Assessment of well performance criteria and aquifer characteristics using step-drawdown tests and hydrogeochemical data, west of Qena area, Egypt

A groundwater investigation was performed to characterize hydrogeological conditions and well performance in a shallow alluvial aquifer using well logs, step-drawdown tests, and hydrogeochemical data. Results from three single-well step-drawdown tests conducted in three recently drilled boreholes located west of the Qena area in Upper Egypt and were analyzed by the Rorabaugh (1953) graphical method. A total of 47 groundwater wells were sampled and analyzed to detect the main hydrochemical facies associated geochemical processes. Results of the step-drawdown tests indicated well losses between 1.5% and 27.7% (14.2% avg.) and aquifer losses of between 72.3% and 98.5% (85.8% avg.), reflective of high well efficiencies. Specific capacity values varied from 183.4 m3/day/m to 278.4 m3/day/m while well efficiency values varied from 72.3% to 98.5%, indicating that the wells had been properly designed and developed. Estimated aquifer transmissivity ranges from 1103.7 m2/day to 1459.7 m2/day (1314.9 m2/day avg.), indicating high yields and water accessibility to the wells. Results indicated laminar flow at the aquifer/well-face contact with negligible turbulent flow. Gibbs and various scatter ionic ratios plots of the geochemical data indicate that water-rock interaction followed by evaporation are the most dominant processes controlling groundwater composition, while a Piper plot reflects mixing with irrigation-return flows subject to evapotranspiration. The approach demonstrates the practical applications of the single-well step-drawdown tests for estimating of the safe and sustained well yields for future groundwater extraction.