Groundwater Hydrodynamics Research Articles

Improving fault zones hydrodynamic characterization and simulation in karstified carbonate environments with GLM and IES invers methods

A quantitative and qualitative estimation of groundwater resources is a challenge for water management in the world, especially in carbonated and karstified aquifers. Within these aquifers, fault zones exert a significant influence on groundwater hydrodynamics and transport. Improving the management of this type of aquifer involves better assessment of its hydrodynamics properties. Sustainability and management solutions can be estimated through numerical modeling. In this study hydrodynamic parameter of fault zone in karstified carbonate environments are estimated from cross-hole pumping test data. These estimations allow the simulation and forecasting of fault zone flow and transport. For this purpose, a flow and transport model has been set up using MODFLOW6 and MODPATH7 codes. Inverse modeling of hydrodynamic parameters is performed with the PEST++ code suite, with both the Gauss-Levenberg-Marquardt algorithm (GLMA) and the iterative ensemble smoother (IES) which is a recent approach with few applications so far. Simulation, parameter estimation, and forecasts of drawdown and pollutant travel time through the fault zone have been first evaluated on a synthetic fault zone and are eventually applied to a real-world fault zone of interest in karst carbonate environments. A comprehensive comparison and analysis of GLMA and IES results are performed for parameter estimation, parametric and predictive uncertainties, ensuring a thorough assessment of results. The findings reveal satisfactory levels of uncertainty associated with the hydraulic conductivity field and both flow and transport forecasts. This approach demonstrates its ability to estimate the hydrodynamic parameter field with a high level of accuracy within the internal structures of the fault zone. This study constitutes valuable and reproducible insights into the simulation and forecasts of fault zones in karst carbonate aquifers. The findings are a step forward in groundwater flow and transport simulation of fault zones and provide relevant practical help for the management and protection of water resources in these critical areas of interest.

Multi-biological risk in groundwater-surface water system under landfill stress: Driven by bacterial size and biological toxicity

The variation in bacterial size and biotoxicity leads to different ecological risks. However, the diversity of bacterial size and virulence in bacterial communities has been neglected, leading to limitations and inaccuracies in risk assessment. Surface-subsurface interactions lead to the complexity, variability, and insidiousness of pathogen transmission in the environment. Mountainous landfills are considered as a major source of pathogens in subsurface systems. Although numerous studies have reported the geographic distribution of microbes in landfills, there is a lack of knowledge regarding the impacts on the microbial spatial distribution of bacterial size, which is a key factor affecting microbial migration and risks. In this study, the groundwater, river water, soil and leachate samples were collected inside and around a typical mountainous urban landfill, which is close to a river with a high hydraulic gradient and a strong surface–subsurface interaction. Small-sized (<0.2 μm) and large-sized (>0.2 μm) bacteria were separated to verify the variability of migration potential and spatial distribution of different sizes of bacteria in groundwater-surface water and soil, investigating the driving factors and accessing the biological risk of different sizes of bacteria. The results revealed notable differences in spatial distribution and driving factors among various bacterial sizes. Small-sized bacterial communities in groundwater and soils exhibited clear trends towards leachate along the water flow direction. In contrast, large-sized bacterial communities remained stable and resembled native bacterial communities. Groundwater hydrodynamics was the main driving force affecting the spatial distribution of small-sized bacteria. The small-sized bacteria showed a higher content of virulence genes which were predominantly expressed for invasion. Thus, small-sized bacteria exhibited a stronger migration potential and a higher biological risk. Due to the surface–subsurface interactions, the bacterial communities in river water were more similar to that in groundwater after rain. Our results provide strong support to guide the management of subsurface system safety in mountainous landfills.

Hydrodynamics control for the well field of in-situ leaching of uranium

In this study, the groundwater hydrodynamics of two adjacent well sites were simulated under different pumping-injection ratios. The aim is to select an optimal pumping-injection ratio that can ensure the groundwater of the two well sites don't affect each other. In addition, the sulfur isotope composition of groundwater in the two well sites were analyzed to verify the simulated results. The results show that the flow velocity at different points outside the edge drilling hole decreases exponentially with the distance between the point and the edge hole. The streamline gradually extends outside of the borehole with the increase of leaching time. It is found that the optimal pumping-injection ratio is 1.003. In this case, the maximum distance between the moving front and the injection borehole is 28.44 m after leaching for 5 years. This indicates that the groundwater flow fields of the two well sites are well controlled. The significant difference in sulfur isotopes between the two well-sites further proves that the SO42− in the acid mining zone does not affect the groundwater in the zone leached by CO2+O2.

Aquifer systems in dry regions: Hydro-geophysical and geochemical investigations providing insights into water resources in southeast Tunisia

Water demands from agriculture and industry have intensified groundwater extraction, prompting a focused study to bolster water resources, particularly at Gabès region (Southeastern Tunisia). Through extensive geologic and geophysical investigations, the reservoir geometry and structural architecture of crucial aquifers, notably the Mio-Plio-Quaternary and Cretaceous aquifers have been studied. The integration of geochemical and geophysical data allows for a nuanced assessment of fault structures and groundwater hydrodynamics. Advanced techniques, like horizontal gradient and upward extension unveils structural features and density contrasts with precision. This study extends to a spatiotemporal analysis of aquifer hydrodynamics and groundwater mineralization. The Gabès aquifer system exhibits four groundwater facies: Ca–Mg–SO4, Na–Cl–NO3, Ca–Mg–HCO3, and Na–K–HCO3. Results reveal relative isotopic depletion, suggesting recharge under colder climates and at higher altitudes. However, the study underscores the impact of climate change, with increasing temperature and dwindling precipitation in North Africa, since the mid-20th century. This research is a relevant contribution to sustainable water management by emphasizing the impact of climate change scenarios and groundwater resources management. The detailed exploration of hydrogeological characteristics and aquifer dynamics in the Gabès region is pivotal on effective management of groundwater resources strategies in semi-arid environments.

The influence of the 2022 extreme drought on groundwater hydrodynamics in the floodplain wetland of Poyang Lake using a modeling assessment

The 2022 extreme drought in Poyang Lake (China) caused severe damage to a wide range of sectors. It also emphasized the fact that, even in regions with abundant surface water resources, groundwater resource is still a crucial component of drought management strategies. However, providing up-to-date assessments of groundwater response remains challenging due to the limited data in complex floodplain settings. This study uses a groundwater flow modeling FEFLOW to investigate the influences of the most extreme drought in 2022 on groundwater hydrology in the floodplain wetland of Poyang Lake. Model simulation indicates that the extreme drought led to a significant decrease in floodplain groundwater levels, with a maximum drop of about 5 m. In addition, the extent of the groundwater level drop varies significantly across the floodplain wetland, particularly for the strongest impact (drop > 4 m) occurring in the eastern area of the floodplain. It is expected that the extreme drought accelerates the groundwater discharge rate that is about 3 times than that of the normal year, and thus resulting in a losing condition of the floodplain wetland. On an annual scale, the groundwater discharge of the floodplain wetland in 2022 is estimated to be about 14.5 times than that of a normal year, demonstrating a significant attenuation of groundwater storage under drought environments. The reduction in rainfall combined with the associated low lake level is most likely to exert substantial influences on reduced floodplain groundwater storage. This study is the first attempt to interrogate the response of wetland groundwater to the unpredictable drought event in Poyang Lake, contributing to improved understanding of future water resources allocation and drought resistance strategy.

Spatial-Temporal Patterns of Shallow Groundwater Levels in the Yellow River Delta, China

Analysis of the various hydrologic features responsible for the spatial and temporal variability in large scale subsurface systems is a critical component of water resources engineering and management. Traditionally, modeling large-scale groundwater flow patterns includes simulations with underlying parameter estimations and associated overarching assumptions. More recently, subsurface hydrologists are using empirical orthogonal function analysis to separate and quantify the primary hydrologic components contributing to observed regional and local-scale groundwater hydrodynamics. In this case study, modern spatiotemporal geostatistics plus primary hydrologic component analysis were conducted on spatially and temporally distributed groundwater levels measured in the Yellow River Delta. The results demonstrate the significant interplay between surface water hydrodynamics, overall groundwater quality, and groundwater utilization at the local scale, plus the significant impact of regional-scale aquifer recharge on groundwater level seasonal variation, largely driven by precipitation events. With increased accessibility to remote sensing data, additional research using these or similar statistical approaches to interpolate, compress, and decompose those features driving subsurface fluid-flow variability will prove to be highly beneficial to water resource engineers and managers.

Water table depth assimilation in integrated terrestrial system models at the larger catchment scale

As an important source of water for human beings, groundwater plays a significant role in human production and life. However, different sources of uncertainty may lead to unsatisfactory simulations of groundwater hydrodynamics with hydrological models. The goal of this study is to investigate the impact of assimilating groundwater data into the Terrestrial System Modeling Platform (TSMP) for improving hydrological modeling in a real-world case. Daily groundwater table depth (WTD) measurements from the year 2018 for the Rur catchment in Germany were assimilated by the Localized Ensemble Kalman Filter (LEnKF) into TSMP. The LEnKF is used with a localization radius so that the assimilated measurements only update model states in a limited radius around the measurements, in order to avoid unphysical updates related to spurious correlations. Due to the mismatch between groundwater measurements and the coarse model resolution (500 m), the measurements need careful screening before data assimilation (DA). Based on the spatial autocorrelation of the WTD deduced from the measurements, three different filter localization radii (2.5, 5, and 10 km) were evaluated for assimilation. The bias in the simulated water table and the root mean square error (RMSE) are reduced after DA, compared with runs without DA [i.e., open loop (OL) runs]. The best results at the assimilated locations are obtained for a localization radius of 10 km, with an 81% reduction of RMSE at the measurement locations, and slightly smaller RMSE reductions for the 5 and 2.5 km radius. The validation with independent WTD data showed the best results for a localization radius of 10 km, but groundwater table characterization could only be improved for sites &amp;lt;2.5 km from measurement locations. In case of a localization radius of 10 km the RMSE-reduction was 30% for those nearby sites. Simulated soil moisture was validated against soil moisture measured by cosmic-ray neutron sensors (CRNS), but no RMSE reduction was observed for DA-runs compared to OL-run. However, in both cases, the correlation between measured and simulated soil moisture content was high (between 0.70 and 0.89, except for the Wuestebach site).

Influence of a proposed hydraulic project on groundwater hydrodynamics of the floodplain of Lake Poyang and its ecological implications

Influence of a proposed hydraulic project on groundwater hydrodynamics of the floodplain of Lake Poyang and its ecological implications

Experimental study of the solitary wave induced groundwater hydrodynamics

Coastal groundwater hydrodynamics are affected by the swash uprush and backwash processes. In this study, laboratory experiments were carried out to investigate the solitary wave induced groundwater hydrodynamics over a coarse-grained sand beach. Pore water pressures at 27 cross-shore positions (covering both the subaqueous and subaerial areas) along 3 different beach depths were measured, and the synchronized shoreline position as well as the local water surface elevations (WSE) were also recorded. Temporal variation of the total water head (TWH) was found almost hydrostatically controlled by the instantaneous WSE in the subaqueous area. In the capillary truncated zone, the capillary effect contributes to the non-hysteresis phenomenon between the TWH and WSE. In other subaerial area, time-varying features of the TWH and WSE show clear differences in terms of their magnitudes and phases. Regarding the experimental observations, four representative regions could be identified along the cross-shore direction, i.e., Region I corresponding to the initially subaqueous area, Region II in between the still water shoreline and the top of capillary fringe (saturated beach), Region III in between the upper boundary of Region II and the maximum swash run-up, and Region IV landward beyond the Region III. With respect to the cross-shore distribution characteristics of the maximum TWH and the maximum WSE, as well as the time instants when the maximum TWH and the maximum WSE occur, different groundwater hydrodynamics were observed during the swash event in these four regions. In addition, spatiotemporal characteristics of the TWH were scrutinized and discussed. Both the vertical and horizontal TWH gradients in different regions were considered to reveal the sophisticated groundwater hydrodynamics. Finally, the groundwater movement pattern and its percolation circulation under the solitary wave swash were also specified. • Solitary wave induced groundwater hydrodynamics are investigated through detailed laboratory experiments. • Four regions are identified regarding the spatial characteristics of the maximum total water head and its occurrence time. • Hydrostatic effect, capillary effect and the wetting front are significant for the swash groundwater hydrodynamics. • Horizontal groundwater seepage flow is evident, even larger than the vertical one, during the entire swash process. • Two groundwater circulations are observed in the subaqueous and subaerial areas during the swash cycle.

The effects of capillary fringe on solitary wave induced groundwater dynamics

The capillary fringe is an important factor influencing the groundwater hydrodynamics in the coastal aquifer. The mechanism of the water table changes with the effect of capillary fringe under the wave action is still unclear. In this study, laboratory wave flume experiments were conducted to investigate the groundwater hydrodynamic features, paying particular attention to the capillary effects, in different areas of the beach under the solitary wave action. In the present experiments, medium sands were used to form the beach, resulting in a large capillary fringe height. Accordingly, the entire swash process occurred within the capillary truncated area. Based on the experiment measurements, three mechanisms are confirmed with respect to the coastal water table fluctuations, i.e., the flux mechanism, the gradient mechanism and the newly-proposed meniscus mechanism. The meniscus mechanism in the capillary truncated zone and the gradient mechanism in the capillary untruncated zone contribute to the non-hysteresis of the pressure head variation in the beach landward of the swash zone. The capillary truncated zone can be deemed as an extent of the swash zone since the effect of the swash process plays roles beyond the swash zone through a truncated capillary fringe. In addition, detailed observation of the evolution of the meniscus profile among the beach surface particles suggests that both vertical and horizontal seepage flows are important in the capillary truncated zone. In the swash zone, temporal variation of the hydraulic head can be classified into four/five stages in the case that the measuring position is near to/far from the uprush limit, and the effects of shoreline, water surface elevation, seepage face and exit point on the groundwater dynamics are discussed. Findings from the present study provide useful insights into the wave-induced coastal groundwater dynamics. • Capillary fringe effects on solitary wave induced groundwater dynamics are investigated through wave flume experiments. • Observation of the meniscus dynamics among beach surface particles provides new insights into the capillary fringe behaviors. • Flux mechanism, gradient mechanism and the newly-proposed meniscus mechanism for groundwater fluctuations are confirmed. • Meniscus mechanism dominates the hydrodynamic process in the capillary truncated zone. • Hydrodynamic process in swash zone can be divided into four or five stages with different dominant influencing factors.

The Lake Chad transboundary aquifer. Estimation of groundwater fluxes through international borders from regional numerical modeling

Study RegionAfrica. The Lake Chad transboundary aquifer Study FocusTo understand transboundary groundwater hydrodynamics and estimate quantitative groundwater fluxes values between aquifer-sharing countries. To enable estimations, we developed an updated 3D ‘quasi steady-state’ regional groundwater flow model of the Chad Formation based on integrating extensive available information and reflecting the best current conceptual understanding to date. The conceptual model was tentatively assessed by a steady-state numerical model based on MODFLOW. New Hydrological Insights for the RegionThis model simulates lateral groundwater flows between neighboring countries, and also provides insights into the large-scale flow pattern and flows among hydroestratigraphic units. Modeling indicated that groundwater fluxes through international borders exist between Basin-sharing countries, except between Central African Republic and Cameroon, where a buffer area was considered for modeling purposes, leading to more uncertain results. From 14ºN parallel to further north, data are scanty and outcomes should be carefully considered. Forecasting transboundary impacts indicated that changes in recharge rates were more sensitive that changes in groundwater abstraction. To date, abstraction represents a small part of the water balance, but if it increases, it can become a driving factor in the future. Land use change and water use in the source areas (southern area) will have the strongest impact on transboundary groundwater flows due to changes in recharge, which will lead to quantitative changes in groundwater levels, artesian conditions, or even water quality.

Water storage, mixing, and fluxes in tile-drained agricultural fields inferred from stable water isotopes

Quantifying hydrological processes that control the upper critical zone water balance and contaminant transport in drained landscapes is needed, especially as precipitation patterns driving water balance dynamics continue to shift due to climate change. Here, hydrometric data are integrated with stable isotope signatures to quantify water storage, mixing, and fluxes to subsurface tile drainage at an agricultural field located in Indiana, USA. Over a 2-yr period, precipitation, soil water sampled with suction lysimeters (10–80 cm depth), groundwater (below tile depth; >1 m), and subsurface tile discharge were sampled 97 times. Results showed that isotopic variability in near-surface soil water (10–20 cm) reflected the seasonality of the precipitation input signal, while groundwater values were relatively consistent indicating that water stored below tile drain depth was recharged during winter. Soil water between 20 and 80 cm depth was a mixture of near-surface water and groundwater that varied seasonally depending upon groundwater hydrodynamics. Mean transit time of water ranged from 12 to 20 d for 10-cm soil water to 225–334 d for groundwater, with tile drainage exhibiting a mean transit time of 245 d. Both two- and three-component hydrograph separation indicated that groundwater was the primary source of water to the tile drain followed by soil water. Tile drain hydrograph response (i.e., celerity) was largely controlled by antecedent wetness. Comparison of tile drain celerities and velocities revealed however varying mechanisms controlling hydrograph response across a range of environmental conditions. Data sets of both water and tracer flux were, thus, useful to track the spatiotemporal variability of water fluxes within and from the critical zone. Such data provide valuable information to improve the representation of critical zone processes in these landscapes within spatially distributed hydrological models.

Is the Combination of Linearized Theoretical Analysis and Sand Column Experiment Always Suitable for Estimating the Complex Effective Porosity?

AbstractGroundwater hydrodynamics are significantly affected by the capillary effect when groundwater table approaches sand surface. A complex effective porosity was suggested to replace the specific yield to represent the capillary effect based on varieties of sand column experiments, and its estimation is based on the assumption that the response of time‐varying groundwater table is a simple harmonic motion. Nevertheless, groundwater hydrodynamics always consist of multiple harmonic components, which should be further examined. In this study, we first conducted laboratory sand column experiments with respect to different periodic oscillation conditions. Then, a fast Fourier transformation algorithm was applied to analyze the measured groundwater table, upon which the high order harmonic components under high frequency wave conditions was demonstrated. Subsequently, based on a perturbation approach, we presented a third order analytical solution of time‐varying groundwater table under a simple harmonic oscillation. The gradient descent method was applied to estimate the complex effective porosity by fitting the high order analytical solution to the experimental data. In addition, effects of various parameters, representing different driving head conditions and sediment properties, were testified through parametric studies, which demonstrates high order harmonic components should not be neglected under the conditions of large relative amplitude of driving head, short period oscillation, and the ratio of hydraulic conductivity to dynamic effective porosity being around 1 m/s, for example, in the scenarios of wave‐dominant swash zone. These new findings are of great importance to extend our understandings of the capillary effect on groundwater hydrodynamics.

An analytical solution of the tide-induced groundwater table overheight under a three-dimensional kinematic boundary condition

Time averaged groundwater table above the mean sea level has been observed in unconfined coastal aquifers. Several theoretical solutions were presented to investigate the groundwater table overheight (super-elevation) in response to tidal oscillations. Nevertheless, previous analytical solutions are generally limited to Dupuit-Forchheimer assumptions or a two-dimensional free surface model. In this paper, we introduced a more general condition that a three-dimensional kinematic boundary condition is considered. An exact analytical solution of the groundwater table overheight under the multi-tidal constituents was derived using the Fourier transform method. The solution shows the local groundwater table overheight is related to the mean aquifer thickness, tidal amplitude, damping coefficient as well as its positions in sand beaches. In addition, the analytical solution illustrates the simple linear superposition is not applicable to the multi-tidal components condition, whose groundwater table overheight becomes weak due to the non-linear effect of the three-dimensional kinematic boundary condition. In addition, concentrations were focused on the time averaged total flux density illustrating the groundwater exchange occurs both in the shore normal and shore parallel directions, which however is missing in the previous two-dimensional solution. Further cognitions on the groundwater circulation mechanism were also achieved, which originates from the large tidal amplitude region and fans out towards the small tidal amplitude region. These new findings are of great importance to extend our understandings of the groundwater hydrodynamics in unconfined coastal aquifers.

Groundwater hydrodynamics and sustainability of Addis Ababa city aquifer

In the past two decades, Addis Ababa city has been under continuous demand of additional water supply improvement due to critical shortage of supply became particularly a serious problem at the outskirts of topographically high places. In order to overcome the existing problem, groundwater development optioned as emergency water supply project. However, the development continued without giving attention to its sustainability and now takes about 63% of the share. Over the last decade, many well-fields have been drilled; Akaki, Legedadi-Legetafo-Ayat, South-Ayat-North-Fanta, and Addis Ababa pocket areas in the same watershed that have an area about 1490 km2. The main objective of this study was to assess the groundwater hydrodynamics and sustainable utilization of the sources. For the study, 166 deep borehole completion and pumping test well fields within and around Addis Ababa were used. From the analysis it was found that hydraulic conductivity and transmissivity in the watershed vary from 0.02 to 256 m/day and 5.4 × 101 to 2.16 × 104 m2/day respectively. The major aquifers are fractured & scoriaceous basalt, scoria, fractured ignimbrite or a combination of these rocks. Analysis of water level contour map for Akaki well-field indicated that 84.50% of the current pumping water levels were below the dynamic water level. In particular, old Akaki well-field has been severely depleted. Out of 24 drilled wells, 13 of them are abandoned as water level and discharge have significantly declined. Despite huge importance of groundwater, it has been understood poorly and undervalued. It is a finite resource and the aquifers can become depleted as this extraction rates which exceed recharge rates. Therefore, groundwater management should be practiced through reliable aquifer characterization, sustainable development, planning of conjunctive use of surface water and artificial recharge.

Assessment of the hydrodynamics role for groundwater quality using an integration of GIS, water quality index and multivariate statistical techniques

To explore the impact of groundwater hydrodynamics on water quality, a cost-effective geospatial model was developed using geographic information system (GIS) technology and the Dupuit assumption. Meanwhile, the groundwater quality in the Dagu River Basin was evaluated based on the water quality index (WQI) and multivariate statistical analyses. In April (dry season) and September (rainy season) 2017, the groundwater level was automatically monitored from 115 wells, and the water quality including 21 hydrochemical parameters was sampled from 37 wells. Results reveal that the WQI values varied from 35.01 to 64.74, with mean values of 51.89 and 47.87 in the rainy and dry seasons. Approximately 80% of the samples exhibited moderate water quality, with no significant difference between the rainy and dry seasons. Nitrate pollution and the integrated water quality in the central and northern regions were generally worse than that in the southern region. The Darcy velocity in the central and northern regions was relatively high with a maximum rate of 0.56 m/d, compared with the southern region. This correlation illustrates the effect of groundwater hydrodynamics on quality. The sowing of greater chemical fertilizers combined with faster groundwater movement is likely responsible for the large–scale nitrate pollution in the central and northern regions. Results also proved the accuracy of the geospatial model with a valid uncertainty. The geospatial model provides a valuable alternative for the spatial analysis of the effect of groundwater hydrodynamics on water quality.

Water-rock interaction and mixing processes of complex urban groundwater flow system subject to intensive exploitation: The case of Mexico City

In complex aquifer systems subject to intensive exploitation it is important to investigate hydrogeochemical processes in the components to understand the hydrodynamics of groundwater. In this respect, understanding the hydrochemical mechanisms of water-rock interactions and mixing processes eventually leads to the development of appropriate strategies for a sustainable groundwater management. In this study, we analyze water-rock interactions processes of the so-called Anáhuac groundwater system underlying part of the Mexico Valley comprising Mexico City and its suburbs. This intensively exploited system has four flow components: 1) local flow, 2) intermediate flow, 3) cold regional flow, and 4) hot regional flow. This is studied using inverse geochemical models, which consider uncertainties of analytical data and constraints from thermodynamic stability diagrams, speciation-solubility models, and petrographic data. Three representative modeling sections were selected for the implementation of the mass-balance approach. The general conceptual model in two sections suggests that rainwater infiltrates the subsoil and begins to dissolve CO2 in the unsaturated zone; by reaching the saturated zone it reacts with silicate minerals of the host rock producing the final chemical composition of waters. On the other hand, the third section shows mixing as the main groundwater process, as well as water-rock interactions. In general, the identified processes of water-rock interaction are dissolution of CO2, dissolution of calcite, gypsum, and halite, Ca/Na ion-exchange, and weathering of silicate minerals such as biotite, muscovite, plagioclase, epidote and pyroxene, and precipitation of kaolinite, SiO2 and Fe (OH)3. Changes between local and intermediate flow components suggest dissolution of andesite rocks and precipitation of pyrite. Changes between local flow component and the cold regional component are explained by large flow trajectories. Transformations between local and hot regional components indicate mixing flows and a deep circulation influenced by the geothermal gradient. The combination of the methods used in this study can be applied in other similar geoenvironments of the world and assist local water authorities to adequately address and manage groundwater.

Hydro-environmental changes assessment after Guadalhorce River mouth channelization. An example of hydromodification in southern Spain

The Guadalhorce River mouth (Málaga, Southern Spain) was channelized between 1997 and 2003 to reduce flooding potential in adjacent densely populated sections of Málaga. The channel was bifurcated near the Mediterranean Sea, surrounding an isolated wetland complex composed of eight different ponds. Groundwater-level and wetland-stage data, combined with water-chemistry data from wells and wetlands, collected since 1977, have documented the hydrological and ecological responses to channelization. The results show that channelization has extended the tidal influence inland from the Mediterranean Sea through the Guadalhorce River and the subjacent coastal aquifers, producing a change in groundwater hydrodynamics. The isolation of the wetlands resulting from channelization has provoked a significant salinization of both surface water and groundwater, the extent of which varies among wetlands. These decadal-scale changes in water chemistry have promoted the appearance or increase of halophilic vegetation and have caused a shift from diving birds to predominantly shorebirds in some wetlands. Documentation of these unexpected ecosystem responses is a necessary first step for land managers who need to consider groundwater and surface water as a single resource, particularly in groundwater-dependent ecosystems along the densely populated and ecologically sensitive Mediterranean coastal areas.

A Quantitative Framework for Comparing Observed and Simulated Pit-Lake Geochemistry

Pit lakes are commonly studied using advanced geochemical models. However, quantitative post-audits of these studies to assess the degree of agreement with observations are rare. This study used a quantitative evaluator (error variance parameter; Δ) to compare predicted and observed geochemistry of nine pit lakes across three continents and five ore-deposit types. The compiled modeling studies applied a variety of methods to incorporate geochemical (sulfide oxidation and mineral precipitation) and hydrologic processes (groundwater flow and hydrodynamics). Several common ions (Ca, Mg, SO4) and pH were shown to compare well with observations. In contrast, comparisons of model simulations and observations for trace metals and metalloids such as Fe and As were less congruent. The discrepancies for these and other species is potentially linked to inappropriate application of equilibrium thermodynamics and temporal model discretization. Model complexity was also shown to be related to the reproducibility of observed geochemistry. Quantitative analysis using Δ in a wider range of studies may increase understanding of prevalent geochemical processes invoked in pit-lake modeling.

Groundwater restoration following in-situ recovery (ISR) mining of uranium

From 1950 through the early 1980's New Mexico accounted for roughly half of domestic uranium (U) production for the nuclear power industry and the nation's weapon programs. Increased interest in nuclear energy has led to proposals for renewed development using both underground mining and uranium in situ recovery (ISR). When feasible, ISR greatly reduces waste generated by the mining and milling processes, however, the ability to restore ground water to acceptable quality after ISR ends is uncertain. This research investigated two methods of stabilizing an aquifer following ISR. Batch and column studies were performed to evaluate chemical and biological methods of stabilization. Columns packed with ore were first leached with an aerated NaHCO3 ground water solution to simulate ISR. Constituents present at elevated concentrations after leaching included molybdenum (Mo), selenium (Se), U, and vanadium (V). Chemical stabilization was studied by passing a phosphate (PO43-) amended solution through the ore to achieve passivation of mineral surfaces by P precipitates. Microbial stabilization was studied by passing a lactate solution through the ore to stimulate growth of anaerobic metal- and sulfate-reducing organisms to reduce U and other elements to less soluble phases. Analyses of the solids from the columns after completion of these experiments by X-ray photo electron spectroscopy (XPS) identified phosphate on samples near the column inlet of the chemically stabilized columns. Microbial populations were characterized by Illumina DNA sequencing and confirmed the presence of metal- and sulfate-reducing organisms. Neither chemical nor microbial stabilization method achieved contaminant immobilization, which is believed due to limited mixing of the stabilization solutions with the contaminated leach solutions. These results emphasize that ground water hydrodynamics, especially mixing, must be considered in aquifer restoration of soluble constituents.