Consequences of well ageing

Sharp decline in water penetration curve

Decline in pumping capacity depending on rehabilitation time
Recommended time for rehablitation (Houben & Treskatis 2003)

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.

Low porosity and permeability of the gravel pack

Correlation of permeability and porosity
Correlation of permeability and porosity (Houben & Treskatis 2003)

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.

Higher drawdown at an equal pumping rate

Well entrance resistance
Well entrance resistance (Houben & Treskatis 2003)

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.

Decrease in dissolving capacity

Dissolving capacity of iron oxides (Houben 2002)

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.