Statistical Evaluation of Geological Influence on Groundwater Radon Concentrations in Gusau Metropolis, Nigeria

Abstract

Groundwater serves as a primary source of domestic water in many urban areas across developing regions, yet naturally occurring radionuclides like Radon-222 can dissolve into aquifer systems and present health risks depending on subsurface geological conditions. This study aimed to statistically evaluate the concentration, spatial distribution, and lithological dependencies of Rn in groundwater across the distinct basement complex formations of Gusau metropolis. A total of 60 groundwater samples (boreholes and hand-dug wells) were collected across seven geological units using a stratified random sampling strategy. Radioactivity levels were analyzed using a Tri-Carb-LSA1000 Liquid Scintillation Counter (LSC) equipped for high-precision analysis after achieving radioactive equilibrium. Data were evaluated using descriptive statistics, frequency distribution modeling, one-way Analysis of Variance (ANOVA), and post-hoc Tukey HSD tests. The overall arithmetic mean concentration of Rn was found to be 26.37 ± 1.14 Bq/L (range: 11.03 - 59.99 Bq/L), with 55% of all samples clustering within the 20 - 30 Bq/L modal range. All measured values complied with the World Health Organization (WHO) reference guideline of 100 Bq/L, though 98.3% exceeded the USEPA maximum contaminant level of 11 Bq/L. Statistically, the data exhibited a positive skewness (1.398) and leptokurtic kurtosis (3.289), indicating localized high-concentration outliers. One-way ANOVA confirmed significant lithological influence on radon concentration (F = 3.066, p = 0.0119 < 0.05). Post-hoc analysis revealed that this statistical variation was primarily driven by a significant difference between the Migmatite (GS4) and Mica Schist (GS7) formations (p = 0.0466). These findings demonstrate that groundwater radon concentrations in Gusau metropolis are inherently controlled by local subsurface lithology. The highly sheared, foliated matrix of the Mica Schist optimizes alpha recoil and elevates radon emanation, whereas dense, recrystallized Migmatite segregations restrict fluid-rock interactions. The results provide essential baseline data for environmental monitoring and suggest that future public health water management strategies in the region should account for localized geological "hotspots" rather than assuming uniform regional risk.