1. GROUND WATER Introduction Sources and Discharge of Ground Water
Water Table and Artesian Aquifer

2. Types of Terrestrial Water
Surface
Water
Soil Water/
Moisture
Ground Water

3. Ground Water
It is usually defined as water found underground in the saturated zone of rocks, i.e. at depths where the entire void space of the rock is filled with water.
It is a term used to denote subsurface water that exists at pressure greater than or equal to atmospheric pressure.
It is an important source of drinking water for humankind.
It is an important renewable source.
The world’s water distribution is shown in Table 1. Groundwater represents about 0.62 % of the world’s total water. Since much of the g/w below a depth of 0.8 km is saline or costs too much to develop with present technologies and economic conditions.
As groundwater supplies are limited, they must be properly managed and protected against undue exploitation and contamination by pollutants.

4. Table 1. Estimated Distribution of World's Water.
Component
Volume 1000 km3
% of Total Water
Atmospheric water 13
0.001
Surface Water
Salt Water in Oceans
Salt water in lakes & inland seas
Fresh water in lakes
Fresh water in stream channels
Fresh water in glaciers and icecaps
Water in the biomass
104
125
1.25
29000 50
97.2
0.008
0.009
0.0001
2.15
0.004
Subsurface water
Vadose water
G/W within depth of 0.8 km
G/W between 0.8 and 4 km depth 67
4200
0.005
0.31
Total (rounded)
100

5. Global Water Supply Distribution
3% of earth’s water is fresh - 97% oceans
1% of fresh water in lakes, streams, rivers
29% of the world’s fresh water exists in aquifers and 70% in glaciers

6. Groundwater Use
Groundwater is used for irrigation, as a drinking water supply, as a source of all household water, for industrial operations needing water, and a whole lot more!
In fact, many cities depend entirely on groundwater for all of their water needs.
If they were to run out of groundwater they wouldn't have any more fresh, clean water.
Unfortunately, many cities have to rely mainly on groundwater because they have polluted their surface waters too badly to be used.

7. Types of Water-Bearing Units
The geologic formations are classified in relation to their capacity to store and transmit the water i.e., the porosity and hydraulic conductivity.
An aquifer is a geologic formation, which contains water and permits significant amount of water to move through it under field conditions.
An aquiclude is a formation which may contain water but is incapable of transmitting significant quantities under ordinary field conditions. A clay layer is an example of an aquiclude. For all practical purposes, an aquiclude is considered an impervious formation.
An aquitard is a geologic formation which is of semi-pervious nature, it transmits water at a very low rate compared to the aquifer.
An aquifuge is an impervious formation, which neither contains nor transmits water.

8. Comparison of Water Bearing Units
Types
Hydraulic Properties
Examples
Store
Transmit
Yield
Aquifer
Yes
Sand, gravel
Aquiclude No
Clay, shale
Aquitard
Slow
Clay
Aquifuge
Granite, basalt

9. Aquifers
A geological unit which can store and supply significant quantities of water.
Aquifers are underground sources of water. However, many people picture them as huge underground lakes.
Aquifers are actually made of the water that is found in the tiny little spaces (or "pores") in between the particles that make up the soils and rock under the ground (or in the "subsurface"). These particles can actually act as a natural filter to help remove impurities from the water. This makes groundwater some of the cleanest water on the planet!
The aquifer portion of the subsurface is the part that is completely soaked (or "saturated") with water is usually called "groundwater".
Aquifers have the following two types:
1. Unconfined (Phreatic or Water Table) Aquifers
2. Confined (Pressure) Aquifers

10. Types of Aquifers Ground Level Perched Aquifer Piezometric Level
Water Table
Unconfined Aquifer
Confining Layer
Confined Aquifer
Confining Layer

11. Aquifer Systems

12. 1. Unconfined Aquifers
The top of an unconfined aquifer is the water table, which is the plane where groundwater pressures are equal to atmospheric pressure.
The lower boundary of unconfined aquifers is a layer of much less permeable material than the aquifer itself.
The water in unconfined aquifers comes from direct rainfall recharge over the aquifer, from connections to surface waters, and/or from other aquifers.

13. 2. Confined Aquifers
An aquifer bounded from above and from below by impervious formations.
Confined aquifers are completely filled with groundwater, and they do not have a free water table.
The pressure condition in a confined aquifer is characterized by the piezometric surface, which is the surface obtained by connecting equilibrium water levels in tubes, or piezometers, penetrating the confined aquifer.
Confined aquifers recharge through formation outcrops - areas where the soil system is exposed to the surface -- or through aquicludes.

14. Confined Aquifer and the Potentiometric Surface
A confined aquifer lies between two aquitards.
The hydraulic head in a confined aquifer lies above the base of the upper confining layer and is generally referred to as the potentiometric surface or piezometric surface.
In a confined aquifer, the water level in a borehole drilled into the aquifer rises above the top of the aquifer. The well is called an artesian well.
In some cases the water level may rise above ground surface, in which case the well is called a flowing artesian well.

15. Leaky and Perched Aquifers
Leaky Aquifers
Aquifers whether confined or unconfined that can lose or gain water through either or both of the formations bounding them from above or below are called leaky aquifers.
Perched Aquifer
A special case of unconfined aquifer is the perched aquifer which occurs whenever an impervious (or semi-pervious) layer of limited areal extent is located between the water table of a unconfined aquifer and the ground surface.

16. Groundwater -- Recharge and Discharge
Water is continually recycled through aquifer systems.
Groundwater recharge is any water added to the aquifer zone. Processes that contribute to groundwater recharge include precipitation, streamflow, leakage (reservoirs, lakes), and artificial means (injection wells).
Groundwater discharge is any process that removes water from an aquifer system. Natural springs and artificial wells are examples of discharge processes.
In many locations groundwater withdrawal exceeds natural recharge rates. This is known as overdraft. In such areas, the water table is drawn down "permanently"; therefore, groundwater is considered a nonrenewable resource.
Groundwater supplies 30% of the water present in our streams. Effluent streams act as discharge zones for groundwater during dry seasons. This phenomenon is known as base flow. Groundwater overdraft reduces the base flow, which results in the reduction of water supplied to our streams.