Contaminant Transport Research Articles

Durability of geopolymer cutoff wall backfill incorporating reactive MgO particles under dry-wet cycles

Vertical cutoff wall has been employed for decades to control groundwater flow and subsurface contaminant transport. The barrier performance of cutoff wall material may significantly deteriorate under dry-wet cycles due to precipitation, drought, and groundwater fluctuation. This study adopted active magnesium oxide (MgO) particles to enhance the durability of geopolymer cutoff wall backfill (GCWB) under dry-wet cycles. The influence of particle size and proportion of MgO on the unconfined compressive strength (UCS), hydraulic conductivity, self-healing capacity and durability of GCWB were comprehensively examined. The results indicate that the incorporation of active MgO particles hindered the geopolymerization process of GCWB to a certain extent, leading to an increase in hydraulic conductivity and a decrease in UCS. But the overall performance of GCWB was still favorable. The hydraulic conductivity of samples with MgO gradually increased to more than 1 × 10−8 m/s after at least two dry-wet cycles. In the subsequent cycles, the samples with MgO exhibited a pattern of first gradually declining then ascending in hydraulic conductivity. This is due to hydration and carbonization of the remained MgO in matrix during the dry-wet cycles, which converts into oxygen-rich carbonates, forming well-ramified networks and reducing the proportion of macropores. Thus, the durability of GCWB with MgO is significantly more favorable than that devoid of MgO. In particular, large particle size MgO can exert more persistent self-healing effect, endowing the samples with superior durability under the prolonged dry-wet cycles.

Prediction and countermeasures of heavy metal copper pollution accident in the Three Gorges Reservoir Area

In order to mitigate the hazards of water pollution in drinking water source areas (DWSAs), developing applicable models and proposing effective solutions is of paramount significance. The study developed the Heshangshan Drinking Water Source Area (HDWSA) Hydrodynamic Model, integrating Geographic Information System (GIS) into a two-dimensional hydrodynamic water quality model using FORTRAN. TECPLOT360 software (Software Tools for Numerical Simulation with Visualization) visualized contamination transportation and diffusion. The model's relative error is less than 6%, indicating its strong stability and high reliability. The HDWSA in the Three Gorges Reservoir Area (TGRA) was used as a case study, focusing on copper (Cu) as a pollutant. By regulating the flow downstream from the Xiangjiaba Reservoir, Scheduling Group 1 and Scheduling Group 2 respectively increased the flow by 4000 m3/s and 8000 m3/s. The study analyzed the spatio-temporal variations of Cu concentration following pollution accident and flow scheduling. Under accident conditions, it took 71, 61, 49, and 56 min for the Cu concentration in the study area to decrease to below the standard value (1 mg/L) during dry, falling, flood, and storage periods. Scheduling Groups 1 and 2 reduced the pollutant exceedance duration by 19–26 min and 12–18 min across the four water periods.

Daughter oil droplet entrainment by oil-coated bubble bursting

Compound bubbles with a liquid coating in another continuous immiscible bulk phase are ubiquitous in a wide range of natural and industrial processes. Their formation, rise and ultimate bursting at the air–liquid interface play crucial roles in the transport and fate of natural organic matter and contaminants. However, the dynamics of compound bubbles has not received considerable attention until recently. Here, inspired by our previous work (Yang et al., Nat. Phys., vol. 19, 2023, pp. 884–890), we investigate the entrainment of daughter oil droplets in bulk water produced by a bursting oil-coated bubble. We document that the size of the entrained daughter oil droplet is affected by the oil coating fraction and the bulk liquid properties. We rationalize this observation by balancing the viscous force exerted by the extensional flow produced by bubble bursting with the capillary force resisting the deformation of the oil coating, and considering the subsequent end-pinching process which finally entrains the daughter oil droplets. We propose a scaling analysis for the daughter oil droplet size that well captures the experimental results for a wide range of oil coating fractions and Ohnesorge numbers of the bulk liquid. In addition, we discuss the non-monotonic variation of daughter droplet size with the Ohnesorge number, and show the eventual absence of daughter droplets because of the strong viscous effect in the high-Ohnesorge-number regime. Our findings may advance the fundamental understanding of compound bubble bursting and provide guidance and modelling constraints for bubble-mediated contaminant transport in liquids.

In the presence of the other: How glyphosate and peptide molecules alter the dynamics of sorption on goethite

The interactions with soil mineral surfaces are among the factors that determine the mobility and bioavailability of organic contaminants and of nutrients present in dissolved organic matter (DOM) in soil and aquatic environments. While most studies focus on high molar mass organic matter fractions (e.g., humic and fulvic acids), very few studies investigate the impact of DOM constituents in competitive sorption. Here we assess the sorption behavior of a heavily used herbicide (i.e., glyphosate) and a component of DOM (i.e., a peptide) at the water/goethite interface, inclusive of potential glyphosate-peptide interactions. We used in-situ ATR-FTIR (attenuated total reflectance Fourier-transform infrared) spectroscopy to study sorption kinetics and mechanisms of interaction as well as conformational changes to the secondary structure of the peptide. NMR (nuclear magnetic resonance) spectroscopy was used to assess the level of interaction between glyphosate and the peptide and changes to the peptide' secondary structure in solution. For the first time, we illustrate competition for sorption sites results in co-sorption of glyphosate and peptide molecules that affects the extent, kinetics, and mechanism of interaction of each with the surface. In the presence of the peptide, the formation of outer-sphere glyphosate-goethite complexes is favored albeit inner-sphere glyphosate-goethite bonds (i.e., POFe) are still formed. The presence of glyphosate induces secondary structural shifts of the sorbed peptide that maximizes the formation of H-bonds with the goethite surface. However, glyphosate and the peptide do not seem to interact with one another in solution nor at the goethite surface upon sorption. The results of this work highlight potential consequences of competition for sorption sites, for example the transport of organic contaminants and nutrient-rich (i.e., nitrogen) DOM components in relevant environmental systems. Predicting the rate and extent with which organic pollutants are removed from solution by a given solid is also one of the most critical factors for the design of effective sorption systems in engineering applications.

Mechanism of nearshore sediment-facilitated oil transport: New insights from causal inference analysis

A quantitative understanding of spilled oil transport in a nearshore environment is challenging due to the complex physicochemical processes in aqueous conditions. The physicochemical processes involved in oil sinking mainly include oil dispersion, sediment settling, and oil-sediment interaction. For the first time, this work attempts to address the sinking mechanism in petroleum contaminant transport using structural causal models based on observed data. The effects of nearshore salinity distribution from the estuary to the ocean on those three processes are examined. The causal inference reveals sediment settling is the crucial process for oil sinking. Salinity indirectly affects oil sinking by promoting sediment settling rather than directly affecting oil-sediment interaction. The increase of salinity from 0‰ to 35‰ provides a natural enhancement for sediment settling. Notably, unbiased causal effect estimates demonstrate the strongest positive causal effect on the settling efficiency of sediments is posed by increasing oil dispersion effectiveness, with a normalized value of 1.023. The highest strength of the causal relationship between oil dispersion and sediment settling highlights the importance of the dispersing characteristics of spilled oil to sediment-facilitated oil transport. The employed logic, a data-driven method, will shed light on adopting advanced causal inference tools to unravel the complicated contaminants’ transport.

Preferential flow in the shallow vadose zone: Effect of rainfall intensity, soil moisture, connectivity, and agricultural management

AbstractPreferential flow is ubiquitous in soils, and it affects water infiltration, runoff, and contaminant transport. Undisturbed soil lysimeters (n = 10; 900 cm2) were collected from an agricultural field to quantify the effect of climate, soil moisture, connectivity, and agricultural practices on water transport through the shallow vadose zone. A series of 10 rainfall simulations was conducted on each lysimeter (n = 100 events) and data were analysed within a framework of five case studies where we assessed the impact of rainfall intensity (n = 30 events), soil moisture (n = 28), and tillage (n = 21). Three lysimeters that had near‐zero flow initially were modified to investigate dynamics of direct surface connectivity through an artificial macropore in which we assessed the impacts of soil moisture (n = 12) and subsequent disruption via tillage (n = 9). Stable water isotopes were used to separate leachate into event (Qe) and pre‐event water (Qpe). Results showed that event water transport in leachate was not affected by rainfall intensity (Qe/Q = 49% ± 21% to 50% ± 24%); however, event water decreased from 65% ± 5% to 23% ± 28% with increasing soil moisture. Lysimeters with artificial macropores resulted in leachate that was nearly all event water (85% ± 12% to 92% ± 4%) irrespective of soil moisture. Tillage decreased event water transport for both lysimeters with and without an artificial macropore by ~30%. Findings show how varying initial and boundary conditions produce a continuum of preferential flow. Water and tracer flux data collected in the current study are therefore essential for predicting conditions with high relevance of preferential flow and contaminant transport when assessing or modelling long‐term hydrographs where these conditions are only met during a small proportion of the flow time.

Two-dimensional inverse energy cascade in a laboratory surf zone for varying wave directional spread

Surfzone eddies enhance the dispersion and transport of contaminants, bacteria, and larvae across the nearshore, altering coastal water quality and ecosystem health. During directionally spread wave conditions, vertical vortices (horizontal eddies) are injected near the ends of breaking crests. Energy associated with these eddies may be transferred to larger-scale, low-frequency rotational motions through an inverse energy cascade, consistent with two-dimensional turbulence. However, our understanding of the relationships between the wave conditions and the dynamics and energetics of low-frequency surfzone eddies are largely based on numerical modeling. Here, we test these relationships with remotely sensed and in situ observations from large-scale directional wave basin experiments with varying wave conditions over alongshore-uniform barred bathymetry. Surface velocities derived with particle image velocimetry were employed to assess the spatial scales of low-frequency surfzone eddies and compute structure functions with alongshore velocities. Second-order structure functions for directionally spread waves (σθ≥10°) are consistent with energy flux to larger or smaller length scales, while normally incident, unidirectional waves do not display this behavior. Third-order structure functions suggest that the surfzone flows exhibit a bidirectional energy cascade—a direct cascade to smaller and inverse cascade to larger length scales—during large directional spreads waves (σθ≥18°). However, there is not decisive evidence of an inverse energy cascade for moderate directional spreads (σθ=10°). Energy flux varies by cross-shore location and increases with increasing directional spread and wave height. Eddy decorrelation length scales weakly depend on wave directional spread. These findings advance our understanding of the dynamics linking wave breaking to large-scale rotational motions that enhance mixing and lead to rip currents, important conduits for cross-shore material exchange.

The Remediation of Congo Red-Contaminated Groundwater by using a Permeable Reactive Barrier Through Modified Waterworks Sludge MgAl-LDH

This investigation aims to explore the potential of waterworks sludge (WS), low-cost byproduct of water treatment processes, as a sorbent for removing Congo Red (CR) dyes. This will be achieved by precipitating nano-sized (MgAl-LDH)-layered double hydroxide onto the surface of the sludge. The efficiency of utilizing MgAl-LDH to modify waterworks sludge (MWS) for use in permeable reactive barrier technology was confirmed through analysis with Fourier transform infrared and X-ray diffraction. The isotherm model was employed to elucidate the adsorption mechanisms involved in the process. Furthermore, the COMSOL model was utilized to establish a continuous testing model for the analysis of contaminant transport under diverse conditions. A strong correlation was indicated, with a coefficient of determination (R2) ≥ 0.97, when the model's predictions were compared to experimental values, indicating the accuracy of the model. Continuous transport exhibited earlier breakthrough points when the bed depth decreased and the initial concentration and flow rate increased.

Emergence of Unstable Focused Flow Induced by Variable‐Density Flows in Vertical Fractures

AbstractFluids with different densities often coexist in subsurface fractures and lead to variable‐density flows that control subsurface processes such as seawater intrusion, contaminant transport, and geologic carbon sequestration. In nature, fractures have dip angles relative to gravity, and density effects are maximized in vertical fractures. However, most studies on flow and transport through fractures are often limited to horizontal fractures. Here, we study the mixing and transport of variable‐density fluids in vertical fractures by combining three‐dimensional (3D) pore‐scale numerical simulations and visual laboratory experiments. Two miscible fluids with different densities are injected through two inlets at the bottom of a fracture and exit from an outlet at the top of the fracture. Laboratory experiments show the emergence of an unstable focused flow path, which we term a “runlet.” We successfully reproduce the unstable runlet using 3D numerical simulations and elucidate the underlying mechanisms triggering the runlet. Dimensionless number analysis shows that the runlet instability arises due to the Rayleigh‐Taylor instability (RTI), and flow topology analysis is applied to identify 3D vortices that are caused by the RTI. Even under laminar flow regimes, fluid inertia is shown to control the runlet instability by affecting the size and movement of vortices. Finally, we confirm the emergence of a runlet in rough‐walled fractures. Since a runlet dramatically affects fluid distribution, residence time, and mixing, the findings in this study have direct implications for the management of groundwater resources and subsurface applications.

A Semi-Analytical Model of Contaminant Transport in Barrier Systems with Arbitrary Numbers of Layers

In regions with sanitary landfills, unsuitable liner designs can result in significant soil and groundwater contamination, leading to substantial environmental remediation costs. Addressing this challenge, we propose a semi-analytical model for solute transport that uses the advection–dispersion–reaction equation in a multi-layered liner system. A distinctive feature of our model is its ability to account for infiltration velocity, arbitrary numbers of layers, thin layers such as geomembranes, and mass flow. We validated our model against existing published models and applied it to a case study of a real sanitary landfill in the capital of Brazil. Through parametric analyses, we simulated contaminant transport across various layers, including the geomembrane (GM), geosynthetic clay liner (GCL), soil liner (SL), and compacted clay liner (CCL). The analyses showed the importance of choosing the most appropriate construction system based on the location and availability of materials. Considering toluene contamination, a GM molecular diffusion coefficient (DGM) greater than 10−13 m2 s−1 exhibited similar efficiency when compared with CCL (60 cm thick). In addition, the results showed that the liner system may have the same efficiency in changing SL (60 cm thick) for a GCL (1 cm thick).

Magnesium and groundwater flow relationship in karst aquifers: a tool for exploitation management of springs

Karst aquifers are characterized by different types of groundwater flow, related to different types of permeability due to the simultaneous presence of matrix, fractures and conduits. The presence of a well-developed karst conduit system leads to a rapid circulation of groundwater within the aquifer and a pulse-type response of the spring flow to the rainfall inputs, with a potential fast transport of contaminants from the hydrogeological basin surface to the discharge zones. Supported by hydro chemical analyses of spring water samples and single discharge measurements, it was possible to develop specific mass balance models, correlating ion content to spring flowrates. Specifically, Mg2+ content revealed a reliable application for spring baseflow separation in karst settings. Once the local model has been set, its conservative behaviour, in mostly limestone-dominant aquifers, allows using Mg2+ as a natural tracer of groundwater flow, distinguishing conduit flow (overflow) and diffuse flow (baseflow) occurrence in the spring outlet, without additional discharge measurements. In karst settings, the difficulty in continuously monitoring the spring discharge values makes this application interesting for exploitation management. This study shows the results obtained for two springs located in Central Italy, confirming that monitoring groundwater quality in karst environments is often the key for successfully characterizing springs and assessing the total yield when direct measurements are not available.

Evaluating the potential of treated municipal wastewater reuse in irrigation and groundwater recharge; 5-year contaminant transport modeling

Evaluating the potential of treated municipal wastewater reuse in irrigation and groundwater recharge; 5-year contaminant transport modeling

Fatala River Basin (Republic of Guinea, Africa): Analysis of Current State, Air Pollution, and Anthropogenic Impact Using Geoinformatics Methods and Remote Sensing Data

This study conducts an in-depth analysis of anthropogenic transformation and air pollution within the confines of the Fatala River Basin situated in the Republic of Guinea, Africa. The foundation of this investigation relies upon interdisciplinary geoinformatics methodologies and data acquired through remote sensing, specifically drawing from Sentinel-5P and Sentinel-2 satellite datasets. The primary objectives encompass scrutinizing the extant ecological conditions characterizing the Fatala River Basin and assessing the anthropogenic influences within its geographic expanse. The utilization of remote sensing data, as facilitated by the Sentinel-5P satellite, emerges as a potent instrument for meticulously monitoring environmental transformations. A comprehensive analysis of the designated area, conducted through remote sensing methodologies, is employed to ascertain the concentrations of various atmospheric constituents, including nitrogen dioxide, sulfur dioxide, formaldehyde, methane, ozone, and carbon monoxide. The findings gleaned from this inquiry reveal that, notwithstanding the dynamic growth of the extractive industry centered around the world’s preeminent bauxite province, the Fouta Djallon–Mandingo, the anthropogenic transformation of the Fatala River Basin exerts a comparatively minor influence on air quality. Statistical assessments, including correlation analysis, conducted between computed parameters delineating anthropogenic alterations within the Fatala River Basin, and a comprehensive atmospheric pollution index elucidate a lack of a significant nexus. It has been determined that air pollution within the Fatala River Basin is notably influenced by topographical features and the transport of contaminants from adjacent river basins. Consequently, this article makes a substantial contribution to our comprehension of the contemporary ecological state of the Fatala River Basin in the Republic of Guinea. It also holds significant importance in elucidating the ecological challenges specific to the researched region.

Detection and quantification of preferential flow using artificial rainfall with multiple experimental approaches

Preferential flow in the unsaturated zone strongly influences important hydrologic processes, such as infiltration, contaminant transport, and aquifer recharge. Because it entails various combinations of physical processes arising from the interactions of water, air, and solid particles in a porous medium, preferential flow is highly complex. Major research is needed to improve the ability to understand, quantify, model, and predict preferential flow. Toward a solution, a combination of diverse experimental measurements at multiple scales, from laboratory scale to mesoscale, has been implemented to detect and quantify preferential paths in carbonate and karstic unsaturated zones. This involves integration of information from (1) core samples, by means of mercury intrusion porosimeter, evaporation, quasi-steady centrifuge and dewpoint potentiometer laboratory methods, to investigate the effect of pore-size distribution on hydraulic characteristics and the potential activation of preferential flow, (2) field plot experiments with artificial sprinkling, to visualize preferential pathways related to secondary porosity, through use of geophysical measurements, and (3) mesoscale evaluation of field data through episodic master recession modeling of episodic recharge. This study demonstrates that preferential flow processes operate from core scale to two different field scales and impact on the qualitative and quantitative groundwater status, by entailing fast flow with subsequent effects on recharge rate and contaminant mobilizing. The presented results represent a rare example of preferential flow detection and numerical modeling by reducing underestimation of the recharge and contamination risks.

Interactions of humic acid with pristine poly (lactic acid) microplastics in aqueous solution

Microplastics and natural organic matter are present in the aquatic environment and their reciprocal interaction plays important roles in the transport and behavior of nutrients and contaminants. Nevertheless, we lack mechanistic understanding on these interactions, especially in the case of biodegradable plastics. Here we investigate the adsorption of a commercial humic acid onto poly (lactic acid) (PLA) microplastics in aqueous solution. While the pseudo-second order kinetic model provided a more accurate representation of the adsorption kinetics, the Elovich model also produced a good fit, suggesting that chemisorption may be the rate-limiting step. The equilibrium data was better fit by the Langmuir model, that provided a maximum adsorption capacity of 0.118 ± 0.006 mg·g−1. The obtained values for the separation factor (RL) and free energy (E) suggest that adsorption of humic acid onto PLA is controlled by physisorption. We studied the effects of pH, ionic strength, and PLA concentration on the adsorption of humic acid onto PLA and demonstrated that electrostatic interactions and aggregation are important. The humic acid was characterized by Fourier-transform infrared (FTIR) spectroscopy, excitation-emission matrix (EEM) fluorescence spectroscopy, and parallel factor analysis (PARAFAC), before and after interacting with PLA. This set of analyses demonstrated that PLA caused alterations in the molecular structure of humic acid, primarily attributed to modifications in hydrogen bonding and hydrophobic interactions. Therefore, we hypothesize that the carboxylic groups of humic acid formed dimers in contact with PLA. This study provides new insights into the interactions between organic matter and a biodegradable microplastic in aqueous systems.

Seasonal recharge mechanism of the upper shallow groundwater in a long-term wastewater leakage and irrigation region of an alluvial aquifer

Understanding the mechanisms that control seasonal groundwater recharge at local and intermediate scales is critical for understanding contaminant transport. The recharge mechanism of seasonal precipitation and irrigation, companied with legacy wastewater in porewater in alluvial aquifer were complicated due to the seasonal variation of multiple recharge sources. In this study, a long-term wastewater leakage and irrigation region along the Tanghe Wastewater Reservoir (TWR) in the alluvial plain area of North China Plain to investigate the recharge mechanism from unsaturated zone to the upper shallow groundwater affected by multiple water sources. Water chemical ions and stable isotopes of water (2H and 18O) of 30 m deep sediment profiles and groundwater boreholes were used to trace the recharge processes. The porewater stable isotopes of the sediment profiles revealed vertical recharge rates ranging from 0.63 to 1.09 m/year for the layered unsaturated zone with silt and silty clay. Due to the matrix flow through unsaturated zone, the legacy wastewater in the unsaturated zone affected the variation of groundwater quality in long term. However, fast flow (i.e., preferential or lateral flow) occurred in sand layers of alluvial aquifers lead to significant precipitation contributions (44 to 61 %) to the upper shallow groundwater (USGW) recharge, resulting in the seasonal variation of stable isotopes and water chemical ions. Affected by the fast flow with seasonal variations and matrix flow with legacy wastewater in the unsaturated zone, the δ2H and δ18O relationship of the USGW showed two types of hysteresis loops in the dual isotope space: 1) groundwater in regions affected by the TWR wastewater leakage shows narrow loops and a nearly straight line with end-members of precipitation that recharged to groundwater by fast flow, and evaporated porewater plotting along the TWR evaporation line; and 2) groundwater in irrigated farmlands with low and high irrigation amounts and intense evaporation shows stronger hysteresis with loops overlapping with shallow porewater, suggesting the impact of legacy wastewater of the unsaturated zone on groundwater. The residual pollutants in soil and the type of fast flow determine the different seasonal variation of groundwater quality. Preferential flow in alluvial aquifer regions can increase the proportion of seasonal recharge from precipitation, resulting in the rapid introduction of contaminants from surface or shallow soils into the alluvial aquifer.

Geocolloidal interactions and relaxation dynamics under nanoconfinement: Effects of salinity and particle concentration

HypothesisEnergy-related contaminants are frequently associated with geocolloids that translocate in underground fissures with dimensions comparable with geocolloids. To assess the transport and impact of energy-related contaminants in geological systems, fundamental understandings of interfacial behaviors of nanoparticles under confinement is imperative. We hypothesize that the dynamic properties of geocolloids, as well as their dependence on aqueous medium conditions would deviate from bulk behaviors under nanoconfinement. ExperimentsForce profiles and rheological properties of 50 nm silica nanoparticles in aqueous media confined between mica surfaces as a function of surface separation, particle concentrations, and salinity were measured utilizing the surface forces apparatus. FindingsForce profiles revealed the critical surface separation for nonlinear rheological behaviors coincides with the onset of exponential repulsion between mica surfaces. When salts were absent, the normal forces and viscosity values of colloidal suspensions resembled pure water. In contrast, with salts, the force profiles and corresponding critical length scales were found to be highly sensitive to the particle concentration and the degree of confinement. A Newtonian to shear-thinning transition was captured with increasing degrees of confinement. Our results show that the interplay among confinement, particle, and ionic concentrations can alter the interparticle forces and rheological responses of true nanosized-colloidal suspensions and thus their transport behaviors under nanoconfinement for the first time.

Thirty years of regional groundwater-quality trend studies in the United States: Major findings and lessons learned

Changes in groundwater quality have been evaluated for more than 2,200 wells in 25 Principal Aquifers in the United States based on repeated decadal sampling (once every 10 years) from 1988 to 2021. The purpose of this study is to identify contaminants with changing concentrations, the locations and magnitude of those changes, the factors driving those changes, the obstacles to interpreting the changes, and approaches to ameliorate those obstacles. Sampling was conducted in 89 networks of 20–30 wells each that represent various geographic regions, aquifer types and land use types. Each network, and the wells that comprise them, are sampled on a rotating basis once every 10 years. Of the 28 constituents evaluated for trends, concentrations of Na, Cl, dissolved solids, SO4, and NO3 exhibited statistically significant increases at the network level more frequently than other constituents. Factors affecting trends in Cl and NO3 are emphasized in this study. Regional patterns show large increases of Cl in urban areas in the Northeast and Midcontinent, where road-deicing salt application rates are 10 to 100 times greater than in other regions of the country, and in semiarid and arid regions of the western United States, where evaporation concentrates solutes in recharge. The largest increases in NO3 were in agricultural areas of the semiarid west, arid west and Pacific regions which are characterized by oxic groundwater, long-term increases in nitrogen fertilizer usage, and high rates of irrigation. However, finding a direct relation between increasing contaminant sources and corresponding groundwater quality response, particularly when sampling once every 10 years, can be complicated by factors such as uncertainty in the timing, mass, and location of contaminant sources, groundwater residence time (recharge date), geochemical conditions in the aquifer that affect contaminant transport, and variability in water quality due to climatic factors such as seasonality and hydrologic conditions. Understanding groundwater residence time allows the changes in groundwater quality to be evaluated in the context of recharge date rather than the sample date. Likewise, information on geochemical characteristics of the aquifer can be helpful for understanding relations between contaminant source inputs and groundwater concentrations. For example, oxic geochemical conditions in the aquifer may allow for conservative transport and accumulation of NO3 in groundwater, whereas reducing environments could favor NO3 degradation. Differences in hydrologic conditions (wetter or drier than average) on the date of sampling could impact the statistical results of sampling at decadal intervals and obscure long-term patterns. Samples collected under substantially different hydrologic conditions can be identified, and high-frequency sampling can improve interpretation of measured results in these cases. Although decadal sampling and associated water-quality interpretations have limitations, repeated, scheduled sampling of thousands of wells over multiple decades has great value for identifying and understanding long-term, regional groundwater-quality trends. Despite these limitations, the concepts presented herein provide options that could be used to interpret trends or changes when sampling over longer timespans, which is less common than trend networks with higher frequency sampling intervals.

A digital twin model for contaminant fate and transport in urban and natural drainage networks with online state estimation

Increased pollutant loads caused by urbanization and climate change have led to widespread impairment of surface water systems. To better manage these threats, water managers are seeking digital twins that combine online models with sensor data to respond to water quality hazards in real-time. This study introduces Pipedream-WQ, a new model for contaminant transport in drainage networks that combines a novel implicit solver for the unsteady advection–reaction–diffusion (ARD) equation with an efficient data assimilation scheme based on Kalman Filtering. We show that this solver reliably reproduces analytical solutions to the ARD equation in steady conditions, and accurately captures unsteady contaminant transport behavior in a complex drainage network. Furthermore, we show that online sensor data assimilation enables better estimation of contaminant concentrations at ungauged locations compared to a model-only approach. This model will enable improved pollutant tracking and source identification, and active water quality management through real-time control of hydraulic infrastructure.

Hydrological Transport and Fate of Brackish and Inorganic Contaminants with Anthropogenic Influence

The objective of our study is to estimate the contamination concentrations in the Permian Basin, US. A total of 481 observation samples were chosen within the following study areas: Andrews, Martin, Midland, Ector, Crane, and Upton Counties. The Dockum, Pecos Valley, Edwards-Trinity Plateau, and Ogallala aquifers were evaluated for inorganic contaminants. Level reports for parameters such as Arsenic (As), Nitrate (NO3−), Fluoride (F), Chloride (Cl), total dissolved solids (TDS), and Uranium (U) were provided by the Texas Water Development Board (TWDB) analyzed with other counties. We demonstrated the average level in each county with different time periods: 1992–2005 and 2006–2019. Our results were compared with the Environmental Protection Agency (EPA) standards and concluded the safety of water consumption in the study areas. We concluded that inorganic pollutants resulted mainly from human impacts such as agriculture, fertilizers, and energy developments. This research offers significant information about inorganic pollutants and brackish aquifers in the Permian Basin, US, contributing to our understanding of how groundwater resources respond to contaminations in dry regions. With freshwater becoming scarcer in arid climates such as the Permian Basin, US, it is important to ensure successful water management in these dry and arid locations.