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1
Rowe, R. Kerry, and John R. Booker. "Contaminant migration through fractured till into an underlying aquifer." Canadian Geotechnical Journal 27, no. 4 (August 1, 1990): 484–95. http://dx.doi.org/10.1139/t90-063.
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This paper examines the potential impact on groundwater quality of contaminant migration from a landfill site, through a fractured till, and into an underlying aquifer. The paper describes a simple, semi-analytic technique for modelling contaminant transport through the fractured till, including consideration of diffusion of contaminants from the fractures into the till matrix, sorption, and radioactive decay. The model also considers the finite mass of contaminant and dilution due to the flow of groundwater in the aquifer. The model can be readily implemented on a microcomputer. The model allows examination of variations in fracture spacing, fracture opening size, thickness of the fractured zone, diffusion coefficient, dispersivity, effective porosity of the matrix, radioactive decay, Darcy velocity, thickness of the aquifer, distribution coefficient, and mass of contaminant. The paper describes the results of a limited parametric study that, inter alia, examines the effects of uncertainty in fracture spacing, the thickness of the fractured till, and the effective porosity of the till matrix. Some of the practical implications are discussed. Key words: contaminant migration, fractures, till, groundwater, pollution, landfill, waste disposal.
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Andrade, Rolland. "Delineation of Fractured Aquifer Using Numerical Analysis (Factor) of Resistivity Data in a Granite Terrain." International Journal of Geophysics 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/585204.
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In hard rock terrain, fractured aquifers comprise the major source of groundwater availability where the phreatic aquifer is desaturated. Identification of fracture zones in hard rock terrain and potential groundwater source delineation had been a perennial problem in hydrology. The purpose of this paper is to highlight the study over a small watershed area, in a granite terrain, wherein an attempt was made to delineate and map the fractured aquifer using numerical (factor) analysis of the conventional vertical electrical sounding data, which was obscure in curve matching technique. This numerical approach in concatenation with resistivity imaging or other techniques would prove to be an effective tool in groundwater exploration.
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Hasan, Muhammad, Yanjun Shang, Weijun Jin, and Gulraiz Akhter. "Assessment of Aquifer Vulnerability Using Integrated Geophysical Approach in Weathered Terrains of South China." Open Geosciences 11, no. 1 (December 31, 2019): 1129–50. http://dx.doi.org/10.1515/geo-2019-0087.
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Abstract Despite being rich in groundwater resources, assessment of hard-rock aquifers in many areas of Asia is difficult given their strong heterogeneity. However, delineation of such aquifers is essential for estimation of the groundwater reserves. In addition, the vulnerability of hard-rock aquifers is controlled by the weathered/fractured zones because it is the place where most of the groundwater reserves are contained. In this work, an integrated approach of the electrical resistivity tomography (ERT), high precision magnetic, X-ray Diffraction (XRD), physicochemical analysis and pumping test data was performed to investigate the hard-rock aquifers occurring in the weathered terrains. This approach reveals seven fractures/faults (F1 to F7) and four discrete layers such as the topsoil cover, highly weathered, partly weathered and unweathered rock. The groundwater resources are estimated as a function of different parameters i.e., aquifer resistivity (ρo), transverse unit resistance (Tr), hydraulic conductivity (K), transmissivity (T), rock formation factor (F) and rock porosity (Φ). These parameters divide the groundwater resources into four aquifer potential zones with specific ranges of ρo, Tr, K, T, F and Φ i.e., high, medium, poor, and negligible potential aquifers. The results suggest that the high potential aquifer reserves are contained within the weathered/fractured and fault zones. The X-ray diffraction (XRD) technique analyzes quartz as the major mineral (>50%). The physicochemical and geophysical analysis suggests good groundwater quality in the investigated area. The integrated results are highly satisfied with the available borehole information. This integrated geophysical approach for the estimation of groundwater resources is not only applicable in the weathered terrains of South China, but also in many other areas of the weathered/fractured aquifer in Asia and beyond.
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Meyzonnat, Guillaume, Florent Barbecot, José Corcho Alvarado, Daniele Luigi Pinti, Jean-Marc Lauzon, and Renald McCormack. "Depth–Sequential Investigation of Major Ions, δ18o, δ2h and δ13C in Fractured Aquifers of the St. Lawrence Lowlands (Quebec, Canada) Using Passive Samplers." Water 13, no. 13 (June 29, 2021): 1806. http://dx.doi.org/10.3390/w13131806.
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General and isotopic geochemistry of groundwater is an essential tool to decipher hydrogeological contexts and flow paths. Different hydrogeochemical patterns may result from the inherent physical aquifer heterogeneity, which may go unnoticed without detailed investigations gathered from multilevel or multiple observation wells. An alternative to overcome the frequent unavailability of multiple wellbores at sites is to perform a detailed investigation on the single wellbore available. In this perspective, the aim of this study is to use passive samplers to sequentially collect groundwater at depths in long–screened wellbores. Such investigation is carried out for major ions and stable isotopes compositions (δ2H, δ18O, δ13C) at ten sites in the context of fractured carbonate aquifers of the St. Lawrence Lowlands (Quebec, Canada). The information gathered from the calco–carbonic system, major ions and stable isotopes report poorly stratified and evolved groundwater bodies. Contribution of water impacted by anthropogenic activities, such as road salts pollution and carbon sources from C4 vegetation, when they occur, are even observed at the greatest depths. Such observations suggest quick flow paths and efficient mixing conditions, which leads to significant contributions of contemporary groundwater bodies in the fractured aquifers investigated down to depths of about 100 m. Although physical aquifer investigation reported few and heterogeneously distributed fractures per wellbore, hydrogeochemical findings point to at overall well interconnected fracture networks in the aquifer and high vulnerability of groundwater, even at significant depths.
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Cotanont, Thidarat, Chalong Buaphan, and Kamonporn Kromkhun. "Correlation of Outcrop Hydraulic Conductivity with its Aquifer: A Case Study of the Phu Phan Sandstone in Northeast, Thailand." Advanced Materials Research 931-932 (May 2014): 823–28. http://dx.doi.org/10.4028/www.scientific.net/amr.931-932.823.
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Fractured rock aquifers provide the most extensive groundwater resources in Northeast Thailand. The hydraulic conductivity (K) of these aquifers controls the flow of water and is therefore, an essential parameter for groundwater modeling and management. K values may be directly determined by conducting pumping tests at the aquifer or by performing fracture analysis using data acquired from outcrops. The K value at outcrop should be greater than that at aquifer of deeper position due to the effect of aperture reduction by overburden compression. The goal of this study was therefor to find the correlation between K values determined from outcrop with those directly measured at an aquifer. This study was conducted on the Phu Phan sandstone aquifer at the Huay Luang watershed, Udon Thani Province of Northeast Thailand. The orientation, aperture, and spacing of fractures were measured at four outcrops and used for determining the K values by fracture analysis. Single well pump test data from 17 wells in the Phu Phan aquifer (30-120 m depth) were analyzed to obtain transmissivity (T) and K. Both sets of the K values, from outcrop and aquifer, were correlated using the plotting position of Weibull. Both plots were linear on a semi-log scale but the outcrop curve was steeper. Lognormal distributions fitted both plotting positions quite well. These results show that for the same probability value, K values found from the pumping test to be about an order of magnitude smaller than K values determined from outcrop data.
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Bello, Rereloluwa, and Toluwaleke Ajayi. "Geoelectric evaluation of groundwater potential within sunshine garden estate, akure southwestern Nigeria." International Journal of Physical Research 7, no. 2 (July 22, 2019): 61. http://dx.doi.org/10.14419/ijpr.v7i2.29172.
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The Vertical Electrical Resistivity surveys in the Sunshine Garden Estate have contributed to a better understanding of the basement complex of Southwestern Nigeria. Nine (9) vertical electrical sounding (VES) using the Schlumberger electrode array were interpreted and the results shows three (3) subsurface geoelectric layers within the study area. These are the weathered layer, topsoil, fresh/fractured basement. Groundwater pockets such as fractured zones, valley fills/basement depressions, and weathered zones were delineated in the study area. Weathered/partially weathered layer and weathered basement/fractured basement were the two major aquifer mapped out and these aquifers are characterized by thick overburden, found within basement depressions. The groundwater potential of the study area was zoned into low, medium and high potentials. Zones where the overburden thickness (which constitutes the main aquifer unit) is greater than 13m and of low clay composition (average resistivity value between 200 - 400Ωm) are considered zones of high groundwater potential. Area where the thickness of the aquifer ranges from 11-13m with less clay composition are considered to have medium groundwater potential and the areas where the thickness of the aquifer is less than 11m are considered to have a low groundwater. The VES station underlained by high and medium groundwater potential zones are envisaged to be viable for groundwater development within the area.
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Petrenko, L. I., I. M. Romanyuk, N. B. Kasteltseva, and I. A. Persits. "MODELLING OF ARTIFICIAL INCREASE IN PRODUCTIVITY OF WATER INTAKE WELLS IN CRYSTALLINE ROCKS (on the example OF ZHASHKIV GROUNDWATER DEPOSIT, UKRAINE)." Geological Journal, no. 2 (July 15, 2021): 47–57. http://dx.doi.org/10.30836/igs.1025-6814.2021.2.224915.
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Global warming, as well as contamination of surface and ground water are currently the main factors that make the search for alternative sources of drinking water extremely pressing. The majority of aquifers commonly exploited for drinking water supply are contained in sedimentary deposits. Utilization of groundwater in fractured crystalline waterbearing rocks may be an alternative source of drinking water. However, experience in effective use of fractured rocks aquifer for water supply is very poor due to the lack of data on the crystalline rocks fracturing and, accordingly, their water-bearing capacity. Improving the effectiveness of using such geological environments is a very challenging task, yet possible with artificial recharge of crystalline rocks aquifers. Computation modeling is a widespread and proven way to study groundwater behavior in sedimentary deposits, unlike in fractured crystalline rocks. The present study focuses on the groundwater flow model to consider the method of improving the productivity of water intake wells in fractured crystalline rocks aquifer through artificially increase of the rocks’ fracturing. On the groundwater flow model for the Zhashkiv groundwater deposit, several scenarios with increase of the crystalline rocks fracturing were simulated and the effect on changing the well pumping rate was evaluated for one of the wells.
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Wilske, Cornelia, Axel Suckow, Ulf Mallast, Christiane Meier, Silke Merchel, Broder Merkel, Stefan Pavetich, et al. "A multi-environmental tracer study to determine groundwater residence times and recharge in a structurally complex multi-aquifer system." Hydrology and Earth System Sciences 24, no. 1 (January 16, 2020): 249–67. http://dx.doi.org/10.5194/hess-24-249-2020.
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Abstract. Despite being the main drinking water resource for over 5 million people, the water balance of the Eastern Mountain Aquifer system on the western side of the Dead Sea is poorly understood. The regional aquifer consists of fractured and karstified limestone – aquifers of Cretaceous age, and it can be separated into a Cenomanian aquifer (upper aquifer) and Albian aquifer (lower aquifer). Both aquifers are exposed along the mountain ridge around Jerusalem, which is the main recharge area. From here, the recharged groundwater flows in a highly karstified aquifer system towards the east and discharges in springs in the lower Jordan Valley and Dead Sea region. We investigated the Eastern Mountain Aquifer system for groundwater flow, groundwater age and potential mixtures, and groundwater recharge. We combined 36Cl ∕ Cl, tritium, and the anthropogenic gases SF6, CFC-12 (chlorofluorocarbon) and CFC-11, while using CFC-113 as “dating” tracers to estimate the young water components inside the Eastern Mountain Aquifer system. By application of lumped parameter models, we verified young groundwater components from the last 10 to 30 years and an admixture of a groundwater component older than about 70 years. Concentrations of nitrate, simazine (pesticide), acesulfame K (ACE-K; artificial sweetener) and naproxen (NAP; drug) in the groundwater were further indications of infiltration during the last 30 years. The combination of multiple environmental tracers and lumped parameter modelling helped to understand the groundwater age distribution and to estimate recharge despite scarce data in this very complex hydrogeological setting. Our groundwater recharge rates support groundwater management of this politically difficult area and can be used to inform and calibrate ongoing groundwater flow models.
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Jonker, B., and T. Abiye. "Groundwater potential of the eastern Kalahari region of South Africa." South African Journal of Geology 120, no. 3 (September 1, 2017): 385–402. http://dx.doi.org/10.25131/gssajg.120.3.385.
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Abstract An integrated approach involving geological, borehole data, hydrogeochemical and environmental isotope analyses was used to determine the groundwater potential of the eastern Kalahari region of South Africa, an area to the west of Mahikeng that stretches northward from the Orange River into Botswana. The total groundwater resource potential for the eastern Kalahari region of South Africa is estimated at 10127 Mm3/a, with the Kalahari Group aquifer showing the greatest potential, comprising 51% of the total resource. The storage capacity of the Kalahari Group aquifer (7130 Mm3) is also impressive, estimated to be more than twice that of the dolomite aquifer (2728 Mm3). Despite having such great potential, the aquifer is not actively recharged and is often associated with very saline water that is not suitable for human and livestock consumption. The limestone and dolomite aquifers of the Campbell Rand Subgroup, as well as the weathered granitic rocks of the Archaean basement, are considered as the most prospective water bearing formations, with a groundwater resource potential estimate of 1981 Mm3/a and 1845 Mm3/a, respectively. Aquifers with the least potential in the project area comprise the fractured basement rocks of the Kraaipan - Amalia greenstone belt, with a groundwater resource potential of 26 Mm3/a, and the fractured sedimentary rocks of the Asbestos Hills Subgroup, with a groundwater resource potential of 108 Mm3/a. The calculated groundwater storage and resource potential in the eastern Kalahari region of South Africa satisfies a large proportion of the water demand in the region.
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White, Alissa, Bryan Moravec, Jennifer McIntosh, Yaniv Olshansky, Ben Paras, R. Andres Sanchez, Ty P. A. Ferré, Thomas Meixner, and Jon Chorover. "Distinct stores and the routing of water in the deep critical zone of a snow-dominated volcanic catchment." Hydrology and Earth System Sciences 23, no. 11 (November 18, 2019): 4661–83. http://dx.doi.org/10.5194/hess-23-4661-2019.
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Abstract. This study combines major ion and isotope chemistry, age tracers, fracture density characterizations, and physical hydrology measurements to understand how the structure of the critical zone (CZ) influences its function, including water routing, storage, mean water residence times, and hydrologic response. In a high elevation rhyolitic tuff catchment in the Jemez River Basin Critical Zone Observatory (JRB-CZO) within the Valles Caldera National Preserve (VCNP) of northern New Mexico, a periodic precipitation pattern creates different hydrologic flow regimes during spring snowmelt, summer monsoon rain, and fall storms. Hydrometric, geochemical, and isotopic analyses of surface water and groundwater from distinct stores, most notably shallow groundwater that is likely a perched aquifer in consolidated collapse breccia and deeper groundwater in a fractured tuff aquifer system, enabled us to untangle the interactions of these groundwater stores and their contribution to streamflow across 1 complete water year (WY). Despite seasonal differences in groundwater response due to water partitioning, major ion chemistry indicates that deep groundwater from the highly fractured site is more representative of groundwater contributing to streamflow across the entire water year. Additionally, the comparison of streamflow and groundwater hydrographs indicates a hydraulic connection between the fractured welded tuff aquifer system and streamflow, while the shallow aquifer within the collapse breccia deposit does not show this same connection. Furthermore, analysis of age tracers and oxygen (δ18O) and stable hydrogen (δ2H) isotopes of water indicates that groundwater is a mix of modern and older waters recharged from snowmelt, and downhole neutron probe surveys suggest that water moves through the vadose zone both by vertical infiltration and subsurface lateral flow, depending on the lithology. We find that in complex geologic terrain like that of the JRB-CZO, differences in the CZ architecture of two hillslopes within a headwater catchment control water stores and routing through the subsurface and suggest that shallow groundwater does not contribute significantly to streams, while deep fractured aquifer systems contribute most to streamflow.
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Mohuba, Seeke C., Tamiru A. Abiye, Molla B. Demlie, and Moneri J. Modiba. "Hydrogeological Characterization of the Thyspunt Area, Eastern Cape Province, South Africa." Hydrology 7, no. 3 (July 31, 2020): 49. http://dx.doi.org/10.3390/hydrology7030049.
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This paper presents a comprehensive hydrogeological investigation that involves field work, aquifer test, hydrogeochemical analysis, environmental isotope analysis, and interpretations around a proposed nuclear power facility in South Africa. The study was undertaken to test the complementarity of the various methods in the coastal aquifer and to verify the hydrogeological conditions within and around the site. The study revealed the presence of two types of aquifers: an upper primary aquifer made up of the Cenozoic deposits of the Algoa Group, and a deeper fractured aquifer made of the Palaezoic Table Mountain Group (TMG) metasedimentary rocks. Owing to ductile deformation in the form of folding, the fractured quartzite and shale aquifers resulted in an artesian condition, often characterized by slightly acidic (pH ≤ 6) and iron-rich groundwater. The most important hydrogeochemical processes responsible for the observed changes in the hydrochemical composition and facies are mineral dissolution, ion exchange and mixing. The environmental isotope results suggest that all groundwater samples are characterized by a depleted δ18O and δ2H signal, indicating high latitude moisture source (southern polar region) and recharge from rainfall, with no or minimal evaporation before and during infiltration. Similarities in the stable isotope signatures between the deeper and shallow aquifer confirm the presence of a strong hydraulic link. The residence time of groundwater in the aquifers underlying the proposed nuclear power plant is estimated using tritium (3H) and 14C, and the results indicate that in the shallow aquifer it ranges from recent recharge to 50 years, and in the deeper aquifer, it ranges from 430 ± 5 years to 1000 ± 10 years, which exists in a quasi-pristine condition.
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Tamburini, Andrea, and Marco Menichetti. "Groundwater Circulation in Fractured and Karstic Aquifers of the Umbria-Marche Apennine." Water 12, no. 4 (April 7, 2020): 1039. http://dx.doi.org/10.3390/w12041039.
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The Umbria-Marche Apennine has a large number of springs that drain water stored in carbonate formations. Spring groundwater constitutes a crucial freshwater resource for many countries, regions, and cities around the world. This study aimed to understand the hydrological mechanisms behind groundwater circulation and their relationship to the structural and stratigraphic settings of specific aquifers. Recession analysis and time series analysis were applied to the daily discharge of six springs monitored over eight years. Both analyses indicated the presence of two types of aquifers: aquifer with unimodal behavior and aquifer with bimodal behavior. The first are characterized by two hydrodynamic sub-regimes, in which fracture networks control the baseflow and conduit networks control the quickflow. In contrast, other springs present only one hydrodynamic sub-regime related to fracture network drainage. Time series analysis confirms the results of recession analysis, showing a large memory effect and a large response time, implying the dominance of the baseflow sub-regime. These results indicate that the Maiolica Formation is characterized by a high degree of fracturation and slight karstification, which control infiltration and percolation, whereas the Calcare Massiccio Formation regulates groundwater circulation in the deeper zones of the aquifer, characterized by a high degree of karstification through moderately developed conduit networks.
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Eissa, Mustafa A. "Application of Multi-Isotopes and Geochemical Modeling for Delineating Recharge and Salinization Sources in Dahab Basin Aquifers (South Sinai, Egypt)." Hydrology 5, no. 3 (August 4, 2018): 41. http://dx.doi.org/10.3390/hydrology5030041.
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The Dahab watershed comprises three aquifers; the alluvial Quaternary, the Early Cambrian sandstone, and the fractured Pre-Cambrian basement aquifers. The Dahab watershed is located in the southeastern part of the arid Sinai Peninsula, where low precipitation and groundwater over-exploitation deteriorate the groundwater quality in the alluvial coastal plain aquifer located downstream. Multi-isotopes including δ18O and δ2H, 87Sr/86Sr, δ81Br and δ11B coupled with groundwater geochemistry were utilized to assess the recharge source(s), water-rock interaction, and seawater mixing to aid sustainable groundwater management strategies. Br and Cl concentrations, used to measure groundwater salinity, were low in the upstream groundwater, while higher concentrations were observed in the deep drilled wells located downstream, in the main well field. The δ18O and δ2H isotopes were depleted in the upstream aquifers, but enriched in the shallow coastal aquifer, indicating slight evaporation and seawater intrusion. Higher mean values of 87Sr/86Sr and δ81Br were observed in the fresh groundwater from high in the watershed (87Sr/86Sr = 0.707716 and δ81Br = +2.05‰), while lower mean values were observed in the saline groundwater located downstream in the main well field (87Sr/86Sr = 0.706631 and δ81Br = +0.11‰). The cumulative mass balance mixing curves and the geochemical NETPATH model confirm the change of groundwater quality from the upper to lower watershed caused by the leaching and evaporation processes, as well as mixing with seawater. The corrected 14C age dating and stable isotopes show that the Quaternary and Pre-Cambrian basement aquifers contain modern groundwater, while the Early Cambrian aquifer holds paleo-groundwater, which has received considerable recharge from recent precipitation. The mixing ratiosin the Quaternary coastal aquifer range between 5% and 13% seawater to 95% and 87% fresh groundwater, respectively. These results indicate that future groundwater withdrawal must be well managed in order to limit further salinization. Groundwater withdrawal from the Quaternary coastal aquifer must be below the natural average recharge in order to be sustainable.
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Masciopinto, Costantino, Rosanna La Mantia, Annalaura Carducci, Beatrice Casini, Agata Calvario, and Edoardo Jatta. "Unsafe tap water in households supplied from groundwater in the Salento Region of Southern Italy." Journal of Water and Health 5, no. 1 (September 1, 2006): 129–48. http://dx.doi.org/10.2166/wh.2006.054.
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Although the fractured aquifer of the Salento supplies over 80% of the drinking water requirements of the local population, its exposure to pollution has recently increased. In recent years, owing to the arid climate and droughts, the spreading of wastewater on soil for irrigation has become much more frequent. Consequently, hazardous and pathogenic microorganisms released with wastewater have been transported into the subsoil and have contaminated groundwater. An elaboration of epidemiological data has shown that the local population has the highest exposure to endemic gastroenteritis in Italy. In order to reduce human exposure to unsafe groundwater, the setback distance for drinking wells necessary to achieve the ‘natural disinfectionߣ criteria, has been determined experimentally at the Nardò aquifer (Salento region), supported by groundwater monitoring results and a mathematical transport model able to determine the apparent pathogenic microorganism pathways in fractures. The results also provided valuable inactivation constants of cultural indicators (coliforms, enterococci, Clostridium spores and somatic coliphages) and viruses in the wastewater that have been injected into the fractured aquifer since 1991. Furthermore, the efficacy of chlorine to remove viral indicators from water in a well 500 m from wastewater injection was tested. Hypochlorination reduces somatic coliphages and Clostridium spores in groundwaters but did not achieve complete inactivation in all tests. Complete disinfection of groundwater samples was possible only when there was an initial Clostridium spores count of ≤10 CFU 100 ml-1.
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Eyankware, M. O., A. O. I. Selemo, P. N. Obasi, and O. M. Nweke. "EVALUATION Of GROUNDWATER VULNERABILITY IN FRACTURED AQUIFER USING GEOELECTRIC LAYER SUSCEPTIBILITY INDEX AT OJU, SOUTHERN BENUE TROUGH NIGERIA." Geological Behavior 4, no. 2 (April 22, 2020): 63–67. http://dx.doi.org/10.26480/gbr.02.2020.63.67.
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A combination of geoelectric and hydrogeologic concept was used in the assessment of groundwater vulnerability in fractured aquifers of Oju and environs. The study area is underlain by the sediments of the Asu River Group, Southern Benue Trough Nigeria. A total of twenty-seven (27) Vertical Electrical Sounding (VES) was carried out within the study area. Geoelectric parameters (layer, resistivity and thickness) of the overlying layers across the study area were determined and used to evaluate the vulnerability of the underlying aquifers. Three charts were compared using geo-electrically derived models; LC (Longitudinal Conductance), GLSI (geoelectric layer susceptibility indexing) and GOD (groundwater occurrence, overlying lithology and depth to the aquifer. Results obtained from LC revealed that the study area fell within the moderate category, GLSI showed that aquifer vulnerability were categorize within negligible to low category and GOD fell within low to moderate category. On the average, groundwater within the study area is considered moderate vulnerable to groundwater contamination.
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Mndaweni, S. S. E., S. Naicker, and D. Blake. "Hydrostratigraphy of the Malmani Subgroup dolomites within the northeastern escarpment (Limpopo and Mpumalanga, South Africa)." South African Journal of Geology 122, no. 3 (September 1, 2019): 283–98. http://dx.doi.org/10.25131/sajg.122.0022.
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Abstract The Late Archaean to Early Proterozoic Malmani Subgroup comprises of dolomites and limestones forming part of the Chuniespoort Group within the Transvaal Supergroup, outcropping as an arc structure east of the Pretoria Group along the Limpopo and Mpumalanga escarpment. These rocks form a fractured karst aquifer in the area and have a high degree of heterogeneity and anisotropy. The aquifers are unconfined to semi-confined, with compartmentalisation by dolerite dykes being a possible effect (if the dykes are large and extensive enough) due to the dykes acting as aquitards or barriers to groundwater flow. The contact zones between the dolomite formations and dolerite dykes are usually fractured however, and along with any other faults and fractures result in preferential dolomite dissolution and the development of groundwater flow paths in the area. Borehole yields ranges between 2 to 5 l/s and potentially >10 l/s per borehole in the vicinity of large regional fractures or dolerite intrusions. Groundwater from the Malmani Subgroup generally meets the drinking water quality standards for major constituents and it is of Mg-Ca-HCO3 nature. Groundwater development within this particular hydrostratigraphy is linked to potential well field target zones that take cognisance of various surface water-groundwater interaction affecting surface water discharge rates as well as groundwater over-abstraction concerns. Preliminary results have indicated that given a groundwater potential of 44 hm3/a, the aquifer will be able to support abstractions of up to 29 hm3/a if systematically developed adaptively and could be used and managed conjunctively with surface water to alleviate the pressure on the already stressed Olifants Water Management Area.
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Gómez-Cruz, Alicia, Helga Madrigal-Solís, Christian Núñez-Solís, Hazel Calderón-Sánchez, and Pablo Jiménez-Gavilán. "Hydrogeological vulnerability in Jacó coastal aquifers, Central Pacific, Costa Rica." Revista Geográfica de América Central 2, no. 63 (June 14, 2019): 165–87. http://dx.doi.org/10.15359/rgac.63-2.6.
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In the last two decades, the Central Pacific of Costa Rica experienced a strong growth in urban and tourism development. If not regulated, this development can result in a pressure to groundwater resources and, therefore, a threat in terms of quality and quantity. In this study, a hydrogeological vulnerability map of Jacó aquifers was performed, by the GOD method. Geological profiles were elaborated, and field verification was performed. It is confirmed that, in the study area, two aquifers are found: a) a detritic, porous, unconfined coastal aquifer, settled in the Jacó alluvial plain and, b) an aquifer in the basaltic fractured rocks of the Nicoya Complex, unconfined in the mountainous zone and underlying the detritic formation in the central area, where the groundwater is integrated to that of the detrital aquifer. The zone of the alluvial aquifer resulted in a medium vulnerability index, whereas the mountainous areas in a low vulnerability. Management recommendations were proposed.
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W. Al-Muqdadi, Sameh, and Broder J. Merkel. "Interpretation of Groundwater Flow into Fractured Aquifer." International Journal of Geosciences 03, no. 02 (2012): 357–64. http://dx.doi.org/10.4236/ijg.2012.32039.
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Lukas, William G., Don J. DeGroot, David W. Ostendorf, and Erich S. Hinlein. "Multi-scale hydrogeologic characterization of a leaky till–mantled fractured bedrock aquifer system." Canadian Geotechnical Journal 52, no. 12 (December 2015): 1945–55. http://dx.doi.org/10.1139/cgj-2014-0296.
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The paper presents hydrogeologic properties for a leaky till–mantled fractured bedrock aquifer system based on geophysical and hydraulic tests performed at a drumlin located in northeastern Massachusetts, USA. The site profile consists of a fractured bedrock aquifer overlain by a 30 m thick unweathered, coarse-grained till aquitard. Steady state, decadal scale, hydraulics varied little until seasonal irrigation pumping was initiated in recent years, causing a substantial annual drawdown in the aquifer and leakage from the overlying till. High frequency hydraulic head data sets collected in monitoring wells record the hydraulic response to the irrigation pumping. These data sets, together with results from small scale slug and purge tests performed in monitoring wells, are used to characterize the hydrogeologic behavior of this groundwater system. Geophysical logging performed in bedrock wells confirmed the presence of numerous flowing fractures. The large-scale continuum analysis of the fractured bedrock aquifer response to the irrigation pumping yields transmissivity values consistent with those determined from the small-scale, short-term purge test results. The low hydraulic conductivity till has a significant impact on the drawdown behavior of the fractured bedrock aquifer. Calibrated values from the collective data sets and analyses result in the following properties for the 30 m thick unweathered till: hydraulic conductivity K′ = 7.2 × 10−9 m/s, transmissivity T′ = 2.3 × 10−8 m2/s, and storativity S′ = 2.7 × 10−4, and for the underlying fractured bedrock aquifer: T = 6.5 × 10−6 m2/s with an average fracture aperture of 46 μm and hydraulic conductivity Kf = 1.3 × 10−3 m/s. These results should describe similar unweathered coarse-grained till–mantled fractured bedrock aquifer systems and provide useful data for preliminary analyses prior to any site-specific investigations.
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Tsepav, Matthew Tersoo, Aliyu Yahaya Badeggi, Obaje Nuhu George, Usman Yusuf Tanko, and Ibrahim Samuel Ibbi. "On the Use of Electrical Resistivity Method in Mapping Potential Sources and Extent of Pollution of Groundwater Systems in Lapai Town, Niger State, Nigeria." Journal of Physics: Theories and Applications 5, no. 1 (March 30, 2021): 18. http://dx.doi.org/10.20961/jphystheor-appl.v5i1.51563.
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<p>Electrical resistivity method employing the Schlumberger array was used to occupy forty four (44) vertical electrical sounding points in Lapai town with the aim of determining the depth to aquifers, aquifer thicknesses and aquifer protective capacity. The G41 Geotron resistivity meter was used in obtaining the apparent resistivity data which was processed using Interpex 1XD resistivity interpretation software. The results revealed four lithologic sections which include top lateritic soil, sandy clay, fractured basement and fresh basement. Both confined and unconfined aquifers were identified within the area, with four classes of aquifer proactive capacities as high, moderate, weak and poor. While the aquifer at VES 20 was highly protected, twenty other aquifers were moderately protected, eight others had weak protection and fifteen aquifers were poorly protected. The aquifers were generally of good thicknesses and at varying reasonable depths, making them good reservoirs of water in appreciable quantity. The average aquifer thickness was estimated to be 48.36m while the average depth to aquifers was estimated to be 56.68m.</p>
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La Mantia, R., C. Masciopinto, C. Levantesi, and V. Tandoi. "Fate and transport of faecal contamination microbial indicators, pathogenic protozoa and Campylobacter in the artificially recharged fractured aquifer of Salento, Italy." Water Science and Technology 57, no. 6 (March 1, 2008): 849–56. http://dx.doi.org/10.2166/wst.2008.183.
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The study investigates the fate and transport of microorganisms introduced by artificial groundwater recharge at the Nardò fractured aquifer in Salento, Italy. Microbial indicators of faecal contamination, parasitic protozoa (Giardia and Cryptosporidium) and pathogenic bacteria (Campylobacter spp.), were monitored into injected water and groundwater to test the efficiency of the “natural disinfection” into the fractured aquifer. A remarkable decrease of microbial indicators and pathogens was observed suggesting that pathogens removal or inactivation may be possible during water flow in fractured aquifer. The recently described PNA probe CJE195 (Lehtola et al. 2005) was utilised for the rapid and specific detection of Campylobacter spp. by fluorescence in situ hybridization (FISH) after enrichment. FISH results were consistent with those of traditional cultural method (ISO 17995) applied in parallel: time required for Campylobacter identification was reduced of 4 days.
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Chelih, Fatha, Chemseddine Fehdi, and Shuhaib Khan. "Characterization of the Hammamet basin aquifer (North-East of Algeria) through geochemical and geostructural methods and analysis." Journal of Water and Land Development 37, no. 1 (June 1, 2018): 39–48. http://dx.doi.org/10.2478/jwld-2018-0023.
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AbstractMorphostructural, hydrogeological and hydrochemical approaches were applied to Hammamet plain and its surrounding mountains in the eastern part of Algeria to characterize the groundwater system and its potential for exploitation. The Essen and Troubia Mountains form the natural boundaries of Hammamet plain. The objective of this study is to utilize remote sensing techniques combined with structural analysis, hydrogeology and hydrogeochemistry to identify the potential fracture zones for groundwater in the strongly fractured and karstified deep aquifers. The delineated zones of potential groundwater resources are verified by detailed hydrogeological field surveys.From a hydrogeological point of view, these two mountains, constitute a unit limited by faults oriented ENE-WSW, NNW-SSE and NNE-SSW. Specifically, fractures of the latter two directions influence the compartmentalization and the hydrogeological functioning of this unit. According to the degree of fracturing and/or karstification, two basic types of aquiferous behaviour have been distinguished: fissured aquifer (Essen Mountain and Troubia Mountain), and porous aquifer (Hammamet plain).The study of the hydrochemical characteristics of groundwater samples shows that the majority of samples are mainly of HCO3− and Ca2+ water type. The ionic speciation and mineral dissolution/precipitation was calculated with the PHREEQC software. The chemical composition of the water is influenced by the dissolution and/or precipitation processes during the water–rock interaction and by the cationic exchange reactions between groundwater and alluvial sediments. The high content of CO2 in the water samples suggests that they circulate in a geochemical open system. The isotopic analysis of some groundwater samples shows a similarity with the meteoric waters, which reflect their short residence time and a low evaporation of the infiltrated water.
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Lerner, D. N., G. P. Wealthall, and A. Steele. "Assessing Risk from DNAPLs in Fractured Aquifers." Journal of Agricultural and Marine Sciences [JAMS] 7, no. 2 (June 1, 2002): 47. http://dx.doi.org/10.24200/jams.vol7iss2pp47-52.
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Chlorinated solvents are among the most widespread pollutants of groundwater. As DNAPLs (dense nonaqueous phase liquids), they can move rapidly and in complex patterns through fractures to reach and contaminate large volumes of aquifer, and then dissolve to cause significant pollution of groundwater. However, clean-up of DNAPLs in fractured rocks is virtually impossible and certainly expensive. Risk assessment should be used to decide whether the pollution is serious enough to justify major expenditure on clean-up or containment. A key aspect of risk assessment for DNAPLs in fractured aquifers is to understand how deep they are likely to have penetrated through the fracture network. This paper addresses two aspects of such predictions: measuring fracture apertures in situ and the connectivity of fracture networks with respect to DNAPLs. Fracture aperture is an in-situ field technique that has been developed and implemented to measure aperture variability and NAPL entry pressure in an undisturbed, water-saturated rock fracture. The field experiment also provided the opportunity to measure the wetting phase relative permeability at residual non-wetting phase saturation. The RADIO (Radial Aperture Determination by the Injection of Oil) method employs a constant rate injection of a non-toxic NAPL into a fracture isolated by a double packer array. The method was applied at the field site in Scotland, and measured apertures out to ~5m from the borehole. It showed that hydraulic aperture (from packer tests) was a poor estimator of the controlling aperture for DNAPL movement. This is the first time such large-scale aperture measurements have been made, and the technique is the first which can provide useful aperture estimates for risk analysis of DNAPL movement.Network connectivity is a fundamental property of the fracture system. DNAPL connectivity extends the concept to take account of the fluid properties.
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Xue, Yi, Yang Liu, Faning Dang, Jia Liu, Zongyuan Ma, Lin Zhu, and Hongwei Yang. "Assessment of the Nonlinear Flow Characteristic of Water Inrush Based on the Brinkman and Forchheimer Seepage Model." Water 11, no. 4 (April 24, 2019): 855. http://dx.doi.org/10.3390/w11040855.
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Underground fault water inrush is a hydrogeological disaster that frequently occurs in underground mining and tunnel construction projects. Groundwater may pour from an aquifer when disasters occur, and aquifers are typically associated with fractured rock formations. Water inrush accidents are likely to occur when fractured rock masses are encountered during excavation. In this study, Comsol Multiphysics, cross-platform multiphysics field coupling software, was used to simulate the evolution characteristics of water flow in different flow fields of faults and aquifers when water inrush from underground faults occurs. First, the Darcy and Brinkman flow field nonlinear seepage models were used to model the seepage law of water flow in aquifers and faults. Second, the Forchheimer flow field was used to modify the seepage of fluid in fault-broken rocks in the Brinkman flow field. In general, this phenomenon does not meet the applicable conditions of Darcy’s formula. Therefore, the Darcy and Forchheimer flow models were coupled in this study. Simulation results show that flow behavior in an aquifer varies depending on fault permeability. An aquifer near a fault is likely to be affected by non-Darcy flow. That is, the non-Darcy effect zone will either increase or decrease as fault permeability increases or decreases. The fault rupture zone that connects the aquifer and upper roadway of the fault leads to fault water inrush due to the considerably improved permeability of the fractured rock mass.
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Jørgensen, N. O., and J. Heinemeier. "Origin of brackish groundwater in a sandstone aquifer on Bornholm, Denmark." Hydrology Research 39, no. 3 (June 1, 2008): 209–22. http://dx.doi.org/10.2166/nh.2008.043.
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A multi-isotope approach in combination with hydrochemical data and borehole logging is applied to identify the source of brackish groundwater in a borehole in the well field of Neksø Municipal Waterworks in Bornholm, Denmark. The aquifer lithology consists of fractured Lower Cambrian sandstones resting on Proterozoic crystalline basement. The water body in the studied borehole is significantly stratified with respect to the hydrochemical and isotopic signatures and reveal a Na–Ca–Cl–HCO3 water type and TDS values >1,000 mg/L below a halocline at 40–55 m below measurement point (bmp). The occurrence of brackish groundwater is remarkable for this aquifer, which otherwise yields potable groundwater of good quality. The stable isotope (18O and 2H) compositions indicate a meteoric origin of the brackish groundwater, which rules out seawater intrusion into the aquifer. 14C activities show apparent 14C ages of the brackish groundwater in the range 2200–4300 yr (BP), whereas the freshwater samples above the halocline indicate modern age. Hydrochemical (Cl/Br and Sr) and isotopic studies (18O, 2H and 87Sr/86Sr) of the brackish groundwater point to a well-mixed and homogeneous water body reflecting long water–rock interaction and suggest a contribution of palaeowater from the fractured crystalline basement which has intruded into the Lower Cambrian sandstone aquifer.
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M.S, Chaanda, and Alaminiokuma G.I. "HYDROGEOPHYSICAL INVESTIGATION FOR GROUNDWATER RESOURCE POTENTIAL IN MASAGAMU, MAGAMA AREA, FRACTURED BASEMENT COMPLEX, NORTH-CENTRAL NIGERIA." Malaysian Journal of Geosciences 4, no. 2 (May 15, 2020): 65–69. http://dx.doi.org/10.26480/mjg.02.2020.65.69.
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Vertical Electrical Sounding (VES) was conducted in Salbi farm in the fractured Basement Complex, North- Central Nigeria to determine the groundwater resource potential to serve for agricultural purposes. Four VES stations using Schlumberger electrode configuration with a maximum current electrode spread of 300m were employed for data acquisition. ZHODY software was employed in computing resistivities, depths and thicknesses of the various layers and curve types. Results indicate that the area is characterized by 3 distinct geoelectric layers inferred differently at the VES locations. One potential groundwater aquifer zone was delineated at VES 1, 2, and 4 within the fractured/weathered basement columns having depths ranging between 48.8 – 59.60m and resistivities ranging between 213 – 513 Ωm. These results suggest that boreholes for sustainable groundwater supply in Salbi farm should be sited either at VES 1, 2 or 4 location and screened at a depth ≥60.0m. Wells to develop this resource should be drilled to an effective depth of 40 to 60 m for optimum yields. It is recommended that pumping test be done in order to further determine the aquifer efficiency and productivity in the area. However, the aquifers at these locations have potentials for groundwater but may be vulnerable to contamination.
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Medici, Giacomo, Landis Jared West, Pippa Joanne Chapman, and Steven Allan Banwart. "Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)." Environmental Science and Pollution Research 26, no. 24 (June 25, 2019): 24863–84. http://dx.doi.org/10.1007/s11356-019-05525-z.
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AbstractViruses and bacteria which are characterized by finite lives in the subsurface are rapidly transported via fractures and cavities in fractured and karst aquifers. Here, we demonstrate how the coupling of a robust outcrop characterization and hydrogeophysical borehole testing is essential for prediction of contaminant velocities and hence wellhead protection areas. To show this, we use the dolostones of the Permian Magnesian Limestone aquifer in NE England, where we incorporated such information in a groundwater flow and particle tracking model. Within this aquifer, flow in relatively narrow (mechanical aperture of ~ 10−1–1 mm) fractures is coupled with that in pipe cavities (~ 0.20-m diameter) following normal faults. Karstic cavities and narrow fractures are hydraulically very different. Thus, the solutional features are represented within the model by a pipe network (which accounts for turbulence) embedded within an equivalent porous medium representing Darcian flowing fractures. Incorporation of fault conduits in a groundwater model shows that they strongly influence particle tracking results. Despite this, away from faulted areas, the effective flow porosity of the equivalent porous medium remains a crucial parameter. Here, we recommend as most appropriate a relatively low value of effective porosity (of 2.8 × 10−4) based on borehole hydrogeophysical testing. This contrasts with earlier studies using particle tracking analyses on analogous carbonate aquifers, which used much higher values of effective porosity, typically ~ 102 times higher than our value, resulting in highly non-conservative estimates of aquifer vulnerability. Low values of effective flow porosities yield modelled flow velocities ranging from ~ 100 up to ~ 500 m/day in un-faulted areas. However, the high fracturing density and presence of karstic cavities yield modelled flow velocities up to ~ 9000 m/day in fault zones. The combination of such flow velocities along particle traces results in 400-day particle traces up to 8-km length, implying the need for large well protection areas and high aquifer vulnerability to slowly degrading contaminants.
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Pastore, Nicola, Claudia Cherubini, and Concetta I. Giasi. "Kinematic diffusion approach to describe recharge phenomena in unsaturated fractured chalk." Journal of Hydrology and Hydromechanics 65, no. 3 (September 1, 2017): 287–96. http://dx.doi.org/10.1515/johh-2017-0033.
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AbstractWhen dealing with groundwater resources, a better knowledge of the hydrological processes governing flow in the unsaturated zone would improve the assessment of the natural aquifer recharge and its vulnerability to contamination. In North West Europe groundwater from unconfined chalk aquifers constitutes a major water resource, therefore the need for a good hydrological understanding of the chalk unsaturated zone is essential, as it is the main control for aquifer recharge. In the North Paris Basin, much of the recharge must pass through a regional chalk bed that is composed of a porous matrix with embedded fractures. The case study regards the role of the thick unsaturated zone of the Cretaceous chalk aquifer in Picardy (North of France) that controls the hydraulic response to rainfall. In order to describe the flow rate that reaches the water table, the kinematic diffusion theory has been applied that treats the unsaturated water flow equation as a wave equation composed of diffusive and gravitational components. The kinematic diffusion model has proved to be a convenient method to study groundwater recharge processes in that it was able to provide a satisfactory fitting both for rising and falling periods of water table fluctuation. It has also proved to give an answer to the question whether unsaturated flow can be described using the theory of kinematic waves. The answer to the question depends principally on the status of soil moisture. For higher values of hydraulic Peclet number (increasing saturation), the pressure wave velocities dominate and the preferential flow paths is provided by the shallow fractures in the vadose zone. With decreasing values of hydraulic Peclet number (increasing water tension), rapid wave velocities are mostly due to the diffusion of the flow wave. Diffusive phenomena are provided by matrix and fracture-matrix interaction.The use of a kinematic wave in this context constitutes a good simplified approach especially in cases when there is a lack of information concerning the hydraulic properties of the fractures/macropores close to saturation.
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Bloomfield, J. P., and B. P. Marchant. "Analysis of groundwater drought using a variant of the Standardised Precipitation Index." Hydrology and Earth System Sciences Discussions 10, no. 6 (June 14, 2013): 7537–74. http://dx.doi.org/10.5194/hessd-10-7537-2013.
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Abstract. A new index for standardising groundwater level time series and characterising groundwater droughts, the Standardised Groundwater level Index (SGI), is described. The SGI is a modification of the Standardised Precipitation Index (SPI) that accounts for differences in the form and characteristics of precipitation and groundwater level time series. The SGI is estimated using a non-parametric normal scores transform of groundwater level data for each calendar month. These monthly estimates are then merged to form a continuous index. The SGI has been calculated for 14 relatively long, up to 103 yr, groundwater level hydrographs from a variety of aquifers and compared with SPI for the same sites. The SPI accumulation period which leads to the strongest correlation between SPI and SGI, qmax, varies between sites. There is a positive linear correlation between qmax and a measure of the range of significant autocorrelation in the SGI series, mmax. For each site the strongest correlation between SPI and SGI is in the range 0.7 to 0.87, and periods of low values of SGI coincide with previously independently documented droughts. Hence SGI is taken to be a robust and meaningful index of groundwater drought. The maximum length of groundwater droughts defined by SGI is an increasing function of mmax, meaning that relatively long groundwater droughts are generally more prevalent at sites where SGI has a relatively long autocorrelation range. Based on correlations between mmax, average unsaturated zone thickness and aquifer hydraulic diffusivity, the source of autocorrelation in SGI is inferred to be dependent on aquifer flow and storage characteristics. For fractured aquifers, such as the Cretaceous Chalk, autocorrelation in SGI is inferred to be primarily related to autocorrelation in the recharge time series, while in granular aquifers, such as the Permo-Triassic Sandstones, autocorrelation in SGI is inferred to be primarily a function of intrinsic aquifer characteristics. These results highlight the need to take into account the hydrogeological context of groundwater monitoring sites when designing and interpreting data from groundwater drought monitoring networks.
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Issah, Mohammed Mansuru, Akwasi Acheampong Aning, Reginald Mensah Noye, and Patrick Amankwaa Mainoo. "Prospecting for Groundwater Using the Continuous Vertical Electrical Sounding Method." European Scientific Journal, ESJ 14, no. 3 (January 31, 2018): 67. http://dx.doi.org/10.19044/esj.2018.v14n3p67.
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2-D CVES surveys using the Wenner configuration was carried out in 22 communities in the Tain District, Ghana. This was done with the objectives of assessing the subsurface geology, identify high groundwater potential zones for drilling high-yielding boreholes that could yield sustainable amount of groundwater. The collected resistivity data were converted from the apparent resistivity to 2-D modelsection using the least-square inversion algorithm with the help of Res2DInv software. The 2-D resistivity model-sections produced a high quality structural resolution leading to the demarcation of the layering of various lithological units, weathered layers and identification of important structures such as joints, fractures and faults. Quantitatively, it can be observed that all the drilled wet wells have aquifer zones between 30 m and 60 m within sandstone, siltstone and phyllite granitic environments. The result of the borehole drill logs revealed that the aquifers were within weathered and fractured zones and is in agreement with the models. The results showed that the boreholes yield within the study area varied between a minimum of 15 litres/min to a maximum 800 litres/min and the mean depth for intercepting aquifer was at about 30 m and below. The study revealed that the potential aquifer zones in the study area are mostly as a result of weathering of the overburden and fracturing of the underlying bedrock. The results suggest that the hydrogeology of the study area is highly complex since the development of groundwater is generally due to secondary porosities.
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Hussain, Yawar, Welitom Borges, Rogerio Uagoda, Cristiane Moura, Susanne Maciel, Omar Hamza, and Hans-Balder Havenith. "Estimation of total groundwater reserves and delineation of weathered/fault zones for aquifer potential: A case study from the Federal District of Brazil." Open Geosciences 13, no. 1 (January 1, 2021): 904–16. http://dx.doi.org/10.1515/geo-2020-0226.
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Abstract In the Federal District of Brazil, groundwater extraction is challenged by fractured aquifers with difficulty in identification of hydraulic traps and significant uncertainty in the estimation of recharge potential. This study aims to optimize the demarcation of new locations of tubular wells by the aid of geophysical investigation. In the first stage of this study, the total exploitable amount of groundwater were calculated from the information of the physical environment and the existing wells. Second, electrical resistivity tomography (ERT) method was carried out on the selected sites – based on their surficial characteristics. The possible hydraulic traps (where groundwater might exist) were identified from the inversion of the resistivity measured by the dipole–dipole array and from the delineation of the resultant conducting zones (including the weathered rocks and fractures). Using this approach, we predicted the position and number of tubular wells required and ranked them according to their potential productivity. The study provides a promising framework for investigating groundwater in fractured aquifers.
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Flinchum, Brady, Luk Peeters, Tim Munday, and Kevin Cahill. "Improving the hydrogeologic conceptualization of a remote semiarid palaeovalley groundwater system using airborne electromagnetics, seismic refraction and reflection, and downhole nuclear magnetic resonance." GEOPHYSICS 86, no. 5 (September 1, 2021): WB207—WB226. http://dx.doi.org/10.1190/geo2020-0614.1.
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A hydrogeologic conceptualization is critical to understand, manage, protect, and sustain groundwater resources, particularly in regions where data are sparse and accessibility is difficult. We used airborne electromagnetics (AEM), shallow seismic reflection and refraction, and downhole nuclear magnetic resonance (NMR) logs to improve our understanding of an arid groundwater system influenced by palaeovalleys. We found that there is a limited connection between the palaeovalley and fractured bedrock aquifers because they are separated by a spatially variable layer of saprolite, which is the layer of chemically altered rock on top of the fractured bedrock. The AEM data provided an estimate of the top of the saprolite but failed to effectively image the bottom. In contrast, the seismic data provided an estimate of the bottom of the saprolite but failed to image the top. This geophysical combination of electrical and seismic data allowed us to map saprolite thickness in detail along a 1.7 km long transect that runs perpendicular the main trunk of a well-defined palaeovalley. These data indicate that the palaeovalley is lined with a heterogeneous layer of saprolite (approximately 3–120 m thick) that is thickest near its edges. Despite the observed variability, only a small percentage of the fractured bedrock aquifer (8%–17%) appears to be in contact with the palaeovalley aquifer. Furthermore, the lack of an elastic boundary at the top of saprolite suggests that the porosity of the saprolite is similar to the palaeovalley sediments — an observation that is supported by the downhole NMR-derived water contents. The electrical change at the top of saprolite is caused by a combination of a decrease in total dissolved solids of the groundwater in the saprolite and a change in pore structure associated weathering in situ versus transported weathered materials. The presence of saprolite, which commonly behaves as an aquitard, may limit the groundwater exchange between the palaeovalley and bedrock aquifers, with implications for the regional groundwater resource potential.
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Walker, David, Geoff Parkin, John Gowing, and Alemseged Tamiru Haile. "Development of a Hydrogeological Conceptual Model for Shallow Aquifers in the Data Scarce Upper Blue Nile Basin." Hydrology 6, no. 2 (May 27, 2019): 43. http://dx.doi.org/10.3390/hydrology6020043.
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Rural communities in sub-Saharan Africa commonly rely on shallow hand-dug wells and springs; consequently, shallow aquifers are an extremely important water source. Increased utilisation of shallow groundwater could help towards achieving multiple sustainable development goals (SDGs) by positively impacting poverty, hunger, and health. However, these shallow aquifers are little studied and poorly understood, partly due to a paucity of existing hydrogeological information in many regions of sub-Saharan Africa. This study develops a hydrogeological conceptual model for Dangila woreda (district) in Northwest Ethiopia, based on extensive field investigations and implementation of a citizen science programme. Geological and water point surveys revealed a thin (3–18 m) weathered volcanic regolith aquifer overlying very low permeability basalt. Hydrochemistry suggested that deep groundwater within fractured and scoriaceous zones of the basalt is not (or is poorly) connected to shallow groundwater. Isotope analysis and well monitoring indicated shallow groundwater flow paths that are not necessarily coincident with surface water flow paths. Characteristics of the prevalent seasonal floodplains are akin to “dambos” that are well-described in literature for Southern Africa. Pumping tests, recharge assessments, and hydrometeorological analysis indicated the regolith aquifer shows potential for increased utilisation. This research is transferrable to the shallow volcanic regolith aquifers that overlie a substantial proportion of Ethiopia and are prevalent throughout the East African Rift and in several areas elsewhere on the continent.
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Feo, Alessandra, Andrea Zanini, Emma Petrella, Rebeca Hernàndez-Diaz, and Fulvio Celico. "Analysis of the Saltwater Wedge in a Coastal Karst Aquifer with a Double Conduit Network, Numerical Simulations and Sensitivity Analysis." Water 11, no. 11 (November 5, 2019): 2311. http://dx.doi.org/10.3390/w11112311.
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We investigate the long-distance salinity in a dual permeability coastal karst aquifer with a double conduit network using a three-dimensional variable-density groundwater flow and multispecies transport SEAWAT model. Sensitivity analyses were used to evaluate the impact of the parameters and boundary conditions on the modeling saltwater wedge in a karstic aquifer situated in the Cuban land territory, including hydraulic conductivity, vertical anisotropy and salinity concentration; both in the conduits network and the fractured medium. These analyses indicated that hydraulic conductivity of the fractured medium and salt concentration were the ones that have a stronger effect on saltwater intrusion in a karstic aquifer. We also show results of the three-dimensional numerical simulations on groundwater salinity for different scenarios with the variabilities of the important parameters and compare results with electric conductivity profiles measured in a well.
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von Scherenberg, N. L., and H. G. P. Seyler. "Assessing the impact of saline intrusion with density dependent flow modelling for the fractured Peninsula Aquifer in Hermanus, South Africa." Water Supply 12, no. 3 (May 1, 2012): 387–97. http://dx.doi.org/10.2166/ws.2012.001.
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In the study area of Hermanus, South Africa, the Gateway Wellfield is used to augment municipal water supply. Due to the coastal location, the impact of saline intrusion needs to be considered. The confined Peninsula Aquifer comprises a complex fault system in a fractured rock environment. Analytical equations do not indicate any negative impact of saline intrusion. The impact of different parameters on the interaction between fresh and sea water was tested in a 2D sensitivity analysis. The hydraulic gradient and dispersivity were identified as crucial parameters. In addition, the impact of discrete fractures within a porous medium was tested. Fracture apertures in the likely range of the case study (b < 1 mm) showed a negligible effect. The geology of the Peninsula Aquifer was modelled as an Equivalent Porous Medium (EPM) whereby highly fractured zones around the faults were assigned high hydraulic conductivity. A maximum increase in salinity of 30 mg/l was predicted for the first 20 years of groundwater abstraction. An impact of vertical fractures with b > 1 mm was detected that is hardly predictable. In order to prove the gained conclusions and completely eliminate a harmful impact, further investigations are recommended.
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Binda, Gilberto, Andrea Pozzi, Davide Spanu, Franz Livio, Sara Trotta, and Raffaele Bitonte. "Integration of photogrammetry from unmanned aerial vehicles, field measurements and discrete fracture network modeling to understand groundwater flow in remote settings: test and comparison with geochemical markers in an Alpine catchment." Hydrogeology Journal 29, no. 3 (February 12, 2021): 1203–18. http://dx.doi.org/10.1007/s10040-021-02304-4.
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AbstractFast and cost-effective techniques for hydrogeological modeling are of broad interest for water resources exploitation, especially in remote settings, where hydrogeological measurements are difficult to perform. Unmanned aerial vehicles (UAV)-based techniques are potentially useful for these aims, but their application is still limited. In this study, a field-based approach and UAV-based approach are integrated for the computation of a discrete fracture network model of a fractured aquifer in the Central Alps. Then, calculated directions of the hydraulic conductivity components were compared with a geostatistical analysis of geochemical markers from sampled spring waters, to infer a conceptual model of groundwater flow. The comparison of field-based and UAV-based fracture measurements confirmed a good matching for fracture orientations and recognized a more reliable estimation of fracture dimensions for the UAV-based dataset. Nonetheless, an important variable for hydrogeological modeling—fracture aperture—is not measurable using UAV, as this requires field measurements. The calculated directions of the main conductivities fit well with the analyzed geochemical markers, indicating the presence of two partially separated fractured aquifers and describing their possible groundwater flow paths. The adopted integrated approach confirms UAV-based measurements as a potential tool for characterization of fracture sets as the input for hydrogeological modeling and for a fast and effective surveying tool, reducing time and cost for other following measurements.
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Bloomfield, J. P., and B. P. Marchant. "Analysis of groundwater drought building on the standardised precipitation index approach." Hydrology and Earth System Sciences 17, no. 12 (December 4, 2013): 4769–87. http://dx.doi.org/10.5194/hess-17-4769-2013.
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Abstract. A new index for standardising groundwater level time series and characterising groundwater droughts, the Standardised Groundwater level Index (SGI), is described. The SGI builds on the Standardised Precipitation Index (SPI) to account for differences in the form and characteristics of groundwater level and precipitation time series. The SGI is estimated using a non-parametric normal scores transform of groundwater level data for each calendar month. These monthly estimates are then merged to form a continuous index. The SGI has been calculated for 14 relatively long, up to 103 yr, groundwater level hydrographs from a variety of aquifers and compared with SPI for the same sites. The relationship between SGI and SPI is site specific and the SPI accumulation period which leads to the strongest correlation between SGI and SPI, qmax, varies between sites. However, there is a consistent positive linear correlation between a measure of the range of significant autocorrelation in the SGI series, mmax, and qmax across all sites. Given this correlation between SGI mmax and SPI qmax, and given that periods of low values of SGI can be shown to coincide with previously independently documented droughts, SGI is taken to be a robust and meaningful index of groundwater drought. The maximum length of groundwater droughts defined by SGI is an increasing function of mmax, meaning that relatively long groundwater droughts are generally more prevalent at sites where SGI has a relatively long autocorrelation range. Based on correlations between mmax, average unsaturated zone thickness and aquifer hydraulic diffusivity, the source of autocorrelation in SGI is inferred to be dependent on dominant aquifer flow and storage characteristics. For fractured aquifers, such as the Cretaceous Chalk, autocorrelation in SGI is inferred to be primarily related to autocorrelation in the recharge time series, while in granular aquifers, such as the Permo–Triassic sandstones, autocorrelation in SGI is inferred to be primarily a function of intrinsic saturated flow and storage properties of aquifer. These results highlight the need to take into account the hydrogeological context of groundwater monitoring sites when designing and interpreting data from groundwater drought monitoring networks.
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Nanni, Arthur Schmidt, Ari Roisenberg, Maria Helena Bezerra Maia de Hollanda, Maria Paula Casagrande Marimon, Antonio Pedro Viero, and Luiz Fernando Scheibe. "Fluoride in the Serra Geral Aquifer System: Source Evaluation Using Stable Isotopes and Principal Component Analysis." Journal of Geological Research 2013 (August 29, 2013): 1–9. http://dx.doi.org/10.1155/2013/309638.
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Groundwater with anomalous fluoride content and water mixture patterns were studied in the fractured Serra Geral Aquifer System, a basaltic to rhyolitic geological unit, using a principal component analysis interpretation of groundwater chemical data from 309 deep wells distributed in the Rio Grande do Sul State, Southern Brazil. A four-component model that explains 81% of the total variance in the Principal Component Analysis is suggested. Six hydrochemical groups were identified. δ18O and δ2H were analyzed in 28 Serra Geral Aquifer System samples in order to identify stable isotopes patterns and make comparisons with data from the Guarani Aquifer System and meteoric waters. The results demonstrated a complex water mixture between the Serra Geral Aquifer System and the Guarani Aquifer System, with meteoric recharge and ascending water infiltration through an intensive tectonic fracturing.
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Grasby, Stephen E., Zhuoheng Chen, Anthony P. Hamblin, Paul R. J. Wozniak, and Arthur R. Sweet. "Regional characterization of the Paskapoo bedrock aquifer system, southern AlbertaGeological Survey of Canada Contribution 2008-0479." Canadian Journal of Earth Sciences 45, no. 12 (December 2008): 1501–16. http://dx.doi.org/10.1139/e08-069.
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The Paskapoo Formation of southern Alberta supports more groundwater wells than any other aquifer system in the Canadian Prairies. Located in a region of rapid population growth and straddling watersheds where no new surface water licenses are available, this aquifer system is under increasing pressure to provide water supply. The Paskapoo Formation represents a foreland deposit of a siltstone- and mudstone-dominated fluvial system. The system is highly heterogeneous with broad ranges in physical properties that impact groundwater production. High-porosity coarse-grained channel sandstone can provide productive wells, whereas thin and fractured sands and siltstones are low producers. The basal Haynes Member and western portion of the Paskpaoo Formation have higher sandstone volumes than other portions of the system. Fracture density shows a strong inverse relationship to bed thickness, such that fracture flow becomes more important for thinner sandstone beds. There is no regional-scale flow system associated with the Paskapoo Formation; rather it is dominated by local-scale recharge processes. The geochemistry of Paskapoo Formation groundwater is largely controlled by the variable composition of immediately overlying glacial deposits.
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Visser, Anna-Neva, Moritz F. Lehmann, Hermann Rügner, Fernando Mazo D’Affonseca, Peter Grathwohl, Nia Blackwell, Andreas Kappler, and Karsten Osenbrück. "Fate of nitrate during groundwater recharge in a fractured karst aquifer in Southwest Germany." Hydrogeology Journal 29, no. 3 (February 18, 2021): 1153–71. http://dx.doi.org/10.1007/s10040-021-02314-2.
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AbstractOver the past decades, fractured and karst groundwater systems have been studied intensively due to their high vulnerability to nitrate (NO3−) contamination, yet nitrogen (N) turnover processes within the recharge area are still poorly understood. This study investigated the role of the karstified recharge area in NO3− transfer and turnover by combining isotopic analysis of NO3− and nitrite (NO2−) with time series data of hydraulic heads and specific electrical conductivity from groundwater monitoring wells and a karstic spring in Germany. A large spatial variability of groundwater NO3− concentrations (0.1–0.8 mM) was observed, which cannot be explained solely by agricultural land use. Natural-abundance N and O isotope measurements of NO3− (δ15N and δ18O) confirm that NO3− derives mainly from manure or fertilizer applications. Fractional N elimination by denitrification is indicated by relatively high δ15N- and δ18O-NO3− values, elevated NO2− concentrations (0.05–0.14 mM), and δ15N-NO2− values that were systematically lower than the corresponding values of δ15N-NO3−. Hydraulic and chemical response patterns of groundwater wells suggest that rain events result in the displacement of water from transient storage compartments such as the epikarst or the fissure network of the phreatic zone. Although O2 levels of the investigated groundwaters were close to saturation, local denitrification might be promoted in microoxic or anoxic niches formed in the ferrous iron-bearing carbonate rock formations. The results revealed that (temporarily) saturated fissure networks in the phreatic zone and the epikarst may play an important role in N turnover during the recharge of fractured aquifers.
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Gómez, Etzar, Viktor Broman, Torleif Dahlin, Gerhard Barmen, and Jan-Erik Rosberg. "Quantitative estimations of aquifer properties from resistivity in the Bolivian highlands." H2Open Journal 2, no. 1 (January 1, 2019): 113–24. http://dx.doi.org/10.2166/h2oj.2019.007.
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Abstract Resistivity data constitute the largest part of the available information to assess the hydrogeological characteristics of the aquifer system near Oruro, in the central part of the Bolivian Altiplano. Two aquifers are part of this system; top unconsolidated sediments storing fresh water in their granular voids, overlying fractured hard rock formations where saline water was detected in connection to some faults. This study proposes an indirect and cost-effective way to estimate aquifer hydraulic properties for the groundwater management in the region. Hydraulic conductivity and transmissivity in the top aquifer were estimated using an empirical linear relationship between hydraulic conductivity and resistivity. This latter parameter, as well as the aquifer thickness, were obtained from the inverted models corresponding to the geoelectrical tests performed in the study area (electrical resistivity tomography, transient electromagnetic soundings and vertical electrical soundings). The highest estimated transmissivity values are ∼4.0 × 10−2 m2/s located in the centre of the study area, the lowest values are ∼3.4 × 10−3 m2/s, located around thermal intrusions to the south and where the top of the bedrock is shallow (∼20 m depth) to the west. The methodology presented in this study makes wider use of resistivity measurements to identify promising groundwater production sites.
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Ju, Jinfeng, Quansheng Li, and Jialin Xu. "Experimental Study on the Self-Healing Behavior of Fractured Rocks Induced by Water-CO2-Rock Interactions in the Shendong Coalfield." Geofluids 2020 (October 8, 2020): 1–14. http://dx.doi.org/10.1155/2020/8863898.
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This study experimentally investigated the self-healing behavior, referring to the naturally occurring water permeability decrease, of fractured rocks exposed to water-CO2-rock interaction (WCRI). The experiment was conducted on prefractured specimens of three rock types typical of the Shendong coalfield: coarse-grained sandrock, fine-grained sandrock, and sandy mudrock. During the experiment, which ran for nearly 15 months, all three specimens exhibited decreasing permeabilities. The coarse- and fine-grained sandrock specimens exhibited smooth decreases in permeability, with approximately parallel permeability time curves, whereas that of the sandy mudrock specimen decreased rapidly during the initial stage and slowly during later stages. The sandrock specimens were rich in feldspars, which were dissolved and/or corroded and involved in ionic exchange reactions with CO2 and groundwater, thereby generating secondary minerals (such as kaolinite, quartz, and sericite) or CaSO4 sediments. These derivative matters adhered to the fracture surface, thereby gradually repairing fractures and decreasing the water permeability of the fractured rocks. In comparison, the sandy mudrock had a high content of clay minerals, and the water-rock interaction caused rapid expansions of illite, mixed illite-smectite, and other clay minerals, thereby narrowing the fractures and causing the rapid permeability decrease during the initial stage. In later stages, the derivative matters generated by the dissolution and/or corrosion of feldspars and other aluminum silicate minerals in the mudrock filled and sealed the fractures, causing the slow permeability decreases during the later stages, as in the sandrock specimens. Neutral and basic groundwater conditions facilitated better self-healing of fractured mudrocks rich in clay minerals, whereas acidic groundwater conditions and the presence of CO2 facilitated better self-healing of fractured sandrocks. Thus, this study’s results are of significant value to aquifer restoration efforts in the Shendong coalfield and other ecologically vulnerable mining areas.
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Ndlovu, M. S., M. Demlie, and M. Butler. "Hydrogeological setting and hydrogeochemical characteristics of the Durban Metropolitan District, eastern South Africa." South African Journal of Geology 122, no. 3 (September 1, 2019): 299–316. http://dx.doi.org/10.25131/sajg.122.0026.
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Abstract Population and economic growth within the Durban Metropolitan region in eastern South Africa have increased the demand for water supply. Though the region’s water supply comes mainly from surface water sources, the ever-increasing demand means that all available water supply sources including groundwater will be looked at, particularly in the peri-urban areas. However, the state of the groundwater resource in the region is poorly understood. This study aims to contribute towards improved understanding of the state of groundwater resources in the Metropolitan District through an integrated hydrogeological, hydrochemical and environmental isotope investigations. Results of the hydrogeological and hydrogeochemical characterization identified at least five hydrostratigraphic units of varying hydraulic and hydrochemical characteristics: the weathered and fractured basement aquifers of the Mapumulo Group, Oribi Gorge, Mzimlilo and Mkhomazi Suites characterized by average borehole yield and transmissivity (T) of 1.2 l/s, and 3.9 m2/day, respectively, and hydrochemical facies of Ca-Mg-HCO3;the fractured Natal Group sandstone characterised by average borehole yield and hydraulic conductivity (K) of 5.6 l/s and 2.8 m/day, respectively and with Na-Mg-HCO3-Cl dominant water type;the fractured aquifers of the Dwyka Group diamictite and tillite characterized by average borehole yield of 0.4 l/s, transmissivity of 1.3 m2/day and Na-Cl-HCO3 dominant water type;the Vryheid Formation of the Ecca Group characterized by average borehole yield of 2.5 l/s, T of 4.9 m2/day, K values 0.17 m/day, and Na-Cl-HCO3 water type. The Pietermaritzburg Formation of the Ecca Group is characterized by a shale lithology with very low borehole yields and average transmissivity of 0.28 m2/d with Na-Ca-Cl dominant water type. It is considered as an aquiclude than an aquifer;the intergranular aquifer of the Maputaland Group which comprises the Bluff, Berea type sands and harbour beds (recent alluvium and estuarine deposits). These units collectively have average borehole yield of 14.8 l/s, transmissivity of up to 406 m2/day and a mainly Na-Cl-HCO3 hydrochemical signature. The region receives mean annual precipitation (MAP) of 935 mm/yr of which an estimated 6.6% recharges the various aquifers. Environmental isotope data (2H, 18O and 3H) indicated that groundwater is recharged from modern precipitation. High concentrations of tritium, as high as 92 T.U., measured around landfill sites, indicates groundwater contamination from leachate leakage posing a risk to human and environmental health.
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Seli, Ahmed Buba, Buba Apagu Ankidawa, and Jackson M. Ishaku. "Dar Zarrouk Parameters for delineation of groundwater potentials in Ganye and Environs, Adamawa State, Northeastern Nigeria." Journal of Tropical Resources and Sustainable Science (JTRSS) 9, no. 1 (August 22, 2021): 20–36. http://dx.doi.org/10.47253/jtrss.v9i1.706.
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Groundwater is the main source of water supply in areas in Nigeria including the research area. The research is aimed at delineating groundwater potentials in Ganye and environs using Dar Zarrouk parameters. Fourteen (14) vertical electrical soundings were conducted across the study area in order to determine Dar Zarrouk parameters to determine groundwater potentials in Ganye and environs. The area is underlain by migmatite-gneiss and Pan African granites. Weathered/fractured basement constitute the aquifer type in the area. The aquifer conductivity in the study area range between 0.00871 to 0.032032 ?-1 with mean value of 0.019493 ?-1. The aquifer longitudinal conductance ranges between 0.22246 to 0.759252 with mean value of 0.432846. The transverse resistance range between 627.8721 to 1,857.282 ?m2 with average value of 1,235.854 ?m2. The aquifer hydraulic conductivity range between 6.9314 to 15.562 m/day with mean value of 9.738 m/day while the transmissivity across the study area range between 114.2152 to 378.774 m2/day with mean value of 216.0487 m2/day.
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Lehman, R. Michael, Frederick S. Colwell, and Greg A. Bala. "Attached and Unattached Microbial Communities in a Simulated Basalt Aquifer under Fracture- and Porous-Flow Conditions." Applied and Environmental Microbiology 67, no. 6 (June 1, 2001): 2799–809. http://dx.doi.org/10.1128/aem.67.6.2799-2809.2001.
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ABSTRACT Bench scale column studies were used to examine the partitioning of microorganisms between groundwater and a geologic medium and to examine the effect of hydrogeology (i.e., porous- versus fracture-flow) on organism partitioning. Replicated columns were constructed with intact basalt core segments that contained natural fractures and with the same basalt crushed into particles. The columns were perfused with groundwater, and upon reaching a steady state, the columns were sacrificed and the attached and unattached communities were analyzed by multiple approaches. The analyses included the total number of cells, the phylogenetic affiliation of the cells (i.e., the α, β, and γ subclasses of the class Proteobacteria and gram positives with high G+C DNA content) by fluorescent in situ hybridization (FISH), number and taxonomic affiliation by fatty acid methyl ester profiles of culturable heterotrophs, most-probable-number estimates of methanotrophs and phenol oxidizers, and whole-community sole carbon source utilization patterns from Biolog GN microplates. In the packed columns, about 99% of the total biomass (per cubic centimeter of porous medium) was attached to the geologic medium. Lack of equitable units precluded a comparison of attached and unattached biomasses in the fractured columns where the attached biomass was expressed per unit of surface area. Compositional differences in the attached and unattached communities were evidenced by (i) the recovery ofPseudomonas stutzeri, an Enterococcus sp., andBacillus psychrophilus from the groundwater and not from the basalt, (ii) differences between community carbon source utilization patterns, and (iii) the relative abundances of different phylogenetic groups estimated by FISH in both column types. In the packed columns, attached communities were depleted of members of the α- and β-Proteobacteria subclasses in comparison to those in the corresponding groundwater. In the fractured columns, attached communities were enriched in gram-positive Bacteriaand γ-Proteobacteria and depleted of β-Proteobacteria, in comparison to those in the corresponding groundwater. Segregation of populations and their activities, possibly modified by attachment to geologic media, may influence contaminant fate and transport in the subsurface and impact other in situ applications.
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Greco, Roberto, Pasquale Marino, Giovanni Francesco Santonastaso, and Emilia Damiano. "Interaction between Perched Epikarst Aquifer and Unsaturated Soil Cover in the Initiation of Shallow Landslides in Pyroclastic Soils." Water 10, no. 7 (July 16, 2018): 948. http://dx.doi.org/10.3390/w10070948.
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A physically based mathematical model of the slope of Cervinara (southern Italy), which is characterized by a shallow pyroclastic soil cover laying upon a limestone fractured bedrock, has been developed. Previous and current ongoing monitoring suggested that leakage through the soil–bedrock interface occurred, with leaking water temporarily stored in a perched aquifer located in the upper part of the fractured limestone (epikarst). This aquifer supplied several springs, and recharge to the deeper groundwater circulation occurred. Hence, in the proposed model, the unsaturated water flow taking place within the soil cover is coupled with the saturated water flow in the perched aquifer. The application of the model to the simulation of the slope hydrologic behavior over a period of 11 years, between 2006–2017, provides realistic results in terms of soil storage, epikarst storage, spring discharge, and groundwater recharge. The different response times of soil and epikarst aquifer to precipitation input allow distinguishing the hydrological predisposing causes of potential landsliding (i.e., a few months of persistent rainfall that is capable of filling the epikarst aquifer) from the triggers, which are represented by single intense rainfall events. The application of the model offers a key of interpretation of the hydrological processes leading to the landslide that occurred on 16 December 1999.
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Terrone, M., G. Paliaga, N. Bazzurro, A. Marchese, and F. Faccini. "Groundwater resources in a fractured-rock aquifer, Conglomerate of Portofino." Journal of Maps 17, no. 2 (April 21, 2021): 268–78. http://dx.doi.org/10.1080/17445647.2021.1911868.
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Diamond, R. E., and C. Harris. "Stable isotope constraints on hydrostratigraphy and aquifer connectivity in the Table Mountain Group." South African Journal of Geology 122, no. 3 (September 1, 2019): 317–30. http://dx.doi.org/10.25131/sajg.122.0021.
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Abstract The Table Mountain Group is a folded, faulted, quartzite-dominated sedimentary sequence, metamorphosed to lower greenschist facies, that forms steep mountains dominating the topography of the Western Cape and causing orographic rainfall in an otherwise semi-arid region. These quartzites are highly fractured to depths of kilometres and act as a complex aquifer system that supplies groundwater directly and indirectly, through baseflow, essential for sustaining the natural environment and human activity in the region. Hydrogen and oxygen isotope data for rain, rivers and groundwater (boreholes and springs) in the region give typical altitude effects of -1.8‰ δD/100 m and -0.33‰ δ18O/100 m, and a very strong continental effect of -30‰ δD/100 km and -4.7‰ δ18O/100 km. This allows for application of stable isotopes as natural hydrological tracers. Groundwater at several locations had stable isotope compositions different from ambient rainfall, but similar to rainfall at high altitudes in adjacent mountains, indicating recharge at high altitude. The groundwater flow is through the Skurweberg Aquifer, here defined as all three formations of the Nardouw Subgroup. Observations on the Peninsula Aquifer suggest a very well mixed aquifer, due to extensive fracturing. Potential exists to delineate groundwater protection zones, detect overabstraction and understand aquifer connectivity better by applying stable isotope hydrology to the Table Mountain Group.
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Cai, Jinbang, Yue Su, Huan Shen, and Yong Huang. "Simulation of Groundwater Flow in Fractured-Karst Aquifer with a Coupled Model in Maling Reservoir, China." Applied Sciences 11, no. 4 (February 21, 2021): 1888. http://dx.doi.org/10.3390/app11041888.
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A coupled model has been developed to simulate groundwater flow in fractured karst systems according to the complex geological and karst hydrogeological conditions of the dam site, where a 3D mathematical model based on Boussinesq equation was used to describe the movement of groundwater flow in fractured medium, and a 1D conduit model for karst medium. The model was solved with the continuous hydraulic heads at the common boundaries. The hydraulic conductivities of karst medium were determined by geometrical parameters and flux of pipes. Furthermore, the permeability parameters for fractured medium were calibrated by the measured and calculated groundwater levels. The calibrated model was employed to predict the variation of groundwater flow field and leakage from the karst pipes and underground powerhouse during the reservoir operation. The simulated results showed that the groundwater level of the powerhouse had decreased by about 2–5 m. The water level of conveyance pipeline had risen by 10–20 m, and the water level on both banks had risen by 15–25 m. The leakage of karst conduits for impervious failure was larger than that for normal seepage control. In addition, the leakage of the powerhouse was estimated to be about 1000–3000 m3/d, and the seepage control of karst pipes had little influence on the leakage of underground powerhouse.
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Kresic, N., A. Mikszewski, J. Manuszak, and M. C. Kavanaugh. "Impact of contaminant mass reduction in residuum sediments on dissolved concentrations in underlying aquifer." Water Supply 7, no. 3 (November 1, 2007): 31–39. http://dx.doi.org/10.2166/ws.2007.064.
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Contamination of aquifers in many cases occurs because of the downward migration of contaminants from the land surface through the vadose zone, including through residuum sediments in case of fractured or karst aquifers. It is therefore critically important to characterize and model fate and transport of contaminants in both the vadose zone/residuum and the underlying saturated zone as part of remedial design for aquifer restoration. Residuum sediments usually contain a significant fraction of clay minerals and fluid flow is often predominantly in vertical direction. Groundwater modeling is useful when evaluating alternatives of contaminant mass removal in the vadose zone/residuum and their impact on the downgradient dissolved concentrations in the underlying aquifer. Two case studies illustrate applicability of such modeling. The first study includes modeling of the expected natural longevity of a residual DNAPL mass accumulation in the saturated residuum, and its comparison to the effects of remedial DNAPL mass removal. The second study includes modeling contaminant transport from a residual DNAPL source within the vadose zone to the saturated zone in the residuum and the underlying bedrock aquifer. The natural longevity of the unsaturated DNAPL source is modeled, focusing on resulting down-gradient concentrations in the residuum and bedrock aquifer. For comparison, two remedial actions are simulated; 90% mass removal and soil flushing.