Hydrogeological Conceptual Model Research Articles

IGW Groundwater Numerical Simulation Software in Power Plant Prediction of Groundwater Contamination

Given the increasing groundwater exploitation, an attempt is enforced to establish the hydro geological conceptual model of this area. This carries on the numerical simulation of groundwater flow by using the IGW, which is known as the international standard software. The mathematical model established in this paper has reflected the local practical hydro geological conditions and can be used to predict and manage groundwater resources.

Application of statistical approaches to analyze geological, geotechnical and hydrogeological data at a fractured-rock mine site in Northern Canada

Mine site characterization often results in the acquisition of geological, geotechnical and hydrogeological data sets that are used in the mine design process but are rarely co-evaluated. For a study site in northern Canada, bivariateandmultivariate(hierarchical)statistical techniques are used to evaluate empirical hydraulic conductivity estimation methods based on traditional rock mass charac- terisation schemes, as well as to assess the regional hydrogeological conceptual model. Bivariate techniques demonstrate that standard geotechnical measures of fractur- ing are poor indicators of the hydraulic potential of a rock mass at the study site. Additionally, rock-mass-permeability schemes which rely on these measures are shown to be poor predictors of hydraulic conductivity in untested areas. Multivariate techniques employing hierarchical cluster anal- ysis of both geotechnical and geological data sets are able to identify general trends in the data. Specifically, the geolog- ical cluster analysis demonstrated spatial relationship be- tween intrusive contacts and increased hydraulic conductivity. This suggests promise in the use of clustering methods in identifying new trends during the early stages of hydrogeological characterization.

Numerical simulation and evaluation of groundwater resources in a fractured chalk aquifer: a case study in Zinder well field, Niger

Groundwater is often a unique water source for agriculture, industry and domestic use for local inhabitants in semi-arid African continent owing to shortage of surface water and rainfall. It is of significance to quantify and assess the groundwater resources for local sustainable development in order to correctly evaluate groundwater resources of Zinder well field with fractured media in Zinder, Niger. A conceptual model of hydrogeology was set up by a geological and hydrogeological survey. For simulating the real conditions, a large multi-well pumping test with designed pumping rate was conducted. In addition, a two-dimensional finite-element transient flow model was developed to simulate groundwater flow at the site. Results show that generally good agreements have been found between the simulated and observed hydrogeology heads for the test. The hydraulic parameters were obtained from the pumping test. A 11-year prediction of groundwater resources has been made under three exploitation schemes, respectively, and it indicates that the well field can offer 7,000 m3/day when the aquifer remains confined. An optimal scheme of exploitation is provided.

Stable isotopes in rain and cloud water in Madeira: contribution for the hydrogeologic framework of a volcanic island

Madeira is a volcanic island whose economy is highly dependent on groundwater. Previous studies suggest that, besides precipitation, cloud water interception contributes to groundwater recharge. As such, the isotopic characterization of the sources of recharge is useful for the hydrogeological framework of the island. The δ 18O and δ 2H content of rain and cloud water was analyzed during three campaigns. Rain plots over a local meteoric water line (LMWL) whose equation is δ 2H = 7.92 δ 18O + 10.49 (R 2 = 0.97, n = 43). The volume-weighted average meteoric line (WLMWL) is given by δ 2H = 7.97 δ 18O + 10.57 (R 2 = 0.98, n = 20). Both are similar to the global meteoric water line which indicates, along with the d-excess values (10.8 and 11 ‰ for the LMWL and WLMWL, respectively), that rain originates, essentially in the Atlantic. Seasonal variations were also observed and rain in Campaign II was isotopically enriched and had a higher d-excess (δ 18Omean −3.63 ‰; δ 2Hmean −16.3 ‰; d-excess 12.7 ‰), than rain in Campaign III (δ 18Omean −7.01 ‰; δ 2Hmean −46.5 ‰; d-excess 9.5 ‰). Campaign I stood in between. These variations were probably the result of differences in temperature, water vapor source areas and rain forming processes. Rain was found to become increasingly depleted with altitude (δ 18O), at a rate of −0.15 ‰/100 m and −0.11 ‰/100 m in the windward and leeward sides, respectively. Cloud water was always isotopically enriched when compared with rain at the same altitude. This was related to constant water vapor replenishment of orographic clouds, to the fact that it usually represents an early stage condensation from air moisture and to the smaller size of cloud water droplets when compared to rain droplets. These results will be useful to refine Madeira’s hydrogeological conceptual model. Future extended sampling during more years, with smaller sampling periods and single rainfall events should be useful to support the conclusions of this study.

Hidrogeologia do norte da Serra de Chiapas, México: modelo concetual baseado na caraterização geoquímica de nascentes cársicas salobras ricas em sulfuretos

Conspicuous sulfide-rich karst springs flow from Cretaceous carbonates in northern Sierra de Chiapas, Mexico. This is a geologically complex, tropical karst area. The physical, geologic, hydrologic and chemical attributes of these springs were determined and integrated into a conceptual hydrogeologic model. A meteoric source and a recharge elevation below 1,500 m are estimated from the spring-water isotopic signature regardless of their chemical composition. Brackish spring water flows at a maximum depth of 2,000 m, as inferred from similar chemical attributes to the produced water from a nearby oil well. Oil reservoirs may be found at depths below 2,000 m. Three subsurface environments or aquifers are identified based on the B, Li+, K+ and SiO2 concentrations, spring water temperatures, and CO2 pressures. There is mixing between these aquifers. The aquifer designated Local is shallow and contains potable water vulnerable to pollution. The aquifer named Northern receives some brackish produced water. The composition of the Southern aquifer is influenced by halite dissolution enhanced at fault detachment surfaces. Epigenic speleogenesis is associated with the Local springs. In contrast, hypogenic speleogenesis is associated with the brackish sulfidic springs from the Northern and the Southern environments.

An investigation of the basement complex aquifer system in Lofa county, Liberia, for the purpose of siting boreholes

Liberia is recovering from a 14 year civil war and only 51% of the rural population has access to safe drinking water. Little hydrogeological knowledge survives in Liberia, increasing the difficulty in successfully siting new boreholes. An understanding of the local hydrogeological environment is therefore needed to improve borehole site selection and increase success rates. This research provides a semi-quantitative characterization of the hydrogeological environment of the basement aquifer in Lofa county, Liberia. Based on literature review and analysis of borehole logs, the study has developed a conceptual hydrogeological model for the local conditions, which is further characterized using 2D geoelectrical sections. Groundwater is predominantly obtained from the saprolite and underlying fractured bedrock, but specific capacities (median 281 l h −1 m −1 ; 25th and 75th percentile of 179 and 490 l h −1 m −1 , respectively) are constrained by the limited thickness of the saturated saprolite. This study has shown that the groundwater resources in the crystalline basement in this part of Liberia conform to the general conceptual model, allowing standard techniques used elsewhere for siting and developing groundwater to be used.

High‐resolution conceptual hydrogeological model of complex basaltic volcanic islands: a Mayotte, Comoros, case study

AbstractWe present a high‐resolution conceptual hydrogeological model for complex basaltic volcanic islands based on Mayotte Island in the Comoros. Its geological structure and hydrogeological functioning are deduced from a large dataset: geological mapping, geophysics, some forty new boreholes, piezometric data, hydraulic conductivity, hydrochemical data, etc. We describe previously unknown deep cut‐and‐fill palaeovalleys. The resulting conceptual geological and hydrogeological model of the island is very different from the Hawaiian model, in that it lacks a low‐elevation basal aquifer and dyke‐impounded high‐level aquifers. It is closer to the Canary Islands model, which has, however, not yet been described at a high‐resolution scale. It does not have a continuous aquifer, but rather a discontinuous succession of perched aquifers separated by aquicludes and aquitards. This results more from the complex geological structure of the island, which has experienced several phases of volcanism, erosion and weathering, than from its age, but is also a result of the high‐resolution scale of the model. High‐resolution conceptual modelling is now necessary to solve problems of applied geology and hydrogeology.

Groundwater salinity and hydrochemical processes in the volcano-sedimentary aquifer of La Aldea, Gran Canaria, Canary Islands, Spain

The origin of the groundwater salinity and hydrochemical conditions of a 44km2 volcano-sedimentary aquifer in the semi-arid to arid La Aldea Valley (western Gran Canaria, Spain) has been studied, using major physical and chemical components. Current aquifer recharge is mainly the result of irrigation return flows and secondarily that of rainfall infiltration. Graphical, multivariate statistical and modeling tools have been applied in order to improve the hydrogeological conceptual model and identify the natural and anthropogenic factors controlling groundwater salinity. Groundwater ranges from Na–Cl–HCO3 type for moderate salinity water to Na–Mg–Cl–SO4 type for high salinity water. This is mainly the result of atmospheric airborne salt deposition; silicate weathering, and recharge incorporating irrigation return flows. High evapotranspiration produces significant evapo-concentration leading to relative high groundwater salinity in the area. Under average conditions, about 70% of the water used for intensive agricultural exploitation in the valley comes from three low salinity water runoff storage reservoirs upstream, out of the area, while the remaining 30% derives from groundwater. The main alluvial aquifer behaves as a short turnover time reservoir that adds to the surface waters to complement irrigation water supply in dry periods, when it reaches 70% of irrigation water requirements. The high seasonality and intra-annual variability of water demand for irrigation press on decision making on aquifer use by a large number of aquifer users acting on their own.

Behaviour of a small sedimentary volcanic aquifer receiving irrigation return flows: La Aldea, Gran Canaria, Canary Islands (Spain)

In many arid and semi-arid areas, intensive cultivation is practiced despite water commonly being a limiting factor. Often, irrigation water is from local aquifers or imported from out-of-area aquifers and surface reservoirs. Irrigation return flows become a significant local recharge source, but they may deteriorate aquifer water quality. La Aldea valley, located in the western sector of Gran Canaria Island (Atlantic Ocean), is a coastal, half-closed depression in altered, low-permeability volcanics with alluvium in the gullies and scree deposits over a large part of the area. This area is intensively cultivated. Irrigation water comes from reservoirs upstream and is supplemented (average 30 %) by local groundwater; supplementation goes up to 70 % in dry years, in which groundwater reserves are used up to exhaustion if the dry period persists. Thus, La Aldea aquifer is key to the water-supply system, whose recharge is mostly from return irrigation flows and the scarce local rainfall recharge on the scree formations, conveyed to the gully deposits. To quantify the hydrogeological conceptual model and check data coherence, a simplified numerical model has been constructed, which can be used as a tool to help in water management.

Regional hydrogeology for groundwater resource management policies. The Latium volcanic domain (central Italy)

Growing urban areas in the Latium volcanic domain has resulted in the increase of water demand. The uncontrolled increase in water withdrawals cause an inexorable reduction of springs discharges and progressive drawdown of groundwater levels. This emergency needs an urgent rationalization of groundwater management thorough understanding of qualitative and quantitative features of the aquifers. The main aim of this paper is to emphasize the importance of the method of study and the results obtained by researchers belonging to the Laboratory of Quantitative Hydrogeology (University of Roma Tre) to support the use and protection of groundwater resources. Therefore, we propose a summary of methods applied in previous hydrogeology studies that have contributed to legislation on groundwater resources management in the volcanic aquifers. The study area corresponds to the Latium volcanic domain and covers approximately 6500 km2. About 3000 stratigraphic data and about 2600 water points have been collected in order to set up a conceptual hydrogeological model. The conceptual model has been validated by the resolution of the hydrological budget. Detailed evaluation of the water supply is essential for the correct setting of the hydrological budget, in fact it represents the main output of the budget. These analysis highlight the condition of the resource. Critical areas have been identified for reshaping of water supply in order to increase environmental remediation and economic development.

Coupling Hydrotoponymy and GIS Cartography: A Case Study of Hydrohistorical Issues in Urban Groundwater Systems, Porto, NW Portugal

AbstractThe aim of this multidisciplinary study is to retrospectively examine hydrohistorical issues, namely hydrogeographic, hydrotoponymical and hydrogeological features, in order to assess the evolution of the Porto urban groundwater system (NW Portugal). To achieve these goals, the comparison of two main field inventories in a large urban region was performed by (i) historical mapping of sources and groundwater data from scientific reports spanning the late 17th century to the early 20th; and (ii) hydrogeologic and hydrotoponymical field inventory performed under current conditions. These field inventories permitted the location of springs, dug wells, fountains, public washing places and underground water galleries, which collected groundwater to supply the population of Porto until the early 20th century. This study also allowed the development of a hydrotoponymical classification for urban areas and a field hydrotoponymical inventory data sheet. This research integrated several techniques based on historical hydrogeography, hydrogeology and urban geosciences. The results of the field inventories were combined into both a database and a Geographical Information System (GIS) platform. This unified methodology allowed a cross‐check and analysis of several levels of information, namely hydrotoponymy, hydroclimatology, hydrogeology, structural geology and geomorphology. This perspective led to an assessment of the evolution of the quality of water resources in large urban areas over time. In addition, the role of hydrotoponymical features is presented in order to support the hydrogeological conceptual model for large urbanised areas.

Modèle conceptuel de la migration d’un lixiviat dans un aquifère poreux, intégrant des données de caractérisation provenant de sources multiples (St-Lambert, Canada)

Numerical models encompassing source zones and receptors, based on representative conceptual models and accounting for aquifer heterogeneity, are needed to understand contaminant migration and fate; however, aquifer characterization seldom provides the necessary data. This study aimed to develop a workflow for field characterization and data integration, which could: (1) be adapted to the definition of subwatershed-scale aquifer heterogeneity (over 10 km2) and (2) adequately support mass transport model development. The study involved the field investigation of a shallow granular aquifer in a 12-km2 subwatershed in Saint-Lambert-de-Lauzon, Canada, in which a decommissioned landfill is emitting a leachate plume managed by natural attenuation. Using proven field methods, the characterization sequence was designed to optimize each method in terms of location, scale of acquisition, density and quality. The emphasis was on the acquisition of detailed indirect geophysical data that were integrated with direct hydraulic and geochemical data. This report focuses on the first qualitative and geostatistical data integration steps of the workflow leading to the development of a hydrogeological conceptual model. This is a prerequisite for further integration steps: prediction of hydrofacies and hydraulic conductivity (K), geostatistical simulations of K, studies of geochemical processes and numerical modeling.

Conceptual hydrogeological model and aquifer system classification of a small volcanic island (La Gomera; Canary Islands)

Conceptual groundwater models in volcanic island aquifers remain an issue in many regions of the world. This study takes advantage of the large number of outcrops exposing the inner structure of La Gomera (Canary Islands), due to its inactivity during the last 2.5Ma, to develop a conceptual groundwater model that helps improving groundwater resource management in the island and increasing knowledge in volcanic aquifers. Based on a volcanostratigraphic model, five hydrostratigraphic units have been defined that include two main aquifers and volcaniclastic deposits located between them that control the vertical movement of the groundwater. The island has been classified into four aquifer systems or water management units based on their hydrogeological features that permit a sustainable and independent management of the resources of one aquifer system in relationship with the other ones. The consideration of the complexity and heterogeneity of La Gomera geology has allowed to develop a conceptual groundwater flow model and to identify four general groundwater situations: 1) groundwater in the Upper aquifer discharging to the sea; 2) groundwater in the Upper aquifer springing out along the main ravines; 3) groundwater in the Basal aquifer impounded by dikes and; 4) groundwater in the Basal aquifer discharging to the sea.

The role of airborne geophysics in facilitating long-term outback water solutions to support mining in South Australia

Mining and energy development in South Australia's far north is set to have significant consequences for the water resources of the region. These sectors generate significant economic value to the State and their support remains a priority for the government. The scale of the planned developments and the potential from current exploration programs facilitated by the South Australian Government through PACE Program will result in a substantial increase in infrastructure requirements, including access to water resources and Aboriginal lands for potential mine developments. Increased demand for water and in particular groundwater is compromised by the limited knowledge we have about these resources. This includes information about their character, variability, sustainability and their relationship to environmental and cultural assets, which is most notable in the priority areas for development. There is a recognised need to develop this knowledge so that water is not a limiting factor to development. In this paper results from the Goyder Institute's Long-Term Outback Water Solutions (G-FLOWS) Project are presented. Particular reference is made to work completed in the Musgrave Province. It illustrates the role of local scale AEM, acquired for exploration, and regional scale airborne magnetics in helping develop a hydrogeological conceptual model for the Province. The AEM data reveal a complex, extensive inset palaeovalley system which contains groundwater of variable quality (2000 - 4500 mg/L TDS). Examination of their location against the regional magnetics indicates a strong lithostructural control on their orientation and distribution. If mineral resources were to be developed in the area, these groundwater systems would represent the best option for water supply. A regional scale water resource map, based on information gleaned from the geophysics, existing hydrogeological and digital elevation data, is presented that provides a framework for groundwater resource determination when/if mineral deposits were to be mined in the region.

Assessment of geochemistry and hydrogeochemical processes in groundwater of the Tefenni plain (Burdur/Turkey)

The Tefenni (Burdur) plain is located in the southwest of Turkey and is semi-closed basin. Groundwater is densely used as drinking, irrigation and domestic water in the Tefenni plain. Hydrogeochemical processes controlling groundwater chemistry and geochemical assessment of groundwater were investigated in the Tefenni (Burdur/Turkey) plain. The conceptual hydrogeological model of the plain was prepared for qualitative description of the underground geology and interpretation of hydrogeochemical processes of the study area. In this study, groundwater samples for two seasons were analyzed and major ion chemistry of groundwater was researched to understand the groundwater geochemistry. Two major hydrochemical facies (Ca2+–Mg2+–HCO3− and Mg2+–Ca2+–HCO3−) were determined in the area. Mg2+, Na+, SO42− and Cl− concentrations of water samples increased seasonally related to ion exchange of minerals in rocks by rainwater in wet season. Various graphical plots and multivariate statistical analysis (Pearson correlation analysis) were used for identifying the occurrence of different geochemical processes. Carbonate weathering in dry season and silicate weathering in wet season were the major hydrogeochemical processes in the study area. In addition, ion exchange and reverse ion exchange were two possible processes of water–rock interaction in the basin. The mechanism controlling groundwater chemistry at the Tefenni plain is originally regulated by the geogenic process rather than antropogenic activities.

Seepage Filed Studies on the Effect of the Proposed Underground Garage

This paper intends to solve the leakage of the surface waters on the proposed underground garage impact from a practical engineering, so we carry on the detailed analysis about the surrounding hydro geological conditions to provide scientific basis for underground garage waterproof design. On that basis, we establish the hydro geological conceptual model, using Visual MODFLOW4.1 software to simulate the seepage field in two kinds of working conditions, and get the result of the surface waters on the proposed garage impact. Thus in the underground garage of the soleplate waterproof design we adopt different block waterproof practices which may save a lot of fund, and have the important theoretical and practical significance to us.

Evaluation of groundwater-surface water interaction through groundwater modelling: simulation of the effects of removal of a dam along a river at a contaminated site in Northern France

A numerical groundwater flow model has been developed for an industrial site bounded by a river in in Basse Normandie, Northern France. The scope of the work was the optimisation of the existing groundwater pump and treat system and the prediction of possible effects on groundwater circulation after the future removal of a dam located along the river. The model has been implemented with the finite difference code MODFLOW 2005 and represents an area with an extension of approximately 800 x 500 m. It has been calibrated using static conditions groundwater head data (wells deactivated) and verified with 1) abstracting conditions (wells abstracting) head data, 2) simulating pumping tests with transient simulations and 3) comparing measured average river baseflow with modelled river drainage. The model indicates that the hydraulic barrier in the present abstraction scenario has some problematic areas and needs some improvements, as confirmed by the hydrochemical data of the river water. A first predictive scenario has been developed to optimise the barrier, indicating that a flow rate of 0.5 m3/h each at three new barrier wells, in addition to the present abstraction scenario, should ensure the hydraulic containment of the site. A second predictive scenario simulates the optimised groundwater abstractions without the presence of the dam along the neighbouring river. In these conditions, the river will increase the drainage effect on the aquifer, requiring a further increase in the rate of abstraction from the existing and new wells to ensure the hydraulic containment. With this paper we would like to present an example of what we think is a correct professional approach, with the design of the simplest model as possible depending on the hydrogeological conceptual model complexity, the abundance of data and the model objectives, and where multiple confirmations of the correctness of groundwater model results have been searched for.

Impact of groundwater withdrawals on the interaction of multi-layered aquifers in the Viterbo geothermal area (central Italy)

The impact of groundwater withdrawals on the interaction between multi-layered aquifers with different water qualities in the Viterbo geothermal area (central Italy) was studied. In this area, deep thermal waters are used to supply thermal spas and public pools. A shallow overlying aquifer carries cold and fresh water, used for irrigation and the local drinking-water supply. Starting with a conceptual hydrogeological model, two simplified numerical models were implemented: a steady-state flow model of the entire groundwater system, and a steady-state flow and heat transport model of a representative area, which included complex interactions between the aquifers. The impact of increased withdrawals associated with potential future development of the thermal aquifer must be considered in terms of the water temperature of the existing thermal sources. However, withdrawals from the shallow aquifer might also influence the discharge of thermal sources and quality of the water withdrawn from the shallow wells. The exploitation of the two aquifers is dependent on the hydraulic conductivity and thickness of the intervening aquitard, which maintains the delicate hydrogeological equilibrium. Effective methods to control this equilibrium include monitoring the vertical gradient between the two aquifers and the residual discharge of natural thermal springs.

Hydro-geochemical impact of CO2 leakage from geological storage on shallow potable aquifers: A field scale pilot experiment

A shallow CO2 injection experiment was conducted in an unconfined, unconsolidated siliclastic aquifer in western Denmark. The aims were to test injection and sampling systems, confirm the conceptual hydrogeological site model and determine the aquifers potential geochemical response to a larger scale, sustained CO2 injection in order to finalize design of the main release experiment. Food grade CO2 (45kg in 48h) was injected at 10m depth into glacial sand and water chemistry subsequently monitored. Results indicate the injection system effectively delivered CO2 gas into the glacial sand layer where it dissolved and moved with advective flow. Dissolved CO2 was not detected in the aeolian sand (0–5m depth) indicating prevention of migration due to permeability heterogeneities. Dissolved CO2 in the glacial sand (5–10m depth) created a plume of depressed pH (5.6–4.7), elevated EC (166–304μS/cm) and concurrent increases in dissolved ion concentrations. EC was the most effective indicator for presence of dissolved CO2. Ionic concentration changes were generally slight with increases in Al, Ba, K, Na, Mg, Si, Sr and Zn forming the major changes. Water quality was not significantly affected and risks from small scale, short duration CO2 contamination appear minimal for this geological setting.

Delineating coastal groundwater discharge processes in a wetland area by means of electrical resistivity imaging, 224Ra and 222Rn

AbstractCoastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peníscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra‐enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra‐rich groundwater have induced high activities of Ra isotopes and 222Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modelling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers (224Ra, 222Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater‐fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd.