Abstract
Several challenges abound with the accurate estimation of aquifer parameters in Groundwater resource development. This paper describes the investigation on the aquifer (mainly Ajali Sandstone Formation) parameters in Nsukka area. The Ajali Sandstone Formation is among the principal sources of groundwater in the area. The investigated area lies within Longitudes 7 o 22 1 30 11 E and 7 o 58 1 30 11 E, and Latitude 6 o 73 1 30 11 N and 7 o 00 1 00 11 N, covering an area of about 482 square kilometres. Sixty (60) cuttings from nine (9) boreholes drilled in the area were analysed texturally using statistical grain size method. Results show that the highly permeable members of Ajali Sandstone are devoid of surface waters and are seen to be friable, medium-grained, poorly sorted, and highly cross-bedded. Recharge is mainly through rainfall. The distribution of major geological units, well log data, static water level data, and surface features were found to have influenced groundwater occurrence and flow pattern in the study area. The lithological logs showed sandy aquifers separated by clayey aquitards, while stratigraphic analyses of well lithological logs revealed the presence of at least four layers of contrasting hydraulic conductivity, making the aquiferous Ajali Sandstone homogenous and anisotropic. Values of permeability (k) from 0.00753 to 0.01512 cm 2 , hydraulic conductivity (K) from 8.2886 to 16.6444 m/s, transmissivity (T) between 455.87 and 1002.48m 2 s -1 , and specific yield from 2.35 to 4.76m 3 were found to be consistently high, thus suggesting thick and prolific aquiferous zones.
Highlights
One of the most common problems encountered in ground water resource development is the accurate estimation of transmissivity (T) and hydraulic conductivity (K) of aquifers
Borehole depths and static water levels The summary of the results of the aquifer characterisation is presented in Tables 3, 4 and 6, while the selected borehole logs are presented in figures 3, 4, 5 and 6
The results indicate that most of the boreholes including those at Abuja Building (A02), Franco Refactory (F03) and the Energy Centre (E04), all penetrated the Ajali Sandstone aquifer; with respective depths up to 720 ft (220m), 670fts (210m) and 682fts (208m)
Summary
One of the most common problems encountered in ground water resource development is the accurate estimation of transmissivity (T) and hydraulic conductivity (K) of aquifers. Aquifer parameters such as hydraulic conductivity (K) and transmissivity (T) were established within the limits of the available data and information collected It has been established by Nwajide and Reijers (1996) that the Nsukka area lies within the Anambra Basin. Egboka (1983) studied the groundwater resources of the Nsukka area and environs while Egboka et al (1989) evaluated the hydraulic conductivity of sandy aquifers in the Nsukka area using the new statistical grain-size method Their findings suggest that the hydraulic conductivity (K) of the Ajali Sandstone is in the order of 1x 10-2 cm/s, while the permeability is between 2.0 cm to 20.7 x 10-10 cm. The Ajali Sandstone Formation shows a wide textural variation across its thickness, borehole data show that below the water table the texture is relatively more homogenous and ranges only from fine to medium grain. The aquifer fall into the first class group as was described in Uma et al (1989)
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