Groundwater Velocity Research Articles

A modified point dilution test for the assessment of groundwater flux in karst aquifers

A parametrization of heterogeneous karst aquifers represents one of the main challenges for hydrogeologist. The aim of this research was to design an easily applicable test that can be used for the assessment of groundwater flux (velocity) in highly permeable karst aquifers. The modified point dilution test (MPDT) is based on the constant-rate injection of tracer solution in a borehole (or sub-vertical cave) and continuous measurement of tracer concentration in the same borehole. When the concentration is stabilized then the groundwater inflow in the borehole can be assessed on the basis of the known injection rate and measured concentrations (initial and stabilized). By the obtained inflow and known borehole cross-sectional area, the apparent groundwater velocity under a natural hydraulic gradient can be assessed. Also, Darcy velocity, hydraulic conductivity and an average linear velocity can be derived from the test results if the borehole-distortion factor, hydraulic gradient and porosity are known. The test was applied in Well B1 (Ljesanska Nahija, Montenegro). The obtained apparent groundwater velocity amounts to 1.71 × 10−4 m/s. In addition to wells and piezometers, the MPDT can also be applied to sub-vertical caves that extend below the water table, and as a results groundwater inflow and the volume of a cave filled with water can be obtained. The MPDT provides satisfactory results only in highly permeable aquifers.

Biased Estimation of Groundwater Velocity from a Push-Pull Tracer Test Due to Plume Density and Pumping Rate

The single-well push-pull tracer test is a convenient and cost-effective tool to estimate hydrogeological properties of a subsurface aquifer system. However, it has a limitation that test results can be affected by various experimental designs. In this study, a series of laboratory-scale push-pull tracer tests were conducted under various conditions controlling input tracer density, pumping rate, drift time, and hydraulic gradient. Based on the laboratory test results, numerical simulations were performed to evaluate the effects of density-induced plume sinking and pumping rate on the proper estimation of groundwater background linear velocity. Laboratory tests and numerical simulations indicated that the actual linear velocity was underestimated for the higher concentration of the input tracer because solute travel distance and direction during drift time were dominantly affected by the plume density. During the pulling phase, reasonable pumping rates were needed to extract the majority of injected tracer mass to obtain a genuine center of mass time (tcom). This study presents a graph showing reasonable pumping rates for different combinations of plume density and background groundwater velocity. The results indicate that careful consideration must be given to the design and interpretation of push-pull tracer tests.

Skin effect on single-well push-pull tests with the presence of regional groundwater flow

Single-well push-pull (SWPP) test is one of the most important ways to estimate flow and transport parameters, e.g. porosity, dispersivity, regional groundwater flow velocity. Usually the wellbore is surrounded by a finite-thickness skin, such as a gravel pack. The positive skin has a smaller hydraulic conductivity than the aquifer formation zone, and the negative skin has a greater one. In this study, a numerical model of a SWPP test considering skin effects was established using the finite-element COMSOL Multiphysics program to estimate aquifer parameters. Several important results were obtained. Firstly, regional groundwater velocity affects the types of breakthrough curves (BTCs) through changing the flow pattern. Secondly, a positive (or negative) skin leads to a slower (or faster) tracer transport process, and a smaller ratio between the hydraulic conductivity of the skin and that of the aquifer formation zone results in greater solute plume retardation in the skin zone. Thirdly, a larger thickness of the positive skin leads to a higher tracer concentration around the well, and the opposite is true if the skin is negative. Besides, the model of Leap and Kaplan (1988) underestimates the regional groundwater velocity for the second type of BTCs, and a larger longitudinal dispersivity can lead to a greater error, where the second type of BTCs has a rising limb at early stage followed by a falling limb at late stage. The general conclusion is that the estimations of groundwater velocity from SWPP tests are also affected by skin effects.

Assessment and validation of groundwater vulnerability to nitrate in porous aquifers based on a DRASTIC method modified by projection pursuit dynamic clustering model

The groundwater vulnerability assessment has been identified as an important tool of groundwater pollution prevention. In this study, the DRASTIC method was modified to estimate the groundwater vulnerability of porous aquifers to nitrate. The parameter system was optimized by replacing the original parameters of aquifer media, soil media, impact of the vadose zone and hydraulic conductivity with quantitative parameters of aquifer thickness, nitrate attenuation intensity, hydraulic resistance and groundwater velocity and adding pollutant input intensity to develop the DRANTHVP method. In addition, the rating scale of the DRASTIC method was revised, and the weight and influence degree of each parameter were determined using the projection pursuit dynamic clustering (PPDC) model. The DRANTHVP method was applied to the plain area of western Jilin Province, and the vulnerability index map of groundwater to nitrate pollution was established. The DRANTHVP method improved the correlation coefficient between vulnerability index and nitrate concentration to 0.720, which was more than three times that of the original DRASTIC method. And the high variance of the (ANOVA) F statistic indicated that there was less overlap between the nitrate values in different vulnerability classes. Furthermore, the DRANTHVP method produced a more uniform distribution of vulnerability classes. In short, the DRANTHVP method using the PPDC model was suitable to assess the groundwater vulnerability of porous aquifers to nitrate in the study area. Hence, the mapping of groundwater vulnerability to nitrate can provide a scientific and reasonable basis for the formulation of groundwater resource protection plan.

Groundwater age dating in fractured rock using [formula omitted]He data

Using environmental tracers to date groundwater age in fractured systems is difficult since mass exchange processes between fractures and matrix might mask the actual distribution of groundwater velocity, thus leading to biased results. Here, we propose an analytical solution to date groundwater age in fractured media using 4He data. The solution, which is an extension of existing solutions based on linear accumulation methods, decouples the transport equation in the flowing fracture from the diffusion equation in the rock matrix, under the assumption of steady-state conditions. In the proposed analytical solution groundwater age and 4He concentration are linearly related, and the 4He bulk production rate in matrix, scaled by the inverse of fracture volume fraction, is the proportionality constant. This scaling factor accounts for the underlying mass exchange processes between fracture and rock matrix. Moreover, an Equivalent Continuous Porous Medium (ECPM)-based formulation for the numerical assessment of steady-state 4He levels in fractured media is presented and used to test the performance of the proposed dating technique in realistic conditions.

Long‐term evaluation of an EHC injection permeable reactive barrier in a sulfate‐rich, high‐flow aquifer

AbstractPermeable reactive barriers (PRBs) have traditionally been constructed via trenching backfilled with granular, long‐lasting materials. Over the last decade, direct push injection PRBs with fine‐grained injectable reagents have gained popularity as a more cost‐efficient and less‐invasive approach compared to trenching. A direct push injection PRB was installed in 2005 to intercept a 2,500 feet (760 meter) long carbon tetrachloride (CT) groundwater plume at a site in Kansas. The PRB was constructed by injecting EHC® in situ chemical reduction reagent slurry into a line of direct push injection points. EHC is composed of slow‐release plant‐derived organic carbon plus microscale zero‐valent iron (ZVI) particles, specifically formulated for injection applications. This project was the first full‐scale application of EHC into a flow‐through reactive zone and provided valuable information about substrate longevity and PRB performance over time. Groundwater velocity at the site is high (1.8 feet per day) and sulfate‐rich (~120 milligrams per liter), potentially affecting the rate of substrate consumption and the PRB reactive life. CT removal rates peaked 16 months after PRB installation with >99% removal observed. Two years post‐installation removal rates decreased to approximately 95% and have since stabilized at that level for the 12 years of monitoring data available after injection. Geochemical data indicate that the organic carbon component of EHC was mostly consumed after 2 years; however, reducing conditions and a high degree of chloromethane treatment were maintained for several years after total organic carbon concentrations returned to background. Redox conditions are slowly reverting and have returned close to background conditions after 12 years, indicating that the PRB may be nearing the end of its reactive life. Direct measurements of iron have not been performed, but stoichiometric demand calculations suggest that the ZVI component of EHC may, in theory, last for up to 33 years. However, the ZVI component by itself would not be expected to support the level of treatment observed after the organic carbon substrate had been depleted. A longevity of up to 5 years was originally estimated for the EHC PRB based on the maximum expected longevity of the organic carbon substrate. While the organic carbon was consumed faster than expected, the PRB has continued to support a high degree of chloromethane treatment for a significantly longer time period of over 12 years. Recycling of biomass and the contribution from a reduced iron sulfide mineral zone are discussed as possible explanations for the sustained reducing conditions and continued chloromethane treatment.

Methane gas transport in unconfined aquifers: A numerical sensitivity study of a controlled release experiment at CFB Borden

Subsurface leakage of natural gas from petroleum wells can impact freshwater aquifers. Accurate prediction of gas migration in the subsurface will depend on knowledge of permeability, porosity, and flow system conditions. A series of two-dimensional numerical multi-phase flow simulations (CFbio) were conducted to investigate the role of multi-phase parameters (relative permeability and air entry pressure), flow system conditions (intrinsic permeability, anisotropy, and groundwater velocity), and geometric properties (layer thickness and layer lateral continuity) on the flow of gas-phase methane emanating from two variable-rate point sources in an unconfined sandy aquifer. Numerical simulations showed that for a homogeneous, weakly anisotropic aquifer, gas migrates almost exclusively vertically due to buoyancy, before venting to the vadose zone and atmosphere. As vertical migration became restricted through increased anisotropy, inclusion of lower-permeable layers, or increased horizontal groundwater velocity, an increase in the lateral component of gas migration was observed. This led to the formation of a broader lateral migration of the gas-phase plume and establishment of variably distributed vertical preferential flow paths, ultimately resulting in increased gas retention in the aquifer with relatively less methane reaching the vadose zone or atmosphere. The inclusion of a thin layer with moderately lower permeability (1–2 orders of magnitude) and increased air entry pressure was used to depict a fine-grained sand lens within a uniform aquifer. This subtle feature led to the formation of thin gas pools extending up- and down-gradient beneath the lens, allowing methane to travel much farther and faster than by groundwater advection alone, which is consistent with field observations during the experiment. In all scenarios investigated gas-phase methane was shown to migrate predominantly vertically due to buoyancy, until the aquitard permeability was <30% of the aquifer permeability. Our modelling demonstrates that even subtle permeability contrasts, together with capillary pressure changes demarcating grain-scale bedding, will lead to extensive lateral free-phase gas migration, and development of a more extensive and complex zone of impacted aquifer than presupposed.

Numerical simulation of frozen wall formation in water-saturated rock mass by solving the Darcy-Stefan problem

Artificial ground freezing (AGF) is a common technology of shaft sinking through water-bearing strata. The AGF technique is used to create a frozen wall preventing shaft flooding. An additional factor that makes shaft sinking more complicated is associated with external groundwater flows occurred due to hydrostatic pressure gradients. In this paper, we study the influence of groundwater seepage on the frozen wall formation in fluid-saturated rock mass in the framework of the two-dimensional two-phase Darcy-Stefan problem. The results of numerical simulation of the thermal and hydraulic properties of the sandstone layer at the site of Petrikov Mining and Processing Plant are presented. It has been found that the external groundwater flow has a significant effect on the growth of a frozen wall in the case when the groundwater velocity magnitude is greater than or equal to 50 mm/day. This critical seepage velocity strongly depends on how quickly the water content and rock mass permeability decrease with decreasing temperature, or on the parameters of the rock mass freezing characteristic curve and permeability versus temperature curve. The proper setting of these parameters is a sine qua non for creating adequate mathematical models of heat and mass processes in the artificially frozen water-saturated rock mass.

A Particle Tracking Algorithm for Arbitrary Unstructured Grids.

A new semi-analytical algorithm for generating the local groundwater velocity field within irregular three-dimensional grid cells (such as a Voronoi cell) is presented. The method supports particle tracking in the MODFLOW-USG software package for a variety of supported unstructured grid formats. It is shown to replicate the results from the fully analytical Pollock's method when used on a rectilinear grid, and is demonstrated for difficult test cases where there is high spatial variability in the flow field within individual cells. The method is now available as an option in the mod-PATH3DU software package and may be used with most MODFLOW-USG packages without additional intervention.

From Grain to Floodplain: Evaluating heterogeneity of floodplain hydrostatigraphy using sedimentology, geophysics, and remote sensing

AbstractStratigraphy is a fundamental component of floodplain heterogeneity and hydraulic conductivity and connectivity of alluvial aquifers, which affect hydrologic processes such as groundwater flow and hyporheic exchange. Watershed‐scale hydrological models commonly simplify the sedimentology and stratigraphy of floodplains, neglecting natural floodplain heterogeneity and anisotropy. This study, conducted in the upper reach of the East River in the East River Basin, Colorado, USA, combines point‐, meander‐, and floodplain‐scale data to determine key features of alluvial aquifers important for estimating hydrologic processes. We compare stratigraphy of two meanders with disparate geometries to explore floodplain heterogeneity and connectivity controls on flow and transport. Meander shape, orientation, and internal stratigraphy affected residence time estimates of laterally exchanged hyporheic water. Although the two meanders share a sediment source, vegetation, and climate, their divergent river migration histories resulted in contrasting meander hydrofacies. In turn, the extent and orientation of these elements controlled the effective hydraulic conductivity and, ultimately, estimates of groundwater transport and hyporheic residence times. Additionally, the meanders’ orientation relative to the valley gradient impacted the hydraulic gradient across the meanders—a key control of groundwater velocity. Lastly, we combine our field data with remotely sensed data and introduce a potential approach to estimate key hydrostratigraphic packages across floodplains. Prospective applications include contaminant transport studies, hyporheic models, and watershed models. © 2019 John Wiley &amp; Sons, Ltd.

Estimation of Interstitial Velocity Using a Direct Drive High-Resolution Passive Profiler.

The fate and transport of groundwater contaminants depends partially on groundwater velocity, which can vary appreciably in highly stratified aquifers. A high-resolution passive profiler (HRPP) was developed to evaluate groundwater velocity, contaminant concentrations, and microbial community structure at ∼20 cm vertical depth resolution in shallow heterogeneous aquifers. The objective of this study was to use mass transfer of bromide (Br- ), a conservative tracer released from cells in the HRPP, to estimate interstitial velocity. Laboratory experiments were conducted to empirically relate velocity and the mass transfer coefficient of Br- based on the relative loss of Br- from HRPP cells. Laboratory-scale HRPPs were deployed in flow boxes containing saturated soils with differing porosities, and the mass transfer coefficient of Br- was measured at multiple interstitial velocities (0 to 100 cm/day). A two-dimensional (2D) quasi-steady-state model was used to relate velocity to mass transfer of Br- for a range of soil porosities (0.2-0.5). The laboratory data indicate that the mass transfer coefficient of Br- , which was directly-but non-linearly-related to velocity, can be determined with a single 3-week deployment of the HRPP. The mass transfer coefficient was relatively unaffected by sampler orientation, length of deployment time, or porosity. The model closely simulated the experimental results. The data suggest that the HRPP will be applicable for estimating groundwater velocity ranging from 1 to 100 cm/day in the field at a minimum depth resolution of 10 cm, depending on sampler design.

New finite volume multiscale finite element model for simultaneously solving groundwater flow and darcian velocity fields in porous media

This paper proposes a new finite volume multiscale finite element model (NFVMSFEM) for groundwater flow and velocity simulation in porous media. The main goal of this method is to simultaneously obtain the heads and continuous x,y direction Darcian velocities, thereby simplifying the simulation process and improving the efficiency. This goal is accomplished by introducing a novel velocity matrix in the control volume boundary flux estimation of the finite volume multiscale finite element method (FVMSFEM) framework. The velocity matrix allows for the NFVMSFEM to directly represent continuous fine-scale velocities by coarse-scale heads, thus merging the two kinds of unknowns into one. Through a modified Yeh’s Galerkin model, the velocity matrix is constructed in each local coarse element before the head computation; thus, the computational cost is very little. Furthermore, the NFVMSFEM inherits the advantageous features of the FVMSFEM, which ensures the local conservation of heads and further improves the efficiency. The results of the comparison between the NFVMSFEM and certain classical methods for head and velocity computation demonstrate its effectiveness and high efficiency.

Validation of basaltic glass adsorption capabilities from geothermal arsenic in a basaltic aquifer: A case study from Bjarnarflag power Station, Iceland

Arsenic is a carcinogen known for its acute toxicity to organisms. Geothermal waters are commonly high in arsenic, as shown at the Bjarnarflag Power Plant, Iceland (∼224 μg/kg of solvent). Development of geothermal energy requires adequate disposal of arsenic-rich waters into groundwater/geothermal systems. The outcome of arsenic transport models that assess the effect of geothermal effluent on the environment and ecosystems may be influenced by the sensitivity of hydraulic parameters. However, previous such studies in Iceland do not consider the sensitivity of hydraulic parameters and thereby the interpretations remain unreliable. Here we used the Lake Mývatn basaltic aquifer system as a case study to identify the sensitive hydraulic parameters and assess their role in arsenic transport. We develop a one-dimensional reactive transport model (PHREEQC ver. 2.), using geochemical data from Bjarnarflag, Iceland.In our model, arsenite (H3AsO3) was predicted to be the dominant species of inorganic arsenic in both groundwater and geothermal water. Dilution reduced arsenic concentration below ∼5 μg/kg. Adsorption reduced the residual contamination below ∼0.4 μg/kg at 250 m along transect. Based on our modelling, we found volumetric input to be the most sensitive parameter in the model. In addition, the adsorption strength of basaltic glass was such that the physical hydrogeological parameters, namely: groundwater velocity and longitudinal dispersivity had little influence on the concentration profile.

Flow parameters in porous alluvial aquifers evaluated by multiple tracers

Dye tracer tests are a good technique useful to determine the hydrogeological parameters of aquifers, especially in alluvial plains, where the heterogeneity of the lithology is a key factor leading the groundwater circulation. In the last decade, new tracers have been developed and introduced in the hydrological and geological context, including DNA tracers, that are used in the same way as the traditionaltracers. In this study, some experiments were performed in a porous aquifer with the aim of comparing the behavior of different tracers for the evaluation of aquifer’s parameters, and of testing the suitability of a DNA tracer in this geological context. Single well and multiwell tests were performed during the winter and spring 2017, involving one piezometer and 4 wells. The tracer test results highlighted fasterzones of flow in the alluvial plain, being located at different depths, whose levels are characterized by gravel and sand layers. A maximum groundwater velocity of around 170 cm/day was revealed by the single well tests, whereas the main direction of flow was along the watercourse axis, as resulted by the multi well tracer test.The overall results obtained confirmed that fluorescent tracers are a very valuable and reliable tool for the determination of groundwater velocity, groundwater flow direction and dispersion parameters, even in cases of multi-layered aquifers, whereas DNA tracers are very helpful in the determination of faster circuits and vertical flow even in multi-layered aquifers.

Using tritium and radiocarbon to determine groundwater age and delineate the flow regime in the Taiyuan Basin, China

Tritium (3H) and radiocarbon (14C) were used to determine the age, to delineate a flow regime, and to estimate flow velocity of medium-depth groundwater (50–200 m) from a Middle and Upper Pleistocene confined aquifer. Young groundwater age was determined using 3H and an exponential piston-flow model (EPM). Three correction models (Tamers, Pearson, and Fontes and Garnier) were chosen to date the 14C age of old groundwater. Groundwater ages of the medium-depth groundwater ranged from 3.5–25,790 a. Groundwater is relatively young in most of the piedmont area, although two high-age zones (with ages > 20,000 a) exist in the center of the plain. Groundwater age distribution characteristics indicated that groundwater flows from the mountain area to the basin area, and that the oldest groundwater in each high-age zone flows toward the depression cones. Two large local flow systems were formed because of overexploitation, and the regional flow system from north to south no longer exists. This study delineated the age of medium-depth groundwater in the entire Taiyuan Basin for the first time. The results can help promote the sustainable use of groundwater in the Taiyuan Basin.

A new method for measuring the flow velocity and direction of groundwater

In this paper, in a karst fissure well with a large water depth, the flow velocity and flow direction of the monitoring wells at different depths (239m, 157m) were measured using The AquaVISION Colloidal Borescope produced by Geotech, USA. The results showed that, the flow direction of 239m deep karst water was 322.73°(37.27°North West), the flow velocity was 1496.60 μm/s. The flow direction of 157m deep karst water was 309.18°(50.82°North West), the flow velocity was 1032.0 μm/s, the flow direction of groundwater was Northwest, and the flow velocity gradually decreased from deep to shallow.

Using water temperature series and hydraulic heads to quantify hyporheic exchange in the riparian zone

Surface-water/groundwater exchange through the evaluation of riparian-zone temperature data has attracted increasing attention in recent years. The Fox Ditch Canal, Nevada, USA, was chosen for this study on seasonal variations of riparian-zone water exchange. Groundwater temperature and hydraulic head real-time monitoring data were collected from March to November 2012. A calibrated hydro-thermal coupling model was used to characterize the riparian-zone temporal and spatial temperature distribution, thereby providing a standard against which the performances of four analytical solution models for calculated riparian-zone vertical seepage velocity could be assessed. The results indicated that the proposed model provided a simulation that was able to represent dynamic changes in riparian-zone soil temperature. Although small variations in patterns and magnitudes of riparian-zone water exchange were evident at a daily scale, they varied significantly over a seasonal scale. Comparison of the results of the four analytical solutions and numerical computation found that the Hatch solution by the amplitude method provided the highest accuracy for calculating groundwater velocity in this area (2.47 × 10−6 to 3.15 × 10−6 m/s). Global sensitivity analysis of hydro-thermal coupling model parameters showed that porosity had the most significant impact on temperature in the model.

Development of possibilistic statistics and its application to quantify uncertainty of subsurface solute transport model

Imprecise information on any system is addressed by possibility theory wherein the system is modeled as a fuzzy set. Alpha level representation of a fuzzy set in the form of an interval defines the possibility theory. Uncertainty of any model in this context is quantified as mean value ± standard deviation of a possibilistic (imprecise) parameter. This paper presents the possibilistic statistical techniques to estimate the mean and standard deviation of a possibilistic parameter of subsurface solute transport model. The solute transport model parameters, such as groundwater velocity, solute dispersion coefficient, etc., are sparse and imprecise in nature. Such parameters are characterized by the possibility distribution. In this paper, analytical expression of solute transport model is used to estimate the mean value and standard deviation of possibilistic spatial and temporal concentration of solute.

Hydrogeological characterization and parameters estimation of the aquifer close to the Adige River (Verona, Italy) for the design of deep excavations

In the framework of the final design of a new hydroelectric plant close to the existing dam on the Adige River in the municipality of San Giovanni Lupatoto (VR, Italy), the design of deep excavations in loose sediments below groundwater level, and the connected risks of piping and excavation bottom heave required a detailed study of hydrogeological characterization, aimed to an accurate aquifer parameterization and so a confident design of excavation supports and dewatering systems. Particularly a three-dimensional analysis of the problem was necessary, because the hydrogeological system was complicated by many “artificial” boundary conditions (dam on the river, deep foundations of the existing and new engineering works) causing vertical not negligible flow paths. The conceptual model has been developed applying, in parallel, different prospecting tools: a preliminary Step Drawdown Test, a long duration Constant Rate Test, a multiple tracing test and the implementation of a three-dimensional numerical model of groundwater flow (MODFLOW-2005 code) and advective transport (MODPATH code). The modeling has allowed a good estimate of the aquifer parameters such as hydraulic conductivity and effective porosity through calibration of the pumping/tracing tests under transient conditions. Moreover, the simulation of post operam conditions and the comparison with ante operam, in terms of flow paths length and filtration velocity, showed that the construction of the new works foundations would have determined a sensitive reduction of groundwater velocities closed to the existing dam.

Actualization of prospects of thermal usage of groundwater of mines during liquidation

The aim of the paper is justification of the economically efficient technological scheme for development of a thermal resource of “Stashkov” mine after its closure, ensuring the maintenance of a favorable energy and ecological-hydrogeological regime in the region. A geotechnological scheme of environmentally safe usage of mine water was justified, involving water pumping up to the surface, heat removal and water reverse pumping into the seams. The suggested circulation system is characterized by an increased energy balance, since it is used to extract almost all the groundwater heat, as well as part of the heat of host rocks. In order to estimate the effectiveness of usage of this technology, calculations of usage of mine water as a source of low-potential energy in heat pumps in comparison with other alternatives (groundwater and surface water streams) using Mathcad software were performed, and it was established that this gives great conversion coefficients of mine water. A geotechnological scheme of usage of mine water was developed, which considers heat transfer, filtration direction, velocity and temperature of groundwater during pumping and removal of heat-transfer fluid from an aquifer for heating and cooling of buildings. The mechanism of heat removal in a flooded rock massif of amine during liquidation was studied with justification of environmentally safe usage of mine water.