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

The main objective of this research paper was to find out the major governing factors controlling fluoride enrichment in groundwater resources in the Jaipur region of India. Chemical analysis of collected water samples revealed that 36% of the collected groundwater samples exhibit fluoride concentration of more than 1.5 mg/L as per BIS, 10,500 and WHO, 2017. An attempt has been made to discuss occurrence of fluoride alongside its spatial distribution in the study area with respect to geology and groundwater flow direction. Chloroalkaline indices, Gibb's plot, Piper diagram and various inter-ionic bivariant plots have been applied to recognize hydrochemical processes and dissolution trends resulting in high concentration of fluoride in groundwater. There exist five water types in the study area: Ca-HCO3, Na-HCO3, Na-Cl, Ca-Mg-Cl and Ca-Na-HCO3. Due to ion association of excess Cl− emanating from wastewater, Na-HCO3 type water finally gets changed as Na-Cl type in aquifer. In the study area, 82% of water samples enriched in F− concentration (>1 ppm) pertain to Na-Cl type. Geochemical modelling confirms that reduced Ca2+ ion activity due to oversaturation of calcite with respect to fluorite might have triggered the favourable condition for dissolution of fluoride bearing minerals leading to fluoride enrichment in groundwater. To further assess the extent of natural and anthropogenic processes, the data was subjected to multivariate statistical analysis by performing correlation analysis, principal component analysis and hierarchical cluster analysis. [ABSTRACT FROM AUTHOR]

The present research aims to determine the sources and concentration of uranium in the groundwater of the hard rock aquifer. Two hundred and fifty-four groundwater samples were collected, and the analysis shows the uranium concentrations range from 0.5 to 113 ppb (pre-monsoon) and 0.5 to 120 ppb (post-monsoon). Factor analysis illustrates that the lower concentrations of uranium in the study region may be due to the poor dissolution of minerals in the subsurface. Saturation Index values confirm that the Uraninite mineral is undersaturated, and the U4O9 has dominant distribution during both seasons. During both seasons, four samples have a uranium concentration of more than 60 ppb, which might be due to the fertilizer usage in the agricultural activities in the study area. The GIS technique highlights the uranium-contaminated location and polluted water quality parameters using the Inverse Distance Weighted spatial interpolation plots. [ABSTRACT FROM AUTHOR]

The Ganges River delta complex contains a transboundary aquifer system shared between India and Bangladesh. Although it serves as the main freshwater source for the population inhabiting the delta, the aquifer system is severely contaminated with arsenic (As). This study aimed to determine the control of the delta hydrostratigraphy on the regional-scale depth distribution of As within the aquifer system. We developed the first high-resolution, regional-scale, transboundary hydrostratigraphic model of the Ganges River delta and analyzed the patterns of As distribution as a function of the hydrostratigraphy. Model results indicate that, despite the presence of a single aquifer system across the delta, the hydrostratigraphy is spatially variable and can be architecturally divided into three distinct aquifer subsystems from northwest to southeast: a single, thick continuous aquifer (type I); a vertically segregated, semiconfined aquifer subsystem (type II); and a multilayered, nearly confined aquifer subsystem (type III). Results indicate that the spatial distribution of As is characteristically different in each subsystem. In the type I aquifer, As concentrations tend to be homogeneous at all depths, while in type II and type III aquifers, As concentrations sharply decrease with depth. The intervening aquitards in the type II and type III aquifer subsystems appear to act as natural barriers to infiltration of surficial As or organic matter-rich water to the deeper aquifer zones. This delineation of the regional-scale hydrostratigraphic architecture and resulting understanding of its plausible controls on the depth-distribution of As within the delta should significantly aid in the systematic framing of sustainable management plans for the As-safe aquifers within the Ganges River delta aquifer system. [ABSTRACT FROM AUTHOR]

Chronic arsenic (As) pollution in aquifers is one of the major challenges faced by economically and socially marginalized sections of the world, which often depend heavily on groundwater for their sustenance. To safeguard these sections against As poisoning, an easy-to-use and sustainable water-treatment solution is warranted. This study was undertaken to systematically evaluate the performance and feasibility of a low-cost modified biosand filter (JalKalp) in providing potable water to affected rural households in India. JalKalp removes As by sorption on rusted-iron nails and pathogens by an additional copper layer. Initially, As-removal efficiencies of this filter were evaluated under laboratory conditions using (1) unpolluted groundwater spiked with variable concentrations (50–500 μg/L) of total dissolved arsenic (AsT), either as As(V), or As(III), or both; and (2) real As-polluted groundwater (∼150 μg/L). Results indicated that the JalKalp filter removed AsT with an efficiency of 95–99% and passed all water quality tests, except hardness and alkalinity. An ∼3-year long "JalKalp" program was then initiated to provide clean drinking water in selected villages of Bihar, India with the support of local agents, nongovernmental and governmental organizations. Filters were installed in select households (n = 22), and the community was involved in the program through training and workshops. The performance of these filters was evaluated through the testing of water and sludge generated, and the conduct of socioeconomic and health surveys. The filter was equally effective under field conditions and removed AsT (<10 μg/L), total iron (<1 mg/L), and fecal coliforms at all locations, at a cost of ∼INR 0.28 (US$ ∼0.004)/L of treated water. JalKalp requires replacement of iron nails after an estimated ∼1.7 years of treatment of ∼6,000 L of water containing 100 μg/L of AsT. Toxicity characteristic leaching procedure on As-containing sludge after filtration indicated that the sludge was not hazardous and could be disposed safely in landfills along with regular municipal waste. Findings from this study could be replicated elsewhere in providing immediate solutions to As-affected water pollution by enabling independent construction and sustainable use of this potentially long-lasting filter. [ABSTRACT FROM AUTHOR]

The behavior of As in aqueous media in the complex crystalline aquifers like that of the present study area is not yet understood properly. To that end, groundwater and river water samples from two different seasons are analyzed for As and physicochemical parameters. The groundwater in the area is evolved by simple dissolution or mixing of two or more different facies (Ca2+–Mg2+–Na+–SO42–). However, the majority of samples with the base-exchange indices (85%) and meteoric genesis indices (77%) value less than unitary (<1) divulges that Na+– SO42– type water and deeper meteoric percolation. The estimation of As in groundwater (<0.1–202 ppb) shows the spatial and temporal inconsistency with 17.31% (pre-monsoon) and 11.67% (post-monsoon) of the samples surpassed the permissible limit of 10 ppb. Furthermore, health risk associated with As in terms of hazard quotient (HQ) values > 1 (pre-monsoon: 21.15% and post-monsoon: 20%) for children and carcinogenic risk values >1.00 × 10−6 for different seasons (44.25% and 33.33% of samples) represents a serious health risk. Furthermore, the different stages of Keratosis and Melanosis diseases reported in the study area establish the severity of As toxicity on the local populace. The study concludes geogenic arsenic contamination in the study area is primarily associated with Rhyolite and its comagmatically formed Dongargarh granite batholith emplacements. [ABSTRACT FROM AUTHOR]

Groundwater based irrigation, which was started in India as early as "Indus Civilizations" got impetus during 3rd five-year plan. In India, at present 78 m ha of irrigation potential is created and 80 percent is utilized. One of the World's highest user of groundwater is India with 63 percent of its dynamic groundwater resources. Similarly, Telangana State is also utilizing the dynamic groundwater resources up to 65 percent. Groundwater a reliable source of irrigation with high yields and brings equity among its users as ∼99 % of structures are owned by individuals. In the state, well irrigation increased from ∼0.46 lakh ha from 1875 to 23.35 lakh ha during 2017–18 and well density increased to ∼13 wells/km2 leading to decrease in irrigation potential under each well to < 1 ha. As a result of it many challenges like water logging & salinity in canal command areas, over-exploitation leading to de-saturation of shallow aquifers, underutilization in north eastern part, groundwater pollution (both geogenic and anthropogenic) and sustainability, etc have cropped up. The management steps taken up in water sector like water transfer through KLIP, providing protected water supply through Mission Bhagiratha, de-siltation through Mission Kakatiya, forest rejuvenation through Haritha Haram, construction of various ARS, modernization of canals, conjunctive use of surface and groundwater, user centred aquifer level groundwater management, tank management, IEC activities etc brought positive changes in water availability in the state more particularly surface water. In order to sustain these efforts, formation of WUA at watershed/village level for agricultural planning, change in cropping pattern from highly intensive paddy to ID crops more particularly from non-command areas, conjunctive use of water, warabandhi (on/off) method of releasing irrigation water, developing intercepting drains, soil treatment, declaring crop holidays, separate electric grids for agriculture and domestic supply, legally separating water and land rights and strict implementation of regulatory measures. The other measures suggested are policy interventions that involve regulatory mechanisms and linking village-based institutions to government departments that manage groundwater etc. [ABSTRACT FROM AUTHOR]

Supply of sustainable water is a priority for urbanization of the country. Managed aquifer recharge (MAR) is recommended to enhance the groundwater resources, but finding the favorable site for MAR is quite challenging, particularly, in urbanized karst terrains because of highly heterogeneous and anisotropic properties of carbonate aquifers. The expansion along Naya Raipur is posing a severe threat to its groundwater resources by altering the hydrological framework in the area. In this work, we characterize the unsaturated zone for finding potential pathways for MAR in karst terrain of central India by using hydro-geophysical techniques. Sub-surface geophysical investigations including electrical sounding and profiling, captured the shallow surface of the area to the depth of around 40 m. The Wenner–Schlumberger and gradient methods could decipher strong lateral and vertical anomalies. The low resistivity in the unsaturated zone, as compared to the high resistivity of limestone bedrock is the main path for infiltration. The low resistivity anomalies in the 2D inverted sections might be water filled conduits or solution channels with uncertain geometry. Hydrogeological heterogeneity based on geophysical data helped to locate the favourable zones for construction of MAR structures. The Chokra Nala in the Telibandha area of Raipur is the favorable zone along which MAR could be more effective in replenishing the groundwater. The Telibandha lake area with the indication of the presence of hidden mafic dyke later intruding the limestone after its deposition, was also inferred from the geophysical data. Highlights: Characterizing the unsaturated zone for finding potential pathways for MAR in karst terrain using hydro-geophysical techniques. Establishing MAR along the solution channels, conduits and fracture network. 3D fracture system in limestone from 2D ERT profiles. Mapping hydrogeological heterogeneity based on geophysical data. [ABSTRACT FROM AUTHOR]

Groundwater vulnerability and risk assessment is an essential step for preventing and controlling contamination in any area. DRASTIC model with modification incorporating land use (LU) widely used for assessing groundwater vulnerability worldwide. The present study used this modified model termed as DRASTIC-LU considering LU as a significant parameter in addition to other conventional DRASTIC parameters. Geographic information system employed to prepare and integrate different parameter maps led to demarcate the risk zones in a catchment of Damodar River, Jharkhand, India. Final DRASTIC-LU map was categorized as low (19.50%), moderate (34.02%), high (29.90%) and very high (16.58%) risk zones of groundwater contamination. Validation of models done through Spearman's rank correlation coefficient (ρ) and receiver operating characteristic curve using nitrate concentration in groundwater, which indicated DRASTIC-LU (ρ = 0.893; AUC = 71.65%) had a better agreement than DRASTIC model (ρ = 0.7818; AUC = 67.36%). Thus, such modification in DRASTIC improves the performance of the model. [ABSTRACT FROM AUTHOR]

Groundwater is the most vulnerable, exploited natural resource which is a key source of freshwater in the world. Its regular decline in both quality and quantity are an important concern of research. The focus of the present study is to understand the important hydrogeochemical processes involved in the groundwater evolution of Vishwamitri River Basin (VRB), Gujarat, India, using Principal Component Analysis (PCA) technique. To achieve a symmetrical data distribution, log-transformation was applied in this study. This statistical approach decreases the data outlier. A Shapiro-Wilk statistic was employed to test the normal distribution of the data set. The results revealed that ten elements (TDS, bicarbonate, chloride, sulfate, sodium, calcium, magnesium, fluoride, iron and strontium) showed normal distribution. The PCA of 60 groundwater samples using 10 normally distributed chemical parameters indicates that the dominant geochemical process is rock-water interaction through dissolution and cation exchange reactions within the VRB aquifers. This study also reveals that, due to over use of chemical and fertilizers, the sulfate loading is high in groundwater. Therefore, the combined process of natural rock-water interaction, weathering and anthropogenic activities play a significant role in controlling the chemical composition of groundwater of VRB. [ABSTRACT FROM AUTHOR]

Unsustainable exploitation of groundwater in northwestern India has led to extreme but spatially variable depletion of the alluvial aquifer system in the region. Mitigation and management of groundwater resources require an understanding of the drivers behind the pattern and magnitude of groundwater depletion, but a regional perspective on these drivers has been lacking. The objectives of this study are to (1) understand the extent to which the observed pattern of groundwater level change can be explained by the drivers of precipitation, potential evapotranspiration, abstraction, and canal irrigation, and (2) understand how the impacts of these drivers may vary depending on the underlying geological heterogeneity of the system. We used a transfer function-noise (TFN) time series approach to quantify the effect of the various driver components in the period 1974–2010, based on predefined impulse response functions (θ). The dynamic response to abstraction, summarized by the zeroth moment of the response M 0, is spatially variable but is generally large across the proximal and middle parts of the study area, particularly where abstraction is high but alluvial aquifer bodies are less abundant. In contrast, the precipitation response is rapid and fairly uniform across the study area. At larger distances from the Himalayan front, observed groundwater level rise can be explained predominantly by canal irrigation. We conclude that the geological heterogeneity of the aquifer system, which is imposed by the geomorphic setting, affects the response of the aquifer system to the imposed drivers. This heterogeneity thus provides a useful framework that can guide mitigation efforts; for example, efforts to decrease abstraction rates should be focused on areas with thinner and less abundant aquifer bodies. [ABSTRACT FROM AUTHOR]

Gravity Recovery and Climate Experiment (GRACE) satellite mission is ground‐breaking information hotspot for the evaluation of groundwater storage. The present study aims at validating the sensitivity of GRACE data to groundwater storage variation within a basaltic aquifer system after its statistical downscaling on a regional scale. The basaltic aquifer system which covers 82.06% area of Maharashtra state in India, is selected as the study area. Five types of basaltic aquifer systems with varying groundwater storage capacities, based on hydrologic characteristics, have been identified within the study area. The spatial and seasonal trend analysis of observed in situ groundwater storage anomalies (ΔGWSano) computed from groundwater level data of 983 wells from the year 2002 to 2016, has been performed to analyze the variation in groundwater storages in the different basaltic aquifer system. The groundwater storage anomalies (ΔGWSDano) have been derived from GRACE Release 05 (RL05) after removing the soil moisture anomaly (ΔSMano) and canopy water storage anomaly (ΔCNOano) obtained from Global Land Data Assimilation System (GLDAS) land surface models (NOAH, MOSAIC, CLM and VIC). The artificial neural network technique has been used to downscale the GRACE and GLDAS data at a finer spatial resolution of 0.125°. The study shows that downscaled GRACE and GLDAS data at a finer spatial resolution is sensitive to seasonal groundwater storage variability in different basaltic aquifer systems and the regression coefficient R has been found satisfactory in the range of 0.696 to 0.818. Article impact statement: Validation of sensitivity of GRACE‐GLDAS data to groundwater storage variations within a basaltic aquifer system by statistical downscaling technique using artificial neural network (ANN). [ABSTRACT FROM AUTHOR]

Reported groundwater recovery in South India has been attributed to both increasing rainfall and political interventions. Findings of increasing groundwater levels, however, are at odds with reports of well failure and decreases in the land area irrigated from shallow wells. We argue that recently reported results are skewed by the problem of survivor bias, with dry or defunct wells being systematically excluded from trend analyses due to missing data. We hypothesize that these dry wells carry critical information about groundwater stress that is missed when data are filtered. Indeed, we find strong correlations between missing well data and metrics related to climate stress and groundwater development, indicative of a systemic bias. Using two alternative metrics, which take into account information from dry and defunct wells, our results demonstrate increasing groundwater stress in South India. Our refined approach for identifying groundwater depletion hot spots is critical for policy interventions and resource allocation. Plain Language Summary: Over the last century, groundwater has become an important source of freshwater to meet agricultural and drinking water needs. Increasing use of groundwater has contributed to depletion of groundwater reserves around the world, with India being at the forefront of this problem. Recent studies suggest that groundwater levels have been increasing in South India due to increasing rainfall and political interventions. This finding is at odds with local reports of groundwater stress, and increasing well failures. Our study explains this disagreement by showing that previous conclusions have been skewed by the problem of survivor bias, with wells with data gaps being routinely excluded from analysis of long‐term groundwater storage trends. We find that traditional groundwater trend assessment methods are not suitable for hard‐rock aquifer systems that characterize South India. Indeed, strong correlation exists between climate and groundwater stress and wells with missing data, indicative of a systemic bias. We develop metrics that use data from these wells, and show using these metrics increasing evidence of groundwater stress in South India over the last two decades (1996 to 2016). Our results provide insight into the management of groundwater depletion in India, while highlighting potential biases in groundwater sustainability assessments globally. Key Points: Reported recovery of groundwater levels in South India is at odds with increasing well failures and reports of groundwater stressApparent paradox is explained by survivor bias, where wells with missing data are routinely excluded from analysis of groundwater trendsLong‐term trend analysis is not appropriate for hard‐rock aquifer of South India; alternative metrics developed that highlight groundwater stress [ABSTRACT FROM AUTHOR]

Groundwater aquifer vulnerability has been assessed by incorporating the major geological and hydrogeological factors that affect and control the groundwater contamination using GIS-based DRASTIC model along with solute transport modeling. This work demonstrates the potential of GIS to derive a vulnerability map by overlying various spatially referenced digital data layers (i.e., depth to water, net recharge, aquifer media, soil media, topography, the impact of vadose zone and hydraulic conductivity) that portrays cumulative aquifer sensitivity ratings in Kishangarh, Rajasthan. It provides a relative indication of groundwater aquifer vulnerability to contamination. The soil moisture flow and solute transport regimes of the vadose zone associated with specific hydrogeological conditions play a crucial role in pollution risk assessment of the underlying groundwater resources. An effort has been made to map the vulnerability of shallow groundwater to surface pollutants of thestudy area, using soil moisture flow and contaminant transport modeling. The classical advection-dispersion equation coupled with Richard’s equation is numerically simulated at different point locations for assessing the intrinsic vulnerability of the valley. The role of soil type, slope, and the land-use cover is considered for estimating the transient flux at the top boundary from daily precipitation and evapotranspiration data of the study area. The time required by the solute peak to travel from the surface to the groundwater table at the bottom of the soil profile is considered as an indicator of avulnerability index. Results show a high vulnerability in the southern region, whereas low vulnerability is observed in the northeast and northern parts. The results have recognized four aquifer vulnerability zones based on DRASTIC vulnerability index (DVI), which ranged from 45 to 178. It has been deduced that approximately 18, 25, 34, and 23% of the area lies in negligible, low, medium and high vulnerability zones, respectively. The study may assist in decision making related to theplanning of industrial locations and the sustainable water resources development of the selected semi-arid area. [ABSTRACT FROM AUTHOR]

• During PRM, major ion concentrations are higher than PM season due to evaporation. • GW types varied from NaCl > CaMgCl > CaHCO 3 (PRM) to CaHCO 3 = NaHCO 3 = NaCl (PM). • PRM - Mineral weathering, reverse ion exchange and evaporation dominant processes. • PM - Mineral weathering, cation exchange and dilution regulate water chemistry. • Monsoon recharge facilitated the pollutant movement from the surface to aquifer. Impact of monsoon recharge on groundwater chemistry and geochemical processes was evaluated using geochemical methods in the shallow hard-rock aquifer, southern India. Groundwater samples were collected from Salem city and its outskirts during pre-monsoon (PRM) and post-monsoon (PM) seasons and analysed for major and minor ions. Results suggest that during PRM, the average concentration of TDS, major ions and electrical conductivity (EC) in groundwater are higher than the PM season except for Na+ and HCO 3 –. The major water types also varied with seasons (PRM: NaCl > CaMgCl > CaHCO 3 ; PM: CaHCO 3 = NaHCO 3 = NaCl). Pearson correlation analysis indicates that Cl− and SO 4 2− show a strong positive correlation with EC, TDS, TH and major cations during PRM season whereas HCO 3 – and NO 3 – have a strong positive correlation with most of the ions during PM season. Before monsoon, the water chemistry is governed by the weathering of carbonate and silicate minerals, reverse ion exchange and evaporation processes, which resulted in high EC, TDS, TH and major ions in the groundwater. After the monsoon, the water chemistry is regulated by the mineral weathering, cation exchange and dilution processes. Geochemical modelling studies indicate that groundwater is saturated and oversaturated with carbonate minerals and undersaturated with sulphate and chloride minerals. During monsoon, the recharging water flushed the weathered layer and dissolved the soil CO 2 in the vadose zone, which subsequently enhanced the concentration of Na+ and HCO 3 – in the aquifer. Further, the high concentrations of Cl−, SO 4 2- and NO 3 – imply that the aquifer is polluted by surface contamination sources. After the monsoon, NO 3 – implies that monsoon recharge facilitated the pollutant movement from surface to the aquifer. Hence, a proper aquifer management plan is required to protect this aquifer and to provide clean and safe drinking water to the local community. [ABSTRACT FROM AUTHOR]

Mapping and managing groundwater resources are essential for socio-economic and sustainable development. Analysis of hydrogeochemical parameters of the groundwater for the Lower Ganga basin is presented to identify the contamination zones and also to understand the groundwater quality in this region. Drainage pattern analysis identifies five sub-basins in the region. Shannon's entropy information theory has been performed to compute the water quality index (WQI) without having any subjective bias in the analysis. The analysis of the WQI shows that sub-basin 2 (WQI = 38.35) has excellent quality of groundwater, whereas sub-basin 1 (WQI = 52.43), 3 (WQI = 63.94), and 5 (WQI = 82.79) are having good groundwater quality. On the other hand, sub-basin 4 (WQI = 102.99), which covers mostly the central part of the main stream, is found to be most contaminated and having a medium quality of the groundwater. Analysis of the groundwater parameters using the PCA indicates that the quality of groundwater in the study area is controlled mainly by three main factors, which are geogenic process (weathering and leaching of rocks), seawater intrusion (natural process), and anthropogenic activities. Furthermore, hydrometeorological analysis shows a gradual drop in precipitation, water level depth, and the percolation index (PI). This indicates an over exploitation of groundwater resources in the study region under the present circumstances of climate variability, population and industrialization. The results obtained in this paper are useful for identifying suitable sites for tube-wells and bore-wells for drinking and agricultural purposes, and also for developing an effective strategy to avoid further contamination of groundwater aquifers in the region. Results are extremely useful for government agencies and policymakers in achieving the United Nations (SDG-6) goals of suitable planning and sustainable development of groundwater resources by 2030. • The Lower Ganga acts as the accumulation zone of contaminants coming from the Upper Ganga Basin in northern India. • Entropy information theory has been used for the assessment of the WQI. • The primary contaminant in this region are TDS, F−, Cl−, and NO 3 −. • Spatio-temporal analysis of the hydrometeorological parameter shows the changing pattern due to climate variability. • Results are useful in achieving the United Nations Goal (SDG-6) for sustainable development of groundwater resources by 2030. [ABSTRACT FROM AUTHOR]