77 research outputs found
The influence of water/rock â water/clay interactions and mixing in the salinization processes of groundwater
Study region: Groundwater from the Precambrian Shield rock and Pleistocene deposit aquifers in Saguenay-Lac-Saint-Jean region ( >13 000 km2) in the province of Quebec, Canada. Study focus: Interpretations are based on the combination of hierarchical cluster analysis (HCA) results, principal component analysis (PCA), binary plots investigations ([Na+, Ca2+, Brâ] vs. Clâ; Ca2+ vs. HCO3â; Ca2+ vs. Na+) and Piper diagram investigations. The HCA and PCA was applied on 321 samples to specifically enable the identification of two very distinct salinization paths that produce the brackish groundwater in the study area.
New hydrological insights for the region: The results show that each of the two salinization paths exerts a major and different influence on the chemical signature of groundwater. Groundwater present in the crystalline bedrock naturally evolve from a recharge-type groundwater (Ca-HCO3-dominant) to a type of brackish groundwater (Ca-(Na)-Cl-dominant) due to water/rock interactions (plagioclase weathering and mixing with deep basement fluids). Groundwater evolution in confined aquifers is dominated by water/clay interactions. The term water/clay interactions was introduced in this paper to account for a combination of processes: ion exchange and/or leaching of salt water trapped in the regional aquitard. Mixing with fossil seawater might also increase the groundwater salinity. PCA revealed that Ca2+, Sr2+, Ba2+ are highly correlated with groundwater from bedrock aquifers, while Mg2+, SiO2, K+, SO42â and HCO3â are more representative of the regional confining conditions
Insights on pumping well interpretation from flow dimension analysis : the learnings of a multi-context field database
The flow dimension parameter n, derived from the Generalized Radial Flow model, is a valuable tool to investigate the actual flow regimes that really occur during a pumping test rather than suppose them to be radial, as postulated by the Theis-derived models. A numerical approach has shown that, when the flow dimension is not radial, using the derivative analysis rather than the conventional Theis and Cooper-Jacob methods helps to estimate much more accurately the hydraulic conductivity of the aquifer. Although n has been analysed in numerous studies including field-based studies, there is a striking lack of knowledge about its occurrence in nature and how it may be related to the hydrogeological setting. This study provides an overview of the occurrence of n in natural aquifers located in various geological contexts including crystalline rock, carbonate rock and granular aquifers. A comprehensive database is compiled from governmental and industrial sources, based on 69 constant-rate pumping tests. By means of a sequential analysis approach, we systematically performed a flow dimension analysis in which straight segments on drawdown-log derivative time series are interpreted as successive, specific and independent flow regimes. To reduce the uncertainties inherent in the identification of n sequences, we used the proprietary SIREN code to execute a dual simultaneous fit on both the drawdown and the drawdown-log derivative signals. Using the stated database, we investigate the frequency with which
the radial and non-radial flow regimes occur in fractured rock and granular aquifers, and also provide outcomes that indicate the lack of applicability of Theis-derived models in representing nature. The results also emphasize the complexity of hydraulic signatures observed in nature by pointing out n sequential signals and non-integer n values that are frequently observed in the database
Numerical modeling for determining the local vertical hydraulic gradient at the wall of a tunnel
The determination of the flow rate in the underground excavation is a very important parameter in the design of the structures. Among all parameters that have an impact on the inflow rate to the tunnel, the hydraulic gradient is one of the most effective one that, according to Darcyâs law, controls the tunnel inflow rate. An empirical-numerical equation is proposed for the determination of the vertical hydraulic gradient in the wall of a tunnel excavated below a water table. The
horizontal hydraulic gradient is not supposed to have a significant impact on the tunnel inflow rate as its value is very low.
By contrast, the existing vertical hydraulic gradient is among the most effective parameters. On the other hand, in the case of an underground excavation, no equation exists for the determination of the hydraulic gradient that considers more than one parameter, i.e., the depth. Using the results of the numerical simulations, it was deduced that the depth of the tunnel, the ratio between principal hydraulic conductivities, and their relevant directions are the most effective parameters that have a significant influence on the hydraulic gradient and inflow rate to the underground tunnels. The resultant hydraulic gradients in the vicinity of the wall of the tunnel were obtained using the RS2 Rocscience software. The mathematical relationship between the input data, i.e., the depth (z), ratio between hydraulic gradients (a) and their relevant directions (α), and the result of the simulation, i.e., the hydraulic gradient (iz), have been derived by curve fitting. Finally, for each orientation of the principal hydraulic conductivity, an equation is proposed for the calculation of the hydraulic gradient.
La détermination du débit dans une excavation souterraine est un paramÚtre trÚs important dans la conception des
structures. Parmi tous les paramÚtres qui ont un impact sur le débit d'entrée dans le tunnel, le gradient hydraulique est l'un des plus influents qui, selon la loi de Darcy, contrÎle le débit d'entrée du tunnel. Une équation empirico-numérique est proposée pour la détermination du gradient hydraulique vertical dans la paroi d'un tunnel creusé sous une nappe phréatique. Le gradient hydraulique horizontal n'est pas censé avoir un impact significatif sur le débit d'entrée du tunnel,
car sa valeur est trÚs faible. En revanche, le gradient hydraulique vertical existant a un impact significatif. En outre, dans le cas d'une excavation souterraine, aucune équation n'existe pour la détermination du gradient hydraulique qui prend en compte plus d'un paramÚtre, c'est-à -dire la profondeur. En utilisant les résultats des simulations numériques, il a été déduit que la profondeur du tunnel, le rapport entre les principales conductivités hydrauliques et leurs directions pertinentes sont les paramÚtres les plus efficaces qui ont une influence significative sur le gradient hydraulique et le débit d'entrée dans les tunnels souterrains. Les gradients hydrauliques résultants au voisinage de la paroi du tunnel ont été obtenus à l'aide du logiciel RS2 Rocscience. La relation mathématique entre les données d'entrée, c'est-à -dire la profondeur (z), le rapport entre les gradients hydrauliques (a) et leurs directions pertinentes (α), et le résultat de la simulation, c'est-à -dire le gradient
hydraulique (iz), ont été dérivés par ajustement de courbe. Enfin, pour chaque orientation de la conductivité hydraulique principale, une équation est proposée pour le calcul du gradient hydraulique
Transient Electromagnetic (TEM) Surveys as a First Approach for Characterizing a Regional Aquifer: The Case of the Saint-Narcisse Moraine, Quebec, Canada
Geological contexts that lack minimal stratigraphic and piezometric information can be challenging to produce an initial hydrogeological map in remote territories. This study proposes an approach to characterize a regional aquifer using transient electromagnetic (TEM) surveys. Given the presence of randomly dispersed boreholes, the Saint-Narcisse moraine in the Mauricie region of Quebec (Canada) is an appropriate site for collecting the required geophysical data, correlating the stratigraphic and piezometric information, and characterizing regional granular aquifers in terms of stratigraphy, geometry, thickness, and extent. In order to use all TEM results (i.e., 47 stations) acquired in the moraine area, we also correlated 13 TEM stations, 7 boreholes, and 6 stratigraphic cross-sections to derive an empirical and local petrophysical relationship and to establish a calibration chart of the sediments. Our TEM data, combined with piezometric mapping and the sedimentary records from boreholes and stratigraphic cross-sections, revealed the compartmentalization of a multi-kilometer morainic system and indicated the presence of two large unconfined granular aquifers overlying the bedrock. These aquifers extend more than 12 km east to west across the study area and are between 25 and >94 m thick. The TEM method provides critical information on groundwater at a regional scale by acquiring information from multiple stations within a short time span to a degree not possible with other existing methodologies
The Specific Length of an Underground Tunnel and the Effects of Rock Block Characteristics on the Inflow Rate
The specific length of a tunnel (STL) and a new analytical model for calculating the block surface area of the rock mass are introduced. First, a method for determining the appropriate length of a tunnel for a numerical simulation is described. The length is then used to examine the correlation between the inflow rate to the tunnel and the block volume, the block surface area, and the fracture intensity (P32) through analytical and numerical modeling. The results indicate that the length of the tunnel should at least be equal to the least common multiple (LCM) of the apparent spacings of the joint sets at the wall of the tunnel to obtain the more reliable and immediate results for the inflow rate to a tunnel that is excavated in a fractured rock mass. A new analytical model was developed to calculate the block surface area and determine the essential joint set parameters, which include the dip, dip direction, and spacing. The determination of the rock block characteristics through numerical modeling requires considering the intact block for calculations. The results indicated that the inflow rate to the tunnel increased with an increase in fracture intensity and a decrease in block volume and surface area. The STL and the analytical model used for calculating the block surface area are validated through numerical simulations with 3DEC software version 7.0
Assessing groundwater recharge and transpiration in a humid northern region dominated by snowmelt using vadose-zone depth profiles
Profiles of the stable isotope ratios of pore water within the vadose zone provide fingerprints of the history of water percolation into a soil. These profiles, combined with profiles of the volumetric water content, can determine the timing and amount of water that has percolated during specific periods. This study aims to: (1) understand water percolation at two sites in Quebec (Canada) that experience thick snow coverage during the winter season; (2) calculate groundwater recharge rates using the peak-shift method; and (3) estimate the transpiration rate based on the water balance budget. A 7-m-deep borehole was drilled at two sites: one site is sparsely covered by vegetation (S1), while the second underlies a pine forest (S2). For all subsamples, ÎŽ18O and ÎŽ2H from the soil pore water were analyzed, volumetric water content of the cores was measured, and grain-size analyses to estimate the hydraulic properties were performed. For both boreholes, the winterâspring and summerâautumn periods were determined. Given the limited evapotranspiration occurring during the winterâspring period, recharge rates were high at both sites (71 and 75%), while the summerâautumn period had lower recharge rates of 63% (S1) and 41% (S2). A transpiration rate of 0.7 mm/day was estimated for the pine trees covering site S2. This study provides new field observations for estimating recharge based on water stable isotope profiles in a humid northern region dominated by snowmelt. Moreover, it confirms the accuracy of the peak-shift method for assessing groundwater recharge and estimating transpiration.
Les profils du taux dâisotopes stables de lâeau des pores de la zone vadose fournissent des empreintes de lâhistoire de la percolation de lâeau dans le sol. Ces profils, combinĂ©s Ă des profils de teneurs volumĂ©triques en eau, peuvent dĂ©terminer le moment et la quantitĂ© dâeau qui a percolĂ© pendant des pĂ©riodes particuliĂšres. Cette Ă©tude a pour objectifs: (1) de comprendre la percolation de lâeau sur deux sites du QuĂ©bec (Canada) qui connaissent un Ă©pais manteau neigeux pendant lâhiver; (2) de calculer les taux de recharge en appliquant la mĂ©thode du « dĂ©calage du pic »; (3) dâestimer le taux de transpiration sur la base du bilan hydrologique. Un forage de 7 m de profondeur a Ă©tĂ© rĂ©alisĂ© sur les deux sites: le premier site est couvert dâune vĂ©gĂ©tation clairsemĂ©e (S1), tandis que le deuxiĂšme se situe sous une forĂȘt de pins (S2). Pour tous les Ă©chantillons, le ÎŽ18O et le ÎŽ2H de lâeau des pores du sol ont Ă©tĂ© analysĂ©s, la teneur volumĂ©trique en eau des carottes mesurĂ©e et des analyses de la granulomĂ©trie conduites afin dâestimer les propriĂ©tĂ©s hydrauliques. Pour les deux forages, les pĂ©riodes hiverâprintemps et Ă©tĂ©âautomne ont Ă©tĂ© dĂ©finies. Etant donnĂ©e la faible Ă©vapotranspiration durant la pĂ©riode hiverâprintemps, les taux de recharge sont Ă©levĂ©s sur les deux sites (71 et 75%), tandis que la pĂ©riode Ă©tĂ©âautomne montre des taux de recharge plus faibles, de 63% (S1) et 41% (S2). Un taux de transpiration de 0,7 mm/jour a Ă©tĂ© estimĂ© pour la forĂȘt de pins couvrant le site S2. Cette Ă©tude fournit des observations de terrain inĂ©dites pour estimer, sur la base de profils dâisotopes stables de lâeau, la recharge dâune rĂ©gion nordique humide dominĂ©e par la fonte des neiges. De plus, elle confirme la prĂ©cision de la mĂ©thode du « dĂ©calage du pic » pour Ă©valuer la recharge et estimer la transpiration
Constraining a flow model with field measurements to assess water transit time through a vadose zone
The modeling of thick vadose zones is particularly challenging because of difficulties in collecting a variety of measured sediment properties, which are required for parameterizing the model. Some models rely on synthetic data, whereas others are simplified by running as homogeneous sediment domains and relying on a single set of sediment properties. Few studies have simulated flow processes through a thick vadose zone using real and comprehensive data sets comprising multiple measurements. Here, we develop a flow model for a 7âmâthick vadose zone. This model, combining the numerical codes CTRAN/W with SEEP/W, includes the measured sediment hydraulic properties of the investigated vadose zone and incorporates the actual climate and subsurface conditions of the study site (precipitations, waterâtable elevations, and stable isotope data). The model is calibrated by fitting the simulated and measured vertical profiles of water content. Our flow model calculates a transit time of 1 year for the travel of water through the 7âm vadose zone; this estimate matches stable isotopeâbased results obtained previously for this site. A homogeneous sediment domain flow model, which considers only a single set of sediment properties, produces a transit time that is approximately half the duration of that of the heterogeneous flow model. This difference highlights the importance of assuming heterogeneous material within models of thick vadose zones and testifies to the advantage gained when using real sediment hydraulic properties to parametrize a flow model
RĂ©sultats du projet dâacquisition de connaissances sur les eaux souterraines du territoire municipalisĂ© de LanaudiĂšre, de lâest de la Mauricie et de la Moyenne-CĂŽte-Nord, PACES-LAMEMCN â section Mauricie-Est
Le Centre dâĂ©tudes sur les ressources minĂ©rales (CERM) de lâUniversitĂ© du QuĂ©bec Ă Chicoutimi (UQAC) a rĂ©alisĂ©
la premiÚre caractérisation régionale des aquifÚres et des eaux souterraines du territoire municipalisé de la
rĂ©gion de lâest de la Mauricie. Cette Ă©tude a Ă©tĂ© effectuĂ©e dans le cadre du projet dâacquisition de connaissances
sur les eaux souterraines des territoires municipalisĂ©s de LanaudiĂšre, de lâest de la Mauricie et de la MoyenneCĂŽte-Nord (PACES-LAMEMCN), gĂ©rĂ© par le ministĂšre provincial de lâEnvironnement et de la Lutte contre les changements climatiques (MELCC). Ce rapport prĂ©sente les rĂ©sultats des trois phases du PACES-LAMEMCN section Mauricie-Est Ă©chelonnĂ©es sur quatre annĂ©es de travail (2018 â 2022)
RĂ©sultats du projet dâacquisition de connaissances sur les eaux souterraines du territoire municipalisĂ© de LanaudiĂšre, de lâest de la Mauricie et de la Moyenne-CĂŽte-Nord, PACES-LAMEMCN â section LanaudiĂšre
Le Centre dâĂ©tudes sur les ressources minĂ©rales (CERM) de lâUniversitĂ© du QuĂ©bec Ă Chicoutimi (UQAC) a rĂ©alisĂ© la premiĂšre caractĂ©risation rĂ©gionale des aquifĂšres et des eaux souterraines du territoire municipalisĂ© de la rĂ©gion de LanaudiĂšre. Cette Ă©tude a Ă©tĂ© effectuĂ©e dans le cadre du projet dâacquisition de connaissances sur les eaux souterraines des territoires municipalisĂ©s de LanaudiĂšre, de lâest de la Mauricie et de la Moyenne-CĂŽte-Nord (PACES-LAMEMCN), gĂ©rĂ© par le ministĂšre provincial de lâEnvironnement et de la Lutte contre les changements climatiques (MELCC). Ce rapport prĂ©sente les rĂ©sultats des trois phases du PACES-LAMEMCN section LanaudiĂšre Ă©chelonnĂ©es sur quatre annĂ©es de travail (2018 â 2022)
Characterization of general and singular features of major aquifer systems in the Saguenay-Lac-Saint-Jean region
The hydrogeology of the municipalized territory (13,210 km2) of the Saguenay-Lac-Saint-Jean (SLSJ) region has been studied as part of the groundwater knowledge acquisition program entitled Programme dâacquisition de connaissances sur les eaux souterraines (PACES) launched in 2008 by the Government of Quebec, Canada. This study involved the collaboration of numerous contributors (municipal policymakers, government agencies, watershed organizations and universities) to meet the programâs multiple and wide-ranging requirements. The key deliverables included a numerical geodatabase, 38 regional-scale maps and a scientific report, all elaborated after 4 years of data gathering and compilation, fieldwork and information synthesis. In addition, numerous collateral research projects were undertaken by undergraduate and graduate students. The results of the SLSJ-PACES project provided new insights into regional groundwater resources and led to a generalized conceptual model of regional hydrostratigraphic features and groundwater quality. This paper summarizes the particular aspects of the major aquifers in the SLSJ region as uncovered by PACES, and presents the emerging challenges for updating and improving the regionâs hydrogeological knowledge and ensuring the sustainable management of regional groundwater resources.
Le gouvernement du QuĂ©bec, au Canada, a lancĂ© un programme scientifique d'acquisition de connaissances sur les eaux souterraines intitulĂ© le «Programme d'acquisition des connaissances sur les eaux souterraines» (PACES) visant Ă amĂ©liorer les connaissances sur les ressources en eaux souterraines. La rĂ©gion du Saguenay-Lac-Saint-Jean (SLSJ, QuĂ©bec, Canada, 13 210 km2) est parmi les premiĂšres rĂ©gions ayant bĂ©nĂ©ficiĂ© de ce programme. Pour rĂ©aliser le projet, plusieurs partenaires (dĂ©cideurs municipaux, organismes gouvernementaux, organisations de bassins versants et universitĂ©s) ont collaborĂ© afin de rĂ©pondre aux exigences multiples et variĂ©es du projet PACES. Le livrable principal est constituĂ© dâune gĂ©odatabase numĂ©rique, Ă laquelle sâajoute 38 cartes d'Ă©chelle rĂ©gionale, et un rapport scientifique. Le tout a Ă©tĂ© livrĂ© aprĂšs 4 ans de travail incluant de la compilation, des levĂ©s sur le terrain et la synthĂšse des rĂ©sultats. En outre, de nombreux projets de recherche parallĂšles ont Ă©tĂ© menĂ©s par des Ă©tudiants de premier cycle et des cycles supĂ©rieurs. Les rĂ©sultats du projet PACES au SLSJ apportent de nouvelles perspectives sur les ressources en eaux souterraines Ă l'Ă©chelle rĂ©gionale et soutiennent un modĂšle conceptuel gĂ©nĂ©ralisĂ© des caractĂ©ristiques hydrostratigraphiques, de mĂȘme que de la qualitĂ© des eaux souterraines pour la rĂ©gion. Cet article rĂ©sume les aspects singuliers des principaux aquifĂšres de la rĂ©gion SLSJ, et permet de discuter des dĂ©fis qui Ă©mergent du PACES-SLSJ pour maintenir les connaissances hydrogĂ©ologiques Ă jour et pour les rendre disponibles dans une optique de gestion durable des ressources en eaux souterraines
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