Lenntech Water treatment & purification Lenntech Water treatment & purification

Properties of groundwater

Composition: The geological nature of the soil determines the chemical composition of the groundwater. Water is constantly in contact with the ground in which it stagnates or circulates, so equilibrium develops between the composition of the soil and that of the water: i.e. water that circulates in a sandy or granitic substratum is acidic and has a few minerals. Water that circulates in limestone contains bicarbonates alkalinity. The following table compares the characteristics of surface water and groundwater based on the major analysis parameters [1].


Surface Water Ground Water


varies with season

relatively constants

Turbidity, SS

Level variable, sometimes high

Low or nil (except in karst soil)


Due mainly to SS (clays, algae) except in

very soft or acidic waters (humic acids)

Due above all to dissolved solids

Mineral content

Varies with soil, rainfall, effluents, etc.

Largely constant, generally

appreciably higher than in

surface water from the same area

Divalent Fe and

Mn in solution

Usually none, except at the bottom of

lakes and ponds in the process of eutrophication

Usually present

Aggressive CO2

Usually none

Often present

Dissolved O2

Often near saturation level,

absent in very polluted water

Usually none


Usually none

Often present


Found only in polluted water

Often found


Level generally low

Level sometimes high


Usually moderate proportions

Level often high

Mineral and organic


Can be present but liable to disappear

rapidly once the source is removed

Usually none but any accidental

pollutionlasts a very long time

Living organisms

Bacteria, viruses, plankton

Iron bacteria frequently found

Chlorinated solvents

Rarely present

Often present

Eutrophic nature

Often. Increased by high temperatures


Some of the most typical characteristics of groundwater are weak turbidity, a constant temperature and chemical composition and almost overall absence of oxygen. Circulating groundwater can have extreme variation in the composition with the appearance of pollutants and various contaminants. Furthermore, groundwater is often very pure microbiologically.


groundwater is in constant motion, although the rate at which it moves is generally slower than it would move in a stream because it must pass through the intricate passageways between free spaces in the rock. First groundwater moves downward due to the pull of gravity. But it can also move upwards because it will flow from higher-pressure areas to lower pressure areas.
The rate of groundwater flow is controlled by two properties of the rock: porosity and permeability. Porosity is the percentage of the volume of the rock that is open space (pore space). This determines the amount of water that a rock can contain. In sediments or sedimentary rocks the porosity depends on grain size, grain shapes, the degree of sorting, and the degree of cementation. Permeability is a measure of the degree to which the pore spaces are interconnected, and the size of the interconnections. Low porosity usually results in low permeability, but high porosity does not necessarily imply high permeability. It is possible to have a highly porous rock with little or no interconnections between pores. A good example of a rock with high porosity and low permeability is a vesicular volcanic rock, where the bubbles that once contained gas give the rock a high porosity, but since these holes are not connected to one another the rock has low permeability [2].

Discharges and velocity:

The rate at which groundwater moves through the saturated zone depends on the permeability of the rock and the hydraulic gradient. The hydraulic gradient is defined as the difference in elevation divided by the distance between two points on the water table. Velocity, V, is then:

V = K(h2 - h1)/L

where K is the coefficient of permeability. If we multiply this expression by the area, A, through which the water is moving, then we get the discharge Q (Darcy's Law).

Q = AK(h2 - h1)/L.

Springs and wells:

A spring is an area on the surface of the Earth where the water table intersects the surface and water flows out of the ground. Springs occur when an impermeable rock (called an aquiclude) intersects a permeable rock that contains groundwater (an aquifer). The occurrence of springs is closely related to the geology of an area. If an impervious layer of rock, such as a clay deposit, underlies a layer of saturated soil or rock, then a line of springs will tend to appear on a slope where the clay layer outcrops. Igneous rocks are also impervious to water, yet they are often extensively fractured, and springs commonly appear where these fractures come to the surface. Fractures in limestone are often enlarged by the dissolving action of groundwater, forming small underground channels and caves.
A well is human-made hole that is dug or drilled deep enough to intersect the water table. If the well is dug beneath the water table, water will fill the open space to the level of the water table, and can be drawn out by a bucket or by pumping. An artesian well is a deep drilled well through which water is forced upward under pressure. The geologic conditions necessary for an artesian well are an inclined aquifer sandwiched between impervious rock layers above and below that trap water in it. Water enters the exposed edge of the aquifer at a high elevation and percolates downward through interconnected pore spaces. The water held in these spaces is under pressure because of the weight of water in the portion of the aquifer above it. If a well is drilled from the land surface through the overlying impervious layer into the aquifer, this pressure will cause the water to rise in the well. In areas where the slope of the aquifer is great enough, pressure will drive the water above ground level in a spectacular, permanent fountain.
Water from an artesian well or spring is usually cold and free of organic contaminants, making it desirable for drinking.

Spring [2]

Well [2]

Check also our information about groundwater definitions, origin and quantities, sources in Europe, contamination.

About Lenntech

Lenntech BV
Distributieweg 3
2645 EG Delfgauw

tel: +31 152 610 900
fax: +31 152 616 289
e-mail: info@lenntech.com

Copyright © 1998-2018 Lenntech B.V. All rights reserved