Hydrochemical Evaluation of Geological Formations in Coastal Karachi and Associated Infrastructure Risks

The hydrogeochemical environment in coastal aquifers is a significant area of study, particularly in regions like Karachi, where seawater intrusion impacts water quality and subsurface infrastructure. The key issue identified in this study is the deterioration of groundwater quality due to seawater intrusion, leading to challenges such as corrosion and scaling, which pose risks to subsurface structures like piles, basements, and utility pipelines. Hydrochemical facies were analyzed using Piper and Durov diagrams, while spatial patterns of corrosion and scaling tendencies were assessed through the Langelier Saturation Index (LSI) and Ryznar Stability Index (RSI). Geographic Information System (GIS) tools were employed to visualize spatial variations in groundwater chemistry and their implications for infrastructure. The results reveal chloride (Cl-) is the dominant anion, indicating high salinity likely due to seawater intrusion or saline sources, with bicarbonates (HCO 3-) and sulfates (SO 4 2-) suggesting mineral dissolution. Sodium (Na +) is the principal cation, reflecting saline influence or anthropogenic input, while calcium (Ca 2+) and magnesium (Mg 2+) are linked to geogenic origins like limestone and dolomite. The impact analysis revealed LSI values ranging from-0.1 to 0.998, identifying regions susceptible to scaling or slight corrosion, and RSI values between 5.912 and 7.47, indicating areas at significant risk of corrosion. These findings imply severe threats to the durability and functionality of underground structures due to aggressive ion infiltration. The study emphasizes the need for targeted mitigation strategies, including protective materials, monitoring, and sustainable groundwater management to minimize long-term impacts on infrastructure.