Spatial and physicochemical assessment of groundwater quality in the urban coastal region of Sri Lanka

Rising sea levels, groundwater exploitation, and urbanization were the primary causes of seawater intrusion, exerting pressure on coastal aquifers. In Sri Lanka's urban coastal region, a comprehensive physicochemical description of groundwater has yet to be identified. Therefore, the objectives of this research were to (a) use a Geographic Information System (GIS) to designate spatial distribution of various water physicochemical characteristics, (b) detect "suitable" groundwater zones for drinking, and (c) estimate groundwater quality by developing a groundwater quality index (GWQI) in Sri Lanka's urban coastal region. The physiochemical parameters of 18 groundwater samples [pH, electrical conductivity (EC), turbidity, total dissolved solids (TDS), Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, and HCO₃^-] were studied in terms of their spatial and temporal variation. According to the World Health Organization (WHO) and Sri Lankan Standard Institution (SLS), EC levels in 11% of samples were above the acceptable range, while turbidity levels in 22% of samples were above the acceptable range. Water was consumable in 77.78% of the locations and unsatisfactory in 22.22%. The main hydrochemical facies detected in groundwater samples were Na⁺- Cl^- and the mixed Ca²⁺- Mg²⁺- Cl^- face, which indicated carbonate dissolution and weathering of silicate minerals and the main mechanism controlling the water chemistry in the study area is water-rock interaction. Based on daily water consumption, it was discovered that the HQ is greater than one, in 61% of males, 78% of females, and 89% of children, indicating a health hazard. Furthermore, groundwater quality in the study region is deteriorating due to significant coastal erosion, making it critical to maintain a comprehensive groundwater management strategy to promote sustainable water consumption.