Groundwater quality of Arattupuzha coastal region of Kerala, India: A study based on pollution index

The hydrogeochemical profile of groundwater in the southern Kerala coast - Arattupuzha, in Alappuzha, Kerala, India is reported for drinking and domestic suitability. People at Arattupuzha mostly depend on public water supply for their domestic and drinking requirements due to limited freshwater availability. In this context, the palatability of coastal groundwater sources was evaluated and presented based on the weighted arithmetic mean Water Quality Index (WQI) and Pollution Index of Groundwater (PIG) methods. Groundwater was collected from 6 shallow (Dug wells) and 5 deep (Bore wells) sources during pre-monsoon (PRM), monsoon (MON) and post-monsoon (POM) seasons in 2019. Water was analysed for various physical and chemical parameters viz. pH, Eh, Electrical Conductivity (EC), Total Dissolved Solids (TDS), Total Alkalinity (TA), Total Hardness (TH), Cl^-, SO₄^2-, HCO₃^-, total iron, Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), NO₃^-, Na⁺, K⁺, Ca²⁺ and Mg²⁺. The results were compared with the WHO and BIS standards for drinking water quality. The WQI showed that most of the groundwater sources are unsuitable (WQI > 100) for direct drinking purposes. This is attributed to the total iron, TH and TA; hence, it requires pre-treatment prior to use. In the PRM season, the WQI values were 74.5±95.5 (Shallow Groundwater - SG) and 315.1±151.4 (Deep Groundwater - DG), indicating poor water quality, while in MON and POM, these were 181.9±125.4 (SG), 413.8±296.7 (DG) and 225.2±97.9 (SG), 406.4±132.6 (DG), respectively showing non-suitability for drinking purpose. Hill-Piper Trilinear diagram revealed Ca-Mg-HCO₃ as the dominant hydrochemical facies. PIG results revealed insignificant pollution (PIG < 1) in water with 0.5±0.3 (SG) and 0.6±0.3 (DG) values in PRM. Additionally, the Durov, Stiff and radial diagrams were used to represent the prominent ionic composition of water sources. Overall, the groundwater quality of Arattupuzha coastal area revealed that groundwater in pre-monsoon was much safer than in the monsoon and post-monsoon seasons.