Contamination Of Shallow Groundwater Research Articles

Investigating dominant factors of coliform contamination in shallow groundwater: A logistic regression and AHP approach

Shallow groundwater is a crucial source of clean water in developing countries like Indonesia. However, population growth has led to declining water quality due to inadequate infrastructure. This study aimed to identify dominant factors contributing to coliform contamination in shallow groundwater, addressing the lack of detailed statistical and multicriteria analyses in previous large-scale studies. The study was conducted in a densely populated urban area in Yogyakarta, Indonesia, and total coliform measurements from 42 groundwater samples were used as the independent variable. There are 14 dependent variables, categorized into three aspects: infrastructure (e.g., well type, well depth, wall of well, DEWATS type, well distance to the septic tank, latrine, and other contaminant sources); specific (e.g., population density and land use); and intrinsic (e.g., groundwater level, rainfall, soil type, and slope). Those parameters were statistically analyzed using logistic regression with IBM SPSS 26 software, and supported by the Analytical Hierarchy Process (AHP) that was employed using Expert Choice software to prioritize the factors. The results showed that 83.3% of the shallow groundwater samples exceeded the acceptable limits for total coliform, with key factors including well's proximity to other contamination sources, slope, distance from septic tanks, groundwater level, and population density. These findings highlight the importance of considering complex environmental factors in managing groundwater quality, particularly in developing countries. It is recommended that local authorities implement stricter regulations and infrastructure improvements to mitigate contamination risks.

Pollution evaluation and health risks assessment of naturally occurring toxic metals in shallow groundwater: A study in southwestern tidal delta of Bangladesh

Groundwater is the main source of potable water in rural regions of Bangladesh. Still, contamination with potentially harmful metals due to natural processes and anthropogenic activities leads to various health impacts. The focus of this research was to determine the extent of metal contamination in shallow groundwater from three southwestern districts of Bangladesh and the health hazards associated with it. A comprehensive analysis of metal, including metalloid, copper (Cu), aluminum (Al), chromium (Cr), Arsenic (As), Manganese (Mn), and boron (B) was performed on a set of 51 samples. Groundwater samples were analyzed for contamination using Atomic Absorption Spectroscopy and a UV–VIS Spectrophotometer, with pollution levels assessed via indices like the Metal Evaluation Index, Nemerow Pollution Index, and Contamination Index. Human health risks were evaluated through Chronic Daily Intake, Hazard Quotient, and Hazard Index calculations following USEPA guidelines. The results indicate that arsenic levels exceeded 25 samples and manganese levels exceeded 34 samples in accordance with WHO drinking water standards. Boron (B) concentrations exceeded the threshold in seven samples, whereas Al, Cu, and Cr exceeded limits in only two samples. The metal evaluation index (MEI), Nemerow pollution index (NI), and degree of contamination (Cd) revealed moderate to severe contamination in groundwater and unsuitability for drinking purposes. Out of the 51 analyzed samples, 48 samples exhibited potential non-carcinogenic health risks for adults, while all samples exceeded the hazard index (HI) threshold value (01) for children. Concentrations of As and Mn were identified as the main contributing factors to the higher HI values in both adults and children. However, the concentrations of Cu, Al, Cr, and B in groundwater were not individually found to be as risky. This study provided valuable insights to conduct a future comprehensive investigation of the designated region to delineate safe and hazardous zones for the installation of shallow tubewells. Furthermore, there's a need to enhance public awareness regarding the long-term ramifications of consuming contaminated water.

Pore-Scale Formation Characteristics of Impermeable Frozen Walls for Shallow Groundwater Contamination Remediation

Impermeability and water blocking are crucial for remediating shallow groundwater contamination. Traditional methods often employ curtain-grouting technology to create impermeable layers. However, cement slurry curing is irreversible, leading to permanent closure of underground aquifers and secondary pollution. This study employs an innovative approach by fabricating cylindrical models that simulate actual strata and utilizing a high-temperature and high-pressure displacement device. It systematically analyzes the variations in soil pore structure, distribution, porosity, and permeability under different temperatures, pressures, and freezing durations. The microscopic characteristics of the freezing process in water-bearing soils were studied. Results demonstrate that longer freezing time improves the effectiveness of soil freezing, reaching complete freezing at temperatures as low as −4 °C for samples with low water content. For water-saturated samples, freezing below −6 °C results in nearly zero porosity. Increased pressure at a certain freezing temperature significantly reduces permeability. When freezing temperature falls below −4 °C, water permeability in saturated samples after freezing reaches near-zero levels, while unsaturated samples experience complete freezing. These findings provide a theoretical foundation for constructing freezing curtains in remediating shallow groundwater pollution.

Recovery of ecosystems pollution by contaminants of potential concern using phytoremediation techniques.

Phytoremediation is a technology that uses plants to break down, remove, and immobilize contaminants in surface water, shallow groundwater, and sediment to achieve cost savings compared with conventional treatments. This study describes a marshy land on an explosives manufacturing site in India that consistently reported elevated concentrations of nitrates, nitrites, ammonia, perchlorate, and lead (contaminants of potential concern-CoPC). The study also illustrates the potential for addressing the human health and environmental risks associated with the explosives manufacturing industrsy in India using innovative, sustainable, and carbon-neutral techniques. This work focuses on reconstructed marshy lands, desedimentation, microwatershed management, and phytoremediation using Phragmites and Vetiveria species (also known as vetiver) to reduce contaminants in surface water and groundwater, improve stormwater management and carbon capture, and increase natural capital like biodiversity. The results obtained during the trial indicate that the selected indigenous species are effective and can be used to remediate sediment and shallow groundwater for many CoPC in tropical climates. Integr Environ Assess Manag 2024;20:1987-2002. © 2024 SETAC.

Responses of microbial communities subjected to hydrodynamically induced disturbances in an organic contaminated site

Organic contaminated sites have gained significant attention as a prominent contributor to shallow groundwater contamination. However, limited knowledge exists regarding the impact of hydrodynamic effects on microbially mediated contaminant degradation at such sites. In this study, we investigated the distribution characteristics and community structure of prokaryotic microorganisms at the selected site during both wet and dry seasons, with a particular focus on their environmental adaptations. The results revealed significant seasonal variations (P < 0.05) in the α-diversity of prokaryotes within groundwater. The dry season showed more exclusive OTUs than the wet season. The response of prokaryotic metabolism to organic pollution pressure in different seasons was explored by PICRUSt2, and enzymes associated with the degradation of organic pollutants were identified based on the predicted functions. The results showed that hormesis was considered as an adaptive response of microbial communities under pollution stress. In addition, structural equation models demonstrated that groundwater level fluctuations can, directly and indirectly, affect the abundance and diversity of prokaryotes through other factors such as oxidation reduction potential (ORP), dissolved oxygen (DO), and naphthalene (Nap). Overall, our findings imply that the taxonomic composition and functional properties of prokaryotes in groundwater in organic contaminated sites is influenced by the interaction between seasonal variations and characteristics of organic pollution. The results provide new insights into microbiological processes in groundwater systems in organic contaminated sites.

Analysis Distribution of Iron (Fe) and Hexavalent Chromium (Cr6+) Contaminants in Shallow Groundwater Due To Leachate Around Landfill Terjun, Medan City

Terjun Landfill Area is currently in a transition period from an open dumping system to a sanitary landfill. The resulting leachate can spread through infiltration into the soil. Leachate seepage into groundwater will affect groundwater quality. This research aims to analyze the distribution of iron (Fe) and hexavalent chromium (Cr6+) contaminants in shallow groundwater resulting from leachate around the Terjun Landfill Area. Model simulations were carried out using the Domenico Robbins (1990) model using the MathLab. The results show that the metal pollutants Fe and Cr6+ in residents’ wells have exceeded the quality standards in Minister of Health Regulation Number 2 of 2023. The results show that the pollutants Fe and Cr6+ have spread up to &gt; 700 m from the landfill. Fe contamination in the estimated 40 years since the landfill operated was spread over a distance of 750 meters with a pollutant concentration of 0.066 mg/L, and in 50 years it increased to 0.092 mg/L. Meanwhile Cr6+ contamination over a period of 40 years at a distance of 750 meters spread with a concentration of 0.426 mg/L and increased in the 50th year by 0.600 mg/L.

Hydrogeochemical processes and nitrate contamination of shallow groundwater in the Gareb-Bouareg region, northeastern Morocco

In semiarid regions, groundwater faces considerable challenges due to both natural and human-induced contaminants, including nitrate contamination. These issues impact the availability of groundwater, a vital resource. Therefore, it is crucial to identify the sources and mechanisms contributing to salinization and nitrate contamination. In this study, we examined the hydrogeochemical characteristics of shallow groundwater in the Gareb-Bouareg region, northeast Morocco. The aim was to determine and understand the key processes that govern its chemical composition and assess nitrate contamination. A total of 50 groundwater samples were collected from existing wells and analysed for major cation and anion concentrations. The results showed that the dissolution of evaporite minerals, cation exchange and evaporation are the predominant processes of groundwater mineralization. In 72% of the samples, nitrate concentrations surpassed the anthropogenic origin threshold value of 10 mg/L, while 16% of the samples exceeded the drinking water standard of 50 mg/L. The highest values were found in the rural and urban areas, at 122 mg/L and 84.24 mg/L, respectively. Nitrate levels and the depth to the water table reveal the impacts of surface contamination sources. The spatial distribution and interrelationship between nitrate and other parameters suggest possible distinct origins of dissolved nitrates associated with various anthropogenic activities.

Characterization of subsurface pathways contributing to freshwater salinization of urban streams using electrical and electromagnetic imaging techniques

Salinization of inland fresh surface waters in temperate climates is a growing concern due to increasing salt inputs from sources including chloride (Cl)-containing road salt de-icers, industrial waste, and landfill leachate. Groundwater pathways play an important role in the year-round delivery of Cl to streams, but quantifying this pathway, including spatiotemporal variability and amount of Cl mass stored in the subsurface, is challenging. The objective of this study was to demonstrate, evaluate, and compare the potential applications of the geoelectrical techniques – electromagnetics (EM) and direct current (DC) resistivity – for mapping salt contamination in shallow urban groundwater and characterizing the groundwater pathways delivering Cl to urban streams. EM and DC surveys were conducted (3D mapping and 2D time-lapse) across a 20 m salt-impacted stream section and surrounding riparian zone that is located near an arterial road and parking lot. Groundwater samples and soil cores were also collected to validate the geoelectrical results. Both the EM and DC surveys detected high salt concentrations in the shallow subsurface (up to 3 m depth) near the road, parking lot, and stream; however, DC more accurately represented groundwater Cl concentrations. DC results were used to calculate the total Cl mass in the subsurface, with the spatial mass distribution used to infer the temporal variability in the subsurface salt plume. Finally, time-lapse DC showed that the highest groundwater salt concentrations existed near the stream between June and October – this is expected to contribute to the elevated salt concentrations in the stream during summer months. This study has shown that EM and DC can be useful for identifying groundwater salt concentration, storage, and transport in a non-intrusive and efficient manner, making them valuable field tools for characterizing and quantifying groundwater salt pathways to urban streams.

Hydrochemical Characteristics and Nitrate-Nitrogen Contamination in Shallow Groundwater in Two Agricultural areas in Korea

Hydrochemical Characteristics and Nitrate-Nitrogen Contamination in Shallow Groundwater in Two Agricultural areas in Korea

Heavy Metal Transport in Different Drip-Irrigated Soil Types with Potato Crop

Heavy metal (HM)-polluted soil is a serious concern, especially as brackish water is widely used for irrigation purposes in water-scarce countries. In this study, the HYDRUS-2D model was used to simulate HM (copper (Cu), lead (Pb), and zinc (Zn)) transport through agricultural land cultivated with potato crops under surface drip irrigation to explore the potential groundwater contamination risk. Three soil types, namely, silty clay loam, sandy loam, and sandy soil, and two irrigation schemes, irrigation every two days (scheme A) and irrigation every four days (scheme B), were considered during the simulations. Firstly, the ability of HYDRUS-2D to simulate water flow was validated using data obtained from a full growing season of the potato crop in a lysimeter irrigated by surface drip irrigation using El-Salam Canal water, Egypt (i.e., water contaminated by HMs). Secondly, the model was calibrated for solute transport parameters. After that, the investigated simulation scenarios were executed. The results showed that HYDRUS-2D effectively simulated water flow. Moreover, a good agreement between the simulations and experimental results of HM concentrations under the calibrated solute parameters was obtained with R2 values of 0.99, 0.91, and 0.71 for Cu, Pb, and Zn concentrations, respectively. HM distribution is considerably influenced by the HMs’ adsorption isotherm. The results of the investigated scenarios reveal that soil texture has a greater impact on HM concentrations in the simulation domain and on the contamination risk of the groundwater than the irrigation scheme. Under both irrigation schemes, lower HM concentrations were observed in sand, while higher values were observed in silty clay loam. Subsequently, the potential shallow groundwater contamination risk is greater when cultivating potatoes in sand, as higher HM concentrations were found in drainage water compared to the two other investigated soils, regardless of the irrigation scheme. The cumulative Cu, Pb, and Zn concentrations in drainage water corresponding to scheme A for silty clay loam and sandy loam were 1.65, 1.67, and 1.67 and 1.15, 1.14, and 1.15 times higher, respectively, than scheme B. To safeguard the sustainability of groundwater and agricultural lands irrigated with water contaminated by HMs, it is recommended to adopt an irrigation frequency of once every four days in soils with silty clay loam and sandy loam textures.

Simulation study of oxytetracycline contamination remediation in groundwater circulation wells enhanced by nano-calcium peroxide and ozone

The widespread use of antibiotics in recent years has led to increasing antibiotic contamination of shallow groundwater. As the most widely used tetracycline antibiotic, oxytetracycline has received a lot of attention from researchers due to its stable molecular structure and difficulty in degradation. Aiming at remediation of oxytetracycline pollution in shallow groundwater, nano-calcium peroxide (nCaO2) and ozone (O3) are used to enhance the degradation of oxytetracycline in groundwater circulation well (GCW). A three-dimensional sand box test device for circulation wells is designed to explore the repair efficiency of circulation wells strengthened by different oxidants. The results show that after nCaO2 and O3 enhancing circulation wells operate for 10 h, the average removal rate of OTC reaches 83%, and the highest removal rate is 88.13%, which is 79.23% and 13.96% respectively higher than that of nCaO2 and O3 enhanced circulation wells alone, and there is no rebound phenomenon after aeration stops. The in-situ treatment of enhanced GCW by nCaO2 and O3 has potential applications for the removal of OTC in groundwater environments.

Hydro-Chemical Studies and Assessment of Trace Elements and Bacterial Contamination of Shallow Groundwater of Oyo Area, Southwestern Nigeria

Groundwater from shallow hand-dug wells is the only reliable source of water supply in the ancient town of Oyo in the southwestern region of Nigeria. The present work studied the water quality in twenty-five wells across this area by measuring the ancillary parameters, and analyzing the major and trace elements and taking the inventory of the wells as well as assessing the total coliform and Escherichia coliform in sampled water. The field measurement showed that the groundwater is slightly acidic with an average pH of 6.6 and fresh from the total dissolved solids values between 70 and 630 mg/L. From the average concentrations of major ions, the dominance order of the cations constituents in groundwater is in the order- Mg 2+ &gt; Ca 2+ &gt; K + &gt; Na + and HCO - &gt; CI - &gt; NO 3 - &gt; SO 4 2- for anions. The ranges of trace elements concentrations were; Iron II- 0.01 – 0.06; Chromium VI: 0 - 0.34; manganese 0 – 1.2 in mg/L, while Copper was between 0.38 – 32.7; Cadmium 0.03 – 1.87; lead 0.02 – 3.57; Zinc 0.01 – 7.79; and Arsenic 0.05 – 7.35 in µg/L. The total coliform count ranges from 6 – 1860 cfu/100 mL while Escherichia coliform (E. coli) units was between 2 and 1640 cfu/100 mL with frequency occurrence from nil in three wells representing 12% of the wells, 1 – 50 units (28%), 51 – 100 (20%), 101 – 500 (20%) and &gt; 500 units (20%). The groundwater is grossly contaminated with nitrate and coliform bacteria while four wells were found to be contaminated with manganese and chromium. It is mandatory that the water be treated for metal and bacterial contaminations prior to consumption and public enlightenment on drinking water guidelines be in place. Keywords : Groundwater. Major ions. Trace elements. Coliform Bacteria. DOI: 10.7176/JEES/13-3-02 Publication date: April 30 th 2023

Sensitivity Assessment of Boron Isotope as Indicator of Contaminated Groundwater for Hydraulic Fracturing Flowback Fluids Produced from the Dameigou Shale of the Northern Qaidam Basin

Hydrogeochemical processes occurring in contaminated groundwater and aquifer systems may reduce the sensitivity of boron isotopes as an indicator of hydraulic fracturing flowback fluids (HFFF) in groundwater. In this paper, based on the Chaiye-1 well (the first continental shale gas well in the northern Qaidam Basin), the hydrogeochemical processes affecting boron isotopes were analyzed in HFFF-contaminated Neogene (NG1 and NG2) and Quaternary (QG1) groundwater around the shale gas field. Then, a model for boron isotopes in HFFF-contaminated groundwater was constructed to assess the sensitivity of boron isotopes as an HFFF indicator. The results show that, limited by the range of pH values and saturation indices (SI) in HFFF-contaminated groundwater, the dissolution of alkali feldspar and precipitation of carbonate have little effect on the boron isotopes in shallow groundwater. For the NG2 aquifer system containing clay minerals, the δ11B of simulated contaminated groundwater (40.0–55.6‰) is always higher than that of the corresponding groundwater mixed conservatively (−6.4–55.6‰) due to preferential adsorption of boron isotopes onto clay minerals, indicating preferential adsorption would reduce the sensitivity of boron isotopes as an indicator of groundwater contamination from HFFF. For the scenario of HFFF contamination, when the mixing ratio of HFFF in contaminated groundwater increases by 5%, boron isotopes in Neogene (NG1 and NG2) and Quaternary (QG1) groundwater have detectable responses to HFFF contamination, suggesting δ11B is a sensitive indicator of HFFF contamination in shallow groundwater from the Dameigou Shale in the northern Qaidam Basin.

Assessment of Groundwater Decontamination Processes around a Dismantled Septic Tank Using GIS and Statistical Analysis

Septic tanks without proper construction and insulation entail a significant risk to the environment. In this study, the environmental impacts of a permeably designed septic tank on shallow groundwater contamination are investigated, and changes in water quality in the period after its elimination in 2014 are assessed. For the purpose of evaluating the pollution level of the site, 10 monitoring wells were installed around the septic tank in 2012 and long-term monitoring was carried out. Analytical measurements revealed a significant level of groundwater contamination in the operational period of the septic tank. Extremely high concentrations of NH4+ (&gt;90 mg/L) were observed in the closest monitoring wells, and in most of the wells, concentrations exceeded the relevant contamination limit. δD and δ18O isotopic ratios of monitoring wells within 1 m from the septic tank indicate continuous recharge of sewage water originating from deeper aquifers. The groundwater dome resulting from the wastewater discharge exceeded 1.1 m, within a distance of 25 m. Statistical analyses also revealed significant changes in water quality depending on the monitoring well location from the septic tank. In the period after the septic tank elimination, considerable changes have been detected. Following the cessation of the wastewater discharge, the groundwater dome around the septic tank disappeared; therefore, differences in groundwater levels have decreased from more than 1 m to a few cm. Significant positive changes were detected in the water quality parameters investigated after the dismantling of the septic tank. Five years after the cessation of the pollutant supply, concentrations still exceeded the contamination limit in most of the monitoring wells, indicating slow decontamination processes with a permanently high level of pollution.

Watershed-Scale Shallow Groundwater Anthropogenic Nitrate Source, Loading, and Contamination Assessment in a Typical Wheat Production Region: Case Study in Yiluo River Watershed, Middle of China

Nitrate pollution in groundwater has become a global concern for agriculture and regional ecology. However, tracing the spatiotemporal groundwater nitrate pollution sources, calculating the total nitrogen loading, and assessing contamination at the watershed scale have not been well documented. In this study, 20 groundwater samplings from 2020 to 2021 (in dry and wet seasons) on the Yiluo River watershed in middle China were collected. Tracing groundwater nitrate pollution sources, calculating total nitrogen loading, and assessing contamination using dual isotopes (18ONO3 and 15NNO3), conservation of mass, and the nitrate pollution index (NPI), respectively. The results indicated that there were three nitrate sources in groundwater: (1) manure and sewage waste input (MSWI), (2) sediment nitrogen input (SNI), and (3) agriculture chemical fertilizer input (ACFI) in the Yiluo River watershed. ACFI and SNI were the main groundwater nitrogen pollution sources. The average nitrogen loading percentages of ACFI, SNI, and MSWI in the whole watershed were 94.7%, 4.34%, and 0.96%, respectively. The total nitrogen loading in the Yiluo River watershed was 7,256,835.99 kg/year, 4,084,870.09 kg/year in downstream areas, 2,121,938.93 kg/year in midstream areas, and 1,050,026.95 kg/year in upstream areas. Sixty percent of groundwater in the Yiluo River watershed has been polluted by nitrate. Nitrate pollution in midstream areas is more severe. Nitrite pollution was more serious in the wet season than in the dry season. The results of this study can provide useful information for watershed-scale groundwater nitrogen pollution control and treatment.

Characterizing shallow groundwater contamination depending on different land use types

Characterizing shallow groundwater contamination depending on different land use types

Assessment of shallow groundwater contamination on Pari Island, Indonesia.

Freshwater on small islands is generally limited and relies on rainwater and groundwater. This study aimed to assess changes in shallow groundwater quality on Pari Island, Indonesia. Pari Island is a small island with an area of 41.32 ha and belongs to a monsoon climate. Also, being a residential island, it attracts many tourists. The approach was to assess the shallow groundwater quality of ten wells during the dry and wet seasons. Changes in water quality were evaluated using traditional hydrochemical analysis methods (Schoeller, Piper, and Gibbs diagrams) and ion ratios. Shallow groundwater quality in the study area showed different responses depending on the season. Therefore, each well responded differently to changes represented by changes in water quality. The change is controlled by various factors: evaporation (or water balance), geology, aquifer characteristics, tides, wind direction, and wave height. These factors trigger the fluctuation of groundwater and seawater interface, affecting the amount of rainwater and seawater transported to the freshwater aquifer layer. This water volume transported affects the process of rock weathering, dissolution, and dilution of contaminants in shallow groundwater.

Source identification and health risks of nitrate contamination in shallow groundwater: a case study in Subei Lake basin.

Nitrate pollution of groundwater has become a global concern as it can affect drinking water quality and human health. In this paper, an extensive hydrochemical investigation was performed to assess the spatial distribution, source identification, and health risk of groundwater nitrate pollution in the Subei Lake basin. The prevalent pollutant, nitrate (NO3-), was identified based on descriptive statistical method and box plots, and most of the other parameters of groundwater samples met water standards and can be used for drinking purpose. The results showed that nearly 23.53% of groundwater samples displays the NO3- concentrations higher than the limit of 50 mg/L recommended by the World Health Organization, and the highest nitrate content (199 mg/L) is mainly distributed around the Mukai Lake. Piper triangle diagram demonstrated that the dominated anions of hydrochemical types exhibit a gradual evolving trend from HCO3- to SO42- and Cl- with increasing nitrate concentration. The correspondence analysis suggested that agricultural activities are identified as the most possible source of nitrate contamination, while the higher content of other parameters in individual groundwater samples may be controlled by natural factors. The impacts of pollutant NO3- on human health were quantified using human health risk assessment method, and results showed that the order of non-carcinogenic health risk values through drinking water intake is Infants>Children>Adult males>Adult females, and 65%, 53%, 41%, and 35% of samples exceed the acceptable risk level (hazard quotient=1), respectively. The main findings obtained from this study can provide valuable insight on drinking water safety and groundwater pollution prevention.

Assessment of Ammonium–N and Nitrate–N Contamination of Shallow Groundwater in a Complex Agricultural Region, Central Western Taiwan

The characteristics of nitrogen contamination of shallow groundwater were evaluated through current status analysis and trend detection of ammonium–N and nitrate–N concentrations under various cropping patterns to assess the effectiveness of rational fertilization in the Choushui River alluvial fan, central Western Taiwan. The influence of cropping patterns on both ammonium–N and nitrate–N contamination associated with redox conditions/dissolved oxygen (DO) in shallow groundwater was also discussed in this study. The analysis revealed that shallow groundwater beneath double rice cropping and rotational cropping regions is still characterized by high ammonium–N concentration despite rational fertilization promotion. However, very few monitoring wells showed an upward trend of ammonium–N/nitrate–N concentrations, indicating that shallow groundwater is not further deteriorated by nitrogen pollution in most parts of the study area. Therefore, the remediation of nitrogen contaminated groundwater will be a long-term process and more effort must be invested. Moreover, the strict redox conditions defined by a single DO threshold value may not account for groundwater nitrogen pollution in the study area. It is difficult to determine the redox conditions and predominant nitrogen pollution patterns of shallow groundwater purely from cropping patterns. Instead, contamination may have resulted from an integrated process governed by several other factors. Tracing the potential sources of nitrogen pollution and establishing a more integral monitoring network should be implemented to formulate a more comprehensive nitrogen pollution control strategy in this area.

A Resilient and Nature-Based Drinking Water Supply Source for Saline and Arsenic Prone Coastal Aquifers of the Bengal Delta

Salinity causes a hostile environmental impact throughout the year in the coastal region of Bangladesh, and its severity increases day by day. Because of upstream freshwater flow reduction and massive groundwater extraction, salinity has increased substantially over the last three decades. Moreover, arsenic contamination in shallow groundwater makes the groundwater unsuitable for potable use. Consequently, the coastal area suffers from acute storage of safe water supply. Salinity also negatively impacts human activities, livelihood, agricultural production, and the aquatic ecosystem. Though the shallow aquifer contains high salinity and a small amount of Arsenic (As), the very shallow aquifer (within 3m to 8m) contains fresh water in many areas in the rainy season due to the direct recharge of rainwater. However, rainfall recharge varies significantly depending on the geological and hydrogeological settings. Specifically, up to 50% of annual rainfall is stored in shallow aquifers of Quaternary sands through direct infiltration. The research’s principal objective is to identify the safe and sustainable drinking water source in the arsenic and saline-prone coastal region. Groundwater samples were collected from the different locations of the study area during both dry and wet seasons and examined seasonal variations in groundwater table and salinity levels. The chemical analyses and Physico-chemical parameters indicate that the groundwater samples are suitable for drinking. Except for some groundwater samples from the wet season, the salinity of all samples was under the allowable limit for Bangladesh (&lt;2000 µS/cm), and the targeted aquifer was almost arsenic (50 µg/l) free. Therefore, a comprehensive analysis has been made to accomplish the study goals. Particularly, the groundwater’s electrical conductivity (EC) values of most samples were measured within the limit of fresh or brackish water (&lt;2000 μS/cm). Overall, the results indicate the prospect of a very shallow aquifer as a source of freshwater for drinking purposes throughout the year, considering both arsenic and salinity, which effectively solve the freshwater shortage, especially in the saline-arsenic prone area.