. Ces facteurs sont considérés comme étant importants pour les rendements des puits dans le bouclier fenno-scandien et ont été soumis à une analyse statistique. Les facteurs régionaux sont le taux de soulèvement postglaciaire et les précipitations moyennes annuelles, alors que le type et l'épaisseur de sol, le type de substratum sont des facteurs sub-régionaux et locaux. Il n'existe pas de tendance dans le rendement des puits selon les gradients régionaux. Les résultats de l'analyse statistique indiquent que pour les variables régionales typiques, le taux de soulèvement postglaciaire et les précipitations moyennes annuelles n'expliquent pas plus de 11,2% de la variation observée du rendement des puits. Certains de ces facteurs, ainsi que d'autres non pris en compte dans cette étude, jouent dans des directions opposées et peuvent s'annuler l'un l'autre. En conclusion, d'autres facteurs, plus locaux, tels que la proximité de linéaments corrélés aux fractures et la topographie peuvent avoir une grande importance pour le rendement des puits dans cette région.

     

Hydrogeology in North America: past and future

This paper is a retrospective on the evolution of hydrogeology in North America over the past two centuries, and a brief speculation of its future. The history of hydrogeology is marked by developments in many different fields such as groundwater hydrology, soil mechanics, soil science, economic geology, petroleum engineering, structural geology, geochemistry, geophysics, marine geology, and more recently, ecology. The field has been enriched by the contributions of distinguished researchers from all these fields. At present, hydrogeology is in transition from a state of discovering new resources and exploiting them efficiently for maximum benefit, to one of judicious management of finite, interconnected resources that are vital for the sustenance of humans and other living things. The future of hydrogeology is likely to be dictated by the subtle balance with which the hydrological, erosional, and nutritional cycles function, and the decision of a technological society to either adapt to the constraints imposed by the balance, or to continue to exploit hydrogeological systems for maximum benefit. Although there is now a trend towards ecological and environmental awareness, human attitudes could change should large parts of the populated world be subjected to the stresses of droughts that last for many decades.

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Resumen Este articulo es una retrospectiva sobre la evolución de la hidrogeología en Norte América en los pasados dos siglos, y una breve especulación de su futuro. La historia de la hidrogeología está marcada por desarrollos en muchos campos diferentes tal como hidrología de aguas subterráneas, mecánica de suelos, ciencia del suelo, geología económica, ingeniería del petróleo, geología estructural, geoquímica, geofísica, geología marina, y más recientemente, ecología. El campo se ha enriquecido por las contribuciones de investigadores distinguidos en todos esos campos. Actualmente, la hidrogeología se encuentra en transición de un estado de descubrir nuevos recursos y explotarlos eficientemente para un beneficio máximo, a un estado de gestión juiciosa de recursos finitos, interconectados, que son vitales para el sustento de humanos y otras cosas vivientes. El futuro de la hidrogeología posiblemente esté determinado por el balance sutil con el cual funcionan los ciclos nutricionales, erosionales e hidrológicos, y la decisión de una sociedad tecnológica para ya sea adaptarse a las restricciones impuestas por el balance o para continuar con la explotación de los sistemas hidrogeológicos para un beneficio máximo. Aunque existe actualmente una tendencia hacia la conciencia ambiental y ecológica, las actitudes humanas podrían cambiar en caso de que grandes partes del mundo poblado estén sujetas a las presiones de sequías que duran por muchas décadas.

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Résumé Cet article est une rétrospective de lévolution de lhydrogéologie en Amérique du Nord sur les deux derniers siècles, et une brève évaluation de son futur. Lhistoire de lhydrogéologie est marquée par le développement de plusieurs techniques de terrain telles, lhydrologie des eaux souterraines, la mécanique des sols, les sciences du sol, la géologie économique, l ingénierie pétrolière, la géologie structurale, la géochimie, la géophysique, la géologie marine et plus récemment lécologie. La science a été enrichie par la contribution de plusieurs chercheurs distingués, provenant de toutes ces branches. A présent, lhydrogéologie est à la transition entre la volonté de découvrir de nouvelles ressources et l exploitation la plus bénéfique au possible, et un management judicieux des ressources finies, interconnectées, qui sont vitales pour l approvisionnement des hommes et autres formes de vie. Le futur de l hydrogéologie sera dicté par la balance subtile dans laquelle intervient les cycles de lhydrologie, de lérosion, de la nutrition, et la décision dune société technologique qui sadapterait aux contraintes de la balance, ou qui continuerait dexploiter les systèmes hydrologiques pour un bénéfice maximum. Par ailleurs il y a une nette tendance à inclure les aspects écologiques, les aspects environnementaux, et les changements humains qui pourraient être influencés par les modifications hydrogéologiques observées depuis une dizaine dannées.

     

Numerical modeling of contaminant transport resulting from dissolution of a coal-tar pool in an experimental aquifer

A previously developed two-dimensional numerical model is further developed for simulating the transport of dissolved contaminants originating from dissolution of a coal tar pool in a stratified, saturated porous medium. The model is used to simulate contaminant transport resulting from a rectangular-shaped coal-tar-pool dissolution experiment conducted in a large-scale experimental aquifer. The experimental porous medium consists of two sand strata, a high-hydraulic-conductivity upper stratum and a low-hydraulic-conductivity bottom stratum. The experiment was conducted to a time of 354 days and the groundwater velocity was changed several times within this duration. Model simulations show good agreement against observed contaminant concentrations, and simulations show that dissolved solute below the pool migrated deeper into the bottom stratum as compared to the upper stratum. Furthermore, simulations also suggest that contaminant concentrations in the lower stratum never reached quasi steady-state during the experimental time frame.     

Predicting long-term contamination potential of perched groundwater in a mine-waste heap using a random-walk method

Mine-waste heaps are potential long-term sources of contamination for surface-water courses and groundwater systems. Application of a novel physically based particle-tracking model to a mine-waste heap in northern England, UK, has enabled predictions to be made of the lifetime of contaminants leaching, revealing a pattern of source-mineral depletion. A mine-waste heap is conceptualised by a series of one-dimensional unsaturated “columns” in which active weathering of source minerals takes place. These columns drain into a saturated zone, through which the contaminants are transported to the heap discharge. Solute transport is simulated within the model by the random-walk method while reaction kinetics are incorporated to account for the timescales of source mineral depletion. Results reveal that the mine-waste heap is likely to remain polluting for several centuries, with the governing factor in the magnitude of pollution being the transport of the reactant, oxygen, to the source-mineral surfaces.     

Protection of karst aquifers in the Dinarides in Croatia

 This paper presents karst water protection measures being introduced in the Dinarides of Croatia. The spring sites for the water supply of the town of Rijeka, for its 200 000 inhabitants and the largest harbor of the northeastern side of the Adriatic Sea, have been used as a pilot research area. The European research project was used, and protection of water was generally divided into three phases. A categorization of springs has been made, and five basic protection zones have been distinguished. The rules of behavior in protected zones have been outlined. For the first time, the term water-supply "reserve" has been introduced, referring to the parts of the mountainous region where karst groundwater is recharged. Received: 26 March 1997 · Accepted: 22 July 1997