Aquifer Material Research Articles

Hydrogeochemical framework of groundwater within the Asutifi-North District of the Brong-Ahafo Region, Ghana

Hydrogeochemical processes responsible for groundwater composition within the Asutifi-North district were assessed. The aim was to delineate the factors influencing groundwater within the district. Results show that the pH values of groundwater within the district are moderately acidic to neutral and ranged from 4.4 to 7.5 with a mean value and standard deviation of 6.1 ± 0.7 pH units. 67.4% of groundwater is acidic (pH 4–6.5) due principally to the influence of aquifer materials on the chemistry of groundwater. Acid mine drainage investigations in groundwater within the district shows that, when exposed, sulphides such as pyrites (FeS2) and arsenopyrite (FeAsS) react with water and oxygen to principally produce Fe(OH)3. The major ion concentrations are within the WHO (2004) Guideline values for drinking water. The relative abundance of cations and anions in groundwater within the district is in the order of: Ca2+ > Na+ > Mg2+ > K+ and HCO3− > Cl− > SO42−, respectively. The study further shows that, albite/anorthite-(plagioclase) and calcite/dolomite(carbonates) dissolution as well as ion-exchange reactions may have contributed significantly to major ion concentrations in groundwater within the district. Hydrochemical facies using Piper trillinear diagrams delineated two major water types, the Ca–Mg–HCO3 and Na–Cl water types, with Ca–Mg–Cl, Ca–Mg–SO4–Cl and Na–K–HCO3 as minor water types. Using principal component analysis (PCA), three (3) main principal components accounting for 73.1% of the total variance with eigenvalues > 1 were extracted. PCA delineated the main natural processes through which groundwater within the district acquires its chemical characteristics, the incongruent dissolution of silicate/aluminosilicates and the prevalence of pollution principally from the application of inorganic fertilizers such as nitrates and ammonia via agricultural activities within the district.

Spatiotemporal Variation of Groundwater Recharge in the Lower Reaches of the Poyang Lake Basin, China: Insights From Stable Hydrogen and Oxygen Isotopes

AbstractUnderstanding of groundwater recharge and associated hydrological processes is important for sustainable management and utilization of water resources, especially in the monsoon regions. However, few systematic studies have been conducted on the spatiotemporal variation of groundwater recharge. In this study, stable isotopes of precipitation and groundwater were used to explore the spatiotemporal variation of groundwater recharge in the lower reaches of the Poyang Lake Basin of China, a region affected by the interplay of different monsoons. The results indicated that isotopic values (δ2H and δ18O) of precipitation exhibited obvious seasonal variations, higher in winter and lower in summer, controlled by different monsoons. The stable isotopes of groundwater also presented distinct seasonal variations, revealing the dominant influence of seasonal precipitation, but they had different characteristics in space. In the northern study area and Rao and Xin Basins, the isotopic signatures of groundwater showed the shift to lower values in summer and higher values in winter, consistent with those of precipitation, while in the Ganfu Plain, which is characterized by poorly permeable strata, isotopic signatures of groundwater presented opposite temporal variations than those of precipitation (lagged behind precipitation). The characteristics of groundwater isotopes might be linked with the spatial heterogeneity of groundwater recharge rate, which was affected by recharge mechanisms, lithology of aquifer materials, and interaction between groundwater and lake water. This study provides insights into the groundwater recharge of the Poyang Lake Basin and other similar areas.

Mechanisms of irreversible density modification using colloidal biliquid aphron for dense nonaqueous phase liquids in contaminated aquifer remediation

The use of colloidal biliquid aphron (CBLA) as density modifier to reduce the density of dense nonaqueous phase liquids (DNAPLs) irreversibly is an efficient strategy to control the migration of DNAPLs in contaminated aquifers. However, the process and mechanism of the density regulation using CBLA is still not clear and there is still a big gap in the application of CBLA in actual contaminated sites. In this study, we carried out density modification of 5 DNAPLs (nitrobenzene (NB), dichloromethane (DCM), trichloroethylene (TCE), carbon tetrachloride (CTC), perchloroethylene (PCE)) using CBLA and studied the effect of co-existing ions by 3D response surface method. We found that DNAPLs changed to light nonaqueous phase liquids (LNAPLs) and float up after interaction with light organic liquid from CBLA. The density modification process is limited by the demulsificaiton of CBLA and the density of DNAPL itself. Density regulation of DNAPLs followed pseudo-second-order kinetics. The co-existing ions affected the stability of CBLA and the demulsification ability of the demulsifier. Aquifer materials and low temperature did not influence the density control effect of CBLA. This research advances the practical application of density control of DNAPLs using CBLA, and makes important contributions for subsequent combined remediation approach.

Assessment of Subsurface Condition of Peat Soil due to Brackish Groundwater Seepage

The purpose of this assessment is to assess the subsurface condition of peat soil due to brackish groundwater seepage along drainages using a numerical method. Visual MODFLOW is applied to conceptualize a condition in the study area and to produce outcomes related to the objectives of the study. The results of the simulation show there is only a small portion of high salt concentration along the drainage. The migration of salt concentration is mostly affected by the groundwater head and velocity vectors of the aquifer materials. Meanwhile, most of the other places in the study area receive a low salt concentration. Therefore, the impact of brackish groundwater on the environment is not significant since the salt concentration is low in most of the study area.

Application of DRASTIC and Modified DRASTIC Models for Modeling Groundwater Vulnerability of Malda District in West Bengal

Groundwater is one of the most important freshwater resources in our daily life. Under the background of global climate change, untreated rate of urbanization, human interferences and policy variations affect the change of global and local groundwater quality which is very common in developing countries like India. Hence, protecting groundwater from different types of contamination is the most accurate and appropriate measures of groundwater conservation. The main objectives of this work are to assess the groundwater vulnerability of Malda district using DRASTIC and modified DRASTIC methods. Seven influencing factors groundwater depth, net recharge, aquifer material, soil media, topography, the impact of vadose zone and hydraulic conductivity were used to complete DRASTIC method, agricultural DRASTIC, land use DRASTIC and AHP land use DRASTIC methods. The multi-model approach has been used to identify the best vulnerability model. For modeling Land use DRASTIC and AHP Land use DRASTIC, the land use layer was added with other layers. The groundwater vulnerability zone has been divided into three categories like high, moderate and low. High-vulnerability zones were found in the northern and southern parts, moderate zones were found in the middle part of the district, and the low-vulnerability zones in the eastern part of the district. The vulnerability model was validated using the ROC curve and Friedman test. The AHP land use DRASTIC shows better performance compared to other vulnerability models.

Groundwater development leads to decreasing arsenic concentrations in the San Joaquin Valley, California

In the San Joaquin Valley (SJV), California, about 10% of drinking water wells since 2010 had arsenic concentrations above the US maximum contaminant level of 10 μg/L. High concentrations of arsenic are often associated with high pH (greater than 7.8) or reduced geochemical conditions. Although most wells have low arsenic (<3 μg/L) and do not have changing arsenic concentrations, this study found that most wells with concentrations above 10 μg/L had arsenic trends. Overall, about 24% of wells had time-series trends since 2010 and 59% had paired-sample trends since 2000. Most wells had decreasing arsenic trends, even in wells with higher arsenic concentrations. These wells often had co-detections of increasing nitrate and sulfate trends that reflect oxic groundwater likely derived from agricultural recharge. Wells with increasing arsenic trends were deeper or located in the valley trough where aquifer materials are more fine-grained and where reducing conditions favor arsenic mobility. Wells with arsenic trends also tend to be clustered near areas of higher well density. Groundwater pumping in these areas has likely increased the contribution of younger, more oxic groundwater in wells with declining arsenic or, less frequently, increased the contribution of higher pH or reduced groundwater in wells with rising arsenic. Projections of arsenic trends indicate that 37 wells with high arsenic presently will be below 10 μg/L in ten years. Unfortunately, these improvements will be largely offset by 31 wells that are expected to increase above 10 μg/L in addition to expected rises in nitrate in wells where arsenic decreased. This study shows how human-altered flow systems can impact the natural geochemical character of water in both beneficial and deleterious ways.

Exploration of processes governing microbial reductive dechlorination in a heterogeneous aquifer flow cell

Although microbial reductive dechlorination (MRD) has proven to be an effective approach for in situ treatment of chlorinated ethenes, field implementation of this technology is complicated by many factors, including subsurface heterogeneity, electron donor availability, and distribution of microbial populations. This work presents a coupled experimental and mathematical modeling study designed to explore the influence of heterogeneity on MRD and to assess the suitability of microcosm-derived rate parameters for modeling complex heterogeneous systems. A Monod-based model is applied to simulate a bioremediation experiment conducted in a laboratory-scale aquifer cell packed with aquifer material from the Commerce Street Superfund site in Williston, VT. Results reveal that (uncalibrated) model application of microcosm-derived dechlorination and microbial growth rates for transformation of trichloroethene (TCE), cis-1,2-dichloroethene (cis-DCE), and vinyl chloride (VC) reproduced observed aquifer cell concentration levels and trends. Mean relative errors between predicted and measured effluent concentrations were quantified as 6.7%, 27.0%, 41.5%, 32.0% and 21.6% over time for TCE, cis-DCE, VC, ethene and total volatile fatty acids (fermentable electron donor substrate and carbon source), respectively. The time-averaged extent of MRD (i.e., ethene formation) was well-predicted (4% underprediction), with modeled MRD exhibiting increased deviation from measured values under electron donor limiting conditions (maximum discrepancy of 14%). In contrast, simulations employing a homogeneous (uniform flow) domain resulted in underprediction of MRD extent by an average of 13%, with a maximum discrepancy of 45%. Model sensitivity analysis suggested that trace amounts of natural dissolved organic carbon served as an important fermentable substrate, providing up to 69% of the reducing equivalents consumed for MRD under donor-limiting conditions. Aquifer cell port concentration data and model simulations revealed that ethene formation varied spatially within the domain and was associated with regions of longer residence times. These results demonstrate the strong influence of subsurface heterogeneity on the accuracy of MRD predictions, and highlight the importance of subsurface characterization and the incorporation of flow field uncertainty in model applications for successful design and assessment of in situ bioremediation.

Dechloromonas and close relatives prevail during hydrogenotrophic denitrification in stimulated microcosms with oxic aquifer material.

Globally occurring nitrate pollution in groundwater is harming the environment and human health. In situ hydrogen addition to stimulate denitrification has been proposed as a remediation strategy. However, observed nitrite accumulation and incomplete denitrification are severe drawbacks that possibly stem from the specific microbial community composition. We set up a microcosm experiment comprising sediment and groundwater from a nitrate polluted oxic oligotrophic aquifer. After the microcosms were sparged with hydrogen gas, samples were taken regularly within 122h for nitrate and nitrite measurements, community composition analysis via 16S rRNA gene amplicon sequencing and gene and transcript quantification via qPCR of reductase genes essential for complete denitrification. The highest nitrate reduction rates and greatest increase in bacterial abundance coincided with a 15.3-fold increase in relative abundance of Rhodocyclaceae, specifically six ASVs that are closely related to the genus Dechloromonas. The denitrification reductase genes napA, nirS and clade I nosZ also increased significantly over the observation period. We conclude that taxa of the genus Dechloromonas are the prevailing hydrogenotrophic denitrifiers in this nitrate polluted aquifer and the ability of hydrogenotrophic denitrification under the given conditions is species-specific.

The influence of aquifer material to the groundwater potency in Ngawi Regency

Until now, groundwater is still the main source of water for domestic needs. Unfortunately not all places can contain groundwater. Groundwater potential in an area is largely determined by the rock layers that make up the aquifer in the area. This study aims to analyze the hydrogeological conditions of the study area and to analyze the potential for groundwater in each geological unit. To achieve this goal, this study is based on the analysis of existing secondary data, such as rock type data obtained from drill data and geological maps. Apart from these data, the main secondary data from this research is geosonar measurement data that has been done previously. In this geosonar estimation, VLF (Very Low Frequency) electromagnetic technology is used, which is a geophysical method that uses very low radio communication frequency signals (15-30 kHz) to determine the anomalies of the electrical properties of rocks. The results showed that hydrogeologically, Ngawi Regency can be divided into two, namely areas with high groundwater potency in the central and southern parts and areas with rare groundwater in the northern part. In addition, it is also known that there is a relationship between the aquifer material and the groundwater potency. Alluvial deposits which are dominated by sand and gravel have high groundwater potency, while the Kalibeng Formation which is composed of solid marl and Anggota Banyak Kalibeng Formation composed of andesite breccias is a scarce groundwater area.

Machine Learning Predictions of pH in the Glacial Aquifer System, Northern USA.

A boosted regression tree model was developed to predict pH conditions in three dimensions throughout the glacial aquifer system of the contiguous United States using pH measurements in samples from 18,386 wells and predictor variables that represent aspects of the hydrogeologic setting. Model results indicate that the carbonate content of soils and aquifer materials strongly controls pH and, when coupled with long flowpaths, results in the most alkaline conditions. Conversely, in areas where glacial sediments are thin and carbonate‐poor, pH conditions remain acidic. At depths typical of drinking‐water supplies, predicted pH >7.5—which is associated with arsenic mobilization—occurs more frequently than predicted pH <6—which is associated with water corrosivity and the mobilization of other trace elements. A novel aspect of this model was the inclusion of numerically based estimates of groundwater flow characteristics (age and flowpath length) as predictor variables. The sensitivity of pH predictions to these variables was consistent with hydrologic understanding of groundwater flow systems and the geochemical evolution of groundwater quality. The model was not developed to provide precise estimates of pH at any given location. Rather, it can be used to more generally identify areas where contaminants may be mobilized into groundwater and where corrosivity issues may be of concern to prioritize areas for future groundwater monitoring.

Heated column experiments: A proxy for investigating the effects of in situ thermal recovery operations on groundwater geochemistry

In situ thermal recovery is utilized extensively for unconventional bitumen extraction in the Cold Lake-Beaver River (CLBR) basin in Alberta, Canada. Public health concerns have been raised over potable groundwater contamination and arsenic release adjacent to these operations within the CLBR basin, which have been linked to subsurface heating of aquifer sediments. Under localized heated conditions, As-bearing aquifer sediments have been shown to undergo water-rock interactions and release constituents at near neutral pH conditions; however, release mechanisms have yet to be conclusively reported. To investigate the hydrogeochemical processes of aquifer heating and solute transport in detail, this study applies a novel heated column design to mimic saturated aquifer materials in contact with a thermal recovery well while constraining flow and geochemical conditions. Two column experiment scenarios were considered using: 1) quartz [SiO2] sand with 0.6 wt% pyrite [FeS2]; and 2) aquifer sediments collected from the CLBR region. Heated temperature gradients between 50 °C and 90 °C were maintained within a 0.6 m section of the 3 m column with a flow rate of one pore volume per week. During heated low oxygen (<3 mg L−1) conditions, results generally show increases in pH, Al, As, B, Mn, Mo, Si and Zn concentrations within and downgradient of the column heating section. Constituent release is primarily attributed to thermal desorption from Fe oxides, clay and silicate mineral dissolution, competitive anion exchange, and increased mixing. Overall results suggest that these mechanisms are responsible for increasing constituent concentrations in groundwater adjacent to in situ thermal recovery operations.

Analysis of spatio-temporal trend in groundwater elevation data from arsenic affected alluvial aquifers – Case study from Murshidabad district, West Bengal, Eastern India

Fluctuation in groundwater level is a time-dependent stochastic process. It is also a function of various inflow and outflow components to and from the hydrologic system concerned. Depth to water level data are measured through a network of observation wells or hydrograph stations to ascertain the degree of fluctuation in groundwater level at the desired scale, on a long-term basis. Basically, these depths to water level data are point measurements, which can be regarded as random variables furnishing changes in groundwater storage over time. The intrinsic in-homogeneity in aquifer materials introduces variations like jumps, trends, and periodicities in such hydrologic time series data. Thus, trending results from certain gradual, natural and/or anthropogenic interventions in the hydrologic environment and analyses of their trends are imperative for assessment of groundwater level scenario in the area of interest. This in turn, is essential for strategic planning and management for exploitation of the precious groundwater resource in the same area. The area of interest in this article, i.e., Murshidabad is one of the nine arsenic affected districts of West Bengal. Here, contamination persist within, shallow, arseniferous, alluvial aquifers, which are otherwise widely exploited for irrigation purposes. According to many researchers working in this area, over-exploitation of groundwater is the root cause for the plummeting water level and the widespread arsenic contamination as well. The present study intends to detect and analyze the trends persisting in the depth to water level data measured over a period from 1996 to 2016, in Murshidabad district of West Bengal, India, amidst its complex and contrasting hydrogeologic set-up and interpret the results in terms of the hydrologic attributes of the Bengal basin as a whole. The non-parametric Mann–Kendall test and the Sen’s slope estimator have been used to identify the linear trend persisting in the time series pre- and post-monsoon groundwater elevation values. The analysis indicates statistically significant decline in water level across the study area especially during the post-monsoon season. This can be attributed to the recharge–discharge disparity within the hydrologic regime; brought through intense pumping over the study area. Its ill effect being particularly observed in the western part of river Bhagirathi. Findings of such study are crucial for assessment of dynamic groundwater resources of the district and subsequently can be utilized as a decision support tool for groundwater management at micro-level.

Profiling microbial community structures and functions in bioremediation strategies for treating 1,4-dioxane-contaminated groundwater

Microbial community compositions and functional profiles were analyzed in microcosms established using aquifer materials from a former automobile factory site, where 1,4-dioxane was identified as the primary contaminant of concern. Propane or oxygen biostimulation resulted in limited 1,4-dioxane degradation, which was markedly enhanced with the addition of nutrients, resulting in abundant Mycobacterium and Methyloversatilis taxa and high expressions of propane monooxygenase gene, prmA. In bioaugmented treatments, Pseudonocardia dioxanivorans CB1190 or Rhodococcus ruber ENV425 strains dominated immediately after augmentation and degraded 1,4-dioxane rapidly which was consistent with increased representation of xenobiotic and lipid metabolism-related functions. Although the bioaugmented microbes decreased due to insufficient growth substrates and microbial competition, they did continue to degrade 1,4-dioxane, presumably by indigenous propanotrophic and heterotrophic bacteria, inducing similar community structures across bioaugmentation conditions. In various treatments, functional redundancy acted as buffer capacity to ensure a stable microbiome, drove the restoration of the structure and microbial functions to original levels, and induced the decoupling between basic metabolic functions and taxonomy. The results of this study provided valuable information for design and decision-making for ex-situ bioreactors and in-situ bioremediation applications. A metagenomics-based understanding of the treatment process will enable efficient and accurate adjustments when encountering unexpected issues in bioremediation.

Criteria for identifying groundwater in rifting basins in arid and semi-arid zones: a case study Sharm El Bahary in Egypt

Some arid and semiarid countries that have large amounts of freshwater stored in rifting basin situations like the Res Sea are probably quite rare internationally. In this paper, we suggest criteria for identifying potential groundwater resource targets in rifting basins based on topographical, geomorphological, morphometric, geological, hydrogeological, hydrological, and vegetation data. The criteria were tested in the Sharm El Bahary basin for identifying targets for groundwater exploration. The priority of these targets depends on the thickness, extent, and lithology of aquifer materials, and the mechanism of recharge. The highest priority groundwater targets have a low topography and are underlain by coarse-textured sediments that have a high infiltration rate. These sites have negligible surface drainage and are located within graben structures where sediment thickness may reach up to 600 m.

Isotopic and hydrochemical evidence for the salinity origin in the coastal aquifers of the Pearl River Delta, Guangzhou, China

To better understand the origin of the saline groundwater in the Pearl River Delta (PRD), China, water samples were collected from local aquifers, rainfall regions and rivers for isotopic and hydrochemical analysis. The hydraulic connections between the aquifers in the study area were tested by analyzing a series of water samples from different months in one hydrological year (January 2017–January 2018). The total dissolved solids (TDS) results show that the highly saline groundwater only occurs in the granites, which indicates that the TDS distribution depends on the permeability of the aquifer material. Variations in the TDS and stable hydrogen and oxygen isotope ratios (δ2H and δ18O, respectively) of the water samples from different months reflect a dynamic balance among evaporation and precipitation in a hydrological year. Additionally, the very old radiocarbon (14C) ages and undetectable amounts of tritium (3H) in most of the groundwater samples suggest that the residence time of the groundwater in the aquifer is high. In general, the saline groundwater (TDS >5 g/L) in the area mainly originated primarily from seawater intrusion in the past. Meanwhile, the water contents of saline groundwater were affected by evaporation and long-term geochemical processes, such as water-rock, sulfate reduction, methanogenesis and ion exchange. The fresh groundwater in the area is from modern meteoric precipitation recharge.

Geogenic sources and chemical controls on fluoride release to groundwater in the Independence Basin, Mexico

High fluoride (F−) concentrations in groundwater are a recognized environmental health concern, and over 200 million people around the world routinely drink well water with F− concentrations that exceed safety guidelines. Groundwater in the Independence Basin of Central Mexico reaches F− concentrations of 15.5 mg L−1, which are over an order of magnitude greater than the World Health Organization limit of 1.5 mg L−1, but knowledge of sources and geochemical conditions responsible for releasing F− into solution is preliminary. The objectives of this work were to define F− hosts within a range of Independence Basin aquifer rock types and quantify chemical controls on F− release into solution. Solid-phase concentrations of F− in well-drill cuttings display no apparent depth dependence but are greatest within andesite, near-surface uncemented alluvium, and well-cemented Paleocene conglomerate samples, and they are least within volcanic glass, rhyolite, and ash matrix samples. Chemical extractions showed that large amounts of F− are bound with metal oxides/oxyhydroxides in all samples. Batch experiments examining F− release from aquifer materials under evolving groundwater conditions (i.e. increasing pH and specific conductance) revealed that F− may be released into solution with elevated pH but only slightly mobilized with increasing specific conductance. Therefore, declining aquifer water levels tapping into older, more mineralized groundwater (with high conductivity) in the Independence Basin may not have as great of an effect on F− release to solution than does evolving and increasing groundwater pH. Accordingly, the degree of rock weathering and pH of solution play the greatest roles in regulating the release of F− to groundwater, and results from this study may be used to better predict where F− groundwater contamination is most probable in aquifers around the world.

Preparation and application of polyaluminum chloride for demulsification of colloidal biliquid aphron and density modification for DNAPLs

The preparation and application of suitable demulsifiers in the process of density control of DNPALs is in urgent demand. In this study, we prepared a demulsifier -polyaluminum chloride (PACl), for density modifier -colloidal biliquid aphron (CBLA). We found that PACl2 (PACl with [OH]/[Al] = 2) can make CBLA to completely release light organic liquids within 30 min. The prepared PACl was characterized by SEM, XRD, the reaction curve of PACl with ferron reagent, 27Al NMR and charge density test in order to identify the reactive groups and elucidate the demulsification mechanisms. The system achieved 95% demlusification efficiency in acidic environment (pH < 4). The demulsification process followed pseudo-second-order kinetics model. A small amount of aquifer material could promote demulsification due to natural demulsifiers. We also used PACl2 to break CBLA and modify the density of two DNPALs, trichloroethylene (from 1.464 g/cm3 to 0.980 g/cm3), and nitrobenzene (from 1.197 g/cm3 to 0.921 g/cm3). The results show that the density of DNAPL can be reduced to less than that of water, which effectively prevents the downward migration of DNAPLs during remediation process. The findings will improve our understanding of the mechanism of CBLA demulsification and its density modification of DNAPLs for enhanced groundwater remediation.

Geology and Aquifer Sensitivity of Quaternary Glacial Deposits Overlying a Portion of the Mahomet Buried Bedrock Valley Aquifer System

To characterize the distribution of Holocene and Late Quaternary deposits and to assess the contamination potential of the Mahomet Aquifer, surficial geologic and aquifer sensitivity maps of the Gibson City East 7.5-Minute Quadrangle were created. Geologic data, extent, and thickness of the geologic materials were coupled with LiDAR topographic data and analyzed using ESRI’s ArcGIS 10.6.1. Aquifer sensitivity to contamination was calculated based on the depth to the first aquifer unit, aquifer thickness, and the lithology of the aquifer materials. The surficial geologic mapping identified five lithostratigraphic units: the Cahokia Formation, the Equality Formation, the Henry Formation, and the Yorkville and Batestown Members of the Lemont Formation. The southeast to northwest trending Illiana Morainic System is the most prominent feature in the study area and delineates the maximum extent of the glaciers during the Livingston Phase of glaciation. Postglacial deposits of the Cahokia Formation, alluvium, interfinger, and overlie with glacial outwash of the Henry Formation along channels and drainage ways downslope of the moraine. The areas of least sensitivity are located over the Illiana Morainic System, whereas the greatest potential to contamination occurs where the thickest deposits of the Henry Formation and Cahokia Formation lie at or just below the land surface.

Evaluating Treatment Requirements for Recycled Water to Manage Well Clogging during Aquifer Storage and Recovery: A Case Study in the Werribee Formation, Australia

Managed aquifer recharge (MAR) is the intentional recharge of water to suitable aquifers for subsequent beneficial use or to achieve environmental benefits. Well injection techniques for MAR, such as Aquifer Storage and Recovery (ASR), rely on implementing appropriate design and defining the operational parameters to minimise well clogging and maintain sustainable rates of recharge over the long term. The purpose of this study was to develop water quality targets and pre-treatment requirements for recycled water to allow sustained recharge and recovery in a medium-coarse siliceous aquifer. The recharge water is a blend of 40% Class A recycled water and 60% reverse osmosis (RO)-treated Class A recycled water. Four source waters for MAR were evaluated: (1) this blend with no further treatment, and this blend with additional treatment using: (2) a 20 µm sediment cartridge filter, (3) a 5 µm sediment cartridge filter, or (4) a 5 µm granular activated carbon (GAC) cartridge filter. All four treatment options were also further disinfected with chlorine. The four blended and treated recycled waters were used in laboratory columns packed with aquifer material under saturated conditions at constant temperature (20.7 °C) with light excluded for up to 42 days. Substantial differences in the changes in hydraulic conductivity of the columns were observed for the different treatments within 14 days of the experiment, despite low turbidity (&lt;2 NTU) of the blend waters. After 14 days, the GAC-treated water had a 7% decline in hydraulic conductivity, which was very different from the other three blend waters, which had declines of 39–52%. Based on these results and consistent with previous studies, a target biodegradable dissolved organic carbon (BDOC) level of &lt;0.2 mg/L was recommended to ensure a biologically stable source of water to reduce clogging during recharge.

Hydrogeochemical contrast between two study areas of Bengal delta, India: A comparative insight to understand arsenic mobilization process in shallow aquifers

A comparative hydrogeochemical study evaluated arsenic release mechanism and differences in contamination levels in the shallow groundwater of two areas within the deltaic environment of West Bengal (i.e. Karimpur and Tehatta blocks of Nadia district) in India. Groundwaters from both the areas are Ca-Na(K)-Cl-HCO3 type with highly reducing character (−110.16 ± 16.85 to −60.77 ± 16.93 mV). Low correlations among As, Fe, and Mn and the higher association between As and DOC are indicative of microbial decomposition of organic matter enhancing the weathering of shallow aquifer materials. Arsenic contamination in groundwater is higher in Karimpur (95 ± 81.17 μg/L) than that in Tehatta (43.05 ± 41.06 μg/L). The release mechanism of arsenic into groundwater is very complex. Low Fe (0.27–4.78 mg/L and 0.81–4.13 mg/L), Mn (0.08–0.2 mg/L and 0.03–0.22 mg/L), and SO42− (3.82 ± 0.31 and 2.78 ± 0.40 mg/L) suggest that the mechanism of arsenic release is not a single mechanistic pathway. Clustering of redox-active parameters in the principal component planes indicate that the reductive dissolution, and/or weathering/co-precipitation of Fe/Mn-bearing minerals in the shallow aquifer sediments control the dominant mechanistic pathway of arsenic release.