Integrated Hydrogeochemical and Pollution Index Assessment of Groundwater from Diverse Lithological Units in the Palakkad District, Kerala, India: Implications for Sustainable Aquifer Management

ABSTRACT This study investigated the hydrogeochemical characteristics and suitability of groundwater for drinking and irrigation in the Palakkad District, Kerala, India, based on samples collected during the pre- and post-monsoon seasons of 2023. Seasonal variations reveal a decrease in most ionic concentrations (except Mg2+, SO42‒ , and Cl‒) during the post-monsoon period compared to the pre-monsoon period. The groundwater chemistry is dominated by Ca2+ among cations (followed by Na+ > Mg2+ > K+) and HCO3‒ among anions (followed by Cl‒ > SO42‒ > NO3‒ > F‒ ). Classified as freshwater and calcium bicarbonate water, the groundwater exhibits pH levels between 6.5 and 8.5, within the WHO’s permissible limits. While most samples met the WHO standards for drinking water, a few from the gneissic and pink-granite terrains exceeded the desirable TDS limit of 500 mg/L. Hardness analysis indicates an increase during the postmonsoon period, with 57% of samples from the gneissic terrane classified as “very hard.” Despite elevated magnesium levels in certain samples during the post-monsoon period, they remained within permissible limits, although long-term use could affect soil quality and agricultural productivity. Water Quality Index (WQI) results suggest that the groundwater is generally good for drinking, with most samples also suitable for irrigation. However, the ion concentrations were notably higher in the eastern part of the district, particularly in the pink-granite and migmatised/Hb-Bt gneiss terrains. Groundwater quality assessment using ICP-MS, Heavy Metal Pollution Index, and Metal Index (MI) also indicates generally safe conditions with minimal contamination. Localised variations in MI highlight moderate impacts in certain geological terrains, primarily influenced by elevated manganese levels. Signs of water-quality deterioration in some bore well samples highlight the need for regular monitoring and proactive management. Sustainable practices, including the adoption of magnesium-tolerant crops and timely soil management strategies, are essential for mitigating the potential impacts on agriculture and ensuring groundwater quality in the region.