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Managed aquifer recharge (MAR) is an increasingly used water management technique that enhances water availability while commonly generating water quality benefits. However, MAR activities may also trigger adverse geochemical reactions, especially during the injection of oxidant-enriched waters into reducing aquifers. Where this occurs, the environmental risks and the viability of mitigating them must be well understood. Here, we develop a rigorous approach for assessing and managing the risks from MAR-induced metal mobilization. First, we develop a process-based reactive transport model to identify and quantify the main hydrogeochemical drivers that control the release of metals and their mobility. We then apply a probabilistic framework to interrogate the inherent uncertainty associated with adjustable model parameters and consider this uncertainty (i) in long-term predictions of groundwater quality changes and (ii) in scenarios that investigate the effectiveness of modifications in the water treatment process to mitigate metal release and mobility. The results suggested that Co, Ni, Zn, and Mn were comobilized during pyrite oxidation and that metal mobility was controlled (i) by the sediment pH buffering capacity and (ii) by the sorption capacity of the native aquifer sediments. Both tested mitigation strategies were shown to be effective at reducing the risk of elevated metal concentrations.

The fate of selected UV filters (UVFs) was investigated in two soil aquifer treatment (SAT) systems, one supplemented with a reactive barrier containing clay and vegetable compost and the other as a traditional SAT reference system. We monitored benzophenone-3 (BP-3) and its transformation products (TPs), including benzophenone-1 (BP-1), 4,4'-dihydroxybenzophenone (4DHB), 4-hydroxybenzophenone (4HB), and 2,2'-dihydroxy-4-methoxybenzophenone (DHMB), along with benzophenone-4 (BP-4) and avobenzone (AVO) in all involved compartments (water, aquifer sediments, and biofilm). The reactive barrier, which enhances biochemical activity and biofilm development, improved the removal of all detected UVFs in water samples. Among monitored UVFs, only 4HB, BP-4, and AVO were detected in sediment and biofilm samples. But the overall retained amounts were several orders of magnitude larger than those dissolved. These amounts were quantitatively reproduced with a specifically developed simple analytical model that consists of a mobile compartment and an immobile compartment. Retention and degradation are restricted to the immobile water compartment, where biofilm absorption was simulated with well-known compound-specific K ow values. The fact that the model reproduced observations, including metabolites detected in the biofilm but not in the (mobile) water samples, supports its validity. The results imply that accumulation ensures significant biodegradation even if the degradation rates are very low and suggest that our experimental findings for UVFs and TPs can be extended to other hydrophobic compounds. Biofilms act as accumulators and biodegraders of hydrophobic compounds.

Managed aquifer recharge can store surface water as safe and reliable groundwater for later recovery. However, most options are problematic in karstic aquifers due to complex hydrodynamics reducing their effectiveness and hence general applicability. River bank filtration and urban stormwater infiltration systems are among the main managed recharge approaches to cope with this complexity. Experiences in Lebanon demonstrate the viability of these and other options in karstic domains. [ABSTRACT FROM AUTHOR]

Two pilot-scale advanced water treatment plants using tertiary-treated biological nutrient removal wastewater effluent were operated simultaneously to demonstrate and compare treatment performances and process operations. Final effluent from both the plants was compared for its suitability to recharge a potable water supply aquifer. The two treatment approaches included a carbon-based treatment process (flocculation/sedimentation, ozone-biofiltration, granular activated carbon (GAC) adsorption, ultraviolet (UV) disinfection; 20,000 L/day) and a membrane-based treatment process (ultrafiltration, reverse osmosis, UV-hydrogen peroxide advanced oxidation; 160,000 L/day). Both processes were found to be reliable in producing water that met all United States Safe Drinking Water Act's primary maximum contaminant levels (MCLs). The carbon-based process often exceeded the secondary MCL for total dissolved solids due to background salinity in the source water. Results showed that both systems performed comparably with respect to removal of pathogens, fecal indicators, and contaminants of emerging concern. Total organic carbon (TOC) was removed to below 0.5 mg/L by the membrane-based process. For the carbon-based process, GAC media exhaustion over the course of the pilot operation resulted in an increase in finished water TOC from <0.5 to ∼4 mg/L. Disinfection byproducts, including trihalomethanes and haloacetic acids were not measured above their respective MCL after 8 h of free chlorine contact in a simulated distribution system test. N-nitrosodimethylamine was removed below 10 ng/L by the GAC with 20 min of empty bed contact time after 20,000 bed volumes. [ABSTRACT FROM AUTHOR]

Featured Application: The experiments presented in this paper are useful for the planning stage of managed aquifer recharge sites. Infiltration experiments in the context of managed aquifer recharge (MAR) are often conducted to assess the processes influencing the operation of full-scale MAR schemes. For this, physical models such as laboratory experiments and, less often, field experiments are used to determine process specifics or operational parameters. Due to several assumptions, scale-related limitations, and differing boundary conditions, the upscaling of results from the physical models is not straightforward. Investigations often lead to over- or underestimations of flow processes that constrain the translation of results to field-like conditions. To understand the restrictions and potential of different physical models for MAR assessment, surface infiltration experiments in different scales and dimensions, which maintained the same operational parameters, were conducted. The results from the different setups were compared against each other regarding the reproduction water flow in the vadose zone and the influence of parameters such as soil type and climate. Results show that mostly qualitative statements can be made, whereas quantitative analysis through laboratory experiments is limited. [ABSTRACT FROM AUTHOR]

• The effective removal of selected TrOCs observed in MAR combined with O 3 and O 3 /H 2 O 2. • MAR showed better performance in reducing CHCl 3 via coupling with O 3 alone. • MAR combined with O 3 and O 3 /H 2 O 2 achieved >50% removal of DOC within the first 5 days. • Pre-oxidation with MAR improved biological stability. A hybrid process of managed aquifer recharge with pre-oxidation was investigated as part of a multiple-barrier approach for safe water production. This study evaluated O 3 and O 3 /H 2 O 2 for the pre-oxidation of urban surface water prior to managed aquifer recharge (MAR) and compared their effectiveness with respect to trace organic contaminants (TrOCs), biostability, and trihalomethane formation potential. The combination of pre-oxidation and MAR was performed using long-term column studies, and the results confirmed the removal of 64 and 56% dissolved organic carbon by using O 3 and O 3 /H 2 O 2 , respectively. MAR combined with O 3 and O 3 /H 2 O 2 achieved >50% removal of dissolved organic carbon with the first 5 days of residence time. O 3 alone showed better performance in alleviating trihalomethane formation potential during chlorination compared to using O 3 /H 2 O 2. The pre-oxidation of urban surface water was effective in attenuating selected TrOCs (35 - >99% removal), and subsequent MAR achieved >99% removal of selected TrOCs within the first 5 days, regardless of pretreatment methods examined in this study. The results of this study provide an understanding of the effects of O 3 and O 3 /H 2 O 2 as pre-oxidation processes on urban surface water prior to MAR, as well as the resulting impact on MAR. [ABSTRACT FROM AUTHOR]

This article looks at the potential for connecting two circumstances present in California and elsewhere in the world: having too much water, in the form of flooding; and not having enough water, as evidenced by overdrafted groundwater. It describes reversing the historical practice of channelizing rivers to obtain a variety of integrated benefits: more effective flood management, improved recreational opportunities and habitat, better water quality, enhanced community vitality and improved groundwater recharge. It identifies planning approaches to connecting flood management and groundwater recharge and considers some of the potential legal issues if used with private property. [ABSTRACT FROM AUTHOR]

Abstract Due to the quality difference between reclaimed water and natural groundwater, managed aquifer recharge (MAR) with reclaimed water may pose environmental risks. A river infiltration of reclaimed water for groundwater recharge in north China has been in operation for over 10 years. To investigate the actual impact on native groundwater under long-term MAR, 10-year monitoring data of recharge water and groundwater were analyzed. Due to the effect of recharge, the hydrochemical type of groundwater rapidly changed from Ca-Mg-HCO 3 into Na-HCO 3 which was the type of recharge water. Cl− was used as a conservative tracer in a physical mixing model, and the mixing was concluded to be dominant in the groundwater hydrochemical change under long-term MAR. The hydraulic travel time to the 30 m depth was determined to be about 6.5 months by obtaining the best-fit linear cross correlation between the concentrations of Cl− in recharge water and those in groundwater. In application of this method, the monitoring wells should be located downstream and as close as possible to the recharge site (e.g., <50 m). Based on the travel time, behaviors of total nitrogen (TN), NO 3 -N, NO 2 -N, and NH 4 -N were determined by attenuation factor (A f). As the main nitrogen compound, NO 3 -N was well attenuated under high hydraulic load, resulting in the A f > 1, with an attenuation rate of 99.6%. The A f < 1 of NH 4 -N indicated the additional input of NH 4 -N in groundwater. Fluctuations of NH 4 -N in recharge water exceeded 4 mg/L changes sorption equilibrium, resulting in the sorption/desorption of NH 4 -N in soil-groundwater system. The concentration of NH 4 -N in groundwater increased in the later period of monitoring. The overall attenuation rate of NH 4 -N was 26.3%. These findings contributed to improving the environmental benefits of this MAR site and provided guidance for other similar projects. Graphical abstract Unlabelled Image Highlights • Mixing is the dominant process in the groundwater hydrochemistry change. • Water vertical travel time is obtained by the correlation of Cl− concentrations. • NO 3 -N is well attenuated under high hydraulic load of the recharge site. • Fluctuation of NH 4 -N input over 4 mg/L changes its sorption equilibrium. [ABSTRACT FROM AUTHOR]

• Preferential flow in the weathering interface controls recharge propagation. • Variable bedrock relief causes aquifer compartmentalization and focused recharge. • Modeling shows compartment dimensions control the rate and amplitude of WL increase. To overcome water scarcity issues, Managed Aquifer Recharge (MAR) structures are currently developed in many parts of the world, including poorly permeable terrain like weathered crystalline rocks. In such geological context, characterized by relatively limited groundwater storage mainly associated with fractures located at the interface between the upper weathered layer (saprolite) and the fractured bedrock, the efficiency of MAR is poorly known. To address this question and better understand the factors that control recharge dynamics, an artificial recharge basin was implemented at the Experimental Hydrogeological Park in Telangana (South India), a well-equipped and continuously monitored site situated in Archean granitic terrain. The thickness of the saprolite and hydraulic properties are relatively well known all over the site from previous geophysical surveys and hydraulic tests. To characterize recharge dynamics, recharge has been monitored in different boreholes surrounding the infiltration basin. Infiltration rates and water level data are interpreted by both a volume balance approach and different analytical solutions. In addition, a simple numerical model was used to show how the depth of the permeable interface between saprolite and granite controls recharge dynamics and observed water levels variations. Results show that the permeability of the saprolite/bedrock interface is sufficiently large to allow an efficient recharge that propagates laterally throughout the aquifer through this well connected interface. However, the variable depth of this permeable pathway controls the water level response, acting as a semi-impervious boundary, leading to remarkable water level variations. Thus, our findings show how the characteristics of the most permeable pathways control recharge dynamics in weathered crystalline rocks. In addition, we show how the depth variations of the permeable interface between saprolite and granite may be inferred from the monitoring of water level during recharge events. [ABSTRACT FROM AUTHOR]

• Norms, values, attitudes account for much of 79% variance in stormwater acceptance. • Perceived approval from others & moral values were main predictors of acceptance. • High acceptance for stormwater reuse; end use a weak predictor of acceptance. • Belief that conserving water was part of Australian culture led to lower acceptance. • Low acceptance of stormwater likely due to high acceptance of water conservation. Urban residents are becoming more aware of water scarcity issues and paying greater attention to their total water consumption. Simultaneously, perceptions of what is considered drinkable water are also evolving. The present study examines whether attitudinal evaluations of stormwater influence the public acceptance of stormwater that is treated and sourced through managed aquifer recharge (MAR). It was hypothesised that treated stormwater used for non-potable purposes would be more acceptable amongst participants, and that select psychological factors (perceptions, values and norms) would be significant predictors of public acceptance for MAR. Participants (N = 408) took part in an online survey which measured public acceptance of stormwater, social norms, stormwater attitudes, water beliefs and water conservation culture. These factors were experimentally examined across two different types of water use: "drinking water" or "non-drinking water". Multiple regression analysis demonstrated that stormwater end use and selected psychological factors accounted for 79% of variance in acceptance of stormwater. While there was significantly higher acceptance for the use of MAR for non-drinking purposes overall, 'end use' was a weak predictor of public acceptance for MAR. The most important predictors of acceptance were social norms and value-driven attitudes towards stormwater. Results showed that perceptions of approval from important others (e.g. family and friends) and personal moral values were influential in explaining acceptance for stormwater. Interestingly, water conservation culture was a negative predictor of acceptance, where people who believed that conserving water was part of the Australian lifestyle tended to have lower acceptance for a supplemental stormwater supply. These people were more likely to support initiatives encouraging conservation of water use as key to managing water supplies. The findings articulate the need to consider existing public attitudes and norms within communities where alternative resources are proposed, to inform policy and practice. [ABSTRACT FROM AUTHOR]

Abstract Subsurface microorganisms must deal with quite extreme environmental conditions. The lack of light, oxygen, and potentially nutrients are the main environmental stresses faced by subsurface microbial communities. Likewise, environmental disruptions providing an unbalanced positive input of nutrients force microorganisms to adapt to varying conditions, visible in the changes in microbial community diversity. In order to test microbial community adaptation to environmental changes, we performed a study in a surface Managed Aquifer Recharge facility, consisting of a settlement basin (two-day residence time) and an infiltration pond. Data on groundwater hydrochemistry, soil texture, and microbial characterization was compiled from surface water, groundwater, and soil samples at two distinct recharge operation conditions. Multivariate statistics by means of Principal Component Analysis (PCA) was the technique used to map the relevant dimensionality reduced combinations of input variables that properly describe the system behavior. The methodology selected allows including variables of different nature and displaying very different range values. Strong differences in the microbial assemblage under recharge conditions were found, coupled to hydrochemistry and grain-size distribution variables. Also, some microbial groups displayed correlations with either carbon or nitrogen cycles, especially showing abundant populations of denitrifying bacteria in groundwater. A significant correlation was found between Methylotenera mobilis and the concentrations of NO 3 and SO 4 , and also between Vogesella indigofera and the presence of DOC in the infiltrating water. Also, microbial communities present at the bottom of the pond correlated with representative descriptors of soil grain size distribution. Graphical abstract Image 1 Highlights • Environmental variables affect microbial phylotypes presence in recharge systems. • PCA allows identifying most relevant environmental variables. • Microbial signature in porewater changes with infiltration operations. • Grain-size distribution drives microbial population behavior in soils. • Infiltration ponds have an impact on biomediated carbon and nitrogen cycles. [ABSTRACT FROM AUTHOR]

Abstract The objective of this study is to develop a Fluoride Index for mitigation of geogenic contamination by Managed Aquifer Recharge (FIMAR). This index was tested by applying to the Pambar river basin in southern India. About 40% of the study area had fluoride >1.5 mg/L, contributed from the dissolution of fluorite, fluorapatite, biotite and hornblende. The relationship between groundwater level and fluoride concentration exhibited two types of relationship. In shallow wells, groundwater recharge during monsoon increases the groundwater level and dilutes the fluoride concentration. During summer, evaporation decreases the groundwater levels and increases the fluoride content. In deep wells, the fluoride-rich salts that is deposited in the unsaturated zone due to evaporation in the pre-monsoon season is flushed during groundwater recharge and thus, the fluoride concentration increases with increase in groundwater level. This relationship was used as a key layer in FIMAR. Overlay analysis including the well type derived from the groundwater level and fluoride fluctuation, average fluoride concentration, geology, geomorphology, soil, drainage density, land use, lineament density and thickness of the weathered zone indicated 30% of the area was suitable for MAR to mitigate fluoride contamination. Since the construction of new MAR structures is cost-intensive, it is proposed to rejuvenate the existing ponds in the areas identified by FIMAR to induce recharge and dilute fluoride concentration. The positive impact was confirmed using numerical and geochemical modelling. This proves that FIMAR can be used as a planning tool in fluoride endemic areas and that the future MAR methods will be beneficial to mitigate geogenic fluoride contamination. Graphical abstract Image 1 Highlights • About 40% of the groundwater samples have fluoride above 1.5 mg/L. • New Fluoride Index applied to identify sites for mitigating geogenic contamination by Managed Aquifer Recharge (FIMAR). • FIMAR indicates 30% of the study area is suitable for MAR. • Results from FIMAR is validated through numerical and geochemical models. • Rejuvenating the existing water bodies will increase recharge by 40% and reduce fluoride below 1.5 mg/L. [ABSTRACT FROM AUTHOR]

Intensive groundwater withdrawals in California have resulted in depletion of streams and aquifers in some regions. Agricultural managed aquifer recharge (Ag‐MAR) initiatives have recently been piloted in California to mitigate the effects of unsustainable groundwater withdrawals. These initiatives rely on capturing wet‐year water and spreading it on large areas of irrigated agricultural lands to enhance recharge to aquifers. While recharge studies typically consider local effects on aquifer storage, few studies have investigated Ag‐MAR benefits and challenges at a regional scale. Here we used the Integrated Water Flow Model, to evaluate how Ag‐MAR projects can affect streamflows, diversions, pumping, and unsaturated zone flows in the southern Central Valley, California. We further tested the sensitivity of three different spatial patterns of Ag‐MAR, each chosen based on different thresholds of soil suitability, on the hydrologic system. This study investigates how the distribution of Ag‐MAR lands benefit the regional groundwater system and other water balance components. The results suggest that Ag‐MAR benefits vary as a function of the location of Ag‐MAR lands. Stream‐aquifer interactions play a crucial factor in determining the ability to increase groundwater storage in overdrafted basins. The results also indicate that Ag‐MAR projects conducted during the November–April recharge season have implications for water rights outside of the Ag‐MAR season. If not properly monitored, Ag‐MAR can cause a rise of groundwater table into the root zone, negatively impacting sensitive crops. Our work also highlights the benefits of using an integrated hydrologic and management model to evaluate Ag‐MAR at a regional scale. Key Points: How regional Ag‐MAR projects can influence streamflows and surface diversions is demonstrated using an integrated management modelThe spatial distribution of agricultural lands for recharge is key to enhance groundwater storageRegional Ag‐MAR projects may affect downstream water rights as well as increase the risk of waterlogging in the root zone [ABSTRACT FROM AUTHOR]

We quantified the distribution of hillslope runoff under different climate and land-use conditions in a coastal, mixed land-use basin, the Pajaro Valley Drainage Basin (PVDB), California, USA, in order to evaluate opportunities to improve groundwater supply. We developed dry, normal, and wet climate scenarios using high-resolution historic data and compared contemporary land use to pre-development land use under the different climate scenarios. Relative to pre-development conditions, urban and agricultural development resulted in more than twice as much simulated runoff generation, greater spatial variability in runoff, and less water available for recharge; these differences were most pronounced during the dry climate scenario. Runoff results were considered in terms of potential to support distributed stormwater collection linked to managed aquifer recharge (DSC-MAR), which routes excess hillslope runoff to sites where it can infiltrate and enhance groundwater recharge. In the PVDB, 10% of the annual groundwater deficit could be addressed by recharging 4.3% of basin-wide hillslope runoff generated during the normal scenario, and 10.0% and 1.5% of runoff during the dry and wet scenarios, respectively. Runoff simulation results were combined with an independent recharge suitability mapping analysis, showing that DSC-MAR could be effective in many parts of the PVDB under a range of climate conditions. These results highlight the importance of strategically locating DSC-MAR projects at the confluence of reliable supply and favorable subsurface hydrologic properties. [ABSTRACT FROM AUTHOR]

To bolster freshwater supplies, water managers are increasingly interested in recharging groundwater using storm water and recycled water. However, such multisupply groundwater recharge projects are hindered by the lack of planning tools to evaluate system design costs and trade‐offs. This study presents modeling advancements that provide enhanced insights into multisupply spreading basin systems (i.e., spreading basins that accommodate both advanced treated recycled water and dynamically available storm water), a form of managed aquifer recharge. The model identifies system designs that optimize infrastructure life cycle cost and water volumes infiltrated for groundwater recharge. To illustrate the model's application under realistic conditions, we present a case study of Los Angeles, California. In this case study, we find that competition between storm water and recycled water for spreading basin use is relatively minor. Moreover, compared to systems based on existing conservative assumptions, our methods identify optimal dynamic system designs that are 5%–20% more cost‐effective, primarily resulting from higher water recycling facility utilization. Overall, this approach, which considers the dynamic nature of storm water availability and variable recycled water production, can inform water planners of the cost, water volume, and energy trade‐offs associated with different multisupply spreading basin system designs, including varying levels of centralization. Key Points: We present an approach for optimizing dynamic management of spreading basin systems receiving storm water and recycled waterOur Los Angeles, CA, case study finds flexible systems are 5%–20% more cost‐effective than systems based on more conservative assumptionsWater planners could adapt our framework to complement existing studies or apply to other planning contexts [ABSTRACT FROM AUTHOR]

The last 60 years has seen unprecedented groundwater extraction and overdraft as well as development of new technologies for water treatment that together drive the advance in intentional groundwater replenishment known as managed aquifer recharge (MAR). This paper is the first known attempt to quantify the volume of MAR at global scale, and to illustrate the advancement of all the major types of MAR and relate these to research and regulatory advancements. Faced with changing climate and rising intensity of climate extremes, MAR is an increasingly important water management strategy, alongside demand management, to maintain, enhance and secure stressed groundwater systems and to protect and improve water quality. During this time, scientific research—on hydraulic design of facilities, tracer studies, managing clogging, recovery efficiency and water quality changes in aquifers—has underpinned practical improvements in MAR and has had broader benefits in hydrogeology. Recharge wells have greatly accelerated recharge, particularly in urban areas and for mine water management. In recent years, research into governance, operating practices, reliability, economics, risk assessment and public acceptance of MAR has been undertaken. Since the 1960s, implementation of MAR has accelerated at a rate of 5%/year, but is not keeping pace with increasing groundwater extraction. Currently, MAR has reached an estimated 10 km3/year, ~2.4% of groundwater extraction in countries reporting MAR (or ~1.0% of global groundwater extraction). MAR is likely to exceed 10% of global extraction, based on experience where MAR is more advanced, to sustain quantity, reliability and quality of water supplies. [ABSTRACT FROM AUTHOR]

Featured Application: The outcomes of the study are useful for the planning and operation of soil aquifer treatment (SAT) facilities. The results of the experiments provide knowledge about the correlations between the grain size fractions of soil and the availability of nutrients as well as oxygen in the soil pore system during the operation of such systems. This makes it possible to choose soils for SAT systems, providing optimal conditions for microbiological growth, and thus to ensure optimal conditions for water quality improvement. Soil aquifer treatment (SAT) is a nature-inspired solution for improving the water quality through soil percolation. The biodegradation of organic matter typically occurs in the shallowest soil layer and it depends on the contaminant's characteristics (water solubility, molecular structure) and specific soil properties (pore size distribution). The present study aims at identifying which grain size fraction of typically used sandy soils in the shallowest layer of SAT systems can provide the optimal conditions for microbiological growth that can be reached by a trade-off between soil moisture as well as nutrients and oxygen supply. For this, soil columns were used at a laboratory scale to determine the relationship between the pore size distribution of four different grain size fractions and biodegradation rates of organic matter from synthetic wastewater. The results obtained from this experimental setup indicate that bacterial colonies reached optimum growth when about 60% of the available pore space was filled with water. For the selected soil, this was achieved by the fraction with grain sizes in the range of 630 µm to 1000 µm, having pore diameters between 87 µm and 320 µm and a mean pore diameter of 230 µm. [ABSTRACT FROM AUTHOR]

Water percolation through infiltration ponds is creating significant synergies for the broad adoption of water reuse as an additional non-conventional water supply. Despite the apparent simplicity of the soil aquifer treatment (SAT) approaches, the complexity of site-specific hydrogeological conditions and the processes occurring at various scales require an exhaustive understanding of the system’s response. The non-saturated zone and underlying aquifers cannot be considered as a black box, nor accept its characterization from few boreholes not well distributed over the area to be investigated. Electrical resistivity tomography (ERT) is a non-invasive technology, highly responsive to geological heterogeneities that has demonstrated useful to provide the detailed subsurface information required for groundwater modeling. The relationships between the electrical resistivity of the alluvial sediments and the bedrock and the difference in salinity of groundwater highlight the potential of geophysical methods over other more costly subsurface exploration techniques. The results of our research show that ERT coupled with implicit modeling tools provides information that can significantly help to identify aquifer geometry and characterize the saltwater intrusion of shallow alluvial aquifers. The proposed approaches could improve the reliability of groundwater models and the commitment of stakeholders to the benefits of SAT procedures.

Saline groundwater (SGW) is an alternative water resource. However, the concentration of sodium, chloride, sulphate, and nitrate in SGW usually exceeds the recommended guideline values for drinking water and irrigation. In this study, the partial desalination performance of three different concentrated SGWs were examined by pressure-driven membrane desalination technologies: nanofiltration (NF), brackish water reverse osmosis (BWRO), and seawater reverse osmosis (SWRO); in addition to one electrochemical-driven desalination technology: membrane capacitive deionisation (MCDI). The desalination performance was evaluated using the specific energy consumption (SEC) and water recovery, determined by experiments and simulations. The experimental results of this study show that the SEC for the desalination of SGW with a total dissolved solid (TDS) concentration of 1 g/L by MCDI and NF is similar and ranges between 0.2–0.4 kWh/m3 achieving a water recovery value of 35–70%. The lowest SECs for the desalination of SGW with a TDS concentration ≥2 g/L were determined by the use of BWRO and SWRO with 0.4–2.9 kWh/m3 for a water recovery of 40–66%. Even though the MCDI technique cannot compete with pressure-driven membrane desalination technologies at higher raw water salinities, this technology shows a high selectivity for nitrate and a high potential for flexible desalination applications.

• Time-dependent pathogen rate reduction in 3-D fracture network fractures. • 3-D E. coli transport simulation in networks of thousands of fractures. • Extended colloid filtration theory predicts pathogen BTC & 3-D plume in groundwater. • Model simulations were supported by field sampling and laboratory filtration tests. • Potential pathogen release to the bathing water is possible during floods. Microbial transport in fractured carbonate rock using enhanced solutions is a significant and neglected research topic in the literature. We propose an extended colloid filtration theory (CFT) combined with a particle-tracking following streamlines (PTFS) model for the rapid prediction of breakthrough curves (BTCs) and plumes of pathogens in three-dimensional (3-D) discrete fracture networks (DFNs). We adapted CFT in porous media to pathogen transport in fractures containing Terra Rossa (soil) deposits. As an example of the model capability, a simulation was used to predict the 3-D motion field and Escherichia coli count in groundwater originating from the Forcatella managed aquifer recharge (MAR) Facility (Brindisi, Italy) using a DFN composed of 3,900 fractures. In arid regions, MAR facilities are significant for sustaining basic human needs, such as freshwater supply for drinking and crop production. The Markov chain Monte Carlo (MCMC) technique was applied to E. coli counts in the collected water samples to increase data representativeness. The pathogen transport coefficients were further supported by batch filtration tests carried out in the CNR/IRSA Laboratory (Bari, Italy). The mean E. coli attachment rate coefficient of 0.15 × 10−8 m2 d–1 (sticking efficiency = 1.1 × 10−8 m) resulted in a 2.1 log 10 removal in 600 m of reclaimed water filtration. The simulation output visualized the E. coli 3-D pathways in groundwater and the positions of contaminated groundwater spring outflows on Forcatella Beach. The simulation results agreed with the mean MCMC output of E. coli concentrations in bathing water under unperturbed geochemical and environmental flow and transport conditions. However, results indicate that concentrations of pathogenic strains, parasites, and enteric viruses may enter the marine environment of MAR sites during flood periods. [Display omitted] [ABSTRACT FROM AUTHOR]

While ensuring adequate drinking water supply is increasingly being a worldwide challenging need, managed aquifer recharge (MAR) schemes may provide reliable solutions in order to guarantee safe and continuous supply of water. This is particularly true in riverbank filtration (RBF) schemes. Several studies aimed at addressing the treatment capabilities of such schemes, but induced aquifer recharge hydrodynamics from surface water bodies caused by pumping wells is seldom analysed and quantified. In this study, after presenting a detailed description of the Serchio River RBF site, we used a multidisciplinary approach entailing hydrodynamics, hydrochemical, and numerical modelling methods in order to evaluate the change in recharge from the Serchio river to the aquifer due to the building of the RBF infrastructures along the Serchio river (Lucca, Italy). In this way, we estimated the increase in aquifer recharge and the ratio of bank filtrate to ambient groundwater abstracted at such RBF scheme. Results highlight that in present conditions the main source of the RBF pumping wells is the Serchio River water and that the groundwater at the Sant’Alessio plain is mainly characterized by mixing between precipitation occurring in the higher part of the plain and the River water. Based on chemical mixing, a precautionary amount of abstracted Serchio River water is estimated to be on average 13.6 Mm3/year, which is 85% of the total amount of water abstracted in a year (~16 Mm3). RBF is a worldwide recognized MAR technique for supplying good quality and reliable amount of water. As in several cases and countries the induced recharge component is not duly acknowledged, the authors suggest including the term “induced” in the definition of this type of MAR technique (to become then IRBF). Thus, clear reference may be made to the fact that the bank filtration is not completely due to natural recharge, as in many cases of surface water/groundwater interactions, but it may be partly/almost all human-made.

ABSTRACT Managed Aquifer Recharge (MAR) is a useful tool for the treatment and use of sewage effluent because it complements conventional treatment, recovers the aquifer and minimizes risk of saltwater intrusion. This study aims to investigate technical data to determine the treatment of wastewater stabilization pond effluent using undisturbed soil columns collected from a coastal watershed study area within the BRAMAR (BRAzil Managed Aquifer Recharge) project. The treatment efficiency was monitored by measuring physico-chemical parameters (BOD 5, COD, DOC, TSS, NH3 and NO3) in two columns filled with undisturbed sandy soil in which sewage effluent was infiltrated under unsaturated condition for 72 days with an average input flow of 10 mm h-1. Results indicated reduction greater than 60% of organic matter, suspended solids and ammoniacal nitrogen. However, high concentrations of nitrate in the outflow were detected originating from nitrification of ammoniacal nitrogen. Moreover, difficulties in relation to soil clogging were observed. Furthermore, this study brought relevant contributions to understanding the influence of the infiltration rate and ability to treat effluent from wastewater stabilization ponds using undisturbed soil columns. Future research should be undertaken to improve the pretreatment methods and the operation of a MAR system in the study area.

Agricultural aquifer storage recovery and transfer (ASTR) stores excess fresh water for later reuse in irrigation. Moreover, water quality improves because chemical pollutants and pathogens will be removed by degradation and attachment to the aquifer material. The source water may contain the bacterial plant pathogen Ralstonia solanacearum which causes plant infections and high yield losses. We used quantitative microbial risk assessment (QMRA) to investigate the removal of R. solanacearum during ASTR to predict infection risks of potato plants after irrigation with the recovered water. Laboratory experiments analyzed the ASTR treatment by investigating the bacterial die-off in the water phase and the removal by attachment to the aquifer sediment. Die-off in the water phase depends on the residence time and ranged between 1.3 and 2.7 log 10 after 10 or 60 days water storage, respectively. A subpopulation of the bacteria persisted for a prolonged time at low concentrations which may pose a risk if the water is recovered too early. However, the natural aquifer sand filtration proofed to be highly effective in removing R. solanacearum by attachment which depends on the distance between injection and abstraction well. The high removal by attachment alone (18 log 10 after 1 m) would reduce bacterial concentrations to negligible numbers. Upscaling to longer soil passages is discussed in the paper. Infection risks of potato plants were calculated using a dose-response model and ASTR treatment resulted in negligible infection risks of a single plant, but also when simulating the irrigation of a 5 ha potato field. This is the first QMRA that analyzed an agricultural ASTR and the fate of a plant pathogen focusing on plant health. QMRA is a useful (water) management tool to evaluate the treatment steps of water reclamation technologies with the aim to provide safe irrigation water and reduce risks disseminating plant diseases., Competing Interests: Declaration of competing interest Author JV was employed by company Acacia Water B.V. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Abstract Previous studies demonstrated that the transformation of trace organic chemicals (TOrCs) in managed aquifer recharge (MAR) systems is favored under carbon-limited and oxic redox conditions especially, if the dissolved organic carbon (DOC) serving as primary substrate has a refractory character. Since co-metabolism is suggested to be the dominant removal mechanism, it is hypothesized that TOrCs transformation is controlled by the concentration of the refractory carbon under oxic redox conditions. A laboratory-scale soil column experiment mimicking MAR was established to investigate the influence of two different concentrations of highly refractory carbon sources on TOrCs transformation, namely drinking water (DW) and drinking water augmented with humic acid (DW + HA). Oxic redox conditions and carbon-limitation were present in both systems (ΔDOC DW+HA ≈ 0.6–0.7 mg/L; ΔDOC DW ≈ 0.1 mg/L). Of the 12 TOrCs investigated seven exhibited moderate to efficient transformation in both systems with only one compound (diclofenac) showing significantly enhanced (co-metabolic) biotransformation by adding humic acids as primary growth substrate. It is postulated that transformation of some TOrCs is characterized by metabolic degradation under starving conditions (ΔDOC ≤ 0.1 mg/L). By comparing the transformation efficiency of selected TOrCs with previous studies operated under carbon-limited and oxic conditions, an inconsistent behavior of some compounds was observed. These results demonstrate that key factors triggering the transformation of TOrCs are still poorly understood and thus, further investigations regarding the biodegradation pathways of TOrCs, upregulation of key enzymes by the microbial community but also more detailed analysis of the composition of the biodegradable DOC are needed. Highlights • Trace organic chemical (TOrC) transformation during managed aquifer recharge. • Establishment of carbon-limited and oxic conditions. • Primary substrate: drinking water (DW) and DW augmented with humic acids (HA). • No benefit of adding HA as refractory carbon source for co-metabolic transformation. • Inconsistent behavior of some TOrCs even under carbon-limited and oxic conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Managed aquifer recharge sustains an Australian wetland of ecological significance. • Wastewater recharge slows throughflow of regional groundwater near the wetland. • Dense, saline water produced by wetland evapotranspiration recharges the aquifer. • Ingress of recycled water to the wetland is prevented by the subsurface flow system. Abstract A proposal to increase wastewater infiltration at the Kwinana Wastewater Treatment Plant (KWTP) to an unconfined aquifer near a groundwater flow-through wetland (The Spectacles) in Western Australia, prompted a study of the groundwater geochemistry and water levels to identify the water types and to develop a conceptual model for groundwater flow and geochemical evolution. Within the catchment, the water table has dramatically declined (e.g up to −70 to −90 mm/yr over three decades) due to the drying climate and increasing demand for groundwater. Annual rainfall has declined by 9 mm/decade on average or about 1.4% of the annual mean over the last three decadesWastewater infiltration began in 1975 and has increased to the current rate of 4.7 thousand cubic meters per day. Groundwater-surface water interactions were interpreted using multivariate statistical analysis of major ion and stable isotope (δ18O, δD) data. Rainwater infiltrating through the aquifer interacts with carbonate minerals while flowing westward to produce a Ca-HCO 3 type of water (Group 1). Below the wetland, groundwater has an evaporative signature (Group 2) that has higher concentrations of TDS (>1 g/L) and distinctively higher δ18O (>2.5 per mil) than groundwater derived from wastewater infiltration (Group 3). The ratio of ions (K:Cl) was used to understand the mixing of water types and to quantify the proportions of wastewater at the site. Water samples collected in 2014 reveal a high proportion (>34%) of wastewater within the uppermost 30 m of aquifer and generally decreasing proportions with distance away from the source. Further investigation of The Spectacles water balance and hydrochemistry is needed to optimally manage and prevent degradation of the water quality. Proposed increases in wastewater recharge may continue to help offset the impact of the drying climate on lake levels. [ABSTRACT FROM AUTHOR]

The ability of a soil to sustain infiltration rates and to attenuate pollutants is critical for the design and operation of Managed Aquifer Recharge/Soil Aquifer Treatment and phyto-treatment schemes, also referred to as "Blue Infrastructures". We investigated the buffering capacity of a sediment sample and a peat soil sample for nutrients and selected pharmaceutical compounds and its evolution under continuous infiltration of secondary treated wastewater (TWW) in column experiments. Samples were obtained from two blue infrastructures, the Sant'Alessio Induced River Bank Filtration plant and the San Niccolò large-scale phyto-treatment plant in Italy, and were mainly different in their organic carbon contents (0.9 and 48%, respectively). In the column experiments, a constant infiltration rate of about 0.5 L/d was maintained for 6 months. After 4 months of operation, diclofenac and carbamazepine were spiked into the TWW to evaluate their fate. Water quality was monitored by periodic water sampling from the column inflow, at sampling ports along the column length, and at the outflow. Hydraulic conductivity (K) was also monitored. The hydraulic conductivity of the Sant'Alessio sediment decreased by a factor of 10 during the first 10 days of infiltration and then stabilized, while for the San Niccolò K (initially lower) remained constant for 50 days until it decreased following a change of the redox condition in the column. The different redox conditions, due to the two different soils tested, influenced also the concentration and mobility of PO43−, Fe, Mn, and NPOC, and the speciation of the redox sensitive elements (nitrogen and sulfur). NOPC and phosphate were enriched during the filtration through San Niccolò peat soil (from 2 to 4 times, respectively), while they were buffered by the Sant'Alessio sediment (from 0.2 to 0.4 times, respectively). Diclofenac removal (69% and below 20% for San Niccolò and Sant'Alessio, respectively) was related to sorption and degradation processes and it was lower than the removal of carbamazepine in both soils (76 and 35%). The buffer capacity differences between the two soils were higher for diclofenac (62%) than carbamazepine (35%). Nevertheless, since no apparent degradation of carbamazepine was detected in both soils, its persistence in the soil may have a larger impact in case of desorption, posing contamination risk to groundwater. The results highlight the importance of the soils or sediments to be used as medium in such nature-based solutions for their operations. They also offer an approach to, e.g., tailor man-made soil layers in infiltration basins. We strongly suggest that soil characteristics and test duration are carefully considered in designing these infrastructures, when nature-based processes are the choice for dealing with reuse of treated wastewater management issues. [ABSTRACT FROM AUTHOR]

The Middle East and North Africa (MENA) region suffers from low precipitation and high evaporation. Coastal areas of the MENA region are usually densely populated; hence, the coastal aquifers are easily over-exploited beyond their safe yield, and seawater intrusion and aquifer salinization have been caused by the groundwater-level declines. Four studies in MENA coastal aquifers, on seawater intrusion modeling and aquifer recharge and salinization using isotopes, have been brought together in a topical collection and are discussed in this essay. A brief overview is given of managed aquifer recharge as an effective method to combat groundwater-level decline, seawater intrusion and aquifer salinization in MENA counties. [ABSTRACT FROM AUTHOR]

Abstract We present results from field experiments linking hydrology, geochemistry, and microbiology during infiltration at a field site that is used for managed aquifer recharge (MAR). These experiments measured how a horizontal permeable reactive barrier (PRB) made of woodchips impacted subsurface nitrate removal and microbial ecology. Concentrations of dissolved organic carbon consistently increased in infiltrating water below the PRB, but not in un-amended native soil. The average nitrate removal rate in soils below the PRB was 1.5 g/m2/day NO 3 -N, despite rapid infiltration (up to 1.9 m/d) and a short fluid residence time within the woodchips (≤6 h). In contrast, 0.09 g/m2/day NO 3 -N was removed on average in native soil. Residual nitrate in infiltrating water below the PRB was enriched in δ15N and δ18O, with low and variable isotopic enrichment factors that are consistent with denitrification during rapid infiltration. Many putative denitrifying bacteria were significantly enhanced in the soil below a PRB; Methylotenera mobilis and genera Microbacterium , Polaromonas , and Novosphingobium had log 2 fold-changes of +4.9, +5.6, +7.2, and +11.8, respectively. These bacteria were present before infiltration and were not enhanced in native soil. It appears that the woodchip PRB contributed to favorable conditions in the underlying soil for enhanced nitrate removal, quantitatively shifting soil microbial ecology. These results suggest that using a horizontal PRB could improve water quality during rapid infiltration for MAR. Graphical abstract Image 1 Highlights • A horizontal permeable reactive barrier (PRB) was tested for impacts on N-cycling. • The PRB was associated with enhanced nitrate removal during rapid infiltration. • Putative denitrifying microbial clades were enhanced in soils below a PRB. • Geochemical, isotopic, and microbial data are consistent with denitrification. • Using a horizontal woodchip PRB could improve water quality during managed recharge. [ABSTRACT FROM AUTHOR]

This study investigated the removal of selected pharmaceuticals and personal care products (PPCPs) in a simulated managed aquifer recharge (MAR) system. The PPCPs included antibiotic, antiepileptic, antihypertensive, anti-inflammatory, and antilipidemic drugs, contrast media, herbicides, and stimulants. We first monitored the occurrence and fate of 22 PPCPs at a water reclamation facility (WRF) in Korea, and found carbamazepine and primidone were not readily removed (below 25% removal in average) by the WRF. This reclaimed water passed through a laboratory-scale soil column set-up at 0.5 m/d over one year, simulating MAR system. Atenolol, propranolol, and trimethoprim exhibited higher removal rates (>80%) than other PPCPs through the simulated MAR, while atrazine, carbamazepine, lincomycin, primidone, and sulfamethazine were not readily removed, exhibiting removal rates below 20%. It can be efficient to monitor and manage these recalcitrant compounds at MAR systems to improve water quality. [ABSTRACT FROM AUTHOR]

Vadose zone infiltration well (VZW) is an important method to implement managed aquifer recharge (MAR) when groundwater table is relatively deep or sufficiently permeable soils at ground and/or sizable land areas for surface infiltration systems are not available. However, the theoretical model for this kind of artificial recharge has rarely been developed. A mathematical model for the coupled unsaturated‐saturated flow process induced by a VZW is presented in this study with the purpose of understanding the overall hydrodynamics of unsaturated flow and recharge efficiency. Semianalytical solutions for hydraulic heads and recharge rate are derived using Laplace‐Hankel transforms. The solutions are tested using a finite‐element numerical solution built with COMSOL. The performance and capacity of VZW are assessed for different unsaturated zone parameters and well structures. For the case of an unsaturated zone with a small storage capacity, a greater proportion of injected water will be stored in the saturated zone, thus is a favored situation for the implement of MAR using VZWs. Both anisotropy and infiltration well structures have nonnegligible effects on the recharge rate of the saturated zone at early times but have negligible influence at later times. The proposed semianalytical solutions can be used to estimate unsaturated parameters and can also be used to assess the effectiveness of VZWs for the purpose of MAR. Key Points: A novel analytical model for managed aquifer recharge using vadose zone infiltration wells was developedAn unsaturated zone with a small storage capacity is a favored situation for managed aquifer rechargeBoth aquifer anisotropy and well structures have negligible influence on efficiency of managed aquifer recharge [ABSTRACT FROM AUTHOR]

The INOWAS platform provides a compilation of free web-based tools for groundwater management. All tools are running on a web server and can be accessed via standard web browsers. The implemented analytical equations enable the assessment of saltwater intrusion induced by pumping or sea level rise, the calculation of travel time through unconfined aquifers and the evaluation of pumping-induced river drawdown. The groundwater mounding calculator can be used to estimate the rise of groundwater levels underneath infiltration basins. To determine the contaminant concentration downgradient of a constant source, an analytical tool solving the advection-dispersion equation can be utilized. All tools are incorporated into a decision support environment. The user is provided with detailed online support that contains the theoretical background of the tools, possible applications and examples. [ABSTRACT FROM AUTHOR]

Over the last few decades, groundwater resources in many regions have been depleted at a higher rate than the underlying aquifers have been replenished. This imbalance has led water management agencies to consider managed aquifer recharge networks, in which infiltration basins are used to replenish the aquifers using previously uncaptured stormwater runoff. In this work, optimization methods were used to select parameter values to minimize the cost associated with constructing such a network while ensuring the network has the ability to supplement demands placed on the aquifer. The objective function considered incorporates land and construction costs, along with rewards for effective aquifer recharge, and constraints were incorporated to enforce capture of a minimum volume of stormwater runoff. Two hybridized global search algorithms were considered, one based on particle swarm optimization and the other on a genetic algorithm approach. Both methods returned solutions that were close in terms of minimal cost but varied in terms of individual basin sizes. Thus, the algorithms are able to aid decision makers by providing several cost-competitive solutions that can then be used to support a community dialogue. [ABSTRACT FROM AUTHOR]

Chlorination is an effective method to protect the safety of groundwater systems during managed aquifer recharge. However, chlorination leads to the formation of disinfection by-products, whose behavior in aquifers remains unclear and has caused public concern. In this study, an in-site test was performed on an anoxic aquifer in Shouguang City, China, to investigate the formation and transformation of chloroform during managed aquifer recharge. The field tests showed that the formation of chloroform in groundwater caused by the recharge of chlorinated water, and that the fate of chloroform was affected by adsorption and biodegradation. The retardation factor was 1.27, and the half-life was 29 days. The formation and transformation of chloroform during continuous recharge under different hydrochemical conditions was further investigated by batch experiments. These experiments showed that the formation of chloroform increased with contact time, tended to be stable after 10 h, and was facilitated by high chloride/TOC ratios, high pH, and low ionic strength (IS) for a given contact time. The adsorption experiments showed that the process accords with the pseudo-second-order kinetic equations and the Freundlich model. The adsorption capacity was pH dependent (1.01–1.66 μg/g at pH 5 and 2.17–3.05 μg/g at pH 9). Increasing the IS promotes adsorption. The results from biodegradation experiments indicated that the biodegradation was well fitted by the Monod equation. The retardation factor in the batch experiments was close to that of the field test, but the half-life was less than the field test. This is mainly due to the difference in the concentration of dissolved oxygen. [ABSTRACT FROM AUTHOR]

In the coastal dunes of the Western Netherlands, managed aquifer recharge (MAR) is applied for drinking water supply since 1957. The MAR systems belong to the Aquifer Transfer Recovery (ATR) type, because recharge and recovery are operated without interruption. This makes these systems very vulnerable to intake interruptions, which are expected to increase in frequency and duration due to climate change. Such interruptions are problematic, because: (i) groundwater recovery from dunes needs to continue to supply fresh drinking water to the Western Netherlands; (ii) risks of salt water intrusion are high, and (iii) MAR bordering wet dune slacks with an EU Natura 2000 status cannot survive for long without MAR. In this paper, effects of intake stops are discussed and quantified. The hydrological effects consist of the decline of water tables, disappearance of flow-through dune lakes, reservoir depletion, salt water intrusion, disruption of rainwater lenses, and entrapped air hampering a rapid refill of the groundwater reservoir. Water quality effects include changes in (i) redox environment of the flushed aquifer, impacting the behavior of nutrients, calcium, sulfate and organic micro-pollutants, and (ii) the mixing ratio of water types. The main ecological impacts comprise the dying of organisms in recharge ponds and dune lakes, and a decline of biodiversity. Effects of very long intake interruptions (years) are predicted via historical observations during the long overexploitation period (1900–1957) prior to MAR. A closed form analytical solution for safe yield of a semiconfined aquifer is proposed, together with a related upconing risk index. Both also apply to the pumping from any fresh water lens without MAR. Some mitigation strategies are discussed, such as a dual intake, raising the storage capacity, earlier mud removal, and accelerated refilling of the reservoir. A magnitude scale for intake stops (MIS) is proposed. [ABSTRACT FROM AUTHOR]