Factors affecting river turbidity in a degrading permafrost environment : the Tasiapik River, Umiujaq (Nunavik)

This study focuses on spatiotemporal changes in water turbidity in relation to permafrost to document the impact of meteorological conditions and water flow on hydro-sedimentary processes in northern regions. Starting in June of 2019, water turbidity data were collected at six sites along the Tasiapik River (Nunavik). A statistical analysis was completed based on records of water turbidity, precipitation, water flow, and air temperature. Our results show a significant correlation between air temperatures and turbidity, with a correlation of up to r = 0.59. These correlations depend on the location of the site along the river and the time of the study period (June–October 2019). The flow rate was the primary factor that caused variations in the turbidity of the Tasiapik River. Our results showed that following an increase in flow rate, there was an almost simultaneous increase in turbidity due to erosion of the banks. The duration and intensity of precipitation events are also important factors affecting the process of sediment transport. Even though meteorological conditions play an important role in turbidity variation, other characteristics of the site such as the topography and the existence of thermokarst lakes are additional factors that influence the dynamics of sediment transport in the Tasiapik River.Les travaux menés en Arctique et Subarctique démontrent une accélération de la dégradation du pergélisol durant les dernières décennies, provoquant des tassements importants du sol et par le fait même, un accroissement du fluage d’eau chargée de sédiments vers les lacs et les rivières. Cette étude vise à mieux comprendre la variation spatio-temporelle de la turbidité fluviale en contexte périglaciaire dans le but de faire avancer les connaissances sur les impacts des conditions météorologiques et du débit sur les processus hydrosédimentaires des régions nordiques. Des données de turbidité de l’eau de la rivière Tasiapik, située à 5 km à l’est du village d’Umiujaq (Nunavik), ont été enregistrées de juin à octobre 2019 dans six sites distincts. Des analyses statistiques réalisées sur ces enregistrements indiquent qu’il existe une corrélation significative (r = 0,59) entre les températures de l’air et la turbidité de la rivière. Ces relations sont plus ou moins importantes selon l’emplacement du site le long de la rivière et selon le moment de la période d’étude. Le débit était le principal facteur à l’origine des variations de la turbidité de la rivière Tasiapik. Nos résultats ont montré qu’à la suite d’une augmentation du débit, il y a eu une augmentation presque simultanée de la turbidité due à l’érosion des berges et de la quantité des sédiments en suspension. La durée et l’intensité des précipitations sont également des facteurs importants ayant fait varier la turbidité de la rivière. Bien que les conditions météorologiques jouent un rôle important dans la variation de la turbidité, il s’est avéré que les caractéristiques du site telles que la topographie et la présence de lacs thermokarstiques sont des facteurs importants dans la dynamique du transport sédimentaire de la rivière Tasiapik

Numerical evaluation of grouting scenarios for reducing water inflows in underground excavations – Goldcorp’s Éléonore mine study case

Water inflows through fracture networks are one of the many challenges that the Éléonore mine has to face. Although pregrouting of pilot holes during mine development has been proven to efficiently reduce water inflows into mine excavations, the actual design methods are empirical and can be optimized to increase grouting efficiency and decrease the associated costs. Optimization of the amount of cement needed for pre-grouting is achieved by designing the grouting approach based on the location of major faults around the excavations. Here, a base case finite-element numerical model and associated sensitivity analyses are used to simulate groundwater inflows into a stope, based on the Éléonore mining site characteristics. Simulations are conducted for testing various grout injection scenarios for various major fault locations around the stope. Sensitivity analyses have shown that for a fault located above the stope, the inflow reduction is greater when the zone between the fault and the stope is grouted instead of directly grouting the fault itself. Also, in the case of a fault intersecting a stope, the results have demonstrated that the fault itself should be grouted as widely as possible, instead of sealing only the immediate surroundings of the stope

Numerical simulation of hydrocarbon fuel dissolution and biodegradation in groundwater

The behaviour of hydrocarbon fuels in contaminated groundwater systems is studied using a multicomponent reactive transport model. The simulated processes include residual NAPL dissolution, aerobic and anaerobic biodegradation with daughter-product transport, and transport of a reactive carrier with mixed equilibrium/kinetic sorption. The solution algorithm is based on a three-dimensional Galerkin finite element scheme with deformable brick elements and capacity for a free watertable search. Nonlinearities are handled through Picard iteration. Convergence is rapid for most applications and mass balance errors for all phases are minimal. The model is first applied to simulate a pilot scale diesel fuel dissolution experiment in which humic acid is used as a natural organic carrier to enhance dissolution and to promote biodegradation of the aqueous components. The pilot scale experiment is described by Lesage et al. (1995) and Van Stempvoort et al. (2000). The conceptual model includes 8 unique components dissolving from 500 mL of residual diesel fuel within a 3D saturated domain. Oxygen-limiting competitive aerobic biodegradation with a dynamic microbial population is also included. A mixed 2-site equilibrium/kinetic model for describing sorption of the carrier to the aquifer solids was adopted to reproduce the observed breakthrough of the humic acid and organic components. Most model parameters were obtained independently with minimal calibration. Batch sorption data were found to fit well at the pilot scale, however biodegradation and dissolution rates were not well known and had to be fitted. Simulations confirmed the observed 10-fold increase in effective solubility of trimethylnaphthalene, and increases on the order of 2-5 for methyl- and dimethylnaphthalene. The simulated plumes showed almost complete attenuation after 5 years, in excellent agreement with observed data. A sensitivity analysis showed the importance of carrier concentrations, binding coefficients, dissolution and biodegradation rates. Compared to a dissolution scenario assuming no carrier, the humic acid-enhanced dissolution case decreased the remediation time by a factor of about 5. The second application of the model involves simulating the effect of ethanol on the persistence of benzene in gasoline-impacted groundwater systems. The conceptual model includes a 4-component residual gasoline source which is dissolving at the watertable into a 3D aquifer. Comparisons are made between dissolved plumes from a gasoline spill and those from an otherwise equivalent gasohol spill. Simulations have shown that under some conditions, a 10% ethanol component in gasoline can extend the travel distance of a benzene plume by at least 150% relative to that from an equivalent ethanol-free gasoline spill. The increase is due to preferred consumption of oxygen by ethanol and a corresponding reduction in the biodegradation rate of benzene while the two plumes overlap. Because of differences in retardation however, the ethanol and benzene plumes gradually separate. The impact therefore becomes limited because oxygen rapidly disperses behind the ethanol plume and benzene degradation eventually resumes. A sensitivity analysis for two common spill scenarios showed that background oxygen concentrations, and benzene retardation had the most significant influence on benzene persistence. A continuous gasohol spill over 10 years was found to increase the benzene travel distance by over 120% and a pure ethanol spill into an existing gasoline plume increased benzene travel distance by 150% after 40 years. The results are highly relevant in light of the forthcoming ban of MTBE in California and its likely replacement by ethanol by the end of 2002

Análisis de sensibilidad de parámetros de un modelo numérico criohidrogeológico bidimensional de degradación del permafrost cerca de Umiujaq (Nunavik, Canadá)

A calibrated field-scale numerical model of groundwater flow and permafrost degradation has been used in a sensitivity analysis of permafrost thaw on thermal and hydraulic parameters. The two-dimensional cryo-hydrogeological model was developed using the HEATFLOW-SMOKER code applied to the Umiujaq field site in Nunavik, Quebec, Canada, and includes coupled groundwater flow and advective–conductive heat transport with latent-heat and temperature-dependent thermal and hydraulic properties. Model sensitivity was evaluated by using the PEST code to systematically vary selected thermal and hydraulic parameters, and was quantified with respect to three system output variables or ‘targets’: subsurface temperature, groundwater velocity and ground-surface heat flux. PEST-derived model sensitivities were similar for all targets which contained subsurface temperature profiles, while sensitivities were slightly higher when only summer conditions were considered as the target compared to a full year of data. This trend was attributed to greater heat exchange at the ground surface during the summer months, leading to a more active groundwater flow system and greater feedback to the thermal regime. For all targets, the hydraulic and thermal parameters of the shallow layers (fine sand and marine silt, respectively) as well as the parameters defining the ground-surface heat exchange layer, were more sensitive compared to the deeper layers (coarse sand and gravel, and unfractured bedrock). Sensitivities were also among the highest for the ground-surface heat flux target. High model sensitivity to these parameters highlights the importance of detailed site characterization in the near-surface zone for more realistic simulations of permafrost dynamics.</p

Hydrogeochemical characterization of groundwater in the Outaouais Region (Québec, Canada) - A regional scale study

As part of the Québec regional groundwater characterization program (PACES), a detailed groundwater quality survey was undertaken in the Outaouais Region (Québec, Canada). During the summers of 2011 and 2012, 139 samples were taken from municipal and private wells which were analysed for major ions, nutrients, metals and sulphides. About 70% of the samples were obtained from bedrock wells, mainly in the Canadian Shield and the remainder from wells screened in Quaternary deposit aquifers. Hydrogeochemical facies were determined for 127 samples which had anion-cation charge balance errors within ×10 %. Ca-HCO3 is the dominant water type (65%) which was mainly found in unconfined aquifers, especially Quaternary deposits, and is typical of recently infiltrated rainwater. Other relevant water types are Na-HCO3 and Na-Cl (17 and 6% respectively), characteristic of confined aquifers. This classification by water type is supported by multivariate statistical analysis, namely Principal Component Analysis (PCA) and Hierarchical Clustering Analysis (HCA). PCA allows the identification of three factors controlling groundwater chemistry: salinity, silicate dissolution and F-bearing mineral dissolution. HCA results show that the samples can be grouped into seven clusters. Clusters 1 to 4 are mostly Ca-HCO3 water type and are representative of the enrichment in major ions due to carbonate and silicate dissolution, cluster 1 being closer to rainwater and cluster 4 the most evolved. Cluster 5, made of one sample with a particular chemistry, is not yet fully understood. Samples from cluster 6 present various degrees of Na-Ca exchange, a consequence of remnant Champlain Sea water (some samples from cluster 7 in confined zones) being replaced by infiltrating recharge water. Samples from cluster 7 are evolved waters with high Total Dissolved Solid (TDS) concentrations: they are remnants of the Champlain Sea in confined aquifers (bromide detected) or diluted/mixed by infiltrating rainwater in unconfined aquifers (bromide below detection limit). Secondary processes, related to the bedrock geology, are responsible for exceedances of Canadian drinking water standards. They include the dissolution of F-, U-, Fe- and Mn-bearing minerals known to be abundant in the region (deposits and mines throughout the study area). Chloride contamination was identified in some recharge areas, related to anthropogenic activities. The study has identified Champlain Sea invasion, cation exchange and freshwater recharge as the main geochemical processes affecting groundwater chemistry in this region. Secondary processes were also identified, based on exceedances of Canadian drinking water standards. These results will be applied at the local scale, along a flow path, to relate geochemical evolution to groundwater flow conditions. More data are available at this scale such as stable isotope content (δ18O and δ2H), groundwater age (tritium and 14C) and noble gas content. These additional data will help improve our understanding about groundwater chemical evolution and define a complete conceptual model

Three-dimensional numerical modeling of cryo-hydrogeological processes in a river-talik System in a continuous permafrost environment

In continuous permafrost environments, understanding complex river-talik system dynamics is fundamental for the sustainable use of talik aquifers as a source of drinking water in remote communities. A conceptual model of a river-talik system was previously developed based on field investigations in the floodplain of the Kuuguluk River at Salluit, Nunavik (Quebec), Canada, including geophysical surveys and monitoring of hydraulic heads and riverbed temperatures. This conceptual model is here used to develop a 3D numerical model for simulating the governing cryo-hydrogeological processes and dynamic system behavior. The numerical simulations, supported by the field data, show that the width and thickness of the river talik is highly correlated to the width of the overlying riverbed. In summer, the river talik is hydraulically connected to the riverbed, and groundwater from the talik aquifer is contributing to river baseflow. In winter, when the river and riverbed freeze, the river talik becomes hydraulically isolated from the riverbed. Under such conditions, the river talik acts as a tube-like conduit system which focusses groundwater flow. Increasing hydraulic heads at constrictions in the talik can be sufficient to fracture the frozen riverbed and ice cover, leading to groundwater overflows and icing formation. This study presents an integrated field and modeling approach for assessing the potential of talik aquifers as reliable sources of drinking water in northern communities