Aquifer Contamination Research Articles

Identifying intrusion of seawater in coastal aquifers by modified GALDIT (M-GALDIT) index

Contamination of coastal aquifers by seawater intrusion (SWI) is a major environmental problem. A modified GALDIT method (M-GALDIT), and multi-criteria decision model AHP has been used to identify regions vulnerable to seawater intrusion. We have used the groundwater suitability index for seawater intrusion (GQISWI) in estimating the M-GALDIT index. While the GALDIT analysis indicates that ∼28% of the area is moderately vulnerable, and 8% of the area is relatively highly vulnerable, our estimates using AHP and M-GALDIT method indicate ∼19% of the area as moderately vulnerable, ∼22% of the area as relatively highly vulnerable zones. The GQISWI values in the region vary between 0 and 96.96, indicating that most of the groundwater samples belong to mixed water types. Faults and fractures, population distribution, water-rock interaction, ionic exchange reactions, and evaporation appear to be the dominant mechanisms, besides seawater intrusion that control the overall groundwater geochemistry in the region. Ca2+-HCO3-, Ca2+-Na+-HCO3−, and Ca2+-Mg2+-Cl− are the most dominant water types in the study area. The seawater mixing index (SMI) reveals that ∼34.5% of samples are of relatively freshwater types, whereas ∼61% of samples appear contaminated to some extent, presumably due to the mixing of seawater, or anthropogenic activities such as mining, agricultural activities, etc. Furthermore, analysis of the HFE-D diagram indicates that ∼23% of samples are directly affected by seawater intrusion.

Hydrochemistry and Contamination in Sedimentary and Fractured-Rock Aquifers of The Upper Rio Negro Basin – Amazonas/Brazil

The Amazon region has the largest hydrographic network on the planet. However, cities and communities along rivers obtain water from tube wells without studying the chemical quality and, consequently, the potability of their water. In specific geological contexts, there is a significant probability of natural contamination by arsenic in groundwater in the region, already attested in previous works in the Solimões, Madeira and Amazonas rivers basins, but not yet found in the Negro river basin. As the Negro is the second largest river in the Amazon Basin, it has become necessary to study the chemical quality of its groundwater, relating it to the geology of the region. In this work, water samples were collected from 21 wells and 4 water springs used for human consumption, following the protocols proposed by the US – EPA. In the field, the physicochemical parameters of the in-situ water were measured, and alkalinity tests were carried out on the samples. The cations were analyzed at INPA and the anions at the Geological Survey of Brazil (SGB). From the 25 samples, 16 had analises results within acceptable ionic balance values, and 12 of the 16 had at least one of the following elements in concentration above World Health Organization and Brazilian Guideline Values: Al, As, Fe, Mn and Pb. The presence of values below the GV, but above what is considered natural, of NO3- in 66% of the contaminated points, associated with the shallow depth of most of the wells, installed in areas of recent sedimentary deposits and that do not show any or few signs of care demonstrate that the contamination in these localities is of anthropic origin. Two samples (16% of the contaminated samples) are from deep wells installed in fractured aquifers, which in this case indicate contamination of geogenic origin. Arsenic was found in association with iron and aluminum in a well installed in alluvial sediments, which indicates that more studies are needed for this specific geologic formation to know the quality of this water. For other locations and cities, short, medium and long-term measures are needed to prevent anthropogenic contamination of aquifers.

Using VES and GIS-Based DRASTIC Analysis to Evaluate Groundwater Aquifer Contamination Vulnerability in Owerri, Southeastern Nigeria

This study assesses groundwater vulnerability in Owerri, Nigeria, using Vertical Electrical Sounding (VES) and Geographic Information System (GIS)-based DRASTIC modeling. The research methodology includes literature review, field survey, geological feature mapping, hydrogeological assessment, geo-electrical sounding, and data interpretation. Owerri, a rapidly developing city with flat topography and a growing population, uses the DRASTIC model to construct a groundwater vulnerability map. The model evaluates the risk of groundwater contamination using seven critical criteria, including depth to water table, net recharge, aquifer media, soil media, topography, vadose zone impact, and hydraulic conductivity. Each parameter was given a weight and rating, and the DRASTIC Index (DI) was calculated by summing the products of the weights and ratings for each factor. The results of the vulnerability assessment indicated that approximately 49% of the study area falls into the high vulnerability category, around 45% is classified as moderate vulnerability, and the remaining 6% is labeled as low vulnerability. The study reveals moderate to high vulnerability zones in Owerri, Nigeria, due to factors like lower slope terrain, permeable aquifer media, and vadose zone impact. The use of VES and GIS-based DRASTIC mapping techniques provides insights into groundwater vulnerability, aiding in sustainable resource management and environmental protection. The findings emphasize the importance of understanding potential risks and the need for effective management strategies to safeguard clean water supplies. Further research and mitigation efforts should focus on highly vulnerable areas.

Predicting natural arsenic enrichment in peat-bearing, alluvial and coastal depositional systems: A generalized model based on sequence stratigraphy

Hazardously high concentrations of arsenic exceeding the threshold limits for soils and drinking waters have been widely reported from Quaternary sedimentary successions and shallow aquifers of alluvial and coastal lowlands worldwide, raising public health concerns due to potential human exposure to arsenic. A combined sedimentological and geochemical analysis of subsurface deposits, 2.5–50 m deep, from the SE Po Plain (Italy) documents a systematic tendency for naturally-occurring arsenic to accumulate in peat-rich layers, with concentrations invariably greater than maximum permissible levels.A total of 366 bulk sediment samples from 40 cores that penetrated peat-bearing deposits were analysed by X-ray fluorescence. Arsenic concentrations associated with 7 peat-free lithofacies associations (fluvial-channel, levee/crevasse, floodplain, swamp, lagoon/bay, beach-barrier, and offshore/prodelta) exhibit background values invariably below threshold levels (<20 mg/kg). In contrast, total arsenic contents from peaty clay and peat showed 2–6 times larger As accumulation. A total of 204 near-surface (0–2.5 m) samples from modern alluvial and coastal depositional environments exhibit the same trends as their deeper counterparts, total arsenic peaking at peat horizons above the threshold values for contaminated soils.The arsenic-bearing, peat-rich Quaternary successions of the Po Plain accumulated under persisting reducing conditions in wetlands of backstepping estuarine and prograding deltaic depositional environments during the Early-Middle Holocene sea-level rise and subsequent stillstand. Contamination of the Holocene and underlying Pleistocene aquifer systems likely occurred through the release of As by microbially-mediated reductive dissolution. Using high-resolution sequence-stratigraphic concepts, we document that the Late Pleistocene-Holocene lithofacies architecture dictates the subsurface distribution of As. The “wetland trajectory”, i.e. the path taken by the landward/seaward shift of peat-rich depositional environments during the Holocene, may help predict spatial patterns of natural As distribution, delineating the highest As-hazard zones and providing a realistic view of aquifer contamination even in unknown areas.

Risk to pollution of aquifers associated with productive activities and environmental management of water resources: bibliometric analysis and trends

Its analyzed the evolution and trends of the concept, and studies the models used to know the vulnerability and risk of aquifers and strategies for their management. The methodological process starts from questions guiding the knowledge of research trends, authors among others to proceed to carry out the analyses from the databases of Scopus, Web of Science and Dimensions. VOSviewer and Bibliometric (Rstudio) software were used. Among the most representative results, it was found that most of the research to determine the risk of aquifer contamination is focused on different models such as improved flux prototypes for NO2 emission from agriculture (IPNOA), pollutant origin surcharge hydraulically (POSH), intrinsic vulnerability methods ground water occurrence, overall aquifer class, depth to groundwater (GOD), depth recharge, aquifer, soil, topography, impact, hydraulic conductivity (DRASTIC), substance, infiltration, not saturated, type of coverage, topographic surface, conductivity (SINTACS) and chlorofluorocarbons (CFC) among others. Different models have been used that integrate both hydrological and hydro-geological aspects as well as social aspects including fundamental rights, other models such as the diffuse model, which has had better results in its application, the gaps in the research, are especially focused on conducting holistic research when assessing the risk of these dynamical systems.

Developing a safe water atlas for sustainable drinking water supply in Sonargaon Upazila, Bangladesh

Bangladesh has been relying heavily on groundwater for drinking and irrigation purposes since the 1960s. The access to safe drinking water has always been a challenge for Bangladesh due to the geogenic contamination in shallow aquifers. The objective of this study was to identify the depth for extracting safe water and to develop a safe water atlas for different unions of Sonargaon Upazila to ensure a year-round safe water supply. The concentrations of Arsenic, Iron and Manganese in groundwater were measured from 63 random water samples and compared with WHO and national drinking water quality standards. A lithological profile of the study area was developed to validate the indigenous knowledge of targeting safe depth based on sediment color. To address the challenges of groundwater depletion and contamination, the study identified and developed the technique of preparing safe water atlas for a specific region in Bangladesh, serving as a decision-making tool for households. The atlas identifies depths at which tube-wells can be installed to obtain uncontaminated groundwater, helping people make informed choices and avoid potential health risks. Additionally, the safe water atlas can support the development of safe drinking water distribution plans and assist local drillers and residents in decision-making processes.

Source identification and potential health risks from elevated groundwater nitrate contamination in Sundarbans coastal aquifers, India

In recent years groundwater contamination through nitrate contamination has increased rapidly in the managementof water research. In our study, fourteen nitrate conditioning factors were used, and multi-collinearity analysis is done. Among all variables, pH is crucial and ranked one, with a value of 0.77, which controls the nitrate concentration in the coastal aquifer in South 24 Parganas. The second important factor is Cl−, the value of which is 0.71. Other factors like—As, F−, EC and Mg2+ ranked third, fourth and fifth position, and their value are 0.69, 0.69, 0.67 and 0.55, respectively. Due to contaminated water, people of this district are suffering from several diseases like kidney damage (around 60%), liver (about 40%), low pressure due to salinity, fever, and headache. The applied method is for other regions to determine the nitrate concentration predictions and for the justifiable alterationof some management strategies.

Unveiling the inhibitory mechanisms of chromium exposure on microbial reductive dechlorination: Kinetics and microbial responses

Chromium and organochlorine solvents, particularly trichloroethene (TCE), are pervasive co-existing contaminants in subsurface aquifers due to their extensive industrial use and improper disposal practices. In this study, we investigated the microbial dechlorination kinetics under different TCE-Cr(Ⅲ/VI) composite pollution conditions and elucidated microbial response mechanisms based on community shift patterns and metagenomic analysis. Our results revealed that the reductive dechlorinating consortium had high resistance to Cr(III) but extreme sensitivity to Cr(VI) disturbance, resulting in a persistent inhibitory effect on subsequent dechlorination. Interestingly, the vinyl chloride-respiring organohalide-respiring bacteria (OHRB) was notably more susceptible to Cr(III/VI) exposure than the trichloroethene-respiring one, possibly due to inferior competition for growth substrates, such as electron donors. In terms of synergistic non-OHRB populations, Cr(III/VI) exposure had limited impacts on lactate fermentation but significantly interfered with H2-producing acetogenesis, leading to inhibited microbial dechlorination due to electron donor deficiencies. However, this inhibition can be effectively mitigated by the amendment of exogenous H2 supply. Furthermore, being the predominant OHRB, Dehalococcoides have inherent Cr(VI) resistance defects and collaborate with synergistic non-OHRB populations to achieve concurrent bio-detoxication of Cr(VI) and TCE. Our findings expand the understanding of the response patterns of different functional populations towards Cr(III/VI) stress, and provide valuable insights for the development of in situ bioremediation strategies for sites co-contaminated with chloroethene and chromium.

Delineation of Potential Groundwater Zones and Assessment of Their Vulnerability to Pollution from Cemeteries Using GIS and AHP Approaches Based on the DRASTIC Index and Specific DRASTIC

The risk of aquifer contamination is determined by the interaction between the pollutant load and the vulnerability of an aquifer. Owing to the decomposition of bodies and degradation of artefacts, cemeteries may have a negative impact on groundwater quality and suitability for use due to the leaching of organic compounds (e.g., biodegradable organics, pharmaceuticals, and formaldehyde), inorganic compounds (e.g., nitrate and heavy metals), pathogenic bacteria, and viruses. Factors such as burial and soil type, rainfall amount, and groundwater depth may increase aquifer vulnerability to pollutants generated in cemeteries. The potential for groundwater contamination was investigated in two cemeteries of the Soure region in Portugal (Samuel–UC9 and Vinha da Rainha–UC10), using the classic DRASTIC model, followed by some adjustments, depending on the particularities of the locations, resulting in a Final Classification considered as Specific DRASTIC. By combining Remote Sensing (RS), Geographic Information System (GIS), and Analytical Hierarchy Process (AHP), groundwater potential zones (GWPZs) were identified, and aquifer vulnerability was assessed, which included the elaboration of thematic maps using GIS operation tools. The maps allowed for the identification of areas with different susceptibilities to contamination: from “Low” to “Very high” for the DRASTIC index and from “Very Low” to “Very high” for the Specific DRASTIC index. Although the difference between the UC9 and UC10 cemeteries is negligible, UC10 is more vulnerable because of its proximity to the community and critically important mineral water resources (such as Bicanho Medical Spa). The Specific model seems better-suited for describing vulnerability to cemeteries. Although there is limited groundwater quality data for the area, the development of vulnerability maps can identify areas that can be sensitive spots for groundwater contamination and establish procedures for pollution prevention.

Using multivariate statistics to link major ion chemistry changes at karst springs to agriculture

Agricultural contamination is a pervasive problem in karst landscapes that negatively impacts groundwater quality, and subsequently harms hydraulically connected springs and associated ecosystems. While most research on agricultural contamination in karst aquifers has focused on nitrate, agricultural operations also alter major ion chemistry in groundwater, which can have significant implications on water rock interactions, geochemical interpretability, and enrichment of harmful contamination. Additionally, recent evidence has questioned the singular role of nutrient enrichment on aquatic ecosystem degradation, thus prompting further investigation into the broader extent of agricultural contamination for improved water quality restoration. In karst aquifers, quantifying the disruption of groundwater quality from agricultural contamination at springs can be challenging as major ions associated with agricultural contamination may be conflated with natural processes and interpretation further compounded by complex flow dynamics. These factors can render traditional statistical methods inadequate for identifying more comprehensive groundwater quality disruptions. To overcome these challenges, we use principal component analysis to classify the major ion covariance signature of agriculturally impaired and unimpaired groundwater and develop a new impairment metric to characterize the relative major ion impairment from agriculture to karst spring water quality. We apply our method to a primarily rural region in northern Florida whereby major ion chemistry has been changing over the last several decades. Our results identify a significant difference in major ion covariance structure between agriculturally impaired and unimpaired groundwater which is exploited to directly link major ion changes at karst springs to agriculture via relating a derived impairment metric to measured nitrate. Our newly developed method is easy to apply and can be used to identify more comprehensive contamination from pollutant sources and prioritize relative water quality restoration.

Aquifer contamination and efficiency of wastewater treatment plants in urban centers of Itapúa, Paraguay

La investigación analiza la calidad del agua subterránea y la eficacia del funcionamiento de dos plantas de tratamiento de efluentes domiciliarios en dos centros urbanos de Paraguay, así como la presencia de metales pesados en lodos residuales de ambas plantas de tratamiento. Para analizar la calidad del agua subterránea se recabaron datos de 59 muestreos de agua de 17 pozos profundos obtenidos en un periodo de 10 años entre el 2006 y el 2016. Para la evaluación del funcionamiento de las plantas de tratamiento se determinó la calidad de los efluentes luego del proceso de depuración. En los lodos generados en ambas plantas se analizó la presencia de metales pesados (Pb, Cr total, Cd y Hg). Los resultados obtenidos fueron contrastados con legislaciones nacionales e internacionales vigentes. Los datos cuantitativos fueron procesados estadísticamente mediante análisis de varianza y contraste de medias (Test de Duncan) con margen de error 5 %. Los principales resultados indican contaminación microbiológica del agua subterránea (acuífero Guaraní). Sin embargo, los parámetros físico-químicos analizados estaban dentro de los rangos establecidos por las normativas vigentes. Se identificó una inadecuada gestión en la planta de tratamiento de aguas residuales en uno de los centros urbanos (Hohenau). Se detectó presencia de Pb, Cr y Hg, a pesar de que las concentraciones se mantuvieron dentro de los rangos permisibles. Para salvaguardar la salud pública y el ambiente, tanto a nivel local como regional, es imperativo aplicar plenamente el marco legal y la implementación de la Gestión Integrada de los Recursos Hídricos.

Pyrrhotite-dependent microbial reduction and magnetic separation for efficient vanadium detoxification and recovery in contaminated aquifer

Microbial reduction under anaerobic condition is a promising method for remediating vanadate [V(V)] contamination in aquifers, while V(V) may be re-generated with redox fluctuations. The inability to remove vanadium after remediation has become a key issue limiting bioremediation. In this study, we proposed the use of pyrrhotite, a natural mineral with magnetic properties, to immobilize V(V) to insoluble V(IV) under microbial action and remove vanadium from the aquifer using a magnetic field, which could avoid the problem of V(V) recontamination under redox fluctuating conditions. Up to 49.0 ± 4.7 % of vanadium could be removed from the aquifer by the applied magnetic field, and the vanadium in the aquifer after the reaction was mainly in the acid-extractable and reducible states. pH had a strong effect on the magnetic recovery of V(V), while the influence of initial V(V) concentration was weak. Microbial community structure analysis showed that Thiobacillus, Proteiniphilum, Fermentimonas, and Desulfurivibrio played key roles for V(V) reduction and pyrrhotite oxidation. Structural equation model indicated the positive correlation between these genera with the magnetic recovery of vanadium. Real time-qPCR confirmed the roles of functional genes of V(V) reduction (napA and nirK) and SO42− reduction (dsrA) in such biological processes. This study provides a novel route to sustainable V(V) remediation in aquifers, with synchronous recovery of vanadium resources without rebound.

PERFORMANCE EVALUATION OF VERY LOW FREQUENCY (VLF) TECHNIQUES FOR AQUIFER CONTAMINATION ASSESSMENT

This study explores the efficacy of VLF techniques in mapping aquifer contamination. Conducted in Agbor, a city within Delta State, Nigeria, the study focuses on a contaminated aquifer of approximately 5 km² known for nitrate, petroleum hydrocarbon, and heavy metal contamination. The methodology involves VLF data collection using a Geonics EM-16 VLF receiver and transmitter, subsequent analysis using Geonics VLF2XYZ software, and comparison with traditional groundwater monitoring methods. The results indicated that VLF surveys effectively differentiate between contaminated and clean areas based on subsurface conductivity. The study demonstrates the cost-effectiveness and efficiency of VLF techniques compared to traditional methods, as VLF surveys cover larger areas in less time without drilling. Interpreting VLF resistivity maps reveals potential contamination areas, aiding in identifying contaminant sources and pathways. The validation framework assesses VLF techniques' accuracy, precision, sensitivity, and robustness, emphasizing the need for careful interpretation and validation with traditional methods. Implications for aquifer contamination assessment include mapping contamination extent, identifying new contamination areas, and monitoring remediation efforts. The study concludes that VLF techniques offer a promising and cost-effective method for aquifer contamination assessment. Recommendations include incorporating VLF techniques into site investigation programs, further research to optimize VLF technologies, site-specific investigations based on VLF survey results, and regular VLF surveys for ongoing monitoring and risk assessment. Overall, the findings contribute to alternative methods for aquifer contamination assessment, enhancing understanding and managing groundwater resources.

Human Health Risk Assessment of Heavy Metals and Nitrates Associated with Oral and Dermal Groundwater Exposure: The Poirino Plateau Case Study (NW Italy)

The Poirino Plateau (northwestern Italy) presents high contamination of the shallow aquifer due to intense agricultural practices and industrial activities. Many inhabitants have exploited shallow wells for personal purposes, coming into contact with contaminants. The aims of this study were to characterize groundwater contamination by heavy metals and nitrates, assess the noncarcinogenic and carcinogenic health risks for oral and dermal exposure in different receptor groups (children, adults, workers) and compare the noncarcinogenic and carcinogenic risk results with the regulatory limits and, therefore, if the actual regulatory limits are able to detect all potential situations of risk. For this purpose, 18 monitoring wells were collected in July 2022, and chemical–physical parameters and heavy metals were detected. The chemical data confirm a relevant anthropogenic contamination by nitrate and heavy metals. The estimated health risks are much higher in children, for oral exposure rather than dermal exposure for all the substances. The comparison between the results of the human health risk assessment and those in respect of threshold values confirms the existence of a transition condition. This condition, with concentrations below regulatory limits and above the noncarcinogenic or carcinogenic limits, reveals that the regulatory limits are not able to identify all the potential risk situations for the population.

Assessment of aquifer specific vulnerability to total nitrate contamination using ensemble learning and geochemical evidence

Henan Province's plain area is the granary of China, yet its regional aquifer is being polluted by industrial wastewater, agricultural pesticide, fertilizer and domestic wastewater. In order to safeguard the security of food and drinking water, and in response to the problem of low prediction accuracy caused by the lack of samples and unevenly distributed groundwater monitoring data, we propose a new way to predict the aquifer vulnerability in large areas by rich small-scale data, so as to identify the pollution risks and to address the issue of sample shortage. In small regions with abundant nitrate data, we employed a Random Forest model to screen key impact indicators, using them as features and nitrate-N concentration as the target variable. Consequently, we established six machine learning prediction models, and then selected the best bagging model (R2 = 0.86) to predict the vulnerability of aquifers in larger regions lacking nitrate data. The predicted results showed that highly vulnerable areas accounted for 20 %, which were mainly affected by aquifer thickness (65.91 %). High nitrate-N concentration implies serious aquifer contamination. Therefore, a long series of groundwater nitrate-N concentration monitoring data in a large scale, the trend and slope of nitrate-N concentration showed a significant correlation with the model prediction results (Spearman's correlation coefficients are 0.75 and 0.58). This study can help identify the risk of aquifer contamination, solve the problem of sample shortage in large areas, thus contributing to the security of food and drinking water.

Material flows as Earth politics: Concepts, methods, and approaches for transdisciplinary diagnostics and repair at Muizenberg East, Cape Town

Muizenberg East, in Cape Town, South Africa, is a peri-urban landscape that encompasses sewage works, tourist beaches, a nature reserve, a waste dump, a Ramsar site for the protection of migrating birds, shack settlements, and a corporate office park. The complex and contradictory uses of this land demonstrate the limitations of social-ecological analysis and ecosystem service approaches to environmental governance. Mapping contemporary struggles over food, housing, aquifer contamination, air pollution, conservation space, safety, and farmland, the study proposes that a new materialist approach combining emerging transdisciplinary fields that focus on material flows and metabolism offers a big-picture science for landscape diagnostics and repair. It is argued that the Earth processes such as metabolism, thermodynamics, and flow offer an integrative basis for environmental governance based on partnerships with Earth processes. Such a constitutional shift in approaches to local governance offers the possibility of amplifying habitability without inserting new modes of profit-taking into the web of life.

Combined effects of aquifer heterogeneity and subsurface dam on nitrate contamination in coastal aquifers

Subsurface dams are effective for seawater intrusion mitigation, yet they can cause upstream nitrate accumulation. This research examines the interplay between subsurface dam construction and aquifer layering on nitrate pollution in coastal settings, employing numerical models to simulate density-driven flow and reactive transport. The study reveals that while subsurface dams are adept at curbing seawater intrusion, they inadvertently broaden the nitrate accumulation zone, especially when a low-K layer is present. Heterogeneous aquifers see more pronounced nitrate accumulation from subsurface dams. This effect is pronounced as it influences dissolved organic carbon dynamics, with a notable retreat inland correlating with the expansion of the nitrate pollution plume. A critical finding is that controlling seawater intrusion via dam height adjustment within the Effective Damming Region effectively reduces nitrate levels and bolsters freshwater output. However, exceeding the critical threshold—where the dam surpasses the low-K layer's bottom—results in a substantial shift in nitrate concentration, underscoring the need for precise dam height calibration to avoid aggravating nitrate pollution. This study's innovative contribution lies in its quantification of the nuanced effects of subsurface dams in stratified aquifers, providing an empirical basis for dam design that considers the layered complexities of coastal aquifers. The insights offer a valuable framework for managing nitrate contamination, thus informing sustainable coastal groundwater management and protection strategies.

Application of Vertical Electrical Sounding Method Using Damped Least-Square Inversion for Leachate Identification at Bakung Landfill, Lampung

This paper has reviewed the application of the damped least square inversion method for the VES (vertical electrical sounding) with Schlumberger array. The damped least squares solved using singular value decomposition were applied in Bakung Landfill to determine the aquifer contaminated by leachate. The ability of damped Least Squares inversion algorithm were verified using the resistivity variation of synthetic model which simulates aquifer layer of subsurface. Based on the results of 1D resistivity model, low resistivity zone can be used to identify the existence leachate contaminants of aquifer.

Continuum model for extraction and retention in porous media

Several natural and industrial processes involve the extraction or retention of a solute by a fluid invading a network of channels. Examples include aquifer contamination, chemical filtration, and coffee extraction. We propose a continuum equation to model these processes, parametrized by the Péclet number and the rate of mass transfer between the solid and the fluid. We study the time dependence of the extracted mass for different values of the parameter space. The continuum description is validated by combining extraction experiments with coffee and computational fluid dynamics. An analytical solution is derived for the limit of slow mass transfer, which is corroborated by numerical simulations.

A parsimonious approach to predict regions affected by sewer-borne contaminants in urban aquifers

Leaky urban drainage networks (UDNs) exfiltrating wastewater can contaminate aquifers. Detailed knowledge on spatiotemporal distributions of water-dissolved, sewer-borne contaminants in groundwater is essential to protect urban aquifers and to optimize monitoring systems. We evaluated the effect of UDN layouts on the spreading of sewer-borne contaminants in groundwater using a parsimonious approach. Due to the UDN’s long-term leakage behavior and the existence of non-degradable sewer-borne contaminants (equivalent to a conservative and constant contaminant source), we employed a concept of horizontal line sources to mimic the UDN layout. This does not require the consideration of bio-degradation processes or temporal delay and effectively bypasses the vadose zone, thus reducing computational requirements associated with a full simulation of leakages. We used a set of synthetic leakage scenarios which were generated using fractals and are based on a real-world UDN layout. We investigated the effects of typical leakage rates, varying groundwater flow directions, and UDN’s layouts on the shape of the contaminant plume, disregarding the resulted concentration. Leakage rates showed minimal effects on the total covered plume area, whereas 89% of the variance of the plume’s geometry is explained by both the UDN’s layout (e.g., length and level of complexity) and groundwater flow direction. We demonstrated the potential of applying this approach to identify possible locations of groundwater observation wells using a real UDN layout. This straightforward and parsimonious method can serve as an initial step to strategically identify optimal monitoring systems locations within urban aquifers, and to improve sewer asset management at city scale.