Hydrogeochemical process, multivariate statistical, geospatial and index approach for evaluation of groundwater quality for irrigation purposes at Visakhapatnam region, Southern India.

Groundwater quality is progressively declining due to over-exploitation and long-term use for irrigation needs. This study aims to assess the suitability of groundwater for irrigation use in an intense agricultural region in Visakhapatnam, southern India. Groundwater samples were collected during the pre-monsoon (PRM) (n = 75) and post-monsoon (POM) (n = 72) seasons. In-situ measurements of pH, electrical conductivity (EC), and total dissolved solids (TDS) were taken using a portable multimeter, while the major ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, F^-, Cl^-, NO₃^-, SO₄^2-) were determined through ion chromatography. The Irrigation Water Quality Index (IWQI), integrated with Geographic Information Systems (GIS), revealed declining groundwater quality from south to north, with higher EC, sodium adsorption ratio (SAR), and chloride concentrations near coastal regions and thermal power plants. IWQI values ranged from 31 to 96 in the PRM and from 30 to 97 in the POM seasons. Approximately 27% of groundwater samples from the PRM and 22% from the POM were unsuitable for irrigation, particularly near industrial areas. Hydrochemical plots, including Wilcox, USSL, and Doneen classifications, highlighted salinity and permeability issues linked to local industrial pollution, affecting groundwater. Multivariate statistical analysis, including PCA, Pearson Correlation, and HCA, revealed that natural and human activities, such as seawater intrusion and agricultural runoff, significantly affect groundwater quality. Salinity, driven by sodium and chloride, persists in both seasons, while nitrate contamination from fertilizers is more prominent during the monsoon. This study highlights the necessity for continuous monitoring and targeted treatment measures for sustainable groundwater use for irrigational practices.