ANALYSIS OF HYDRAULIC CHARACTERIZATION AND GROUNDWATER QUALITY ASSESSMENT OF UPPER AND DEEP AQUIFER PROSPECTS IN OGONILAND, SOUTHERN NIGERIA

Groundwater is the primary source of potable water in Ogoniland, Southern Nigeria, where increasing anthropogenic pressures particularly oil exploration activities pose significant risks to aquifer systems. Understanding the hydraulic characteristics and groundwater quality variation across aquifer depths is therefore essential for sustainable water resource management in the Niger Delta. This study investigates the hydraulic properties and hydrochemical characteristics of the upper and deep aquifer systems in Ogoniland, with emphasis on vertical variability, aquifer connectivity, and water quality status. The study employed an integrated hydrogeological approach involving borehole lithologic data, downhole logging, pumping test analysis, and groundwater sampling across selected communities in four Local Government Areas. Hydraulic parameters such as hydraulic conductivity, transmissivity, storativity, static water level, and hydraulic head were determined. Physicochemical, hydrochemical, heavy metal, hydrocarbon, and microbiological analyses were conducted using standard laboratory procedures, while hydrochemical facies were evaluated using Piper diagram interpretation. Statistical analyses were performed using descriptive and inferential methods to assess spatial variations. Results indicate that the upper aquifer thickness ranges from 15 to 80 m, while the deep aquifer varies from 20 to 85 m, confirming significant spatial heterogeneity. Hydraulic conductivity in the upper aquifer ranges from 15.31 to 264 m/day, with transmissivity between 371 and 20,880 m²/day, while the deep aquifer shows conductivity values of 7.92 to 264 m/day and transmissivity between 158.39 and 7,776 m²/day. Storativity values (10⁻⁴–10⁻⁷) indicate semi-confined conditions in both aquifers. Groundwater flow is predominantly from northern elevated zones (up to 41.27 masl) toward southern low-lying areas (as low as 26.21 masl). Hydrochemical analysis reveals low total dissolved solids (3–58 mg/L) and electrical conductivity (7–116 µS/cm), indicating fresh groundwater, with pH ranging from 5.66 to 7.05. The dominant hydrochemical facies is calcium–chloride (Ca–Cl), suggesting the influence of marine processes, ion exchange, and water–rock interactions. Most heavy metals and hydrocarbons are below permissible limits, although localized iron concentrations (up to 1.03 mg/L) and minor PAH presence indicate site-specific contamination. Microbiological analysis shows minimal contamination, with low total coliform counts in some locations. The study concludes that groundwater in Ogoniland is generally of good quality and suitable for domestic use; however, the semi-confined nature of the aquifer system and the presence of a discontinuous clay layer increase vulnerability to contamination and saline intrusion. Hydraulic connectivity between aquifers further enhances the risk of vertical pollutant migration. It is recommended that continuous groundwater monitoring be implemented, particularly in oil-producing and coastal areas. Improved borehole design and protection of recharge zones are necessary to reduce contamination risks. Additionally, stricter environmental regulations and further studies incorporating advanced hydrogeochemical and isotopic techniques are essential for sustainable groundwater management in the region.