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Assessment of groundwater and surface water quality along a river is important as it directly affects the agricultural, industrial activities and population. The objective of the study is to assess the quality of the Cauvery river water and adjacent groundwater for drinking and irrigational purposes and to identify the infuence of geogenic and anthropogenic sources. Groundwater and surface water samples were collected along the course of the river at approximate intervals of 25 km. The samples were analysed for electrical conductivity, pH, sodium, calcium, magnesium, potassium, bicarbonate, chloride and sulphate. Sodium was identified as the dominant cation and bicarbonate was the dominant anion for both river water and groundwater. These values were compared with limits recommended by the Bureau of Indian Standards for drinking purposes. The total dissolved solids were found to exceed the permissible limits for drinking water in most of the groundwater samples, and it was below the permissible limits in river water samples. Most of the river water samples were found to be suitable as per the drinking water quality standards, but most of the groundwater samples were unsuitable based on the concentration of major ions. Irrigation water quality was also assessed based on magnesium hazard, residual sodium carbonate, sodium percentage, sodium adsorption ratio, permeability index and salinity hazard. Most of the river water samples collected were suitable for irrigation, whereas most of the groundwater samples collected were doubtful for irrigation based on residual sodium carbonate and sodium percentage. Drinking water and irrigation water quality indices were also computed to assess the characteristics of water. Groundwater quality in locations nearer to the confluence of tributaries and industrial areas was of poor quality, while both river water and groundwater near the coast were poor, both for drinking and irrigation purposes. Comparison of the dissolved load with other rivers of the world was also made, which reveals that the Cauvery River yields comparatively higher dissolved load per area than most of the rivers. The chemical load in the river is due to natural and anthropogenic sources. Therefore, it is necessary to enforce the existing norms for the discharge of treated effluents by industries and townships along the river so as to reduce the chemicals contributed by anthropogenic sources.

Assessment of suitability of groundwater for domestic and agricultural purposes was carried out in Tondiar river basin, Tamil Nadu, India. The study area covers an area of 315 km 2 and lies in a semiarid region. Groundwater is the major source for domestic and agricultural activity in this area. Groundwater samples were collected from 45 wells during pre-monsoon and post-monsoon period in the year 2006. The water samples were analysed for physical and chemical characteristics. Suitability of groundwater for irrigation was evaluated based on salinity hazard, sodium percent, sodium adsorption ratio, residual sodium carbonate, US salinity diagram, Wilcox’s diagram, Kelly’s ratio and permeability index. Ca-HCO 3 , mixed Ca–Mg–Cl and Na–Cl were the dominant groundwater types. High hardness and electrical conductivity in this area makes the groundwater unsuitable for drinking and agricultural purposes. Concentration of trace elements (Mn, Cu, Zn, Pb and Ni) did not exceed the permissible limit for drinking and agricultural purposes. Majority of the groundwater samples were unsuitable for domestic and agricultural purposes except for 31% and 36%, which were suitable for drinking and irrigation purposes, respectively.

Hydrogeochemical investigations were carried out in Chithar River basin, Tamil Nadu, India to identify the major geochemical processes that regulate groundwater chemistry. For this study, long-term (1991-1997) and recent water quality data (2001-2002) for 30 groundwater wells spread over the study area were used to understand the groundwater geochemistry and hydrogeochemical process regulating groundwater quality. Groundwater quality data obtained from more than 400 water samples were employed. Results of electrical conductivity and chloride express large variation between minimum and maximum values and high standard deviation, which suggests that the water chemistry in the study region is not homogeneous and influenced by complex contamination sources and geochemical process. Nitrate and depth to water table expose the influences of surface contamination sources, whereas dissolved silica, fluoride and alkalinity strongly suggest the effect of rock-water interaction. In the study region, weathering of carbonate and silicate minerals and ion exchange reactions predominantly regulate major ion chemistry. Besides, the concentrations of sulphate, chloride and nitrate firmly suggest the impact of agricultural activities such as irrigation return flow, fertiliser application, etc on water chemistry in the study region.

The present study was carried out to determine the hydrogeochemical processes and the impact of tanning industries on groundwater in Ambur, Vellore district, Tamil Nadu, India. Thirty groundwater samples were collected during pre monsoon (July 2015) and post monsoon (January 2016) from the open and shallow wells around this region and were analyzed for major ions and chromium. The major ion concentration follows the order of Na + > Ca 2+ > Mg 2+ > K + (cations) and Cl − > HCO 3 − > SO 4 2− > NO 3 − (anions) for both seasons. The high concentrations of Na + , Cl − , and Cr around the tannery regions indicate the impact of effluent discharged from tannery units. In general, the groundwater of this study area is of Na + -Cl − type, which is due to the mixing of tannery effluent and cation exchange process. Ionic ratio indicates that the silicate weathering influences the groundwater chemistry. The permissible limit of chromium in the groundwater exceeds in over 50 % of the sampling wells. The factor analysis reveals that the dominant source for ionic contents is due to tannery effluents and cation exchange processes. To overcome this situation, it is essential to improve the performance of the effluent treatment plants so as to remove the salinity of wastewater and to plan for rainfall recharge structures for improving the groundwater recharge.

Remote sensing and GIS tools have broadly helped hydrogeologists to delineate the groundwater prospective zones for watershed development and management. The origin, movement and existence of groundwater depends on several factors such as slope, drainage density, land use, geology, lineament density and geomorphology. Based on these, the mapping and identification of groundwater potential zones were carried out in a part of Nalgonda district, Telangana, India. The regions were categorised as high, moderate and low groundwater potential, and they were validated with the groundwater levels and yield of wells located in the corresponding zones. Extensive possibility for watershed development is possible in 41 % of the total 724 km 2 and 46 % of the area offers moderate options. Any groundwater management project implemented in these favourable areas will bring maximum benefit. Similar studies should be considered necessary before designing a water resource development activity as it will reduce the cost on detailed field visits which are time-consuming.

Seawater intrusion promotes the salinity of groundwater, and it poses a great environmental impact on a global scale. The present study was carried out to determine the hydrogeochemical processes and influence of seawater intrusion in the coastal aquifers using geophysical, geochemical, and stable isotope techniques. The true resistivity value ranges from 0.5 to 8008.5 Ω-m which has been measured using vertical electrical sounding (VES) based on the Schlumberger method. About 33 groundwater samples were collected during post-monsoon (POM) (January 2012) and pre-monsoon (PRM) (June 2012) seasons from open and bore wells and were analyzed for major ions and stable isotopes. EC, Na + , and Cl − were high in groundwater of wells near salt pan, the Buckingham Canal, and backwater regions. Around 45% of the groundwater of this study area is of Na + -Cl − type due to salinisation. Reverse ion exchange and silicate weathering are the dominant processes controlling the geochemistry of groundwater. Saturation indexes (SI) of halite (SI halite ) and gypsum (SI gypsum ) versus sulfate show an increasing trend line from > 0 to < 0, which implies higher dissolution of minerals and hints increasing salinization during both seasons. The value of Na + /Cl − ranges between 0.7 and 2.4 (POM) and from 0.6 to 2.8 (PRM). The molar ratio suggested that around 25% of the groundwater samples are with values similar to those of seawater. Further, the groundwater is also affected by saline backwater, salt pan activities, and Buckingham Canal. Some locations are also are affected by anthropogenic, agricultural activities and geochemical processes. Heavy stable isotopes were found to be dominant in the coastal region due to seawater intrusion. Stable isotopes of δ 18 O range from − 5.6 to − 2.9‰ during both periods. About 201 km 2 of this area is affected by salinization. It is necessary to reduce pumping and plan for physical barriers to create freshwater ridges for controling the seawater intrusion.

Drinking water containing heavy metals above the maximum permissible limits cause potential risk to human health. The aim of this study was to determine the groundwater suitability for drinking use based on heavy metal concentration and the associated human exposure risk in an intensively irrigated part of the Cauvery river basin, Tamil Nadu, India. Sixteen heavy metals analysed were in the order of dominance of chromium < zinc < copper < cadmium < cobalt < iron < aluminium < nickel < titanium < zirconium < boron < silver < manganese < lead < lithium < silicon in groundwater. Chromium and zinc were within permissible limits of the Bureau of Indian Standards for drinking water quality, and silver, lead and nickel were above limits in all the groundwater samples. In less than 50 % of the groundwater samples, aluminium, boron, cadmium, copper, iron and manganese exceeded their individual permissible limits. Heavy metal pollution index based on 11 heavy metals indicated that groundwater quality of this area is poor-to-unsuitable. Non-carcinogenic risk for humans due to ingestion of groundwater through drinking water pathway was very high for infants, children and adults. Silver, lead, nickel, cadmium and manganese largely contributed to the health hazard. Sources of heavy metals were identified to be geological and from human activities, i.e., application of fertilizers in agricultural fields, seawater intrusion due to intensive pumping for agriculture and wastewater from industries. Groundwater and surface water in this area pose large threat due to high levels of heavy metals, and it is necessary to avoid this water for drinking due to potential risk of health hazard. This study also demonstrated the application of HPI and human exposure hazard index to study the groundwater quality based on heavy metals’ concentration.

Climatic condition, geology, and geochemical processes in an area play a major role on groundwater quality. Impact of these on the fluoride content of groundwater was studied in three regions—part of Nalgonda district in Telangana, Pambar River basin, and Vaniyar River basin in Tamil Nadu, southern India, which experience semi-arid climate and are predominantly made of Precambrian rocks. High concentration of fluoride in groundwater above 4 mg/l was recorded. Human exposure dose for fluoride through groundwater was higher in Nalgonda than the other areas. With evaporation and rainfall being one of the major contributors for high fluoride apart from the weathering of fluoride rich minerals from rocks, the effect of increase in groundwater level on fluoride concentration was studied. This study reveals that groundwater in shallow environment of all three regions shows dilution effect due to rainfall recharge. Suitable managed aquifer recharge (MAR) methods can be adopted to dilute the fluoride rich groundwater in such regions which is explained with two case studies. However, in deep groundwater, increase in fluoride concentration with increase in groundwater level due to leaching of fluoride rich salts from the unsaturated zone was observed. Occurrence of fluoride above 1.5 mg/l was more in areas with deeper groundwater environment. Hence, practicing MAR in these regions will increase the fluoride content in groundwater and so physical or chemical treatment has to be adopted. This study brought out the fact that MAR cannot be practiced in all regions for dilution of ions in groundwater and that it is essential to analyze the fluctuation in groundwater level and the fluoride content before suggesting it as a suitable solution. Also, this study emphasizes that long-term monitoring of these factors is an important criterion for choosing the recharge areas.

Disposal of industrial waste is of great concern because it releases toxic metals resulting into the degradation of environments and consequently causes health effects on humans. The present study was carried out with the objectives of identifying the possible source and migration of contaminants in the surface water and groundwater and the associated health risks in the industrial region of Ranipet, Tamil Nadu, India. A total of 22 water samples were collected and analysed for the concentration of major ions and trace elements. Chemical speciation of chromium and lead in surface and groundwater was calculated using the geochemical code, PHREEQC. The concentration of total dissolved solids, chromium and lead was high in the surface water than groundwater in this region. The chromium in most of the sampled water is dominated with Cr(OH) 2+ and Cr(OH) 3 species and the dominant species of lead was PbCO 3 . The major source of contamination is the waste dumped in this region and also the improper disposal of effluents from the small-scale industries in this region. Use of groundwater with the present level of chromium and lead in this region will cause several health effects through oral and dermal pathways. Hence, stringent monitoring of quality of water sources of this region, enforcement of regulation of the disposal of wastes from the industries, recover and treat the dumped solid waste are very much necessary to prevent the spread of contamination.

Assessment of rainfall variability and drought is essential to address the existing water crisis and water resources management. This study was carried out to assess the rainfall variability, meteorological drought and relative response of a water supply reservoir located in Chennai Metropolitan, India. Spatial and temporal variation of rainfall and drought across the river basin was assessed using historical rainfall records from 1978 to 2016. A significant number of rainfall stations show increasing trends in post-monsoon and northeast monsoon. The annual rainfall is concentrated for less than six months and shows an irregular to strongly irregular distribution. The degree of variability in monthly rainfall reveals markedly seasonal with long dry periods. Three different drought indices such as rainfall deviation method, Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI) were used and compared to identify the meteorological droughts. The duration of meteorological drought events in this region ranged from 3 to 9 months. Identified drought events reveal that the rainfall deficiency in the northeast monsoon causes most of the meteorological drought. The reservoir system has higher response and coherence with SPI at a higher time scale. So, SPI can be used to represent the hydrological drought in higher time scales. Hence, SPI is recommended as more appropriate for drought assessments for this region. The large scale atmospheric circulations have moderate impacts on drought events in this region. The outcomes of this study could be useful for better drought and water resources management. Research Highlights Chennai region has higher interannual rainfall variability and susceptible to droughts once in about four years. About 44.44% of droughts in this region when India witnessed drought indicating large scale atmospheric circulations. Deficiency in rainfall during both southwest and northeast monsoon increase the gap between water demand and supply.