An excavation, rectangular in dimensions of 55 mx 95 m at the base and approximately 120 mx 160 m at the ground surface was made possible by the use of multi-staged wellpoint dewatering system. Groundwater table was lowered more than 20 meters using four stage wellpoint system to construct the main wastewater pump station for the city of Izmir. The most significant soil parameter affecting the planning and design of the dewatering work is the coefficient of field permeability, and it has been directly measured by a large scale pumping test at the site. During dewatering and construction stages, piezometers, inclinometers, extensometers and both conventional surveying and EDM methods were used. Total discharge rate was measured at different stages and it is compared with the theoretical approaches. Partial penetration factor for the well into aquifer is estimated.