Abstract
In the current study, an effort was made to assess the geochemistry of groundwater by random collection of the samples from 15 different borewells located in various parts of Varanasi City, Uttar Pradesh, India. Geology of the study region is dominated by Quaternary alluvial sediments of Pleistocene to recent times where the younger alluvium receives fresh deposits of silt, clay and loam from periodic flood events. Ca–Mg–HCO3was inferred as major hydrogeochemical facies from Piper trilinear diagram. Ca–Mg type and HCO3− type were the dominating cation and anion facies, respectively. Hydrogeochemistry reveals that the cation abundance follows the order Na+> Mg2+ > Ca2+ > K+ and anion abundance HCO3− > Cl− > NO3− > SO42− > F−. As per Gibb’s plot, chemical weathering of rock minerals is affecting the quality of groundwater. Overall, most of the samples for majority of parameters lie within the allowable limits as set by WHO (guideline for drinking water quality, fourth edn, WHO, Geneva, p 340, 2004) except nitrate, which varied in the range of 40.32–78.97 mg/l. 80% of the groundwater samples in which nitrate exceeded beyond acceptable limit (50 mg/l), as per WHO standard, which may be due to poor sewerage, human excreta leakage from septic tanks, poorly maintained disposal of solid waste locally, agricultural activities, wastewater irrigation and irrigation runoff. The Water quality index (WQI) value of the study region depicts that 93% samples lie in the category of excellent water and 7% in good water category. Good positive correlation of NO3–Cl (r = 0.60) and Na–NO3 (r = 0.55) signifies an anthropogenic input of these ions into the subsurface water of the study region. The various indices such as electrical conductivity (EC), salinity, percent sodium, sodium absorption ratio (SAR), residual sodium carbonate (RSC), permeability index (PI), Kelly’s ratio and magnesium ratio are used to check the fitness of ground water for irrigation uses which shows that groundwater samples of the study region is good to permissible for agricultural uses.
Highlights
The most concerning issues to water authorities are to provide safe and potable drinking water to every individual for their good health (Jamshidzadeh and Barzi 2018)
The standard ranges for drinking water, as per WHO standards, were considered to determine its fitness for drinking purposes
Since the groundwater of the recent study lies under freshwater class and the total dissolved solids (TDS) values for all samples are below 1000 mg/l, it may be used for drinking and irrigation purposes (Davis and De Weist 1966)
Summary
The most concerning issues to water authorities are to provide safe and potable drinking water to every individual for their good health (Jamshidzadeh and Barzi 2018). Due to deterioration of surface water quality and its shrinkage,. The residence time of water and the primary mineralogy control the rate of reaction with parent rocks. Knowledge of groundwater quality is significant because it is an important aspect which determines its fitness for different purposes. The water quality index (WQI) is a productive tool to estimate the quality of water by integrating a composite set of data and generating a score which signify the overall water quality category (Jamshidzadeh and Barzi 2018). WQI could be an easy communication tool about the groundwater quality for local residents and government agencies in terms of better management in near future. The agrarian belt of Varanasi basically uses groundwater for irrigation purpose which is directly linked with crop yield. It is necessary step to examine the groundwater geochemistry and its irrigation suitability (Li et al 2013)
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