Modelling and Simulation of Groundwater Flow and Radionuclide Transport in Aquifers of Dahomeyan System of the Accra Plains in Ghana

ABSTRACT Locating a suitable radioactive waste disposal site in the Dahomeyan System of the Accra Plains has become necessary in isolating radionuclide waste from the biosphere to reduce risk to human and environment. Radionuclide as leaked from canister into the groundwater is carried by groundwater through fractured domain in space and time lead to groundwater contamination that poses threat to humans and the environment. Previous researches carried out in the study area modelled radionuclide flow in unsaturated and saturated zones used published hydraulic properties. Modelling and simulation of groundwater flow and radionuclide transport in the Dahomeyan System was used to better understand the aquifer system. Detailed site characterisation was done as prerequisite for accurate modelling results using pumping test and borehole logs data. Effective porosity and hydraulic properties (e.g. T, K, S) were estimated using field methods. The flow path and flow rate were also determined for the domain. The groundwater flow was simulated using ANSYS FLUENT 13.0 software to validate the field flow rate estimated and the range of storativity values estimated for the domain. Analytical and numerical solutions developed for 1D ADDE were simulated using MATLAB R2013a codes. 2D ADDE solution was also simulated to show the behaviour of groundwater flow and radionuclide spread in aquifers of the domain. C-14 and Sr-90 contaminants simulations showed that for a simulation time far less than half-life of the radionuclide the error between analytical and numerical solutions are negligible. The flow path determined was in SSE direction and dispersion was faster initially transversally than longitudinally due to preferential flow paths. The low values of the hydraulic parameters determined qualify Accra Plains as a host rock for radionuclide waste repository especially where transmissivity and storativity values were smallest.