Nitrate contamination in groundwater at farmlands in Nsawam, Ghana: The role of fractures from azimuthal resistivity surveys

Nitrate contamination of groundwater at farmlands in Nsawam, Ghana, has become a growing concern in recent times. Water samples were obtained from water groundwater wells in the study area and concentrations of nitrates, lead, arsenic, cadmium, copper, zinc and chromium were measured and analyzed. Three of the wells showed nitrate concentrations levels that reached 3-5 times the permissible limits for human consumption. The bed rock in the area is fractured and information about the orientations, apertures and lengths of fractures in the study area was obtained from geological mapping of few exposed outcrops. Azimuthal resistivity surveys (ARS) using the square array configuration were conducted in the vicinity of the wells with the aim of estimating the orientation and hydraulic properties of unexposed subsurface fractures which may serve as conduits for fluid flow and contaminant transport. It is thus shown that in the absence of rock exposure, ARS could be a viable complement in mapping subsurface fractures. Characteristic fracture parameters, fracture porosity, specific surface area which could give potential information on the hydraulic properties correlated with nitrate concentration in a given locality. The results serve to establish the role of fractures in groundwater contamination in the study area.