Groundwater vulnerability assessment using multivariate statistics and heavy metal pollution index in Ibadan Metropolis, Nigeria

Abstract

Groundwater is a vital source of potable water in urban and peri-urban areas, especially where surface water is either inadequate or contaminated. In the Ibadan Metropolitan Area of Nigeria, increasing urbanization and diverse land use activities have raised concerns about the quality and safety of groundwater resources. This study assessed groundwater vulnerability by integrating hydrogeochemical characterization, multivariate statistical techniques, and the Heavy Metal Pollution Index (HMPI). A total of 100 groundwater samples were collected across five local government areas and analyzed for physicochemical parameters and heavy metals using standard methods. The results revealed pH values ranging from 4.40 to 7.70 (mean 6.58), with several samples below the WHO-recommended minimum of 6.5. Electrical conductivity (EC) ranged from 54.30 to 1870.00 µS/cm (mean 715.91 µS/cm), and total dissolved solids (TDS) varied between 10.04 and 1720.00 mgL−1 (mean 438.90 mgL−1), with 23% of samples exceeding the WHO threshold of 500 mgL−1. Arsenic concentrations reached up to 0.52 mgL−1 and lead up to 0.96 mgL−1, both far above the 0.01 mgL−1 maximum limits set by WHO and USEPA. Principal component analysis (PCA) identified nine key components explaining 81.13% of the total variance in water chemistry, while hierarchical cluster analysis (HCA) grouped groundwater samples by lithological influence. Rocks such as garnet amphibolite and biotite gneiss were associated with higher trace metal content. Despite the elevated concentrations in some locations, HMPI values ranged from 0.20 to 6.43, indicating low overall pollution. However, continuous monitoring is recommended to prevent future degradation and to inform safe groundwater use and urban water management strategies.