Lead and benzene contamination in drinking water wells of an unconfined aquifer in the Niger Delta, Nigeria.

Groundwater in the Niger Delta remains a critical source of potable water, yet it is increasingly threatened by contamination from petroleum-related activities and other anthropogenic sources. Few studies have comprehensively assessed the presence of contaminants in unconfined Niger Delta aquifers. This study investigates the spatial distribution of lead and benzene in both closed and open wells within the highly permeable floodplain sands of the Benin Formation underlying oil-producing municipalities in Rivers State, Nigeria. Groundwater samples were collected during the dry season in January 2025. Benzene was analysed from closed wells only, and lead was measured in both well types, ensuring representative spatial coverage. Results reveal significant spatial variation of benzene concentration, with the highest detected concentration reaching 26,460 µg/L, near petroleum infrastructure. A total of 16.7% of groundwater samples exceeded the WHO standard limit of 0.01 mg/L for lead in drinking water. More closed wells, which sample deeper into the aquifer, are contaminated with lead (20.6%) compared to shallower open wells (4.5%). Dissolved oxygen (DO), averaged 5.88 mg/L, was lower in samples containing benzene, suggesting natural attenuation processes. Ongoing work seeks to contextualize these findings relative to groundwater recharge estimates using a water balance approach based on climatic data. By translating our conceptual model into a numerical flow and transport model, we aim to shed light on the potential long-term implications of lead contamination in the aquifer. Our results highlight the urgent need for improved management and stricter regulation of petroleum activities to safeguard groundwater resources in the Niger Delta.