It depends mainly on how permeable the ground is, how far groundwater has to come down, and the size and depth of the excavation.
Sump pumping suits shallow excavations in stable ground with modest inflows. Wellpoints suit sands and sandy gravels and lower groundwater by about five to six metres per stage, so deeper excavations use two or more stages. Ejector wells work in lower-permeability silts and silty sands, where flows are small but the water still has to come down. Deep wells suit permeable ground and larger, deeper drawdowns, and can relieve pressure in a confined aquifer below the excavation base.
ACTION International Services’ hydrogeologists review the site investigation, recommend a pumping test where permeability data is thin, and model the drawdown before recommending a system. Many sites use a combination of methods.
