ABSTRACT
Groundwater appearance on the land surface in the Sphinx and Pyramids area in Egypt prompted a study to identify the sources of this rising groundwater and propose short term solutions to the problem. Although a short-term solution was designed and implemented in the site, concerns remained regarding the potential interactions between the leaking water (mostly sewage water) and the limestone aquifer underlying Sphinx and the Pyramids area. These interactions may lead to widening the fracture and fault openings, thereby increasing their permeability, increasing the volumes of groundwater passing through them and affecting the stability of the archaeological structures. In this study, a two dimensional numerical model is developed to investigate the effect of limestone dissolution on groundwater fluxes entering the subsurface domain underneath the Sphinx and Pyramids area. The model generates zones of high hydraulic conductivities to represent fractures and the hydraulic conductivity field coupled with appropriate boundary conditions is used to solve the flow equation to obtain the potential field and subsequently the velocity field. The particle tracking approach is adapted to solve the transport and dissolution reactions problems. The model considered the rate of dissolution reactions at mineral surface, mass transfer of reaction products between the mineral surface and bulk fluid, and reactions involving the distribution of CO2 gas in water as the three potential limiting conditions for dissolution. Comparisons between the case with dissolution and that without the effect of dissolution reveal the importance of the process.
