ASSOCIATION BETWEEN GROUNDWATER SOURCE CONFIGURATION AND ²²²Rn OCCURRENCE: IMPLICATIONS FOR RADON SURVEILLANCE IN OYE EKITI, SOUTHWESTERN NIGERIA

Abstract

Groundwater ²²²Rn occurrence is influenced by geological and hydrogeological conditions, and the configuration through which groundwater is accessed may contribute to the concentration encountered at the point of use. This study examined the association between groundwater source configuration and ²²²Rn activity concentration in Oye Ekiti, southwestern Nigeria, and evaluated its relevance to radon surveillance. Forty groundwater sources, comprising 20 open wells and 20 borehole or pumped sources, were sampled during the dry season and analysed using a calibrated electronic radon detector. The median ²²²Rn activity concentration was 17.50 Bq L?¹ in borehole or pumped sources and 2.99 Bq L?¹ in open wells, with a significant difference between distributions (Mann Whitney U = 287.0, p = 0.019) and a moderate distributional effect (Cliff's delta = 0.435). Concentrations exceeding 11.1 Bq L?¹ occurred in 60% of borehole or pumped sources compared with 5% of open wells, demonstrating a pronounced source related difference in elevated ²²²Rn occurrence. The distributional contrast remained evident when the highest concentration of 120.40 Bq L?¹ was excluded (Mann Whitney U = 267.0, p = 0.032; Cliff's delta = 0.405), indicating that the observed pattern was not dependent on the extreme observation. The findings demonstrate that groundwater source configuration is associated with systematic variation in ²²²Rn occurrence within the Oye Ekiti crystalline basement setting and may provide a useful basis for stratifying radon surveillance. Nevertheless, variability within both source categories indicates that source configuration should complement rather than replace direct measurement of individual groundwater supplies.