Geotechnical and environmental problems related to shales in the Abakaliki area, Southeastern Nigeria

Six (6) samples of shale and five (5) water samples from hand-dug wells and boreholes, from different locations within the Abakaliki shale formation, have been assessed to evaluate the impact of the shale formation to the geotechnical and hydrogeo-environmental problems prevalent in the Abakaliki area (Southeastern Nigeria). Results indicated that the shale samples have Atterberg limits that might be considered moderate to high; while Liquid Limit (LL) ranged from 49 – 54, the Plasticity Index (PI) ranged from 34 – 38. These relatively high LL and PI suggested presence of expansive clays, some swelling of the shale on moisture influx and high compressibility. Natural moisture content (with mean value of 20%) was also significantly high. Hydrochemical analyses, on the other hand, revealed that the water samples had comparatively high content of ions and dissolved particles; Ca2+ ranged from 8.0 – 134.0 mg/l, Mg2+ ranged from 0.2 – 3.3 mg/l, HCO-3 ranged from 21.8 – 1176.1 mg/l and total dissolved solids ranged 56.9 – 1415.0 mg/l. Dissolution of soluble minerals (predominantly calcite and other rock salts) contained in the shale might likely be responsible for the release of these particles. Geotechnical behaviours of the shale and hydrogeochemical characteristics of water samples from the shale formation, thus, provided insights into the probable causes of seasonal waterlogging, consistent poor groundwater quantity and quality, structural and foundation problems that are prevalent in the Abakaliki area.Key words: Abakaliki shale, dissolution, environmental problems, geotechnical analysis, groundwater quality, structural failure

Hydrogeochemical analysis and quality evaluation of groundwater from Onicha-Uburu, Southeastern Nigeria for irrigation purposes

A total of 20 groundwater samples from boreholes and hand dug wells withinOnicha-Uburu and its environs were assessed to determine their suitability for irrigation purposes. Physical and hydrogeochemical parameters were evaluated, while techniques such as sodium absorption ratio (SAR), sodium percent, residual sodium carbonate (RSC) and magnesium adsorption ratio (MAR) were used to assess the suitability of these groundwater samples for the intended purpose. Results indicated that temperature ranges between 20 and 26°C for hand dug wells and 19 and 23°C for borehole samples. The electrical conductivity (EC) varies from 8.4 to 36.4 μs/cm for the hand dug wells and 10.0 to 76.4 μs/cm for the borehole water samples, while pH values range between 7.0 and 9.0 for the entire samples and indicate alkaline water. Statistical analysis shows appreciable concentrations of basic ions (average value of 28.8 mg/l for Na+, 9.1 mg/l for K+, 16.0 mg/l for Ca2+, 14.6 mg/l for Mg2+, Nil for C032-, as well as 45.0 mg/l for HC03 -, 20.5 for mg/l Cl- and 8.7 mg/l for S04 2-). While Na+ and Ca2+ are the predominant cations, HC03- and Cl-1 are the anions that predominate. The chemical analysis revealed that the total hardness (measured in terms of CaCO3) varied from 16 to 140 mg/l for both sets of samples indicating soft to moderately hard water. Based on the values of EC, percent sodium, SAR (which vary from 0.3 to 1.7 meq/l), RSC (from 0.1 to 0.99 meq/l less than the standard value of 1.25 meq/l) and the magnesium hazard (MH) values which range between 0.99 and 89.8%, revealed that water samples from the study area are generally suitable for irrigation purposes except for few locations.Key words: Groundwater, hydrochemical facies, hydro-geochemical analysis, irrigation purposes, Onicha- Uburu area

Groundwater exploitation in the Abakaliki metropolis (southeastern Nigeria): Issues and challenges

This paper assesses and evaluates geologically related problems and issues associated with five ‘abortive’ boreholes drilled within the Abakaliki metropolis, southeastern Nigeria. Results of the vertical electrical  geophysical soundings (VES), carried out in these borehole locations, show that the underlying Abakaliki Shale Formation in those areas has six layered model. While the uppermost layer has an apparent resistivity value of range 240 to 1120 ohm-m and a thickness of range 1.0 to 1.2 m, and is interpreted as lateritic overburden. The 2nd to 5th layers have apparent resistivity values that range from of 25 to 1025 ohm-m, with depth that range from 0.8 to 25 m. The 6th layer has mean apparent resistivity value of 443.25 ohm-m and undetermined thickness. The range of the apparent resistivity values and a correlation with local geological data reveal that the formation, although layered, is predominantly shaley, which become fresh, unweathered and ‘unfractured’ at greater depth. Although the studied boreholes all exceeded the depth to watertable of some functional boreholes in the area (28-50 m below the surface), they are all sparsely productive to abortive, suggesting that the concept of aground water table with regional flow is very likely to be unrealistic in the area. Hence, an integrated geophysical survey method is required to identify productive spots.Key words: Abakaliki Shale, abortive boreholes, aquiclude, vertical electrical sounding