There are different types of underground formations that can store and transmit groundwater. An aquifer readily transmits significant quantities of water and can support water wells. It may be unconfined, with a water table, or confined under pressure between low-permeability layers. An aquitard has low permeability and does not yield much water to wells. Other formations may contain water but not transmit it (aquiclude) or contain no water (aquifuge). Perched aquifers occur above discontinuous low-permeability layers and are separated from the main groundwater body. The type of aquifer depends on its geology and subsurface position.

1. TYPES OF AQUIFERS
Submitted to: Prof Pallavi Chattopadhyay
Submitted by: Ananya Mittal
GT - 4th yr
17410003

2. There is a wide range of porosity and permeability in geological materials. Groundwater exists everywhere
there is porosity. However, whether that groundwater is able to flow in significant quantities depends on the
permeability.
1. AQUIFER
● Any water bearing, permeable geological formation that stores and transmits water is called as an
aquifer.
● These rocks may readily transmit water to wells and springs due to very good hydraulic conductivity
● A body of rock or unconsolidated sediment that has sufficient permeability to allow water to flow
through it.
● Unconsolidated materials like gravel, sand, and even silt make relatively good aquifers, as do rocks like
sandstone. Other rocks can be good aquifers if they are well fractured.
● Wells can be drilled into the aquifers and water can be pumped out.
1. AQUITARD
● An aquitard is a body that does not allow transmission of a significant amount of water, such as a clay,
a till, or a poorly fractured igneous or metamorphic rock.
● A bed of low permeability adjacent to an aquifer; may serve as a storage unit for groundwater although
it does not yield water readily wells.
AQUIFER, AQUITARD , AQUICLUDE, AQUIFUGE

3. 3. Aquiclude
● Aquiclude are the impermeable formation which contains water but are not capable of transmitting
and supplying a significant quantity .
4. Aquifuge
● An impermeable body of rock which contains no interconnected openings or interstices and
therefore neither absorbs nor transmits water.
These are relative terms, not absolute, and are usually defined based on someone’s desire to pump
groundwater; what is an aquifer to someone who does not need a lot of water, may be an aquitard to
someone else who does.
Source : http://civildiscussion1.blogspot.com/2018/06/definition-of-aquifer-aquiclude.html

4. TYPES OF AQUIFERS
Based on the nature and distribution of water bearing zones,their geometry and relationship to topography
and the subsurface geology aquifers could be classified into three main types.
1. Unconfined
2. Confined (Artesian aquifers are special category of aquifers)
3. Perched
A cross-section showing materials that might serve as aquifers and confining layers. The relative permeabilities are
denoted by hydraulic conductivity (K = m/s). The pink rock is granite; the other layers are various sedimentary layers.
SOURCE: https://opentextbc.ca/geology/chapter/14-1-groundwater-and-aquifers/

5. ● An aquifer that is exposed at the ground surface that is the aquifer formation extends essentially to the
land surface is called an unconfined aquifer.
● As a result, the aquifer is in pressure communication with the atmosphere.
● A water table serves as the upper surface of the zone of saturation so called Water Table aquifer.
● In such an aquifer, the water table varies in undulating form and in slope.
● Rises and falls in the water table corresponds to changes in the volume of water in storage within
unconfined aquifer.
UNCONFINED AQUIFER(Water Table aquifer)
Schematic cross-sectional diagram showing a layered system with an upper unconfined aquifer above a confining unit, and
underlain by a confined aquifer. In the unconfined aquifer, the water level in the well is the same as the height of the water table.
SOURCE: USGS Water Science Photo Gallery

6. CONFINED AQUIFER(Artesian aquifer)
● It is the one in which groundwater is confined under pressure greater than atmospheric pressure by overlying and
underlying,impervious layers.
● Water in wells stand above the top of the aquifer rather than storage changes.
● Confined aquifers exhibit only minor changes in storage and act as conduits from zones of recharge to those of
discharge.
● Artesian aquifer usually have relatively small recharge areas as compared with unconfined aquifers.
● When water is withdrawn from an artesian well, a local depression of the piezometric surface results. This decrease
in pressure permits a slight expansion of the water and in some cases a compaction of the aquifer.
● Confined aquifers differ from unconfined aquifers in two fundamental and important ways.
○ confined aquifers are typically under considerable pressure and the pressure is high enough that wells drilled into the aquifer are
free-flowing. This condition requires that the water pressure in the aquifer is sufficient to drive water up the wellbore and above the
land surface, and such wells are called artesian wells .
○ confined aquifers typically remain saturated over their entire thickness, even as water is removed by pumping wells.
● When the water level in a well is below the ground level, but is above the local water table it is known as the artesian well.
● Imaginary surface to which water rises in wells tapping an artesian aquifer is known as piezometric surface

7. PERCHED AQUIFER
● It is a special type of unconfined aquifer, and occurs where a ground water body is separated from the
main ground water by a relatively impermeable stratum of small aerial extent and by the zone of
aeration above the main body of groundwater.
● Perched aquifers occur above discontinuous aquitards, which allow groundwater to “mound” above
them. These aquifers are perched, in that they sit above the regional water table, and within the regional
vadose zone (i.e. there is an unsaturated zone below the perched aquifer).
● The dimensions of perched aquifers are typically small (dictated by climate conditions and the size of
aquitard layers), and the volume of water they contain is sensitive to climate conditions and therefore
highly variable in time.
Schematic cross-section showing the occurrence of perched aquifers above an unconfined aquifer.
Source: D.T. Snyder, U.S. Geological Survey Scientific Investigations Report 2008–5059, Estimated Depth
to Ground Water and Configuration of the Water Table in the Portland, Oregon Area

8. Semi-confined Aquifer (Leaky) An aquifer that is partly confined by layers of lower permeability material through which
recharge and discharge may occur.
Semi unconfined aquifer: If the hydraulic conductivity of the semi impervious layer of the above case is very high an aquifer
intermediate between semi-confined and unconfined aquifers may exit, and is called as semi unconfined.
Source : NPTEL- Lec1 Introduction to groundwater hydrology
Source : NPTEL- Lec1 Introduction to groundwater hydrology

9. REFERENCES
● Principles of Hydrogeology, Second Edition Paul F. Hudak
● https://nptel.ac.in/content/storage2/courses/105103026/module1/lec1/4.ht
ml