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Groundwater occurrence and characteristics of Niger State, Nigeria was studied using a combination of geological, hydrogeological and geophysical survey methods. Geological studies involved a determination of the various rock types and lithology, hydrogeological investigations involved the use of water levels in open hand dug wells and boreholes, while geophysical survey methods involved the use of electrical resistivity methods to determine subsurface conditions. The state is basically underlain by crystalline and the sedimentary rocks occurring in equal proportion. The crystalline rocks comprises mainly of granite, gneisses, migmatite and schist while the sedimentary deposits are mostly made up of sandstone, clays and shale. Groundwater occurs in the area in three broad categories; fractured/weathered aquifers in hard rock terrain, sandstone/grit aquifer in the sedimentary rock terrain and sandstone/conglomerate/ fractured rock in geologic contact areas. Groundwater yield varies widely in the three categories. /d) groundwater in the schist is low (below 0.6 lt/s) and sometimes wells placed in them are non-productive. Groundwater yields in the geologic contact areas vary from very low, where non fractured rock is overlain by clay, while very high yield is obtained in areas where the contact point is represented by conglomerate. Groundwater development in the state can best be achieved through a combination of geological, hydrogeological and geophysical survey methods.

The geology and groundwater condition of the area was studied with the aim of understanding their impact on the instability of the road in the study area. These include the petrology, geophysics and groundwater fluctuation (percentage in water table fluctuation). The methodology included geological field mapping, thin section preparation, resistivity and water table monitoring in dry and wet seasons. The study reveals that the road is underlain by schist, amphibolites and poorly fractured granite with quartz, biotite, hornblende and muscovite as the constituent minerals. The rocks have been altered through weathering to clayey minerals with resistivity values as low as 14 Ohm with the depth of weathering as high as 20 meter especially in the schist. The percentage of groundwater variation ranges between 154% and 2400% indicating medium to very high percentage of variation of groundwater fluctuation. These clay minerals absorb water and swell during the raining season and dry during the dry season. The result is the instability of the road pavement especially within the schist and where the elevation is lower. Proper design of the road and the provision of good drainage that will reduce the ingress of water are advised.