Geostatistical and hydrogeochemical characterization of a probable borehole disposal site for radioactive waste in Accra, Ghana

The increasing dependence on groundwater resources especially in developing countries requires an in-depth evaluation of the hydrogeochemical characteristics associated with any potential geological disposal site for radioactive waste. In particular, the borehole disposal system (BDS) for disused sealed radioactive sources (DSRS) interfaces with groundwater resources thereby necessitating detailed site characterization to generate requisite geostatistical information. In this study, the potential BDS site for the conditioned DSRS was characterized by assessing the hydrogeochemical nature and processes at varied depths of investigatory boreholes. Conventional hydrogeochemical, multivariate statistical, and multi-criteria decision-making (MCDM) analysis were used. Durov and Piper diagrams show that sodium chloride constituted the primary water type. Na versus Cl, and Gibbs diagrams demonstrated that weathering is a probable primary source of Na and Cl ions. Major ions ratios demonstrated the occurrence of both ion exchange and reverse ion exchange hydrogeochemical processes. Multivariate principal component analysis indicated three clusters of groundwater, whereby borehole BF cluster was influenced mainly by nitrate due to associated agricultural activities. Na+ and Cl- ions primarily influenced boreholes BH1 and BH2 clusters. MCDM preference ranking organization method for enrichment evaluation and geometrical analysis for interactive aid modeling demonstrated that the shallow depth BF borehole offered the most conducive reducing hydrogeochemical environment to host the borehole disposal system. The BF rock formation is associated with an alternating band of phyllite and quartzite. Schist mixed with a brownish quartzitic formation that is within 110-130 m depth in BH1 also provides favorable reducing conditions for the future disposal of conditioned DSRSs in Ghana.