Evaluation of Groundwater Quality for Irrigation in Various Mandals of Nellore District in Andhra Pradesh

Abstract

Groundwater is the main source of irrigation in arid and semi-arid regions of India. In order to appraise the quality of groundwater for sustainable production, a survey was undertaken during the year 2018 in various mandals of Nellore district, Andhra Pradesh. Two hundred forty six (246) groundwater sampled were collected and analyzed for pH, electricity conductivity (EC), cations (Na+, Ca2+, Mg2+ and K+) and anions (Cl- > HCO3- > SO42- > CO32-) and water quality indices like sodium adsorption ratio (SAR) and residual sodium carbonate (RSC) were calculated. The EC and pH of groundwater samples varied from 0.20 to 9.3 dS m-1 and 6.0 to 8.9 with a mean of 2.31 dS m-1 and 7.5, respectively. The relative abundance of major ions for most of the water samples were Na+ > Ca2+ > Mg2+ > K+ for cations and Cl- > HCO3- > SO42- for anions. The SAR and RSC were varied from 0.13 to 18.84 (mmol L-1)½ and -40.0 to 16.6 (me L-1) with a mean value of 4.91 (mmol L-1)½ and -0.41 (me L-1), respectively. Correlation matrix indicated that EC was highly correlated with Na+, Ca2+, Mg2+, K+, Cl-, HCO3- and SO42-. However, based on EC, SAR and RSC, 93 groundwater samples (37.8%) were found to be good, 55 samples (22.5%) were marginally saline, 17 samples (7.0%) were saline, 12 samples (5.0%) were high SAR saline, 15 samples were marginally alkali (6.0%), 34 samples (14%) were alkali and 19 samples (7.7%) were highly alkali waters. Spatial variability maps for EC, pH, SAR, RSC and quality of groundwater used for irrigation in the district were also generated by using ARC-GIS, which provide first-hand information about the distribution of quality of groundwater. In general, the analysis of various parameters indicated that quality of groundwater showed varied degree of suitability.