Types of Aquifier

a) Unconfined aquifer:

• It is a permeable bed only partly filled with water and overlying a relatively impervious layer.
• Its boundary is formed by a free water table or phreatic water table or non-artesian aquifer.
• The water in a well penetrating unconfined aquifer doesn’t in general, rise above the phreatic level.
• The upper surface of the zone of saturation is called water table in which the water in the pores of aquifer is at atmospheric pressure.
• Here, pressure need to be exerted to take out the water.

Static water level:

• The level at which the water stands in a well before pumping starts is called static water level.
• Here, the pressure of water is at atmospheric pressure.

b) Confined aquifer:

• An aquifer found between impermeable layers above and below it is called confined aquifer.
• It is also called an artesian aquifer.
• Here, because of the presence of the upper confining layer, the water of the aquifer is not open to atmospheric pressure.

Note:

a) Unconfined: water bearing layer laid over the impervious layer.

b) Confined: Water bearing layer which is below impervious or in between two impervious layers.

c) Piezometric surface: It is an imaginary boundary of underground water of the confined aquifer raised due to hydrostatic pressure.