Rehabilitation measures should be implemented when the yield has dropped 10%. At this stage the rehabilitation costs will be moderate and the original yield can easily be restored.
Over time pore spaces in a gravel pack become smaller due to the formation of incrustations. More energy is required for groundwater to flow through clogged pores.
A higher drawdown is required to achieve the same pumping rate due to increased entrance resistance. Power consumption will increase and the well pump may have to be upgraded to achieve the required head lift and capacity.
Young ferrihydrite is much more reactive and easier to be removed than older iron incrustations which have recrystallized to goethite. Well rehabilitations should be carried out when the incrustations consist of easily soluble mineral phases.