Geological And Topographical Influences On Hydrogeology Of Kenyan Marble Quarry Areas, Kajiado County, Sw Kenya: Possible Indications For Pollution

The Kenyan Marble Quarry (KMQ) community is famous for its abundant crystalline limestone deposits, mined for the past eight decades or more at an industrial scale. The area is underlain by a lithologically and structurally complex mix of basement system rocks, and being semi-arid, there are no perennial waters in the area; hence, almost total dependence is on groundwater derived from confined basement aquifers whose occurrence is affected by geological and morphological intricacies. Long-term active mining, coupled with intense weathering processes, are potential geological triggers that could influence the hydrogeological makeup of the area, hence affecting groundwater flow and the physicochemical character of the aquifer. This study aims to interpret data from geological ground-truthing, remote sensing, and existing borehole logs to gain insights into the likely morphological, geological, and structural impacts on surface run-off and sub-surface flow in the KMQ community and its surrounding localities. Run-off flow patterns over the drainage area correlate strongly with surface elevation trends, but the multi-directional dendritic stream flow is highly impacted by soil nature and surface lineaments, evidenced by a SE mean directional stream flow, which correlates with the NW-SE principal orientation of foliations in the area. Patterns of spatial groundwater table elevation over the area show average correlation with surface elevation patterns. Subsurface water flow directions differ to some extent, indicating strong geological controls with NEE-SWW and NW-SE major trending fractures serving as conduits. Accurate point information from borehole logs indicates that weathered and fractured biotite gneisses are the main aquiferous zones over the study area. They are confined by fresh metamorphic basements and clays, which raise the water table upward to depths of up to 17m in some places. The weathered aquifers are highly prone to chemical reactions such as hydrolysis, leaching, or dissolution, all favouring pollution. Also, rock disintegration from mining, exposed surfaces of abandoned mines, and mine tailings could favour acidic conditions and pollution by metallic and non-metallic agents, washed down the drains as run-off. This paper provides a background for further scientific research into possible soil and water pollution from geogenic sources triggered by industrial mining in the KMQ area and extending to its neighbouring localities.