Assessment of Groundwater Quality, Contamination Risk, and Hydrogeochemical Characteristics Around Okitipupa Dumpsites, Southwestern Nigeria

Abstract

Groundwater contamination from unmanaged dumpsites threatens water quality and public health in many developing countries. This study evaluated the physicochemical properties and contamination risk of groundwater around dumpsites in Okitipupa, Ondo State, Nigeria, during the dry season, January 2025. Sixteen samples were collected from Ayeka, Igodan, Market Area, and Irele Road as the reference site and analyzed for physicochemical parameters using standard methods. Data were analyzed with PCA, Water Quality Index (WQI), and health risk assessment in R and MicroCal Origin. The groundwater was generally acidic, with a pH below the WHO range of 6.5 to 8.5. The Market Area showed elevated electrical conductivity, total dissolved solids, and chloride, indicating strong leachate influence. After excluding phosphate and total suspended solids and verifying standards, WQI values ranged from 64.6 to 117.6. The Market Area had the poorest quality (WQI = 117.6; poor), while Ayeka, Igodan, and Irele Road were classified as good. The non-carcinogenic health-risk assessment, based on the stated reference doses for nitrate and phosphate, yielded HQ and HI values below 1 for adults and children at all locations. The Market Area remained the most impacted site overall, while contamination at the more distant locations suggests additional anthropogenic sources. A limitation is that sampling was limited to the dry season and to physicochemical parameters only.