No abstract

Groundwater potential of some parts of Cross River State, Nigeria, was assessed involving vertical electrical sounding (VES) and high-resolution aeromagnetic methods (HRAM). The VES and HRAM dataset were used to delineate the hydro-lithostratigraphic units and map the spatial distributions of geologic structures, respectively. The electro-stratigraphic sections revealed the various hydro-lithostratigraphic units composed of fractured/weathered crystalline basement, sandstones, siltstones, sandy shales, and highly baked and fractured shales occurring at different depths. Generally, the unsaturated top layer is composed of shales, marl, clay, silt, gravel and lateritic materials with resistivity ranging from ~ 3.0 to ~ 550 Ω m. This layer is underlain by various aquifer units like sandstones, siltstones, fractured shales and limestone/marl, and fractured/weathered basement occurring at different depths (~ 30 to ≤ 100 m) as revealed by the electro-stratigraphic sections obtained in the study area. In the Calabar Flank (CF), Oban Massif (OM) and Ikom-Mamfe Embayment (IME), the apparent resistivity for these hydro-lithostratigraphic units varied between ~ 8.50 and ~ 59.50 Ω m, ~ 120.2 and ~ 1562.6 Ω m and ~ 30.8 and ~ 277.2 Ω m, respectively. The enhanced total magnetic intensity maps and source parameter imaging result showed that the OM and IME are characterized by high concentration of short-wavelength anomalies, while the CF is dominated by relatively undisturbed thick sedimentation (~ 6217 m). HRAM results show that such areas are predominated by geologic structures like faults, fractures, fissure, dyke swamps, etc. caused by tectonics. Such geologic structures create secondary porosity and enhance permeability. From all the results obtained, OM and IME represent areas with moderate groundwater potential. The CF dominated by argillites with no significant tectonic activity is observed to have low groundwater potential.

This work was carried out in collaboration between both authors generally. Both authors EAK and WTA together designed the concept of this study. Author EAK managed aspect of the write-up that centres on literature review, geology/stratigraphy of the basin and the hydrogeology of the study area. Author WTA performed aspects on the GIS analysis and interpretations. Both authors read and approved the final manuscript.

The present work was aimed at assessing the surface and groundwater quality of the area within and around Obajana using physico-chemical characteristics. Surface and groundwater samples were collected at the peak of dry season in March, 2013, from 24 locations within Obajana and its surrounding areas and were subjected to a comprehensive quality analysis. The following parameters were considered; pH, total dissolved solids, electrical conductivity, turbidity, dissolved oxygen, redox, potassium, sodium, calcium, magnesium, iron, zinc, chloride, nitrate, sulphate and bi-carbonate. Different statistical tools were used to analyse the results. Piper diagrams and Schoeller plots were used to suggest models for predicting water quality. Results from the physico-chemical analysis revealed that the concentrations of the analyzed parameters were within the acceptable limits for drinking water recommended by the World Health Organisation except for iron which had elevated concentration in one location. Surface and groundwater within Obajana and environs are thus considered safe for drinking and domestic use with respect to these analyzed parameters but needs to be protected from the perils of contamination by pollution from the continuous production of cement from the cement company over time. Plots on Piper and Schoeller diagrams indicate a Ca-Mg-HCO 3 -water type.

The assessment of the level of heavy metal concentrations in water sources around quarries and barite mine sites in central Cross River State, Southeastern Nigeria, was carried out to evaluate the degree of contamination due to mining and quarrying activity in the area. The investigation involved the collection of twelve water samples from ponds, streams, river and boreholes around the area. The water samples were passed through 0.45 µm filter paper and preserved with a drop of 0.1M HNO3 acid. The preserved samples were analyzed for their heavy metal (Ba, Cr, Cu, Fe, Mn, Pb and Zn) content, using inductively coupled plasma-mass spectrometry (ICP-MS). The results show that the average concentration of Ba, Cu, MN, Pb and Zn were above WHO guideline value for drinking water quality, hence not suitable for drinking. The average concentration of the metals is in the order Ba>Mn>Cu>Fe>Pb>Zn>Cr. Computed values of contamination index show that the samples from four locations were contaminated. Single factor pollution index computation indicates that the waters are not contaminated with Cr, but slightly polluted with Fe and Zn, moderately polluted with Ba and severely polluted with Cu, Mn and Pb. Further, Nemerow comprehensive pollution index indicates that samples from four locations were severely contaminated. The study revealed that the water sources around the barite mines had elevated level of heavy metal concentration compared to location around the quarries. It is recommended therefore, that the water be treated before use for drinking purpose. Keywords: heavy metals, contamination index, pollution index, barite mine, quarry