Integrated hydrogeophysical and GIS based demarcation of groundwater potential and vulnerability zones in a hard rock and sedimentary terrain of Southern India.

This research has identified the groundwater potential and vulnerability zones in Tiruchirappalli district of Tamil Nadu, India. The Schlumberger electrode array has been used to conduct vertical electrical sounding (VES) at 95 sites with a maximum electrode spacing of 150 m. The study area comprises of hard rock and sedimentary formations. Geographical Information System (GIS) has been used to integrate the geoelectrical data and to prepare spatial variation maps for various parameters. Finally, groundwater potential and vulnerability zones have been demarcated, and these outputs have been validated using water level and nitrate data, respectively. The Dar-Zarrouk parameters such as longitudinal conductance (S), transverse unit resistance (T), and aquifer anisotropy (λ) have been used along with the spatial variation of resistivity and aquifer thickness to find out groundwater potential areas with the support of GIS. The thickness of topsoil, weathered zone and fractured zone are not uniform in the research area. Top soil plus weathered zone acts as a water table (phreatic) aquifer, which extends up to 38 m from the surface. Fractured zone extends up to 45 m, which acts as a kind of confined/semi-confined aquifer. Open and bore wells have been constructed to tap groundwater from the unconfined (water table) and confined/semi-confined aquifers, respectively. High to very high groundwater potential areas are associated with low resistivity, high thickness, low longitudinal conductance, high transverse unit resistance and high aquifer anisotropy areas. Very high groundwater potential areas are mostly confined to flood plain (alluvium) deposits in the central portion of the study area. High potential areas are noticed in the northern part, whereas low potential areas are noticed in the southern part. The areas with high longitudinal conductance indicate low permeable zones with less possibility of external pollution. Since agriculture is an important activity in the study region, this work will be useful to provide water supply for irrigation as well as for domestic needs.

Environmental chemistry, toxicity and health risk assessment of groundwater: Environmental persistence and management strategies.

Groundwater is a significant supply of freshwater for the world's population, being used for residence, agricultural, and industrial purposes. One-third of the world's population relies on groundwater for drinking applications. Groundwater pollution is a global issue with serious consequences for human health and the environment. It needs a thorough understanding because access to safe drinking water is a basic human right. However, groundwater quality is being threatened by urbanisation, agricultural activities, industrial activities, and climate change, among others. Pollutants like hydrocarbons, toxic metals, pesticides, microplastics, nanoparticles and other emerging contaminants mean a risk to human health and sustainable socioeconomic development. To ensure sustained groundwater usage to assess, monitor, and regulate groundwater quality issues is essential. Excess withdrawal alters groundwater flow together with contaminants like uranium, radon, radium, salinity, arsenic and fluoride, resulting in mediocre water quality. Consequently, chemical and biological contaminants owing to domestic, industrial, and agricultural practices alter water quality and threaten human health. Controlling and management of groundwater pollution and related health risks require developing vulnerability, hazard, and risk maps.

Hydrogeochemical assessment of groundwater quality and suitability for irrigation in the coastal part of Cuddalore district, Tamil Nadu, India.

A study was undertaken to identify in the irrigational suitability of groundwater in the cuddalore district (coastal part), Tamil Nadu, India. An entire study, 132 shallow and deep groundwater samples was gathered during Pre monsoon period (PRM) year of 2017 and post monsoon (POM) period samples collected year of 2018. Rock water interaction, silicate weathering and domestic waste are dominant sources for the water quality in the study area. The groundwater classification and irrigational suitability of groundwater were performed for both seasons. From the results of Chloro-Alkaline Indices (CAI I), and Chloro-Alkaline Indices (CAI II), during both seasons and classes, the direct ions exchange processes are predominant when compare with reverse ions exchange processes. The r1 and r2 results represents that most of the samples found as saline sources as Na+ - SO42- facies and performing with Deep Meteoric Percolation (DMP) than shallow meteoric percolation During PRM season, r1 represents 65 (98%) samples for Na+ - SO42- facies and 1 (2%) sample represents Na+ - HCO3- facies and during POM season, r1 represents 63 (95%) samples for Na+ - SO42- facies and 3 (5%) samples represent Na+ - HCO3- facies respectively. Irrigation water quality parameters like and satisfied the analysed water's irrigation suitability. However, according to MAR parameters, 5% of water samples were unsuitable for irrigation in PRM based on KR parameters, 41% of samples collected in the PRM season only were unsuitable for irrigation. The Wilcox diagram showed that 35% of water samples are suitable for irrigation. Sodium Adsorption Ratio (SAR), Soluble Sodium Percentage (SSP), Magnesium Adsorption Ratio (MAR), Permeability Index (PI), Potential Salinity (PS), and Total Dissolved Solids (TDS) are indicating the irrigational appropriateness of the groundwater samples, which is more suitable in post monsoon season compare to pre monsoon due to enrichment of Na+ by seawater intrusion and other processes. During POM season, the most number of groundwater samples are representing excellent to good categories might be due to an effective rainfall recharge by the monsoonal rain in the study area. The parameters indicated the introduction of geogenic and anthropogenic pollutions. The coastal community's knowledge is crucial to the long conservation of coastal water resources.

Provincial and seasonal influences on heavy metals in the Noyyal River of South India and their human health hazards.

This study was carried out to evaluate the heavy metals (Lead (Pb), Nickel (Ni), Chromium (Cr), Copper (Cu), Cadmium (Cd) and Zinc (Zn)) pollution in the Noyyal River of South India by collecting 130 river water samples (65 each in pre- and post-monsoon). The heavy metals were measured using Atomic Absorption Spectrophotometer (AAS). The data were used to calculate the associated health hazards for the inhabitants consume river water. Correlation analyses and average concentration of heavy metals denoted that post-monsoon metal concentrations were lesser compared to the pre-monsoon due to dilution effect. Modified Contamination Degree (MCD) indicated that 45% of pre-monsoon and 25% of post-monsoon samples were classified under extremely polluted category. Heavy metal pollution index (HPI) showed that all the regions fall under highly polluted category except 'Region I' where 20% of samples were under safe category during the pre-monsoon, whereas 9%,28%, 17% and 26% of samples in Regions I, II, III and IV were highly polluted during the post-monsoon season, respectively. Ecological Risk Index (ERI) revealed that high risks attained in Regions II (78%) and III (82%) during pre-monsoon, and reduced risks found in Regions II (28%) and III (45%) during post-monsoon season due to dilution by monsoon rainfall. Non-carcinogenic risks as inferred by the Hazard Index (HI) indicated that 78% and 52% of samples for infants, 75% and 49% of samples for teens and 71% and 45% of samples for adults exceeded the threshold limits of USEPA (HI > 1) and possessed risks during pre- and post-monsoon, respectively. The cancer risk assessment based on ingestion of heavy metals indicated that the order of risk is Ni > Cr > Cu. The HI for infants and teens was notably high to that of adults in both the seasons. This study will be useful to develop effective strategies for improving river water quality and to reduce human health hazards.

Effects of COVID-19 pandemic lockdown on microbial and metals contaminations in a part of Thirumanimuthar River, South India: A comparative health hazard perspective.

Twenty-two water samples from the Thirumanimuthar River course in southern India were collected before COVID-19 lockdown and during COVID-19 lockdown periods and were analyzed for microbiological parameters (fecal coliform bacteria, total coliform bacteria, Escherichia coli, and fecal streptococci) and heavy metals (Fe, Mn, Zn, Cu, Cd, Ni, Pb and Cr). The lockdown has decreased microbial populations and heavy metals. Fe, Cu, Cd, Ni, Pb and Cr exceeded the drinking water limits, respectively, in 77%, 45%, 27%, 18%, 9% and 91% of the pre-lockdown samples. During the lockdown period, Fe, Cu and Cd concentrations in 23% and Cr in 50% of the samples exceeded the limits. Heavy Metal Pollution Index (PI) expressed that 27%, 64% and 9% of the pre-lockdown samples represented 'low', 'medium' and 'high' pollution categories, respectively, but 68% and 32% of the lockdown period samples represented 'low' and 'medium' categories, respectively. The Metal Index (MI) exposed that all samples of pre-lockdown were under the seriously affected category, whereas 54% and 46% of lockdown samples were under strongly and seriously affected categories, respectively. Health risk evaluation predicted that 95%, 91% and 86% of pre-lockdown samples and 45%, 36% and 33% of lockdown period samples were at risk among children, teenagers and adults, respectively. As there is no integrated study on river water quality of COVID-19 lockdown this work is uniquely carried out by combining heavy metal pollution, microbial contamination and human health risk evaluation.

Investigation of health risks related with multipath entry of groundwater nitrate using Sobol sensitivity indicators in an urban-industrial sector of south India.

In the present study, we used a variance decomposition based global sensitivity index to evaluate the sensitivity of input variables and their contribution for non-carcinogenic health risks via intake and dermal pathways. Groundwater samples were collected from an industrial sector (Tiruppur region) of south India during the month of January 2020. These samples were analysed for nitrate, which varied from 10 to 290 mg L-1 having the mean of 87 mg L-1. Nearly 58% of the samples surpassed the permissible limit (45 mg L-1) defined by the World Health Organization. Total hazard index (THI) ranged from 0.29 to 8.52 for children, 0.28 to 8.26 for women, and 0.24 to 6.99 for men. The first-order effect (FOE) and second-order effect (SOE) were derived for the three different age groups using Sobol sensitivity approach. The FOE scores showed that nitrate concentration in groundwater is the most sensitive parameter followed by exposure frequency for children, men and women via oral pathway. The SOE scores showed that nitrate concentration along with ingestion rate had greater sensitiveness in the oral input model. The higher SOE was obtained for the interaction of nitrate with skin surface area for children via dermal pathway, but it was not significant for women and men. These results suggest that epidemiology due to nitrate risk should be studied taking into account of concentration of nitrate, exposure frequency, fraction of contact and body weight. Additionally, ingestion rate and skin surface area were considered for the assessment of health risks for children.

Integrated use of inverse and biotic ligand modelling for lake water quality resilience estimation: A case of Ramsar wetland, (Deepor Beel), Assam, India.

The present study evaluates the vulnerability of the lake system (Deepor Beel) due to the combined exposure of toxic metals, major ions and mineral dissociation. The hydro-chemistry of the Deepor Beel lake reveals the dominance of carbonate weathering with strong evidences of ion-exchange reaction occurring throughout the monsoon season of 2014 and 2015. Through an integrated application of multivariate analysis, the occurrence of albite weathering was confirmed, although as an isolated incidence only, along-with substantial evidence of waste water intrusion from fertilizer industries. The moderate cation exchange capacity (CEC) of the soil, indicates the presence of illite, chlorite and kaolinite which provides a strong buffering action in terms of phosphorous and nutrient retention. However, occurrences of chemical waste in the form of bleaching powder (Ca(OCl)2) are causing acidification of lake soil, which will trigger the release of phosphorous and may enhance the eutrophication level in near future. Through the simulations of Biotic Ligand (BL) model on ceriodaphnia dubia, it is being revealed, that the free availability of Ca2+ in the lake water, provides a higher adsorptive competition for labile metal species especially for Cu and Zn. Additionally, the risk among children from drinking lake water, has increased by three to seven times in a duration of just one year. The present study is a pioneering work, which has evaluated the vulnerability of Deepor Beel lake by adopting a sequential assessment strategy of lake internal as well as external ecology. Our proposed methodology can be a used as a scientific basis for future assessment of the lake health.

Chromium contamination in groundwater and Sobol sensitivity model based human health risk evaluation from leather tanning industrial region of South India.

The present investigation was conducted to find the possible chromium contamination in groundwater and the related health risks in a leather industrial region of south India using Sobol sensitivity modeling. Thirty-five groundwater samples were sampled from the field sites and were analyzed for pH, TDS (Total Dissolved Solids), EC (Electrical Conductivity), F- (Fluoride), NO3- (Nitrate) and Cr (Chromium). The concentration of nitrate varied from 3 to 81 mg/L with a mean of 48.6 mg/L. About 57% (n = 20) of the wells surpassed the drinkable limit (45 mg/L) for NO3- as per World Health Organization (WHO). The fluoride ion ranged from 0.1 to 2.7 mg/L with a mean of 1.5 mg/L. Around 51% (n = 18) of the samples crossed the recommended limit of WHO for F- (1.5 mg/L). The chromium varied from 0.01 to 0.19 mg/L in groundwater with a mean of 0.1 mg/L. About 66% (n = 23) of the samples overshoot the permissible limit of WHO standards (0.05 mg/L) for Cr. The spatial distribution map of chromium in the groundwater showed that 271.76 km2 area is under risk. Based on total hazard index (THI), 66%, 46%, and 43% of the groundwater samples surpassed the allowable limit (THI > 1) for children, women and men, correspondingly. Children pose severe health risks than women and men in this region. Using Sobol sensitivity indices, three different categories of risk effects were assessed: first order effect (FOE), total effect (TE) and second order effect (SOE). In the oral sensitivity model, concentration of Cr (Cw) in water and ingestion rate (IR) had the dominant role, whereas in the dermal model, skin surface area (SA) and contact fraction by skin (F) had vital role in addition to the concentration (Cw). Further, the outcome of this study insists the responsibilities of industrial, municipal and agricultural sectors to keep the environment pollution free and to ensure the supply of potable water to the people.

Sources and Consequences of Groundwater Contamination.

Groundwater contamination is a global problem that has a significant impact on human health and ecological services. Studies reported in this special issue focus on contaminants in groundwater of geogenic and anthropogenic origin distributed over a wide geographic range, with contributions from researchers studying groundwater contamination in India, China, Pakistan, Turkey, Ethiopia, and Nigeria. Thus, this special issue reports on the latest research conducted in the eastern hemisphere on the sources and scale of groundwater contamination and the consequences for human health and the environment, as well as technologies for removing selected contaminants from groundwater. In this article, the state of the science on groundwater contamination is reviewed, and the papers published in this special issue are summarized in terms of their contributions to the literature. Finally, some key issues for advancing research on groundwater contamination are proposed.

Groundwater Pollution and Human Health Risks in an Industrialized Region of Southern India: Impacts of the COVID-19 Lockdown and the Monsoon Seasonal Cycles.

Samples of groundwater were collected during a post-monsoon period (January) and a pre-monsoon period (May) in 2020 from 30 locations in the rapidly developing industrial and residential area of the Coimbatore region in southern India. These sampling periods coincided with times before and during the lockdown in industrial activity and reduced agricultural activity that occurred in the region due to the COVID-19 pandemic. This provided a unique opportunity to evaluate the effects of reduced anthropogenic activity on groundwater quality. Approximately 17% of the wells affected by high fluoride concentrations in the post-monsoon period returned to levels suitable for human consumption in samples collected in the pre-monsoon period. This was probably due to ion exchange processes, infiltration of rainwater during the seasonal monsoon that diluted concentrations of ions including geogenic fluoride, as well as a reduction in anthropogenic inputs during the lockdown. The total hazard index for fluoride in the post-monsoon samples calculated for children, adult women, and adult men indicated that 73%, 60%, and 50% of the groundwater samples, respectively, had fluoride levels higher than the permissible limit. In this study, nitrate pollution declined by 33.4% by the pre-monsoon period relative to the post-monsoon period. The chemical facies of groundwater reverted from the Na-HCO3-Cl and Na-Cl to the Ca-HCO3 type in pre-monsoon samples. Various geogenic indicators like molar ratios, inter-ionic relations along with graphical tools demonstrated that plagioclase mineral weathering, carbonate dissolution, reverse ion exchange, and anthropogenic inputs are influencing the groundwater chemistry of this region. These findings were further supported by the saturation index assessed for the post- and pre-monsoon samples. COVID-19 lockdown considerably reduced groundwater pollution by Na+, K+, Cl-, NO3¯, and F- ions due to shutdown of industries and reduced agricultural activities. Further groundwater quality improvement during lockdown period there is evidence that the COVID-19 lockdown by increased HCO3¯ ion concentration. Overall results illustrate the positive benefits to groundwater quality that could occur as a result of measures to control anthropogenic inputs of pollutants.

Revealing drinking water quality issues and possible health risks based on water quality index (WQI) method in the Shanmuganadhi River basin of South India.

The aim of the study is to address the issues and associated health risks due to consumption of high-fluoride water supplied for drinking in a rural part of Shanmuganadhi River basin, Tamil Nadu, India. In this study, 61 groundwater samples were gathered from various tube and open wells and analysed for fluoride and other physicochemical parameters. The abundance of cations is Na+ > Ca2+ > Mg2+ > K+, and that of anions is HCO3- > SO42- > Cl- > F-. The fluoride concentration in drinking groundwater varied from 0.10 to 3.3 mg/l. According to the WHO standards, about 26% of the samples were unfit for drinking requirements (16 out of 61 samples) Water quality index (WQI) method was adopted to categorize the water into different classes to understand its suitability for drinking requirements. WQI signified that nearly 52% of the samples denoted poor, very poor and not suitable categories, whereas 48% of samples denoted good and excellent categories for consumption. Health risks associated with high-fluoride drinking water were assessed for various age groups of inhabitants such as children, teens and adults. The hazard quotient estimated based on the oral intake ranged from 0.00E+00 to 5.50E+00, from 0.00E+00 to 4.22E+00 and from 0.00E+00 to 3.45E+00 for children, teens and adults, respectively. It suggested that the health risks are associated with 75%, 59% and 43% of samples, respectively, among children, teens and adults. Therefore, children are more inclined towards risk than teens and adults in this region based on the intake of fluoride-rich drinking water. To improve the present scenario, groundwater should be either treated before drinking water supply or must be artificially recharged to lower the concentration of ions.

Promoting artificial recharge to enhance groundwater potential in the lower Bhavani River basin of South India using geospatial techniques.

The artificial recharge is an alternative technique to augment surface water and groundwater and for providing continuous supply of water to the demand regions. The scope of contemporary study helps in evaluation of groundwater potential zones and to find proper zones and sites for groundwater recharge using geospatial and multi-criteria decision analysis (MCDA) techniques. In this study, the pragmatic methodology was proposed for the implementation of water harvesting structures. The satellite and conventional datasets with field inferences were systematically processed to obtain various thematic information of the study area. The analytical hierarchical process (AHP) in geographical information system (GIS) was utilized to assign the geometric mean and the normalized weight for the individual features. Further, groundwater potential zones were identified, and they were categorized into four types viz. very high (523.58 km2), high (798.22 km2), moderate (646.04 km2) and low (456.66 km2). Nearly, 54.52% of the study area falls in the 'very high' to 'high' potential categories. The GIS-based Boolean logical method was also executed to identify suitable areas for creating recharge structures such as check dams (127.47 km2), percolation ponds (115.23 km2), flood and furrows (63.01 km2) and ditch and furrows (1046.31 km2). Based on the above results, 36 water harvesting structures were promoted to augment the groundwater resources of the basin. The highest priority was given to check dams (19 Nos), followed by percolation ponds (7 Nos), flood and furrows (5 Nos) and ditch and furrows (5 Nos). The suggested structures would improve the groundwater availability for agriculture and domestic purposes in the study area. Further, the outcomes could deliver a scientific procedure to the decision makers and water scientists for effective water resources development and management planning. Overall, the integrated remote sensing, GIS and MCDA methods are an efficient and useful tool for planning and improving groundwater recharge in the basin scale.

Health risks associated with fluoride intake from rural drinking water supply and inverse mass balance modeling to decipher hydrogeochemical processes in Vattamalaikarai River basin, South India.

Preliminary investigation reveals that fluorosis is reported due to the continuous intake of fluoride-rich groundwater in Vattamalikarai River basin, Tamil Nadu, India. A detailed study was attempted for evaluating the health risks associated with the intake of fluoride-rich groundwater supplied to the rural community. Groundwater samples were collected from 60 and 58 dug and tube wells during winter and southwest (SW) monsoon seasons respectively. The samples were analyzed for the determination of fluoride and other chemical parameters to examine the fitness for drinking water. Spatio-temporal variation maps reveal that fluoride concentration is high during SW monsoon season when compared with the winter season in this region. The fluoride bearing minerals present in hornblende-biotite gneiss and charnockite rock formations leached into the groundwater during rock-water interaction. To understand the subsurface hydrogeochemical reactions, inverse mass balance model was developed using NETPATH code. The model output indicates that calcite dilution, silicate (hornblende and biotite) weathering, ion exchange (Ca/Na and Mg/Na) and illite precipitation are the dominant processes controlling the groundwater chemistry along the flow paths. Non-carcinogenic risks to children and adults (women and men) were evaluated by working out intake exposure of groundwater. Hazard quotient (HQ) based on fluoride intake was calculated for children and adults. It varied from 0.08 to 2.21 with an average of 1.07 for adults. For children, it varied from 0.01 to 2.99 with the mean of 1.44. About 78%, 69% and 61% of the samples fall under the risk category for children, women and men during winter season. However, more number of samples possessed health risks (83% of samples for children, 73% of samples for women and 64% of samples for men) during SW monsoon season.

Appraisal of subsurface hydrogeochemical processes in a geologically heterogeneous semi-arid region of south India based on mass transfer and fuzzy comprehensive modeling.

The main aim of the present study was to examine the quality of the groundwater and decipher the sources of groundwater fluoride through mass balance modeling based on fluoride exposure in a geologically heterogeneous semi-arid region of southern India. This was achieved by hydrogeochemical analysis, graphical methods, and mass transfer modeling approaches. Fuzzy comprehensive technique was applied to evaluate the quality of groundwater for groundwater management. In this regard, 61 groundwater samples were obtained from open wells and bore wells and analyzed for different physicochemical parameters. The major cation and anion abundances follow the order Na+ > Ca2+ > Mg2+ > K+ and Cl- > HCO3- > SO42- > NO3- > PO43-. About 88.4% and 34.4% of the total water samples were dominated with Na+ and Cl- ions in this region, respectively. The fluoride level in groundwater ranged from 0.10 to 3.30 mg/l with a mean value of 1.04 mg/l. Nearly 25% of the groundwater samples collected from 15 villages showed fluoride concentrations exceeding the maximum permissible limit of 1.5 mg/l as per the World Health Organization recommendations for human intake. More than 85% of the samples fell under strong acid (Cl- and SO42-) type. The amount of groundwater salinization in this region was 70.5% since the Revelle index (RI) was excess in the groundwater samples (RI > 0.5 meq/l). Silicate weathering, cation exchange, and gypsum dissolution were the dominant geogenic processes in the aquifer system influencing groundwater chemistry and nullified the possibility of carbonate dissolution. Saturation indices revealed the contribution of sequestration of CaCO3 in F- enrichment. Total dissolved solids showed strong positive correlations with Na+, Ca2+, Mg2+, Cl-, SO42- and NO3- indicating the contribution of anthropogenic inputs to groundwater chemistry in addition to geogenic sources. The results of the fuzzy comprehensive method indicated that 33% of the groundwater samples fell under fair water type, 2% and 11% of the samples fell under poor and very poor quality water types, respectively. Therefore, this work will be helpful for the decision-makers to plan for the sustainable management of groundwater resources.

Groundwater quality evolution based on geochemical modeling and aptness testing for ingestion using entropy water quality and total hazard indexes in an urban-industrial area (Tiruppur) of Southern India.

This study used geochemical modeling to understand the chemical evolution of groundwater, entropy water quality index to assess the aptness of groundwater for human consumption, and total hazard index to determine the possible non-carcinogenic risks among children, women, and men in an urban-industrial area (Tiruppur region) of southern India. For the above purposes, 40 groundwater samples were collected from tube and dug wells, and they were tested for various physicochemical parameters. Fluoride and nitrate levels ranged from 0.10 to 2.70 mg/l and 10 to 290 mg/l, respectively. Nearly, 50% of the fluoride samples and 58% of the nitrate samples exceeded the WHO limits of 1.5 and 45 mg/l, respectively. The majority of the groundwater samples (22.5%) represented Ca2+-Na+-Cl- water type while the remaining samples exhibited mixed water types. Approximately, 85% of the samples indicated high levels of salinization since they had Revelle index > 0.5 meq/l. The saturation index (SI) revealed that mineral weathering; dissolution of halite, gypsum, and anhydrite; and precipitation of calcite and dolomite contributed to groundwater chemistry. Based on the entropy water quality index (EWQI), none of the groundwater samples was characterized as excellent or good water quality while 57.5% of the samples had medium water quality, and 32.5% and 10% of the samples exhibited poor and extremely poor water qualities, respectively. The last two categories are designated as unfit for consumption. The cumulative health risk (nitrate and fluoride together) ranged from 0.97 to 11.16 for children, 0.60 to 10.54 for women, and 0.39 to 6.92 for men. These values represent health risks among 88%, 80%, and 73% of the groundwater samples for children, women, and men, respectively. Therefore, proper measures should to be done to reduce the health risks associated with high nitrate and fluoride in the groundwater of the study area, which is used for drinking purposes.

Demarcation of groundwater quality domains using GIS for best agricultural practices in the drought-prone Shanmuganadhi River basin of South India.

A study was conducted to evaluate the suitability of groundwater in the drought-prone Shanmuganadhi River basin of south India for best agricultural practices since the surface water that exists in this basin is not sufficient to meet out the demand. As the quality of groundwater is not uniform in the hard rock aquifers of this basin, the work was carried out to demarcate the suitable groundwater quality zones for the agricultural activities. Sixty-one groundwater samples were collected and analyzed for various parameters such as electrical conductivity (EC), pH, TDS, major cations (Ca2+, Mg2+, Na+, and K+) and anions (Cl-, SO42-, HCO3-, PO43-, NO3-, and F-). To demarcate the feasible zones for agricultural practices, irrigation water quality parameters like EC, sodium adsorption ratio (SAR), percent sodium (Na %), residual sodium carbonate (RSC), magnesium hazard ratio (MHR), Kelly's ratio (KR), and permeability index (PI) were computed. Furthermore, the irrigation water quality representation diagrams like USSL, Wilcox, and Doneen were prepared, and their outputs were spatially plotted using the Geographical Information System (GIS) to identify the suitability domains of groundwater for irrigational practices. Interpretation of irrigation water quality parameters and diagrams indicate that 2% of groundwater samples represented "low" salinity, 26% of samples represented "medium" salinity, 66% of samples represented "high" salinity, and 6% of samples represented "very high" salinity. Similarly, about 59% of samples represented the low alkaline/sodium category and 41% of them represented the medium alkaline category. The USSL output shows that about 2% of samples of the basin signified "low salinity with low alkalinity" category (C1S1), 28% of samples signified the "medium salinity with low alkalinity" category (C2S1), 33% of samples signified "high salinity with low alkalinity" category (C3S1), 28% of samples signified the "high salinity with medium alkalinity" category (C3S2), and 10% of samples signified the "very high salinity with medium alkalinity" category (C4S2). Groundwater is suitable for irrigation in 277.52 km2 area of the basin. It is moderately suitable in an area of 318.46 km2 and poorly suitable over 38.64 km2. This study recommends that groundwater with moderate suitability could only be used for irrigating permeable soils and for cultivating salt-tolerant crops. The addition of gypsum to soil might be helpful to increase the infiltration capacity and osmotic activity. However, poorly suitable area should be avoided for agricultural practices.