HYDRAULIC CHARACTERIZATIONS FOR AQUIFER PRODUCTIVE CAPACITY IN A TYPICAL SEDIMENTARY TERRAIN, SOUTH-WEST NIGERIA

Abstract

Pumping tests were conducted on existing 50 wells (twenty five each) with constant rate pumping test for boreholes and recovery method test for hand-dug wells within district to evaluate aquifer hydraulic parameters within Papalanto district, South-West Nigeria adopting standard methods of Cooper and Jacob straight line solution to time-drawdown data collected from observation wells. Fractured shale released water to the hand-dug wells because the required depth could not be reached for fresh water aquifer with depth range of 4.5m to 17m with a mean depth of 8.86m; mean static water level (SWL) of 5.18m and mean drawdown (DD) of 1.01m while the boreholes tapped fresh water from cavernous limestone/sandstone aquifer with a depth range of 38m to 108m with a mean depth of 75.36m, SWL of 33.8m and DD of 2.65m. Borehole discharge varied from 2.89 10^-2 l/s to 8.74 10^-2 l/s with a mean of 5.0 10^-2 l/s with exhibited transmissibility that varied from 10^-3 m²/s to 10^-2 m²/s with an mean of 9.0 10^-3 m²/s (777.6 m²/day) while discharge from hand-dug wells ranged from 1.0 10^-2 to 4.0 10^-2 l/s with an average of 1.4 10^-2 l/s. The transmissibility varied from 1.0 10^-1 (8.64 m²/day) to 1.9 10^-1 m²/s(16,416 m²/day). The hydraulic conductivity of the study area varied from 9.005 10^-5 m²/s(7.780 m²/day) to 1.012 10^-3 m²/s(87.437 m²/day) in Papalanto boreholes and 9.367 10^-5 m²/s (8.0931 m²/day) to 8.921 10^-4 m²/s(77.077 m²/day) in Papalanto hand-dug wells. The mean recovery period of 2248 seconds and 9658 seconds were reported for Papalanto boreholes and hand-dug wells respectively. Output from the two water sources revealed that the aquiferous zones are classified as high in potentials in the designation of transmissivity magnitude for boreholes (777.6 m²/day) and good/high potentials  in the transmissibility magnitude for hand-dug wells (311.04 m²/day) based on standard aquifer potentiality classification. This correlates well with the lithological description of the study area displaying fractured shale and cavernous limestone/sandstone as groundwater bearing unit releasing water into the well with good correlation obtained between transmissibility and specific capacity with correlation coefficient ( = -0.33 and = 1.00) respectively reported for Papalanto boreholes and hand-dug wells; implying higher specific capacity of an aquifer and its transmissibility, the greater the prolificacy or production capacity of the well; serving as a baseline for future development of groundwater resources in the study area.