Well Interference.
Well interference occurs when the water table (or potentiometric level) in one well is significantly lowered as a result of the pumping of a nearby well. Sometimes the interference can be so great that the water table (or potentiometric level) in the first well is lowered below the pump intakes or even below the bottom of the well itself.
How can wells interfere with one another? When pumping begins, the water table (or potentiometric surface) around the well begins to drop as the aquifer supplies water to the well. This drop in water levels is called drawdown. The area of drawdown is shaped like a three-dimensional, funnel-shaped cone, centered on the well. Pumping rate and aquifer characteristic determine the depth of the drawdown cone and the areal extent (horizontal) of the drawdown.
The following illustration represents the water table as the top of the lower cube; the aquifer as the lower cube itself; and the well as a pipe extending from the land surface (top of the upper cube) down to the aquifer, below the water table. The drawdown cone, also known as a cone of depression, is indicated.