Aquifers are underground layers of rock that are saturated with water. This water can be brought to the surface through natural sources or by pumping.
Groundwater contained in aquifers is one of the most important sources of water on Earth. About 30% of our fresh liquid water is underground. Data are from the National Oceanic and Atmospheric Administration (NOAA).
The rest of fresh water is found on the surface in streams, lakes, rivers and wetlands. Most of the world's fresh water, about 69%, is in glaciers and ice caps.
Groundwater can be found in different types of rock. However, the most productive aquifers are found in permeable rocks. Examples of these rocks are: sandstone and limestone.
Groundwater moves more readily through these materials. This allows for faster pumping than other water extraction methods. Aquifers can also be found in regions where the rock is made of denser material such as granite or basalt.
Dense, impervious materials such as shale can act as a blocker. That is, a layer of rock or other material prevents the full passage of water. Geological faults or mountains can also block groundwater movement.
How Groundwater Moves
- Free Online Inclusive Education Course
- Free Online Toy Library and Learning Course
- Free Online Preschool Math Games Course
- Free Online Pedagogical Cultural Workshops Course
Aquifer recharge occurs mainly near mountains. This is where groundwater usually flows down slopes, towards streams and rivers. All according to the force of gravity. Depending on the density of the rock and the soil through which the groundwater moves, it can flow either slowly or quickly.
PUBLICITY
The water in an aquifer can be kept below the Earth's surface for many centuries. Hydrologists estimate that the water in some aquifers is more than 10,000 years old. The oldest groundwater source ever found was discovered 2.4 km deep in a Canadian mine. In it there is water from 1.5 to 2.64 billion years ago.
The deeper you dig, the saltier the liquid becomes. Groundwater can become a brine. For fresh water, depths are very limited. Much of the drinking water that society depends on is contained in shallow aquifers.
Threats to aquifers
Pumping groundwater results in a lowering of the water table. It can get so low that it is below the depth of a well. In these cases, the well “dries up” and the water cannot be removed until the groundwater is recharged – which in some cases can take hundreds or thousands of years.
When the soil sinks due to the pumping of groundwater, it is called subsidence. Land subsidence is a threat to aquifers as well as surface infrastructure.
In addition to groundwater levels, the water quality in an aquifer can be threatened by saltwater intrusion (a particular problem in coastal areas). Biological contaminants such as manure or septic tank sewage, and industrial chemicals such as pesticides or petroleum derivatives also play a role.
Once an aquifer is contaminated, it is notoriously difficult to recover.
The password has been sent to your email.
