Groundwater Flow Rates Research Articles

Physical and Chemical Controls on the Simultaneous Occurrence of Young and Old Groundwater Inferred From Multiple Age Tracers

AbstractUnderstanding groundwater ages within an aquifer system has the potential to better constrain estimates of groundwater recharge and flow rates and therefore increase the reliability of groundwater models. Groundwater ages are generally interpreted from field‐observed environmental tracer concentrations, but in many cases in which multiple groundwater age tracers have been analyzed simultaneously the results show significant disparities among tracer‐specific estimated ages. The disparities are generally attributed to physical mixing between waters of different ages. However, especially in the geochemical literature environmental tracer concentrations are often analyzed with simplistic models in which the degree of the simulated mixing might be considered unrealistic for natural heterogeneous geologic media. In this study we use numerical experiments to examine under which physical conditions measured concentrations of selected environmental tracers (CFC‐12, 39Ar, and 14C) may return discrepant ages. Our model simulations suggest that matrix diffusion has the greatest potential to cause mixing of different‐aged water and to generate age biases between tracers. The multitracer simulations also suggest that there is a limit to the magnitude of the discrepancies that can be attributed to physical processes. When comparing data collected from the Pilbara region of Western Australia with our numerical modeling studies, it was found that a dual‐domain mass transfer model was required to explain the field‐observed age discrepancies.

Use of U-isotopes in exploring groundwater flow and inter-aquifer leakage in the south-western margin of the Great Artesian Basin and Arckaringa Basin, central Australia

The distribution of uranium isotopes (238U and 234U) in groundwaters of the south-western margin of the Great Artesian Basin (GAB), Australia, and underlying Arckaringa Basin were examined using groundwater samples and a sequential extraction of aquifer sediments. Rock weathering, the geochemical environment and α-recoil of daughter products control the 238U and 234U isotope distributions giving rise to large spatial variations. Generally, the shallowest aquifer (J aquifer) contains groundwater with higher 238U activity concentrations and 234U/238U activity ratios close to secular equilibrium. However, the source input of uranium is spatially variable as intermittent recharge from ephemeral rivers passes through rocks that have already undergone extensive weathering and contain low 238U activity concentrations. Other locations in the J aquifer that receive little or no recharge contain higher 238U activity concentrations because uranium from localised uranium-rich rocks have been leached into solution and the geochemical environment allows the uranium to be kept in solution. The geochemical conditions of the deeper aquifers generally result in lower 238U activity concentrations in the groundwater accompanied by higher 234U/238U activity ratios. The sequential extraction of aquifer sediments showed that α-recoil of 234U from the solid mineral phases into the groundwater, rather than dissolution of, or exchange with the groundwater accessible minerals in the aquifer, caused enrichment of groundwater 234U/238U activity ratios in the Boorthanna Formation. Decay of 238U in uranium-rich coatings on J aquifer sediments caused resistant phase 234U/238U activity ratio enrichment. The groundwater 234U/238U activity ratio is dependent on groundwater residence time or flow rate, depending on the flow path trajectory. Thus, uranium isotope variations confirmed earlier groundwater flow interpretations based on other tracers; however, spatial heterogeneity, and the lack of clear regional correlations, made it difficult to identify recharge and inter-aquifer leakage.

Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments

AbstractUnderstanding terrestrial carbon cycling has relied primarily on studies of topsoils that are typically characterized to depths shallower than 0.5 m. At a semiarid site instrumented down to 7 m, we measured seasonal‐ and depth‐resolved carbon inventories and fluxes and groundwater and unsaturated zone flow rates. Measurements showed that ~30% of the CO2efflux to the atmosphere (60% in winter) originates from below 1 m, contrary to predictions of less than 1% by Earth System Model land modules. Respiration from deeper roots and deeper microbial communities is supported by favorable subsurface temperatures, moisture, and oxygen availability. Below 1 m, dissolved organic carbon fluxes from the overlying soil and C from deep roots and exudates are expected to be important in sustaining microbial respiration. Because these conditions are characteristic of semiarid climate regions, we contend that Earth System Model land modules should incorporate such deeper soil processes to improve CO2flux predictions.

Deposition rate of supersaturated silicic acid on Na-type bentonite as a backfilled material in the geological disposal

When constructing geological disposal systems for radioactive waste, saline groundwater, originating from fractured rock matrices surrounding disposal tunnels, may reduce bentonite swelling properties and accelerate radionuclide migration. In contrast, high alkaline groundwater, caused by the use of cementitious materials, induces supersaturated conditions with regard to silicic acid. The resulting deposition of silicic acid may decrease the hydraulic conductivity of flow paths. Therefore, this study experimentally examined the apparent deposition rate constant, k (m/s), by considering the supersaturated concentration of silicic acid and deep-underground temperatures (288–323 K). As a result, the apparent deposition rate constants, obtained experimentally, were not affected by an initial supersaturated concentration and were only slightly affected by temperature. We estimated the apparent activation energy at 8.9 kJ/mol. Furthermore, because the Damköhler number, described by the ratio between the apparent deposition rate constant and the groundwater flow rate, had a large value, exceeding 103, the deposition of supersaturated silicic acid may cause the narrowing flow paths. These results suggest that silicic acid deposition contributes to retardation effects via the decrease of the hydraulic conductivity in backfilled tunnels.

Improving estimates of groundwater velocity in a fractured rock borehole using hydraulic and tracer dilution methods

A straddle-packer system for use in boreholes in fractured rock was modified to investigate the average linear groundwater velocity (v¯f) in fractures under ambient flow conditions. This packer system allows two different tests to be conducted in the same interval between packers without redeploying the system: (1) forced gradient hydraulic tests to determine the interval transmissivity (T), and (2) borehole dilution experiments to determine the groundwater flow rate (Qt) across the test interval. The constant head step test method provides assurance that flow is Darcian when determining T for each interval and identifies the flow rate at the onset of non-Darcian flow. The critical Reynolds number method uses this flow rate to provide the number of hydraulically active fractures (N) in each interval, the average hydraulic aperture for the test interval and the effective bulk fracture porosity. The borehole dilution method provides Qt values for the interval at the time of the test, and v¯f can be estimated from Qt using the flow area derived from the hydraulic tests. The method was assessed by application to seven test intervals in a borehole 73 m deep in a densely fractured dolostone aquifer used for municipal water supply. The critical Reynolds number method identified one or two fractures in each test interval (1.1 m long), which provided v¯f values in the range of 10 to 8000 m/day. This velocity range is consistent with values reported in the literature for ambient flow in this aquifer. However, when hydraulically active fractures in each interval is identified and measured from acoustic and optical televiewer logs, the calculated v¯f values are unreasonably low as are the calculated values of the hydraulic gradient needed to provide the Qt value for each tested interval. The combination of hydraulic and dilution tests in the same interval is an improved method to obtain values of groundwater velocity in fractured rock aquifers.

Numerical simulation of ground source heat pump systems considering unsaturated soil properties and groundwater flow

This paper analyzes the influence of unsaturated soil properties and groundwater flow on the performance of ground source heat pump (GSHP) systems. A mathematical model of GSHP systems, which considers the influence of varying unsaturated soil thermal properties, groundwater table depth and saturated groundwater flow, is introduced and coupled to a heat pump model to consider dynamically-changing loads due to specific heat pump coefficient of performance (COP) characteristics. The model is validated against experiment results and an analytical model reported by others. Finally, numerical simulations are performed to investigate the effect of inclusion of a heat pump, moisture content variations, groundwater table fluctuations and groundwater flow rates on the performance of the GSHP system. Results show that neglecting variations in moisture content in unsaturated soil could lead to underestimating the heat transfer capacity of the soil. A rising groundwater table is beneficial to the operation of the GSHP system. The influence of groundwater table fluctuations should be considered, otherwise it may result in a error of 3–4% in the outlet fluid temperature. When calculating the influence of groundwater flow rates on the performance of the GSHP system, the effect of the position of the groundwater table should also be considered.

New Approach for Simulating Groundwater Flow in Discrete Fracture Network

AbstractIn this study, a new approach is developed to compute groundwater flow rate and hydraulic head distribution in a two-dimensional discrete fracture network (DFN) in which both laminar and in...

A Class of Exact Solutions of the Boussinesq Equation for Horizontal and Sloping Aquifers

AbstractThe nonlinear equation of Boussinesq (1877) is a foundational approach for studying groundwater flow through an unconfined aquifer, but solving the full nonlinear version of the Boussinesq equation remains a challenge. Here, we present an exact solution to the full nonlinear Boussinesq equation that not only applies to sloping aquifers but also accounts for source and sink terms such as bedrock seepage, an often significant flux in headwater catchments. This new solution captures the hysteretic relationship (a loop rating curve) between the groundwater flow rate and the water table height, which may be used to provide a more realistic representation of streamflow and groundwater dynamics in hillslopes. In addition, the solution provides an expression where the flow recession varies based on hillslope parameters such as bedrock slope, bedrock seepage, aquifer recharge, plant transpiration, and other factors that vary across landscape types.

PEMANFAATAN AIR TANAH JAKARTA

The Jakarta groundwater is one of the water resources in which people rely on it in great deal. With the limitation of the Water Supply Company to serve its user, groundwater becomes very valuable and dependable resource. The magnitude of extraction reaches out above it’s save yield. In the year of 2002 about 1230 to 1590 millions cubic meters water were accumulated from precipitation. Approximately of 1027 million cubic meters each year about to be consumed by the people of Jakarta. The groundwater consumption tend to increase while the land capability to absorb groundwater decreasing as the land development expanding. Hidrologically the hydraulic conductivity of the Jakarta groundwater aquifer system is very low, so that the groundwater flowrate from the south region of Jakarta basin is also low. With the magnitude of extraction’s very havily, the cone of depression incident has been occurring in the north Jakarta region. Along with this incident, a land subsidence was also occurring in the neighboring area. To overcome these problems, the assessment of the artificial recharge to the Jakarta aquifer particularly at the critical locations has been done. Schemes of the artificial recharges were simulated. Locations and magnitudes of these schemes were recommended to prevent further depression and saltwater intrusions. Key words : groundwater, aquifer, basin Jakarta, simulation, artificial recharge.

Tracking the Subsurface Signal of Decadal Climate Warming to Quantify Vertical Groundwater Flow Rates

AbstractSustained ground surface warming on a decadal time scale leads to an inversion of thermal gradients in the upper tens of meters. The magnitude and direction of vertical groundwater flow should influence the propagation of this warming signal, but direct field observations of this phenomenon are rare. Comparison of temperature‐depth profiles in boreholes in the Veluwe area, Netherlands, collected in 1978–1982 and 2016 provided such direct measurement. We used these repeated profiles to track the downward propagation rate of the depth at which the thermal gradient is zero. Numerical modeling of the migration of this thermal gradient “inflection point” yielded estimates of downward groundwater flow rates (0–0.24 m a−1) that generally concurred with known hydrogeological conditions in the area. We conclude that analysis of inflection point depths in temperature‐depth profiles impacted by surface warming provides a largely untapped opportunity to inform sustainable groundwater management plans that rely on accurate estimates of long‐term vertical groundwater fluxes.

Electrical resistivity imaging and dye tracer test for the estimation of water leakage paths from reservoir of Akdeğirmen Dam in Afyonkarahisar, Turkey

The seepage occurrence from the reservoir on the right bank of the Akdegirmen Dam located in Afyonkarahisar province in the Turkey has been investigated. When the reservoir began to fill with water, a large amount of water seepage occurred at the dam. The seepage developed at the base of the spillway and the right downstream slope of the dam. The various attempts have been made to reduce the seepage using grouting. Although the additional grouting operations was reduced the seepage at the base of the spillway, there has not been a reduction in seepage at the water outlet location at the downstream slope. Electrical resistivity measurements along the eight lines with the dipole–dipole array and dye tracer tests were performed in order to identify the seepage locations. The interpretation of electrical resistivity data showed the distribution of strata and the seepage zone along the right downstream of the dam. Groundwater flow rates calculated from dye tests indicated that there is an excessive seepage south-eastwardly on the downstream slope of the dam. Integrated interpretation of resistivity data and dye tests indicate that the seepage paths are in the direction from NW to E and SE.

Weathering of ancient and medieval glasses—potential proxy for nuclear fuel waste glasses. A perennial challenge revisited

AbstractAncient and medieval glasses that have survived the deleterious attack of the environment for millennia have long since proposed as proxy to estimate and predict the corrosion mechanism of nuclear waste glasses. However, because both composition and environmental burial conditions vastly differ between hydrolytically less stable ancient glasses and modern advanced nuclear waste glasses, only semiquantitative conclusions can be drawn about the likely performance of the latter as long‐term stable immobilization matrices for high‐level radioactive nuclear waste. In this contribution, special emphasis has been devoted to the behavior of manganese, present as both iron decolorant and coloring ions in ancient Roman and medieval glasses. Study of the behavior of manganese in ancient glasses during weathering may provide some limited clues to the behavior of long‐lived radioactive technetium‐99. Knowledge of the corrosion kinetics of ancient glasses will allow, eventually, a reasonable prediction of the long‐term performance of glassy nuclear waste forms as function of their composition and environmental parameters, i.e. groundwater composition, flow rate, pH, solution volume, and surface area.

The hot stack performance of the shallow geothermal heat pump system with/without intensification state of groundwater seepage in Nanjing (China)

As a renewable and clean energy, the shallow geothermal energy and its corresponding buried pipe heat pump technology applications have become a hot topic of domestic and foreign scholars as well as industry researches. While the hot stack problem around rock and soil is a serious problem, which is harmful for the thermal performance and actual operation of the buried pipe heat pump system. In this paper, the numerical analysis and thermal response test on the hot stack problems of surrounding rock soil after continuous operation with or without intensification state groundwater seepage have been studied. Besides, the static reserves and exploitation amount for the Nanjing Hexi area test site on shallow geothermal energy development and utilization have been conducted. Results show that under the non-flow conditions, the increase of buried pipe inlet velocity, inlet temperature and buried depth of pipe are as effective way to increase the thermal performance of the heat exchanger. In the case of groundwater seepage, the distribution of the temperature of rock and soil mass is influenced by the groundwater seepage, and the hot stack problem can be not considered when the groundwater flow rate is greater than 5×10−6m/s. The static reservation is 1.60E+13kJ in summer and 8.01E+12kJ in winter, which is accounts for the proportion of up to 72% of shallow ground thermal resources, meaning the buried pipe of GSHP application potential is very considerable.

Visualisation study on Pseudomonas migulae AN-1 transport in saturated porous media

Influence of granular size and groundwater flow rate on transport of Pseudomonas migulae AN-1 in saturated porous media was non-invasively and visually investigated with a novel imaging technique based on our previously established green fluorescent protein-tagging approach. AN-1 was transported faster than water was. The finer the media were, the greater the enhancement of bacterial velocity was. Mass recovery (MR) increased, while deposition rate coefficient (Kc) decreased, with increasing granular size. Similar and linear trends of MR and Kc, respectively, were quantitatively observed with increasing water flow rate. The images revealed that the initial shape of bacterial plume after injection was a narrow strip along the injection well and an ellipsoid in the lower part of the injection well in medium and coarse sand, respectively. Bacterial plume migrated horizontally in medium sand, but shifted slightly downward in coarse sand. Under similar conditions, the fluorescent area carrying AN-1 in medium sand was larger than that carrying AN-1 in coarse sand during the same period. The visualisation method of this study captured both the movement of free-state and retained bacteria that adhered to sediments. A continuous biological zone composed of planktonic and retained AN-1 was observed. These findings are significant for actual bioremediation.

Sulphide-transport control of the corrosion of copper canisters

ABSTRACTThe long-term anaerobic corrosion rate of copper canisters in a KBS-3 repository is calculated on the basis of sulphide-transport control. The nature of the anodic and cathodic rate-determining steps, as well as the controlling process for the overall corrosion reaction of copper in sulphide environments, are considered. Evidence indicates that the assumption of sulphide-transport control is valid for the overwhelming majority of ground water flow rates and sulphide concentrations considered in the Swedish SR-Site safety assessment. There is no evidence that canister lifetimes calculated on the basis of sulphide-transport control are non-conservative.This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

Balanço hídrico e modelagem computacional visando estimar recarga subterrânea

As águas subterrâneas são a principal fonte hídrica em diversos países e regiões na América do Sul e Brasil. Entretanto, os volumes extraídos desses mananciais já ultrapassam a capacidade de reposição, resultando na diminuição dos níveis dos aquíferos. Assim, a garantia de disponibilidade futura depende do correto gerenciamento desses recursos hídricos. Para isso, é necessário conhecer as taxas de recarga e o fluxo subterrâneo que ocorrem nos aquíferos. Neste trabalho, avalia-se a recarga subterrânea para diferentes usos agrícolas com base no balanço hídrico da zona não saturada do solo. A avaliação foi feita, primeiramente, por meio da comparação com estimativas obtidas pelo método da Flutuação da Superfície Livre (WTF - Water Table Fluctuation). Em seguida, as taxas computadas foram usadas como entradas num modelo transiente de fluxo com intuito de verificar sua consistência por meio da comparação com dados de níveis medidos em campo. Os resultados indicam que o método aplicado apresentou desempenho satisfatório e, apesar de limitações inerentes, evidenciam a vantagem de sua utilização em relação a outras técnicas por requerer dados de maior facilidade de obtenção.

Performance and Sustainability of District-Scale Ground Coupled Heat Pump Systems

This study proposes a solution to the problem of maintaining the performance and sustainability of district-scale, cooling-dominated ground coupled heat pump (GCHP) systems. These systems tend to overheat because heat dissipates slowly in relation to the size of the borefields. To demonstrate this problem, a 2000-borehole field is considered at a district-scale GCHP system in the Upper Midwest, US. The borefield’s ground and fluid temperature responses to its design heating and cooling loads are simulated using computational fluid dynamics implemented by applying the finite volume method. The ground temperature is predicted by applying the thermal loads uniformly over the borefield and simulating heat dissipation to the surrounding geology through conduction coupled with advection due to groundwater flow. The results show that a significant energy imbalance will develop in the ground after the first few years of GCHP operation, even with high rates of groundwater flow. The model presented in this study predicts that the temperature at the center of the borefield will reach 18 °C after 5 years and approximately 50 °C after 20 years of operation in the absence of any mitigation strategies. The fluid temperature in the boreholes is then simulated using a single borehole model to estimate the heat pump coefficient of performance, which decreases as the modeled system heats up. To balance the energy inputs/outputs to the ground—thus maintaining the system’s performance—an operating scheme utilizing cold-water circulation during the winter is evaluated. Under the simulated conditions, this mitigation strategy carries the excess energy out of the borefield. Therefore, the proposed mitigation strategy may be a viable measure to sustaining the operating efficiency of cooling-dominated, district-scale borefields in climates with cold winters.

Representing Glaciations and Subglacial Processes in Hydrogeological Models: A Numerical Investigation

The specific impact of glacial processes on groundwater flow and solute transport under ice-sheets was determined by means of numerical simulations. Groundwater flow and the transport of δ18O, TDS, and groundwater age were simulated in a generic sedimentary basin during a single glacial event followed by a postglacial period. Results show that simulating subglacial recharge with a fixed flux boundary condition is relevant only for small fluxes, which could be the case under partially wet-based ice-sheets. Glacial loading decreases overpressures, which appear only in thick and low hydraulic diffusivity layers. If subglacial recharge is low, glacial loading can lead to underpressures after the retreat of the ice-sheet. Isostasy reduces considerably the infiltration of meltwater and the groundwater flow rates. Below permafrost, groundwater flow is reduced under the ice-sheet but is enhanced beyond the ice-sheet front. Accounting for salinity-dependent density reduces the infiltration of meltwater at depth. This study shows that each glacial process is potentially relevant in models of subglacial groundwater flow and solute transport. It provides a good basis for building and interpreting such models in the future.

Hydrogeological and Geochemical Comparison of High Arsenic Groundwaters in Inland Basins, P.R. China

High As groundwater has been widely found in inland basins of P.R. China, which has posed a serious heath effect on local residents. Although these inland basins experience arid-semiarid climate, and are filled with Quaternary sediments, As concentrations show big variations. Three inlands basins (the Hetao basin (HT), the Yinchuan basin (YC), and the Songnen basin (SN)) have been investigated to characterize chemistry and geochemistry of groundwaters and sediments and to evaluate their controls on As concentrations. Arsenic concentrations ranged between <0.1 and 105 μg/L (average 27.8 μg/L), between <0.1 and 338 μg/L (average 94.0 μg/L), and between 0.33 and 857 μg/L (average 130 μg/L) in YC, SN, and HT, respectively. In those basins, HCO3− is the major anions, and Na+ the major cation. Both Cl− and SO42− concentrations are much lower in SN than those in HT and YC. In YC, although Fe and Mn concentrations are the highest, groundwaters have the lowest As concentration. Contents of ionically bound As (S1) and strongly adsorbed As (S2) are the highest in HT and the lowest in YC. Results show that groundwater As is predominantly regulated by active As forms in sediments (S1 and S2). At the scale of multi-basin, groundwater flushing evidently regulates groundwater As. Due to the similar groundwater flow rate at the scale of the site, redox conditions are the key factor controlling groundwater As, with high groundwater As under reducing conditions.

New Analytical Expressions for Two-Dimensional Aquifer Adjoining with Streams of Varying Water Level

This research presents new analytical expressions to analyze interactions between streams of varying water level and a confined aquifer. The stream water level is assumed to vary exponentially with time. The expressions are obtained by means of Laplace and Fourier transform methods and the results are verified with those obtained from MODFLOW. In fact, we derive a new analytical expression for predicting of the groundwater level and flow rate in a confined aquifer between two streams of varying water level at the north and the right boundaries and two constant head boundaries at the left and the south ends. Also, a numerical example is used to investigate about the aquifer response to stream water level changes. Therefore the effects of variation water level of each stream on the flow rate at the left and the south boundaries and also at four points of the aquifer are discussed. Finally, some other new analytical expressions are also deduced for other types of boundary conditions.